System and method for operating heat recovery steam generators

Abstract

A system includes a heat recovery steam generator (HRSG), a waste heat exchanger coupled to the HRSG and configured to transfer heat from the HRSG to a purge stream to generate a heated purge stream, and a heated purge stream path configured to transfer the heated purge stream from the waste heat exchanger to an inlet of the HRSG.

1 . A system, comprising:
 a heat recovery steam generator (HRSG);   a waste heat exchanger coupled to the HRSG and configured to transfer heat from the HRSG to a purge stream to generate a heated purge stream; and   a heated purge stream path configured to transfer the heated purge stream from the waste heat exchanger to an inlet of the HRSG.   
     
     
         2 . The system of  claim 1 , wherein the waste heat exchanger is disposed downstream of a low-pressure section of the HRSG. 
     
     
         3 . The system of  claim 1 , wherein the waste heat exchanger is disposed in an exhaust stack of the HRSG. 
     
     
         4 . The system of  claim 1 , wherein the heated purge stream path is configured to transfer the heated purge stream from the waste heat exchanger to a gas turbine engine coupled to the inlet of the HRSG. 
     
     
         5 . The system of  claim 1 , comprising a first damper disposed in the inlet of the HRSG and a second damper disposed in the inlet of the HRSG, wherein the first damper is configured to control a first flow rate of the heated purge stream and the second damper is configured to block the HRSG from a gas turbine engine. 
     
     
         6 . The system of  claim 1 , comprising a gas turbine engine coupled to the inlet of the HRSG and configured to transfer the heated purge stream through the HRSG. 
     
     
         7 . The system of  claim 1 , comprising an induced draft fan disposed downstream of a low-pressure section of the HRSG and configured to pull the heated purge stream through the HRSG. 
     
     
         8 . The system of  claim 7 , comprising a damper disposed upstream of the induced draft fan and configured to block the induced draft fan from the HRSG. 
     
     
         9 . The system of  claim 7 , comprising an induced draft stack disposed downstream of the induced draft fan, wherein the waste heat exchanger is disposed in the induced draft stack. 
     
     
         10 . The system of  claim 9 , wherein the induced draft stack is coupled to an exhaust stack of the HRSG. 
     
     
         11 . The system of  claim 1 , wherein the waste heat exchanger is configured to be reversibly coupled to the HRSG, wherein the waste heat exchanger is reversibly inserted into the HRSG to generate the heated purge stream and the waste heat exchanger is reversibly removed from the HRSG during normal operation of the HRSG. 
     
     
         12 . A system, comprising:
 a heat recovery steam generator (HRSG);   a blower coupled to the HRSG and configured to transfer a purge stream to a waste heat exchanger disposed in the HRSG, wherein the waste heat exchanger is configured to transfer heat from the HRSG to the purge stream to generate a heated purge stream;   a heated purge stream path configured to transfer the heated purge stream from the waste heat exchanger to an inlet of the HRSG; and   a controller configured to adjust a flow rate of the heated purge stream in response to feedback from a sensor disposed in the HRSG.   
     
     
         13 . The system of  claim 12 , wherein the sensor is configured to sense at least one of a combustible gas, a product of combustion, an exhaust gas, oxygen, or a temperature, or a combination thereof 
     
     
         14 . The system of  claim 12 , wherein the heated purge stream path is configured to mix the heated purge stream with the purge stream. 
     
     
         15 . The system of  claim 12 , wherein the blower is configured to transfer ambient air as the purge stream to the waste heat exchanger. 
     
     
         16 . The system of  claim 12 , wherein the controller is configured to adjust the flow rate of the heated purge stream such that a temperature of the heated purge stream downstream of a low-pressure section of the HRSG is greater than a steam condensation temperature. 
     
     
         17 . A method, comprising:
 flowing a purge stream through a waste heat exchanger coupled to a heat recovery steam generator (HRSG);   transferring heat from the HRSG to the purge stream in the waste heat exchanger to generate a heated purge stream;   flowing the heated purge stream to an inlet of the HRSG via a heated purge stream flow path; and   purging the HRSG with the heated purge stream.   
     
     
         18 . The method of  claim 17 , comprising flowing the heated purge stream to a gas turbine engine coupled to the inlet of the HRSG. 
     
     
         19 . The method of  claim 17 , wherein purging the HRSG with the heated purge stream comprises pulling the heated purge stream through the HRSG using an induced draft fan. 
     
     
         20 . The method of  claim 17 , comprising mixing the heated purge stream with the purge stream using the heated purge stream flow path.