Studies On Hydrothermal Dewatering And Upgrading Of Sludge With Lignite And Its Co-slurryability

Hydrothermal dewatering and upgrading of sludge with low rank lignite for preparing low viscosity and high concentration slurry fuel, can not only turn the bound water to free water for slurry, but also make it reduction, harmlessness and resource utilization of the sludge. However, the coalification mechanism in the process of sludge and coal hydrothermal upgrading and the effects on the slurry characteristics need to be further studied. In this paper, the effects of hydrothermal treatment temperature and sludge addition on the physicochemical properties of upgraded products and the slurryability, rheological properties, stability of the slurry fuel were investigated. Proximate and Ultimate analysis, FTIR,13C-NMR, GC-MS and other facilities were used to characterize the physicochemical properties of the upgraded solid products. The carbon distribution in the gas, liquid and solid three-phase products from raw materials were obtained and the coalification mechanism occurred in the hydrothermal upgrading process was studied.The results of Proximate and Ultimate analysis showed that with the increase of upgrading temperature, moisture and oxygen content of the upgraded solid products significantly decreased; fixed carbon and calorific value greatly improved; hydrophobicity of the solid products enhanced; water re-absorption capacity weakened; and the coalification degree deepened. With the increase of sludge addition, the equilibrium water content of the solid products and water re-absorption rate gradually decreased; O/C atomic number ratio significantly decreased, hydrophobicity enhanced. GC-MS analysis showed that the organic components in liquid products were mainly phenols, ketones, heterocyclic, amines, esters and alkanes. With the increase of upgrading temperature, the content of heterocyclic and amine in liquid products showed an increasing trend, the content of ketone was relatively higher when the upgrading temperature was 200?-250?. Amines were mainly from the hydroly-sis of proteins in the sludge, phenols were mainly from the partially hydrolysis of lignin or relatively weak bonds fracture in molecular side chain of lignite. Decarboxylation, demethanation and decomposition reactions occurred in the upgrading process which generated a certain amount of gas products, mainly being CO2, CO, H2 and CH4. The oxygen in raw materials was released mainly in the form of CO2.The results of FTIR analysis indicated that the relative absorption intensity of -OH in hydroxyl or carboxyl groups and -C=O in amide or carboxyl groups were significantly reduced, indicating that dehydration and decarboxylation reactions occurred during the upgrading process. From the 13C NMR spectrum, it was found that the content of aliphatic and O-alkyl carbon in raw sludge was higher, accounting for 43.35% and 30.53% of the total organic carbon, respectively. With the increase of upgrading temperature, O-alkyl carbon showed the highest rate of decomposition, and the relative content of it was reduced by at least 40.97%. The relative content of carboxyl and carbonyl were lessened by at least 12.5% and 15.63%, respectively, which suggested that oxygen loss not only corresponds to dewatering, but also desplays a significant correlation with conversion of C=O and COOH and the change of O-alkyl carbons.More than 90% of the carbon retained in the slurry after hydrothermal upgrading of lignite mixed with sludge, which is very important for the carbon maximum conversion in the gasification process of the slurry fuel. Hydrothermal dewatering and upgrading effectively eliminated the internal combined water, changed the hydrophilic properties of the raw materials, and improved the constant viscosity solid concentration of slurry. Large amount of phenol, benzopyrene, low ring benzene et al. contained in the liquid products play a role of decentralized stabilization during the preparation of slurry fuel due to its basic molecular structure like dispersion agent for coal water slurry. The constant viscosity solid concentration of the slurry increased after hydrothermal upgrading and still kept good rheological properties of pseudoplastic fluid and high stability. When the sludge addition was 50%, the constant viscosity solid concentration of the coal sludge slurry of Inner Mongolia lignite and Yunnan lignite with sludge reached 58.13% and 64.78%, respectively.