The addition of dolomite to the combustion of biomass fuel forms: the study of ashes agglomeration and fusibility

The combustion of biomass often leads to the formation of agglomerated deposits. The problems related to ash agglomeration may be reduced by added dolomite. The occurrence of agglomeration may be indicated by the mass ratio of the formed silicates and inert material. Excess alkali oxides may sublimate and form deposits in the duct systems and on heat transfer surfaces. We used optical microscopy and photography to document the changes during the combustion tests of five types of biomass (hay, rice husk, spruce, miscanthus, and wheat straw) under different temperatures and with/out added dolomite. In rice husk the ratio of alkali metals and SiO2 approaches the stoichiometry of the reaction of K2Si4O9 formation. The mass ratio of the silicate and inert ash approaches 1 and agglomeration does not occur. The fusing point of ash exceeds 1200 degrees C. To prevent agglomeration in combusting spruce and miscanthus, it is convenient to add 2 wt% of dolomite for the temperature of 1180 degrees C. In the case of wheat straw, 2 wt% of dolomite should be dosed for 900 degrees C, 5 wt% for 1000 degrees C, and 10 wt% for 1100 and 1180 degrees C. In hay, it is suitable to add 2 wt% of dolomite for the temperature of 1000 degrees C, 5 wt% for 1100 degrees C, and 10 wt% for 1180 degrees C. In all the cases, the addition of dolomite ensures the ratio of silicate and inert material to be below 1, and agglomeration is avoided.