Slagging/fouling and corrosion. The inorganic constituents of biomass materials, and the ashes produced in combustion and other thermal processes, are of particular interest for plant designers and operators. These materials are very different in a number of important respects from coal ashes. They are not alumino-silicate systems, and commonly comprise mixtures of a limited number of relatively simple inorganic compounds, principally silica, and the oxides, sulphates, chlorides and phosphates of the alkali and the alkaline earth metals. In general terms, therefore, the biomass ashes are relatively rich in elements that are effective fluxes for coal ash systems and that tend to be volatile processes. at elevated temperatures in combustion and other thermal The overall result is that many of the potential impacts of the co-firing of biomass materials in coal combustion and other thermal processing plants are associated with the changes in the ash composition and the ash behaviour that occur when co-firing. The principal ash-related impacts on plant operation and integrity that may be affected by biomass co-firing include: - The formation of fused or partly-fused ash deposits on surfaces in furnaces and reactors; - The formation of bonded ash deposits on convective section heat exchangers; - The formation of aggressive ash deposits on high temperature surfaces, resulting in accelerated metal wastage; - The formation of aggressive ash deposits on surfaces at saturated steam temperature, resulting in accelerated metal wastage in the area from the burner to the first convective heat exchangers; - The formation and emission of fine inorganic aerosols and fumes; - The impact on the performance of flue gas cleaning equipment; - The impact on the handling and the utilisation/disposal of the thermal processes. ash discards from These impacts are dependent on a number of factors, including the chemistry and behaviour of the coal and the biomass ashes, the co-firing ratio and the plant configuration. The ability to assess these risks and importance to the industry. to minimise the impacts on plant performance are of key The industry has a suite of laboratory test procedures and other methods for the analysis and characterisation of coal ashes, and these have been applied, with appropriate modification where necessary, to biomass ashes and the ashes from co-firing. To date, the industrial experience has been principally with the co-firing of clean biomass materials in large pulverised coal boilers at...
