Chapter 124

A MODEL EXPERIMENTAL GALLERY IN INDIA TO STUDY OPEN FIRE DYNAMICS IN MINES - ITS DESIGN AND INSTRUMENTATION

R.P.Singh Scientist Central Mining Research Institute Dhanbad, India	I. Ahmed A.K. Singh S.M. Verma B.C. Bhowmick
	Scientist Central Mining Research Institute Dhanbad, India

ABSTRACT

A mine fire model gallery has been constructed at Central Mining Research Institute, DHANBAD, INDIA to study the phenomenon of open fire and to evolve suitable fire fighting technique for control/combat of such fire. The gallery is 65.5 m long and 2.40 m wide, in arch shape with crown height of 2.70 m and is provided with two cross cut galleries, two stoppings, two sliding doors and a rolling shutter etc. To generate air flow through the gallery an AF- 50 (BS) axial flow exhaust fan having capacity to deal with 75 m3/sec of air has been installed at the end of the gallery. The gallery is equipped with computer aided online tele-monitoring system consisting of 130 sensors for monitoring of different parameters like gas concentration, temperature, pressure, velocity, heat flux, smoke density and particulate matter. A data aquisition system with SCADA software is also incorporated in the system. The paper deals with design of the gallery and its instrumentation.

KEYWORDS

Model gallery, design, construction, instrumentation, on-line tele monitoring system, data acquisition system

INTRODUCTION

Serious problems like generation of toxic gases, poor visibility, high temperature, and risk of fire damp explosion were experienced during fire fighting and rescue operation in a number of coal mines. A lot of research work has been done in different parts of the world on small intermediate and large scale models to study the dynamics of open fire (1-4). In recent past no such facility was available in India to study and understand the complex phenomenon of open fire. It was felt by mining community of India that to formulate guidelines for safe recovery of trapped miners and successful control of fire a systematic in-depth study on a large scale model representing the actual mine gallery is needed. Central Mining Research Institute Dhanbad, INDIA took initiative in this regard and constructed a large scale mine fire model gallery funded by Ministry of Coal, Government of INDIA.

The Mine Fire Model gallery constructed at CMRI campus is arch shaped, 65.5 m long and 2.40m wide. It is basically divided into two zones i.e., firing and non firing zones. One cross-cut gallery with two stoppings have been provided in the firing zone and another cross-cut gallery with an axial flow fan is provided at the end of the gallery in the non firing zone.

The gallery is equipped with computer aided on line tele-monitoring system for continuous monitoring of different parameters like gas concentration, temperature, pressure across fire zone, velocity of air, heat flux, dust and particulate matter concentration during experimentation. The entire monitoring system consists of 130 sensors connected with a data logger and computer peripheral and is placed in a monitoring room adjacent to the gallery.

For data analysis, graphical presentation, and fault detection, a SCADA software is incorporated in the system. CMRI “EXPLO” programme to assess the explosibility range of the gases in the gallery during experimentation is also incorporated in the main programme.

Coal slabs will be lined on all four inner sides of the gallery in the firing zone and will be ignited artificially after establishing desired air flow rate through the gallery. Desired parameters will be continuously monitored till the fire dies down.

The paper deals with some details of design of the gallery and its instrumentation.

BACKGROUND OF MINE FIRE
MODEL GALLERY

The tragic incidence at New Kenda colliery ECL, INDIA where 55 persons lost their lives due to outbreak of open fire in main intake gallery of the mine drew attention of mining engineers for solution of such problem and it was realised that a systematic in-depth study on different aspects of open mine fire was needed. Initially an experiment was conducted on a big block (1m x 1m) of coal from Dobrana seam of New Kenda Colliery. The experiment was conducted by making 50 mm diameter hole through the middle of the coal block and setting it on fire after establishing air flow through the hole maintaining a velocity generally found in a working mine gallery. Temperature and gas concentration at different locations in the hole of the coal block were recorded during the experiment. The results were not given much weightage by the mining community as it was not realistic to the mining condition. Subsequently, in advancement of the above study a small scale model (19 m long & 8 cm x 8 cm opening) was constructed at CMRI. Two sets of experiment were conducted on coal from the same Dobrana seam. The parameters like pressure across fire zone, velocity of air, temperature, gas concentration, dust and particulate matter were monitored continuously for about 8 hours. The findings of these experiments were encouraging. However, it was felt that the results were not very convincing as the results of small scale model study could not be accurately extrapolated to actual mining condition due to absence of reliable upscalling procedure. Therefore to get acquainted with

fire dynamics in more realistic fashion an idea for construction of large scale model gallery was conceived.

