Air cooling system and method for a heat recovery steam generator inlet

Abstract

The air cooling system and method for a heat recovery steam generator (HRSG) inlet provides a combined cycle power plant utilizing a powerful fan coupled to ductwork connected to pipes that enter the HRSG inlet duct coupled to an exhaust duct of a Combustion Turbine (CT) for lowering the temperature of the CT exhaust gas provided to the heat recovery steam generator by the CT. The cool air injection system is utilized during low load operation or startup of the CT to ensure that spray water from an inter-stage desuperheater in an HRSG is fully evaporated prior to entering the downstream superheater or reheater. A feedback system includes temperature elements measuring the mix temperature that regulates the cooling air injection rate into the HRSG inlet.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates generally to cooling systems for steam generators used in power plants and the like, and particularly to an air cooling system and method for a heat recovery steam generator inlet that provides temperature reduction control for a heat recovery steam generator (HRSG) air inlet to mitigate overspray during an inter-stage cooling procedure performed in a desuperheater.[0003]2. Description of the Related Art[0004]Combined cycle and cogeneration are processes that use the exhaust heat discharged from a Combustion Turbine (CT) to provide heat to a boiler, which, in turn, makes steam to power a Steam Turbine (ST). A heat recovery steam generator (HRSG) is a boiler that has an inlet coupled to an exhaust of a CT engine or other heat source and typically includes an inter-stage desuperheater.[0005]Desuperheater overspray is a term used to describe a condition where spray water from an inter-stage de...

AI Technical Summary

Benefits of technology

[0009]The air cooling system and method for a heat recovery steam generator inlet includes a powerful fan coupled to ductwork connected to pipes or ducts that enter the exhaust duct of a Combustion Turbine (CT) for lowering the temperature of the CT exhaust gas provided to the heat recovery steam generator by the CT. The cool air injection system is utilized during low load operation of the CT to ensure that spray water from an inter-stage desuperheater in the HRSG is minimized so that it is not calling for spraying to within 50° F. of saturation prior to entering the downstream superheater or reheater. This eliminates the damaging thermal fatigue cycle in the downstream pressure retaining components of the HRSG.

[0011]The system and method disclosed herein reduce the peak gas temperature, thereby protecting the plant equipment. The system and method has successfully mitigated overspray in a GE 7FA turbine combined cycle system, where unchecked exhaust temperature reaches a peak of 1200° F. at low flow. The system and method are theorized to work with any constant temperature CT or other direct fired heat source.

Problems solved by technology

Many plants spend significant time operating at minimum CT load.

This minimum load operation results in very high exhaust temperatures, which may also cause overspray in the HRSG's desuperheater.

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