The MSHA rules, passed in 1996, outlined requirements to maintain worker health and safety in underground coal mines where diesel equipment is used.
These requirements included a weekly carbon monoxide check from the exhausts of equipment to ensure CO concentrations do not exceed 2500 parts per million to maintain safe and steady breathing environments for all workers.
After primary testing at one of its four western US operations (three in Utah, one in Colorado) showed high levels of CO, AWBG opted to use the federal laws as the basis of its own progressive Emission Based Maintenance Program (EBMP).
A series of weekly tests at the AWBG mines found fleet median readouts to be 1597ppm of CO and 997ppm for nitrogen oxide (NOX).
AWBG used these results as a baseline for improvement, the first step in the development of EBMP in consultation with the Underground Coal Diesel Partnership.
The results gathered from the weekly tests showed AWBG’s fleets were 5 to 10 times higher than certification levels for the tested engines. Determining that fuel rates for engines were set by the OEM, the company dedicated its efforts in its EBMP development to keep emissions values lower than OEM specifications.
The next step in the EBMP process was more complex, as the group’s technicians worked through their own testing program to reach the CO levels that matched the certified levels for each engine, a process that ultimately came down to trial and error.
After a few dozen tests to determine settings, CO levels dropped 90% and NOX 50% - or a mean reading of 160ppm CO and 447ppm NOX.
A give-and-take scenario resulted, according to AWBG’s Steve Forbush. “Achieving improved emissions did not come without a compromise in diesel powered unit performance - reduced fuel rates decreased the power.
“The power loss was not equal to the reduction in fuel, but the loss meant that most of the vehicles were underpowered,” he said.
With this in mind AWBG hired a consultant to find a solution. The two decided to change the torque converter ratios, which allowed the engine’s drive trains to use the power more optimally. “This change had a very positive effect on the overall performance of the vehicles,” said Forbush.
Long term, Arch has opted for predictive maintenance to ensure emission levels are kept below MSHA regulations. The group’s new baseline values for emissions is now used to determine when machines need to be pulled offline for maintenance.
According to Forbush, a simple equation is used to determine those in need of service.
Approximately 95% of affected machines are repaired onsite, while the balance are taken for shop repairs.
“When weekly test results (required by MSHA) indicate a unit’s emissions exceed baseline by 20%, [we] remove the unit from service.”
Fuel systems, combustion cylinders, heads and valves, and drive train issues can all benefit from predictive maintenance under the program.
AWBG has achieved cost savings from the project through greater fuel efficiency, lower maintenance and repair costs, and a longer life span for engines’ exhaust filters.
Forbush noted that one vital item is needed for the program to succeed: cooperation. “A successful EBMP requires full support from every manager within an organisation.
“Implementing such a program to meet mandated regulations would not seem at first to provide benefits. [Our] experience proved that other benefits accrued to the organisation from its efforts to meet the mandated regulations.”
Article based on a paper submitted to the 11th U.S. / North American Mine Ventilation Symposium by Arch Western Bituminous Group’s Steve Forbush.
