The Survey of Ash Agglomeration Phenomena in a Commercial Circulating Fluidised Bed (CFB)

Sammanfattning: Renewable energy sources will act an important roll in the development of sustainability in the future in order to protect environment and ecological cycle.Amongst the Kyoto protocol conclusions there is an agreements for the EU a reduction of 8 % of greenhouse gas emissions (corresponding of around 6 million tonnes of CO2 equivalents ) between 2008-2012 (compared to 1990 level). To reach the European Unions objectives an increase of the share of renewable sources, all the different technologies including geothermal, solar, wind and ocean have to be supported. Further increasing of biomass will also be necessary, and biomass will be expected to cover 8 % of the global energy supply by 2010.In line with EU, national and regional policy these research effort has been initiated.The use of biomass in Combined Heat and Power production (CHP) introduces several technical problem needed to be solved. The most common combustion technique is Circulated Fluidized Bed (CFB). In this technique bed material (typically silica sand) that assumes to be inert is present in the combustion process. Due to chemical reaction between the wood ashes and bed material, there is as tendency of adhesion, which result in agglomeration of the bed and/or depositions that cause blockage of material transport in the whole process.The investigated samples were collected from a full-scale combustion boiler (104 MWth). With intention to survey the problem different analytic techniques have been used for chemical characterisation – X-ray Fluorescence, ICP-Mass, Atomic Absorption, and Scanning Electron Microscopy. For physical characterisation the sample was fractionated mechanically and also leached in different solvents in order to understand the solubility of the compounds in order to determine the alkali compounds presence in ash.Mechanical fractionating was employed to identify a marker in early stage of combustion process to prevent costly blockage tendency in the boiler. This has shown to be a simple device to optimise the exchange of bed material.A future change of biomass resources will demand a more specific understanding and mechanistic clarification of the agglomeration tendency.