Review article
An overview of the chemical composition of biomass
Stanislav V. Vassilev
a,b,*
, David Baxter
b
, Lars K. Andersen
b
, Christina G. Vassileva
a
a
Central Laboratory of Mineralogy and Crystallography, Bulgarian Academy of Sciences, Acad. G. Bonchev Street, Block 107, Sofia 1113, Bulgaria
b
Institute for Energy, Joint Research Centre, European Commission, P.O. Box 2, NL-1755 ZG Petten, The Netherlands
a r t i c l e
i n f o
Article history:
Received 13 July 2009
Received in revised form 20 October 2009
Accepted 21 October 2009
Available online 10 November 2009
Keywords:
Biomass
Biomass ash
Chemical composition
Chemical associations
a b s t r a c t
An extended overview of the chemical composition of biomass was conducted. The general consider-
ations and some problems related to biomass and particularly the composition of this fuel are discussed.
Reference peer-reviewed data for chemical composition of 86 varieties of biomass, including traditional
and complete proximate, ultimate and ash analyses (21 characteristics), were used to describe the bio-
mass system. It was shown that the chemical composition of biomass and especially ash components
are highly variable due to the extremely high variations of moisture, ash yield, and different genetic types
of inorganic matter in biomass. However, when the proximate and ultimate data are recalculated respec-
tively on dry and dry ash-free basis, the characteristics show quite narrow ranges. In decreasing order of
abundance, the elements in biomass are commonly C, O, H, N, Ca, K, Si, Mg, Al, S, Fe, P, Cl, Na, Mn, and Ti. It
was identified that the chemical distinctions among the specified natural and anthropogenic biomass
groups and sub-groups are significant and they are related to different biomass sources and origin,
namely from plant and animal products or from mixtures of plant, animal, and manufacture materials.
Respective chemical data for 38 solid fossil fuels were also applied as subsidiary information for clarifying
the biomass composition and for comparisons. It was found that the chemical composition of natural bio-
mass system is simpler than that of solid fossil fuels. However, the semi-biomass system is quite compli-
cated as a result of incorporation of various non-biomass materials during biomass processing. It was
identified that the biomass composition is significantly different from that of coal and the variations
among biomass composition were also found to be greater than for coal. Natural biomass is: (1) highly
enriched in Mn > K > P > Cl > Ca > (Mg, Na) > O > moisture > volatile matter; (2) slightly enriched in H;
and (3) depleted in ash, Al, C, Fe, N, S, Si, and Ti in comparison with coal. The correlations and associations
among 20 chemical characteristics are also studied to find some basic trends and important relationships
occurring in the natural biomass system. As a result of that five strong and important associations,
namely: (1) C–H; (2) N–S–Cl; (3) Si–Al–Fe–Na–Ti; (4) Ca–Mg–Mn; and (5) K–P–S–Cl; were identified
and discussed. The potential applications of these associations for initial and preliminary classification,
prediction and indicator purposes related to biomass were also introduced or suggested. However, future
detailed data on the phase–mineral composition of biomass are required to explain actually such chem-
ical trends and associations.
Ó 2009 Elsevier Ltd. All rights reserved.
Contents
1.
Introduction and scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 914
1.1.
General considerations about biomass. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 914
1.2.
Some problems related to biomass investigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 914
1.3.
Common issues concerning biomass composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 916
1.4.
Common issues concerning chemical composition of biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 917
2.
Data and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 923
2.1.
Chemical composition of biomass and comparisons with solid fossil fuels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 923
2.1.1.
General observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 923
2.1.2.
Proximate composition of biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 924
0016-2361/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:
*
Corresponding author. Address: Central Laboratory of Mineralogy and Crystallography, Bulgarian Academy of Sciences, Acad. G. Bonchev Street, Block 107, Sofia 1113,
Bulgaria. Tel.: +359 2 9797055; fax: +359 2 9797056.
E-mail address:
(S.V. Vassilev).
Fuel 89 (2010) 913–933
Contents lists available at
Fuel
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / f u e l
2.1.3.
Ultimate composition of biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 925
2.1.4.
High-temperature ash (HTA) composition of biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 926
2.2.
Correlations and associations among chemical composition of biomass and their potential applications . . . . . . . . . . . . . . . . . . . . . . . . . 928
2.2.1.
Correlations and associations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 928
2.2.2.
Potential applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 928
3.
Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 931
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 932
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 932
1. Introduction and scope
1.1. General considerations about biomass
Biomass is contemporaneous (non-fossil) and complex biogenic
organic–inorganic solid product generated by natural and anthro-
pogenic (technogenic) processes, and comprises: (1) natural con-
stituents
originated
from
growing
land-
and
water-based
vegetation via photosynthesis or generated via animal and human
food digestion; and (2) technogenic products derived via process-
ing of the above natural constituents. The general classification of
biomass varieties as fuel resources can be divided preliminary and
roughly into several groups and sub-groups according to their dis-
tinct biological diversity and similar source and origin (
).
Biomass fuels or biofuels are technogenic solid, liquid or gaseous
fuels generated from natural biomass resources via some process-
ing. Respectively, the bioenergy is the energy produced from
biomass fuels. The major advantages and disadvantages offered
by biomass or biomass fuels are summarized and listed in
as most of them have been described earlier
.
Natural biomass is a renewable energy source, while biomass
fuel is still an incomplete renewable energy resource. Since it is
considered that the biomass system and respective biofuels as
sub-systems do not contribute to the greenhouse effect due to
the CO
2
neutral conversion, extensive investigations have been car-
ried out worldwide to enhance the biomass use by substituting fos-
sil fuels for energy conversion
. The focus on bioenergy as an
alternative has increased tremendously during the last years be-
cause of global warming problems originated mostly from fossil
fuels combustion. However, the scientific community has been
stressed recently that ‘‘under current policies, the environmental
effects from biofuel production might be worse than those from
fossil fuels”
Reasonably, two fundamental aspects related to biomass use as
fuel are: (1) to extend and improve the basic knowledge on compo-
sition and properties; and (2) to apply this knowledge for the most
advanced and environmentally safe utilization. Numerous studies
have been conducted worldwide and extensive data for biomass
and its conversion products have been generated, particularly dur-
ing the last two decades. These results provide a sound foundation
for an initial database that can be used for characterization and
subsequent classification and sustainable exploitation of biomass.
Therefore, a detailed review of the scientific literature including
more than 280 mostly peer-reviewed references and data compila-
tions have been conducted to systematise the results collected for
biomass.
1.2. Some problems related to biomass investigations
It is well-known that ‘‘the methodology and logic from coal
experiments can be applied to biomass”
. Surprisingly, it was
found that the long term experience and knowledge achieved for
the most studied solid fuels (coal, peat, petroleum coke, municipal
solid waste, and refuse-derived fuel or char) and their products
have not been implemented very successfully in the field of bio-
mass. Furthermore, additional problems also occur in many bio-
mass
investigations
due
to
use
of
unsuitable
scientific
approaches, incomplete data or unusual and sometimes inappro-
priate terms that lead to inaccurate interpretations and misunder-
standings about the biomass and biomass fuels. The occurrence of
such problems cannot be ignored and an attempt to summarize
them initially is undertaken below:
(1) There is a general agreement that biomass fuel is renewable
energy resource. However, it is still not fully correct to claim
this at present due to the occurrence of some unsolved envi-
ronmental problems during planting, growing, harvesting,
transport and use of biomass fuels, as well as utilization of
biomass waste products, when considering the complete life
cycle assessment
.
(2) The lack of generally accepted terminology, classification
systems and standards worldwide about biomass and biofu-
els lead to some serious misunderstanding during the inves-
tigations. Analytical and representative sampling problems
Table 1
General classification of biomass varieties as solid fuel resources according to their biological diversity, source and origin.
Biomass groups
Biomass sub-groups, varieties and species
1. Wood and woody biomass
Coniferous or deciduous; angiospermous or gymnospermous; soft or hard; stems, branches, foliage, bark, chips,
lumps, pellets, briquettes, sawdust, sawmill and others from various wood species
2. Herbaceous and agricultural biomass
Annual or perennial and field-based or processed-based such as:
2.1. Grasses and flowers (alfalfa, arundo, bamboo, bana, brassica, cane, cynara, miscanthus, switchgrass, timothy,
others)
2.2. Straws (barley, bean, flax, corn, mint, oat, rape, rice, rye, sesame, sunflower, wheat, others)
2.3. Other residues (fruits, shells, husks, hulls, pits, pips, grains, seeds, coir, stalks, cobs, kernels, bagasse, food,
fodder, pulps, cakes, others)
3. Aquatic biomass
Marine or freshwater algae; macroalgae (blue, green, blue-green, brown, red) or microalgae; seaweed, kelp, lake
weed, water hyacinth, others
4. Animal and human biomass wastes
Bones, meat-bone meal, chicken litter, various manures, others
5. Contaminated biomass and industrial biomass
wastes (semi-biomass)
Municipal solid waste, demolition wood, refuse-derived fuel, sewage sludge, hospital waste, paper-pulp sludge,
waste papers, paperboard waste, chipboard, fibreboard, plywood, wood pallets and boxes, railway sleepers,
tannery waste, others
6. Biomass mixtures
Blends from the above varieties
914
S.V. Vassilev et al. / Fuel 89 (2010) 913–933
associated with biomass also occur and some of them have
been discussed
.
(3) There is a huge amount of data about the biomass in numer-
ous project reports, scientific proceedings or Internet; how-
ever, the use of such information is insecure because the
data are not peer-reviewed.
(4) The common practice is to avoid the complete description of
biomass used (as samples or feedstock), their place and
manner of collection, as well as storage and processing con-
ditions. For instance, the use of biomass specification such as
wood, fuelwood, firewood, forest or agricultural residue,
bark, straw, grass, manure, coppicing or dedicated energy
crop and short rotation coppice or crop, do not bring suffi-
cient information for the real identification and character-
ization of a particular type of biomass. Additionally, the
exact fuel status of the samples studied, namely as collected
(harvested), as received, air-dried (at ambient temperature)
or oven-dried (at specific temperature up to 105 °C) basis is
also very often not reported which is a serious omission.
(5) Some studies include peat as biomass resource, but peat is
fossil fuel. Additionally, it should be always considered that
significant part (occasionally dominant) of contaminated
biomass contains other non-biomass products
. Hence,
contaminated biomass (semi-biomass) should be considered
separately.
(6) The systematic and complete data from simultaneous prox-
imate, ultimate and ash analyses, as well as from phase,
mineral and trace elements analyses for the biomass varie-
ties and their products are missing or they are very scarce.
(7) It is commonly accepted that the concentration and behav-
iour of elements such as Ca, Cl, K, Na, P, S, Si and heavy metals
(more precisely trace elements) are mostly responsible for
many technological and environmental problems during bio-
mass processing. However, the experience from the studies
of other solid fuels
shows that the actual reasons for
such problems are most likely connected with the abundance
and behaviour of modes of element occurrence (specific
phases or minerals) in biomass and biomass products.
(8) Most studies used the data from ash yield (shortly ash) or the
bulk chemical composition of ash to explain mineral matter,
mineral composition, minerals, inorganic matter or inorgan-
ics, which is not fully correct and can lead to confusion. Fur-
thermore, the inorganic matter in biomass has generally
been divided into two classes, namely inherent (or intrinsic)
and entrained (or extraneous, adventitious, extrinsic, added,
dirt) materials. However, the actual inorganic matter in
biomass could be divided into detrital (terrigenous) and
authigenic genetic classes which are more informative,
well-known and accepted for the solid fossil fuels (SFFs)
(9) Many findings about the behaviour of organic and inorganic
matter during biomass heating are based only on theoretical
equilibrium and stoichiometric calculations of chemical
data. These indirect investigations may be quite unrealistic
for actual predictions of phases in a multicomponent (poly-
component) system under non-equilibrium conditions. Such
calculations can be used only as a subsidiary prediction pro-
cedure of the real and direct (input, output) phase studies of
the systems.
Table 2
Major advantages and disadvantages of biomass or biomass fuels.
Advantages
Disadvantages
Renewable energy source for natural biomass
Incomplete renewable energy resource for biomass fuel with
respect to the complete life cycle assessment
CO
2
neutral conversion and climate change benefits
Miss of accepted terminology, classification systems and
standards worldwide
Commonly low contents of ash, C, S, N, and trace elements
Insufficient knowledge and variability of composition, properties
and quality
Normally high concentrations of volatile matter, Ca, H, Mg, O, and P
Commonly high contents of moisture, Cl, K, Na, Mn, and some
trace elements
Great reactivity during conversion
Low energy density
Mitigation of hazardous emissions (CH
4
, CO
2
, NO
X
, SO
X
, trace elements) and wastes separated
Potential competition with food and feed production
Capture of some hazardous components by ash during combustion
Possible soil damage and loss of biodiversity
Huge availability and relatively cheap resource
Odour, potential emission and leaching of hazardous
components during disposal
Diversification of fuel supply and energy security
Possible hazardous emissions during heat treatment
Rural revitalization with creation of new jobs
Potential technological problems during heat treatment
Potential use of oceans and low-quality soils, and restoration of degraded lands
Regional availability
Reduction of biomass-containing wastes
Great collection, transportation, storage and pre-treatment costs
Cheap resource for production of sorbents, fertilizers, liming and neutralizing agents, building
materials, and for some synthesis or recovery of certain elements and compounds
Unclear utilization of waste products
Nomenclature
A
ash yield
AB
animal biomass
am
as measured
CB
contaminated biomass
daf
dry, ash-free basis
db
dry basis
EDF
enrichment/depletion factor
FC
fixed carbon
HAB
herbaceous and agricultural biomass
HAG
herbaceous and agricultural grass
HAS
herbaceous and agricultural straw
HAR
herbaceous and agricultural residue
HTA
high-temperature ash (>500 °C)
LTA
low-temperature ash (100–250 °C)
M
moisture
R
2
correlation coefficient
SFF
solid fossil fuel
VM
volatile matter
WWB
wood and woody biomass
%
weight%
S.V. Vassilev et al. / Fuel 89 (2010) 913–933
915
(10) Sequential chemical fractionation is mostly used to distin-
guish the speciation of elements in biomass fuels and their
ashes. However, this indirect procedure cannot be applied
to identify the actual modes of element occurrence. Leaching
alone has many limitations and can be used only as preli-
minary information for some possible associations of ele-
ments. Other direct methods applied for coal
and coal
ash
should be used for such a purpose.
(11) The problems related to biomass ash utilization are only at
an initial stage of investigation and they need further clarifi-
cation. For instance, there is no doubt that biomass ashes
contain plant nutrients, namely some compounds of Ca,
Mg, Na, K and P, that have to be recycled back to the soil.
However, the problem is if these compounds occur in acces-
sible (bioavailable) forms in the ash. There are indications
that significant proportions of the above nutrients are pres-
ent as water insoluble phases (glass, silicates, phosphates),
while other dangerous trace elements are highly mobile
impurities in surface enriched salts on ash particles. In this
case the fundamental question is what amount of: (1) acces-
sible (water-soluble) or non-accessible (bound into glass)
nutrients; and (2) bioavailable or non-bioavailable trace-ele-
ment contaminants; will be returned to the biomass cycle
with these ashes? Furthermore, washing of alkali-rich bio-
mass fuels prior to their use may reduce some technological
and environmental problems. However, such future large-
scale washing may create new environmental concerns
related to the fate of alkali metals, Cl, S, P, and some hazard-
ous trace elements leached from biomass.
(12) There is a strange acceptance that biomass ash does not con-
tain toxic metals like in the case of coal ash. However, cer-
tain results for biomass ashes are very disturbing. For
example, maximum concentrations of elements such as As
(243 ppm), Ba (0.37%), Cd (657 ppm), Cr (0.17%), Cu
(0.24%), Hg (7.3 ppm), Mn (4.7%), Mo (114 ppm), Pb (5.0%),
Sb (264 ppm), and Zn (16.4%) were detected in some bio-
mass ashes, particularly filter fly ashes
. These con-
centrations are much greater than in coal ash and they
even have a unique resource recovery potential. Addition-
ally, the trace elements in biomass ash tend to occur in much
more mobile and hazardous compounds than in coal ash
. Systematic studies about the trace ele-
ments in biomass and biomass products are also only at an
initial stage of investigation.
