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To allow a large gas fired combined cycle power plant to restart very quickly ( to 100% MCR load in 15 minutes) , it is proposed to add to the plant a 15% MCR capacity "pony" CTG
About
In order to allow very fast restarts of a large gas fired combined cycle power plant CCPP, it is neccesary to maintain the steam turbine operating in spinning reserve service , and it is also neccesary to maintain the HRSG thick wall parts hot and to maintain vaccuum in the ACC continously. This can be accomplished by adding a 15% MCR capacity small CTG ( pony gas turbine) and a small HRSG sized to provide 14% MCR hot reheat steam flow at 14% design RH pressure tot he IP steam turbine's intercept valve during spinning reserve operations. This configuration will allow the large CCPP to automatically increase load to 100% MCR load witihin 15 minutes of recieving demand signal from the ISO system dispatcher. This operating capability is required in locations where there is large wind turbine input to the electrical system , such as in Texas ERCOT region, in the event the wind turbine farms unexpectedly shutdown due to overspeed conditions. The CCPP should be configured as a single reheat steam cycle with a 100% capacity steam to reheat bypass system, and the steam turbine would operate during spinning reserve operations with the HP turbine bypasses and maintained hot using a reverse flow valves and a ventilation valve to the ACC.IN this mode the steam turbine will produce about 8% MCR electrical output during spinning reserve operations and the requried hot reheat flow is about 10% MCR flow to avoid LP steam turbine L-1 blade vibrations.
Key Benefits
A large CCPP can quickly restart within 15 minutes to 100% capacity to respond to sudden increases in system electrical demand, as might occur during shutdown of large wind farms due to wind overspeed scenarios. The small pony CTG will also provide the plant with "black start" capabilities. The continuous overnight power output during spinning reserve operations will be about 8% MCR steam turione output ( or about 3 % MCR plant output). The spinning reserve speed operation of the steam turbine provides system VARS stability .
Applications
This upgrade can be applied to existing large gas fired combined cycle power plants in areas that will be using a large amount of electical power supplied by large wind farms, such as texas ERCOT. In such areas, system black outs might occur due to sudden unexpected loss of wind turbine farm output due to their requirement to shut down if wind speed exceeds 55 mph. The spining reserve opration of the stem turbione also improves system VARS stability in areas that use a large amount of distributed renewable energy.