TN 295 No. 9052 / V^-v° v^v" V^-'V v<^ >j*' .vaSte %„ <* >bV * **, V*0* o . , - G^ V **"*XT* ' A ' ^^n ~ J ^liill?« A Vy X. o%^?^" ^^ 6 ' A oVo'1%^0, .4*.-^*.^ ,0*...^ % *O o A* -' l " •by ^°^ ^ a^ ,*-^^-'- *- ^ ' o . a * ,G V o °0 * ?^~* .0° V ^^TV* .^ %.**•»'•• A?° "^ » ' ^ w ^ .. V * <& *, .& /^J?A, # o V ^ » V 1 * ^ 5 . . , ^ 3?V V /.. %^v v^-V v*^V v^V p «? V '^^ % V V \/''°-'\V' V'^^V^ \*''o$**\S ^W./ V''-.^'' a* *°-v r»* ^ \> °y .** V I '^CT °o J.°V. •***■•. \/ .•«•, w :Jfe\ \/ #&. v** •«"•- \/ " " ^0< -4 mi ^ m 'W/NES 75TH AV^ Information Circular 9052 Determining Face Methane-Liberation Patterns During Longwall Mining By Andrew B. Cecala, Robert A. Jankowski, and Fred N. Kissell UNITED STATES DEPARTMENT OF THE INTERIOR Donald Paul Hodel, Secretary BUREAU OF MINES Robert C. Horton, Director TA/29S- no. fo^z Library of Congress Cataloging in Publication Data; Cecala, Andrew B Determining face methane- iberation patterns during ongwall mining. tin formation circu ar / United St ates Department of the Interior, Bu- reau of Mines ; 9052) Supt. of Docs, no.: I 28.27 : 9052 1. Coal— Methane content. 2. Longwall minin g. I. Jankowski, Robert A. II. Kissell , Fred N III. Title. IV. Series: Information cir- cular (United States. Bureau o f Mines) ;9052. TN295.U4 [TP325] 622s [622'. 334] 85 -17397 1 /^ Page ^ CONTENTS Abstract 1 Introduction 2 Test setup for methane monitoring 2 Testing 3 Results 3 Longwall panel 1 4 Longwall panel 2 7 Discussion 8 Conclusions 9 ILLUSTRATIONS 1. Sampling location on shearer for longwall faces tested 3 2. Shearer methane levels for both cut directions 4 3. Airflow patterns around longwall shearer 5 4. Increased methane liberation during bumps 6 5. Typical airflow patterns in headgate area 6 6. Methane concentrations during headgate cutout 6 7. Gradual increase in methane from headgate to tailgate 7 8. Gradual increase in methane at tailgate as day progressed 7 9. Gradual increase in methane from headgate to tailgate as day progressed.... 8 TABLES 1. Geological conditions of each longwall panel 3 2. Average methane level downstream from shearer 5 3. Methane levels measured simultaneously at shearer and tailgate 5 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT ft foot L/rain liter per minute f t/min foot per minute min minute f t 3 /min cubic foot per minute pet percent in inch s second DETERMINING FACE METHANE-LIBERATION PATTERNS DURING LONGWALL MINING By Andrew B. Cecala, 1 Robert A. Jankowski, 2 and Fred N. Kissell 3 ABSTRACT As deeper seams are continually mined, methane liberation will con- tinue to increase and must be monitored effectively. To effectively monitor and develop appropriate control technology, methane-liberation patterns must be known. The Bureau of Mines recently completed a study to identify specific patterns of face methane liberation during long- wall mining. Both of the longwall faces surveyed had high methane lib- eration rates. At one longwall face, most of the methane was liberated during cutting of coal by the shearer mining machine. At the second face, a significant portion of methane was emitted from the face and floor. An effective methane-monitoring system would be different for each longwall panel because of the differences in how the gas is re- leased along the face. 'Mining engineer. ^Supervisory physical scientist. •^Research supervisor. Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. INTRODUCTION The Bureau of Mines conducted a study to measure and record methane levels in an attempt to identify the specific liberation patterns on longwall faces. Ignitions on longwall panels have been increasing over the past few years. To effectively monitor methane, it is nec- essary to know the specific libera- tion areas. Once liberation patterns are known for a longwall panel, effective monitoring systems can be installed, and effective control procedures can be implemented. Methane ignition is still one of the most serious hazards facing the coal mine operator. Over the past few years, there have been a number of coal mine fatal- ities due to methane ignitions. Records for the past 15 years indicate an average of approximately 50 reported methane ig- nitions a year in U.S. coal mines. Since 1975, the number of ignitions has in- creased due in part to ignitions occur- ring on longwall panels where the high rate of extraction liberates methane at a higher rate. As mining continues to ex- pand to greater depths, it is estimated that methane levels will also increase. 