China Conference - Monitoring methane in gassy salt mines
Authors: Albert E. Ketler P.E., Lauren E. Sargent, Craig D. Mattock, Thayananthan Narayanan, and Brian A. Dale.
Abstract: Over the past two decades Rel-Tek developed and supplied permissible gas detection systems (GDS) for two large salt mine – Morton Salt, Weeks Island Facility, New Iberia, Louisiana, USA and Compass Minerals (formerly North American Salt,) Franklin, Louisiana, USA. Both underground mines were deemed hazardous (i.e. containing methane gas) by MSHA (US Dept of Labor, Mine Safety and Health Administration,) so all of the electrical gas detection equipment required protection against methane gas ignitions throughout the mine. This required a combination of MSHA-approved Explosion Proof (XP) and Intrinsically Safe (IS) products. A two-stage Blast Timer software feature was included to aid in production management. Data and alarm logging provides historical records, printable off line. Multiple Touch screen display terminals distribute information throughout the operation. The GDS is modularly expandable to suit virtually any mine configuration, and is particularly applicable to Chinese coal mines where they are fully hazardous, from the portable to the face.
Classified environment -- The two salt mines were MSHA (US Mine Safety and Health Administration) classified under US-CFR30, Part 57 as Class IIA mines. Originally, before the introduction of the Rel-Tek gas detection system, the mines deployed intrinsically safe methane sensors connected to the surface with long, heavy gage cables extending thousands of feet (x1.6m) from the underground locations to the surface, where intrinsically safe barriers, power supplies and 4-20ma signal detection systems monitored the mine for methane. Eventually the connecting cables grew so long that this concept became unwieldy, unreliable, and subject to unacceptable voltage losses over the cable lengths. Rel-Tek Corp. was called on to provide an electronic replacement for the long cable concepts, employing high speed digital telemetry combined with permissible (MSHA-approved) underground equipment.
Modular arrangement -- Figure 1 shows a typical equipment arrangement, each mine having variations on the concept to suit their particular needs. Confidential details of each mine are not shown. The equipment arrangement shown is illustrative of the principles only. Both mines had underground shop areas which required separate on-line video displays. One mine also had six remote display terminals, consisting of 21” (534mm) touch screen video monitors stationed in fresh air supervisory offices. Remote terminals were connected to the primary gas monitoring computer over this client’s existing Ethernet LAN.
XP outstations and optical fiber cable -- Rel-Tek supplied its explosion proof (XP) outstation boxes or panels that can be placed at AC-powered sites underground, near to the working faces where blasting can uncover pockets of methane gas. Figures 2a and 2B show these XP outstation boxes. Each contains 12 intrinsic safety barriers capable of accessing as many as 11
methane sensors and one alarm unit per panel. Sensors were connected with reasonably short cable lengths, i.e. less than 200 ft (61 m) of 18 AWG, three-conductor, shielded. High-speed telemetry (19.2KB, with 120 sensors per second processing rate) was provided over a mix of multi-mode and single mode optical fiber cables among the boxes and the surface monitoring stations. Some of these fiber cables were 2,500 ft (762m) long.
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Originally, before the introduction of the Rel-Tek gas detection system, the mines deployed intrinsically safe methane sensors connected to the surface with long, heavy gage cables extending thousands of feet (x1.6m) from the underground locations to the surface, where intrinsically safe barriers, power supplies and 4-20ma signal detection systems monitored the mine for methane. Eventually the connecting cables grew so long that this concept became unwieldy, unreliable, and subject to unacceptable voltage losses over the cable lengths. Rel-Tek Corp. was called on to provide an electronic replacement for the long cable concepts, employing high speed digital telemetry combined with permissible (MSHA-approved) underground equipment.
of methane gas. Figures 2a and 2B show these XP outstation boxes. Each contains 12 intrinsic safety barriers capable of accessing as many as 11
methane sensors and one alarm unit per panel. Sensors were connected with reasonably short cable lengths, i.e. less than 200 ft (61 m) of 18 AWG, three-conductor, shielded. High-speed telemetry (19.2KB, with 120 sensors per second processing rate) was provided over a mix of multi-mode and single mode optical fiber cables among the boxes and the surface monitoring stations. Some of these fiber cables were 2,500 ft (762m) long.
