Supplier of fliteration and safety equipment for the mining industry John Ratcliffe GM Andre Robberts says that diesel particulate matter (DPM) has been classified as carcinogenic to humans by the International Agency for Research on Cancer and the World Health Organisation, noting that the John Ratcliffe filter system can mitigate this risk.

He tells Mining Weekly that, although the technology for reducing DPM has existed for years, using it generally creates more downtime on machinery because of the eight-hour cleaning cycles or the regeneration of the filters that the machines require.

“DPM filters are typically made from a cordierite substance. Although new developments with regard to additives and diesel oxidation catalysts have extended these cleaning cycles to 1 000 hours, the ceramic filters still need to be cleaned in a special oven and subsequently an ash extractor after three to four cleaning cycles,” Robberts explains.

He notes that these procedures limit the life span of the filter to between three and four extraction cycles, adding that the John Ratcliffe product consists of a sintered metal filter that does not need to be cleaned as frequently.

The accumulated ash needs to be rinsed out using compressed water only, after which it is ready for use within an hour, and, therefore, can be cleaned as part of the 1 000-hour service intervals.

There are two main types of filter technology – sintered metal filters and cordierite wall-flow filters, Robberts says. Both capture soot, which is then regenerated automatically. This ash must be removed at specific intervals.

He notes that cordierite wall-flow filters are more brittle and crack over time, as the nonregenerated soot needs to be burned off in a specific oven. Accumulated ash then needs to be extracted after three or four oven cycles.

Robberts points out that there are currently no ash-extracting units available in South Africa for wall-flow filters.

“The filters can be shipped to Germany for cleaning. Should anyone consider buying the ash extractor, the breakeven point will be at least 300 filters a year before the cost of importing this unit can be justified.”

The John Ratcliffe diesel particulate filter system reduces DPM by 99% at the exhaust outlet and increases productivity, as more machines can be operated in specific sections. The systems are low maintenance owing to the cleaning method and there is no need for replacement filters,” he states.

Secondary benefits include a reduction in decibels and an increase in engine efficiency owing to the data logging capability of the engine control unit. The logged data can be used to identify inefficiencies in the engine work cycle and then to adjust the engine parameters to negate these inefficiencies

He concludes that using the filters is beneficial because they contribute to a reduction in soot particles and fine particulate matter, with a high ash-holding capacity and low exhaust back pressure.