Repowering

Many studies are being carried out to create new electric power sources by raising the output of an existing power station to increase its efficiency.
The simplest way to achieve this is repowering or remodeling an existing power station by combining it, in whole or in part, with a gas turbine into a combined cycle plant.

There are two main options available when deciding to repower ;
(1) Fully Fired Combined Cycle Repowering,
(2) Heat Recovery Combined Cycle Repowering

The design concept of Fully Fired Combined Cycle Repowering is as follows;
A gas turbine is installed in place of a F.D.Fan and high temperature gas turbine exhaust is fed directly into a boiler, which effectively utilizes the calorific value of the gas turbine exhaust.
The figure shows an existing 375 megawatt plant that was repowered.

	Before Repowering	After Repowering
Gas Turbine	None	154 MW
Steam Turbine	375 MW	375 MW
Total	375 MW	529 MW (Output up 41%)
Plant Efficiency	Base	10% up

Outline of Original Plant
- Output: 375 megawatt
- Steam Condition: 169 atg / 566 degrees C / 538 degrees C
- In Service: 1966, Repowered: 1995

The design concept of Heat Recovery Combined Cycle Repowering is that the existing boiler is decommissioned and replaced it with a highly efficient gas turbine and an HRSG (Heat Recovery Steam Generator)
The figure shows an existing 125 megawatt plant that was repowered.

	Before Repowering	After Repowering
Plant System	Boiler+steam turbine	2(gas turbine+HRSG)+steam turbine
Gas Turbine	None	146 MW x 2
Steam Turbine	125 MW	140 MW
Total	125 MW	432 MW (Output up 246%)
Plant Efficiency	Base	33% up

Outline of Original Plant
- Output: 125 megawatt x 2 units
- Steam Condition: 102 atg / 538 degrees C / 538 degrees C
- In Service: 1957, Repowered: 1993

Alternatively there is the repowering plant that utilizes the existing boiler (utilizes both the present boiler and present steam cycle), with addition of a gas turbine and an HRSG.