| Biomass ash,the solid waste from biomass combustion,contains almost all nutrients required by plants during growing.If they are returned to farmland as fertilizer,costs for solid waste treatment,chemical fertilizer utilization,and agricultural production can be decreased significantly.Recycling of nutrients will benefit the health of the agro-ecosystem and plays a great role in sustainable development.However,few investigation on assessment of fertilizer property of ash and effects of combustion conditions have been reported.In this paper,fertilizer property of ash from corn-stover and effects of combustion conditions have been investigated.Contents and results are shown as following:(1)Based on the summary of literature and results of our experiments,a matrix originated from the idea of sequential extraction method was proposed to describe fertilizer property of ash,and the testing method was established.Deionized water,mixture of 0.5 mol/L acetic acid & 0.5 mol/L ammonium acetate with the volume ratio of 1:10,and citric acid with the mass fraction of 2% were selected as solvents in our sequential extraction and contents of major nutrients in insoluble matter were measured by X-ray Fluorescence analyzer.Meanwhile,a matrix expression were proposed to describe various phases and various types of nutrients.In the matrix of fertilizer property of ash,types of nutrients in ash were used as rows of matrix,and total amounts and soluble contents in our sequential extraction were used as column of matrix.(2)An experimental set-up for pellets combustion was built and experiments of corn-stover pellets were performed in a horizontal tube furnace at different operational conditions(temperature,length of corn-stover pellets,air flow rates).Fertilizer property of ash from corn-stover pellets were measured according to our measurement method.Results showed that: 1)Effect of temperature on burning behavior was slight when the temperature was higher than 700 ?.Effect of pellet size and air flowrate on burning behavior was almost ignorable.Compared with wood pellet,less secondary air and more residue time were needed in the combustion of corn-stover pellets.2)Comparison of solubility of ash from pellets and powder showed that almost all solubilities of ash from pellets were less than 13%.Solubility of powder was twice as much as that of pellets when temperature was less than 700 ?.There is a great potential in balancing nutrients for farmland via recycling ash of corn-stover pellets burnt at low temperature,and corn-stover produced from farmland were returned to soil which can be satisfied with potassium required by plants(34% of nutrients for per hectare farmland can be provided by one hectare corn-stover ash via calculation,66% of potassium can be provided by soil).(3)Combustion of corn-stover powder were investigated experimentally in a muffle furnace and a horizontal tube furnace,and fertilizer property of ash from corn-stover powder were measured.Resulted showed that: effect of temperature on the solubility of metallic nutrients(potassium,calcium,magnesium)in the ash was more significant than that of non-metallic nutrients(phosphorus,sulfur);effect of temperature on the contents of nutrients in ash was almost slight;effect of temperature on the release characteristics of nutrients in ash was obvious;this indicates that phase of potassium in the ash was changed with increasing temperature;compare of fertilizer property of ash from pellets and powder,soluble amount of nutrients in the ash from pellets was less than that of powder,total amounts and soluble amounts of nutrients in powder ash were 80%,148% larger than that in pellets ash at 550 ?,respectively.(4)Data of fertilizer property of ash from corn-stover powder at different conditions were analyzed.Results showed that kinetic equation of chemical reaction is hard to express history of fertilizer property of biomass ash.Next,effects of diffusion and other flow characteristics on fertilizer property of ash will be investigated in the future. |
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