FEATURE ENERGY MANAGEMENT THE MCPD AND STANDING BY THE DIESEL GENERATOR


The new Medium Combustion Plant Directive (MCPD) has had a far-reaching impact on new and existing combustion plant operations. With diesel-fueled generators often being vital to many plants’ on-site power generation, Jason Harryman, sales and business development manager, Electric Power-Diesel for Finning (UK and Ireland), explains how new innovations can still ensure standby diesel engine technology remains a sound investment


I


ntroduced in December 2018, the MCPD aims to reduce levels of harmful


particulates, nitrogen oxides (NOx) and sulphur dioxide (SO2


) present in exhaust


gases from combustion plants rated between 1MW and 50MW thermal input. Though existing plants under 1MW have until 1 January 2024 to become compliant (or 1 January 2029 for those from 1MW to 5MW) operators should consider their next steps now. Faced with the MCPD, plant operators


have a choice to upgrade or replace their installation. If the installation is already performing reliably and efficiently, and especially considering the long life of existing plant equipment, upgrading may be a more attractive option.


REDUCING NOX LEVELS Operators should first consider their diesel generator’s application and operating hours. Standby Generators are exempt under 50 hours of operation. Certain compliant equipment, which may include generators, are MCPD- exempt if they operate for under 500 hours per year when measured as a three-year rolling average for new plants, and a five-year rolling average for existing plants. For power generation equipment up to


50MWth for thermal and 17MWe for electric output, the regulations set strict NOx limits ranging between 190- 205 mg of NOx per Nm3


. This limits,


but does not exclude, diesel’s potential as a 24/7 power source when running in an emergency. Reducing NOx emissions for


conventional four-stroke engines to the levels required for continuous operation may not be feasible. Yet, because diesel generators are mainly used on a standby basis, they will fall under the threshold if operated for under 50 hours annually. With a vast estate already installed UK- wide, manufacturers must now identify engineered solutions that reduce NOx emissions without compromising high- power output.


INNOVATIVE COOLING By combining good fuel efficiency with high thermal efficiencies, diesel engines emit low levels of carbon dioxide. However, while high combustion chamber


26 SPRING 2019 | INDUSTRIAL COMPLIANCE


temperature reduces soot production, it also increases nitric oxide (NO) levels. This released NO oxidises rapidly


in the atmosphere, creating NOx. Though cooling combustion chambers lower NOx levels, it also makes soot formation more likely. Technological advances from engine suppliers like Finning and Caterpillar are helping tackle this issue. A good example of this is


Finning’s range of air-to-air aftercooled, or charge-air cooled engines from the Cat 3516 range. By cooling engine air that has passed through the turbocharger before it enters the combustion chamber, this technology can yield optimum power. This is because the decreased air intake temperature allows a denser engine intake charge. Consequently, more air and fuel is combusted per engine cycle, increasing engine output and lowering combustion temperature, while limiting NOx production.


SELECTIVE CATALYTIC REDUCTION (SCR) Operators may also want to consider selective catalytic reduction, which is already well-proven in plant-based applications. SCR reduces harmful NOx emissions by using urea-based diesel exhaust fluid (DEF) and a catalytic converter. Mixing DEF with the hot exhaust gas


present in the exhaust air stream makes this NOx evaporate into ammonia. Upon reaching the SCR catalyst, the ammonia and exhaust gas decomposes into water vapour and nitrogen gas. But while operators may expect these lowered emissions to lead to increased fuel consumption, this is not the case. Indeed, NOx emissions and fuel


consumption are inversely proportional, so rising engine-out NOx lowers the amount of fuel used. As a result, DEF costs are often offset by this decreasing engine fuel demand. Also, unlike other NOx reduction technologies, engines fitted with an SCR system will operate without interruption even in the event of SCR failure, or if the system runs out of DEF.


CHOOSING THE CORRECT DEF A key concern when specifying SCR systems is the quantity of DEF that will be consumed. This depends on many variables, including the engine’s duty cycle, yearly running hours and the DEF’s concentration (32.5 per cent and 40 per cent concentrations of high-purity urea are available). To better identify DEF usage, it is recommended operators work with an SCR specialist. Only pre-mixed DEF solutions from


trusted partners should be used in a SCR system, to guarantee correct urea concentration and purity. The supplier should also be able to demonstrate the DEF has passed ISO 22241-1 standards, ensuring it adheres to correct standards on storage, transportation, handling, testing and quality. Using incorrectly- blended DEF can lead to irreversible damage and even engine failure. In conclusion, manufacturers and


suppliers are making great strides to ensure the stand-by market can ensure continued compliance below the 50 MWth emissions threshold. By using retrofit solutions such as SCR technology, diesel’s future in plant operations continues to look positive.


Finning www.finning.com


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