DESIGN OF MINE FIRE MODEL GALLERY

CMRI mine fire model gallery is 65.5 m long in arch shape with a base of 2.4 m and crown height of 2.7 m. The cross section of the gallery is 5.86 sq.m. The gallery is basically divided in two zones. First 10.5 m long segment is known as non firing zone, the middle 22 m long firing zone and the last 33 m long segment is again a non firing zone. One cross cut gallery of 3m long with two stoppings have been provided in the center of the firing zone and another cross cut gallery of same cross section and 13.75 m long has also been provided at the end of the gallery. It may be noted that this cross cut gallery is also considered as non-firing zone. One axial flow fan equivalent to the AF-50 (BS) has been installed at the end of the cross cut gallery. To avoid air pollution due to burning of coal in the surroundings, 10 m height and 1m dia. chimney made of 6mm thick steel plates has been provided with the fan evasee. Two sliding doors one at 5 m from the gallery entry and another at end of the gallery have been provided for sealing of the fire after experimentation. One rolling shutter is fitted at the end of the cross cut gallery opposite the fan to regulate and dilute the incoming hot and toxic gases from the firing zone. A monitoring room for installation of sensors, data logger, computer printer, plotter etc. adjacent to the gallery has been constructed. An isometric diagram of CMRI mine fire model gallery is given in Figure 1.

Figure 1. Isometric view of mine fire gallery

Figure 2. Sectional view of firing and non-firing zone

The wall thickness of the gallery varies in firing and non firing zone and detail description of walls are as follows:

Firing Zone

The total wall thickness of the 22 m long firing zone is 650 mm comprising 150 mm thick outer most layer of RCC, 120mm thick red brick and 380 mm thick inner most layer of fire clay brick of IS: 8 quality. To avoid excessive heat loss through walls, one layer of 25 mm thick mineral wool matress was also provided in the wall between red brick and fire brick in this zone. Thermowell slabs of 50 mm thick have been provided at the roof of the gallery between red brick and RCC layers to avoid damage to the gallery due to vertical expansion. Coal slabs will be lined in this zone which will be set into fire after establishing desired air velocity in the gallery for the experimentation.

Non Firing Zone

The first 10.5 m segment from the entry of the gallery is a non firing zone. The total wall thickness of the gallery in this zone is 650 mm which comprises 150 mm thick RCC cover, 380 mm thick red brick and 120 mm thick inner most layer of fire clay brick of IS: 6 quality.

Again 33 m long segment just down stream of the firing zone is non firing zone. The wall thickness of this zone is similar to the earlier non firing zone. A cross cut gallery of 13.75 m long and 2.40 m wide is provided at the end of the main gallery. The wall thickness of this cross cut gallery is 650mm which consists of only 150 mm thick RCC cover and 500 mm thick red brick.

Zone wise wall specifications and its sectional view are depicted in Figure-2

Design criteria

The design of CMRI mine fire model gallery was finalized after detail literature survey on existing model galleries of the world specially large scale model gallery of Pittsburgh research center NISOH, USA in consultation with reputed mining and civil engineers of the country. The design evolved for the gallery incorporates all aspects necessary to understand the basic problems of fire of Indian coal mining industry. The basic criteria considered at the time of designing of above gallery are:

1. The cross section of model gallery should be close to the actual cross section generally found in Indian coal mines

2. The open and sealed fire condition can be simulated in the gallery.

3. The air flow rate can be established as in normal working of Indian coal mines.

4. Temperature gradient and maximum rise in temperature and its distribution in the gallery can be assessed.

5. Rate of propagation of fire in the gallery can be determined.

6. Effect of fire on ventilation and fan pressure can be assessed.

7. Rate of generation of toxic/combustible gases, dust and particulate matter can be estimated.

8. Phenomenon as to how fire jumps from one pillar to another can be understood.

9. The design of gallery should be such that it can withstand fire damp explosion and temperature of 1200°C when subjected to periodic heating over a long period.

