CHP from Updraft Gasifier and Stirling Engine

The combination of thermal gasification with a Stirling engine is an interesting concept for use in small combined heat and power plants based on biomass. By combining the two technologies a synergism can potentially be achieved. Technical problems, e.g. gas cleaning and fouling of the Stirling engine heat exchanger, can be eliminated and the overall electric efficiency of the system can be improved.

At the Technical University of Denmark a Stirling engine fueled by gasification gas has been developed. In this engine the combustion system and the geometry of the hot heat exchanger of the Stirling engine has been adapted to the use of a gas with a low specific energy content and a high content of tar and particles.

In the spring of 2001 a demonstration plant has been built in the western part of Denmark where this Stirling engine is combined with an updraft gasifier. A mathematical simulation model has been developed as a tool to analyse a system combining the Stirling engine with a gasifier. The paper presents simulation results for the demonstration plant at typical operating conditions.

A result from the simulation is that a net electric efficiency of 17,7 % based on the higher heating value of the biomass is obtained. Finally the special features of a system combining thermal gasification and Stirling engine technology are discussed and the status of the demonstration plant is presented.