(13) Regulations exist in some countries which specify the limit-
ing and guiding values for the contents of Ca, Cl, K, N, S, and
some trace elements (Cd, Co, Cr, Cu, Ni, Pb, V, Zn) in biomass
fuel or ash in respect of their unrestricted use. However, the
bulk concentrations of these elements are less informative
than the abundance of their modes of element occurrence.
(14) There are quite limited data about the exploration of the
impact of biomass varieties during their blending with other
solid fuels.
The above listed problems show that additional, systematic and
detailed studies based on proved or new approaches and methods
are required to reduce uncertainties. Therefore, from a critical
review of publications and some own investigations an attempt
will be undertaken: (1) to compile a reliable database; (2) to define
the basic achievements; (3) to supply additional results; (4) to clar-
ify some of the problems related to composition, properties and
perspectives of biomass; and finally (5) to understand how the fun-
damental knowledge on the composition and properties may be
implemented for the most advanced and environmentally safe uti-
lization of biomass. Peer-reviewed data and own key investigations
on biomass, other solid fuels and their products will be used for
that purpose in the present and future publications.
1.3. Common issues concerning biomass composition
The identification and characterization of chemical and phase
composition of a given solid fuel is the initial and most important
step during the investigation and application of such fuel. This
composition is a unique fundamental code that characterizes and
determines the properties, quality, potential applications and
environmental problems related to any fuel. For that purpose,
well-known physical, chemical, petrographic, mineralogical and
geochemical studies have been used for characterization of solid
fuels. For example, data from: (1) proximate analysis, namely fixed
carbon (FC), volatile matter (VM), ash yield (A), and moisture (M);
(2) ultimate analysis (C, O, H, S, N); (3) ash analysis (Si, Al, Fe, Ca, S,
Mg, K, Ti, Na, P, plus occasionally Mn, Cl and trace elements); (4)
petrographic analysis (organic and inorganic ingredients); (5) min-
eralogical analysis (minerals and inorganic phases); (6) separation
procedures (different fractions); and (7) other analyses of fuel,
low-temperature ash (LTA) or high-temperature ash (HTA) have
been traditionally used to characterize specific solid fuels
. Identical or similar analyses are also applicable for bio-
mass characterization despite of some peculiarities and limitations
Biomass, similar to SFF, is a complex heterogeneous mixture of
organic matter and, to a lesser extent, inorganic matter, containing
various solid and fluid intimately associated phases or minerals
with different origins (
and
). The genesis of
the phases in biomass is a result of natural (authigenic and detrital)
and anthropogenic processes during pre-syngenesis, syngenesis,
epigenesis and post-epigenesis of biomass according to the leading
formation process and place, time and mechanism of phase forma-
tion (
). These observations indicate that the natural biomass
system is simpler than that of SFF. This is due to the absence of an-
cient (less-known) plant species and lithiphication (diagenetic)
processes accompanied by highly variable physico-chemical condi-
tions (changes in temperature, pressure, pH and oxidation–reduc-
tion potential), which are typical of peat and coal systems.
However, the semi-biomass sub-system (
) is more complex
and quite complicated as a result of incorporation of various non-
biomass materials during biomass processing.
Table 3
Phase composition of biomass.
Matter
State and type of
constituents
Phases and components
1. Organic matter
1.1. Solid, non-crystalline
Structural ingredients, namely cellulose, hemicellulose, lignin, extractives, others
1.2. Solid, crystalline
Organic minerals such as Ca–Mg–K–Na oxalates, others
2. Inorganic matter
2.1. Solid, crystalline
Mineral species from phosphates, carbonates, silicates, chlorides, sulphates, oxyhydroxides, nitrates, and other
mineral classes
2.2. Solid, semi-crystalline
Poorly crystallized mineraloids of some silicates, phosphates, hydroxides, others
2.3. Solid, amorphous
Amorphous phases such as various glasses, silicates, others
3. Fluid matter
Fluid, liquid, gas
Moisture, gas and gas–liquid inclusions associated with both organic and inorganic matter
916
S.V. Vassilev et al. / Fuel 89 (2010) 913–933
Little information is available on the combined chemical and
phase composition of biomass and biomass ashes
. It was
found repeatedly that biomass shows a wide diversity and its com-
position is significantly or highly variable
, especially
with respect to inorganic constituents
. On the other
hand, it was noted that the biomass composition is significantly
to fundamentally
different from that of coal.
Furthermore, the variations among biomass composition were
found to be greater than for coals
. The composition of nat-
ural biomass depends on various factors, namely:
type of biomass, plant species or part of plants
;
growth processes, including the ability of plant species to uptake
(extract) selectively specific compounds from water, soil and air,
and to transport and deposit them within the plant tissues
growing conditions
such as sunlight
, geographic
location
, climate
, seasons
, soil
types
, water
, pH
, nutrients
edge of forest
, and near sea
or polluted area
;
age of the plants
;
fertilizer and pesticide doses used
which are highly important for some elements (Cl, K, N, P, S,
and certain trace elements);
plant distance from source of pollution such as highways, cities,
factories, and ore mines
;
harvesting time
and collection technique, as
well as transport and storage conditions
pick-up of extraneous material (dust, dirt, soil) and entrained as
inclusions during biomass harvesting, transport and handling
variation in ash fraction and type
;
blending of different biomass types
It has been emphasised that the plant species is more important
than soil type
, growing region
and treatment by fertil-
izers
. For example, wood species grown in different regions
showed small differences of elemental composition
. On the
other hand, the occurrence of inorganic and organic non-biomass
contaminants is common in semi-biomass (
). This
contaminated biomass contains post-epigenic natural or industrial
components, which are introduced during processing of natural
biomass. For instance, such components in semi-biomass can be
dust particles and various remains from construction materials,
plastics, rubbers, metals, chemicals, glass, porcelain, coloured pa-
per, paints, detergents, char, others
.
1.4. Common issues concerning chemical composition of biomass
Data on bulk chemical composition, as well as some similarities
or differences in common chemical characteristics for biomass
varieties have been reported in almost all investigations. As a
result a huge amount of chemical data exists and some of them
have been summarized earlier
[1,4,20,23,33,34,36–39,44,47–49,
. They reveal similar contents of C, H, O and significant
differences in the contents of N and ash-forming elements in
biomass varieties
. Larger variations for Al, Mn, Na, and Si than
for Ca, Cl, Fe, K, Mg, and P were identified in woody biomass
The bark has higher contents of ash, Al and Si than wood
. The wood and woody fuels commonly show lower
values of ash, Cl, K, N, S, and Si and higher concentrations of
C
and
Ca
in
comparison
with
other
biomass
varieties
. Agricultural biomass contains higher ash yields
and thus much more ash-forming elements than most of forestry
biomass
. Straws and grasses have relatively high Cl, K, N, Na,
S and Si concentrations
. It was also found that annual
and fast-growing crops (small branches and foliage of trees, short-
rotation woods, straws, grasses, fruits) have the greatest contents
of ash, moisture and highly mobile Cl, K, Mg, N, P, and S (occasion-
ally Na) in comparison with stems, trunks, barks and large
branches of trees
. On the other hand,
elements like Al, Ca, Mn, and Si are considered to be immobile
and they are accumulated in the tissues by other means than mo-
bile elements
.
Despite the above listed observations, it was found that the tra-
ditional, complete and peer-reviewed chemical data from simulta-
neous proximate, ultimate and ash analyses for many varieties of
biomass are quite limited. Therefore, such data only for 86 varieties
of biomass (148 samples) were collected for the present study. The
chemical data compiled and used are from 33 references including
an advanced scientific report
, subsequently published
, and other peer-reviewed articles and monographs
[19,25,31,35,40,43,52–54,64–82]
. It should also be noted that some
of these data are mean values from numerous determinations for a
given biomass variety.
The purpose of the present work is to elucidate the chemical
composition of 86 varieties of biomass and their ashes based on
the traditional and complete proximate, ultimate and ash analyses
(19 parameters) plus additional data for other important elements
such as Cl and Mn. The correlations and associations among the
chemical characteristics are also studied to find some basic trends
and important relationships occurring in the biomass system and
specified biomass groups and sub-groups. Respective traditional
and complete chemical data for 38 SFFs, namely peat
,
Table 4
Origin of phases in biomass.
Formation process
Place of formation
Time of formation
Formation mechanism
1. Natural
1.1. Authigenic (formed in
biomass)
1.1.1. Syngenetic (during plant
growing)
Generated by biogenic processes of growing plants
(photosynthesis, diffusion, adsorption, pinocytose, endocytose,
exocytose, hydrolysis, precipitation, others)
1.1.2. Epigenetic (after plant
died)
Originated by natural processes after plants died (evaporation,
precipitation)
1.2. Detrital (formed outside
biomass, but fixed in/on
biomass)
1.2.1. Pre-syngenetic (before
plant growing)
Pre-existing and finely dispersed mineral grains
(commonly < 1
l
m) introduced into the plant by water
suspensions during syngenesis (endocytose)
1.2.2. Pre-syngenetic, syngenetic
or epigenetic
Pre-existing and fine-grained particles (normally < 10–100
l
m)
introduced by water and wind on plant surfaces and fixed in
pores, voids, and cracks
2. Anthropogenic
Technogenic (formed outside or
inside biomass and fixed in/on
biomass)
Post-epigenetic (during and after
plant collecting)
Natural and/or industrial components (dust, materials, additives,
contaminants, others) introduced in biomass during collecting,
handling, transport and subsequent processing
S.V. Vassilev et al. / Fuel 89 (2010) 913–933
917
Table 5
Chemical composition of 86 varieties of biomass plus algae and four solid fossil fuel types based on proximate and ultimate analyses. The Cl contents are additionally given, wt.%.
Biomass group, sub-group and variety
Proximate analysis (am)
Proximate analysis (db)
Ultimate analysis (daf)
Cl (db)
Reference used
VM
FC
M
A
Sum
VM
FC
A
Sum
C
O
H
N
S
Sum
1. Wood and woody biomass (WWB)
1. Alder-fir sawdust
36.3
9.1
52.6
2.0
100.0
76.6
19.2
4.2
100.0
53.2
40.2
6.1
0.5
0.04
100.04
0.02
1
2. Balsam bark
70.9
18.3
8.4
2.4
100.0
77.4
20.0
2.6
100.0
54.0
39.5
6.2
0.2
0.10
100.00
1
3. Beech bark
67.5
17.0
8.4
7.1
100.0
73.7
18.5
7.8
100.0
51.4
41.8
6.0
0.7
0.11
100.01
1
4. Birch bark
71.9
17.8
8.4
1.9
100.0
78.5
19.4
2.1
100.0
57.0
35.7
6.7
0.5
0.10
100.00
2
5. Christmas trees
46.1
12.9
37.8
3.2
100.0
74.2
20.7
5.1
100.0
54.5
38.7
5.9
0.5
0.42
100.02
1
6. Elm bark
67.0
17.2
8.4
7.4
100.0
73.1
18.8
8.1
100.0
50.9
42.5
5.8
0.7
0.11
100.01
1
7. Eucalyptus bark
68.7
15.1
12.0
4.2
100.0
78.0
17.2
4.8
100.0
48.7
45.3
5.7
0.3
0.05
100.05
0.26
1
8. Fir mill residue
30.4
6.5
62.9
0.2
100.0
82.0
17.5
0.5
100.0
51.4
42.5
6.0
0.1
0.03
100.03
0.19
1
9. Forest residue
34.5
7.3
56.8
1.4
100.0
79.9
16.9
3.2
100.0
52.7
41.1
5.4
0.7
0.10
100.00
0.03
2
10. Hemlock bark
65.9
23.4
8.4
2.3
100.0
72.0
25.5
2.5
100.0
55.0
38.8
5.9
0.2
0.10
100.00
1
11. Land clearing wood
35.4
7.0
49.2
8.4
100.0
69.7
13.8
16.5
100.0
50.7
42.8
6.0
0.4
0.07
99.97
0.02
1
12. Maple bark
70.1
17.8
8.4
3.7
100.0
76.6
19.4
4.0
100.0
52.0
41.3
6.2
0.4
0.11
100.01
2
13. Oak sawdust
76.3
11.9
11.5
0.3
100.0
86.3
13.4
0.3
100.0
50.1
43.9
5.9
0.1
0.01
100.01
0.01
1
14. Oak wood
73.0
20.0
6.5
0.5
100.0
78.1
21.4
0.5
100.0
50.6
42.9
6.1
0.3
0.10
100.00
1
15. Olive wood
74.3
16.1
6.6
3.0
100.0
79.6
17.2
3.2
100.0
49.0
44.9
5.4
0.7
0.03
100.03
1
16. Pine bark
70.2
23.3
4.7
1.8
100.0
73.7
24.4
1.9
100.0
53.8
39.9
5.9
0.3
0.07
99.97
0.01
2
17. Pine chips
66.9
20.0
7.6
5.5
100.0
72.4
21.6
6.0
100.0
52.8
40.5
6.1
0.5
0.09
99.99
0.06
1
18. Pine pruning
43.3
7.9
47.4
1.4
100.0
82.2
15.1
2.7
100.0
51.9
41.3
6.3
0.5
0.01
100.01
1
19. Pine sawdust
70.4
14.2
15.3
0.1
100.0
83.1
16.8
0.1
100.0
51.0
42.9
6.0
0.1
0.01
100.01
0.01
1
20. Poplar
79.7
11.5
6.8
2.0
100.0
85.6
12.3
2.1
100.0
51.6
41.7
6.1
0.6
0.02
100.02
0.03
2
21. Poplar bark
73.6
16.0
8.4
2.0
100.0
80.3
17.5
2.2
100.0
53.6
39.3
6.7
0.3
0.10
100.00
1
22. Sawdust
55.1
9.3
34.9
0.7
100.0
84.6
14.3
1.1
100.0
49.8
43.7
6.0
0.5
0.02
100.02
1
23. Spruce bark
67.3
21.4
8.4
2.9
100.0
73.4
23.4
3.2
100.0
53.6
40.0
6.2
0.1
0.10
100.00
0.03
4
24. Spruce wood
75.7
17.1
6.7
0.5
100.0
81.2
18.3
0.5
100.0
52.3
41.2
6.1
0.3
0.10
100.00
0.01
1
25. Tamarack bark
63.7
24.1
8.4
3.8
100.0
69.5
26.3
4.2
100.0
57.0
32.0
10.2
0.7
0.11
100.01
1
26. Willow
74.2
14.3
10.1
1.4
100.0
82.5
15.9
1.6
100.0
49.8
43.4
6.1
0.6
0.06
99.96
0.01
11
27. Wood
77.5
14.5
7.8
0.2
100.0
84.1
15.7
0.2
100.0
49.6
44.1
6.1
0.1
0.06
99.96
0.01
1
28. Wood residue
57.4
12.2
26.4
4.0
100.0
78.0
16.6
5.4
100.0
51.4
41.9
6.1
0.5
0.08
99.98
0.05
2
Mean
62.9
15.1
19.3
2.7
100.0
78.0
18.5
3.5
100.0
52.1
41.2
6.2
0.4
0.08
99.98
0.02
28
Minimum
30.4
6.5
4.7
0.1
69.5
12.3
0.1
48.7
32.0
5.4
0.1
0.01
0.01
28
Maximum
79.7
24.1
62.9
8.4
86.3
26.3
16.5
57.0
45.3
10.2
0.7
0.42
0.05
28
2. Herbaceous and agricultural biomass (HAB)
Mean
66.0
16.9
12.0
5.1
100.0
75.2
19.1
5.7
100.0
49.9
42.6
6.2
1.2
0.15
100.05
0.20
44
Minimum
41.5
9.1
4.4
0.8
59.3
12.4
0.9
42.2
34.2
3.2
0.1
0.01
0.01
44
Maximum
76.6
35.3
47.9
18.6
85.5
37.9
20.1
58.4
49.0
9.2
3.4
0.60
0.83
44
2.1. Grasses (HAG)
29. Arundo grass
46.5
9.5
42.0
2.0
100.0
80.2
16.4
3.4
100.0
48.7
44.5
6.1
0.6
0.13
100.03
0.20
1
30. Bamboo whole
71.0
15.2
13.0
0.8
100.0
81.6
17.5
0.9
100.0
52.0
42.5
5.1
0.4
0.04
100.04
0.08
3
31. Bana grass
70.2
15.9
4.5
9.4
100.0
73.6
16.6
9.8
100.0
50.1
42.9
6.0
0.9
0.13
100.03
0.83
1
32. Buffalo gourd grass
73.5
12.3
10.0
4.2
100.0
81.6
13.7
4.7
100.0
46.1
44.5
6.5
2.6
0.27
99.97
1
33. Kenaf grass
73.5
15.7
7.5
3.3
100.0
79.4
17.0
3.6
100.0
48.4
44.5
6.0
1.0
0.15
100.05
0.17
1
34. Miscanthus grass
71.9
14.0
11.4
2.7
100.0
81.2
15.8
3.0
100.0
49.2
44.2
6.0
0.4
0.15
99.95
0.13
3
35. Reed canary grass
67.8
16.3
7.7
8.2
100.0
73.4
17.7
8.9
100.0
49.4
42.7
6.3
1.5
0.15
100.05
0.06
1
36. Sorghastrum grass
72.4
12.6
11.3
3.7
100.0
81.6
14.2
4.2
100.0
49.4
44.0
6.3
0.3
0.05
100.05
0.04
1
37. Sweet sorghum grass
71.8
16.8
7.0
4.4
100.0
77.2
18.1
4.7
100.0
49.7
43.7
6.1
0.4
0.09
99.99
0.30
1
38. Switchgrass
70.8
12.8
11.9
4.5
100.0
80.4
14.5
5.1
100.0
49.7
43.4
6.1
0.7
0.11
100.01
0.08
3
Mean
69.0
14.1
12.6
4.3
100.0
79.0
16.2
4.8
100.0
49.2
43.7
6.1
0.9
0.13
100.03
0.21
10
Minimum
46.5
9.5
4.5
0.8
73.4
13.7
0.9
46.1
42.5
5.1
0.3
0.04
0.04
10
Maximum
73.5
16.8
42.0
9.4
81.6
18.1
9.8
52.0
44.5
6.5
2.6
0.27
0.83
10
2.2. Straws (HAS)
39. Alfalfa straw
71.6
14.3
9.3
4.8
100.0
78.9
15.8
5.3
100.0
49.9
40.8
6.3
2.8
0.21
100.01
0.50
1
40. Barley straw
67.4
16.4
11.5
4.7
100.0
76.2
18.5
5.3
100.0
49.4
43.6
6.2
0.7
0.13
100.03
0.27
2
41. Corn straw
67.7
17.8
7.4
7.1
100.0
73.1
19.2
7.7
100.0
48.7
44.1
6.4
0.7
0.08
99.98
0.64
1
918
S.V.
