Agglomeration of silica sand in a fluidized bed gasifier operating on wheat straw

The effects of straw feed rate and ash composition on the agglomeration characteristics of the bed material (silica sand) in a fluidized bed gasification system were investigated. By changing the air flow rate and/or straw feed rate, the effects of four equivalence ratios (0.26, 0.38, 0.57 and 0.76) on agglomeration were investigated. The effect of straw ash content (0.0, 3.3, 27.8 and 43.5%) on the agglomeration of the bed material was also investigated at various temperatures (620, 740 and 850°C) using a high temperature furnace. It was found that a fluidized bed of silica sand agglomerated at around 800°C in the presence of straw ash, resulting in serious channelling and defluidization. A very hard and brittle structure was formed at 850°C. Changes in air velocity and/or fuel rate did not improve agglomeration characteristics. K 2O, which is present at a high weight percentage in the straw ash and has a relatively low melting temperature, was the major contributor to the agglomeration process.