| Biomass energy is a kind of renewable clean energy with large reserves,so it is veryhelpful foralleviating pressure from energy shortage and pollution in the world. However,biomass isrich in alkali/alkaline earth metal, which may cause some problems, suchasagglomeration,deposition, slag and corrosion on the heating surfaces. Moreover, chlorinehas greatinfluence on the alkali migration. So to understand the alkali behavior andmaster therules of alkali emission and transformation is of great significance to solve the problem causeby alkali metal.In this paper, the transformation behavior of alkali and the related elements during thebagasse combustion processand the effect of different additives are studied by using fixed-bedreactor and the equilibriumanalysis software FactSage. The purpose is to find a way to avoidor alleviatethe problems existing in the using process of bagasse direct combustion.Combustion experiment of bagasse samples were put on fixed-bed reactor. The results showthat the combustion characteristic has a pronounced effect on the alkalis transfer characteristicof bagasse. Alkalis released rapidly along with the exhalation of volatile at the initial stage ofcombustion, but at the later stage of combustion alkalis evaporated in the form of alkali saltdue to the fixed carbon combustion. The results of Cl content analysis show that thetemperature has little effect on Cl transfer characteristic when the reaction temperature ishigher than500℃. Cl released rapidly in the form of HCl and KCl in the first60seconds ofthe combustion. In the combustion process, most of the alkaline earth metal calcium andmagnesiumremaining in the ash. The calcium in the ash may form the melt compose of highlydepolymerized network, adding gaseous alkali metal. The results of HCl content analysisshow that the HCl emission curve taked on a single peak under different temperature.Andwith the temperaturethe peak valuedecreased first and then increased, and decreased at last.Adding decoking agent, kaolin, calcium oxide and coal in the bagasse as additive, allthe samples were burned in a fixed-bed reactor. The results show that the kaolin and decokingagent was the most capable to catchthe potassium to stay in the ash. In the components of decoking agent, kaolin is the most important to catch potassium. As coal have a low contentofaluminum and silicon compare with the other additive, the volume of addition should beincrease to have a good potassium retention ratio.At high temperature, the potassiumaluminium silicatedissociated and released gaseous potassium chloride, so in the actualoperation the residence time of bagasse in high temperature should be controled.The result of numerical simulationcalculated by Fastsage show that the related elementsmainly existed in the form of stable solid while the temperature is lower than800℃. ThenSolid potassiumsalt wouldbe transformed into KCl(g),(KCl)2(g) with increasing temperature.Atmiddle or high temperature, KAlSi2O6(s) with high melting point would beformed by KCl（s）,Al2O3and SiO2along with the released of gaseous HCl.Apart of KCl(s) and K2SO4(s)wouldbe transformed into K2SO4(salt) and K2O(slag). The influence of additive had twoaspects, on the one hand, catching the potassium to stay in the ash,no the other hand, releasinggaseous HCl. |
