In-situ Preparation And Desulfurization Performance Of Nano-zinc Oxide Sorbent For Hot Coal Gas

With the continuous development of the economy of our country, the energy consumption will continue to maintain a trend of rapid growth, and the position of coal as the main energy consumption pattern may not change in the near future. To control the haze weather, it is imperative to improve the energy efficiency and enhance the use of clean coal. The integrated coal gasification combined cycle power generation technology combines with environmentally friendly coal gasification technology and high efficiency of gas-steam combined cycle power generation technology, achieving the clean and efficient use of the coal. It is one of the most promising clean coal power generation technology in the 21 st century. During coal gasification, the sulfur species present in coal（0.1³%） are inevitably transformed into H2 S which may not only corrode the gas turbine blades, also may do harm to human health. Thus, gas desulfurization purification is an indispensable part in IGCC system. But pulverization of the sorbent is one of the obstacles of the large-scale industrialization, therefore, a new method is used to prepare the sorbent to improve the pulverization problems during the application.This method uses red clay as support and binder, nano Zn S as the active specie of the precursor. They were mixed the water and the paste is extruded in to strips and the precursor obtained. The paper investigated the effect of different in situ regeneration temperature, regeneration space velocity and oxygen concentration on the properties of sorbents. Multiple desulfurization-regeneration cycles of fresh sorbent which was prepared under optimum conditions were conducted in a fixed bed reactor. The structures and morphology properties of sorbents were characterized by X-ray diffraction, Scanning Electron Microscopy, N2 adsorption and X-Ray Photoelectron Spectroscopy. At the same time, the regeneration kinetics of the precursor under the O₂ atmosphere were analyzed using homogeneous reaction model and the shrinking core model. The conclusions are as follows:（1）When the PH of solution is 3, C[（CH₃COO）₂Zn]:C（Na₂S₂O3） is 1:1, and the adding a certain amount of cetyl trimethyl ammonium bromide as the surfactant, the nano Zn S prepared with a smaller grain size, better dispersion and particle size distribution.（2）The optimum condition for preparing the sorbent is that the in situ regeneration temperature is 650 oC, regeneration space velocity is 3000 h-1 and oxygen concentration is 6 vol%. After four times of desulfurization-regernation cycles, the sulfur capacity decreased by 18.17%. From the XRD patterns, it can be seen that Zn2 Si O4 generated, which caused decline of the desulfurization activity of the sorbent. From the SEM, relatively abundant pore structure was generated after in situ regeneration. But the active species agglomeration took place after multiple desulfurization-regernation cycles and the grain size grow larger, which may cause the decrease of the sulfur capacity of the sorbent. From the S2 p XPS spectra, there was a small amount of sulfate in the used sorbent after multiple desulfurization-regernation cycles.（3）Based on the uniform conversion model, the relationship of regeneration reaction rate and oxygen concentration of the precursor in oxygen atmosphere can be assumed as first order reaction. Shrinking core model was employed to describe the kinetic of oxidative regeneration process of the precursor. The result showed that, when the regeneration conversion rate was less than 80%, the regeneration reaction was mainly controlled by surface chemical reaction. When the regeneration conversion rate was more than 85%, the regeneration reaction was mainly controlled by intra-particle diffusion. According to Arrhenius equation, pre-exponential factor of the apparent reaction rate constant was 1.01 m/s, and the activation energy of chemical reaction was 65.76 k J/mol, the effective diffusivity factor was 1.29×10-3 m2/s, the apparent activation energy of internal diffusion was 43.29 k J/mol. The diffusion process during the regeneration was the lattice diffusion within the solid.