4 Methane is liberated at the face in two ways during longwall mining. First, gas is liberated by the cutting action of the shearer mining machine during the cutting sequence. Second, gas is emitted from the exposed coal along the total face, floor, and roof; this is also known as face bleeding. Ventilation is the primary means of controlling face methane liberation. In room-and-pillar mining, increased gas levels are usually reduced by increasing the airflow. On some longwall panels, this control method has produced face airflows that have exceeded 100,000 ft 3 / min with air velocities of over 1,000 ft/ min. In a few cases, these airflows have not been sufficient to dilulte and dis- perse the methane liberated during long- wall mining. TEST SETUP FOR METHANE MONITORING In the current study, both remote- sensing and handheld methane monitors were used. Two remote-sensing methane monitors were used, one on the shearer and the other at the tail end of the face. Handheld monitors were used to de- tect methane downwind of the shearer. The remote-sensing CSE 180R Monitors 5 have a remote sensor head; connecting ca- bles are available in lengths of 10 to 100 ft. The sensor head uses a catalytic diffusion-type sensor to monitor methane. From the temperature differential across a wheatstone bridge in the sensor head, the instrument calculates methane concen- trations in air from to 5 pet. The level of concentration is recorded con- tinuously on an internal strip-chart re- corder and is displayed on the monitor. The monitor located on the shearer was used to determine methane liberated during face cutting. This unit monitored a point on the face side of the shearer body near the tailside drum (fig. 1). The monitoring location at panel 1 was at the tailside splitter arm of the shearer. Since the shearer at panel 2 did not have a splitter arm, the monitor was placed on the body of the shearer. Because of the amount of water and coal thrown by the tail drum at these locations, the sensor head was housed in a sensor chamber on the walkway side of the shearer machine instead of at the sampling point. This chamber was 6 in. on all sides. Hard tubing extended from the chamber to the sampling point from which air was drawn into the chamber at about 4 L/min by two 4 Irani, M. C, E. D. Thimons, T. G. Bobick, M. Duel, and M. C. Zabetakis. Methane Emissions From U.S. Coal Mines, A Survey. BuMines IC 8558, 1972, p. 57. ^Reference to specific manufacturers is for information only and does not imply endorsement by the Bureau of Mines. Shearer monitor location FIGURE 1. - Sampling location on shearer for longwall faces tested. sampling pumps. This monitor had a re- sponse time of approximately 35 s. The second monitor, located at the tail end of the face, was used to deter- mine face liberation. This monitor was strapped to a hydraulic support, approxi- mately five supports from the tailgate. The sensor head was extended up and out to the front of the support. The sam- pling point was approximately 6 in. from the roof, and 2 ft from the face. Handheld monitors were used to de- termine methane levels downwind of the shearer. Readings were taken near the roof a few feet from the face, 30 ft downstream from the shearer, at 5-ft intervals . Federal regulations require that all working sections in coal mines have a methane monitor at the face to measure methane levels. In some cases, these values were correlated with values ob- tained from the monitor at the tail end of the face. TESTING Tests were performed at two different longwall faces to determine liberation and flow patterns during longwall mining. These faces were known to have high meth- ane liberation, and each panel had com- pletely different geological conditions (table 1). Both of these longwall panels were ventilated from head to tail. These faces are considered to be extremes for methane liberation for longwall mining today, but as deeper seams are mined, these could someday become the norms. Testing was performed at each panel by two Bureau personnel for one shift per day for 1 week. RESULTS The significant liberation and flow patterns of each longwall face were obtained. The results from testing at each face will be listed separately be- cause of the major differences in how the methane is emitted for each panel. TABLE 1. - Geological conditions of each longwall panel Approximate values Seam height ft, Overburden ft, Roof strength Cutting direction Longwall type Panel 1 Panel 2 24 (mining top 10) 2,000 Medium: shale. Unidirectional. Advancing. 