Guidelines published late last year by Brian Davies, Victoria University of Technology, and Alan Rogers, Alan Rogers OH&S, for the Australian Institute of Occupational Hygienists explored the technologies available to the underground coal industry to control diesel particulate.
The duo noted it was important to be aware no single simple solution existed for the control of diesel particulate and in many cases combinations of technologies may be required.
Fuel quality has been extensively investigated with the introduction of low sulphur fuel. Low emission fuel use in the mining industry has reduced particulate levels, mainly eliminating eye and upper respiratory tract irritation. Davies and Rogers said much has been made of the benefits of biofuels in reducing diesel emissions. However, trials in underground mines have found employee acceptance of such products were low, due to strong odours. Higher costs has also caused a barrier for widespread acceptance, but future government incentives may reduce this gap.
Ventilation has been a major factor in controlling gaseous emissions underground. Davies and Rogers said ventilation tended to control gaseous emissions rather than particulate and that it was better to focus on the control of diesel particulate at the source of emission rather than rely on controls that are implemented post generation.
Post engine exhaust treatment devices have been subject to substantial research and development over the past 40 years, with the forerunner as the catalytic converter. Davies and Rogers said data suggested catalytic converters were effective in reducing particulates, however extensive research has demonstrated reductions to be from the removal of organic carbon with the level of elemental carbon remaining unchanged, thus giving a false impression of improvement in diesel particulate.
The reduction in particulate using water baths has been confirmed for equipment used in New South Wales coal mines. The Davies / Roger paper said water baths were a NSW statutory requirement and it could be concluded all vehicle fitted with such devices were achieving a 20% to 30% defacto reduction in particulates from that present in the raw exhaust.
An array of disposable exhaust filters have been released onto the market, and have the ability to significantly reduce particulate. Recent research by Davies has demonstrated disposable filters can reduce elemental carbon levels in the raw exhaust of diesel engines by approximately 85%. Recent improvements in filter life by reducing the number of pleats and keeping pleats separated to increase surface area has also improved the effectiveness of disposable filters.
Davies and Rogers suggest two of the greatest possibilities for reducing particulate are engine design and engine maintenance. Design can control fuel-air supply and efficient combustion while maintenance ensures optimal fuel air mix for optimal combustion and power conditions.
A recent study within the New South Wales coal mining industry by Brian Davies where the raw exhaust of 66 diesel engines was monitored for elemental carbon found only seven engines with elevated concentrations. The offending engines were found to have worn injectors or blocked water baths.
In order to ensure correct engine maintenance, MSHA have recommended the following are checked to minimise diesel particulate generation:
Clogged air filters and leaks in the air intake system.
Correct fuel injection rate.
Correct fuel injection timing.
Correct operation of all fuel injection system components (fuel filters, water separators, fuel pumps and fuel injectors).
Correct operation of electronic engine controls.
High oil consumption
Increased carbon monoxide emissions.
Clogged disposable diesel exhaust filters.
