TN295 No. 9169 / I • V : v, ■ 4^ ^ ' ».;*' A <. */^T* ' G* X9. *'o . » * * a o~ V °^'*»To" - .0° \ °o r oV * V^V v^?V \"V V ** ^ \M& # ' * $ i& ^ ^ •*-* o<°^ . ■ : \s .-ate-. \./ c^ '^«' a>«^ y 4 .•■'•♦ *^ ^* y °o sPv\, ^°* l V . t • -> ^' s°* - O- * ^ °^ *. "o. *^0* & \ <, */^r* - jr ^. '«r.»* a _ ^ ^** /^fe'v \/ .-isM,-. ^** .-attfi. %../ •>' • a v< ^ " A V< ^ J ■or 'J* ."g' v ^ v -l ^ ** v> fl 4 0ft • " A. V *^ ». 'O . 4 * A 4.^ ^^Bk- %> c C s ^ ^ • A>«^ » » * A °o ^ •* • f\ • '• 4? ^ ol «*v 4 4." . '"•'• * V >0 40* w* ;«\ w *fe \^ &m\ \s :mki \^ j0 tv -^ 4? ^, • A>"tf "*J-> ,<2v V .o«o. ^ **** rt^ .i'»„ "^- "" A ^' >v *- ..-♦ «> ^ a* V ** 4 0. 1 » «o » *0 «j\ »■ *_, -"• --V /.-^fe- *- ^:«feV y^.\. X-«fc\" ^ /. :- -o^ JO. i « * • ^^U rf* ... V. <"< ^ _ tl lV^. ^°^ ^^' *^ <3^ . i • ^^\/ °^^^/ \^^\/ V 3 ^'^ %-^^v V M rife: \/ -*ffi^\ \^ .*afe- \/ .'^^•. V«* .-aK\ 1 cv * * 'o ,40. > 6? .-0. >> *" / DW „ %/ : A': \/ -:A, %S ;Mk\ \f 0° *\ £°* .0 V v^> * A y, Cf ■ V*^ A*'^ J .^iii^. ^> IC9169 Bureau of Mines Information Circular/1987 Coal Combustion in a Ventilated Tunnel By Margaret R. Egan UNITED STATES DEPARTMENT OF THE INTERIOR c i£ t S]UA&* i L -TvU-vU* ) Information Circular; 91 69 Coal Combustion in a Ventilated Tunnel By Margaret R. Egan UNITED STATES DEPARTMENT OF THE INTERIOR Donald Paul Hodel, Secretary BUREAU OF MINES David S. Brown, Acting Director ^\\l^ \]H n b< ■\ l&1 Library of Congress Cataloging in Publication Data: Egan, Margaret R. Coal combustion in a ventilated tunnel. (Bureau of Mines information circular; 9169) Bibliography: p. 12. Supt. of Docs, no.: I 28.27: 9169. 1. Coal mines and mining — Fires and fire prevention. I. Title. II. Series: Information circular (United States. Bureau of Mines); 9169. TN295.U4 [TN315] 622 s [622'.8] 87-600251 CONTENTS Page Abstract 1 Introduction 2 Properties of coal 2 Fire tunne 1 2 Instrumentation 3 Thermocouples 3 Flow probes and pressure transducers 3 Gas monitors 4 Smoke monitors 4 Fuel-consumption monitor 5 Typical test procedure 5 Calculations 5 Product generation rates 5 Combustion yields 6 Heat-release rates 6 Production constants 6 Smoke particle diameters 7 Coal combustion results and discussion 7 Gas concentrations and heat production 8 Smoke characteristics 9 Combustion yields 9 Production constants 10 Fuel comparison results and discussion 10 References 12 Appendix. — Symbols used in this report 13 ILLUSTRATIONS 1. Schematic of intermediate-scale tunnel and data-acquisition system 3 2. Results of a typical coal combustion test 8 TABLES 1. Ventilation, ignition, and mass loss for coal experiments 7 2. Gas concentrations, generation rates, heat-release rates, and heats of combustion 9 3. Smoke characteristics for coal 9 4. Mean particle sizes and smoke obscuration 10 5. Combustion yields for coal 10 6. Production constants for coal 10 7. Ignition source and ventilation rates for the three fuels tested 10 8. Gas, heat, and smoke concentrations 11 9. Normalized gas and smoke concentrations 11 10. Particle size and smoke obscuration 11 11. Production constants 11 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT Btu/lb British thermal unit per pound kW m kilowatt meter cm centimeter mg/m 3 milligram per cubic cm cubic centimeter meter g gram min minute g/cm 3 gram per cubic centimeter Mm micrometer g/(m 3 *ppm) gram per cubic meter part per million times m 3 /s cubic meter per second g/g gram per gram p/cm 3 particle per cubic centimeter g/kJ gram per kilojoule p/g particle per gram g/s gram per second p/kJ particle per kg kilogram kilojoule kJ kilojoule ppm part per million 1 kJ/g kilojoule per gram V volt COAL COMBUSTION IN A VENTILATED TUNNEL By Margaret R. Egan' ABSTRACT The Bureau of Mines experimentally burned Pittsburgh Seam coal and other combustible materials found in mines in order to obtain a better knowledge of their emission products. These experiments were conducted in the Bureau's intermediate-scale fire tunnel, which simulates environ- mental conditions in underground mines. Smoke characteristics, gas concentrations, mass loss, and ventilation were measured. From these values, heat-release rates, particle sizes, obscuration rates, combus- tion yields, and production constants were calculated. This information was sought as part of a comprehensive study of combustible materials that will ultimately advance the design of more efficient fire detection and suppression systems. The coal combustion measurements presented in this report, together with previous analyses of wood and transformer fluid fires form a data base by which future studies of other mine combustibles can be compared. 