8 550 Medium: sandstone and siltstone. Bidirectional. Retreating. LONGWALL PANEL 1 There were four significant findings: 1. Methane levels were lowest during the tail-to-head pass (even when cutting was bidirectional) . 2. Substantial methane dilution was occurring downstream from the shearer. 3. Methane levels increased during bumps. 4. Methane levels were highest during the headgate cutout. Methane Levels Were Lowest During Tail-to-Head Pass the airflow patterns around the shearer for the two cut directions (fig. 3). For the tail-to-head pass , the air coming down face flowed directly to the drums , and was forced out around the cowl and into the midsection of the work area. As more air reached the drums , turbulence increased and methane levels decreased. For the head-to-tail pass , the cowl par- tially blocked airflow to the drums, and methane liberated during cutting was not diluted with as much air at the shearer. Thus methane levels were higher at the shearer and immediately downstream from the shearer. Regardless of the cut direction, meth- ane liberation is the same because a unit volume of coal contains a certain unit volume of methane gas. As the coal is cut, the methane gas is released. Meth- ane levels around the shearer are deter- mined from the dilution by the primary airflow. Figure 2 shows typical methane levels at the shearer monitor for a head- to-tail (A) and a tail-to-head (B) pass. The average methane concentration for the head— to-tail pass was 0.72 pet; the aver- age concentration for the tail-to-head pass was 0.53 pet. These readings were also supported by handheld measurements taken at the tail end of the shearer. The differences can be accounted for by Substantial Methane Dilution was Occurring Downstream from Shearer This was supported by the level down- stream from the shearer taken by the handheld monitors , and from the measure- ments the remote methane monitor. Table 2 shows the average level downstream from the shearer for the head-to-tail pass. At 10 ft downstream from the shearer, the methane concentration was 29 pet less than at the shearer. The methane level at the tail end of the face is based on a combination of the face emission (bleedoff along the entire face) , and the liberation during coal ex- traction. Table 3 compares the methane o a. •» O z o o UJ < X r- LU 80 60 SUPPORT NUMBER FIGURE 2. - Shearer methane levels for both cut directions. CUTTING TAIL-TO-HEAD Heo.dgo.te Tailgate Direction of airflow Direction of cut CUTTING HEAD-TO-TAIL V////////////////////////////////////////////////////.////, KEY £) ►• Airflow — •■ Methane Direction of airflow Direction of cut FIGURE 3. - Airflow patterns around longwall shearer. TABLE 2. - Average methane level downstream from shearer TABLE 3. - Methane levels measured simul- taneously at shearer and tailgate Distance , ft Concentration, pet 5 0.78 .68 .67 .63 .59 .55 10 15 20 25 30 levels measured at the shearer and at the tailgate section of the face during a half shift. The methane levels at the tailgate at this longwall panel usually remained low because the methane was throughly diluted and mixed with the face airflow. Methane levels at the tailgate varied relative to those measured at the shearer with a lag time that depended on the location of the shearer on the face. Methane levels at the shearer at this panel consistently were higher than those measured at the Time Support No. Concentration, pet Shearer Tailgate 8:40 9:00 9:20 9:40 10:00 11:00 115 120 87 55 20 25 35 35 35 0.2 .7 .3 .3 .5 1.1 .2 .2 .3 1.2 0.2 .3 .3 .3 .4 .4 .3 .2 .2 .3 tail; under certain conditions, these levels were four to five times higher. Methane Levels Increased During Bumps Many times when mining deep seams, the overburden pressure builds and is spontaneously released through bumps. ^ 1.25 < X LU .00 o ■z. o o Uj" .75 .50 .25 Normal cutting 120 FIGURE 4 100 80 60 SUPPORT NUMBER Increased methane liberation during bumps. This occurs even more often on longwall panels because of the pressure created by the gob. When bumps occur, the excess pressures are transferred to the face causing additional fracturing of the coal seam, which liberates additional meth- ane. When a substantial bump occurs, the methane levels can increase significant- ly. This can be seen in figure 4, which represents the remote monitor on the shearer. The tail-to-head pass was pro- ceeding as normal up to support 70, at which time three