Cogeneration & Combined Cycles

Prof. Osama A El Masry

Mechanical Engineering DepartmentME332 Operation and Management of Power Plants

Prof. O. El Masry

An Ideal Cogeneration PlantAn Ideal Cogeneration Plant

(Fig. 9-21)

Prof. O. El Masry

Schematic and T-s Diagram for Cogeneration Cycle

(Fig. 9-23)

Prof. O. El Masry

Combined Cycles•The overall thermal efficiency of a power plant can be increased by using binary cycles or combined cycles.

•A binary cycle is composed of two separate cycles, one at high temperatures (topping cycle) and the other at relatively low temperatures.

•The most common combined cycle is the gas-steam combined cycle where a gas-turbine cycle operates at the high-temperature range and a steam-turbine cycle at the low-temperature range.

Mercury-Water Binary Vapor Cycle

Mercury-Water Binary Vapor Cycle

Prof. O. El Masry

(Fig. 9-24)

Prof. O. El Masry

Combined Cycles• The gas-steam combined cycle uses a gas-turbine cycle operating in a high-temperature range and a steam-turbine cycle in a low-temperature range.

•Steam is heated by the high-temperature exhaust gases leaving the gas turbine.

•Combined cycles have a higher thermal efficiency than the steam- or gas-turbine cycles operating alone.

Prof. O. El Masry

Combined Gas-Steam Power Plant

HRSG(Heat Recovery Steam Generator)

Types of HRSG

2 bar 20 bar

1 ton/h 10 ton/h

up to 180 bar

150 300 ton/h

Configurations of HRHG

Evaporator section

Superheater section :

Economizer section :

Economizer designs would normally follow along with the evaporator type that is being used and be similar in design to the superheater. The configurations would be similar to the ones shown above for the superheaters

Preparing a flow schematic for the HRSG :

• Pinch point .• Approach point .

Single pressure :