| Hydrothermal Conversion Technology has been widely concerned by researchers for transforming low-grade biomass resources into high-grade solid fuels.According to the characteristics of biomass waste,such as low energy density,widely distribution and large yield,aiming at high value utilization,the research on hydrothermal utilization based on different biomass was carried out to explore and reveal the mechanism of hydrothermal transformation of different kinds of biomass.Firstly,based on the ash content and resource endowment,this paper studies hydrothermal conversion of several typical biomass wastes using high-value biomass?bamboo?,common biomass?Chinese fan palm,garden waste?and inferior biomass?water hyacinth?as raw materials.The results show that:no matter what biomass,hydrothermal treatment has a strong effect on improving the fuel quality under certain experimental conditions.And it's conducive to subsequent heat treatment.The hydrochar and oil phase is the main process products,gas only occupied a small proportion.During the hydrothermal treatment process,most carbon elements can be retained in the solid phase,and oxygen elements can be significantly removed.After hydrothermal treatment,the energy grade and fuel utilization grade of hydrochar can be improved to varying degrees,achieving the goal of upgrading of energy via hydrothermal treatment.For example,with the increase of temperature,the fuel ratio of garden waste increased significantly from 0.21 to 0.80.HHV increased from 18.29 MJ/kg to 28.90 MJ/kg,which had a promotion of 58%.In addition,the influence of treatment temperature and residence time on the thermodynamic behavior of hydrochar during combustion and pyrolysis was studied by means of thermogravimetric analyzer.The results show that the effect of hydrothermal conversion temperature is higher than the reaction time for hydrochar.The thermokinetic analysis of co-combustion between hydrochar and oil shale was investigated by model-free method.The minimum average activation energies calculated by Starink method and OFW method are 98.5 k J/mol and 103.5 k J/mol,respectively.The co-pyrolysis behavior of hydrochar and paper sludge was investigated by n-order order kinetic reaction model,and the change of activation energy of the system was calculated.The activation energies of the first,second and third stages are 34.2?173.0 k J/mol,160.5?207.2 k J/mol and 186.8?278.9 k J/mol,respectively.Then,the co-hydrothermal treatment of bamboo and PVC was studied.The presence of bamboo had obvious synergistic effect on the dechlorination of PVC,mainly the hydroxyl from bamboo promoted the dechlorination of PVC.Because of the presence of biomass,-OH substituted-Cl,thus the substitution reaction occurs and the reaction intermediate is formed.In the hydrothermal process,crosslinking,cyclization,aromatization,polymerization and other reactions occurred,which strengthened the dechlorination process and generated hydrochar with dense structure.When the ratio of the two feedstocks is 1:1 and the hydrothermal treatment temperature is 200°C,the dechlorination efficiency of the mixture is 18.33%,which is higher than the hydrothermal dechlorination efficiency of PVC?6.53%?.At 230°C and 260°C,dechlorination showed negative synergistic effect.The dechlorination efficiency of the mixture was 39.05%and 91.79%respectively,which was lower than that of PVC?56.11%and96.97%?.Through the analysis of Fourier infrared spectrum?FTIR?,scanning electron microscope?SEM?,13C NMR spectroscopy and thermo-gravimetric?TG?research platform,the hydrochar formation mechanism and its intermediate reaction process are put forward.It revealed the hydrochar formed by dissolution,decomposition,aggregation,cyclization,aromatization.And the fuel properties are explored through the combustion analysis.Then,the hydrothermal treatment and subsequent pyrolysis of Chinese fan plam were discussed.The distribution of the total products,mainly composed of hydrochar,water soluble phase and gas phase,was studied.In addition,the ICP-OES test showed that the hydrothermal treatment could remove alkali metals by more than 88%,meanwhile the enrichment effect of heavy metals occurred.In addition,the pyrolysis process and composition of pyrolysis products can be significantly affected.The hydrochar obtained from hydrothermal treatment at 180,210,240?was analyzed,which their volatiles are divided into 11 groups including acids,ketones,phenols,aldehydes,furans,esters,hydrocarbons,ethers,alcohols,sugars and carbon dioxide to show the composition of pyrolysis volatiles.Phenols,acids,sugars and hydrocarbons have always been the most important chemical components in all samples,accounting for21.01%?13.49%,15.40%?1.03%,30.58%?4.79%and 17.44%?41.20%,respectively.The RPA of ethers,ketones,aldehydes,furans,alcohols and esters are less than 5%.Finally,hydrothermal treatment,torrefaction and other pretreatment methods are compared.TG-DTG-DSC analysis shows that,there are three stages corresponding to heat absorption and heat release in the pyrolysis process.The first stage thermal decomposition temperature below160°C is due to water evaporation.Several exothermic peaks were observed in the pyrolysis temperature range of 160?570?,mainly caused by the volatilization ofof molecular bond and formation of new compounds.In the last stage?570?800°C?,significant heat absorption occurred due to the combination of semi-coke condensation and mineral decomposition.In addition,the CPI of the samples after hydrothermal treatment which were2.99,6.60 and 9.26×10-7/?min2°C 3?,were lower than those of the Tr-R,Tr-W and Tr-A samples(23.91,13.93 and 18.85×10-7/?min2°C 3?,respectively.The Py-GC/MS analysis showed that acids,phenols,ketones,aromatic hydrocarbons,nitrogen-containing products and aliphatic&alicyclic hydrocarbons accounted for a high proportion.N-heterocyclic compounds were formed by Maillard reaction and Amadori rearrangement of the carbonyl group in reducing sugar and nitrogenous products.In a word,biomass waste is upgraded to clean solid fuel after hydrothermal treatment,which provides a new method for pretreatment and subsequent thermal utilization of biomass waste. |
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