major bumps occurred within a few minutes , and the methane concentration jumped from an average 0.52 pet to an average value of 1.03 pet. Fracturing by the bumps had released ad- ditional methane trapped within the seam, which would ordinarily not have been released until the coal was cut. Methane Levels Were Highest During Headgate Cutout As previously mentioned, the methane liberation rate is fairly constant under normal conditions for the entire face area. However, measured methane levels vary due to the extent of dilution with ventilation air. During the headgate cutout, the liberated methane was not adequately mixed and diluted by the primary face airflow (fig. 5). Due to blockage by the shearer and the 90° turn, a good portion of air often leaked into the gob. Because of this, the first 5 to 10 shields were often poorly ventilated, and the methane levels increased (fig. LEGEND Face airflow O — - Methane flow FIGURE 5. - Typical airflow patterns in head- gate area. 15 10 5 Cutout SUPPORT NUMBER FIGURE 6. - Methane concentrations during headgate cutout. 6) . Typical methane concentration levels measured during the tail-to-head pass averaged 0.53 pet. From support 10 to the headgate, methane concentration at the shearer increased significantly, with a peak, value of 2.3 pet near support 5. LONGWALL PANEL 2 There were three signif during the testing perf longwall panel: 1. Methane built up g the face from headgate to 2. Methane built up g day progressed. 3. Methane was not li icantly by the cutting shearer, but was emitted and floor. icant findings ormed at this radually along tailgate, radually as the berated signif- action of the along the face Methane Built Up Gradually Alon g Face From Headgate to Tailgate Methane levels recorded at the shearer indicated a gradual buildup of methane along the face from the headgate to the tailgate. Figure 7 shows this gradual buildup of methane at the shearer for one pass, cutting from tail to head. At the beginning of the pass, the methane con- centration at the shearer was 0.8 pet and decreased continually to the headgate, where the methane concentration was 0.35 pet. This gradual reduction in the meth- ane concentration from tailgate to head- gate was seen for all tests at this long- wall panel. Methane Built U p Gradually as Day Progressed This gradual buildup of methane dur- ing the work shift was detected by all the monitors. In figure 8, the station- ary methane monitor at support 159 shows the buildup for one pass. The methane concentration initially was 0.65 pet at the beginning of the pass and increased during the tail-to-head pass to a peak concentration of 0.95 pet. Figure 9 shows the methane concentrations at the shearer. On the tail-to-head pass and the head-to-tail pass, the methane con- centration was greater at the tailgate than at the headgate. Also, the methane 20 40 60 80 SUPPORT NUMBER 100 20 140 FIGURE 7. - Gradual increase in methane from headgate to tailgate. 1230 TIME,h FIGURE 8. - Gradual increase in methane at tailgate as day progressed. 1.00 ° 75 o o LU < X H LU .50 .25- KEY Direction of cut oo p.m. y 9=00 a.m. I2 : I0 p.m.^ 10=15 a.m. 20 40 60 80 100 120 140 160 SUPPORT NUMBER FIGURE 9. - Gradual increase in methane from headgate to tailgate as day progressed. concentration at the tailgate increased 0.4 pet from 9:00 a.m. to 1:00 p.m., con- firming that there was a gradually build up of methane as the day progressed. Methane was Not Liber ated Significant! y By Cutting Action of Shearer, But Was Emitted Along Total Face and Floor It is common to observe substantial methane dilution as the distance increases downstream from the shearer be- cause, in most cases, a portion of meth- ane is liberated from the coal cut by the cutting drums. However, at this longwall panel, there was no significant methane liberation by the cutting of the shearer. The methane level was the same at the shearer as it was 25 ft upstream or down- stream from it. DISCUSSION The two longwall surveys showed totally opposite results. These mines are at the extremes for methane liberation today, but in the future as mining continues to go deeper, similar panels may be the norm for longwall mining. At the first mine, most of the methane was liberated during cutting of the coal by the shearer; at the second mine, most of the methane was from face and floor emission. Because of these differences, an effective methane- monitoring system would need to be dif- ferent for each longwall panel. At