Vassilev
et
al.
/Fuel
89
(2010)
913–933
42. Mint straw
58.0
16.2
16.8
9.0
100.0
69.7
19.5
10.8
100.0
50.6
40.1
6.2
2.8
0.28
99.98
0.43
1
43. Oat straw
73.9
12.5
8.2
5.4
100.0
80.5
13.6
5.9
100.0
48.8
44.6
6.0
0.5
0.08
99.98
0.09
1
44. Rape straw
70.7
16.3
8.7
4.3
100.0
77.4
17.9
4.7
100.0
48.5
44.5
6.4
0.5
0.10
100.00
0.03
1
45. Rice straw
59.4
14.4
7.6
18.6
100.0
64.3
15.6
20.1
100.0
50.1
43.0
5.7
1.0
0.16
99.96
0.58
3
46. Straw
64.3
13.8
12.4
9.5
100.0
73.4
15.8
10.8
100.0
48.8
44.5
5.6
1.0
0.13
100.03
0.54
2
47. Wheat straw
67.2
16.3
10.1
6.4
100.0
74.8
18.1
7.1
100.0
49.4
43.6
6.1
0.7
0.17
99.97
0.61
12
Mean
66.7
15.3
10.2
7.8
100.0
74.3
17.1
8.6
100.0
49.4
43.2
6.1
1.2
0.15
100.05
0.41
9
Minimum
58.0
12.5
7.4
4.3
64.3
13.6
4.7
48.5
40.1
5.6
0.5
0.08
0.03
9
Maximum
73.9
17.8
16.8
18.6
80.5
19.5
20.1
50.6
44.6
6.4
2.8
0.28
0.64
9
2.3. Other residues (HAR)
48. Almond hulls
69.0
18.8
6.5
5.7
100.0
73.8
20.1
6.1
100.0
50.6
41.7
6.4
1.2
0.07
99.97
0.02
1
49. Almond shells
69.5
20.2
7.2
3.1
100.0
74.9
21.8
3.3
100.0
50.3
42.5
6.2
1.0
0.05
100.05
0.06
2
50. Coconut shells
70.5
22.0
4.4
3.1
100.0
73.8
23.0
3.2
100.0
51.1
43.1
5.6
0.1
0.10
100.00
1
51. Coffee husks
68.2
18.5
10.8
2.5
100.0
76.5
20.7
2.8
100.0
45.4
48.3
4.9
1.1
0.35
100.05
2
52. Cotton husks
73.0
16.9
6.9
3.2
100.0
78.4
18.2
3.4
100.0
50.4
39.8
8.4
1.4
0.01
100.01
1
53. Grape marc
59.2
23.8
10.0
7.0
100.0
65.8
26.4
7.8
100.0
54.0
37.4
6.1
2.4
0.15
100.05
1
54. Groundnut shells
68.1
20.9
7.9
3.1
100.0
73.9
22.7
3.4
100.0
50.9
40.4
7.5
1.2
0.02
100.02
0.01
2
55. Hazelnut shells
71.5
19.9
7.2
1.4
100.0
77.1
21.4
1.5
100.0
51.5
41.6
5.5
1.4
0.04
100.04
0.20
1
56. Mustard husks
68.5
22.0
5.6
3.9
100.0
72.6
23.3
4.1
100.0
45.8
44.4
9.2
0.4
0.20
100.00
1
57. Olive husks
73.7
17.4
6.8
2.1
100.0
79.0
18.7
2.3
100.0
50.0
42.1
6.2
1.6
0.05
99.95
0.20
1
58. Olive pits
72.3
18.7
6.1
2.9
100.0
77.0
19.9
3.1
100.0
52.8
39.4
6.6
1.1
0.07
99.97
0.04
2
59. Olive residue
60.2
22.8
10.6
6.4
100.0
67.3
25.5
7.2
100.0
58.4
34.2
5.8
1.4
0.23
100.03
0.20
1
60. Palm fibres-husks
46.3
12.0
36.4
5.3
100.0
72.8
18.9
8.3
100.0
51.5
40.1
6.6
1.5
0.30
100.00
1
61. Palm kernels
68.8
15.6
11.0
4.6
100.0
77.3
17.5
5.2
100.0
51.0
39.5
6.5
2.7
0.27
99.97
0.21
1
62. Pepper plant
60.5
19.5
6.5
13.5
100.0
64.7
20.9
14.4
100.0
42.2
49.0
5.0
3.2
0.57
99.97
0.13
1
63. Pepper residue
58.5
24.4
9.7
7.4
100.0
64.8
27.0
8.2
100.0
45.7
47.1
3.2
3.4
0.60
100.00
1
64. Pistachio shells
75.5
15.7
7.5
1.3
100.0
81.6
17.0
1.4
100.0
50.9
41.8
6.4
0.7
0.22
100.02
0.01
1
65. Plum pits
53.7
11.8
33.6
0.9
100.0
80.8
17.8
1.4
100.0
49.9
42.4
6.7
0.9
0.08
99.98
0.01
1
66. Rice husks
56.1
17.2
10.6
16.1
100.0
62.8
19.2
18.0
100.0
49.3
43.7
6.1
0.8
0.08
99.98
0.12
2
67. Soya husks
69.6
19.0
6.3
5.1
100.0
74.3
20.3
5.4
100.0
45.4
46.9
6.7
0.9
0.10
100.00
1
68. Sugar cane bagasse
76.6
11.1
10.4
1.9
100.0
85.5
12.4
2.1
100.0
49.8
43.9
6.0
0.2
0.06
99.96
0.03
2
69. Sunflower husks
69.1
19.0
9.1
2.8
100.0
76.0
20.9
3.1
100.0
50.4
43.0
5.5
1.1
0.03
100.03
0.10
2
70. Walnut blows
61.8
12.9
23.5
1.8
100.0
80.7
16.9
2.4
100.0
54.9
36.9
6.7
1.4
0.11
100.01
0.02
1
71. Walnut hulls and blows
41.5
9.1
47.9
1.5
100.0
79.6
17.5
2.9
100.0
55.1
36.5
6.7
1.6
0.12
100.02
0.02
1
72. Walnut shells
55.3
35.3
6.8
2.6
100.0
59.3
37.9
2.8
100.0
49.9
42.4
6.2
1.4
0.09
99.99
0.15
1
Mean
64.6
18.6
12.4
4.4
100.0
74.0
21.0
5.0
100.0
50.2
41.9
6.3
1.4
0.16
99.96
0.09
25
Minimum
41.5
9.1
4.4
0.9
59.3
12.4
1.4
42.2
34.2
3.2
0.1
0.01
0.01
25
Maximum
76.6
35.3
47.9
16.1
85.5
37.9
18.0
58.4
49.0
9.2
3.4
0.60
0.21
25
3. Animal biomass (AB)
73. Chicken litter
43.3
13.1
9.3
34.3
100.0
47.8
14.4
37.8
100.0
60.5
25.3
6.8
6.2
1.20
100.00
0.50
1
74. Meat-bone meal
61.7
12.4
2.5
23.4
100.0
63.3
12.7
24.0
100.0
57.3
20.8
8.0
12.2
1.69
99.99
0.87
1
Mean
52.5
12.8
5.9
28.8
100.0
55.5
13.6
30.9
100.0
58.9
23.1
7.4
9.2
1.45
100.05
0.69
2
4. Mixture of biomass
75. Biomass mixture
63.3
16.5
8.8
11.4
100.0
69.4
18.1
12.5
100.0
56.7
33.1
6.6
2.7
0.85
99.95
0.09
1
76. Wood-agricultural residue
54.7
12.7
30.3
2.3
100.0
78.5
18.2
3.3
100.0
52.4
41.2
6.0
0.4
0.04
100.04
0.03
2
77. Wood-almond residue
59.7
12.3
22.7
5.3
100.0
77.2
15.9
6.9
100.0
50.9
42.5
5.9
0.6
0.08
99.98
0.03
1
78. Wood-straw residue
69.6
15.5
7.3
7.6
100.0
75.1
16.7
8.2
100.0
51.7
41.5
6.3
0.4
0.13
100.03
0.13
1
Mean
61.8
14.2
17.3
6.7
100.0
75.1
17.2
7.7
100.0
52.9
39.6
6.2
1.0
0.28
99.98
0.07
4
Minimum
54.7
12.3
7.3
2.3
69.4
15.9
3.3
50.9
33.1
5.9
0.4
0.04
0.03
4
Maximum
69.6
16.5
30.3
11.4
78.5
18.2
12.5
56.7
42.5
6.6
2.7
0.85
0.13
4
5. Contaminated biomass (CB)
79. Currency shredded
79.0
11.1
4.7
5.2
100.0
82.9
11.6
5.5
100.0
45.4
46.1
6.3
1.9
0.32
100.02
1
80. Demolition wood
63.4
14.5
16.3
5.8
100.0
75.8
17.3
6.9
100.0
51.7
40.7
6.4
1.1
0.09
99.99
0.06
4
81. Furniture waste
72.9
11.8
12.1
3.2
100.0
83.0
13.4
3.6
100.0
51.8
41.8
6.1
0.3
0.04
100.04
0.01
1
82. Mixed waste paper
76.8
6.8
8.8
7.6
100.0
84.2
7.5
8.3
100.0
52.3
40.2
7.2
0.2
0.08
99.98
1
83. Greenhouse-plastic waste
61.0
5.5
2.5
31.0
100.0
62.6
5.6
31.8
100.0
70.9
16.4
11.2
1.5
0.01
100.01
0.05
1
84. Refuse-derived fuel
70.3
0.5
4.2
25.0
100.0
73.4
0.5
26.1
100.0
53.8
36.8
7.8
1.1
0.47
99.97
0.83
2
(continued on next page)
S.V.
Vassilev
et
al.
/Fuel
89
(2010)
913–933
919
Table 5 (continued)
Biomass group, sub-group and variety
Proximate analysis (am)
Proximate analysis (db)
Ultimate analysis (daf)
Cl (db)
n
Reference used
VM
FC
M
A
Sum
VM
FC
A
Sum
C
O
H
N
S
Sum
85. Sewage sludge
45.0
5.3
6.4
43.3
100.0
48.0
5.7
46.3
100.0
50.9
33.4
7.3
6.1
2.33
100.03
0.04
2
86. Wood yard waste
40.9
8.4
38.1
12.6
100.0
66.0
13.6
20.4
100.0
52.2
40.4
6.0
1.1
0.30
100.00
0.30
1
Mean
63.7
8.0
11.6
16.7
100.0
72.0
9.4
18.6
100.0
53.6
37.0
7.3
1.7
0.46
100.06
0.31
8
Minimum
40.9
0.5
2.5
3.2
48.0
0.5
3.6
45.4
16.4
6.0
0.2
0.01
0.04
8
Maximum
79.0
14.5
38.1
43.3
84.2
17.3
46.3
70.9
46.1
11.2
6.1
2.33
0.83
8
All varieties of biomass
Mean
64.3
15.3
14.4
6.0
100.0
75.4
17.8
6.8
100.0
51.3
41.0
6.3
1.2
0.19
99.99
0.17
86
Minimum
30.4
0.5
2.5
0.1
47.8
0.5
0.1
42.2
16.4
3.2
0.1
0.01
0.01
86
Maximum
79.7
35.3
62.9
43.3
86.3
37.9
46.3
70.9
49.0
11.2
12.2
2.33
0.87
86
Natural biomass
Mean
64.4
16.0
14.7
4.9
100.0
75.8
18.6
5.6
100.0
51.1
41.4
6.2
1.1
0.20
100.00
0.17
78
Minimum
30.4
6.5
2.5
0.1
47.8
12.3
0.1
42.2
20.8
3.2
0.1
0.01
0.01
78
Maximum
79.7
35.3
62.9
34.3
86.3
37.9
37.8
60.5
49.0
10.2
12.2
1.69
0.87
78
Aquatic biomass
Marine macroalgae
45.1
23.1
10.7
21.1
100.0
50.5
25.9
23.6
100.0
43.2
45.8
6.2
2.2
2.60
100.00
3.34
11
Solid fossil fuels
Peat
57.8
24.3
14.6
3.3
100.0
67.6
28.5
3.9
100.0
56.3
36.2
5.8
1.5
0.2
100.0
0.04
1
Coal
30.8
43.9
5.5
19.8
100.0
32.8
46.3
20.9
100.0
78.2
13.6
5.2
1.3
1.7
100.0
0.03
37
Coal (minimum)
12.2
17.9
0.4
5.0
12.4
20.0
5.7
62.9
4.4
3.5
0.5
0.2
0.005
37
Coal (maximum)
44.5
70.4
20.2
48.9
51.8
71.8
52.0
86.9
29.9
6.3
2.9
9.8
0.11
37
Lignite
32.8
25.7
10.5
31.0
100.0
36.7
28.7
34.6
100.0
64.0
23.7
5.5
1.0
5.8
100.0
0.01
5
Sub-bituminous coal
33.4
34.1
8.2
24.3
100.0
36.4
37.2
26.4
100.0
74.4
17.7
5.6
1.4
0.9
100.0
0.03
10
Bituminous coal
29.1
52.6
3.1
15.2
100.0
30.0
54.3
15.7
100.0
83.1
9.5
5.0
1.3
1.1
100.0
0.04
22
a
As measured at different basis. For some samples without moisture data the mean contents measured for similar biomass varieties were used.
b
Dry basis.
c
Dry, ash-free basis.
d
Number of samples.
920
S.V.
Vassilev
et
al.
/Fuel
89
(2010)
913–933
Table 6
Chemical ash composition of 86 varieties of biomass plus algae and four solid fossil fuel types based on high-temperature ash analyses (normalized to 100%), wt.%. The Mn
contents are additionally given, ppm.
