Diesel emission control for underground vehicles

NON-THERMAL plasma may offer a practical method of managing emissions in mining vehicles in the not too distant future.

Staff Reporter

Writing in a company newsletter, Phil Berriman, managing director of specialist vehicle manufacturer PJ Berriman, said recent research suggests it is the smoke we cannot see – nano-particles - that present a significant risk.

“If this is confirmed to be the case, then most of the current exhaust filter technology may be proven to be less than effective,” Berriman said.

While the negative impact of NO, NO2, C0 and C02 on the human anatomy is understood, there are many opinions regarding setting appropriate workplace exposure standards for PAH’s (polyaromatic hydrocarbons or polycyclic hydrocarbons), EC (elemental carbon), HCHO’s (aldehydes) and DPM (diesel particulate matter).

The use of NTD (non-thermal plasma) exhaust after-treatment offers exciting prospects for the reduction of harmful materials, including DPM, in exhaust gas streams.

The method works in this way: a magnetron (corona discharge device, CDD) is inserted before the catalytic converter producing an excited electron stream which promotes a number of oxidisation reactions. NO is oxidised to NO2 which is then further treated in the catalytic converter to non-harmful gasses. In addition, the NTP generated NO2 enables continuous regeneration of particulate filters.

“Test reports indicate that the NTP system provides a 55% reduction in NOX emissions without any increase in hydrocarbons and very significant reduction in particulate emissions,” Berriman said in the newsletter.

“The system greatly increases the sulphur tolerance of stoichiometric, three-way catalytic converters and has been demonstrated to reverse the poisoning of converters which had been operated long term (10,000hrs) on fuels of 300ppm sulphur. Converter ‘light-off’ temperatures are greatly reduced, countering the effects of sulphur and phosphorus in fuel and oil.”

The technology is currently under development and will be available to the mining industry within the next few years. Berriman pointed out that there would be problems, however, in meeting high voltage requirements. Accurate and repeatable field measurements remain problematic and the most accurate instrument is presently expensive and cumbersome.

Despite these drawbacks, Berriman said the combination of an NTP system, three-way catalytic converter, water-based conditioner (latent/vaporising) and post filtration offers the current "world’s best practice" in managing diesel exhaust emissions.

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