Cogeneration systems that improve overall energy utilization by simultaneously generating electricity and heat from a single fuel source have been in the news a lot recently. Distributed generation equipment, a type of cogeneration system, is driven by a gas or diesel engine. Advantages of the gas engine, which is widely used, include high thermal efficiency and secure fuel supply. However, the exhaust is likely to include pollutants such as nitrogen oxides (NOx) because of the high combustion temperature in such engines. To prevent air pollution, it is critical to control the exhaust gases.
NOx removal equipment based on an ammonia injection process is commonly used to reduce NOx emissions. Optimum control of ammonia injection is achieved by NOx measurement, thereby reducing the cost of running such equipment. The highly sensitive and reliable SG700 stack gas analyzer is most suitable for the continuous measurement of NOx concentrations.

NOx in gas engine exhaust can be reduced by decomposition with a catalyst or the use of a reducing agent such as ammonia. Since solid catalysts have a short life, a more stable wet denitration process using liquid ammonia is generally employed. By mixing exhaust gases with ammonia, NOx is converted to harmless nitrogen and water. The reaction is expressed as follows:
           NOx + NH3 + (catalyst) --> N2 + H2O
The running cost of a liquid ammonia process is high, necessitating NOx measurements before and after the operation of NOx removal equipment to control the amount of ammonia that is injected.

Process Conditions

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