Biomass group, sub-group
and variety
SiO
2
CaO
K
2
O
P
2
O
5
Al
2
O
3
MgO
Fe
2
O
3
SO
3
Na
2
O
TiO
2
Sum
Mn
(ppm)
Reference used
1. Wood and woody biomass (WWB)
1. Alder-fir sawdust
37.49
26.41
6.10
2.02
12.23
4.04
8.09
0.83
1.81
0.98
100.00
1
2. Balsam bark
26.06
45.76
10.70
4.87
1.91
2.33
2.65
2.86
2.65
0.21
100.00
20160
1
3. Beech bark
12.40
68.20
2.60
2.30
0.12
11.50
1.10
0.80
0.90
0.10
100.00
3100
1
4. Birch bark
4.38
69.06
8.99
4.13
0.55
5.92
2.24
2.75
1.85
0.13
100.00
22870
2
5. Christmas trees
39.91
9.75
8.06
2.46
15.12
2.59
9.54
11.66
0.54
0.37
100.00
1
6. Elm bark
4.48
83.46
5.47
1.62
0.12
2.49
0.37
1.00
0.87
0.12
100.00
775
1
7. Eucalyptus bark
10.04
57.74
9.29
2.35
3.10
10.91
1.12
3.47
1.86
0.12
100.00
10850
1
8. Fir mill residue
19.26
15.10
8.89
3.65
5.02
5.83
8.36
3.72
29.82
0.35
100.00
13640
2
9. Forest residue
20.65
47.55
10.23
5.05
2.99
7.20
1.42
2.91
1.60
0.40
100.00
13180
3
10. Hemlock bark
11.12
59.62
5.12
2.34
2.34
14.57
1.45
2.11
1.22
0.11
100.00
9300
1
11. Land clearing wood
65.82
5.79
2.19
0.66
14.85
1.81
5.27
0.36
2.70
0.55
100.00
1
12. Maple bark
8.95
67.36
7.03
0.79
3.98
6.59
1.43
1.99
1.76
0.12
100.00
5430
2
13. Oak sawdust
29.93
15.56
31.99
1.90
4.27
5.92
4.20
3.84
2.00
0.39
100.00
1
14. Oak wood
48.95
17.48
9.49
1.80
9.49
1.10
8.49
2.60
0.50
0.10
100.00
14900
2
15. Olive wood
10.24
41.47
25.16
10.75
2.02
3.03
0.88
2.65
3.67
0.13
100.00
1
16. Pine bark
9.20
56.83
7.78
5.02
7.20
6.19
2.79
2.83
1.97
0.19
100.00
12400
2
17. Pine chips
68.18
7.89
4.51
1.56
7.04
2.43
5.45
1.19
1.20
0.55
100.00
2090
1
18. Pine pruning
7.76
44.10
22.32
5.73
2.75
11.33
1.25
4.18
0.42
0.17
100.00
1
19. Pine sawdust
9.71
48.88
14.38
6.08
2.34
13.80
2.10
2.22
0.35
0.14
100.00
10550
2
20. Poplar
3.87
57.33
18.73
0.85
0.68
13.11
1.16
3.77
0.22
0.28
100.00
4500
3
21. Poplar bark
1.86
77.31
8.93
2.48
0.62
2.36
0.74
0.74
4.84
0.12
100.00
2330
1
22. Sawdust
26.17
44.11
10.83
2.27
4.53
5.34
1.82
2.05
2.48
0.40
100.00
27910
2
23. Spruce bark
6.13
72.39
7.22
2.69
0.68
4.97
1.90
1.88
2.02
0.12
100.00
13950
3
24. Spruce wood
49.30
17.20
9.60
1.90
9.40
1.10
8.30
2.60
0.50
0.10
100.00
1
25. Tamarack bark
7.77
53.50
5.64
5.00
8.94
9.04
3.83
2.77
3.40
0.11
100.00
26360
1
26. Willow
6.10
46.09
23.40
13.01
1.96
4.03
0.74
3.00
1.61
0.06
100.00
11
27. Wood
23.15
37.35
11.59
2.90
5.75
7.26
3.27
4.95
2.57
1.20
100.00
35740
1
28. Wood residue
53.15
11.66
4.85
1.37
12.64
3.06
6.24
1.99
4.47
0.57
100.00
2
Mean
22.22
43.03
10.75
3.48
5.09
6.07
3.44
2.78
2.85
0.29
100.00
13160
28
Minimum
1.86
5.79
2.19
0.66
0.12
1.10
0.37
0.36
0.22
0.06
775
28
Maximum
68.18
83.46
31.99
13.01
15.12
14.57
9.54
11.66
29.82
1.20
35740
28
2. Herbaceous and agricultural biomass (HAB)
Mean
33.39
14.86
26.65
6.48
3.66
5.62
3.26
3.61
2.29
0.18
100.00
1330
44
Minimum
2.01
0.97
2.29
0.54
0.10
0.19
0.22
0.01
0.09
0.01
155
44
Maximum
94.48
44.32
63.90
31.06
14.60
16.21
36.27
14.74
26.20
2.02
4570
44
2.1. Grasses (HAG)
29. Arundo grass
47.38
2.98
32.16
6.60
0.86
3.29
0.92
5.17
0.53
0.11
100.00
1
30. Bamboo whole
9.92
4.46
53.38
20.33
0.67
6.57
0.67
3.68
0.31
0.01
100.00
3
31. Bana grass
38.59
4.09
49.08
3.14
0.92
1.96
0.73
0.97
0.44
0.08
100.00
1
32. Buffalo gourd grass
8.73
14.74
41.40
10.96
1.88
5.24
0.90
9.89
6.20
0.06
100.00
1
33. Kenaf grass
9.50
44.32
19.14
3.89
2.59
8.64
1.73
8.20
1.87
0.12
100.00
1
34. Miscanthus grass
56.42
10.77
19.75
5.54
0.79
3.01
0.94
2.28
0.47
0.03
100.00
3100
4
35. Reed canary grass
84.92
3.31
2.93
3.88
1.32
1.42
1.04
1.04
0.09
0.05
100.00
1
36. Sorghastrum grass
73.21
7.02
8.97
4.43
1.83
2.21
0.95
1.11
0.25
0.02
100.00
1
37. Sweet sorghum grass
66.85
10.41
9.49
3.47
0.81
3.12
0.58
3.47
1.74
0.06
100.00
1
38. Switchgrass
66.25
10.21
9.64
3.92
2.22
4.71
1.36
0.83
0.58
0.28
100.00
3
Mean
46.18
11.23
24.59
6.62
1.39
4.02
0.98
3.66
1.25
0.08
100.00
3100
10
Minimum
8.73
2.98
2.93
3.14
0.67
1.42
0.58
0.83
0.09
0.01
10
Maximum
84.92
44.32
53.38
20.33
2.59
8.64
1.73
9.89
6.20
0.28
10
2.2. Straws (HAS)
39. Alfalfa straw
7.87
24.87
38.14
10.38
0.10
14.10
0.41
2.62
1.49
0.02
100.00
1
40. Barley straw
50.78
9.89
28.18
2.97
0.67
2.87
0.95
2.22
1.39
0.08
100.00
2
41. Corn straw
49.95
14.73
18.53
2.42
5.06
4.49
2.53
1.84
0.16
0.29
100.00
620
1
42. Mint straw
23.49
17.63
32.01
5.77
5.57
6.90
2.82
3.50
1.98
0.33
100.00
1
43. Oat straw
37.79
12.03
26.84
6.14
4.69
4.45
2.17
4.93
0.72
0.24
100.00
775
1
44. Rape straw
40.80
30.68
13.45
2.22
5.45
2.00
2.00
2.67
0.44
0.29
100.00
310
1
45. Rice straw
77.20
2.46
12.59
0.98
0.55
2.71
0.50
1.18
1.79
0.04
100.00
2790
3
46. Straw
57.14
6.70
25.82
2.74
0.76
1.67
0.53
3.89
0.70
0.05
100.00
155
2
47. Wheat straw
50.35
8.21
24.89
3.54
1.54
2.74
0.88
4.24
3.52
0.09
100.00
540
14
Mean
43.94
14.13
24.49
4.13
2.71
4.66
1.42
3.01
1.35
0.16
100.00
865
9
Minimum
7.87
2.46
12.59
0.98
0.10
1.67
0.41
1.18
0.16
0.02
155
9
Maximum
77.20
30.68
38.14
10.38
5.57
14.10
2.82
4.93
3.52
0.33
2790
9
2.3. Other residues (HAR)
48. Almond hulls
11.21
9.75
63.90
6.17
2.52
4.00
0.92
0.41
1.06
0.06
100.00
1
49. Almond shells
16.96
11.55
53.48
4.93
2.99
4.51
2.78
0.93
1.76
0.11
100.00
2
50. Coconut shells
66.75
2.41
8.48
1.54
8.48
1.54
6.16
0.01
4.62
0.01
100.00
1
51. Coffee husks
14.65
13.05
52.45
4.94
7.07
4.32
2.06
0.53
0.66
0.27
100.00
3
52. Cotton husks
10.93
20.95
50.20
4.05
1.32
7.59
1.92
1.72
1.31
0.01
100.00
1
53. Grape marc
9.53
28.52
36.84
8.80
2.63
4.77
1.77
6.29
0.67
0.18
100.00
1
54. Groundnut shells
27.70
24.80
8.50
3.70
8.30
5.40
10.30
10.40
0.80
0.10
100.00
1
(continued on next page)
S.V. Vassilev et al. / Fuel 89 (2010) 913–933
921
lignites, sub-bituminous coals, and bituminous coals
are
also used as subsidiary information for clarifying the biomass com-
position, as well as for some comparisons and preliminary classifi-
cation purposes.
Table 6 (continued)
Biomass group, sub-group
and variety
SiO
2
CaO
K
2
O
P
2
O
5
Al
2
O
3
MgO
Fe
2
O
3
SO
3
Na
2
O
TiO
2
Sum
Mn
(ppm)
n
Reference used
55. Hazelnut shells
33.70
15.40
30.40
3.20
3.10
7.90
3.80
1.10
1.30
0.10
100.00
1
56. Mustard husks
17.43
44.13
7.63
2.06
1.55
9.48
0.82
14.74
2.06
0.10
100.00
1
57. Olive husks
32.70
14.50
4.30
2.50
8.40
4.20
6.30
0.60
26.20
0.30
100.00
1
58. Olive pits
21.48
19.97
16.44
9.71
5.95
3.84
4.25
2.30
15.77
0.29
100.00
2
59. Olive residue
22.26
12.93
42.79
6.09
4.10
5.84
1.99
3.73
0.12
0.15
100.00
310
1
60. Palm fibres-husks
63.20
9.00
9.00
2.80
4.50
3.80
3.90
2.80
0.80
0.20
100.00
1
61. Palm kernels
18.26
9.33
16.54
31.06
6.19
6.59
9.23
2.54
0.14
0.12
100.00
4570
1
62. Pepper plant
12.60
32.20
24.60
5.20
4.90
7.40
2.00
9.70
0.90
0.50
100.00
1320
1
63. Pepper residue
15.39
10.02
35.32
11.19
8.39
4.55
3.38
10.61
1.05
0.10
100.00
1
64. Pistachio shells
8.43
10.26
18.66
12.10
2.23
3.34
36.27
3.89
4.61
0.21
100.00
1
65. Plum pits
3.64
14.86
45.51
20.40
0.11
11.79
0.69
2.51
0.47
0.02
100.00
1
66. Rice husks
94.48
0.97
2.29
0.54
0.21
0.19
0.22
0.92
0.16
0.02
100.00
155
5
67. Soya husks
2.01
25.26
36.00
5.79
8.74
8.38
2.95
4.37
6.26
0.24
100.00
1
68. Sugar cane bagasse
46.79
4.91
6.95
3.87
14.60
4.56
11.12
3.57
1.61
2.02
100.00
2
69. Sunflower husks
23.66
15.31
28.53
7.13
8.75
7.33
4.27
4.07
0.80
0.15
100.00
2
70. Walnut blows
6.41
27.64
34.67
10.28
2.25
14.34
1.05
2.33
0.92
0.11
100.00
1
71. Walnut hulls and blows
8.29
20.03
39.65
7.52
2.92
16.21
1.37
2.71
1.19
0.11
100.00
1
72. Walnut shells
23.32
16.72
33.03
6.21
2.40
13.51
1.50
2.20
1.00
0.10
100.00
1
Mean
24.47
16.58
28.25
7.27
4.90
6.62
4.84
3.80
3.05
0.22
100.00
1590
25
Minimum
2.01
0.97
2.29
0.54
0.11
0.19
0.22
0.01
0.12
0.01
155
25
Maximum
94.48
44.13
63.90
31.06
14.60
16.21
36.27
14.74
26.20
2.02
4570
25
3. Animal biomass (AB)
73. Chicken litter
5.77
56.85
12.19
15.40
1.01
4.11
0.45
3.59
0.60
0.03
100.00
853
1
74. Meat-bone meal
0.02
41.22
3.16
40.94
2.37
1.38
0.25
4.24
6.41
0.01
100.00
78
1
Mean
2.90
49.04
7.67
28.17
1.69
2.75
0.35
3.91
3.50
0.02
100.00
466
2
4. Mixture of biomass
75. Biomass mixture
34.75
13.15
3.11
18.07
11.35
2.31
10.44
4.62
1.25
0.95
100.00
1550
1
76. Wood-agricultural
residue
37.18
25.70
7.76
2.22
11.07
4.77
5.77
2.03
2.57
0.93
100.00
2
77. Wood-almond residue
47.00
19.55
6.45
1.52
11.08
4.35
4.19
2.12
3.18
0.56
100.00
1
78. Wood-straw residue
57.83
11.51
6.67
1.08
9.77
2.66
4.97
1.88
3.11
0.52
100.00
1
Mean
44.19
17.48
6.00
5.72
10.82
3.52
6.34
2.66
2.53
0.74
100.00
1550
4
Minimum
34.75
11.51
3.11
1.08
9.77
2.31
4.19
1.88
1.25
0.52
4
Maximum
57.83
25.70
7.76
18.07
11.35
4.77
10.44
4.62
3.18
0.95
4
5. Contaminated biomass (CB)
79. Currency shredded
3.39
14.05
2.20
0.89
13.53
1.57
22.18
10.55
4.06
27.58
100.00
1
80. Demolition wood
36.27
21.36
6.98
5.09
9.67
4.77
7.31
4.12
2.83
1.60
100.00
1940
3
81. Furniture waste
57.17
13.78
3.74
0.50
12.14
3.25
5.59
0.99
2.34
0.50
100.00
1
82. Mixed waste paper
28.62
7.63
0.16
0.20
53.53
2.40
0.82
1.73
0.54
4.37
100.00
1
83. Greenhouse-plastic
waste
28.40
25.80
9.70
3.84
3.90
5.70
18.40
2.65
0.80
0.81
100.00
2330
1
84. Refuse-derived fuel
38.67
26.81
0.23
0.77
14.54
6.45
6.26
3.01
1.36
1.90
100.00
1
85. Sewage sludge
33.28
13.04
1.60
15.88
12.91
2.49
15.70
2.05
2.25
0.80
100.00
155
2
86. Wood yard waste
60.10
23.92
2.98
1.98
3.08
2.17
1.98
2.46
1.01
0.32
100.00
1
Mean
35.73
18.30
3.45
3.64
15.41
3.60
9.78
3.45
1.90
4.74
100.00
1475
8
Minimum
3.39
7.63
0.16
0.20
3.08
1.57
0.82
0.99
0.54
0.32
155
8
Maximum
60.10
26.81
9.70
15.88
53.53
6.45
22.18
10.55
4.06
27.58
2330
8
All varieties of biomass
Mean
29.76
25.27
17.91
5.71
5.51
5.42
4.00
3.28
2.48
0.66
100.00
7540
86
Minimum
0.02
0.97
0.16
0.20
0.10
0.19
0.22
0.01
0.09
0.01
78
86
Maximum
94.48
83.46
63.90
40.94
53.53
16.21
36.27
14.74
29.82
27.58
35740
86
Natural biomass
Mean
29.14
25.99
19.40
5.92
4.49
5.60
3.41
3.27
2.54
0.24
100.00
8096
78
Minimum
0.02
0.97
2.19
0.54
0.10
0.19
0.22
0.01
0.09
0.01
78
78
Maximum
94.48
83.46
63.90
40.94
15.12
16.21
36.27
14.74
29.82
2.02
35740
78
Aquatic biomass
Marine macroalgae
1.65
12.39
15.35
9.76
0.85
12.50
1.87
25.74
19.88
99.99
326
11
Solid fossil fuels
Peat
37.53
9.97
1.12
2.75
20.14
2.14
13.83
12.11
0.10
0.31
100.00
775
1
Coal
54.06
6.57
1.60
0.50
23.18
1.83
6.85
3.54
0.82
1.05
100.00
543
37
Coal (minimum)
32.04
0.43
0.29
0.10
11.32
0.31
0.79
0.27
0.09
0.62
233
37
Coal (maximum)
68.35
27.78
4.15
1.70
35.23
3.98
16.44
14.42
2.90
1.61
1780
37
Lignite
44.87
13.11
1.48
0.20
17.11
2.50
10.80
8.64
0.48
0.81
100.00
736
5
Sub-bituminous coal
54.74
7.05
1.67
0.08
22.86
2.14
5.30
4.07
1.09
1.00
100.00
509
10
Bituminous coal
56.14
4.90
1.61
0.22
24.82
1.55
6.68
2.16
0.77
1.15
100.00
511
22
a
Number of samples.