Precaution against heat loss

To protect the RCC cover of the gallery against high temperature, care has been taken to minimise the heat loss through the wall by providing two layers of fire clay bricks (380 mm) IS:8 quality and one layer 25 mm thick mineral wool mattress between red brick and fire clay bricks.

The fire clay bricks lined in the gallery were tested at Central Glass & Ceramic Research Institute Calcutta for various properties. The test results are depicted in
Table I.

Table I. Test Results of Fire clay Bricks

Type of test	IS: 8 Brick		IS: 6 Brick
	Test Values	Stand. values as per IS:8 specifications	Test Values	Stand. values as per IS:6 specifications
Apparent porosity(%)	26.36	30 maximum	21.85	25 maximum
Cold crushing strength (Kg/cm^2)	335.74	175 minimum	360.50	200 minimum
Pyromatrick cone equivalent (ASTM)	32-33 orton cone close to 32 orton cone	32 minimum	31-32 orton cone close to 31 orton cone	30 minimum
Refractoriness under load (RUL)	ta = 1320°C te = 1575°C	ta = 1400°C te = 1600°C	ta = 1410°C te = 1595°C	1300°C minimum
Permanent linear change on reheating (PLCR) at 1400 °C/5hour Chemical Analysis a - Al2O3 b - SiO2	(+) 0.72 54.47% 34.72%	1.5 max 40 minimum	(-) 0.78 32.82% 62.78%	1.0 maximum 30% min 65% max

It can be seen from the table that both types of fire bricks used in the construction of the gallery satisfy the requirements of BIS specification.

Calculation of heat flow through wall in the firing zone

Calculation for heat flow through wall in the firing zone has been done to evaluate the temperature of outer most cement concrete layer taking into consideration that maximum temperature inside the gallery would be about 1200°C which was found during experimentation in small scale model earlier at CMRI.

Heat flow rate through a wall of composite material can be calculated using the formula

(θ1 - θ2)

Q (Kw) = A------------------------------------------* t - (1)

(I₁/K₁ + I₂/K₂ + I₃/K₃ + I₄/K₄)

Where,

Q = amount of heat flowing through an area A in time *t second.

I₁, I₂, I₃ and I₄ are thickness of coal layer, fire brick, red brick and RCC walls respectively.

K₁, K₂, K₃ and K₄ are the thermal conductivity of coal layer, fire brick, red brick and RCC walls respectively.

Thermal conductivity is defined as the quantity of heat that flows in one second through a centimeter cube substance whose opposite faces are maintained at a temperature difference of 1°C.

(θ1 - θ2)

------------- = rate at which temperature changes with

l distance in the direction of heat flow

is called temperature gradient

Heat flux may be defined as

Q (θ1 - θ2)

Φ = ----- =------------------------------------------*t --(2)

A (I₁/K₁ + I₂/K₂ + I₃/K₃ + I₄/K₄)

Assuming,

Temperature in side the gallery θ1 is 1200 °C =1473°k

Temperatureof air outside the gallery θ2is 50°C=323°k

Thickness of coal layer = 0.10 m

Thermal conductivity = 0.40 W/m°k

Thickness of fire clay brick = 0.38 m

Thermal conductivity = 1.44 W/m°k Thickness

Thickness of red brick = 0.12 m

Thermal conductivity = 2.00 W/m°k

Thickness of RCC = 0.15 m

Thermal conductivity = 1.728 W/m°k

*t is time = 1.0 second

Putting these values in equation (2)

Heat flux Φ = 1,75 Kw/m² .

Hence maximum expected heat flux would be 1.75 Kw/m².

