Research Of Stability And Improvement Of Iron-Based Sorbent

Medium and high temperature desulfurization is regarded as one of the key techniques in poly-generation system based on coal gasification.The price of sorbent for deep removal of sulfur is high and the preparation is complex in the two-step desulfurization technique.In order to reduce the burden of sulfur and operation in the secondary desulfufization of deep removal of sulfur,it should be require to decrease the quantity of sulfur in coal gas into the secondary desulfurization and increase the physical stability and the sulfur capacity of sorbent in the primary desulfurization.In the past years,mixed-metal oxide containing iron with the high sulfur capacity,the high reactivity and low price is considered as one of the most favorable sorbents for high temperature desulfurization.However,the stability and life of iron-based desulfurizers are still the main difficult problem existing in the hot gas clean-up techniques.This paper mainly studied the effects of different auxiliary to the physical stability, the capability of removal sulfur and the sulfur capacity of iron-based sorbent.In the primary experiments,there are obtained that the calcium oxide does not affect the physical stability,and is also not effect to the sulfur capacity and the desulfurization efficiency;zinc oxide is positive to the deep removal of sulfur,but is negative to the physical stability;silicon dioxide,cerium oxide and magnesium oxide are active to improve the deep removal of sulfur,especially, the magnesium oxide is active to increase the sulfur capacity and they are not affect the physical stability.Experimental results in the fixed-bed reactor without sorbent show that the COS comes from the reactions:H₂S+CO→H₂+COS and H₂S+CO₂→H₂O +COS.H₂S,CO and CO₂ in the reactive gas have obvious contribution to the formation of COS,while H₂,H₂O in gas decreases the formation of COS and and the temperature increasing is also negative for the formation of COS.Effects of composition of feed gases,reactive temperature for sulfidation experiments on the physical degradation of ZF sorbents with different zinc oxide content were studied in detail.The results show that the degree of physical degradation increase with the quantity of zinc oxide in sorbent increase;zinc ferrite from the zinc oxide and iron oxide reduces the resistive-reduction capability of iron-based sorbent;the CO together with H₂ in the mixed gases for sulfurization results in the instability of the ZF sorbent.The composition in the outlet and the XRD results indicate that the reaction:CO+H₂→C+H₂O and C + 2H₂→CH₄ and the formation of Fe_1-xC are the factors influencing the physical degradation of iron-based sorbent.The physical stability of sorbent could be also improved by decreasing the sulfidation temperature and increasing the calcination temperature. Results of steam content in coal gas,sulfidation temperature and regeneration temperature influencing on the desulfurization properties of sorbent M3F with different magnesium oxide content and sorbent MFT with different titanium dioxide content show that the better physical stability and deep remove of sulfur and high sulfur capacity of the sorbent MF;it could remove also the COS,the ability of deep removal of COS decreased with the sulfidation temperature increasing from 723K to 873K;the sulfur capacity of the sorbent MF increases with the quanlity of magnesium oxide increased;the existence of steam in coal gas is negative to the deep removal of H₂S and the sulfur capacity of sorbent;the regeneration temperature of 873K is optimal;the titanium dioxide is active to improve the primary reactivity and the capability of removal of COS,and reduce the reactive sulfidition temperature.A spot of of zinc in coal may transfer into coal gas could affect the physical stability of iron-based sorbent.