Behaviour of trace elements during the pyrolysis of biomass and sewage sludge

摘要

Biomass and sewage sludge attract increasing interest in power plant technology as sources of carbon dioxide neutral fuels.' Besides using solid pulverized biomass or sewage sludge as an additional fuel in coal-fired boilers a further possibility to run a combined coal and biomass/sewage sludge process is to pre-pyrolyse or pre-gasify biomass or sewage sludge and to use the generated gas as reburn fuel in the coal-fired boiler. The separation of coal and biomass/sewage sludge ash within this co-combustion process enables a specialized use of the residuals. The advantage of this pretreatment process is that undesired components like inorganic compounds, which may cause problems like slagging, fouling, and corrosion, or which are problematically to dispose or to utilize together with coal ash in other processes, can be kept away from the coal-fired boiler.Investigations on the pyrolysis behaviour of biofuels continue with regard on the path of trace elements, like heavy metals, and alkali compounds, during the pyrolysis process varying different parameters. Detailed analysis of char samples, collected from two locations of the test facility with different characteristic particle sizes, give a picture of the behaviour of trace elements during the pyrolysis at different temperatures. The investigation of biomass pyrolysis shows a specific behaviour of the most important elements depending on the pyrolysis temperature and the particle size of the pyro-lyzed char. The share of ash in small particles is higher than in the coarse samples. The release of potassium and calcium during the pyrolysis of biomass increases only at temperatures above 800°C. During the pyrolysis of sewage sludge there is no distinct influence of the temperature on the release of the investigated components.