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Regeneration Behavior of (Fe, Zn, Ce) Medium High Temperature Coal Gas Desulfurizer in Oxygen and the Mixed Atmosphere of Oxygen and Water Vapour

Author: CaoJunChang
Tutor: MiJie
School: Taiyuan University of Technology
Course: Chemical processes
Keywords: hot coal gas deulfurizer desulfurization regeneration ZnFe2O4 CeO2 semi-coke
CLC: X701.3
Type: Master's thesis
Year: 2011
Downloads: 98
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Abstract


Because of its convenient and thermal efficiency, high temperature gas purification is the recent research focus areas in gas purification. The composite metal oxide sorbents with advantages of two or more single-metal oxides have big sulfur capacity, good mechanical strength and can be easily regenerated.In this paper the semi-coke based (Fe, Zn, Ce) as the sorbent active components, and the iron and zinc oxide are loaded on the semi-coke by method of co-precipitation. This type of sorbent has advantages of the high desulfurization precision of zinc oxide, the big sulfur capacity of iron oxide and the regeneration advantages of cerium oxide. By the method of loading the active component on the semi-coke, the distribution of active component is more uniform, the crystalline of metal oxide is better and the sorbent sulfur capacity is much bigger than before. Choose 15% of the active component as the sorbent for desulfurization in the simulation hot coal gas, make the sorbent saturation. Then in a fixed bed reactor the sorbents are regenerated by oxygen and the mixed atmosphere of oxygen and water vapour. The impacts of temperature, space velocity and gas concentration to the regeneration of sorbent are tested. And the regeneration kinetics were studied in the atmosphere of the oxygen. After regeneration experiments of XRD, SEM and some other means were studied. The conclusion is as follows:(1) In the regeneration of oxygen atmosphere, the mainly components of exhaust gas are SO2 and little elemental sulfur. The regenerated sorbents are mainly composed by ZnFe2O4 and CeO2. Improving the regeneration temperature, space velocity and oxygen concentration could affect the concentration of tail gas. From the XRD and XPS characterizations, the sulfate, which affects the rate of sorbent regeneration and sulfur capacity, can be easily generated between 400℃-500℃. To reduce the regenerative time and the formation of sulfate, the best regeneration condition for the (Fe, Zn, Ce) metal oxide sorbents in oxygen atmosphere is:650℃,4000h-1, and 4%(vol) O2.(2) There is a significant weight gain at about 400℃when the sorbent is heated at the programmed temperature by TGA. It indicates that at this temperature a large number of sulfate is formatted. And the test shows that when the temperature is higher than 600℃, the oxidation rate of sulfide was significantly higher than formation rate of sulfate. By citing shrinking core model on the sorbent to analyze the dynamic behavior, the corresponding frequency factor and apparent activation energy of the chemical reaction are 0.132m/s and 16.66kJ/mol, respectively; the corresponding frequency factor and the diffusion activation energy are 52.91kJ/mol and 6.63×10-5m2/s, respectively.(3)The regeneration reactions of the sulfide compounds with oxygen and water vapor are exothermic and endothermic reaction, so the sorbent can avoid to be sintered. After the regeneration, the products are mainly Fe2O3, ZnFe2O4and CeO2.The tail gases are mainly consist of H2S, SO2 and a certain amount of elemental S. The sulfide reacted with the water producing H2S and sulfide reacted with the oxygen producing SO2, respectively. The hydrogen sulfide and sulfur dioxide occurs Claus reaction to produce the sulfur. Experimental results showed that a lower temperature and higher rate of H2O/O2 were good for the formation of sulfur. The experiment showed that water vapor could expanse of the pore of the sorbent. The high rate of H2O/O2 could increase the rate of sorbent regeneration and ensure the regeneration rate of the sorbent. In order to ensure the regeneration rate of the sorbent and improve the yield of elemental sulfur, the best regeneration condition is:650℃,4000h-1, H2O/O2 40.

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CLC: > Environmental science, safety science > Processing and comprehensive utilization of waste > General issues > Exhaust gas processing and utilization > Desulfurization and desulfurization
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