This is a combined cycle with brayton cycle on top and steam

This is a combined cycle with brayton cycle on top and steam cycle on the bottom, with an open feed water incorporate to the steam cycle.

why do we used pump1 and 2? and does this follow under single, double or triple pressure HRSG( heat recovery steam generator) between points d and e? and why?

Solution

Function of Pump P1:
Some part of the feed water from the low-pressure zone is transferred to the high-pressure economizer by a booster pump. This economizer heats up the water to its saturation temperature. This saturated water goes through the high-temperature zone of the boiler and is supplied to the high-pressure turbine.

Function of Pump P2:

It is used to transfer the low pressure feed water through heat exchanger back to turbine.

The combined-cycle system includes single-shaft and multi-shaft configurations. The single-shaft system consists of one gas turbine, one steam turbine, one generator and one Heat Recovery Steam Generator (HRSG), with the gas turbine and steam turbine coupled to the single generator in a tandem arrangement on a single shaft. Key advantages of the single-shaft arrangement are operating simplicity, smaller footprint, and lower startup cost. Single-shaft arrangements, however, will tend to have less flexibility and equivalent reliability than multi-shaft blocks. Additional operational flexibility is provided with a steam turbine which can be disconnected, using a synchro-self-shifting (SSS) Clutch,for start up or for simple cycle operation of the gas turbine.

Multi-shaft systems have one or more gas turbine-generators and HRSGs that supply steam through a common header to a separate single steam turbine-generator. In terms of overall investment a multi-shaft system is about 5% higher in costs.