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Diesel locomotive engines are a major contributor to air pollution. The culprits are NOx SO2. Both are readily produced by diesel locomotives and both cause an array of health and environmental problems. Nitrogen dioxide (NO2), a type of NOx is particularly worrisome as it is 240 times more destructive to the ozone layer than carbon dioxide, making it a primary contributor to climate change. Likewise, urban smog and acid rain, the latter of which wreaks havoc on fragile ecosystems.
To solve this inherent inefficiency in diesel locomotives, the EU-funded ENSPIRIT project aimed to create an innovative emissions abatement system. The objective was to build a system capable of reducing pollution levels and meeting stringent global regulations, some of which require the levels of sulphur in locomotive fuel to be decreased by 99 %.
Standards in the EU and the US are based on the application of high-efficiency catalytic after-treatment technology for diesel engines manufactured in 2015 and later. However, the ENSPIRIT solution took this one step further so that not only can new locomotives meet these emission regulations, but, thanks to remanufacturing, old locomotives can too.
A new approach to an old problem
Although selective catalytic reduction (SCR) is a well-established after-treatment technology, it falls short in its ability to effectively convert nitric oxide at ambient temperatures and low concentrations. For example, SCR requires high reaction temperatures, which sometimes means the flue gas must be reheated, the reactor must be large in volume, and reductant ammonia must be available.
“As nitrogen pentoxide (N2O5) is easily removed by water, oxidation of NO and NO2 to N2O5 at a low temperature is a promising way of removing NO in flue gas,” says project participant Howard Davis. “This is exactly what the ENSPIRIT solution does.”
To accomplish this, started with a two-step approach. First, it looked to develop an advanced oxidative reactor device using controlled Ozone mixing that enables nitric oxide to be converted into NO2 and, later, to N2O5 at ambient temperature. “At the same time this happens, the system also uses extremely fine water sprays in the special reactor in order to capture particle matters that are then removed downstream,” says Davis.
Change in plans
Originally, the ENSPIRIT emission abatement system was to be located in a tender behind the locomotive(s), with one system capable of eliminating emissions from at least two locomotives working in tandem. However, subsequent research indicates the system is more readily applicable to railway sidings, depots and stations as a mechanism for treating trains not currently in use. Market research on this matter continues.
“Regardless of how it is used, ultimately the ENSPIRIT device will be integrated into a system of combined devices for the removal of heat, moisture, sulphur oxides, ultrafine particulate matter and nitrogen oxides,” explains Davis. “This will provide a complete, cost-effective and energy-efficient way of making new and older diesel trains more efficient.”