1 Chemist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. INTRODUCTION The Bureau of Mines conducts research to ensure that mines are safe and healthy places to work. Exceptional circum- stances, such as an underground fire, pose dangers affecting escape and rescue. In any fire, each burning material con- tributes hazardous combustion products. Each component of the smoke poses unique dangers to escape and rescue, and in combination, the components become even more dangerous. The life-threatening hazards of smoke and toxic gas produced by burning mine materials may be carried throughout the mine by the ventila- tion system. Therefore, the Bureau has been investigating fire characteristics in ventilated passageways. Once the hazardous products of combustible ma- terials are determined, more efficient detection and rescue equipment can be designed. This report supplements previous Bureau studies Q. - .^) 2 of other combustible ma- terials burned in a simulated mine envi- ronment. The intermediate-scale fire tunnel used for the current studies was shown to successfully predict full-scale fire conditions ( 3_) . The tunnel was instrumented with gas and smoke analyzers as well as a data collection system that can perform calculations and plot data as the input information is received. The objectives of this study were to analyze the gas production and smoke characteristics of burning coal and to compare these findings with data for the other combustible materials previously studied. PROPERTIES OF COAL Coal is a familiar substance, but it has no fixed chemical formula. It was formed from decomposing plant material that was subjected to increased tempera- ture and pressure for a prolonged period of time. The composition of the coal is, therefore, dependent upon the composition of the original plant material. However, all coals have carbon, hydrogen, and oxy- gen as major elements, with sulfur and nitrogen as minor elements. Bituminous coal from the Pittsburgh Seam was used for all experiments. Its ultimate analy- sis revealed the following: 78% C, 5.3% H, 8.2% 0, 5.6% ash, 1.6% N, and 1.3% S (4_). The proximate analysis showed the following: moisture content, 1.7%; ash content, 5.6%; volatile matter, 38.8%; and fixed carbon 53.9% ( 4_) . The heating value was 13,947 Btu/lb (4). As coal is heated, it decomposes into an ash residue and gaseous volatiles. Among these gases are CO2, CO, nitrogen, steam, oxides of sulfur and nitrogen, and hydrocarbons such as methane. The two most important gases for calculating heat release are CO2 and CO. These were measured continuously throughout these experiments. FIRE TUNNEL The coal fires were conducted in the Bureau's intermediate-scale fire tunnel. The tunnel and its data-acquisition sys- tem are shown in figure 1. The tunnel measures 0. 8 m wide by 0.8 m high by 10 m long and is divided into several sec- tions. The first horizontal section is 1.5 m long and can be lifted to allow en- trance for the placement of the coal. It begins with an air-intake cylinder that measures 0.25 m long by 0.3 m in diameter and gradually enlarges until it matches the tunnel dimensions at the hinged area. Next is the fire zone, where the coal pile and a gas burner are located. The fire zone and the remaining horizontal section are lined with fire brick and instrumented with thermocouples, flow probes, and sampling ports. The dif- fusing grid begins the vertical section 2 Under lined numbers in parentheses re- fer to items in the list of references preceding the appendix. 