Effects of the alkali metal oxides and bed material compositions on agglomeration phenomena in CFB boiler

Circulating fluidized bed boiler is environmentally friendly technology in power generation. However, agglomeration related operational standard has not been established yet. As a basis of establishing standard, the fixed bed agglomeration mechanism of bed inventory was investigated. The melting temperature reduction occurred with induced change of alkali metal compositions. The melting temperature reduction result in viscous surface on particles and ease of being agglomerated. The temperature reduction appeared more clearly in silica sand than bottom ash. This was caused by the high SiO2 composition of the sand and alkali silica reaction occurred because activated alkali compositions were reacted with SiO2 forming alkali silicates. Further analyses of agglomerates produced in bubbling fluidized bed reactor were conducted. The expected agglomeration effect has similar trend with melting temperature reduction. And the agglomeration effect appeared more in silica sand because of high SiO2 composition and sodium was more effective in forming agglomerates than potassium. Therefore, bottom ash can replace silica sand as bed material in CFB boiler. And sodium composition must be managed more strictly than potassium composition. •Bed material compositional change during fluidized bed combustion process.•Viscosity and agglomeration by melting point reduction with alkali metal.•Effect of agglomeration compared in compositions on fluidized bed condition.