| In recent years,with the wide application of dry bag dedusting technology in Blast Furnace Gas(BFG),a series of serious acid corrosion problems have generally appeared in the downstream gas transportation pipe network region.These corrosion problems caused by the trace amount of HCl and H2S in BFG gas mainly include:corrosion perforation of transportation pipeline,salt deposition and scaling on TRT(Blast Furnace Top Gas Recovery Turbine Unit)blade,poisoning and deactivation of noble metal catalysts,cracking of refractory brick in hot blast stove,etc.At present,the passive protection as TRT blade passivation treatment and wet deacidification after TRT are selected for anti-corrosion treatment,with relatively limited deacidification effect and high cost.For this,we put forward a novel idea of total dry-method dechlorination and desulfurization for selective removing acid gases and purification BFG from the source.In this thesis,the dry-type low-temperature dechlorination and desulfurization adsorbents with excellent performance,low cost and high selectivity was prepared basing on physical and chemical modification of porous carrier and composite multi-component treatment.And the mechanisms of adsorption reaction and kinetic on capturing HCl and H2S over porous agents were systematically studied,in order to lay a theoretical foundation and provide technical reference for the low-temperature purification of industrial gas.Firstly,the sodium based porous network fiber structure dechlorination agent was prepared by alkali impregnation modification of activated alumina balls,and its physicochemical properties and low-temperature dechlorination performance were systematically characterized and analyzed.The results showed that a preliminary high efficiency dechlorination performance was achieved over the alumina supported Na2CO3 fiber adsorbent for removing high concentration HCl at 150℃.The optimal dechlorination performance was obtained with 20 wt%Na2CO3 loading,corresponding with breakthrough HCl capacity and conversion up to 3.56mmol/g and 0.98,respectively.Secondly,in order to enhance the low temperature dechlorination selectivity and deep dechlorination performance of Na-based adsorbent,metal oxides(Fe,Mn,Ce and Cu)nanoparticles supported on the Na2CO3 fibers were firstly prepared via ultrasonic atomization loading method,respectively.The dechlorination results indicated that the composite of CuOx provided an excellent enhancement effect on capturing trace HCl by Na2CO3 fiber.The deep dechlorination time and breakthrough time increased by 330%and 50%,respectively,and the conversion of Na2CO3 increased to 0.89.After three times of dissociation regeneration cycles,the dechlorination agent can maintain the 90%of initial dechlorination performance,indicating an excellent regeneration performance of the adsorbents.Then,the influencing factors and reaction kinetics mechanism of dechlorination process were systematically explored.The random pore model could accurately describe the dechlorination process.The overall reaction rate in first stage was controlled by interfacial chemical reaction,and the later stage was dominated by gas diffusion in the product layer,and the corresponding apparent diffusion activation energy was 23.11 kJ/mol.The mechanism of synergistically enhancing dechlorination of Na2CO3 by compositing CuOx could be explained as following:highly dispersed CuO nanoparticles exposed adsorption sites for rapid capture HCl molecules,and the reaction product CuCl2 acted as the new active centers to promote the reaction activity of Na2CO3;the amorphous phase transition zone at the Cu-Na interface accelerated the gas phase diffusion mass transfer,and finally realize the synergistic efficient dechlorination.Thirdly,a ribbon-like basic copper carbonate precursor supported on the activated semi-coke(ASC)was successfully synthesized in situ by hydrothermal method,and the graded porous composite desulfurizer was obtained after calcination.The selective depth removal of H2S was realized at low temperature(150℃),anaerobic and drying conditions by adjusting calcination temperature,copper loading amount and zinc composite loading amount.The optimal breakthrough H2S capacity reached 126 mg/g,and the conversion rate of desulfurizer was over 0.72.The kinetics of desulfurization process follows:before the conversion rate reached 0.5,the overall reaction rate was controlled by chemical reaction;then,the diffusion in the product layer replaced as the speed-limiting step.The corresponding diffusion apparent activation energy was 19.09 kJ/mol.Through the comprehensive analysis of the surface chemical properties and morphology and structure characteristics of desulfurizer,it was found that:the graded porous structure,highly dispersed active CuO,Cu-Zn composite structure and riched oxygen defects created favorable conditions for the low-temperature anaerobic selective desulfurizationIn addition,the adsorption breakthrough curves of the above two kinds of dechlorination and desulfurization materials were numerically fitted by adopting the Bohart-Adams model,and the prediction error was controlled within 4%and 2%respectively,which indicated that the model could be applied to accurately predict the breakthrough curve of acid gases adsorption process in fixed bed reactor.It provides a theoretical reference for forecasting the effective life of adsorbents in industrial scale gas-cleaning.Finally,the simultaneous dechlorination and desulfurization performance was tested based on the above two kinds of composite materials,and the reasonable style of composite packing was further explored.When packed alone,it can be found that simultaneous desulfurization and dechlorination can’t be achieved alone by CuOx composited Na2CO3 adsorbent(Cu@Na)or ASC supported Cu-Zn adsorbent(Cu@ASC).Therefore,through the composite packing and adjusting the packing mode,it was found that the mixed uniform packing was the best packing mode,which ensured the most effective residence time of the mixed gas.The simultaneous removal of HCl&H2S can be successfully realized when the mass ratio of Cu@Na to Cu@ASC was 7:3,and the maximum breakthrough capacity was 2.63 mmol/g and 105 mg/g,respectively.In addition,among the simultaneous dechlorination and desulfurization process,reaction temperature and CO2 concentration showed a slight impact,while the existence of water vapor contributed to a higher adsorption capacity.In general,the dechlorination desulfurizer showed high stability in the complex mixed gases stream of HCl/H2S/CO2/N2/H2O.In this work,the prepared porous composite materials exhibit excellent synergistic dechlorination and desulfurization performance under low-temperature anaerobic drying conditions.These adsorbents with simple preparation process and low cost have a potential industrial development and application prospect in the field of selective deep removal of HCl and H2S at low temperature. |
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