10m 12m /0.61m -diam duct 1.22m Fire zone — i Air • __ — ^— *- 0.8m- square duct intake Sd HI ^p^ — i — * Coal pile A, ^ 1 Air exhaust Manually Ventilation ^U\ adjustable . J an , . Fy or if ir.P nlntP Load eel ice plate Diffusing grid -0.305m- diam entrance duct ( hinged and movable) DECNET- TEOM CNM CO meter CO2 meter Pressure transducers MM 48" channel data- acqui- sition system 3\ - detector -Load cell -Digital input for CNM range PDP II /44 Control terminal VAX 11/780 Printer CALCOMP plotter VAX terminal "••• 28 •••• thermocouples Pressure transducer (flow probe Differential pressure transducer 3X detector Thermocouples Sampling ports KEY CALCOMP California computer products CNM Condensation nuclei monitor DECNET Digital equipment networking PDP Programmed data processor TEOM Tapered-element oscillating microbalance VAX Virtual address extension FIGURE 1. — Schematic of intermediate-scale tunnel (top) and data-acquisition system (bottom). of the tunnel. Located in this section is an orifice plate that can be manually adjusted to attain the desired airflow. INSTRUMENTATION The final section is horizontal and ends at an exterior exhaust fan. All instruments were periodically cleaned and calibrated according to manu- facturers ' instructions for the quantity of smoke and the amount of use each had received. THERMOCOUPLES Thermocouple arrays were located 1.57, 2.36, 3.15, 4.72, 6.30, and 7.87 m from the gas burner. Additional thermocouples were located on the air-intake cone and at the exhaust. In all, a total of 28 thermocouples were used to measure the temperature distributions resulting from the fires. Their locations are shown in figure 1. FLOW PROBES AND PRESSURE TRANSDUCERS The velocity data were acquired using a bidirectional flow probe (_5) in con- junction with a pressure transducer. The airflow produced by the exhaust ventilation was detected by the flow probe and converted to a linear electri- cal signal by the pressure transducer. This signal was then scanned and recorded by the data collection system. The loca- tions of all of the flow probes are shown in figure 1. The flow probe used to obtain the velocity measurements was the one centered in the air-intake cylinder. The stated accuracy of the flow probe is ±7%. The pressure transducer added a maximum error of ±5.3%. Assuming the error to be accumulative, the maximum velocity error for one data point was estimated to be ±12.3%. Averaging over 10 data points improves the accuracy by the square root of 10, resulting in a total estimated error of ±3.9% for the average data presented. Additional velocity readings were made with a vane-type anemometer. This was done before each experiment to insure that the air-intake velocity was approxi- mately the same for all tests. GAS MONITORS The CO analyzer used measures accurate- ly within 1% of full range or ±5 ppm. The C0 2 analyzer measures accurately within 1% of full range or ±250 ppm. These analyzers were calibrated at the beginning of each experiment. In addi- tion, the concentrations of the span gases were checked at the beginning of each series of experiments. The hydrogen cyanide (HCN) detector's accuracy is stated as ±1% of the reading. Its calibration was checked before this series of experiments began and rechecked after its completion. SMOKE MONITORS The number concentration (N Q ) was ob- tained with a Condensation Nuclei Monitor (CNM), manufactured by Environment One Corp., Schenectady, NY. 3 This monitor uses a cloud chamber to measure the concentration of submicrometer airborne -^Reference to specific products does not imply endorsement by the Bureau of Mines. particles (p). The particulate cloud attenuates a light beam which ultimately produces a measurable electrical signal. The accuracy is stated as ±20% of a point above 30% of scale within the linear ranges from 3,000 to 300,000 p/cm 3 . Therefore, in these experiments, the cal- culated error could have been ±18,000 p/cm 3 . To reduce the particulate count to within the range of the CNM, a 10% dilu- tion of the smoke was necessary. Two flow meters, with a stated accuracy of ±2%, were