Mining Contract: Safe and Economical Inerting of Sealed Mine Areas

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Contract #	200-2008-24811c
Start Date	3/31/2008
End Date	5/30/2009
Research Concept	On Site Gas Systems, Inc., was tasked to design and construct an in-mine mobile gas generation plant to extract nitrogen gas from mine air and inject it into sealed mine areas to maintain a safe environment. The extracted gas will then be used to create and maintain a safe environment inside a sealed mine area. The plant is based on a novel design that uses pressure swing adsorption technology to remove nitrogen gas from the mine atmosphere. The plant is capable of producing about 300 scf/min of gas and is sized to fit on a standard shield car for transport in an underground coal mine. After an exhaustive series of laboratory tests, the plant will be field tested at the NIOSH Safety Research Coal Mine where a portion of the mine will be sealed and rendered inert. During the test, movement of the injected gas will be monitored to observe the progress and extent of the inerting process and to test the plant’s ability to maintain safe conditions.
Topic Areas	Explosion Prevention

Contract Status & Impact

This contract is complete. To receive a copy of the final report, send a request to mining@cdc.gov.

The objective of this effort was to build a high-volume, high-purity underground Pressure Swing Adsorption (PSA) nitrogen generator that lets mine operators inert a sealed mine area for as long as needed without the obstacles associated with injecting nitrogen from the ground surface through a borehole. With this new technology, the nitrogen generation system is placed at or near the underground sealed mine area. The on-site plant uses a novel sieve bed construction to accommodate mine heights 4 ft and above. The original contract called for constructing three separate units that would be connected to form the plant; however, the sieve bed design permits the same output capacity in a smaller space.

The system was designed for use in the underground mine environment, considering factors such as minimal power requirements, sturdiness of construction, ease of use, ease of maintenance, reliability, and transportability. The sieve beds are sensitive to excessive moisture in the feedstock gas (mine atmosphere), and therefore a gas drying system was designed and constructed. The drying system will ensure continuous plant operation and will be added as a system component to the plant.

After undergoing a series of exhaustive tests at the On Site Gas Systems facilities, the unit was moved to the NIOSH Safety Research Coal Mine for a series of instrumented inerting tests. During the first test, the system successfully reduced the oxygen concentration in the 62,000-ft three-sealed mine area from 19.6% to 5.4% in 23.3 hrs. (It should be noted that the system reduced the oxygen content below the MSHA standard of 10% in 7 hrs 10 min.) During the first portion of the second test, the system reduced the oxygen concentration to below 7% in about 14 hrs (below the MSHA standard of 10% in 7 hrs 14 min). Next, a series of injection and equilibration periods successfully brought the sealed mine atmosphere from 8 to 7%, then from 7.5 to 7%. These tests showed that the system, under these conditions, was fully capable of rendering and maintaining the sealed mine area inert. The Contractor generated a draft report that summarizes the design, development, and testing of the gas generator.

The contract was modified to include a six-week field test of the system at a mine site. A contract final report was generated that provided details of the field test, an analysis of plant performance, and the results of the inerting work.