Use of Jet Engine at Loveridge

    Coal Inertisation Technology was the name of a presentation given by Bart Hyita, Vice President – Operations Support, CONSOL Energy who described the use of a jet engine at the Loveridge mine fire to the West Virginia Mine Safety Innovation Conference in Morgantown, WV. Hyita said that the project was a collaborative effort between the Queensland Mines Rescue Service from Australia, MSHA, the West Virginia Department of Miner’s Health Safety and Training, the United Mine Workers of America, the U.S. Department of Energy, and NIOSH.
    Loveridge Mine is located in northern WV, near Fairview. The mine has a 260-meter deep shaft and slope, which supports 100 square kilometers underground area. The mine has one longwall and three continuous mining units and produces annually 5.5 million metric tons.
    The initial fire events were that it was a trolley related fire in an outby trash car. The motor men discharged fire extinguishers into the car but the fire reignited as the car was being pulled out of the track shoot. The car was now located in the main air course and the car derailed with the power kicking off. The mine ventilation rekindled the fire. The mine was evacuated and temporarily sealed within 22 hours after the fire began.
    The closest opening to the fire was the Sugar Run Slope at 1000 meters from the surface. A water line was established during temporary sealing efforts to flood the fire area. Six bore holes were established around the fire perimeter. In the first week the six boreholes were completed to:
• Monitor mine atmosphere and outgas constituents,
• Allow pumping of water to establish isolated pools,
• Measurement of water pool levels,
• Measurement of mine atmospheric temperature,
• Mine condition observation with remote camera,
• Injection of nitrogen and other inert gases,
• Potential injection of foaming agents,
• Potential pumping of remote mine seals.
Within two weeks:
• Maximum pool levels had been reached,
• Mine shafts, seals, and boreholes began outgassing,
• Temperature and water levels were measured,
• Visual fire area inspections were completed using thermocouples, M-scope, and remote bore hole camera.
Within three weeks:
• Several openings at the far side of the mine had reached explosive gas concentrations,
• Discussions regarding mine atmosphere inertization, remote sealing, fire area stabilization techniques, mine reentry options were completed,
• Several alternatives were discussed: most posed low success probability and a substantial financial commitment.
    Alterative one was to use remote sealing at the location allowing partial or full water inundation to isolate the fire area. Additional bore holes would be established at potential remote sealing locations and existing roof falls and stoppings would be used as seal barriers around the fire area to create an isolated zone of low oxygen, inert atmosphere. Low strength, fast setting concrete would be pumped from the surface through boreholes into potential seal locations surrounding the fire area. Nitrogen would be used as the inert medium for foam generation and to help stabilize the fire area. Alternative two was to utilize a high volume, jet engine based CO2 generator to provide inertization of the immediate fire area and potentially the entire mine atmosphere. This method has been previously used in Australia. Alternative three was to allow the natural process of mine atmosphere neutralization to occur with the associated extended job loss, loss of coal production revenues and twelve to eighteen months of waiting time.
    The jet engine based inertization technology was selected with the operation of a stationary jet engine from the surface to produce a CO2 rich oxygen deficient atmosphere see Figure 1 (Slide 16). The jet exhaust gas flow was directed underground to the fire area with a 32” diameter flow pipe inserted into a fabricated steel hood placed over the concrete slope portal. The Sugar Run Slope was 17 degree grade and 1000 meters long. The primary objective was to displace the fire atmosphere with inert gases. The average quantity of inert jet wet engine exhaust was approximately 14 m3/s.

    A secondary objective was to displace the explosive mine atmosphere throughout several kilometers of underground workings and ventilation shaft openings. The estimated time required for total mine atmosphere displacement was four to five days based on eight million cubic meters of mine volume. The jet engine functioned at an almost continuous rate for 240 hours, see Figure 2 (Slide 19).

A number of jet engine preparation and procedures were carried out:
•A timeline was developed outlining the major steps and expected progress,
• Jet engine support personnel were identified,
• Gas sampling frequency and chromatography analysis was developed,
• Instantaneous O2, CO detection and sampling were determined,
• Infrared remote temperature sensing equipment was specified,
• Mass flow quantity measurement procedures were developed,
• Heating protection was considered (160 dB at open jet engine exit; 100 dB when flow diverted into mine)

Also considered were:
• Awareness of Australian electrical equipment, single phase 50 Hz 240v,
• Welding/power buffer zones,
• Engine staging pad at 7% inclination,
• Intake baffle placed outby inlet to minimize “engine whine”,
• 38,000 liter stationary diesel fuel tank,
• 28,000 liter mobile diesel fuel tanker,
•Two-way communication and mine phone system.

    Hyita emphasized the safety procedures undertaken in the project and said that written risk assessments were completed and regularly reviewed. Site specific requirements were considered including:
• Operational issues,
• Personnel safeguards,
• Weather impacts,
• Engine crew training, 
• Mine data,
• First aid, 
• Collaborative support.

    The Jet Engine in action is shown in Figure 3 (Slide 24). Actual operation results were as follows: Jet engine inert gas output was optimized at an oxygen level between 3.5% to 4.0%. Jet–A Fuel consumption averaged 1,560 liters/hour. Total fuel consumption was 370,000 liters averaging 26,000 liters per day. Engine routing maintenance/inspection shutdown took place for 1-2 hours. The diffuser rings were considered a wear item dependant on the position of the flame in the afterburner. The cleaning of carbon deposits had to be done.

    Water was used for both active and passive cooling with a total of 450 liters/minute, 225 liters/minute active, 225 liters/minute passive. Half of the flow used was for direct exhaust cooling. Half of the flow was for the heat exchanger and external cooling sprays.
The mass flow calculations showed that the Jet Engine produced approximately 14 cubic meters per second of wet exhaust consisting of five cubic meters per second dry exhaust and water vapor at 1,560 liters/hour fuel consumption.
    Mine ventilation simulations were carried out with the jet engine running. It was assumed that there was a restart of three of the four exhaust fans while maintaining an “inert atmosphere envelope” around the fire area. The Jet Engine needed to run intermittently to recharge the fire area with inert exhaust gas.     

    Temporary seals were removed from six shafts: three intake and three return. Actual ventilation results indicated that the balance of “inert atmosphere envelope” could best be controlled with only two fans operating.
    A detailed step-by-step reentry plan was developed in conjunction with union, state, and federal agencies to reestablish mine ventilation and explore the fire area. Ten CONSOL mine rescue teams were dispatched, consulted within the planning process and then mobilized into reentry operations. Mine reentry began April 14, exactly two months after the fire began.
    With regard to the reentry, an intake split was established to allow exploration while maintaining the inert atmosphere in the fire area. There was careful balance of ventilating pressure and quantities. Resididual heat and humidity created by the engine mass flow made team advancement in the inertization zone difficult. Temporary barriers were constructed around the fire area, which were eventually replaced with temporary metal stoppings. Nitrogen generators were used to maintain the inert atmosphere. On April 18, active Jet Engine use was discontinued. After 14 days, engine demobilization occurred April 20.
    “Use of the GAG3A Jet Engine at Loveridge provided ground breaking technology for stabilization of the mine fire atmosphere,” said Hyita. “Cooperation from federal, state, and union representatives was instrumental in the success of the Loveridge inertization effort. Stringent attention to monitoring procedures, evaluation of mine atmospheric readings, gas analysis, and detailed record keeping ensured the success of eventual recovery operations.”
    Mine reentry within two months versus twelve months, allowed mine recovery operations to commence immediately with restarting of development production within six months of the fire incident and reinstatement of the workforce and dependant industries. cl

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