used. One measured the flow of the sample, and the other measured fil- tered room air. The dilution error was calculated to be from -15.2 to +22%. Over 10 data points, this error was reduced to ±7%. Adding this error to the already stated error of the CNM increases the total error to ±27%, making this the least accurate of all the instruments. The mass concentration (M ) was ob- tained by a tapered-element oscillating microbalance (TEOM) developed by Rup- precht & Patashnick Co. , Inc. , Voorhees- ville, NY. (6) It measures the mass directly by depositing the particles on a filter attached to an oscillating tapered element. The oscillating frequency of the tapered element decreases as the deposited mass increases. The apparatus is capable of measuring the particulate concentration with a better than 5% ac- curacy at the level used. According to the manufacturer, the filter collects at least 50% of all particles with a volume mean diameter of 0.05 ym, with increasing collection efficiency as the diameter increases. Actual data obtained by the Bureau using particles of volume mean diameter equal to 0.048 ym indicated a collection efficiency closer to 90%. Since the diameter of average mass is calculated from the mass and number con- centrations, its accuracy was dependent upon the precision of the TEOM and CNM. Considering the error band of the mass and number concentration produced by the coal combustion experiments, the diameter of average mass could vary by 14%. A three -wave length light-transmission technique developed by the Bureau (_7) was also used to measure smoke concentration and obscuration. White light was trans- mitted through a smoke cloud to the detector. The beam was split into three parts, and each passed through an inter- ference filter centered at wavelengths of either 0.45, 0.63, or 1.00 um. Each photodiode output was amplified and re- corded as a linear electric signal. FUEL-CONSUMPTION MONITOR The weight-loss data were obtained by a strain-gauge conditioner in conjunction with a load cell that has a range up to 22.68 kg. Their combined accuracy is stated as 0.05% of full scale or ±11.3 g. TYPICAL TEST PROCEDURE Approximately 18 kg of coal was broken into pieces measuring 125 cm or less and placed in a 59- by 68-cm stainless steel pan. The pan was supported by a shaft that extended through the tunnel floor and was mounted on the load cell so that continuous weight loss could be recorded. Prior to each experiment, background readings were obtained after the coal was loaded and the exhaust fan started. All instruments were continuously scanned and recorded throughout the experiment. The coal was ignited by three strip heaters that were equidistantly imbedded in the coal approximately 2.5 cm beneath the surface. The timing of all experi- ments began when the strip heaters were turned on. The power was gradually increased for three 5-min intervals until it reached a maximum of 90 V. After 20 min at that level, the power was turned off and the coal continued to burn. After sufficient data were obtained, the fire was extinguished and the experiment was concluded. The 21 experiments were divided into three phases. In the first phase (tests 1 through 6), the strip heaters were of unequal length. The two end ones were 52 cm long, and the center one was 37 cm long. The ventilation rate averaged 0.24 m /s. In the second phase (tests 7 through 8), the ventilation rate was raised to an average speed of 0.44 m /s. In the third phase (tests 9 through 21), the ventilation rate averaged 0.23 m /s , and three 52-cm-long strip heaters were used. In phase three, the instruments used to measure smoke characteristics, the CNM and the TEOM, were malfunction- ing, and the data could not be used. CALCULATIONS It is necessary to measure certain parameters in order to compare the steady-state combustion products and ultimately the hazards of various fuels. Among these measurements are gas concen- trations, smoke particle mass and number concentrations, ventilation rate, and mass-loss rate. Other combustion prop- erties can be calculated once