Study On Ash Characteristics Of Biomass During Combustion And Potassium Resource Utilization

As a large amount of ash-forming elements especially the alkali metal present in biomass,a lot of ash related issues are easy to be found during biomass combustion.It is well known that ash related issues will seriously inhibit boiler efficiency.Meanwhile,with the sustained growth of capacity of biomass power plant all around the world,a lot of biomass ash are emerging during biomass combustion,so the ash must be handled properly.In order to solve the problem above,this paper made a deep analysis on the characteristics of fly ash derived from nine biomass power plants,and identified the strategy of premixing of ammonium dihydrogen phosphate with biomass prior to combustion for solving ash related issues.The acting mechanisms of ammonium dihydrogen phosphate on the behavior of potassium during combustion of rice straw was studied by chemical fractionation analysis.And the effect of ammonium dihydrogen phosphate and kaolin on potassium retention and the melting characteristic of ash during combustion of rice straw were compared studied.Finally,in order to achieve potassium resource recycling from biomass ash,this paper regard the fly ash as potassium ore and actively explored the optional experimental conditions during the extraction of potassium from fly ash.The main conclusions are as follows:The low temperature eutectic reaction of potassium with silicon is the main cause of ash melting during combustion of biomass.The content of potassium in the fly ash derived from biomass power plants is relatively large,however the mian occurrence forms of potassium are insolubility.Water-soluble potassium will actively react with PO43-and was converted to insoluble potassium,thus avoided being migrated to the gas phase.The influence of PO43-/K molar ratio on potassium’s retention ability was related to the combustion temperature.Within the temperature range of 750-950℃ and relative to PO43-/K molar ratio of 1:2,the rate of change of potassium’s retention for PO43-/K molar ratio of I:I increased by 4.95%,23.12%and 47.99%,respectively.750-950℃,ammonium dihydrogen phosphate could restrain the release of KCl effectively.When the temperature was increased,the higher PO43-/K molar ratio became more favorable to potassium’s retention.At the temperature of 850℃,the effect of ammonium dihydrogen phosphate is superior to kaolin on the promotion of potassium retention rate.Furthermore,attributed to phosphate’s dominance over Si in the competition for potassium,water-soluble potassium was converted to high melting point K-Ca-P ternary compounds,which was conducive to alleviating the problem of ash fusion.The results of orthogonal experiment showed that,the best experimental conditions is 75℃,90min,water cement ratio 4:1,and the potassium extraction ratio from fly ash will reach at maximum 20.32%.