Effect of in-bed gas atmosphere on agglomeration in fluidized bed combustion and gasification of wheat straw

Systematic experiments were carried out on agglomeration in fluidized bed combustion and gasification of wheat straw within a range of equivalence ratios (ERs) from 0.04 to 1.45 at a temperature of 850 °C. The study further examined the impact of various gasification agents, including air, steam, and CO 2 , on the agglomeration behavior. The results indicate that the bed atmosphere in the fluidized bed strongly influences the agglomeration tendency during wheat straw combustion and gasification. A reducing atmosphere in gasification could accelerate the agglomeration by decreasing the melting point of the ash. Conversely, an increase in the amount of unconverted carbon at low ERs mitigates agglomeration by decreasing ash fusion, inhibiting the interaction between ash and bed materials, as well as fixing more potassium in the carbon. The competition between the reducing atmosphere and the unconverted carbon at low ERs leads to a maximal agglomeration tendency at a critical ER value. Additionally, the presence of steam promotes agglomeration by reducing the quantity of unconverted carbon and increasing the fusion degree of straw ash. Based on these new findings, a mechanistic explanation for the agglomeration phenomenon during wheat straw gasification in a fluidized bed, considering the effects of ER and steam, was proposed. • Reducing atmosphere (RA) enhances agglomeration via lower ash fusion temperature (AFT) • Steam promotes agglomeration via reduction in unconverted carbon (UC) and AFT • UC reduces agglomeration via elevated AFT and hindered ash-bed interaction • Competition between RA and UC causes peak agglomeration tendency at a critical ER