Straw fired CHP plant in Austria : technical and economical evaluation

Abstract

The following work analyzes the technical and economical feasibility for using straw for power production in Austria as renewable energy. It also discuss the opportunity to reduce the use of fossil fuels and their emission in using biomass instead of fossil fuel by means of a case study. Especially straw from cereals (wheat, barley, rye, oat) will be technical useable for straw combustion. With adoption of a 50-km radius around Wulzeshofen (Lower Austria) the freely available quantity of cereal straw was calculated with around 160,000 t/a. This amount would sufficient for a CHP plant with a size of 83 MWth. The energy use of straw already practices for long time in Denmark. There the necessary know-how is already available and technologies are developed and proven for a long time. In the new straw incinerators chlorine causes no unsolvable combustion problems any more: Protection remedy by slag on super heater. A coincineration of up to 50% other biomass should be possible. The co firing of biogas should be avoided. For straw combustion there are different combustion systems available but it has been found that especially the grate combustion system would be the appropriate technology. An important and sensitive technical application in a straw fired CHP plant will be feeding system of the boiler. The suitable and approved system for grate firing will be the pulper system. An important success factor for the economical feasibility is an efficient logistics for straw storage and transportation. This efficient management of the fuel delivery (just in time) is an challenge of every straw combustion project. It has been figured out that the power plant has to be a heat led application. Currently it is technical possible to reach a electrification efficiency of up to 32 % in a straw fired CHP plant. Also the fuel prices (incl. handling and transport costs), the steam price and the use of the slag as by-product are one of the main factors for the economical feasibility. The slag maybe can be recovered for agriculture on the field, whereas the fly ash (heavy metal) has to be deposit.<br />