| China is a big agricultural country,and the total amount of agricultural waste generated every year is the highest in the world.The burning and discarding of agricultural waste in the field has caused huge air pollution and waste of resources.At the same time,a large amount of CO2 is generated by the coal-fired power generation method,so that the use of renewable agricultural waste as an energy source can achieve better economic benefits.However,the high content of chlorine and alkali metals in agricultural wastes will cause serious problems such as ash accumulation,slagging and corrosion in the process of heat utilization,which seriously threaten the safe and efficient operation of equipment.At the same time,the presence of chlorine promotes the release of alkali metal at high temperatures,which increases the problem of slag corrosion.Therefore,reducing the chlorine content in the fuel has become the key to solving the problem of slag corrosion.Torrefaction is an effective means of pretreatment of biomass,which can reduce moisture,enhance hydrophobicity,grindability,increase energy density,and effectively improve the quality of biomass.However,current studies have insufficient research on the conversion characteristics of chlorine,sulfur,alkali metals and alkaline earth metals during the torrefaction process.If the bio-fuel characteristics can be improved while reducing the chlorine and sulfur content and improving the reaction characteristics of the alkali metal,the energy utilization of the biomass can be greatly expanded.In view of this,this study relies on the National Natural Science Foundation of China,“Study on the Formation Mechanism of Biomass-Formed Fuel Combustion Particles” and the National Youth Science Fund Project “Study on the Migration and Enrichment and Regulation Mechanism of Phosphorus-rich Agricultural Waste Gasification and Phosphorus Migration”.The migration and transformation characteristics of chlorine,sulfur,alkali and alkaline earth metals in the torrefaction process of high-chlorine biomass corn stalks were studied.Two kinds of regulation methods of mixed torrefaction and phosphorus-based additives are proposed to promote the release of chlorine in the torrefaction process to solve the problems of corrosion and ash caused by chlorine in the subsequent thermal conversion process.The main research contents of this study are as follows:First,the corn stalks is torrefied by a horizontal furnace fixed bed reactor,and the chlorine content of the solid product is detected by high temperature combustion hydrolysis-ion chromatography.The form of chlorine is analyzed by XPS,and the alkali and alkaline earth content and appearance are detected by digestion,chemical fractionation.It was found that the chlorine in the corn stalk mainly exists in the form of alkali metal chloride,and the inorganic chlorine decreases after torrefaction,and the organic bound chlorine increases.With the increase of torrefaction temperature,the release rate and content of chlorine increased,and the release rate of chlorine in corn stalk at 300 °C was about 40%;the release rate of sulfur increased,but the sulfur content in the product decreased.The alkali metal K is the most abundant in corn stalk,the content of alkaline earth metal Ca and Mg is equivalent,and the Na content is extremely low.During the torrefaction process,the release rates of alkali and alkaline earth metals were lower,but the morphology of the alkalinity changed significantly.The ratio of ion exchange state of K increased and the ratio of ion exchange state and acid dissolution state of Ca and Mg increased.Subsequently,using KCl wet mixed cellulose,hemicellulose and lignin,The effects of three components of biomass on chlorine release and the effects of three components on chlorine release from actual biomass corn stalks were studied.The results showed that the three components of biomass could promote the release of chlorine in KCl,and the release of chlorine promoted the effect of lignin>xylan>cellulose,but the release of cellulose from chlorine was significantly affected by the torrefaction temperature,while lignin and xylan are less affected by temperature.For corn stalks,studies have found that lignin and xylan can significantly promote the release of chlorine from corn stalks,and the promotion effect of lignin is better.When the lignin content reaches 20%,the lignin content no longer affects chlorine release rate,at this time,the chlorine release rate is 60%.Xylan and cellulose also promote the release of sulfur from mixed samples,and the release rate of sulfur is linear with the amount of xylan and cellulose added.Finally,the addition of ammonium dihydrogen phosphate(ADP)was carried out by wet mixing.The effect of ADP addition on the release of chlorine under different torrefaction temperatures of corn stalk was studied.The results showed that the addition of ADP could significantly promote the release of chlorine from corn stalks.The release rate of chlorine was up to 88.4%,and the chlorine content in torrefied solid products was also reduced to about 1.5 mg/g,but the relative content of inorganic chlorine in solid products decreased,and the relative content of organic chlorine increased significantly.It was also found that the addition of ADP can promote the release of sulfur in corn stalk to some extent,but the release rate of sulfur does not change with the amount of ADP added.The addition promoted the release of Mg in the ion exchange state,and the effect of promoting the release rate of K and Ca was not obvious,but Ca was converted from the ion exchange state to the acid dissolution state. |
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