The efficiency of heat and power production from combustion and gasification

Abstract

A survey of the state of the art of existing biomass heat and power plants in Bavaria has been performed and promising technologies utilising combined heat and power production from solid biomass fuels have been examined. The resulting efficiencies are compared. Moreover principle considerations comparing heat and power production using combustion or gasification are presented.

It was found that there are about 200 biomass combustion plants installed in Bavaria, with a peak in the number of plants in the capacity range of about 1 MW (fuel input). The vast majority are producing heat only. Combined heat and power production is done in general by the conventional steam process with a turbine but there is also one installation using a steam engine. The smallest combined heat and power plant has a fuel input of 2 MW. The electrical efficiencies range between 10 and 20%.

The prospect of future technologies was examined as well. Gasification of biomass in combination with a gas engine or gas turbine appears to be most promising but so far problems with tar content of the gas are not solved satisfactorily. Disregarding technical problems the combination of the gasification of biomass and an energy conversion system using the product gas yields higher electrical efficiencies compared to combustion and a system utilising heat of the flue gas.

There are several options available to realise a combined heat and power plant fired by biomass. The final choice is determined by the size and the profile of the heat and power demand.