Viscous components of waste tend to cause agglomeration during incineration. Previous studies have investigated the influence of various components of coal on tendency to agglomerate. However, the effect of single elements on agglomeration has rarely been examined. Accordingly, this investigation focuses on the effect of various different elements and operating parameters on agglomeration/defluidization during incineration. The nitrates of alkali (Na) and earth alkali metals (Mg, Ca) were added to artificial wastes, to simulate agglomeration. The effects of gas velocity, operating temperature, particle size and static bed height on agglomeration were also evaluated. Increasing the concentration of sodium reduced the time required to reach defluidization. However, the earth alkali metals (Mg, Ca) apparently inhibited agglomeration. The effect of the inhibition of the earth alkali metals reduced as the concentration of sodium was increased. When the concentration of sodium was 3.0 wt%, the earth alkali metals promoted agglomeration. The concentration of sodium determined the behavior of agglomeration/defluidization during incineration. Increasing the operating temperature reduced the time required to reach defluidization, which increased with gas velocity. The particle sizes of Geldart B powder (545, 645, 770 mum) used as bed materials had similar defluidization times. However, the use of D powder (920 mum) accelerated agglomeration to reduce defluidization time. (C) 2004 Elsevier Ltd. All rights reserved.