| As a typical invasive species in China's water ecosystem,water hyacinth(WH)has brought severe challenges to the environmental management of South China,Central China and East China.Meanwhile,because water hyacinth is rich in organic matter such as cellulose,hemicellulose and lignin,it can also be used as a high-quality biomass resource.Considering that water hyacinth contains very high moisture and hydrothermal carbonization(HTC)has great advantages in processing biomass with high moisture(HTC can completely eliminate the pre-drying process),this paper investigates the feasibility of converting water hyacinth into value-added solid fuel through HTC and conducts basic research on the reaction mechanism.In addition,this paper also proposes the method of co-hydrothermal carbonization(co-HTC)of water hyacinth and polyvinyl chloride(PVC)to further improve the fuel properties of hydrochar.The specific research results are as follows:First of all,this paper explores the changes in the physical and chemical characteristics,combustion characteristics and polluting gas emission characteristics of water hyacinth derived hydrochar under different hydrothermal conditions.The results show that the increase of reaction temperature and residence time as well as the addition of acid and alkali catalysts during HTC process can make the dehydration and decarboxylation reactions more severe.Compared with water hyacinth,the atomic ratios of H/C and O/C in hydrochar have dropped significantly,revealing that coalification degree has increased.The higher heating value(HHV)of hydrochar has also increased from 14.68MJ/kg to 18.17-20.93MJ/kg.TG-FTIR analysis shows that compared with water hyacinth,the combustibility index S and combustion stability index Rw of hydrochar have been upgraded greatly,which means that hydrochar has better combustion performance.Besides,this paper also finds that the addition of alkali catalyst(NaOH)is beneficial to reduce the emission concentration of typical gaseous pollutants(sulfur dioxide and nitrogen oxides)during the combustion process of hydrochar.Although HTC process can upgrade the energy quality of water hyacinth,the HHV of water hyacinth derived hydrochar still does not meet the standards of high-quality coal substitutes.To this end,this paper attempts to achieve a further increase in the HHV of hydrochar through co-HTC of water hyacinth and PVC.Moreover,this paper also tries to establish multiple quadratic regression equations in which hydrochar characteristics(dechlorination efficiency,yield,HHV,energy recovery efficiency and electricity consumption index)respond to the change of process parameters(including reaction temperature,residence time and water hyacinth/PVC mixing ratio)and achieve the optimization of process parameters through response surface methodology.Experimental results have proved that co-HTC treatment can indeed achieve a significant increase in HHV of hydrochar and superior dechlorination efficiency.Under the reaction condition of 260-60-0.5(260-60-0.5 represents that the reaction temperature is 260?,the residence time is 60 min,and the water hyacinth/PVC mixing ratio is 0.5,the same below),hydrochar with HHV of 33.03MJ/kg can be obtained,which has reached the standard of Chinese extra-high calorific coal.Additionally,under the reaction condition of 260-60-2,hydrochar with chlorine content of only 0.81% can be obtained.Through parameter optimization,the hydrochar with the optimal energy recovery efficiency and electricity consumption index can be obtained at the same time when the reaction condition is 200-30-0.5,and the values reach 94.96% and 13.81,respectively.In summary,the co-HTC of water hyacinth and PVC can indeed further improve the energy quality of hydrochar,which makes it possible to use hydrochar as a kind of high-quality coal substitute. |
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