HEAT RECOVERY STEAM GENERATOR UNIT(HRSG UNIT)

  Fig. HRSG (HEAT RECOVERY STEAM GENERATOR)

 

PROCESS DESCRIPTION

The Flue gas produced by the Power Generation is sent to the Heat Recovery Steam Generator(HRSG) with the purpose to recover the heat generated by the combustion of the MP Fuel Gas.

In case of insufficient exhaust from gas turbine and to provide an extra steam demand, 

supplementary firing shall supply the required duty. Fresh air firing facilities for cold start up and operation of HRSG without GTG exhaust gas are provided.

LP fuel gasfrom fuel gas unit is used for supplementary firing and fresh air firing. A HRSG Control 

System shall keep constant temperature and pressure of the steam produced by the HRSG. Steam 

flowrate will be controlled as per demand. The same system shall keep constant the level inside 

the steam drum with a level control in cascade with a flow control installed on the inlet BFW(Boiler Feed Water) line.

To maintain the salt concentration levels in the required range, blowdown facilities for the steam 

drum are provided. The continuous and intermittent blowdown are sent respectively to the Captive Power Plant(CPP) Continuous Blowdown Drum and Atmospheric KO Drum.

Fresh Air System:

Fresh air system is provided for operation of the HRSG in FA mode. The FA System consist of 

one forced draft fan with outlet damper isolating the FA system from the turbine exhaust gas.

The Fail position of the FA damper to HRSG is closed, which is provided with seal air to provide 

100% tightness. 

In TEG mode operation the FA damper is closed and the seal air valve is open.

  Burner and Ignition source:

There are two duct burners in the HRSG.

Both burners are fired with fuel gas within the burner turn down ratio. Burner 1 and Burner 2 has 

6 elements each. Burner 1 is located between the GT outlet and the combustion chamber inlet of 

the HRSG. Burner 2 is located between HP Superheater 1 and HP Evaporator 3.

Operating modes and their firing:

1. In Turbine Exhaust Gas mode, only three elements are fired. 

2. In FA mode, all the elements are fired. 

The Ignition gas is branched off from the main gas supply and is provided with the necessary 

equipment for control and safeguarding of the fuel gas supply to the ignition burner.

Instrument Air and Cooling Air System:

Instrument air is essential for the functioning of the burner. To safeguard the system, 3 pressure 

transmitters is provided to monitor the IA supply with 2 out of 3 pressure failure.

For cooling of the ignition burners, flame scanners, burner and boiler view port, ambient air is supplied by two cooling air fans.

The Supply of cooling air shall be available prior to start-up and during the normal functioning of all the operating modes.