General Electric recently received the patent for an asymmetrical combined cycle power plant that includes a first engine, a second engine, a first heat recovery steam generator, a second heat recovery steam generator, and a steam turbine. The plant has the productivity characteristics of a large frame machine and efficiency characteristics of an aeroderivative turbine.
The second engine is relatively more productive but less efficient than the first engine. The first engine generates a first exhaust gas, and the second engine generates a second exhaust gas. The first heat recovery steam generator transfers excess energy from the first exhaust gas to a first flow of water, creating a first flow of steam.
The second heat recovery steam generator transfers excess energy from the second exhaust gas to a second flow of water, creating a second flow of steam. The second heat recovery steam generator further transfers excessive energy from the second exhaust gas to the first flow of steam and the second flow of steam, creating a flow of superheated steam. The steam turbine receives the flow of superheated steam from the second heat recovery steam generator.
The combined cycle power plant is "asymmetrical" because the topping cycle engines differ from each other. One of the topping cycle engines is more productive but less efficient than the other topping cycle engine due to at least one difference between the engines. For example, the more productive topping cycle engine may be different from the more efficient topping cycle engine in terms of pressure ratio, size, power output, efficiency, exhaust gas temperature, or combinations thereof.
The term "productive" with reference to an engine generally refers to the ability of the engine to generate useful shaft work, and in some cases, the productivity of the engine may be represented by the maximum temperature and pressure ratio of the engine for a particular cycle.
In some embodiments, the more productive topping cycle engine is an industrial heavy-duty gas turbine, while the more efficient topping cycle engine is an aeroderivative gas turbine or a reciprocating engine, such as a natural-gas-fired diesel engine. The bottoming cycle engine is generally a steam turbine. However, the principles of the present disclosure can be employed with reference to asymmetrical combined cycle power plants that have other numbers or combinations of engines.