922
S.V. Vassilev et al. / Fuel 89 (2010) 913–933
2. Data and discussion
2.1. Chemical composition of biomass and comparisons with solid
fossil fuels
2.1.1. General observations
The bulk chemical composition of biomass is the first step and
common approach for initial characterization and simplified
expression of this complex system, in contrast to phase–mineral
composition. The individual, mean and range values for the tradi-
tional chemical characteristics plus Cl and Mn of the biomass vari-
eties and their groups and sub-groups specified, as well as of other
SFFs are given in
. The biomass groups studied in-
clude terrestrial wood and woody biomass (WWB), herbaceous
and agricultural biomass (HAB), animal biomass (AB), contami-
nated biomass (CB), and mixture of biomass. The biomass
sub-groups investigated are these of grass (HAG), straw (HAS)
and other residues (HAR) specified from the broadest HAB group
(
). Hence, the varieties studied herein belong to
all of the biomass groups and sub-groups listed in
, exclud-
ing only the aquatic biomass group. However, some incomplete
data for algae are provided and discussed additionally for compar-
ison (see Section 2.2.2).
The elements in biomass can be classified into major (>1.0%),
minor (0.1–1.0%) and trace (<0.1%) elements according to their ele-
mental concentrations recalculated from
as dry ba-
sis (db). In decreasing order of abundance, the major elements are
commonly C, O, H, N, Ca and K, while the minor elements normally
include Si, Mg, Al, S, Fe, P, Cl, and Na. The trace elements are Mn
and Ti plus other elements which are not discussed herein. Never-
theless, there are many cases among biomass varieties where the
above order for certain elements is changeable. The organic-form-
ing elements in biomass are normally C, O, H, N, and S, whereas the
inorganic-forming elements are commonly the other 11 elements.
However, some proportions from the organic-forming elements
also occur in inorganic matter, while parts of the inorganic-forming
elements are also present in organic matter (similar to coal). For
example, the ash-forming elements in biomass can be all 16 ele-
ments listed above.
In contrast to the above chemical investigations (see Section
1.4), the present compilation of chemical data (
) is
based on many more biomass varieties and set of samples. The lat-
ter data confirm that there are significant differences in the chem-
ical
composition
of
biomass
varieties.
The
characteristic
enrichment or depletion chemical trends among biomass groups
and sub-groups specified are given in
. These trends are in
accordance with most of the literature findings. However, both
AB and CB groups show the most significant differences in the bio-
mass system with their high enrichment in ash, C, Cl, H, N, Na, S,
and occasionally Al, Ca, Fe, P, and Ti. The above distinctions are re-
lated to different biomass sources and origin, namely from plant
(WWB, HAB) and animal (AB) products or from mixtures of plant,
animal and manufacture materials (CB). The decreasing order of
mean values for the chemical characteristics of the biomass groups
and sub-groups are listed in
. The identical or similar orders
of moisture – volatile matter–MgO; fixed carbon–K
2
O; N–S; ash–
N–S–Cl; P
2
O
5
–SO
3
; and Al
2
O
3
–Fe
2
O
3
–TiO
2
for biomass groups and
sub-groups indicate some association between these parameters
in the biomass system.
The present chemical data show that there are some significant
differences and interesting comparative trends between natural
biomass and coal. For instance, biomass or biomass ash are nor-
mally enriched in moisture, volatile matter, CaO, Cl, H, K
2
O, MgO,
Mn, Na
2
O, O, and P
2
O
5
, and depleted in ash, fixed carbon, Al
2
O
3
,
C, Fe
2
O
3
, N, S, SiO
2
, SO
3
, and TiO
2
in comparison with coal or coal
ash (
). This comparison is evaluated by the enrich-
ment/depletion factor (EDF) defined as a ratio of the content in bio-
mass (or biomass ash) to the content in coal (or coal ash),
respectively. For that purpose, the mean values for 78 varieties of
natural biomass and for 37 coals were used. The calculation reveals
that the decreasing order of EDF is: Mn (14.9) > K
2
O (12.1) > P
2
O
5
(11.8) > Cl (5.7) > CaO (4.0) > MgO, Na
2
O (3.1) > O (3.0) > moisture
(2.7) > volatile matter (2.1) > H (1.2) > SO
3
(0.9) > N (0.8) > C
(0.7) > Fe
2
O
3
, SiO
2
(0.5) > fixed carbon (0.4) > ash, Al
2
O
3
, TiO
2
(0.2) > S (0.1).
The different position of S and SO
3
in this order is related to the
higher capture behaviour of S in biomass ash than in coal ash due
to ‘‘self-cleaning” properties of some fuels
. The highest enrich-
ment (EDF > 2.0) in biomass or biomass ash shows moisture, vola-
tile matter, Ca, Cl, K, Mg, Mn, Na, O, and P. On the other hand, the
highest depletion (EDF 6 0.7) in biomass or biomass ash reveals
Table 7
Characteristic enrichment and depletion trends for the chemical characteristics (mean values) among the biomass groups and sub-groups specified.
Biomass group and sub-group
Enriched in
Depleted in
1. Wood and woody biomass (WWB)
CaO, M, MgO, Mn, VM
A, Cl, N, P
2
O
5
, S, SiO
2
, SO
3
2. Herbaceous and agricultural biomass (HAB)
FC, K
2
O, O, VM
C, H, CaO
2.1. Grasses (HAG)
K
2
O, O, SiO
2
, VM
Al
2
O
3
, C, CaO, H, Na
2
O
2.2. Straws (HAS)
Cl, K
2
O, O, SiO
2
C, H, Na
2
O
2.3. Other residues (HAR)
FC, K
2
O, MgO, P
2
O
5
Cl
3. Animal biomass (AB)
A, C, CaO, Cl, H, N, Na
2
O, P
2
O
5
, S, SO
3
Al
2
O
3
, Fe
2
O
3
, M, MgO, Mn, O, SiO
2
, TiO
2
, VM
4. Contaminated biomass (CB)
A, Al
2
O
3
, C, Cl, Fe
2
O
3
, H, N, S, TiO
2
FC, K
2
O, P
2
O
5
Table 8
Decreasing order of mean values for the chemical characteristics of the biomass
groups and sub-groups specified.
Symbol
Order for groups and sub-groups
M (am)
WWB > HAG > HAR > HAB > CB > HAS > AB
VM (db)
HAG > WWB > HAB > HAS > HAR > CB > AB
FC (db)
HAR > HAB > WWB > HAS > HAG > AB > CB
A (db)
AB > CB > HAS > HAB > HAR > HAG > WWB
C (daf)
AB > CB > WWB > HAR > HAB > HAS > HAG
O (daf)
HAG > HAS > HAB > HAR > WWB > CB > AB
H (daf)
AB > CB > HAR > (WWB, HAB) > (HAG, HAS)
N (daf)
AB > CB > HAR > (HAB, HAS) > HAG > WWB
S (daf)
AB > CB > HAR > (HAB, HAS) > HAG > WWB
Cl (db)
AB > HAS > CB > HAG > HAB > HAR > WWB
SiO
2
HAG > HAS > CB > HAB > HAR > WWB > AB
CaO
AB > WWB > CB > HAR > HAB > HAS > HAG
K
2
O
HAR > HAB > HAG > HAS > WWB > AB > CB
P
2
O
5
AB > HAR > HAG > HAB > HAS > CB > WWB
Al
2
O
3
CB > WWB > HAR > HAB > HAS > AB > HAG
MgO
HAR > WWB > HAB > HAS > HAG > CB > AB
Fe
2
O
3
CB > HAR > WWB > HAB > HAS > HAG > AB
SO
3
AB > HAR > HAG > HAB > CB > HAS > WWB
Na
2
O
AB > HAR > WWB > HAB > CB > HAS > HAG
TiO
2
CB > WWB > HAR > HAB > HAS > HAG > AB
Mn
WWB > HAG > HAR > CB > HAB > HAS > AB
Abbreviations: AB, animal biomass; CB, contaminated biomass; HAB, herbaceous
and agricultural biomass; HAG, herbaceous and agricultural grass; HAR, herbaceous
and agricultural residue; HAS, herbaceous and agricultural straw; WWB, wood and
woody biomass.
S.V. Vassilev et al. / Fuel 89 (2010) 913–933
923
ash yield, fixed carbon, Al, C, Fe, S, Si, and Ti. Relatively comparable
contents (EDF = 0.8–1.2) show H, N and sulphate S. Similar EDF
trends are also observed between natural biomass and the differ-
ent SFF types (
). The literature data show that bio-
mass or biomass ash generally has greater moisture, volatile
matter, Ca, Cl, H, K, Mg, Mn, O and Si contents, and lower Al, C,
Fe, N, S and Ti concentrations in comparison with coal or coal
ash
. The relatively comparable N content in
biomass and coal has been also reported earlier
. Hence,
there is agreement between the present data and reference obser-
vations, excluding only Si and the additional results supplied for
ash, fixed carbon, Na, and P in the present study. The disagreement
for Si could be related to the much lesser set of coal and biomass
samples used in the reference investigations than herein.
The present data also indicate some leading tendencies for the
chemical composition of biomass and SFFs. For example, the above
listed EDF trend is indicative for the potential of biomass and bio-
mass products to contain preferably phases with:
(1) more oxygen-containing functional groups (hydroxyl, car-
boxyl, ether and ketone groups) with highly reactive func-
tionalities (–COOH, –OCH
3
and –OH), chelates, light
hydrocarbons, carbohydrates, oxyhydroxides, carbonates,
chlorides, and phosphates; and
(2) less aromaticity, functionalities, silicates, and sulphates-
sulphides; in comparison with SFFs
The plant materials (dominantly ancient species) are a precur-
sor for coal formation. Therefore, the above EDF trend also indi-
cates the subsequent transformation of plant materials and
formation of SFFs. For instance, coal is enriched in ash, fixed car-
bon, Al, C, Fe, N, S, Si and Ti, and depleted in moisture, volatile mat-
ter, Ca, Cl, H, K, Mg, Mn, Na, O, and P in comparison with the
biomass. This observation is in a good agreement with the findings
about the mobilization, redistribution and formation of stable (en-
riched in coal) and unstable (depleted in coal) discrete phases or
minerals which are bearing constituents of the above elements,
during coal formation and coal rank advance
2.1.2. Proximate composition of biomass
There are large variations for the characteristics determined by
the proximate and ultimate analyses of biomass samples (
).
However, these variations are mostly due to the moisture contents
and ash yields, which vary in the greatest intervals. When the mea-
sured parameters are recalculated on dry and dry ash-free basis
their variations are in more narrow ranges for biomass groups
and sub-groups (
). For example, the range values of volatile
matter and fixed carbon as measured in grasses are respectively
46.5–73.5% and 9.5–16.8%, while these values on dry basis are only
73.4–81.6% and 13.7–18.1%, respectively. Therefore, it is better to
use dry, dry ash-free or ash basis for comparative chemical charac-
terization of biomass varieties. The moisture content and ash yield
are important parameters of the biomass system and require a
more detail discussion.
2.1.2.1. Moisture. The moisture content in biomass as measured (at
different basis, but normally as received, air-dried and oven-dried
basis) varies in the interval of 3–63% (
) and it can reach even
80% for raw wood species
. The moisture value seems to de-
crease in the order: WWB > HAG > HAR > HAB > CB > HAS > AB (
). In contrast, the moisture occurrence in peat and coal as
measured (mostly air-dried basis) is commonly in the more narrow
range of 1–20% (
). This characteristic seems to have much
higher contents in biomass than in SFFs at least on raw basis,
respectively as collected (harvested) and run of mine status. Simi-
lar observations have been also mentioned earlier
The moisture in biomass is mineralized aqueous solution con-
taining cations (Al, Ca, Fe, K, Mg, Mn, Na, Ti), anions (Br, Cl, CO
3
,
F, HCO
3
, H
2
PO
4
, I, NO
3
, OH, PO
4
, SO
4
) or non-charged species
(H
4
SiO
4
)
. This fluid plays a key role for the composi-
tion of biomass because of: (1) high water content in the living
cells; (2) variable total mineralization of water (dissolved solid
matter); and (3) different chemical specification (predominant an-
ions, cations and their ratios) of these water solutions. Therefore,
there is intensive mineral precipitation from a saturated solution
due to moisture evaporation after biomass harvesting and during
biomass drying. This process results mostly in consecutive forma-
tion of water-soluble: (1) phosphates; (2) carbonates; (3) sul-
phates; (4) chlorides; and (5) nitrates, which are a general
sequence of precipitation from less soluble to highly soluble min-
erals in the water system
. Such mineral formations are
the reason for enhanced leaching of Ca, Cl, K, Mg, Na, P, and S from
biomass harvested and left in the field for a prolonged period of
time
. Additional confirmation of the above
statement is also the observation that young foliage of wood (bio-
logically active tissues) shows the highest contents of water and
elements such as Cl, K, Mg, P, and S
. These are typical mobile
elements not only in the plant physiology
, but also in the nat-
ural water system
. The above observations show the impor-
tance
of
specifying
the
exact
status
used
for
biomass
characterization.
2.1.2.2. Ash yield. The ash yield (db) determined at 550–600 °C for
biomass varies in the interval of 0.1–46% (
) and normally
decreases in the order: AB > CB > HAS > HAB > HAR > HAG > WWB
(
). In contrast, the ash content (815 °C) in peat and coal
(db) is in the relatively more narrow range of 4–52% (commonly
4–30%) (
). The ash normally shows much lower value in bio-
mass than in SFFs, excluding AB and some CB and HAB samples
(
). The extremely high ash content is characteristic of sew-
age sludge, chicken litter, greenhouse-plastic waste, refuse-derived
fuel, meat-bone meal, and rice straw. The reference data show that
WWB has much lower ash content comparing with HAB because
straws, grasses, cereals, and fruits take up nutrients during their
growing periods
. The ash in WWB decreases in the or-
der: foliage > bark > wood
. The high ash yields of some wood
fuels such as chemically treated wood and waste wood are an indi-
cation for increased amounts of mineral and metallic impurities
and other contaminants due to the manufacturing process
. Hence, there is agreement between the present and refer-
ence data, but some additional elucidation of this important
parameter is required.
The ash is one of the most studied characteristics of biomass,
but unfortunately with the poorest understanding. The complex
character of this parameter is the reason for such a problem be-
cause ash originates simultaneously from natural and technogenic
inorganic, organic and fluid matter during biomass combustion. It
should be stated that the terms ash, inorganic matter and mineral
matter of biomass (
) are not synonymous because
they comprise constituents with different nature and quantity,
similar to coal
. The inorganic matter comprises solid
crystalline, semi-crystalline and amorphous phases in biomass.
The actual mineral matter, as a part of inorganic matter, excludes
inorganic amorphous matter and includes only minerals and min-
eraloids in biomass that belong to mineral classes, groups and spe-
cies strictly divided and defined in the mineralogical sense. In
contrast, the ash yield is the inorganic residue that results from
the complete combustion (or oxidation) of biomass and is com-
posed of original and newly formed inorganic phases generated
from the inorganic, organic and fluid components in biomass.
