Supercritical Water Co-gasification Of Dianchi Sediment And Lignite For Hydrogen

Dianchi Lake is a very important environmental protection goal of the "three lakes" in China. Sediment dredging is a main measure to clear Dianchi endogenous pollution. The Dianchi Lake dredged sediment not only has obvious pollution characteristics, but also occupys a lot of land. Dianchi Caohai storage yard total capacity is more than6.23million m3, occupys1965acres. As an energy source, Dianchi Lake dredged sediment is similar with coal-water slurry in many aspects, because it’s a solid waste of large amount of high moisture content, calorific value and high organic matter content. Supercritical water gasification(SCWG) is an emerging way for hydrogen production in recent years, which is energy-saving and efficient. The lignite is a mature material in SCWG, Yunnan is one of provinces of lignite concentrated area in China. Lignite has high moisture so that long-distance transport for lignite which has high moisture and low calorie is not economical. And the economic cost of dried lignite is also very high. If the co-gasification of Dianchi Lake dredged sediment and lignite can be a synergistic way, carbon, hydrogen and other elements can be transformed to a hydrogen-rich gas, heavy metals and nutritious elements will be separated effectively, so that the co-gasification not only can solve the Dianchi Lake dredged sediment occupation of land, but also can be reasonably make the sediment to be harmless, reductive and regenerative.SCWG of lignite and sediment for hydrogen production were investigated in a batch autoclave.Gaseous product were detected by GasChromatography(GC), liquid productwere detected by Gas Chromatography-Mass Spectrometer(GC-MS)and solid product were detected by Scanning Electron Microscopy(SEM) and Energy Dispersive Spectrometer(EDS). First, the optimum operating conditions for SCWG of lignite were investigated mainly for the temperature, catalyst, reaction residence time, and coal-water ratio this four operating conditions. Then SCWG of lignite and sediment independently for hydrogen production were investigated for influence of different feedstocks. The effect of different mixed ratio i.e.1:9,2:8,3:7,4:6,5:5on hydrogen production were also investigated.The main results are as follows:(1) The main gaseous products of SCWG both of lignite and sediment are:H2, CO2, CH4, CO.(2) The best SCWG condition is:550℃, about25MPa, the amount of20%catalyst (K2CO3), the residence time20min, water-coal ratio10:1. Under the best SCWG condition, lignite carbon gasification rate is32.2%; gas phase yield is699mL/g; H2production rate is285mL/g.(3)The results indicated that gasification of sediment led that a rich composition of hydrogen, high recovery of gaseous products but low gasification yields of gaseous products; meanwhile, gasification of lignite led that high carbon gasification efficiency and gasification yields of gaseous products. Although the gaseous yields of gasification of lignite were lower than that of sediment, which increased to834mL/g under co-gasification. The obvious synergistic effect on carbon gasification efficiency and hydrogen production were observed in co-gasification process. Carbon gasification efficiency and hydrogen were3.12%and55mL/g respectively, higher than that by average value. The optimal ratios existed in co-gasification, after3:7, carbon gasification efficiency declined. Therefore, co-gasification under optimal ratio not only could achieve effective sediment disposal, but also with high gaseous yields about350mL/g H2and113mL/g CH4.(4) The SCWG of lignite is a total of41liquid products sediment’s is a total of48liquid products and co-gasification’s is a total of68liquid products. The main component of liquid product of the SCWG are Phenol and its derivatives.