Study On The Migration Characteristics Of Alkali And Alkaline Earth Metals During The Hydrothermal Carbonization(HTC) Of Rice Straw

Hydrothermal carbonization technology is one of the effective methods for biomass treatment.The special properties of water at higher temperatures can be used to rapidly degrade biomass and convert it into a carbon-rich solid product,hydrothermal coke.Biomass ash contains a large amount of alkali and alkaline earth metals.It migrates and transforms under the combined action of small molecular organic acids and water autoionization in hydrothermal carbonization,which not only affects the aromatization path of hydrothermal coke,but also affects the aromatization path.The physical and chemical characteristics and applications of hydrothermal coke,and the study of its migration mechanism in hydrothermal carbonization are of great significance for the regulation of hydrothermal coke characteristics.This research is based on the National Natural Science Foundation of China's "Research on the Mechanism of Carbon Element Migration and Retention in Biomass Hydrolyzed Residues in a Hydrolytic Environment" and uses rice straw as an experimental raw material to conduct hydrothermal carbonization experiments under different reaction intensities Based on the composition of organic and inorganic elements and combustion behavior of hydrothermal coke,the evolution of organic elements and the migration of alkali and alkaline earth metals during the hydrothermal carbonization of rice straw were deeply analyzed.At the same time,in order to clarify the carbonization process of hydrothermal coke of rice straw The effect of hydrothermal carbonization on acid-eluted gray rice straw was studied,and the physical and chemical characteristics of hydrothermal char of acid-eluted gray rice straw were systematically analyzed.The specific work and conclusions are as follows:(1)Using rice straw as raw material,hydrothermal carbonization experiments were performed in the range of 3.85 ~ 8.27(reaction temperature 150 ~ 300 ?,reaction time 60 ~600 min),and the hydrothermal effect of rice straw under different reaction Focus characteristics are analyzed in depth.Studies have shown that the yield of rice straw hydrothermal coke is reduced from 60.8% to 35.6%,and the liquid product yield is increased from 32% to 53.2%.If carbonization is the main factor,the reaction intensity should not exceed 6.5(240 ?,240 min).In the range of reaction intensity,the maximum C mass fraction and high calorific value of hydrothermal coke of rice straw reached 62.59% and 26MJ/kg,respectively.More than 80% of alkali metals and about 30% of alkaline earth metals were removed by hydrothermal carbonation.(2)With the increase of the reaction intensity,the mass fraction of hydrothermal coke ash in rice straw increased from 10.26% to 18.49%,and the residual rate of hydrothermalcoke ash showed a trend of first increase and then decrease.When the reaction intensity was At 8.27(300 ?,240 min),the ash residue rate dropped to 66.76%,at which time about 34%of the ash was removed.After the hydrothermal carbonization reaction of the rice straw,the slagging and contamination index of the hydrothermal coke are greatly reduced,and the value is far lower than the reference standard of the slagging and contamination index.(3)After pickling rice stalks with 0.5 mol/L of dilute nitric acid solution,compared with raw materials,the ash mass fraction is reduced by about 50%,the alkali metal K and Na mass fractions are reduced by about 99% and 86%,and the mass of alkaline earth metal Ca is reduced.The score increased by about 12%,and the mass fraction of Mg decreased by about62%.Under the reaction conditions of 150 ~ 300 ? and 240 min,the yield of hydrothermal coke from deashed straw was reduced from 70.9% to 36.2%.The rate and the degree of hydrothermal coke carbonization have increased.(4)Analysis of the combustion behavior of deashed rice stalk hydrothermal coke and rice stalk hydrothermal coke showed that the acid-eluted ash treatment removed part of the ash and extracts from the rice stalk and made water molecules during the hydrothermal carbonization reaction.The diffusion resistance is reduced,so that the degree of carbonization of the hydrothermal coke of the ash-free rice straw is increased,and the lower boiling point volatile content in the rice straw is reduced after pickling,which further enhances the thermal stability of the rice straw when the hydrothermal coke is burned.