y , p, , 

and S. J. Pepperney 
Report of Investigations 8424 

A Fail-Safe Control System 

for a Mine Methane Pipeline 

By M. C. Irani, F. F. Kapsch, P. W. Jeran, 

and S. J. Pepperney 

UNITED STATES DEPARTMENT OF THE INTERIOR 

Cecil D. Andrus, Secretary 

BUREAU OF MINES 

Lindsay D. Norman, Acting Director 
This publication has been cataloged as follows: 

, 

United States. Bureau of Mines. 

A fail-safe control system for a mine methane pipeline. 

(Report of investigations ; 8424) 

Bibliography: p. 11. 

lU Mine gases-Pipe lines-Automatic control, 2. Methane-Pipe 

lines-Automatic control. 3, Coal mines and mining-Safety measures. 

1. Irani, M. (1. 11. Title, 111. Series: United States. Bureau of Mines, Report of investigations ; 8424. 

TN23.U43 [TN305] 622l.8 79-20999 

I 
CONTENTS 

Page 

Abstract ................................................................ 1 

Introduction ............................................................ 1 

General description of system operation ................................. 3 

Major components of the system .......................................... 5 

Detection equipment ................................................ 5 

The methane sensors ........................................... 5 

External power supply ......................................... 6 

The receiving station ......................................... 6 

Shutdown equipment ................................................. 8 

Borehole valve and pneumatic actuator ......................... 9 

Air line made of brittle PVC tubing ........................... 10 

Conclusions ............................................................. 10 

Bibliography ............................................................ 11 

ILLUSTRATIONS 

1 . Actuator mounted on threaded ball valve ............................. 2 . Methane sensor assembly ............................................. 3 . Diagram of mine installation ........................................ 4 . Schematic of detection and shutdown equipment ....................... 5 . Aboveground receiving station ....................................... 6 . Underground installation of shutdown equipment ...................... 7 . Cutaway view of valve actuator ...................................... 
A FAIL-SAFE CONTROL SYSTEM FOR A MINE METHANE PIPELINE 

by 

M. C. Irani, 1 F. F. Kapsch, 2 P. W. ~eran,3 and S. J. Pepperney4 

ABSTRACT 

The Bureau of Mines has designed and put into operation a fail-safe control system for use in underground coal mines equipped with methane drainage 

pipelines. This control system can detect certain unsafe conditions and 

respond by automatically shutting off the flow of methane from the degasification borehole to the drainage pipeline. Methane flow is shut off when the 

methane content in the return airways reaches a predetermined level (typically 

1.5 pct), when the methane drainage pipeline is ruptured by roof fall, or when 

there is an electric power failure. 

The fail-safe control system was designed using commercially available 

components and a methane analyzer system previously developed by the Bureau. 

The fail-safe system consists of a unit that combines a shutoff valve and 

pneumatic valve actuator, and electronic and mechanical equipment designed to 

detect hazards and effect shutdown. 

The fail-safe control system was designed to meet regulatory requirements 

issued by the Mine Safety and Health Administration (MSHA), U.S. Department of 

Labor, and State regulatory bodies for the safe operation of underground 

methane pipelines used for mine degasification. MSHA has inspected and tested 

this system and permitted its use in two mines. The Bureau installed the 

fail-safe system in two working coal mines, where successful performance has 

been demonstrated. 

INTRODUCTION 

The Bureau of Mines has conducted research on methane control in bituminous coal mines since it was first organized. This research has been carried 

out on an accelerated basis since 1964. An important objective of this 

lsupervisory mining engineer. 

2Mining engineer. 

3~eologis t . 4~hysical science technician. 

All authors are with the Pittsburgh Research Center, Bureau of Mines, 

Pittsburgh, Pa. 
research is to reduce the hazard of methane emissions during mining (3). One 

successful approach is to drain methane using degasification boreholes drilled 

horizontally into the coalbed from underground locations (4-1). Boreholes are 

drilled from locations near active workings and from the bottom of shafts dug 

for future use at locations remote from active workings. The boreholes provide low-resistance channels to conduct methane from the coalbed. Advantages 

of this borehole method of degasification are increased ventilation and production efficiency that can reduce mining cost. 