Further on calculation at above heat flux the maximum temperature at the inner side of outer most layer i.e. RCC wall would be about 200°C. Since RCC can easily withstand a temperature of 200°C, the possibility of development of cracks in the RCC wall during experimentation is least.

INSTRUMENTATION SYSTEM

The mine fire model gallery is equipped with a state-of- the-art computer aided on line tele- monitoring system. The system consists of 130 sensors with data logger, computer peripherial etc. for continuous monitoring of various parameters like gas concentration, air velocity, pressure across fire zone, temperature, heat flux, dust and particulate matter concentration inside the gallery. It is expected that during experimentation the temperature inside the gallery may go upto 1200°C, under such condition only temperature sensors can be placed inside the gallery and other sensors have to be placed either in the monitoring room or outer side of the gallery wall with proper cooling arrangements. For better understanding the entire monitoring system may be explained in two stages

Instrumentation in the gallery for data generation

The computer aided on line tele-monitoring system comprises 130 sensors installed in the gallery as well as in the monitoring room. It may be noted that temperature, pressure, velocity, heat flux, dust and particulate sensors are installed inside the gallery with proper cooling arrangements and gas sensors are mounted on a panel in the monitoring room for continuous monitoring of CO, CO₂, CH₄, O₂ & H₂ gases. Gas samples from inside the gallery will be

Figure 3. Sampling system flow diagram

Sensor representation:-

1== Sensor in brick at the roof of the Gallery; 2== Sensor in coal at the roof of the Gallery; 3== Sensor in air at the roof of the Gallery; 4== Sensor in brick at the side of the Gallery (1.3m from the floor); 5== Sensor in coal at the side of the Gallery (1.2m from the floor); 6== Sensor in air at the middle of the Gallery (1.3m from the floor); 7== Sensor in air at the floor of the Gallery (0.2m from the floor); 8== Sensor in coal at the floor of the Gallery; T1== Sensor in air at the distance of 1.8m from the floor of the Gallery; T2== Sensor in air at the distance of 1.1m from the floor of the Gallery; T3== Sensor in air at the distance of 0.6m from the floor of the Gallery; T4== Sensor in air at the distance of 1.1m from the floor of the Gallery

Figure 4. Temperature sensor distribution in the roof sides and floor at different location in the firing zone

Table II. Instruments for mine fire model gallery

S.N	Name of the equipment	Range	Number	Purpose
1	Temperature sensors	-50 to 1200°C	98	For continuous recording of temperature in the gallery
2	Gas Sensors IR based CO analyser IR based CO2 analyser IR based CH4 analyser Para magnetic type O2 analyser with recorder Thermal conductivity based H2 analyser (single pass type)	0 - 10% 0 - 20 % 0 - 100% 0 - 25% 0 - 5%	5 Nos. each	For continuous measurement of CO, CO2, CH4, O2 & H2 gases at different locations in the gallery
3	I- Heat flux meter II- Heat flux meter	0 - 5 watt /Cm^2 0 - 2 watt /Cm^2	1No. 1No.	To measure the conductive and convective heat in the gallery
4	Durage smoke density meter D-R 216 - 40	Opacity range 100 %	1 No.	To measure the smoke and dust particulate down stream of fire
5	Velocity sensor	0.5 to 5 m /sec	1No.	To measure air velocity at the entry of the duct
6	Differential pressure sensors	0 - 50 mm.wg	3 Nos.	To measure fan pressure and differential pressure across fire zone
7	Axial flow fan Model-AF-50 (BS) with 30 HP motor	75 Cum / sec	1 No.	To ensure air supply through the gallery
8	1-PC based data logger I- Data logger -98 channel II- Data logger-48 channel Model-8030 - MI and 484 port 2-PC specification Pentium- III -17” colour monitor with CD writer with CITECT Scada software 3.Colour printer, plotter and UPS	Mixed universal type RAM - 128 MB, HD-4 GB, Window -98 operating system with internet modem	2 Nos. 1 No. 1 No.	To collect data from different sensors in the gallery and there after its analysis and graphical presentation

continuously drawn out by membrane pump. The gases so drawn would be passed through the stack of gas sensors after being cooled and filtered. Altogether five sampling system are provided at five gas monitoring stations. Details of sampling system and flow diagram of the instrumentation scheme are shown in the Figure-3.

