Comparative study of gas engines and gas turbines in cogeneration (CHP)

Besides the reinforced expansion of renewable energies one other central target in the German Energiewende is the efficiency enhancement using fossil energy. Due to the German climatic conditions, the combined heat and power (CHP) generation is a suitable instrument to achieve this goal. Therefore, it is part of the new energy concept of the German Federal Government. But owing to the changing market associated to the Energiewende, also other technologies move into spotlight, like large, stationary, high-efficient gas engines.

As modules of a power plant network these engines can provide thermal energy to a district heating network alternatively to a gas turbine combined cycle power plant (CCPP) in CHPmode. The engine’s waste heat originating from cooling water and exhaust gas can be used either directly for heat supply or in a water-/steam cycle with an extraction back-pressure turbine and following heating condensers (HeaCo). These three systems (CCPP, engine, engine + HeaCo) have been modeled, simulated and evaluated based on annual data of a representative district heating network.

All systems comply the values for primary energy saving and fuel utilization ratio required by the German KWK-act. Regarding the annual exergetic utilization ratio the engine systems offer an advantage of 1-2 %-points. Due to the higher power production the system engine + WSC is economically favorable. In addition, these engines have an enormous ability for residual load management with load transients of up to 33% MWel,inst/min.

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