| Hydrogen is a kind of renewable energy carrier,and snygas is also an important chemical raw material.Chemical-looping Steam Methane Reforming(CL-SMR)is a new technology for hydrogen production.The method is through two steps of oxidation reduction reaction of methane and water vapour reaction process is divided into methane reduction reaction section and the water oxidation reaction part respectively to produce H2/CO ratio is 2 and hydrogen,the method avoid the separation process for hydrogen and oxygen at high temperature,the snygas also can be suitable for industrial methanol synthesis gas,the technology has good prospects for development.The technique is by oxygen carrier in two steps of oxidation reduction reaction in the process to realize the preparation of snygas and hydrogen,and the performance of oxygen directly determines the pros and cons of the reaction system,the core problem of the technique is to find an efficient and stable oxygen carrier.In the paper,firstly,the oxygen which is suitable for CL-SMR technology is selected from the point view of thermodynamic,secondly,the performance of the oxygen which produce snygas and hydrogen in the reduction reaction of methane and the oxidation reaction of water were studied by respectively,and the optimal reaction conditions of the oxygen carrier in the two step were determined respectively.Finally,ten times cycle experiments were carried our in the optimal conditions,the stability of the oxygen carrier was investigated,and the feasibility of the oxygen carrier in CL-SMR process was proved.the main results of this paper are as follows:(1)The elements in the periodic table are selected based on the physical properties of metals and their oxides,then based on the minimization of the Gibbs free energy principle,the remainder of the metal oxide for methane reduction reaction and water oxidation reaction on the thermodynamic feasibility is analyzed used the HSC chemistry thermodynamics analysis software.The results show that:the oxide systems of FeO/Fe,Fe2O3/Fe,Fe3O4/Fe,Fe3O4/FeO,MoO2/Mo,SnO2/SnO,WO2/W and WO3/W have been proved suitable for the low temperatures(500-700℃)CL-SMR process.The systems of V2O5/V,Mn2O3/Mn,Mn3O4/Mn,Nb2O5/NbO2,CeO2/Ce2O3 and Eu3O4/EuO were suitable for medium temperatures(700-900℃)CL-SMR process.In addition,TiO2/Ti2O3,Cr2O3/Cr,Nb2O5/Nb,NbO2/NbO and Nb2O/NbO systems only worked successfully in high temperatures(900-1100℃).(2)In the paper,W03 is used as the oxygen carrier,and the experimental on the methane reduction reaction was studied used WO3-SiO2 and WO3-Al2O3 which were prepared three different inert carrier added percentage(2:8、4:6、6:4)using impregnation method.The effects of the reaction temperature(900℃ 950℃,1000℃),inert carrier(2:8,4:6,6:4)and oxygen carrier(SiO2,Al2O3)on the reaction performance were investigated.The results of experimental show that:The increase of temperature is beneficial to the improvement of the selection of CO,which is favorable to the direction of the reaction to generate CO,which is helpful to increase the yield of CO and H2.When the reaction temperature is 1000℃,the ratio of H2/CO is closer to 2 than temperature is 950℃ and 900℃.The optimum methane reduction reaction temperature of WO3-SiO2 and WO3-Al2O3 is 1000℃.The optimal methane reduction methane concentration of WO3-SiO2 and WO3-Al2O3 is 10%.For WO3-Al2O3 and WO3-SiO2,when the ratio is 4:6,the ratio of H2/CO is more close to the ideal value 2.During the methane reduction reaction of WO3-Al2O3,the selectivity of CO was greater than that of WO3-SiO2 when the CO was selected for methane reduction;The ratio of WO3-Al2O3 to H2/CO is much closer to 2 than that of W03-SiO2;WO3-Al2O3 oxygen carrier unit time of syngas in higher yield than WO3-SiO2 oxygen carrier in unit time synthesis gas production;The performance of the WO3-Al2O3 carrier is better than that of the WO3-SiO2 carrier.(3)The reduced state WO3-SiO2 and WO3-Al2O3 oxygen carriers were prepared by the optimum conditions of the methane reduction reaction part,and the hydrogen production performance was studied,The effects of reaction temperature(750 C,800 C,850 C,900 C,950 C),steam flow rate(0.34L/h,0.43L/h,0.57L/h),oxygen carrier species(SiO2,Al2O3)on the performance of hydrogen production were investigated.The results of experimental show that:Increasing the reaction temperature is beneficial to increase the rate of hydrogen production,However,the total hydrogen yield was similar in 30 minutes at 950℃ and 900℃,From the point of view of energy consumption,The optimal reaction temperature of the hydrogen producing part of water oxidation of the WO3-SiO2 and WO3-Al2O3 oxygen carrier at 900℃;To improve the flow rate of water,hydrogen production reached the peak,But with the increase in water vapor flow in the total hydrogen production in 30 minutes instead of reducing,When the water flow rate is 0.34L/h,the total hydrogen production is the largest in 30 minutes;Water flow rate of 0.34L/h is the best flow;The reduced W03-SiO2 oxygen carrier and the water reaction are more easily controlled,and the reaction is more stable,and the performance is better than that of the reduced WO3-Al2O3 carrier.(4)Finally,the optimal reaction conditions has identifited of methane reduction and water vapor oxidation were carried out on WO3-SiO2 and WO3-Al2O3 in ten cycles,and the stability of the reaction under ten cycles was investigated.The results of experimental show that:WO3-SiO2,WO3-Al2O3 oxygen carrier in the ten cycle of the experiment,the reaction of methane reduction and partial oxidation of water vapor decreased,This is because of the high temperature reaction of long time,sintering,and the methane reduction reaction accompanied by the phenomenon of carbon deposition and thus reducing its activity;The ratio of WO3-Al2O3 in the sygas H2/CO ratio of the ten cycles of the oxygen carrier is fluctuating between 1.65～2.39,the W03-SiO2 ratio of the syngas H2/CO ratio in the ten cycle of the 1.88-2.12 carrier wave,which is more close to the ideal value 2;In the CL-SMR process,the performance of WO3-SiO2 is better than that of WO3-Al2O3. |
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