Efficiency is improved because the borehole method of degasification 

reduces methane emissions from the face area, allowing mining machinery to be 

safely operated for more total time than if degasification is not used. The 

modern high-capacity coal mining machines that are used to mine very gassy 

coalbeds are designed to shut down automatically when methane concentrations 

exceed a predetermined safe level. With borehole degasification, methane concentrations are kept at lower levels, and so the machines can operate more of 

the time than if degasification were not used. 

In the past, methane drainage boreholes were 100 to 150 feet long, and so 

the quantities of methane they drained were relatively small. With the successful development of techniques for drilling boreholes as long as 2,500 feet, 

the quantities of methane drained became excessive from a safety and economics 

standpoint. It is hazardous to discharge large quantities of methane into the 

mine atmosphere, because of the potential for explosion. Furthermore, this 

methane has potential use as a source of energy, although sometimes there are 

certain economic constraints and legal problems regarding ownership of the 

methane. At one project site, the methane drained by seven boreholes has been 

used for industrial and residential purposes (2). Large-scale production over 

several years has .demonstrated the economic potential of methane produced in 

this manner. To make use of methane drained from mines, it is necessary to 

design and build underground pipelines to safely collect and convey the methane from the boreholes to the surface. 

Federal and State regulatory bodies have prepared specifications and 

other design requirements for a safe methane collection system for use in 

underground coal mines (8). Included in these design requirements is a failsafe control system to close the methane drainage pipeline when unsafe conditions develop in the mine. A system is required that will stop the flow of 

methane from the coalbed to the drainage pipeline when there is methane leakage due to corrosion, rupture of the pipeline res.ulting from a roof fall, or 

for other reasons. In order to design a system that would meet these regulatory and performance requirements, the Bureau drew upon knowledge derived from 

years of research in methane monitoring systems. Particularly useful was a 

methane analyzer system (6) previously developed by the Bureau and incorporated into the fail-safe system. 

The fail-safe control system that resulted from the ~ureau's efforts has 

successfully detected and responded to unsafe conditions in fieldinstallations 

Sunderlined numbers in parentheses refer to items in the bibliography at the 

end of this report. 
FIGURE 1. - Actuator mounted on threaded ball valve. 
p, 

and is shattered- by the 

FIGURE 2. - Methane sensor assembly. 

Horizontal degasification Methane sensor I 

rborehole (every IPOO ft ) Brittle PVC r air line 

Pneumatically actuated I --,,--J 

borehole valve 8 " Cased borehole 

n 

to surface 

- - - - - - - - - , , -- - , , 

/ Brittle PVC air line - 

FCoolbed '!-pipeline 

FIGURE 3. - Diagram of mine installation. 
impact of a roof fall. When the tube shatters, air pressure drops throughout 

the system, causing the borehole valve to close. 

In case of power failure, the air compressor will stop functioning. This, 

too, will result in a drop in air pressure, and the borehole valve will close 

off the flow of methane. The system is also designed so that any failure in 

electronic circuitry will result in shutdown of the methane pipeline. 

MAJOR COMPONENTS OF THE SYSTEM 

The electronic equipment used for methane detection and shutdown was 

developed by the Bureau of Mines and the Mine Safety Appliances Co., and is 

now commercially manufactured. The equipment was originally developed to 

record continuously the methane content of mine air (6). This equipment was 

later modified to actuate control devices, cut off electric power, and sound 

alarms. 

For the fail-safe control system, this electronic detection and shutdown 

equipment has the capability of (1) indicating continuously, on meters, the 

methane content of the mine air at each sensor, (2) recording this methane 

data on individual strip charts, (3) flashing a red warning light when the 

methane content of the sampled mine air reaches a predetermined level (usually 

1.0 pct), (4) opening a solenoid valve to release air pressure so that the 

borehole valve will close when the methane content reaches a higher predetermined level (usually 1.5 pct), and (5) cutting off power to the air compressor 

when pressure in the air lines drops below 40 psi. This electronic equipment 

works together with the mechanical components of the fail-safe system, such as 

the borehole valve and the brittle PVC tube. 

