PROTOTYPE 5 KW STEAM COGENERATOR WITH LINEAR ALTERNATOR

A prototype micro-cogeneration system based on a reciprocating steam engine has been built and is now starting its experimental operation. The system has a biomass fuelled boiler, working at moderate pressure (5 bar). A condenser interfaces the steam circuit with the heat load, preferably at low temperature, such as household heating. The whole system is conceived for use in rural areas in order to reduce electricity and fossil fuel consumption. The reciprocating engine piston is directly coupled with a linear alternator. This dramatically simplifies the engine and eliminates the side forces due to the crank mechanism. Hence, cylinder wear is reduced and operation without lubrication is allowed. Vibrations are reduced as well. On the other hand, the system oscillation must be controlled in order to produce energy at grid frequency. This has been accomplished by an electrically operated intake valve rotating at fixed speed. An air spring has been used to balance the steam force on the piston. In this way, the reaction force can be controlled by varying the air spring volume. This document describes the computer code that simulates the thermodynamic, mechanic and electric behaviour of the engine-alternator group. This code has been used for the design and optimization of the prototype. Furthermore, the relevant prototype features are presented.