these values are known. PRODUCT GENERATION RATES In a ventilated system, the generation rates (Gx) of CO2 and CO are related to the bulk average concentration increases above ambient, ACO2 and ACO, by the expressions Gco 2 ■ MC0 2 x v oAo * AC0 2 (1) and Geo = Mco x VqAq x ACO, (2) where Mx = density of the given gas, g/(m 3 *ppm), M C o 2 = 1.97 x 10" 3 g/(m 3 -ppm), Mco = 1.25 x 10 -3 g/(m 3 -ppm), and V A = incoming coal airflow, m 3 /s. COMBUSTION YIELDS Once the generation rates are known and the mass-loss rate of the fuel (Mf) is calculated using the load-cell assembly, the true yield of the combustion product (Y x ) can be calculated by the expression Y X = Gx/M f . (3) The yields for mass (M ) and number (N ) concentrations are calculated in a similar manner by the expression Y X = AX (C X )(VoA )/Mf, (4) Kx = stoichiometric yield of the given gas, g/g, Kco 2 = stiochiometric yield of CO2 (2.86 g/g), and Kqq = stoichiometric yield of CO (1.82 g/g). Substituting the values in equations 1, 2, and 5 yields Qa = VoA o [0.0214(AC0 2 ) + 8.5 x 10" 3 (AC0)]. (6) where Cx = appropriate units conversion factor: 1.00 x 10" 3 when M Q is in milligram per cubic meter or 1.00 x 10 6 when N is in particle per cubic centimeter ; and AX = smoke concentration increase above ambient (when M is measured in milligram per cubic meter and N Q is mea- sured in particle per cubic centimeter) . HEAT-RELEASE RATES It has been shown (8) that the actual heat-release rate realized during a fire can be calculated from the expression 5a ■ (& &c °-- Hq - Hep (Kco) KCO Geo, (5) where Qa = actual heat release, kW, He = net heat of complete combus- tion of the coal (31.0 kJ/g), Hco = heat of combustion of CO (10.1 kJ/g), Since measurements of VqAo, ACO2, and ACO were made continuously, the actual heat- release rates could be calculated using equation 6. A typical fire rarely realizes the state of complete combustion. For this reason, the actual heat of combustion (Ha) during a fire is usually less than the net heat of combustion (He). By mea- suring both the actual heat-release rate (equation 6) and the fuel mass-loss rate, (Mf), the actual heat of combustion can be calculated from the expression H A = Q A /M f . PRODUCTION CONSTANTS (7) In an actual mine fire, it is often difficult, if not impossible, to calcu- late the actual heat of combustion. Moreover, since the true yield of a com- bustion product depends upon this infor- mation, significant errors can result in predicting the resultant concentration increases. For flaming fires, the rela- tive hazards tend to increase with the actual heat-release rate that results. For this reason, production constants, or beta values (8x), can be calculated for a given product by the expression Bx = G x /Qa. (8) Using the rate of formation of gas or smoke as a function of the fire size is also beneficial in comparing the combus- tion hazards of different fuels. SMOKE PARTICLE DIAMETERS Measurements of both number and mass concentrations of the smoke provide im- portant information relative to the yields (equation 4) and production con- stants (equation 7). They can also be used to calculate the average size of the smoke particles, using the expression ird, (Pp)(N Q ) = 1 x 10 3 M< (9) where Pp = individual particle den- sity, g/cm , d m = diameter of average mass, Mm, and 1 x 10 3 = the appropriate units con- version factor. Assuming a value of p p = 1.4 g/cm 3 , the diameter of average mass can be calcu- lated from 1/3 d m = 11.09 ( -^ ) > (10) ■-(£) when the particle diameter is expressed in micrometers. Using the three-wavelength smoke detec- tor, the transmittance (T) of the light through the smoke can be calculated for each wavelength. The extinction- coefficient ratio can be calculated for each pair of wavelengths (A) from the following log-transmission ratios: lnT(Xl.OO) lnT(Al.OO) lnT(A0.63) lnT(A0.45) or lnT(A0.63) lnT(A0.45) Using these extinction coefficients and the curve in reference (_7) figure 11, the surface mean particle size (d32) can be determined. (Calculation of the extinction-coefficient curves assumes