The purpose of this work is to study how the amount of silica bed material affects the distribution of the inorganic elements in a bubbling fluidised bed (BFB) combustion pilot plant (1 MWth). Combustion tests with poplar biomass at similar fluidisation velocities and other operational conditions were assayed. The degree of interaction between the sand bed material and the biomass ash is a very important factor in the distribution of the inorganic elements in a BFB combustor. The higher the amount of silica bed material, the greater the retention of elements in the bed material. Bed accumulation can be very significant and can even retain more than 40% for major elements in poplar ash, such as calcium and potassium, as well as for trace elements such as barium, manganese, nickel, strontium and vanadium. The bed accumulation of an element depends specifically on the volatility of each element. (c) 2006 Elsevier Ltd. All rights reserved.