Experimental Study On Combustion And Ash Formation Of Pretreated Biomass

Agricultural waste,as an important biomass energy,has attracted extensive attention from countries all over the world.As a large agricultural country,China has abundant biomass resource reserve,which is of great significance to the development and utilization of biomass in China.However,in the process of biomass combustion,alkali metals and mineral elements will cause serious ash accumulation,slagging,corrosion and other problems in the thermal transformation process,thus seriously affecting the utilization of biomass in China.Therefore,the selection of economic and effective pretreatment means to remove these elements for improving biomass combustion characteristics,ash and slagging phenomenon,promote the development and utilization of biomass is of great significance.In this paper,rice husks,a typical crop in China,were taken as the research object,and the pretreatment method of water washing was adopted to make a comparative analysis of various properties of biomass before and after water washing by changing the pretreatment method and working condition.The results showed that water washing could effectively improve the combustion characteristics,combustion stability and reaction activation energy of rice husk at low temperature.When the type of water is tap water,the rice husk after washing is more likely to burn,which increases the reaction time of fixed carbon stage,and relatively improves the incomplete combustion phenomenon of rice husk during combustion.Moreover,the influence on the unground rice husk is greater than that on the rice husk powder.The higher the water washing temperature is,the higher the burnout rate is and the more stable the combustion is.Moreover,compared with other working conditions,the heat change of rice husk after water washing is more easily affected by temperature.Washing time should not be too long,or ion-exchange reaction will occur,thus reducing the washing effect.Relatively speaking,the influence of washing time on unground husk is more significant.Is obtained by muffle furnace burning experiments under different combustion temperature rice husk ash,respectively through microscope,electron scanning electron microscope（SEM）and XRD test observation,ashing characteristics of rice husk were analyzed,and found that with the increase of temperature system of ash,gradually reduce the quantity of ash changes its color changed from gray brown to grey pink,finally become a pure white.After washing,the ash slagging phenomenon was significantly improved,and the gray color of unground rice husk was obviously dark,and there was a slight bond phenomenon.The ash particles in the rice husk ash made at 600℃exist in various forms.With the increase of the ash temperature,the particles in the ash gradually exist in the form of small pieces and clumps.Water washing can slow down this change.The agglomeration of gray particles after washing was reduced,and the K content decreased from 4-5%to 1-2%.And the long washing time makes the ash particles more finely broken.Water washing can promote the conversion of Si O₂in rice husk ash.The calculation of heat balance of waste heat utilization of biomass boiler shows that the washed rice husk is first filtered and pumped,and then the waste heat of boiler is used for drying,and the dried rice husk is then used for normal combustion and utilization.The water content of rice husk required by such a closed-loop utilization system is much less than that of rice husk after initial filtration.Therefore,other means are needed to further dry rice husks.