A Study into the Influence of Different Factors on the Behavior of Alkaline Element Concentrations that Cause Bed Agglomeration

In recent years, studies into the processes of bed agglomeration during the combustion of biomass have become increasingly relevant. The agglomeration processes are most largely influenced by the alkaline components of ash, which form low-melting eutectics by reacting with silicates. Therefore, it is very important to determine the critical concentration, primarily, of potassium that forms the most low-melting eutectics in the bed, at which the particles begin to sinter. The experimental studies are aimed at to investigate the effect of the temperature and the concentrations of alkaline elements on the process of particle agglomeration during the combustion of various types of biomass as well as biomass and coal, studying the presence of bed drain, determining the critical concentration of potassium in the bed, and calculating the estimated time before the start of sintering under conditions of an increase of potassium concentration in the bed. The experimental techniques and characteristics of the four studied types of biomass are described. Data on the fraction of agglomerated particles in the bed at different temperatures and concentrations of alkaline elements are given. Upon replacing a part of the sand by iron oxides, agglomeration is observed only at high temperatures (850°C and more). The obtained data are compared with the results of similar experiments carried out under conditions of the fluidized bed; in these experiments, the effects of the fluidization rate, particle size, and excess air on the agglomeration processes are considered. It is noted that the limiting potassium concentration is lowest in the case of a fixed bed. It is shown that real objects should be used when studying the dependence of the behavior of the potassium concentration in the bed on the operation time. The choice of the fraction of bed drain with the addition of a screened material or fresh sand is of practical interest. The calculation techniques and calculated data obtained with use of them on the behavior of the potassium concentration in the bed under various conditions are presented. The fractions of bed drain during combustion of sunflower husks and bark and wood waste are determined. In addition, it is shown that the joint combustion of husks and coal sharply reduces the probability of bed agglomeration.