To get acquainted with temperature distribution along the gallery and to monitor the temperature of coal brick and air in the roof sides and floor at about 2.5 m intervals 98 temperature sensors are placed in the gallery. The temperature sensors distribution at different locations in roof, sides in the firing zone are depicted in the Figure-4.

To monitor air velocity inside the gallery a velocity sensor has been intalled at the entry of the gallery. Three pressure sensors, two across fire zone and one at fan site are installed for monitoring of pressure difference across fire zone and fan pressure respectively. Two heat flux and one smoke density meter are also installed in the gallery for monitoring of heat flux (conductive & convective) and dust / particulate (opacity). Details of various monitoring stations and sensor locations along the gallery length are indicated in Fig - 5.

Detailed specifications of the equipments/Sensors are indicated in the table - II.

Data acquisition system for collection, storage and analysis of data

Data acquisition system consists of signal processor and transmitter, data logger, computer peripherial, printer, plotter and software for transmition and analysis of data obtained during experimentation. The details of the data acquisition system is represented in Fig. 6.

As mentioned earlier, about 130 sensors are installed in the mine fire model gallery and signal will be transmitted to the data logger therefore to meet these requirements two Nos. PC- based data logger of 98 and 48 channels model-8030-MI are provided.

Figure 5. Details of various monitoring stations and sensors location along the gallery length

Figure 6. Block diagram of data acquisition system

A SCADA software in Window-98 operating system for analysis, graphical presentation and fault detection is also incorporated.

Software procured for the system have the following features:

1. It can store data on daily basis and can be retrieved in future.

2. It will give digital and graphical representation of indivisual channel daily and for entire period of the experiment.

3. It can identify each sensor and have alarm generation facility for critical values of different parameters.

4. Outline diagram of tunnel along with location of sensor can be displayed on the monitor along with current reading as and when required (User configurable mimic display).

5. Facility for incorporation of EXPLO program developed by CMRI in the main software to determine the explosibility of gases during experimentation.

6. It will calculate the heat flux, throttling effect, propogation of fire etc. continuously.

7. Software can detect the errors like sensor failure, cable fault and any other fault in the system.

CONCLUSION

The construction of model gallery and installation of computer aided on line tele-monitoring system including fan, doors and chimney etc. is completed. The entire system will now be subjected to calibration and trial run. First set of experiment with coal from a seam noted for its susceptibility towards spontaneous heating will be taken up during first quarter of 2001. The mine fire model gallery has generated great interest in the country and it is hoped that experiment carried out will find solution to many of the nagging problems of fire in our coal mines.

ACKNOWLEDGEMENT

The authors are thankful to the Director, Central Mining Research Institute for giving permission to present this paper. We are thankful to the Ministry of Coal, Government of India for their financial support to conduct this study. The authors would like to acknowledge sincerely to the members of Project Advisory and Monitoring Committee specially, Prof. B.B. Dhar Ex- Director,CMRI and H.B.Ghosh Ex-CMD, CMPDIL and DGMS for their valuable suggestions during construction of the mine fire model gallery. The authors are also thankful to all member of Ventilation & Special Projects of CMRI for their Cooperation during construction of the gallery.

REFERENCES

Dziurynski W; Tracz I; and Trutwin W; (1988) Simulation of mine fire, Fourth International Mine Ventilation Congress, pp 357-363

Chaiken.R. F, and Singer J M; ( 1976 ) Experimental mine fire Research, Proc. 2nd ann. Underground coal Gasification Symposium, Morgantown, W. Va. August. 10-12; MERC/SP- 7613, pp 96-104

Margarate R. Egan, (1987) Coal combustion in a ventilation tunnel, Bu. Mines IC. 9169, pp1-12

Chalers D Litton; M DeRosa; and Jing-Shuli; (1987) Calculation of fire throttling of mine ventilation air flow, RI 9076, pp 1-21

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A MODEL EXPERIMENTAL GALLERY IN INDIA TO STUDY OPEN

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