Building Blocks of Heat Recovery Steam Generator Systems (HRSG)
Exhaust Gas Sub-System
Each heat recovery steam generators (HRSGs) has three pressure natural circulation units that use the gas turbine exhaust to produce superheated steam for the steam turbines.
Included in the HRSG exhaust gas path are modules consisting of feedwater preheater, economiser, evaporator, superheater and reheater heat transfer elements. These elements have been arranged and sized for effective absorption of the residual heat from the exhaust gas. The exhaust gas passes horizontally through the top supported, vertically hung heat exchanger elements.
HP Steam Sub-System
Each HRSGs has three pressure, natural circulation units that use the gas turbine exhaust to produce superheated steam for the steam turbine.
The high pressure (HP) section contains the economiser, evaporator, and superheater heat transfer elements.
The economiser is designed to heat the inlet feedwater to approach a temperature below the saturation temperature in the steam drum while minimizing the potential for phase change in the economiser tubes during any HRSG operating mode. The feedwater pumps deliver feedwater to the HP economisers.
The evaporator section includes a steam drum. The steam drums are designed to accommodate surges during unit starts and operating transients and to ensure proper steam purity by efficient removal of moisture and dissolved impurities. Evaporator downcomers are configured for natural circulation within the evaporator. The evaporator sections, including the associated steam drum, are designed to generate the specified steam capacity of dry, saturated steam at full load. Each drum is protected from over pressurisation by relief valves.
Saturated steam generated in the steam drum enters the superheater section to increase the energy in the steam prior to final delivery to the steam turbine. Relief valves protect the superheater sections and piping from over pressurisation. The HP superheater is provided with an attemperator for steam temperature control. HP feedwater, from the feedwater system, is supplied for spraywater.
Library Components Used:
- Control Valve (HP feedwater control valve, HP feedwater bypass control valve)
- Non-return Valve (Check valve)
- Control Valve (HP feedwater isolation valve, HP intermittent blowdown valve, Auxiliary steam to HP isolation valve, Auxiliary steam to HP control valve, HP continuous blowdown valve, Drain valves)
- Two Phase Tank (HP steam drum)
- Pressure relief Valve (HP drum pressure relief valve, HP drum pressure relief valve)
- Heat Transfer (HP steam Desuperheater)
- Heat Exchangers (HP superheater, HP economisers, HP evaporators)
- Pipes
IP Steam Sub-System
Each HRSGs has three pressure, natural circulation units that use the gas turbine exhaust to produce superheated steam for the steam turbine
The intermediate pressure (IP) section contains the economiser, evaporator, and superheater heat transfer elements.
The economiser is designed to heat the inlet feedwater to approach a temperature below the saturation temperature in the respective steam drum while minimizing the potential for phase change in the economiser tubes during any HRSG operating mode. The feedwater pumps deliver feedwater to the IP economisers. A side stream of heated IP feedwater discharging from the IP economiser is sent to the fuel gas heat exchanger to heat the fuel gas; this improves the gas turbine performance. The remaining IP feedwater enters the IP drum.
The evaporator section includes a steam drum. The steam drums are designed to accommodate surges during unit starts and operating transients and to ensure proper steam purity by efficient removal of moisture and dissolved impurities. Evaporator downcomers are configured for natural circulation within the evaporator. The evaporator sections, including the associated steam drum, are designed to generate the specified steam capacity of dry, saturated steam at full load. Each drum is protected from over pressurisation by relief valves.
Saturated steam generated in the steam drum enters the superheater section to increase the energy in the steam prior to final delivery to the steam turbine. Relief valves protect the superheater sections and piping from over pressurisation.
Library Components Used:
- Control Valve (IP feedwater control valve, IP feedwater bypass control valve)
- Non-return Valve (Check valve)
- Control Valve (IP feedwater isolation valve, IP intermittent blowdown valve, Auxiliary steam to IP isolation valve, Auxiliary steam to IP control valve, IP continuous blowdown valve, Drain valves)
- Two Phase Tank (IP steam drum)
- Pressure relief Valve (IP drum pressure relief valve, IP drum pressure relief valve)
- Heat Transfer (IP steam Desuperheater)
- Heat Exchangers (IP superheater, IP economisers, IP evaporators)
- Pipes
HP Steam Sub-System
Each HRSGs has three pressure, natural circulation units that use the gas turbine exhaust to produce superheated steam for the steam turbine.
The low pressure (LP) section contains the feedwater preheater, evaporator, and superheater heat transfer elements.
The feedwater preheater is designed to heat the inlet feedwater to approach a temperature below the saturation temperature in the steam drum while minimizing the potential for phase change in the economiser tubes during any HRSG operating mode. Condensate is supplied to the feedwater preheater by the condensate system. To prevent cold end corrosion, the feedwater preheater recirculation pump and control valve operate to maintain feedwater temperature above the exhaust gas dew point temperature.
The evaporator section includes a steam drum. The steam drum is designed to accommodate surges during unit starts and operating transients and to ensure proper steam purity by efficient removal of moisture and dissolved impurities. Evaporator downcomers is configured for natural circulation within the evaporator. The evaporator sections, including the associated steam drum, are designed to generate the specified steam capacity of dry, saturated steam at full load. The steam drum is protected from over pressurisation by relief valves.
Saturated steam generated in the steam drum enters the superheater section to increase the energy in the steam prior to final delivery to the steam turbine. Relief valves protect the superheater sections and piping from over pressurisation.
Library Components Used:
- Control Valve (LP feedwater control valve, LP feedwater bypass control valve)
- Non-return Valve (Check valve)
- Control Valve (LP feedwater isolation valve, LP intermittent blowdown valve, Auxiliary steam to LP isolation valve, Auxiliary steam to LP control valve, LP continuous blowdown valve, Drain valves)
- Two Phase Tank (LP steam drum)
- Pressure relief Valve (LP drum pressure relief valve, IP drum pressure relief valve)
- Heat Transfer (LP steam Desuperheater)
- Heat Exchangers (LP superheater, IP pre heater, LP evaporators)
- Pipes
Reheater Sub-System
The reheater sub-system accepts cold reheat steam from the HP steam turbine exhaust combined with steam flow from the IP superheater steam flow. This aggregate steam flow then passes through the reheater sections, taking the steam further into the superheated domain. The reheater is provided with an attemperator for steam temperature control. IP feedwater from the feedwater system is supplied for spraywater.
Library Components Used:
- Control Valve s
- Non-return Valves
- Control Valve s
- Pressure relief Valves
- Heat Exchanger (Reheater)
- Pipes
Boiler Blow-down Sub-System
This sub-system provides the sink for drain and vent flows.
Water chemistry is also maintained by continuous and intermittent blow down of the steam drums to the boiler blow down tank.
Library Components Used:
- Two Phase Tank (Blow down tank)
- Variable Speed Pump (Blow down water sumps)
- Pipes