Strategies and technologies towards zero emission biomass combustion by primary measures

To satisfy the market demand for fuel-flexible low-emission biomass combustion systems a new approach based on an updraft gasifier directly coupled with a multi-stage gas burner and a boiler has been developed. In the gasifier semi-volatile ash forming elements (i.e. mainly K) are released in the hot charcoal combustion zone and are precipitated again in the upper regions of the fuel bed. Therefore, an almost particle free product gas can be achieved which can then be efficiently combusted at low excess air ratios in the subsequent multi-stage burner. In this paper the principle of ash embedding in the gasifier is described with a special focus on the K chemistry. Combining this approach with appropriate fuel bed cooling measures, the new technology can be applied for a wide spectrum of biomass fuels reaching from conventional wood fuels over short rotation coppice to agricultural fuels/residues such as miscanthus and olive stones. Test runs performed at a lab-scale testing plant confirmed this high fuel flexibility and the possibility to operate this system at almost zero CO and OGC emissions as well as dust emissions of less than 5 mg/MJNCV.