Applicant: Thermal PowerTec Ltd., Zürich

The invention relates to a method for simplifying the water steam cycle and the Heat Recovery Steam Generator in combined cycle power stations. In a triple steam pressure cycle, the IP and LP evaporator heating surfaces, their associated IP and LP water steam drums and circulation pumps are eliminated and replaced by a water heating surface and two expansion vessels.

A water recycle stream from the feed water tank is conveyed by a water circulation pump, heated by a feedwater heating surface, and expanded through a throttle valve in an IP expansion vessel . The resulting vapor stream is introduced after overheating in the reheater in the IP steam turbine (2) and the condensate stream is expanded by a throttle valve in the LP expansion vessel, the resulting vapor stream is fed into the LP steam turbine (2) and the condensate stream is expanded by a throttle valve in the feedwater tank.

This process allows a continuous course of temperature difference between gas and feed water and simplifies the classification without interruptions of the feedwater heating surface in the steam generator. By eliminating the IP and LP evaporator heating surface and the reduction of the pumps from 6 to 4 large savings in construction costs of water steam circuit in combined power plants are achieved.
Figure 050 shows an execution of the new HRSG with IP and LP expansion vessels.

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Welcome to TPT Company

The new HRSG can be build in two constructions:
- Vertical HRSG with horizontal heat transfer tubes and vertical gas flow
- Horizontal HRSG with vertical heat transfer tubes and horizontal gas flow

With the new HRSG, the LP and IP evaporators are eliminated.
In the case of new vertical HRSG, only one circulation pump is needed for the HP evaporator.
The vertical new HRSG can be built more frequently in the future due to the removal of IP & LP evaporator and the minimum space requirement.

Gas side pressure drop:
The gas-side pressure drop between the feed water inlet and the HP evaporator in the standard HRSG consists of the pressure drop over HP-Eco's, IP-Eco-Eva and LP-Eco-Eva.
The gas-side pressure drops over the IP-Eva and LP-Eco-Eva are not available in the new HRSG.
The gas-side pressure drop over tube bundle with converging HP-Eco and IP-Eco tube bundle of the new HRSG is smaller than over the tube bundle with sequence sections of HP, IP and LP Eco-Eva tube bundle of the standart HRSG.