Solid Fuel Production And Alkali Recovry Performance Analysis By Hydrothermal Carbonization Of Cotton Linter Pulp Black Liquor

In this paper,the soda pulping black liquor of cotton linter was took as raw material,it's chemical composition and physical properties were analysed.And the feasibility of the hydrothermal carbonization of cotton linter pulp black liquor to produce hydrochar and ailkali recovery were discussed.As well as the pyrolysis characteristics of cotton pulp black liquor was also analysed,in order to regard the cotton pulp black liquor as a resources,and provide theoretical guidance for its application in thermal conversion technologies.First,the chemical composition of black liquor,including solids,inorganic,organic,lignin,total sugar,effective alkali,total base?NaOH?,the content of elements in the black liquor solids,and the physical properties of black liquor,including viscosity,chrominance,CODCr,BOD5,pH value were investigated.From the chemical composition it can be seen that the lignin content was 4.0 g·L-1,the polysaccharide content was 9.41 g·L-1,and the total alkali content up to 32.6 g·L-1.From the elementary analysis the carbon element content of 27.35%,and the High Heat Value?HHV?of 11.4 MJ?Kg-1 can be clear.So it's hard for the direct combustion.From the physical properties it can be seen that the black liquor had a dark color,a high pH reached 13.4,and BOD5 / CODCr < 0.3,it's difficult for the biochemical treatment.Then the CO₂ was took as acidifying agent and flocculants,the initial pressure of CO₂?1.1-1.6 MPa?and the preserving temperature?200-280 ??were as variables in this paper.The yield,element analysis,industrial analysis,energy,carbon recovery,recovery of lignin conversion of the hydrochar were analysed,which was the solid production of the hydrothermal carbonization of cotton linter pulp black liquor.The results showed that when the control preserving temperature was 240 ? and the preserving time was 8h,the optimal pressure conditions of CO₂ was 1.4 MPa.At this time the solid yield is 12.7%,the carbon content is 48.8%,the C recovery efficiency was 21.5%,the total energy recovery efficiency was 31.7%,the High Heat Value?HHV?value was 21.6 MJ?Kg-1,which proved that it was practicable for hydrothermal carbonization of cotton linter black liquor to produce the hydrochar.And when the control initial pressure of CO₂ was 1.4 MPa and the preserving time was 8h,the yield,HHV,carbon content,volatile,fixed carbon content,energy recovery rate,carbon recovery rate,as well as lignin conversion rate of the hydrochar were respectively between 12.2% and 15.4%,21.43 MJ?Kg-1 and 25.44 MJ?Kg-1,43.59% and 51.01%,38.4% and 52.3%,35.5% and 40.3%?32.37% and 35.38%,22.4% and 24.54%,24.43% and 56.59% at the different temperature from 200 ? to 280 ?.But when the temperature exceeds 260 ?,the process of the hydrothermal carbonization of cotton linter black liquor changed.Furthermore,the property of the production achieved at different temperature were researched,as well as the alkali recovery feasibility of the hydrothermal carbonization liquor.The FT-IR result showed that there were no significant functional changes of the hydrochar comparison to solid black liquor,except for the strength of the peak.But the peak dispeared at 1124 cm-1,which means that it was easy for the break of C-O bond at the hydrothermal carbonization condition.And when the temperature reached 280 ? the peaks of the hydrochar significantly increased than others,which displayed that at this temperature the process of the hydrothermal carbonization of cotton linter black liquor changed,echoes the previous conclusion.At the same time the TGA result also showed that the thermal stability of the hydrochar increased.Meanwhile the pH value,GC-MS,chromaticity and total alkali content of liquor production of hydrothermal carbonization were also analysed.The pH value and GC-MS results showed that the decrease of pH was mainly caused by CO₂ and small molecular organic acid produced by hydrothermal carbonization reaction.The total alkali content were between 77.90% and 93.07% in the liquor production of hydrothermal carbonization,as high as which in the black liquor 96.76%,proofed that the alkali metal were mainly dissolved in solution in the process of hydrothermal carbonization of cotton linter pulp black liquor.Then the alkali in the liquor production of hydrothermal carbonization with the way of causticization was recovered.The result showed that the highest causticizing rate can reaches 45.2%,and the liquor alkali can be used in pulp making or the impregnation before cooking.Finally,the thermogravimetric and kinetics analysis of BLS,lignin as well as polysaccharide were conducted.The results showed that there were four stages for the pyrolysis BLS,the second stage was the pyrolysis stage of organic content in the BLS.Also,the second stage was the pyrolysis stage of organic content in the lignin and polysaccharide.In the dynamic experiments for the second stage of BLS,lignin and polysaccharide,it can be seen that BLS and polysaccharide had the same mechanism function,which was different from lignin's.It meant that the polysaccharide had more significant influence on the pyrolysis characteristics of BLS more than lignin.