Reducing diesel emissions in mining utilizes engineering, technology and best practice to obtain less toxic by-products from reactions that result in different types of diesel emissions. One good example is the use of diesel exhaust fluid. To put its function into perspective, high temperature of most diesel combustion causes the nitrogen to react with residual oxygen to create various oxides of nitrogen. In the atmosphere the NOx molecules react as free radicals that further react to result in smog. Diesel Exhaust Fluid reacts with and neutralizes the NOx in the exhaust, so it does not pollute the atmosphere. Our previous article, touched on the origins and chemistry of diesel emissions in mining. The in-depth analysis of the different type of emissions and facts to answer the question of whether diesel causes cancer were addressed. In this follow up article, the focus is related to evaluating methods used to reduce diesel emissions in mining. We ask a couple of questions in our synopsis of the article. The questions are as follows:
- Why is it important to reduce diesel emissions?
- What in diesel emissions is a cause for concern?
- How do you reduce diesel emissions?
The article wraps up with a brief section evaluating the reduction of diesel emissions in a typical case of workplace safety and health (WSH) in underground mines.
What in diesel emissions is a cause for concern?
The biggest emission problems with diesel engines are NOx and particulates (smoke). Carbon monoxide (CO) levels are typically less than on petrol engines as diesel engines work with excess air at all load levels so less potential for half burned fuel which is normally the cause for CO emissions. NOx is higher on diesel engines as its formation is enhanced by high pressures and high temperatures both of which are higher compared to petrol engines. Particulates are partially burned fuel particles. As diesel fuel is relatively slow burning with high viscosity, it is difficult to atomize it sufficiently for all fuel molecules to get into contact with oxygen and burn completely. Diesel is a very ‘dirty’ fuel in terms of the pollution it causes. It has more energy per pound of gasoline and generates less carbon dioxide BUT it generates more particulates (soot), NOx and other bad stuff. The engineering aspects of diesel engines ties in with the physical and chemical properties of diesel as an aerosol. The parent crude used for refining into diesel and lubricating oil used in diesel engines contributes to the type of diesel emissions. The primary constituents of concern are elemental carbon, traces of metallic compounds, sulfates, nitrates, ash, and hundreds of different free or particle-bound organic compounds of varying volatility. It also includes adsorbed organic materials including aromatic hydrocarbons, polycyclic aromatic hydrocarbons, aldehydes, and nitrogen oxides. Diesel particles in their various forms tend to be very small, hence they are highly respirable and can penetrate deep into the lungs and so cause temporary exposure related symptoms, chronic respiratory effects, and lung cancer.
How do you reduce diesel emissions?
Are environmental regulations, health and safety concerns or potential profit loss a concern right now?
In answering, the question on how you reduce diesel emissions, the article focuses on four methods namely:
- Exhaust gas re-circulation (EGR)
- Catalytic converters
- Diesel particulate filter (DPF)
- Selective catalytic reduction (SCR)
Exhaust gas recirculation involves diversion of some part exhaust hot gases into the engine cylinder via EGR cooler. The cooling process of high combustion temperature gases happens by adding inert gas to the charge. This process is carried out, to reduce peak temperatures inside engine cylinder. Peak temperatures contribute to production of nitrogen oxide compounds which are harmful to the environment. Catalytic converters use catalysts such as palladium or rhodium to reduce carbon monoxide and hydrocarbons from exhaust gas to carbon dioxide and water. This reduction helps to reduce pollution to some extent. The DPF separates heavy soot particles from exhaust, which causes respiratory problems to humans and animals. This process helps in removing soot particulate which are produced during combustion. SCR is utilized to separate nitrogen oxides. In this process, a urea solution is injected into exhaust system and it is converted into nitrogen dioxide and nitrogen. The conversion through the reaction between urea and nitrogen oxides results in the benign compounds. Urea on its own does nothing for performance, but it allows the engine to have a higher performance by mopping up the nitrogen oxides.
Reducing diesel emissions – A case for WSH in underground mines
The increasing use of diesel-powered equipment in confined spaces of underground mines has the potential to overexpose underground miners to the risk and hazard of diesel particulate matter. Miners in underground mines can be exposed to diesel particulate matter far more than workers in other industries. Short term or acute exposure to diesel emissions induces negative health effects such as acute irritation, asthma, cough, and light headaches. Long-term exposure to high concentrations of diesel particulate matter causes lung cancer. In 2012, based on sufficient evidence of animal and epidemiological studies, the International Agency for Research on Cancer (IARC) classified diesel particulate matter as a Group 1 carcinogen to humans. The strong argument for reducing diesel emissions in workplaces such as mines is a matter of life or death. Cancer is lethal and exposure to diesel emissions results in development of cancer. GRT builds a strong case for Workplace Safety and Health (WSH) with suggestions of everyday approaches which are in synergy with embracing technological advancement. Changing the existing technology of the vehicles to higher levels offers better ways to control emissions. Fuel injection can be made electronic which allows for better combustion compared to mechanically operated injection systems. This reduces exposure of underground mine workers to harmful gases. GRT encourages continuously servicing of vehicles for better health and efficiency, the more efficient a vehicle is, the less emission it will cause. Servicing includes changing oil, air filters, fuel filters and lube oil filters. From crude oil to application matters in the context of chemistry of diesel. The chemical fingerprint of the parent crude oil is reflected in the quality of diesel. Therefore, stringent legislation from government should be complemented with use of technology and best practice for the good of mine workers.
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REFERENCES
Smagala et al. 2012. Hydrocarbon Renewable and Synthetic Diesel Fuel Blendstocks: Composition and Properties. Energy & Fuels. Yoo et al. 2013. Optimization of Diesel Combustion System for Reducing PM to Meet Tier4-Final Emission Regulation without Diesel Particulate Filter. SAE International.