Detection Equipment 

The methane analyzer system is used in the fail-safe control system to 

detect dangerous levels of methane in the air along the drainage pipeline. 

The analyzer system consists of methane sensors, a power supply, and a receiving station. Figure 4 shows the relationship of these components to each 

other and to other components of the fail-safe system. Components of the 

methane analyzer system are commercially available in a package that includes 

four methane sensors. 

The Methane Sensors 

The methane sensors (fig. 2) are located along the underground methane 

pipeline to detect leakage. They are hung downwind from the boreholes at 

1,000-foot intervals, to the point where the pipeline exits the mine. These 

sensors continuously monitor the methane content of the ventilation air, 

operating on the principle of catalytic combustion. 

The sensing element is enclosed in a circular air deflector for dust and 

moisture protection. A rectangular box houses the sensing circuits, a twostage signal-voltage amplifier, the amplifier power supply, and a nickelcadmium battery that can operate the unit for up to 6 hours if power fails. 

When the sensors detect a hazardous concentration of methane, the red 

warning light flashes and the solenoid valve is automatically tripped. The 
FIGURE 4. - Schematic of detection and shutdown equipment. 

solenoid valve causes a pressure release from the air lines of the fail-safe 

system, and this closes the borehole valve. 

Extern,al Power Supply 

The 120-vac power supply is used to operate up to four methane sensors. 

Power supply output is limited to 13.5 vdc at a maximum current rate of 800 ma. 

The cable carries operating current to the sensor and methane signals from the 

sensor to the power supply, From there the signals are directed to the receiving station via another cable. 

Because the sensor assemblies are intrinsically safe, they may be placed 

anywhere in the mine up to 3,500 feet from the power supply, Requirements for 

the size of the connecting cables between the power supply and sensors vary 

according to distance. 

The Receiving Station 

The receiving station (fig. 5) is located above ground to allow surface 

observation of data generated by the sensors. It can-monitor as many as 
FIGURE 5. - Aboveground receiving station. 
FIGURE 6. - Underground instal lotion of shutdown equipment (not including system of brittle 

PVC tubing; the brattice cloth shown here was used for photographic purposes 

and is not necessary for operation of the system). 
Borehole Valve and Pneumatic Actuator 

The pneumatically actuated ball valve (the borehole valve) is located in 

the pipeline, near the junction of the pipeline and the borehole, as shown in 

figure 3. Here, the flow of methane can be shut off as closely as possible 

to the borehole opening. To permit installation in the pipeline, the valve 

and actuator are combined into a single unit, as shown in figure 1. 

The force required to open the borehole valve is provided by the pneumatic actuator (fig. 7). The valve is closed by a return spring. 

Air pressure from the system's air compressor acts on a piston in the 

valve actuator to hold the borehole valve open as long as no unsafe condition 

is detected in the mine. A mechanical linkage converts the lateral motion of 

the piston into the rotational motion of the output shaft that turns the valve 

on or off. As the piston moves to open the valve, it compresses the return 

spring. When air pressure is released, the return spring expands, reverses 

the motion of the piston, and causes the valve to close. It is this sequence 

of events that closes off the methane flow when a drop in air pressure indicates an unsafe condition in the mine. 

An indicator on the actuator shows when the valve is closed. Maximum 

rotation is one-quarter turn of the shaft. Operating pressure is from 40 to 

100 psi; the return spring will close the valve when pressure drops below 

40 psi. 

All moving parts of the actuator are enclosed to eliminate the possibility of dirt accumulation, which could cause failure. Interior porting is used 

to conduct the compressed air. External tubing was not used because it would 

be subject to damage that could cause a failure in valve operation. 

