Characteristic Study Of Dense Particle System In The Field Of Biomass Utilization

As a renewable energy source, biomass is getting more and more attention. However, the special characteristics of biomass fuel, such as low calorific value, high alkali metal content, large difference in size of fuel, low density, high water content, poor flowability, often make the process of biomass utilization encounter a lot of problems.Agglomeration occurs in the process of biomass CFB combustion. The first part of this thesis focuses on the formation mechanism of agglomeration and how to detect agglomeration in terms of the interaction between bed material particles. Defluidization is directly caused by that the driven force of fluidizing gas can’t counter the resistance between particles. We try to take the bed material out from the fluidized bed to research the mechanical characteristic between particles with rotating cylinder test bench, expecting to quantitatively conduct the agglomeration detection in fluidized bed. The effects of fuel form, combustion time and spherical degree of bed material on agglomeration were analyzed. The results show that the form of fuel has a significant effect on agglomeration. When the fuel has a good fluidization performance, and can mix with bed material evenly, the bed temperature distribution tend to be uniform and local high temperature is hard to attain which can make fuel ash melt. The test research of the interaction between bed material particles showed that fuel ash on the surface of the bed material adhered to bed material particles to form small agglomerate and the biomass ash melted at high temperature in the process of agglomeration. Resistance between bed material slag particles after combusting different form of rice straw can be well reflected.Biomass fuel generally has a high moisture content, rough surface, highly irregular form, low density, which make the flowability of dense biomass particles in natural accumulation poor. Arching problem frequently happens in the biomass bin before furnace and other mouth push feeder link. Arching can make fuel supply unstable. The second part of this thesis, The PFC software based on discrete element method was adopted to simulate arching phenomenon of biomass particles in dense accumulation. The effects of opening size, pile height, wall friction coefficient on arching were analyzed. The results showed that the greater the opening size, the higher the discharging rate and the lower the possibility of arching; a high pile height make the possibility of arching high. When the length of material decreased, the possibility of arching decreased prominently. The length of material has a significant effect on arching. Several verification tests were conducted in a small bin, and the results coincided with the simulation well.