Experimental Study on the Effects of Washing Time, Washing Temperature, and Particle Size on the Combustion and Ash Formation Characteristics of Rice Husk

There are many problems in the direct combustion of biomass, such as low combustion efficiency and easy slagging. In this paper, rice husk (RH) was taken as the research object, and the effects of different washing pretreatment conditions (washing time (WTI), washing temperature (WTE), and particle size) on the combustion characteristics and ash formation characteristics were discussed. The results show that the combustion characteristics of RH were significantly coupling-affected by the WTE and WTI, and the comprehensive characteristics of volatile release were significantly coupling-affected by the particle size and WTI. Specifically, under the condition of high-temperature washing, prolonging the WTI will increase the ignition temperature of washed RH powder. The particle size could affect the temperature of the maximum rate of decomposition. Under the same conditions, the temperature difference of maximum rate of decomposition between washed RH powder and RH was 5-10 °C. For the original RH, the longer the WTI, the more unfavorable it was to increase the maximum weight loss rate, and the opposite was true for RH powder. With the increase in WTE, the flammability index, burnout temperature, and volatile devolatilization initial temperature increased obviously. In addition, washing pretreatment could reduce the ashing quality of RH and RH powder to varying degrees, and the ash quality was decreased by about 15% compared with that of unwashed RH. The alkali metal removal effect of washed RH powder was better than that of washed RH. The proportion of alkali metal K was decreased from 1 to 4% (washed RH) to 0.2-1% (washed RH powder). The ash deposit and slagging phenomenon were obviously improved. Under the same WTI, the higher the WTE was, the better the removal effect of alkali metals was. Correspondingly, the proportion of the eutectic composite salt of Mg-Fe-Al with a high melting point increased in the high-temperature sintering stage, which effectively improved the ash melting point and reduced the probability of ash deposit and slagging.