Vale’s Sudbury operation is leading the way in reducing diesel particulate matter for its light-duty underground vehicles.
With more than 800 diesel-powered pieces of equipment used in its Sudbury mines and more stringent regulations pending, Vale spearheaded the Diesel Emissions Evaluation Program (DEEP), a research consortium of mining companies, government agencies and unions in 2001.
Dr. Jozef Stachulak, manager, strategic ventilation, Canadian Operations, Vale Ltd., has been working in concert with the DEEP consortium and other international players for more than 10 years to reduce diesel particulate matter (DPM), a byproduct of diesel-powered equipment.
Diesel exhaust contains hundreds of organic and inorganic compounds emitted either as gases or as particles. Controlling these emissions at the source of generation is necessary for a healthy work environment and more cost effective than increasing fresh air ventilation to reduce contaminant concentrations.
In Ontario, it is anticipated that the guidelines for current exposure limits for DPM will decrease from 1.5 milligrams per cubic metre (mg/m3) of respirable combustible dust to 0.4 mg/m3 of total carbon.
“The exposure level at our mines is less than 0.4 milligrams per cubic metre,” Stachulak said.
It was no simple task to come up with a diesel particulate filter (DPF) system that would significantly reduce diesel soot, he added. “The work performed in DEEP was fundamental. It paved the way to do more research to seek out and evaluate innovative systems that would not require human intervention, because that was an important objective.”
The DEEP project evaluated nine DPF systems on five heavy-duty and two light-duty underground mining vehicles over a period of four years at Vale’s Stobie Mine. From that work, it was determined that the filter systems must regenerate on their own and eliminate human intervention.
“The main challenge was that the previous nine systems required extensive human intervention,” Stachulak said, explaining that when the DPM is captured, it must be burned off. Otherwise, it creates back pressure on the engine, hindering performance. One option was to remove the filter and clean it every shift.
“That was not sustainable,” Stachulak said. “It is like driving with a tire that is flat.”
It was determined that to operate in an efficient manner, an automatic filter regeneration system was necessary. The German-made MANN+HUMMEL SMF®-AR diesel particulate filter system was placed on two light-duty vehicles in Vale’s Creighton Mine for about 1,600 hours. The system has proven successful in filter regeneration, longevity and reliability.
This DPF system uses a sintered metal filter element, a base metal, fuel-borne catalyst with an on-board dosing system, an electric heater that uses on-board power and a sensor-based control unit. Software in the control unit adjusts fuel dosing rates and heater timing to ensure filter regeneration for different engines and operating scenarios.
Stachulak described it as an active system.
“During the process of regeneration, the diesel particulate is trapped in the sinter metal filter until a specific volume of soot or DPM is deposited on the filter,” he said. “Then the DPM is oxidized. The oxidation is made through heat radiated from the heating elements without physical contact. Even under extreme conditions, the fully-automatic oxidation of the layer of DPMs can take place in a heating period of just two minutes. During the process, the machine continues its operation.”
The filter system was tested on a locomotive with a 60 kilowatt Deutz engine and a forklift with a 33 kW Kubota engine. The tests on the locomotive showed the heater was activated, which helped burn off the soot and keep the back pressure under control. The system actively regenerated. The forklift’s cleaner engine produced less soot. Higher exhaust temperatures allowed the fuel additive in the catalyst to frequently auto-ignite the soot and burn it off. This was described as passive regeneration.
The benefit of the SMF®-AR DPF system was that it eliminates human intervention, has a compact design, is robust and has long-service intervals of between 500 and 800 hours. The costs and longevity of the filter have yet to be determined because the product is still in the testing phase.
“We want to do a little more testing on fuel additives,” Stachulak said, adding he is confident this filter system will work well for Vale’s light-duty diesel equipment, which accounts for about 60 per cent of its diesel-powered fleet.
The SMF®-AR DPF system works on diesel engines of up to 130 kilowatts. Currently, MANN + HUMMEL are working on designing filter elements that can work efficiently with larger engines used in heavy-duty vehicles, which will be Vale’s next challenge.
In the meantime, Stachulak will finalize the report and continue to foster established local and international connections to find future solutions for larger diesel engines.