Mining Contract: Safe and Economical Inerting of Sealed Mine Areas

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.