HRSG exhaust gas flow in combined cycle power plant

The Heat Recovery Steam Generator (HRSG) is designed to operate at the range of gas turbine exhaust conditions and constructed of gas tight components such as the exhaust gas inlet ducting, the casing and the exhaust gas stack. The system also includes dedicated measurement instruments for performance monitoring purposes. The gas turbine exhaust gas flows through the inlet ducting and the HRSG before being guided to atmosphere, via the exhaust gas stack. In this specific design, the HRSG key element heating surfaces installed in the following order, in the direction of the exhaust flow: HP Superheater 2, Reheater, HP Superheater 1, HP Economizer 3, HP Evaporator, IP Superheater, LP Superheater, HP Economizer 2, IP Evaporator, HP Economizer 1, LP Evaporator, Condensate Preheater.

Where the emission requirements are stringent, an SCR or CO catalyst system is located in the exhaust temperature section of the HRSG. The purpose of the SCR system is to convert the oxides of nitrogen (NOx) produced by the combustion turbine and the burner system to nitrogen and water vapor. The system consists of an ammonia supply unit, distribution manifold, injection grid, and catalyst bed to create an SCR reactor section.

Duct burners are used to burn natural gas or oil in the gas turbine exhaust stream to increase the gas temperature and thus increase the steam output, in case the energy available in the gas turbine exhaust is not sufficient to meet system demands. The duct burner heats the exhaust gas to up to 800˚C. Duct burner systems consists of duct burner elements, the pilot and pilot fuel supply with igniters, and the main fuel supply which includes scanners, fuel gas metering, a cooling air system and a burner measurement and control system.

The OPTIFLEX 2200 guided radar is a reliable and maintenance free TDR level meter suitable for the measurement and control of ammonia levels in the ammonia storage tank. OPTIMASS 6400 is a sophisticated Coriolis mass flow meter to monitor the dosing of the gaseous ammonia to the AIG. Furthermore the density information from the OPTIMASS can be used to monitor the flawless operation of the ammonia evaporation process. The OPTISONIC 7300 ultrasonic gas flowmeter can cope with intermittent operation and transient flow changes of the fuel gas flow to the duct burners. KROHNE offers sophisticated instruments and solutions from single flowmeters up to flow computers and complete fuel gas skids.