A Cogeneration Plant Based on a Steam Injection Gas Turbine With Recovery of the Water Injected: Design Criteria and Initial Operating Experience

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Abstract
The idea of re-injecting into a gas turbine cycle the steam generated by the heat recovery steam generator (HRSG) is a well-established practice, especially in small-medium size cogeneration plants operating under variable heat demand. Power augmentation, electrical efficiency increase, NOx reduction and operating flexibility are the most obvious advantages brought about by steam injection. On the other hand, the discharge to the ambient of the injected steam has two major drawbacks: (i) a relevant water consumption and (ii) the large thermal loss related to the latent heat of steam. The addition of a recuperator downstream of the HRSG, whereby steam condensation takes place, can solve both problems, by achieving very high first-law efficiencies (over 100%, if reference is made to the lower heating value) and the integral recovery of water. The present paper describes the design philosophy and the operational experience of a cogeneration plant where such a condensation is accomplished. To the Authors’s knowledge, it is the first time in the world that this is achieved with gas turbine exhausts. The plant is located inside the “CARROZZERIA BERTONE”, a car manufacturing factory near Turin, Italy. It was designed to fulfill all the energy needs of the factory: it supplies all the electricity, steam and hot water required by the industrial process and during peaking hours, sells excess electricity to the national grid, at special increased tariffs offered to energy-saving plants in Italy. The plant erection (including the recuperator/condenser) was completed in December 1992; commercial operation began in February 1993.

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