Running Stirling Engine with Steam as Working Fluid by Using Heat
Energy from Producer Gas
Rattanachai Pairintra*, Danai Aramtumrnaphon **, Authai Kalchoung ***
and Jongjit Hirunlabh**
*School of Bioresources and Technology, ** School of Energy and Materials
*** Department of Mechanical Engineering, Faculty of Engineering, King
Mongkut's Institute of Technology Thonburi Suksawas 48 Rd., Bangkok,
Thailand
ABSTRACT
The main objective of this research is to run Stirling engine by vapor
obtained from liquid state of working fluid that received heating energy from
the producer gas. In this research, two types of Stirling engine are used and
steam is used as the working fluid. The operation of Stirling cycle in this
research is an open cycle system which is different from the conventional
Stirling cycle because the low temperature of the exhaust steam is not
appropriate to be reused in the regenerator. In addition, the high friction
occuring when the steam flows through the regenerator causes the pressure
drop which results in low efficiency of engine. The Stirling engines run by
fully and gradually openning the steam valve. In both cases, the experiments,
are conducted with and without driving a water pump. For running Stirling
engine by fully openning the valve steam without driving a water pump, the
first Stirling engine without the exhaust working fluid control valve can
produce the indicated horse-power of about 1.82 hp with the maximum speed
of 950 rpm, while the second Stirling engine that is developed from the first
Stirling engine by equipping the exhaust working fluid control valve and using
more powerful driving mechanism can produce the indicated horse-power of
around 3.92 hp with maximum speed of 2200 rpm. When driving a water
pump, the first Stirling engine can produce maximum speed of 870 rpm and
head pump of 6.96 m. For the experiment run by slightly openning the valve to
let the steam out gradually without driving a water pump, it is found that the
first Stirling engine can produce the indicated horse-power of about 0.74 hp
with maximum speed of 550 rpm, while the second Stirling engine can produce
the indicated horse-power of about 1.75 hp with speed of 1300 rpm. The
experiment with driving a water pump shows that the second Stirling engine
can produce head pump of23.82 m with speed of 1300 rpm.
Keywords: Biomass/ Producer gas/ Stirling engine/ Indicated horse-power/
Head pump
INTRODUCTION
Biomass is directly or indirectly derived from living organisms. Typical
biomass resources now utilized are classified in three forms: I) residues and
by-product of crops grown primarily for food, 2) surplus of or arising from
food crops such as grain. sugar. vegetable oil. and 3) purpose-grown fuel
crops. Most developing countries have a surplus of biomass resources and
there are many ways to derive energy from it. Gasification is the thennal
conversion process of solid biomass into gas. The gas which is obtained from
the process of gasification is usually called the producer gas. The main
combustible gases are CO. Hz and CH4 which are generated from the
reduction reaction in gasification zone. There are many possible ways to
design gasifier, but most of them vary only in minor details. In general, there
are three main categories: 1) Up-flow, 2) Down-flow and 3) Cross-flow.
Energy from producer gas can be used for many purposes such as drying
agricultural products (direct combustion) or driving internal combustion
engine (I.C.E) or shaft power (indirect combustion).
The Diesel engines are, presently, the world's prime movers because of
thear reliability, reasonable efficiency and low maintenance cost. However. the
problems are the air pollution and uncertainty petroleum supply, besides that
its fluctuation price. One of the alternative engine to face with those problems
is the Stirling engine. One reason for the interest in the Stirling engine is that it
uses external-combustion which can be controlled more effectively than
intemal-combustion and produce less air pollution unlike the I.C.E. The
Stirling engine can be driven by just an appropriate temperature difference
between hot and cold heat sources without exploded combustion such as the
I.C.E. requires. The Stirling engine that can operate on almost any source of
heat including sunlight and biomass is a highly efficient prime mover. The
working fluid for the Stirling engine may be Helium, Hydrogen or air. The
Stirling engine that used Helium or Hydrogen as a working fluid has much
higher engine efficiency more than that using air. However, it has to run under
the high pressurti, thus leakage problem occurs.
Normally the Stirling engine is classifed into 2 types, there are : 1) Single
Acting Stirling Engine and' 2) Double Acting Stirling Engine. The Stirling
engine in this research was the Single Acting Stirling Engine, it was run by
vapor obtained from liquid state of working fluid that received heating energy
from the combustion of the producer gas. In the fonner experiment air was
used as the working fluid but it had some problems with leakage and low
efficiency, due to low heat capacity. The specific objectives of the study are:
1) To examine the gasification process and to evaluate the heating value of the
producer gas and 2) To design and evaluate the Stirling engine operating by
such renewable energy resources as biomass via gasification process using
steam as working fluid.
MATERIAL AND METHOD
The up-flow gasifier body was fabricated of 3 refractory cylinders cement
with 35 em inside diameter 5 cm thickness and, 36 cm height. and the total