spherical particles with an estimated refractive index). The smoke obscuration is the percentage of light absorbed by the smoke or 100% of the light minus the percent transmission. It is calculated using the following equation: Obscuration = 100(1 - T) (ID The obscuration percentages presented below are an average of those calculated from the three wavelengths. COAL COMBUSTION RESULTS AND DISCUSSION All values listed in this report are averages for the steady-state burning stage, which was arbitrarily selected to be a 10-min period beginning 27 min after ignition. Figure 2 shows the results of a typical test. Ignition of the coal occurred at 23 min. The strip heaters were turned off at 43 min. The flames were quenched at 60 min. In this experiment, the steady-state values were obtained from 49 to 59 min. Table 1 lists the ignition times and mass-loss data. At the higher ventila- tion rate, the coal ignited faster and burned more efficiently, as evidenced by the larger mass loss. Increasing the length of the strip heaters had about the same effect as raising the ventilation rate. TABLE 1. - Ventilation, ignition, and mass loss for the three phases of the coal experiments VoAo, Smoke Ignition Mass-loss Total mass Test m 3 /s sighted, sighted, rate, loss, min min g/s g 1-6.. 0.24 12.0 21.2 0.39 187 7-8.. .44 12.0 18.0 .45 247 9-21. .23 11.5 18.2 .44 231 UJ CO < UJ _l UJ or UJ X 1 u 1 1 1 1 1 1 1 KEY ~ Heat loss n / Mass loss / 1 / 9 8 7 / >^A 6 " / / 5 4 '-B J J L^-J— ^^-l— ; — -— . 3 2 1 o KEY Mass Number E 3 o> g or UJ » h- CO CO o Ul 5 _l < CO Q CO Ul < _l 2> CJ 1- cc < 0_ -2.0 -1.8 ro Hl-6 .o 10 20 30 40 50 60 70 80 90 TIME, min 80 90 FIGURE 2.— Results of a typical coal combustion test. A, CO and C0 2 concentrations; B, particle mass and number concentrations; C, heat-release and mass-loss rates; D, diameter of average mass (d m ) and mean particle diameter (d 32 ). GAS CONCENTRATIONS AND HEAT PRODUCTION Figure 2A shows the typical gas produc- tion plot. The highest concentrations were produced while the strip heaters were on. Subsequently, the concentra- tions reached the steady state and re- mained there until the fire was quenched, which produced the final CO spike. Table 2 presents the CO and C0 2 con- centrations and generation rates and the corresponding heat-release rates and heats of combustion. At the higher ventilation rate, the gas concentrations were reduced owing to a greater dilution with incoming air. However, the genera- tion rates increased. This increase was more evident for CO2 because with an in- creased oxygen supply, the rapidly burn- ing coal was better able to support com- plete combustion. Increased oxygen was also responsible for a hotter fire, as can be seen from the greater heat-release rate. Using a larger ignition source produced a still hotter fire that doubled the gas production. These increased concentrations may have been the result of the strip heaters being in direct con- tact with more coal. Figure 25 shows how the heat-release rate corresponded to the mass loss. The mass loss rate dipped slightly after the strip heaters were turned off. HCN concentrations were also measured throughout experiments 1 through 6. The steady-state average concentration was 6.5±1.5 ppm HCN. This is an indication of other potentially toxic gases, which are produced in trace amounts. At the same time, hydrogen sulfide was not detected (using the Draeger tube method). SMOKE CHARACTERISTICS Figure 1C shows the typical mass and number concentrations. The initial visu- al observation of smoke was confirmed by the number concentration, which showed an increase at 11 min. The concentration decreased while the coal was rapidly burning and increased again after the strip heaters were turned off. The mass concentration, however, showed a marked increase while the strip heaters were on and decreased when they were turned off. The smoke characteristics data are pre- sented in table 3. With increased ven- tilation, the burning coal seemed to produce more, but lighter, smoke parti- cles. Therefore, the calculated particle size was