Ammonia control system for NOx emission control for gas turbine exhaust

摘要

A steam and gas turbine combined cycle plant STAG* employs a catalyst in a heat recovery steam generator to react injected ammonia with NOx from the combustor of the gas turbine to reduce atmospheric emission of NOx from the system. Rapid control of ammonia injection is achieved using a prediction of the NOx being generated in dependence upon the operating conditions of the combustor. A trimming signal from a measurement of NOx being emitted from the heat recovery steam generator downstream of the catalyst is employed to complete the NOx control loop. Compensation is provided to relate the measured NOx downstream of the catalyst with the NOx in the output of the gas turbine taking into account the catalyst efficiency.