LTA and HTA are laboratory-produced biomass ashes at regulated
temperatures, respectively: (1) in oxygen plasma at 100–250 °C;
924
S.V. Vassilev et al. / Fuel 89 (2010) 913–933
and (2) in air above 500 °C. The combustion temperature signifi-
cantly affects the total yield of ash from biomass. For example,
the ash yields determined at 1000–1300 °C are 20–70% lower than
those produced by LTA or HTA at 500–550 °C
. Such
weight losses for biomass are much higher than for coal and these
differences are a result of more intensive phase transformations
and subsequent volatilization of elements from biomass phases
in the high temperature intervals
. It should be stated that
the ash yield itself brings relatively limited information when the
composition, abundance and origin of the biomass constituents
are not considered. Hence, the ash should always be interpreted to-
gether with the genesis of constituents in biomass. Such interpre-
tations have a great importance for both organic and inorganic
elements in biomass because their modes of occurrence are related
to mixed natural (authigenic and detrital) and technogenic origin.
Despite the above limitations, the ash yields of biomass can be
measured routinely, while the actual determination of inorganic
constituents is a complex procedure and cannot be quickly and
routinely achieved. Therefore, ash is still an important parameter
for approximating: (1) the bulk inorganic matter; (2) predominant
affinity of elements and compounds to inorganic or organic matter;
and (3) possible contamination of biomass.
2.1.2.3. Volatile matter. The volatile matter content (db) in biomass
varies in the interval of 48–86% (
) and normally decreases in
the order: HAG > WWB > HAB > HAS > HAR > CB > AB (
). In
contrast, the volatile matter value in peat and coal (db) is com-
monly in the larger range of 12–68% (
). This parameter typ-
ically shows much higher content in biomass than in SFFs (
). The extremely high volatile matter value is characteristic of
some WWB, sugar cane bagasse, and paper waste (
). The
volatile matter yield of biomass commonly includes light hydro-
carbons, CO, CO
2
, H
2
, moisture, and tars
.
2.1.2.4. Fixed carbon. The fixed carbon content (db) in biomass var-
ies in the interval of 1–38% (
) and normally decreases in the
order: HAR > HAB > WWB > HAS > HAG > AB > CB (
). In con-
trast, the fixed carbon value in peat and coal (db) is commonly in
the larger range of 20–72% (
). This parameter typically re-
veals lower content in biomass than in SFFs (
). The extre-
mely high fixed carbon content is characteristic of some wood
barks and HAB residues (
). Furthermore, biomass commonly
has a volatile matter/fixed carbon ratio >3.5, while this ratio for
peat and coal is normally in the interval 0.6–2.4 (
).
The plotted mean proximate composition (db) of solid fuel
types in
illustrates: (1) the differentiations between the bio-
mass and coals; (2) the relatively closer position of peat to biomass
than coals; and (3) the similarities among various biomass groups
and sub-groups, excluding only AB and CB biomass groups. The
distinctions for the last groups are evidenced by their plots in
and maximum or minimum values in the above-listed orders
for the proximate characteristics. Both AB and CB groups com-
monly have intermediate positions between SFFs and other bio-
mass groups and sub-groups.
2.1.3. Ultimate composition of biomass
Due to the strong influence of moisture and ash yield on the
contents of other chemical characteristics in the biomass system,
the dry ash-free (daf) basis of biomass varieties and SFF types are
used for comparative characterizations of the ultimate analysis
(five elements) plus additional data for Cl contents (db) (
2.1.3.1. Carbon (C). The C content in biomass varies in the interval
of 42–71% (
) and normally decreases in the order:
AB > CB > WWB > HAR > HAB > HAS > HAG (
). In contrast,
the C value in peat and coal is commonly in the range of 56–87%
(
). This element typically shows lower content in biomass
than in SFFs (
). The extremely high C content is characteris-
tic of some wood barks and high-ash greenhouse-plastic waste,
chicken litter, meat-bone meal, and refuse-derived fuel (
).
The higher C content in woody biomass than in herbaceous bio-
mass has been also mentioned earlier
.
2.1.3.2. Oxygen (O). The O content in biomass is mostly calculated
by difference and varies in the interval of 16–49% (
). It nor-
mally decreases in the order: HAG > HAS > HAB > HAR > WWB > C-
B > AB (
). In contrast, the O value in peat and coal is
commonly in the range of 4–36% (
). This element typically
shows much higher content in biomass than in SFFs (
). The
extremely high O content is characteristic of pepper residues, cof-
fee and soya husks (
).
WWB - wood and woody biomass
HAB - herbaceous and agricultural biomass
HAG - herbaceous and agricultural grass
HAS - herbaceous and agricultural straw
HAR - herbaceous and agricultural residue
AB - animal biomass
MB - mixture of biomass
CB - contaminated biomass
AVB - all varieties of biomass
P - peat
L - lignite
S - sub-bituminous coal
B - bituminous coal
A - algae
Fig. 1. Mean proximate composition of solid fuel types, wt.%.
S.V. Vassilev et al. / Fuel 89 (2010) 913–933
925
2.1.3.3. Hydrogen (H). The H content in biomass varies in the inter-
val of 3–11% (
). In contrast, the H concentration in peat and
coal is in the narrow range of 4–6% (
). This element com-
monly shows higher content in biomass than in SFFs (
).
The extremely high H content is characteristic of greenhouse-plas-
tic waste, tamarack bark, mustard and cotton husks, meat-bone
meal, refuse-derived fuel, and groundnut shells (
). The H va-
lue normally decreases in the order: AB > CB > HAR > (WWB, HAB)
> (HAG, HAS) (
). The similar order of H and C indicates their
association (occurrence and behaviour) in biomass probably as
hydrocarbons and carbohydrates. It is well-known that photosyn-
thesis results in the production of structural and non-structural
carbohydrates comprising the plant tissues
.
2.1.3.4. Nitrogen (N). The N content in biomass varies in the interval
of 0.1–12% (
) and normally decreases in the order:
AB > CB > HAR > (HAB, HAS) > HAG > WWB (
). In contrast,
the N value in peat and coal is in the narrow range of 1–3% (
). This mobile element normally has slightly lower content in bio-
mass than in SFFs, excluding AB and some varieties from CB and
HAB groups. The extremely high N content is characteristic of
meat-bone meal, chicken litter, sewage sludge, pepper residues, al-
falfa and mint straws, palm kernels, and buffalo gourd grass (
). The samples from WWB group typically show the lowest N con-
centration (
) and this finding has been reported earlier
It was also noted that grasses usually show the highest N values
; however, the present data do not support this observation.
2.1.3.5. Sulphur (S). The S content in biomass varies in the interval
of 0.01–2.3% (
) and normally decreases in the order:
AB > CB > HAR > (HAB, HAS) > HAG > WWB (
). This order is
identical to N and indicates the close association of both N and S.
In contrast, the S concentration in peat and coal is in the range of
0.2–9.8% (
). This mobile element has typically much lower
content in biomass than in SFFs, excluding AB and some varieties
from CB and HAB groups (
). The extremely high S content
is characteristic of sewage sludge, meat-bone meal, chicken litter,
biomass mixture, pepper residues, refuse-derived fuel, and Christ-
mas trees (
). It was also noted that bark and straw have a
higher S content than wood, but some wood products (pellets
and briquettes) can also contain S-bearing additives
.
2.1.3.6. Chlorine (Cl). The Cl content in biomass (db) varies in the
interval of 0.01–0.9% (
) and normally decreases in the order:
AB > HAS > CB > HAG > HAB > HAR > WWB (
). This order is
similar to those of N and S, which indicates their association in bio-
mass probably as salts. In contrast, the Cl value (db) in peat and
coal is in the large range of 0.005–0.1% (
). This mobile ele-
ment has commonly much higher content in biomass than in SFFs,
in particular AB and many varieties from CB and HAB groups. The
extremely high Cl content is characteristic of meat-bone meal, re-
fuse-derived fuel, most straws (alfalfa, barley, corn, mint, rice,
wheat), some grasses (bana, sweet sorghum), and chicken litter
(
). On the other hand, most of the WWB and HAR samples
show the lowest Cl contents (
). It was noted that wood con-
tains generally very low Cl concentrations, but certain wood prod-
ucts can contain Cl-bearing additives
. The reference data
also show high Cl contents in some: wood barks and straws
herbaceous biomass, grains and fruit residues
; crops inten-
sively cultivated with fertilizers
; wood foliage, trees growing
at the edge of forests, near to motor highways (due to de-icing
salts), and in the cities (from Cl aerosols)
; and even close to
the sea
.
The plotted mean ultimate composition (daf) of solid fuel types
in Fig. 2 (see the reason for its creation in Section 2.2.2) illustrates:
(1) the differentiations between the biomass and coals; (2) the clo-
ser position of peat to biomass than coals; and (3) the similarities
among various biomass groups and sub-groups, excluding again
(like the proximate composition) only the AB and CB biomass
groups. The distinctions for the last groups are evidenced by their
plots in Fig. 2 and maximum or minimum values in the above-
listed orders for the ultimate characteristics. Both AB and CB
groups also have intermediate positions between SFFs and other
biomass groups and sub-groups.
2.1.4. High-temperature ash (HTA) composition of biomass
The traditional chemical data for 10 oxides (normalized to
100%) plus Mn contents in HTAs of biomass varieties, groups and
sub-groups (550–600 °C), as well as SFF types (815 °C) are given
in
and used for comparative characterizations. It should
be noted that the most abundant oxides could have slightly over-
estimated values after the normalization. It can be seen that the
chemical composition of biomass HTAs shows extremely large
variations. This is due to the highly variable contents of bulk
WWB - wood and woody biomass
HAB - herbaceous and agricultural biomass
HAG - herbaceous and agricultural grass
HAS - herbaceous and agricultural straw
HAR - herbaceous and agricultural residue
AB - animal biomass
MB - mixture of biomass
CB - contaminated biomass
AVB - all varieties of biomass
P - peat
L - lignite
S - sub-bituminous coal
B - bituminous coal
A - algae
Fig. 2. Mean ultimate composition of solid fuel types, wt.%.
926
S.V. Vassilev et al. / Fuel 89 (2010) 913–933
inorganic matter and different genetic classes of inorganic matter
in biomass varieties. The characteristic enrichment and depletion
trends for the HTA characteristics in the biomass groups and
sub-groups specified are listed in
. The decreasing order
of these characteristics (mean values) for the biomass groups and
sub-groups are also given in
. The above orders reveal that
there is differentiation between the components as some similari-
ties were observed only for P–S and Al–Fe–Ti oxides. On the other
hand, according to the mean contents (
) of the most abun-
dant six oxides, their order in decreasing values for the specified
groups and sub-groups are:
CaO > SiO
2
> K
2
O > MgO > Al
2
O
3
> P
2
O
5
for WWB;
SiO
2
> K
2
O > CaO > P
2
O
5
> MgO > Al
2
O
3
for HAB and HAG;
SiO
2
> K
2
O > CaO > MgO > P
2
O
5
> Al
2
O
3
for HAS;
K
2
O > SiO
2
> CaO > P
2
O
5
> MgO > Al
2
O
3
for HAR;
CaO > P
2
O
5
> K
2
O > SiO
2
> MgO > Al
2
O
3
for AB;
SiO
2
> CaO > Al
2
O
3
> P
2
O
5
> MgO > K
2
O for CB.
Hence, there is a characteristic differentiation between the
groups and significant similarity between the sub-groups (particu-
larly HAG and HAS) among the orders of these six oxides. Three
types of biomass ash system have been described elsewhere in
terms of their chemical composition, namely (1)>Si/>K/<Ca ashes
(grasses); (2)<Si/>K/>Ca ashes (woody materials, pits and shells);
and (3)>Ca/>P ashes (manures, poultry litters and animal wastes)
. So, there is some agreement between the present data and
reference observations, but the present study supplies more data
and indicates that an additional clarification of chemical ash con-
stituents is required.
2.1.4.1. SiO
2
. The SiO
2
content in biomass HTAs varies in the large
interval of 0.02–94% (
) and the value of this oxide normally
decreases in the order: HAG > HAS > CB > HAB > HAR > WWB > AB
(
). In contrast, the SiO
2
concentration in peat and coal HTAs
is commonly in the more narrow range of 32–68% (
). This
oxide represents less mobile Si components in biomass and nor-
mally shows lower content in biomass ash than in SFF ash, exclud-
ing some HAB, WWB and CB samples. The extremely high SiO
2
content is characteristic of reed canary grass, sorghastrum grass,
rice straw, and rice husks (
). The reference data also show
that the wood stems contain very little Si, while in some grasses,
straws (especially rice straws), rice husks
and spruce
needles
substantial to high amounts of silica were found. It
is interesting to note that some tall grasses and straws contain a
high amount of Si that contributes to the plant’s sturdiness or rig-
idness
. This Si is introduced in plant as silicic acid and pre-
cipitates in the form of amorphous and occasionally crystalline
silica as Al is likely to co-precipitate with Si
. On the
other hand, Si (plus Al, Ti, Fe, and Na) may also be introduced in
biomass fuels as sand, clays and other soil components during har-
vest and transport or through processing operations and manufac-
tured products
2.1.4.2. CaO. The CaO content in biomass HTAs varies in the large
interval of 1–83% (
) and the value of this oxide normally de-
creases in the order: AB > WWB > CB > HAR > HAB > HAS > HAG
(
). In contrast, the CaO concentration in peat and coal HTAs
is commonly in the more narrow range of 0.4–28% (
). This
oxide represents less mobile Ca components in biomass and nor-
mally shows much higher content in biomass ash than in SFF
ash, excluding some biomass samples mostly from HAB group.
The extremely high CaO content is characteristic of wood barks
and chicken litter (
). The reference data also reveal that
the wood stems, trunks and large branches contain high Ca con-
centrations
. Calcium and Mn show similar concentration
trends in biomass and they are accumulated in the foliage and bark
through the precipitation of Ca oxalate as Mn co-precipitates in the
oxalate as solid solution with Ca
.
2.1.4.3. K
2
O. The K
2
O content in biomass HTAs varies in the large
interval of 0.2–64% (
) and the value of this oxide normally
decreases in the order: HAR > HAB > HAG > HAS > WWB > AB > CB
(
). In contrast, the K
2
O concentration in peat and coal HTAs
is commonly in the narrow range of 0.3–4% (
). This oxide
represents mobile K components in biomass and mostly shows
much higher content in biomass ash than in SFF ash, excluding
some CB varieties and individual WWB, HAG and AB samples.
The extremely high K
2
O content is characteristic of HAB group
and particularly HAR sub-group (
). These observations are
in accordance with the literature data. For example, it was found
that the biomass with high annual growth is abundant in alkaline
elements because they are readily taken up from the soil
2.1.4.4. P
2
O
5
. The P
2
O
5
content in biomass HTAs varies in the large
interval of 0.2–41% (
) and the value of this oxide normally
decreases in the order: AB > HAR > HAG > HAB > HAS > CB > WWB
(
). In contrast, the P
2
O
5
concentration in peat and coal HTAs
is commonly in the more narrow range of 0.1–3% (
). This
oxide represents mobile P components in biomass and mostly
shows much higher content in biomass ash than in SFF ash, exclud-
ing some CB varieties. The extremely high P
2
O
5
content is charac-
teristic of AB group, sewage sludge and some HAB samples (
). The enrichment of this oxide in cereals has been also noted
2.1.4.5. Al
2
O
3
. The Al
2
O
3
content in biomass HTAs varies in the large
interval of 0.1–54% (
) and the value of this oxide normally
decreases in the order: CB > WWB > HAR > HAB > HAS > AB > HAG
(
). In contrast, the Al
2
O
3
concentration in peat and coal
HTAs is commonly in the more narrow range of 11–35% (
). This oxide represents less mobile Al components in biomass
and mostly shows much lower content in biomass ash than in
SFF ash, excluding some CB varieties and individual samples from
WWB group and HAR sub-group. The extremely high Al
2
O
3
content
is characteristic of mixed waste paper probably due to the tradi-
tional kaolinite additive used in paper production (
). The
high Al concentration is also usually considered as a marker for
contamination of biomass by soil inclusions (predominantly clays
and oxides), dust or dirt
2.1.4.6. MgO. The MgO content in biomass HTAs varies in the large
interval of 0.2–16% (
) and the value of this oxide normally
decreases in the order: HAR > WWB > HAB > HAS > HAG > CB > AB
(
). In contrast, the MgO concentration in peat and coal HTAs
is commonly in the more narrow range of 0.3–4% (
). This
oxide represents mobile Mg components in biomass and normally
shows much higher content in biomass ash than in SFF ash, exclud-
ing individual samples from all of the groups and sub-groups spec-
ified. The extremely high MgO content is characteristic of alfalfa
straw and some WWB and HAR varieties (
).