smaller. However, considering the broad diameter range at the lower ventilation rate, the size difference may be insignificant. When using the three- wavelength light transmission technique to calculate the particle size, the di- ameters seemed to overlap. Table 4 lists the diameters and smoke obscurations calculated from the three wavelength smoke detector data. Since all the diameters were in the same range, there may not have been an actual difference when comparing either the method of cal- culation or the effects of the ventila- tion rate. However, the larger ignition source seemed to produce a smokier fire, as indicated by the higher obscuration percentage. Figure 2D shows the par- ticle diameters as calculated by both methods. COMBUSTION YIELDS At the increased ventilation rate, all combustion yields were higher, especially the number and mass concentrations. The additional air supply caused a more pro- ductive fire; i.e., more gas and smoke was produced per gram of coal consumed. Using a larger ignition source caused an additional increase in the yield of CO and doubled the yield of CO2. The average yields are listed in table 5. TABLE 2. - Gas concentrations, generation rates, heat-release rates, and heats of combustion for the coal experiments Test CO, ppm CO2, Ppm Geo, 10' 2 g/s Gco 2 > g/ s Qa, kW Ha, kJ/g 1-6 89 52 176 1,095 834 2,321 2.7 2.9 5.1 0.5 .7 1.1 5.9 8.0 11.9 15.2 17.8 27.1 TABLE 3. - Smoke characteristics for the coal experiments N , 10 6 p/cm 3 M , mg/m 3 d m Test Average, Range , um um 1.5 11.4 0.21 0.12-0.34 7-8 2.1 8.1 .17 .15- .20 9-21 ND ND ND ND ND Not determined. 10 TABLE 4. - Mean particle sizes and smoke obscuration for the coal experiments lnT(Xl.OO) lnT(Xl.OO) lnT(X0.63) Average d32, ym Test lnT(X0.63) lnT(X0.45) lnT(X0.45) Obscuration, Average, ym Range, ym Average, ym Range, ym Average, ym Range, ym % 1-6... 7-8... 9-21.. 0.24 .27 .25 0.17-0.31 .16- .39 .21- .30 0.22 .26 .22 0.16-0.29 .19- .32 .16- .29 0.22 .22 .23 0.18-0.26 .18- .25 .16- .36 0.23 .25 .24 20 19 29 TABLE 5. - Combustion yields for coal experiments Test Yco, 10- 2 g/g Yco 2 > g/g Y N , 10 11 p/g Y Mq , 10" 3 g/g 1-6 7-8 9-21 7.8 11.6 12.7 1.3 2.0 2.6 9.2 34.8 ND 8.2 18.3 ND ND Not determined. PRODUCTION CONSTANTS Table 6 lists the production constants or beta values. These constants calcu- lated as a function of the fire size. The values for CO and CO2 remain fairly constant for all tests. However, at the higher ventilation rate, more inten- sive smoke production was reflected by the increased number and mass concentrations . FUEL COMPARISON RESULTS AND DISCUSSION The different combustion kinetics of coal and other fuels previously studied necessitated a modification of the ex- perimental conditions, but a comparison of their combustion products was still possible. Earlier studies of wood and transformer fluid fires were conducted in the same intermediate-scale fire tunnel using the same instrumentation and cali- bration techniques. However, the venti- lation rates and ignition sources varied with the fuel (table 7). The gas, heat, and smoke concentrations for the three fuels studied are found in table 8. The largest fire was produced by wood. (Heat release was used to TABLE 6. - Production constants for coal experiments Test 6co, 10" 3 g/kJ 6co 2 , 10" 2 g/kJ Bn , 10 10 P/kJ 6 Mo , 10- 4 g/kJ 1-6 4.8 4.5 4.3 8.9 8.9 8.9 6.8 13.7 ND 4.7 7-8 6.6 9-21 ND ND Not determined. TABLE 7. - Ignition source and ventilation rates for the three fuels tested Fuel Ignition source VqAo, m 3 /s Coal Electric strip heaters... 