longwall panel 1, the significant part of the liberation was from the coal being cut by the shearer. Although the amount of methane liberated is indepen- dent of the cut direction or location on the face, recorded methane levels were 26 pet higher on the head-to-tail pass than on the tail-to-head pass, owing to the additional turbulence and mixing of the ventilating air during cutting from tail to head. Recorded methane levels were highest during the headgate cutout, during which the liberated methane was not adequately mixed and diluted by the primary face airflow mainly because of blockage by the shearer and the 90° turn at the headgate. During the headgate cutout, a major portion of the air is forced back into the gob for the first 10 to 15 supports. It was also observed that when overburden pressure builds and spontaneously released through bumps, methane levels increase significantly. Methane levels at the tailgate varied relative to those measured at the shearer with a lag time that depended on the shearer's face location. The changes at the tailgate were not proportional to those at the shearer; however, measured changes in concentrations at the tailgate were very minor except when the shearer was cutting out at the tailgate. This was due to the dilution of liberated methane with the primary airflow as the distance increased downstream from the shearer. This dilution downstream from the shearer was detected with the hand- held monitors. To effectively monitor a longwall panel of this nature, the sensing instrument should be located on or near the shearer. Hazardous methane levels could be encoun- tered at the shearer yet not substan- tially increase the methane level at the tailgate end of the face. At longwall panel 2, the significant part of the methane was due to face and floor emission. There was a gradual buildup of methane along the entire face from headgate to tailgate, and there was a gradual buildup of methane as the day progressed due to the additional face and floor exposure. Coal was mined on this face for only one shift; during the other two shifts, the face had time to bleed off a portion of the methane.. As cutting progressed through the day, new coal was exposed and the methane level increased. No significant methane was liberated by the cutting of coal by the shearer, as evidenced by the fact that concentration at the shearer was the same as that 25 ft upstream or downstream from the shearer. For this longwall panel, the most ef- fective monitoring location is at the tail end of the face. Since the methane is not being liberated by cutting of coal by the shearer, a monitor located on the shearer would not be of benefit unless conditions were to change. CONCLUSIONS As the depth of seams increases, meth- ane liberation will increase. To effec- tively monitor methane, liberation pat- terns must be known. At the two longwall panels surveyed for this study, these patterns were totally different. At the first panel, most of the methane was lib- erated during cutting of coal by the shearer. The substantial variation in methane levels during the mining cycle were dependent on the effectiveness of dilution by the primary airflow. Methane levels were higher during the head-to- tail pass than during the tail-to-head pass, and they were highest during the headgate cutout. At the second panel, most of the methane was due to face and floor emission. Because of this, methane levels at the tailgate end of the face were substantially higher than those in the headgate area, independent of the lo- cation of the shearer at the face. An effective methane-monitoring system must vary according to how the gas is released from each longwall panel. Whether the methane is liberated by the shearer or emitted from the face and floor, more effective dilution methods must be developed. GPO: 198S-30S-O19 20.112 INT.-BU.OF MINES, PGH..P A. 28 125 U.S. Department of the Interior Bureau of Mines— Prod, and Distr. Cochrans Mill Road P.O. Box 18070 Pittsburgh. Pa. 15236 AN EQUAL OPPORTUNITY EMPLOYER OFFICIAL£USINESS PENALTY FOR PRIVATE USE, $300 ] Do not wi sh to recei ve thi s material, please remove from your mailing list. "2 Address change* Please correct as indicated* ^ °Jlflll r ^ * .0^ \ ^" A* % 'S^ ^ V W '"^o* :^'; *b^ ."""^IS'". '"^o* " *'&DV%5*** *r>»m. %/ .•»-•. \/ :'M^-, \s ._ tt-t rr- r »•;•• .\v v o n,i R* * ^ '«§&v ^ *W ^ ; -^fe^ ****** % ^ :% MB^'' "W* V -Si °^ valjv ^°- R" > ^ •JBi3k : ^°* i » <\ *+ . ..^ ^ N ' ■*> *• a> *..o' *