Feature sponsored by Test & measurement
ABB OXYGEN ANALYSERS HELP KEEP SEAS GREEN BY OPTIMISING MARINE DIESEL ENGINES
T
he world’s largest producer of marine diesel engines has adopted the highly accurate ABB AZ10 Zirconia combustion oxygen analyser to help its engines meet the latest strict
marine emissions standard.
The diesel engine manufacturer used comparative tests and found that the ABB AZ10 was more accurate, required less calibration and was easier to maintain than alternatives from other vendors. The International Maritime Organization (IMO) has gradually introduced stricter emissions levels for Sulphur Oxide (SOx) and Nitrogen Oxide (NOx). In the latest Tier III standard, which applies to ships with keels laid from 1 January 2016, marine engines must emit pollutants at levels no greater than 3.4g/kWhr. It has become imperative for marine diesel engine manufacturers to ensure their engines meet the strict emissions limits.
These limits currently apply to the North American Emission Controlled Area (ECA) and were introduced in the North and Baltic Seas for vessels with keels laid from 1 January 2021. Companies selling marine 2-stroke are working to ensure customers can easily and efficiently meet the latest standards. In order to meet the stricter emissions limits, the company selling marine diesel engines needed to ensure the efficiency of the Exhaust Gas Reduction (EGR) system used by its two-stroke engines. This takes a proportion of the exhaust and mixes it with
carbon dioxide (CO2), feeding it back to the air inlet. With a higher heat capacity than oxygen (O2), the CO2 reduces the peak
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engine temperature, leading to a reduction in the formation of NOx.
In a series of experiments, the marine diesel engine manufacturer found that mixing the exhaust air with the inlet air to give an oxygen inlet percentage of 16 to 17 per cent, rather than natural air’s 21 per cent, reduced NOx production by 85 per cent. A portion of exhaust gas with around two to three per
cent O2 is passed through the scrubber and cleaned, then recirculated back into the EGR. Both inlets are turbocharged and mixed to arrive at the optimum level of 16
per cent O2 at the EGR receiver. For maximum emissions reduction, the key to managing this oxygen intake is highly
February 2023 Instrumentation Monthly
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