Air intoke I plug 

Spring cylinder, 

shaft 

driver 

iaf t 

Output shaft / 

FIGURE 7. - Cutaway view of valve actuator (shown in closed position). 
Air Line Made of Brittle PVC Tubing 

A system independent of the methane detection system was designed toreact 

to roof falls. Its primary component is a brittle PVC tube securely strapped 

to the top of the methane pipeline. This tube carries compressed air and is 

connected to the compressor and the borehole valve actuator by branch lines 

made of flexible plastic tubing. 

The impact of a roof fall easily shatters the brittle PVC tube, and the 

result is a drop in air pressure that triggers a limiting switch that controls 

the compressor. When air pressure drops below 40 psi, as it would if the brittle tube were shattered, the limiting switch cuts off power to the compressor. 

At this pressure, the borehole valve will close. 

CONCLUSIONS 

The fail-safe control system was built as a safety system for an underground coal mine degasification pipeline. The system was designed to satisfy 

the safety requirements of Federal and State regulatory bodies, particularly 

those of the Mine Safety and Health Administration. It has been inspected and 

tested by MSHA, and MSHA has permitted its use in working mines. This system 

has successfully detected and responded to methane hazards in two working coal 

mines where it is now in use. The fail-safe control system is a necessary 

part of the technology required to safely pipe methane from coal mines for 

degasification and for use as a source of energy. 

 TO maintain air pressure in the system while mine conditions are safe, the 

compressor starts automatically when the pressure drops to50 psi. However, 

if the brittle tube is shattered, the loss of air pressure is too great to 

allow the compressor to start. Therefore, the compressor cannot counteract 

the operation of other components of the system as they work to close the 

borehole valve. 
BIBLIOGRAPHY 

1. Cervik, J. An Investigation of the Behavior and Control of Methane Gas. 

Min. Cong. J., v. 53, No. 7, July 1967, pp. 52-57. 

2* - .Behavior of Coal-Gas Reservoir. Pres. at 4th Ann. Eastern 

Regional Meeting, Soc. Petrol. Eng., AIME, Pittsburgh, Pa., Nov. 2-3, 

1967, SPE Preprint 1973, 4 pp.; available from the Society of Petroleum 

Engineers of the AIME, 6200 North Central Expressway, Dallas, Tex. 75206. 

3. Deul, M. Methane Drainage From Coalbeds: A Program of Applied Research. 

Proc. 60th Meeting, Rocky Mountain Coal Mining Inst., Estes Park, Colo., 

June 28-July 1, 1964, Rocky Mountain Coal Mining Institute, 1964, 

pp. 54-60. 

4. Fields, H. H., S. Krickovic, A. Sainato, and M. G. Zabetakis. Degasification of Virgin Pittsburgh Coalbed Through a Large Borehole. BuMines 

RI 7800, 1973, 27 pp. 

5. Fields, H. H., J. H. Perry, and M. Deul. Commercial Quality Gas From a 

Multipurpose Borehole Located in the Pittsburgh Coalbed. BuMines 

RI 8025, 1975, 14 pp. 

6. Irani, M. C., P. W. Jeran, and D. H. Lawhead. Methane Analyzer System 

To Record Continuously the Methane Content of Coal Mine Ventilation Air. 

BuMines RI 8009, 1975, 14 pp. 

7. Kissell, F. N. Methane Migration Characteristics of the Pocahontas No. 3 

Coalbed. BuMines RI 7649, 1972, 19 pp. 

8. Tongue, D. W., D. D. Schuster, R. Neidbala, and D. M. Bondurant. Design 

and Recommended Specifications for a Safe Methane Gas Piping System. 

BuMines Open File Rept. 100-76, 1976, 76 pp.; axailable from National 

Technical Information Service, Springfield, Va., PB 259 340/A~. 

SrU.S. GOVERNMENT PRINTING OFFICE: 1980-603-1 02/24 INT.-BU.0 F MlN ES,PGH.,PA. 24342