| Biomass carbonization technology can efficiently utilize waste materials such as straw to produce biochar,which can be used in the fields of materials,energy,environment,and agriculture to achieve carbon sequestration and emission reduction,thereby promoting carbon neutrality.However,traditional carbonization technology is unable to handle raw materials with high water content,such as fresh straw,and has high energy consumption for high-temperature carbonization.Therefore,hydrothermal carbonization technology,as a new means of carbonization organic matter,has gradually become the main way of treating organic waste.The main reaction of hydrothermal carbonization is dehydration and decarboxylation,which can effectively treat fresh biomass feedstocks with high water content.Additionally,hydrothermal carbonization reaction conditions are mild and have broad application prospects.However,existing studies have shown that hydrothermal carbonization technology has problems such as high water consumption and difficulties in wastewater treatment,which seriously hinder its large-scale application.At the same time,most of the current hydrothermal carbonization equipment uses flange bolts to connect the kettle lid to the kettle body,making the opening and closing of the kettle lid complicated and difficult to operate,and the continuous production efficiency is low,which is not conducive to the practical application of hydrothermal carbonization.This study proposes a new approach to reduce the high water consumption and difficult wastewater treatment in hydrothermal carbonization.By conducting hydrothermal carbonization experiments with different liquid-to-solid ratios(10:1,5:1-1:1),the basic physicochemical properties of hydrochar were analyzed and characterized,and the basic properties,soil application potential,and economic benefits of hydrochar at different liquid-to-solid ratios were comprehensively evaluated.The results showed that a lower liquid-to-solid ratio increased the p H of the hydrochar from 3.77 to 5.53,while the elemental content,thermal stability,and functional group types were not significantly affected.Since incomplete carbonization occurred,the specific surface area and pore volume of the hydrochar decreased by 61.8% and 70.9%,respectively,when the liquidto-solid ratio was reduced to 1:1.The soil application potential study showed that as the liquid-to-solid ratio decreased from 10:1 to 2:1,the dissolved organic carbon content in the hydrochar increased by 55.0%,while the main nutrient content and carbon sequestration potential of the hydrochar did not decrease significantly.According to the results of the gray correlation analysis,the hydrochar with a liquid-to-solid ratio of 10:1and 2:1 had the highest correlation,which were 0.80 and 0.70,respectively,indicating that these two types of hydrochar had better soil application potential.However,reducing the liquid-to-solid ratio from 10:1 to 2:1 increased the profit from a single production process from-388 ￥ to 968 ￥,and reduced the amount of wastewater generated by 80%.Therefore,hydrothermal carbonization with a liquid-to-solid ratio of 2:1 is more valuable for practical application.Considering the large-scale application of hydrothermal carbonization in farmland improvement and environmental governance,the comprehensive advantages of reducing the liquid-to-solid ratio will be further highlighted.Based on previous experiments on hydrothermal carbonization,this study aimed to address the difficulties in equipment start-up and shutdown,complicated operation,and low continuous production efficiency.The design goals of the equipment,including the target pressure(10 MPa),operating temperature(300 ℃),and main dimensions,were determined based on previous hydrothermal carbonization experiments.The main structure and processing materials of the equipment were determined according to relevant standards for high-pressure vessel design.By analyzing and comparing the current mainstream quick-opening structure layout forms and applicable conditions,a segmented ring-type quick-opening structure was selected as the opening and closing method for the reaction equipment cover and body.To address the problem of poor sealing performance in the mid-late stages of the reaction,a self-tightening sealing structure that can improve sealing performance with increasing internal pressure was designed.The mechanical and sealing performance of the equipment was analyzed through theoretical research and numerical simulation.It was found that the overall structure of the equipment was stable,with good pressure-bearing performance,and the stress in each structure was lower than the allowable stress of the material.The contact pressure at the sealing joint was greater than the internal pressure of the equipment,and the sealing structure could meet the sealing requirements of the equipment.Through the study of low liquid-solid ratio hydrothermal carbonization and quickopening carbonization equipment,it has been effectively demonstrated that low liquidsolid ratio hydrothermal carbonization is feasible.This provides theoretical support and a reference for the realization of low-cost hydrothermal carbonization of straw and the promotion of large-scale application of hydrothermal carbonization technology. |