1.0 .24 Transformer fluid... .47 11 determine fire size. ) The configuration of the wood sticks may have improved the air circulation, which could have supported more complete combustion than was achieved using the other fuels. For better comparison, the other fuels were normalized to the heat-release rate pro- duced by wood fires. Table 9 shows these normalized values. At the projected fire intensity, burning coal produced the most smoke and higher gas concentrations. However, burning transformer fluid pro- duced a thick, dense smoke. Of the fuels tested, the transformer fluid generated the largest particles and obscured the most light. These values are listed in table 10. Burning coal generated the most CO and the highest number of smoke particles, using the rate of formation of gas or smoke as a function of the heat produced. The production constants are found in table 11, and are confirmed by the con- centrations found in table 8, in which wood generated the most CO2 relative to the fire size. From these experiments, it would be misleading to say one fuel is more haz- ardous than the other two, since each one generates dangerous combustion products. In any mine fire, all the burning ma- terials combine to produce a wide variety of smoke particles and volatile gases that may be transported by the ventilat- ing system. If more efficient smoke de- tectors are to be developed, the indi- vidual components of the smoke should be known. TABLE 8. - Gas, heat, and smoke concentrations for the three fuels tested Fuel Wood Coal Transformer fluid CO, ppm 145 89 113 CO2, ppm 6,759 1,095 1,769 Qa, kW 110.2 5.9 21.1 N , 10' p/c rrr 6.0 1.5 1.1 M , mg/m 4971 11.4 35.3 TABLE 9. - Normalized gas and smoke concentrations for the three fuels Fuel Wood , Coal , Transformer fluid. CO, ppm 145 1,662 590 CO- ppm 6,759 20,452 9,239 N o, 10' p/cm 3 6.0 28.0 5.7 M , mg/m 3 49.1 213.3 184.4 TABLE 10. - Particle size and smoke obscuration for the three fuels tested Fuel Wood Coal Transformer fluid. . ND Not determined. d m , Pm d 3 2 , ym 0.22 ND .21 0.23 .39 .39 Obscuration, % 9 20 46 TABLE 11. - Production constants for the three fuels tested Fuel Bco, 10" 3 g/kJ 6co 2 , 10~ 2 g/kJ Bn q , 10 10 p/kJ $M o , 10" 4 g/kJ 1.6 4.8 3.1 10.4 8.9 7.7 5.8 6.8 2.5 4.9 4.7 7.8 Coal Transformer fluid. . 12 REFERENCES 1. Egan, M. R. , and C. D. Litton. Wood Crib Fires in a Ventilated Tunnel. BuMines RI 9045, 1986, 18 pp. 2. Egan, M. R. Transformer Fluid Fires in a Ventilated Tunnel. BuMines IC 9117, 1986, 13 pp. 3. Lee, C. K. , R. F. Chaiken, J. M. Singer, and M. E. Harris. Behavior of Wood Fires in Model Tunnels Under Forced Ventilation Flow. BuMines RI 8450, 1980, 58 pp. 4. Smith, A. C, and C. P. Lazzara. Spontaneous Combustion Studies of U.S. Coals. BuMines RI 9079, 1987, 28 pp. 5. McCaffrey, B. J., and G. Heskestad. A Robust Bidirectional Low-Velocity Probe for Flame and Fire Application. Combust, and Flame, v. 26, No. 1, 1976, pp. 125-127. 6. Patashnick, H. , and G. Rupprecht. Microweighing Goes On -Line in Real Time. Res. and Development, v. 28, No. 6, 1986, pp. 74-78. 7. Cashdollar, K. L. , C. K. Lee, and J. M. Singer. Three-Wavelength Light Transmission Technique to Measure Smoke Particle Size and Concentration. Appl. Optics, v. 18, No. 11, 1979, pp. 1763-1769. 8. Tewarson, A. Heat Release Rate in Fires. Fire and Mater, v. 4, No. 4, 1980, pp. 185-191. 13 APPENDIX. —SYMBOLS USED IN THIS REPORT Cx conversion factor of a given combustion product dm diameter of a particle of average mass, urn d32 mean particle size, ym Geo generation rate of CO, g/s Gco 2 generation rate of CO2, g/s Gx generation rate of a given combustion product, g/s Ha actual heat of combustion, kJ/g He net heat of combustion of fuel, kJ/g Hco heat of combustion of CO, kJ/g Kco stoichiometric yield of CO, g/g Kco 2 stoichiometric yield of CO2, g/g Kx stoichiometric yield of the given gas, g/g In logarithm, natural Mco density of CO, g/(m 3 «ppm) Mco 2 density of C0 2 . g/(m 3 *ppm) M f fuel mass loss rate, g/s M particle mass concentration, rag/cm 3 M x density of the given gas, g/(m 3 *ppm) N particle number concentration, p/cm 3 p particle Qa actual heat-release rate, kW T transmission of light, V V0A.0 ventilation rate, m 3 /s Yx yield of a given combustion product, g/g or p/g beta value (production constant) of a given combustion product, g/kJ or p/kJ measured change in a given quantity * wavelength, ym Pp individual particle density, g/cm 3 3x AX U.S. GOVERNMENT PRINTING OFFICE: 1987-605-017.60130 INT.-BU.OF Ml NES, PGH. ,PA . 28617 Bureau of MInee-Prod. and Oistr. 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