2.1.4.7. Fe
2
O
3
. The Fe
2
O
3
content in biomass HTAs varies in the
large interval of 0.2–36% (
) and the value of this oxide nor-
mally decreases in the order: CB > HAR > WWB > HAB > HAS > HA-
G > AB (
). In contrast, the Fe
2
O
3
concentration in peat and
coal HTAs is commonly in the more narrow range of 0.8–16% (
). This oxide represents less mobile Fe components in biomass
and normally shows lower content in biomass ash than in SFF ash,
excluding some WWB, HAR and CB varieties. The extremely high
Fe
2
O
3
content is characteristic of pistachio shells (probably con-
taminated by Fe oxyhydroxides), some industrial wastes, sewage
sludge, sugar cane baggase, and groundnut shells (
).
S.V. Vassilev et al. / Fuel 89 (2010) 913–933
927
2.1.4.8. SO
3
. The SO
3
content in biomass HTAs varies in the large
interval of 0.01–15% (
) and the value of this oxide normally
decreases in the order: AB > HAR > HAG > HAB > CB > HAS > WWB
(
). In contrast, the SO
3
concentration in peat and coal HTAs
is in relatively more narrow range of 0.3–14% (
). This oxide
represents the mobile S components in biomass that are captured
in biomass ash as sulphates. SO
3
normally shows lower content in
biomass ash than in SFF ash, excluding AB and some WWB, HAB
and CB varieties. The extremely high SO
3
content is characteristic
of groundnut shells, mustard husks, and pepper residues. The great
SO
3
concentration in Christmas trees, and currency shredded (
) is probably due to S-bearing contaminants and additives,
respectively.
2.1.4.9. Na
2
O. The Na
2
O content in biomass HTAs varies in the large
interval of 0.1–30% (
) and the value of this oxide normally
decreases in the order: AB > HAR > WWB > HAB > CB > HAS > HAG
(
). In contrast, the Na
2
O concentration in peat and coal HTAs
is commonly in the more narrow range of 0.1–3% (
). This
oxide represents relatively less mobile Na components in biomass
and normally shows much higher content in biomass ash than in
SFF ash, excluding some WWB, HAB, AB and CB varieties. The ex-
tremely high Na
2
O content is characteristic of olive husks and pits,
and fir mill residue probably contaminated by solution with halite
composition (see
). For example, it was noted that
the high Na concentrations are frequently an indication of intru-
sion of salt water or a process additive
.
2.1.4.10. TiO
2
. The TiO
2
content in biomass HTAs varies in the large
interval of 0.01–28% (
) and the value of this oxide normally
decreases in the order: CB > WWB > HAR > HAB > HAS > HAG > AB
(
). In contrast, the TiO
2
concentration in peat and coal HTAs
is commonly in the narrow range of 0.3–1.6% (
). This oxide
represents less mobile Ti components in biomass and normally
shows much lower content in biomass ash than in SFF ash, exclud-
ing some CB varieties, sugar cane bagasse and individual wood
samples. The extremely high TiO
2
content is characteristic of cur-
rency shredded and mixed waste paper probably due to the tradi-
tional Ti-bearing additives (
2.1.4.11. Mn. The Mn content in biomass HTAs varies in the large
interval of 0.01–3.6% (
) and the value of this element nor-
mally decreases in the order: WWB > HAG > HAR > CB > HAB > HA-
S > AB (
). In contrast, the Mn concentration in peat and coal
HTAs is commonly in the narrow range of 0.02–0.18% (
).
This less mobile element in biomass mostly shows much higher
content in biomass ash than in SFF ash, excluding some HAB, AB
and CB varieties. The extremely high Mn content (together with
Ca) is characteristic of some WWB samples (
The contents of CO
2
and water are occasionally determined and
included in the bulk chemical composition of biomass HTAs
[23,34,36,44,51,60,63–65,67,68,76,91]
. These are useful subsidiary
characteristics during the phase identification and characterization
of ashes. However, they are less informative for the bulk balance
and actual chemical ash composition because significant parts of
them are fixed in HTAs from the air CO
2
and moisture. Both com-
pounds intensively react with the active and highly abundant alka-
line and alkaline-earth oxides to form hydrates, hydroxides, and
carbonates in ash during the sample oxidation and storage
On the other hand, the loss on ignition content is occasionally also
determined (450–1000 °C) and included in the bulk chemical com-
position of biomass HTAs to represent the unburned matter
. However, this parameter is also less informa-
tive because it could not represent the actual organic matter con-
tent in biomass ashes due to their specific phase composition
and ash transformations during heating
.
2.2. Correlations and associations among chemical composition of
biomass and their potential applications
2.2.1. Correlations and associations
In contrast to biomass from similar plant species or growth re-
gions, the significant chemical correlations between numerous bio-
mass varieties worldwide are not common, and defining these
similarities requires special attention. The results from such study
can provide valuable information for the understanding of some
fundamental relationships and trends in biomass. For that purpose,
the complete chemical data obtained from the proximate (db), ulti-
mate (daf) and ash analyses plus results for Cl and Mn (
) were used. Data for 78 varieties of natural biomass were
subjected to the Pearson’s correlation test
to calculate correla-
tion coefficient values among 20 characteristics. The CB biomass
group (8 varieties) was excluded from this database due to the
obvious occurrence of technogenic products. The moisture was
also excluded because of different and insecure biomass basis used
for moisture measurement. The calculated correlation coefficient
values (R
2
) include the statistically significant relationships,
namely positive and negative R
2
at 99% and 95% confidence levels,
as well as statistically insignificant R
2
). The correlation
data should be used with caution because they could not be exclu-
sive and future use of a larger number of biomass samples (in par-
ticular from aquatic biomass) would likely lead to some changes.
The significant correlations among elements can be a result of both
direct and indirect genetic associations in biomass. The direct ge-
netic associations in biomass comprise: (1) phase parageneses,
namely simultaneous authigenic phase formations or detrital in-
flux; and (2) phase generations such as subsequent authigenic for-
mations and detrital influx of phases at different stages. On the
other hand, the indirect genetic associations include only the coex-
istence of phase assemblages in this complex system. Hence, addi-
tional subsidiary studies and literature data about the modes of
occurrence of elements, phases or minerals in biomass should al-
ways be applied together with such correlation tests for an expla-
nation of the significant relationships. Finally, some statistically
insignificant correlations could be important, while other signifi-
cant correlations could not be explained by the present knowledge
of biomass.
The present data (
and Fig. 3) show that there are some
strong:
(1) positive correlations and associations among characteristics
such as ash–S–N–Cl–P, C–H–Ca–S, Ca–Mg–C–Mn, Si–ash–
Al–Ti, Al–Ti–Fe, K–Mg–P, Na–Fe; and
(2) negative correlations between couples, namely ash–Mn,
ash–O, ash–Mg, C–O, O–N, O–S, O–P, O–H, Cl–Mn, Cl–Al,
Si–Ca, Si–Mg, Si–P, Si–K, Si–Mn, Ca–K, Ca–Al, K–Al, K–Ti,
Fe–Cl, and Fe–Ca, that also confirm the above associations.
It should be stated that similar: (1) strong positive correlations
and associations for ash–S–N–Cl
, ash–Si
, S–P, Si–Al
, Cl–P, K–P
, K–Mg, ash–P, ash–S, N–P, S–Cl, Cl–K
and (2) strong negative correlations for ash–O, Si–Ca, and Si–Mg
; have been also detected for biomass varieties in the
literature.
2.2.2. Potential applications
As a result of the present correlations and associations two fig-
ures (Figs. 2 and 4) were created using the intersections of three
end members in triangular graphs. Fig. 2 includes: (1) C + H, (2)
O, and (3) N + S + Cl for biomass; whereas
comprises: (1)
SiO
2
+ Al
2
O
3
+ Fe
2
O
3
+ Na
2
O + TiO
2
, (2) CaO + MgO + MnO, and (3)
K
2
O + P
2
O
5
+ SO
3
+ Cl
2
O for biomass ash as end members.
928
S.V. Vassilev et al. / Fuel 89 (2010) 913–933
The specification of elements from ultimate analysis (Fig. 2) into
three groups is based on: (1) the strong and significant positive
correlations for C–H; and N–S–Cl (P also belongs to this associa-
tion); and (2) the strong and significant negative correlations be-
tween O and other elements (
). The differentiations and
similarities among solid fuel types according to their mean ulti-
mate composition (daf) plotted in Fig. 2 were listed above (see Sec-
tion 2.1.3.6).
On the other hand, the most abundant six oxides in biomass
HTAs are these of Si, Al, Ca, Mg, K, and P (
) and they were
grouped into three couples (Si–Al, Ca–Mg, and K–P oxides) accord-
ing to their positive and negative R
2
values. The specification of
these couples is based on the strong positive correlations between
the oxides in the couples and their negative correlations with other
oxides. Respectively, the remaining subordinate six oxides or ele-
ments are redistributed to the above couples on the basis of their
strong positive correlations with the oxides in the couples specified
(
and
). It was found that K
2
O has also significant po-
sitive correlation with MgO; however, the latter oxide has stronger
positive value with CaO than with K
2
O (
). Similar twofold
behaviour could be also expected for Na
2
O depending on its dom-
inant mobile or immobile occurrence. For example, highly mobile
Na can occur in algae (seaweeds), which are greatly abundant in
this element
.
The plotted mean HTA composition of solid fuel types in
illustrates: (1) the distinctions between the biomass and SFFs;
(2) the closer position of peat to coals than biomass (in contrast
to
); (3) the differentiations among the biomass groups
and the similarities for HAB sub-groups; (4) the distinctions for the
CB and AB with other biomass groups evidenced by their plots and
maximum or minimum values in the above-listed orders for the
ash characteristics; and (5) the intermediate position of CB be-
tween SFFs and other biomass groups and sub-groups. These
observations show significant differences in comparison with
those detected from proximate (
) and ultimate (Fig. 2) analy-
ses as a result of the highly variable composition of inorganic com-
ponents in biomass. Therefore, the plotted mean HTA composition
of these solid fuel types in
can be used as initial and prelimin-
ary chemical classification system for the inorganic matter of bio-
mass. This is due to the distinctive and highly informative plot
distributions of:
(1) all varieties of biomass (close to the centre of the triangular
graph);
(2) WWB (Ca + Mg + Mn oxides above 30%);
(3) HAB, HAG, HAS and HAR (K + P + S + Cl oxides above 30%);
(4) AB (both sums of Ca + Mg + Mn oxides and K + P + S + Cl oxi-
des above 30% and Si + Al + Fe + Na + Ti oxides below 40%);
Table 9
Significant positive (+) and negative ( ) correlation coefficient values (R
2
) at 99% (bold font)
and 95% (italic font)
confidence levels, and insignificant (normal font) R
2
values for
the chemical composition of 78 varieties of natural biomass (excluding eight contaminated biomass varieties).
