Alternative Bed Materials for High Alkali Fuels

Fluidized bed combustion of high alkali fuels may cause agglomeration and defluidization of the bed as sodium and potassium react with quartz particles in the bed, forming alkali-silicate layers causing the particles to stick together. In certain cases the use of quartz free bed materials has been shown successful, like “Ofita” in the combustion of the residues from olive oil production in Spain. There are alternatives available to be used as quartz-free bed materials but some of them may be more expensive compared to natural sand. They are not always found in suitable form or particle sizes. Furthermore, the knowledge of the alternatives, and when it would beneficial to use them, is limited. The economics are not always favorable to using the alternative, effective but expensive bed materials since the build-up of harmful elements in bed usually can be avoided with sufficient make-up sand addition. A minimum level of make-up material addition is in any case necessary when combusting fuels with ashes that do not maintain the bed inventory. A study of minerals and materials available in Finland and elsewhere as possible bed make-up materials was carried out. The differences between these materials compared to quartz as a reference are investigated. The economics of the use of the alternative bed materials are discussed.