Symbol
Correlation coefficient value with:
VM (78)
(+) Mn(0.43) O(0.41) TiO
2
(0.20) MgO(0.17) Fe
2
O
3
(0.16) Na
2
O(0.13) K
2
O(0.08) Al
2
O
3
(0.01) CaO(0.01)
( ) A( 0.80) S( 0.58) N( 0.52) Cl( 0.46) FC( 0.44) C( 0.24) P
2
O
5
( 0.15) SiO
2
( 0.10) SO
3
( 0.09) H( 0.06)
FC (78)
(+) MgO(0.19) Mn(0.16) K
2
O(0.13) SO
3
(0.13) Al
2
O
3
(0.08) C(0.07) CaO(0.06) H(0.02) Fe
2
O
3
(0.01)
( ) VM( 0.44) TiO
2
( 0.21) A( 0.19) SiO
2
( 0.16) Cl( 0.13) P
2
O
5
( 0.12) S( 0.09) N( 0.08) Na
2
O( 0.04) O( 0.02)
A (78)
(+) S(0.70) N(0.63) Cl(0.55) P
2
O
5
(0.24) C(0.22) SiO
2
(0.21) H(0.05) SO
3
(0.01)
( ) VM( 0.80) Mn( 0.49) O( 0.44) MgO( 0.31) FC( 0.19) Fe
2
O
3
( 0.18) K
2
O( 0.17) Na
2
O( 0.12) TiO
2
( 0.08) Al
2
O
3
( 0.07) CaO( 0.05)
C (78)
(+) H(0.31) CaO(0.30) S(0.29) N(0.24) P
2
O
5
(0.23) A(0.22) Mn(0.12) Fe
2
O
3
(0.08) FC(0.07) Cl(0.06) Al
2
O
3
(0.05) MgO(0.04) TiO
2
(0.01) Na
2
O(0.00)
( ) O( 0.88) K
2
O( 0.25) SO
3
( 0.24) VM( 0.24) SiO
2
( 0.18)
O (78)
(+) VM(0.41) SiO
2
(0.26) K
2
O(0.19) SO
3
(0.07) TiO
2
(0.07) Mn(0.03) Al
2
O
3
(0.01)
( ) C( 0.88) N( 0.63) S( 0.62) P
2
O
5
( 0.50) H( 0.49) A( 0.44) Cl( 0.30) CaO( 0.26) MgO( 0.03) Na
2
O( 0.03) FC( 0.02) Fe
2
O
3
( 0.02)
H (78)
(+) C(0.31) Mn(0.24) CaO(0.20) Cl(0.16) N(0.16) MgO(0.14) P
2
O
5
(0.14) S(0.10) SO
3
(0.09) Na
2
O(0.07) A(0.05) FC(0.02) Fe
2
O
3
(0.02)
( ) O( 0.49) SiO
2
( 0.16) K
2
O( 0.15) TiO
2
( 0.11) Al
2
O
3
( 0.06) VM( 0.06)
N (78)
(+) S(0.90) P
2
O
5
(0.72) A(0.63) Cl(0.53) C(0.24) SO
3
(0.18) H(0.16) K
2
O(0.06) Na
2
O(0.04) CaO(0.02)
( ) O( 0.63) VM( 0.52) Mn( 0.31) SiO
2
( 0.24) TiO
2
( 0.15) Al
2
O
3
( 0.10) Fe
2
O
3
( 0.10) FC( 0.08) MgO( 0.05)
S (78)
(+) N(0.90) A(0.70) P
2
O
5
(0.63) Cl(0.49) C(0.29) SO
3
(0.26) H(0.10) CaO(0.04) Al
2
O
3
(0.01) Fe
2
O
3
(0.00)
( ) O( 0.62) VM( 0.58) Mn( 0.32) MgO( 0.18) SiO
2
( 0.15) FC( 0.09) K
2
O( 0.09) TiO
2
( 0.04) Na
2
O( 0.03)
Cl (56)
(+) A(0.55) N(0.53) S(0.49) P
2
O
5
(0.24) H(0.16) K
2
O(0.10) SiO
2
(0.08) C(0.06) Na
2
O(0.03) SO
3
(0.00)
( ) VM( 0.46) Mn( 0.42) Al
2
O
3
( 0.34) O( 0.30) TiO
2
( 0.29) Fe
2
O
3
( 0.27) MgO( 0.19) FC( 0.13) CaO( 0.10)
SiO
2
(78)
(+) O(0.26) A(0.21) Al
2
O
3
(0.21) TiO
2
(0.15) Cl(0.08) Fe
2
O
3
(0.03)
( ) CaO( 0.63) MgO( 0.58) P
2
O
5
( 0.39) K
2
O( 0.36) Mn( 0.28) SO
3
( 0.24) N( 0.24) C( 0.18) FC( 0.16) H( 0.16) S( 0.15) Na
2
O( 0.10) VM( 0.10)
CaO (78)
(+) MgO(0.35) C(0.30) Mn(0.30) H(0.20) FC(0.06) S(0.04) N(0.02) SO
3
(0.01) VM(0.01)
( ) SiO
2
( 0.63) K
2
O( 0.31) Al
2
O
3
( 0.27) O( 0.26) Fe
2
O
3
( 0.24) TiO
2
( 0.11) Cl( 0.10) A( 0.05) Na
2
O( 0.05) P
2
O
5
( 0.05)
K
2
O (78)
(+) MgO(0.26) P
2
O
5
(0.22) O(0.19) FC(0.13) Cl(0.10) VM(0.08) N(0.06) SO
3
(0.06)
( ) SiO
2
( 0.36) CaO( 0.31) Al
2
O
3
( 0.30) TiO
2
( 0.29) Mn( 0.27) C( 0.25) Fe
2
O
3
( 0.20) A( 0.17) Na
2
O( 0.16) H( 0.15) S( 0.09)
P
2
O
5
(78)
(+) N(0.72) S(0.63) A(0.24) Cl(0.24) C(0.23) K
2
O(0.22) H(0.14) SO
3
(0.13) MgO(0.07) Fe
2
O
3
(0.06) Na
2
O(0.01)
( ) O( 0.50) SiO
2
( 0.39) Mn( 0.20) TiO
2
( 0.16) VM( 0.15) Al
2
O
3
( 0.14) FC( 0.12) CaO( 0.05)
Al
2
O
3
(78)
(+) TiO
2
(0.63) Fe
2
O
3
(0.44) Mn(0.24) SiO
2
(0.21) Na
2
O(0.14) SO
3
(0.09) FC(0.08) C(0.05) O(0.01) S (0.01) VM(0.01)
( ) Cl( 0.34) K
2
O( 0.30) CaO( 0.27) MgO( 0.23) P
2
O
5
( 0.14) N( 0.10) A( 0.07) H( 0.06)
MgO (78)
(+) CaO(0.35) Mn(0.27) K
2
O(0.26) FC(0.19) VM(0.17) H(0.14) SO
3
(0.12) P
2
O
5
(0.07) C(0.04)
( ) SiO
2
( 0.58) A( 0.31) Al
2
O
3
( 0.23) Cl( 0.19) Fe
2
O
3
( 0.19) S( 0.18) TiO
2
( 0.10) Na
2
O( 0.08) N( 0.05) O( 0.03)
Fe
2
O
3
(78)
(+) Al
2
O
3
(0.44) TiO
2
(0.32) Na
2
O(0.19) Mn(0.18) VM(0.16) SO
3
(0.09) C(0.08) P
2
O
5
(0.06) SiO
2
(0.03) H(0.02) FC(0.01) S(0.00)
( ) Cl( 0.27) CaO( 0.24) K
2
O( 0.20) MgO( 0.19) A( 0.18) N( 0.10) O( 0.02)
SO
3
(78)
(+) S(0.26) N(0.18) FC(0.13) P
2
O
5
(0.13) MgO(0.12) Al
2
O
3
(0.09) Fe
2
O
3
(0.09) H(0.09) O(0.07) K
2
O(0.06) A(0.01) CaO(0.01) Mn(0.01) TiO
2
(0.01) Cl(0.00)
( ) C( 0.24) SiO
2
( 0.24) VM( 0.09) Na
2
O( 0.05)
Na
2
O (78)
(+) Fe
2
O
3
(0.19) Mn(0.17) Al
2
O
3
(0.14) VM(0.13) H(0.07) TiO
2
(0.07) N(0.04) Cl(0.03) P
2
O
5
(0.01) C(0.00)
( ) K
2
O( 0.16) A( 0.12) SiO
2
( 0.10) MgO( 0.08) CaO( 0.05) SO
3
( 0.05) FC( 0.04) O( 0.03) S( 0.03)
TiO
2
(78)
(+) Al
2
O
3
(0.63) Mn(0.36) Fe
2
O
3
(0.32) VM(0.20) SiO
2
(0.15) Na
2
O(0.07) O(0.07) C(0.01) SO
3
(0.01)
( ) Cl( 0.29) K
2
O( 0.29) FC( 0.21) P
2
O
5
( 0.16) N( 0.15) CaO( 0.11) H( 0.11) MgO( 0.10) A ( 0.08) S( 0.04)
Mn (33)
(+) VM(0.43) TiO
2
(0.36) CaO(0.30) MgO(0.27) Al
2
O
3
(0.24) H(0.24) Fe
2
O
3
(0.18) Na
2
O(0.17) FC(0.16) C(0.12) O(0.03) SO
3
(0.01)
( ) A( 0.49) Cl( 0.42) S( 0.32) N( 0.31) SiO
2
( 0.28) K
2
O( 0.27) P
2
O
5
( 0.20)
a
The significant R
2
values at 99% confidence level are: P0.28 and 6 0.28, P0.32 and 6 0.32, and P0.42 and 6 0.42 for 78, 56 and 33 variables, respectively.
b
The significant R
2
values at 95% confidence level are: P0.22 and 6 0.22, P0.25 and 6 0.25, and P0.33 and 6 0.33 for 78, 56 and 33 variables, respectively.
c
In the parentheses are the number of variables.
S.V. Vassilev et al. / Fuel 89 (2010) 913–933
929
(5) SFFs (Si + Al + Fe + Na + Ti oxides above 70%);
(6) CB (Si + Al + Fe + Na + Ti oxides between 40 and 70%).
This approach resulted in four chemical biomass ash types (S, C,
K and CK types) further specified into seven sub-types (with high,
medium and low acid tendencies). The positions of all samples
from the present study were also plotted in
for illustration.
The above approach, composition-based criteria and explanation
of the three end members in
are also comparable to those
identified and applied earlier for the chemical classification of coal
fly ashes
and HTAs
of coals despite the different constit-
uents included as end members and borders used. The chemical
biomass ash types and sub-types specified would have different
behaviour during biomass processing as it was found for coal
. Such approach could also be useful for the development
of new combined biomass and coal classification systems to permit
fuel prediction and selection for co-combustion applications.
Furthermore, Figs. 2 and 4 demonstrate the closest chemical
composition between HAG and HAS sub-groups. Hence, they may
be combined in one biomass sub-group and their future separate
characterization can be avoided. On the other hand, HAR sub-group
may be split in several sub-sub-groups due to the more variable
composition. Additionally, the unusual position of some samples
in
may indicate their possible contamination by detrital
and/or technogenic materials. For instance, certain biomass varie-
ties from the WWB group (samples 1, 5, 8, 11, 13, 14, 17, 24, and
28) and HAR sub-group (samples 57 and 68) are most likely
influenced by such contamination and some of these samples were
mentioned above.
It is interesting to note that the mean composition of 11 algae
(seaweed) samples
from the aquatic biomass group was also
plotted in
for comparison, despite incomplete chem-
ical analyses. These marine macroalgae show higher contents of ash,
fixed carbon, Cl, MgO, N, Na
2
O, O, P
2
O
5
, S, and SO
3
(particularly ash,
Cl, S, Na, and Mg) than the mean values for the terrestrial biomass
(
). The seaweeds reveal relatively similar ultimate
(Fig. 2) and different proximate (
) composition
in comparison with other terrestrial biomass groups and sub-
groups. It can be seen that the algae belong to K ash type with low
acid tendency and its position is closer to ash samples mostly from
HAR sub-group and, to a lesser extent, HAG sub-group (
Finally, the specified oxide associations in biomass HTAs (
are also indicative for the preferable occurrence and possible gen-
esis of inorganic elements in biomass. For example, the upper cor-
ner (SiO
2
+ Al
2
O
3
+ Fe
2
O
3
+ Na
2
O + TiO
2
) in
may represent
commonly the occurrence of Fe–Na–Ti-bearing silicates, alumino-
silicates and hydroxides with detrital, authigenic and technogenic
origin. The left corner (CaO + MgO + MnO) could include normally
Ca–Mg–Mn-containing carbonates, oxyhydroxides and oxalates
with preferable authigenic origin. The right corner (K
2
O + P
2
O
5
+
SO
3
+ Cl
2
O, as N also belongs to this association) may represent
commonly the mobile K-bearing phosphates, sulphates, chlorides
and nitrates with authigenic origin. The last association also fits
to the typical fertilizers. Certainly, some of the phases or minerals
could have mixed contribution to the different corners because of
their complex composition and genesis.
It should be stated that the actual explanation of the above-
described chemical differentiations, similarities, trends, and
Fig. 3. Some significant correlations among the chemical composition of biomass, wt.%.
930
S.V. Vassilev et al. / Fuel 89 (2010) 913–933
associations is only possible after significant knowledge of the
phase–mineral composition of biomass varieties. The presence,
abundance and distribution of modes of element occurrence have
a leading role for the characterization of biomass composition.
These are actual phases or minerals with well-known forms of
element combination and properties and are of vital importance
for understanding the biomass system. For example, most of the
elements in biomass occur in both organic and inorganic matter,
and each element is combined in different phases or minerals with
variable genesis and proportions, and has dominant associations
and affinities with the constituents. Unfortunately, the bulk chem-
ical composition of biomass does not provide any direct informa-
tion about the actual modes of element occurrence in this fuel.
3. Conclusions
Some conclusions for the chemical composition of biomass
based on the available and peer-reviewed reference data from tra-
ditional and complete proximate, ultimate and ash analyses for 86
varieties of biomass can be made:
(1) The chemical composition of biomass is highly variable as
determined by proximate, ultimate and particularly ash
analyses. When the proximate and ultimate data are recal-
culated respectively on dry and dry ash-free basis, the char-
acteristics show quite narrow ranges. This is due to the
extremely high variations of moisture, bulk ash yield and
different genetic types of inorganic matter in biomass.
(2) In decreasing order of abundance, the elements in biomass
are commonly C, O, H, N, Ca, K, Si, Mg, Al, S, Fe, P, Cl, Na,
Mn, and Ti. The determination of Cl and Mn contents in
biomass is required and such data should be always included
in the complete ultimate and ash analyses because these ele-
ments also have an important role for the biomass system.
(3) The typical enrichment trends for chemical characteristics
among biomass groups and sub-groups are: moisture, vola-
tile matter, Ca, Mg, and Mn for WWB; fixed carbon, volatile
matter, K, and O for HAB; volatile matter, K, O, and Si for
HAG; Cl, K, O, and Si for HAS; fixed carbon, K, Mg, and P
for HAR; ash, C, Ca, Cl, H, N, Na, P, and S for AB; ash, Al, C,
Cl, Fe, H, N, S, and Ti for CB. Both AB and CB groups show
the most significant differences in the biomass system. The
above distinctions are related to different biomass sources
and origin, namely from plant (WWB, HAB) and animal
(AB) products or from mixtures of plant, animal and manu-
facture materials (CB). On the other hand, the aquatic bio-
mass group is highly enriched in ash, Cl, Mg, Na, and S.
(4) The chemical composition of natural biomass system is sim-
pler than that of solid fossil fuels; however, the semi-bio-
mass
system
is
quite
complicated
as
a
result
of
incorporation of various non-biomass materials during bio-
mass processing. The biomass composition is significantly
different from that of coal. The variations among biomass
composition were also found to be greater than for coal.
(5) Natural biomass is normally enriched in moisture, volatile
matter, Ca, Cl, H, K, Mg, Mn, Na, O, and P and depleted in
ash, fixed carbon, Al, C, Fe, N, S, Si, S, and Ti in comparison
with the respective characteristics in coal. The highest
enrichment
in
biomass
commonly
shows
Mn > K > P > Cl > Ca > (Mg, Na) > O > moisture > volatile mat-
ter, whereas the highest depletion normally reveals S > (ash,
Al, Ti) > fixed carbon > (Fe, Si) > C.
WWB - wood and woody biomass (samples 1-28)
HAB - herbaceous and agricultural biomass (samples 29-72)
HAG - herbaceous and agricultural grass (samples 29-38)
HAS - herbaceous and agricultural straw (samples 39-47)
HAR - herbaceous and agricultural residue (samples 48-72)
AB - animal biomass (samples 73-74)
MB - mixture of biomass (samples 75-78)
CB - contaminated biomass (samples 79-86)
AVB - all varieties of biomass (samples 1-86)
P - peat
L - lignite
S - sub-bituminous coal
B - bituminous coal
A - algae
Fig. 4. Chemical classification system of the inorganic matter in high-temperature biomass ashes based on 78 varieties of biomass, wt.%.
S.V. Vassilev et al. / Fuel 89 (2010) 913–933
931
(6) The correlation analysis among the chemical characteristics
found five strong and important associations in the natural
biomass system, namely C–H, N–S–Cl, Si–Al–Fe–Na–Ti, Ca–
Mg–Mn, and K–P–S–Cl. As a result of that two figures were
created using the intersections of three end members in tri-
angular graphs. The first figure includes (1) C + H, (2) O, and
(3) N + S + Cl for biomass; whereas the second figure com-
prises (1) SiO
2
+ Al
2
O
3
+ Fe
2
O
3
+ Na
2
O + TiO
2
,
(2) CaO +
MgO + MnO, and (3) K
2
O + P
2
O
5
+ SO
3
+ Cl
2
O for biomass
ash as end members. Both figures can be used for classifica-
tion, prediction and indicator purposes:
The plotted chemical characteristics of biomass varieties
in both figures show: the similar chemical composition
between HAG and HAS sub-groups and their possible
combination in one biomass sub-group for future
descriptions; the variable composition of HAR sub-group
and its possible split in several sub-sub-groups; and the
possibility for identification of some contamination in
biomass fuels by detrital and/or technogenic materials.
The plotted associations Si + Al + Fe + Na + Ti oxides,
Ca + Mg + Mn oxides, and K + P + S + Cl oxides were
applied for an initial specification of the inorganic matter
in biomass system. This approach resulted in four chem-
ical biomass ash types (S, C, K and CK types) further spec-
ified into seven sub-types (with high, medium and low
acid tendencies). The above approach, composition-based
criteria and explanation of the three end members are
also comparable to those identified and applied earlier
for the chemical classification of coal ashes despite the
different constituents and borders used. Such approach
could be useful for the development of new combined
biomass and coal classification systems to permit fuel
prediction and selection for co-combustion applications.
The specified associations in biomass HTAs are also indic-
ative for the preferable occurrence and possible genesis
of inorganic elements in biomass. For example, the sum
SiO
2
+ Al
2
O
3
+ Fe
2
O
3
+ Na
2
O + TiO
2
may represent com-
monly the occurrence of Fe–Na–Ti-bearing silicates, alu-
mino-silicates and hydroxides with detrital, authigenic
and
technogenic
origin.
The
association
CaO +
MgO + MnO could include normally Ca–Mg–Mn-contain-
ing
carbonates,
oxyhydroxides
and
oxalates
with
preferable authigenic origin. The sum K
2
O + P
2
O
5
+
SO
3
+ Cl
2
O (as N also belongs to this association) may
represent commonly the mobile K-bearing phosphates,
sulphates, chlorides and nitrates with authigenic origin.
Finally, it should be stated that the actual explanation of the
above-described chemical differentiations, similarities, trends,
and associations is only possible after significant knowledge of
the phase–mineral composition of biomass varieties. The presence,
abundance and distribution of modes of element occurrence have a
leading role for the characterization of biomass composition.
Unfortunately, the bulk chemical composition of biomass does
not provide any direct information about the actual modes of ele-
ment occurrence in this fuel. The crucial importance of the phase–
mineral composition and modes of element occurrence, as well as
trace element contents, thermal behaviour of phases, and some
properties and applications of biomass and biomass ash will be de-
scribed in future publications.
Acknowledgements
The present work was carried out in part within the European
Commission’s research programme and in part within the research
programme of the Bulgarian Academy of Sciences. Stanislav
Vassilev would like to express his gratitude to the Joint Research
Centre (European Commission) for the possibility to perform
studies at the Institute for Energy (Petten, The Netherlands) as a
Detached National Expert.
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933
Document Outline
- An overview of the chemical composition of biomass
- Introduction and scope
- Data and discussion
- Chemical composition of biomass and comparisons with solid fossil fuels
- Correlations and associations among chemical composition of biomass and their potential applications
- Conclusions
- Acknowledgements
- References
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