| The sulfur contained in coal will be transferring into the synthesis gas during gasification process,resulting in problems such as catalyst poisoning,equipment and pipeline corrosion and environment pollution.Therefore,desulfurization must be done before the utilization of gas.As a technology for coal gas desulfurization,dry desulfurization has been widely employed in deep desulfurization and fine removal of various sulfides in different operating conditions.It has the advantages of simple operation and small footprint,as well as high thermal efficiency.However,although there are a lot of manpower and materials have been invested into the research of high temperature coal gas desulfurization,some technical problems,such as easy agglomeration of active component,sintering of desulfurizer internal structure,poor stability and low mechanical strength of desulfurization sorbents in the repeatedly desulfurization and regeneration cycles still making the industrialization road of high temperature coal gas desulfurization technology full of thorns.Therefore,preparing a hot coal gas desulfurization sorbent with good desulfurization performance and excellent cycling stability has far-reaching significance for coal desulfurization technology and China's energy strategy.As a non-ionized electromagnetic energy,microwave has the characteristics of fast heating,volume heating and special non-thermal effect.Compared to the traditional heating method,the desulfurization sorbent prepared by microwave solid state method not only has a short processing time,but also has the merits as simple processing,convenient operation,controllable control and low in the pollution of the environment.Based on this,this paper focuses on the study and comparison of microwave and conventional solid state method in the preparation process of iron oxide based sorbents.The influence of active component content,calcination temperature and time on the desulfurization performance,pore structure and stability of desulfurization sorbent curing properties have also been investigated.By taking the initial sulfur capacity and mechanical stability as desulfurizing sorbent evaluation indexes,optimizing the preparation method and processing conditions through the association the structure parameters and the performance of desulfurization sorbent;with the second sulfur capacity and regeneration rate as the indexes,the regeneration conditions of desulfurization sorbent under oxygen were optimized and the desulfurization-regeneration cyclic performance was also tested.In addition,the simulation models based on desulfurization and regeneration processes were established.Through the COMSOL Multiphysics simulation,the mechanisms of H2S removal and regeneration of desulfurization sorbent were clear from the view of theory.Specific conclusions are as follows:?1?Iron oxide desulfurizer was prepared by microwave solid state method.The effects of the content of active component,calcination temperature and calcination time on the performance of iron oxide desulfurizer were investigated.When the amount of active component Fe2O3 is 30%,the desulfurizer has the largest specific surface area of 27.605 m2/g,the total pore volume of 0.0736cm3/g and the average pore size of 13.487 nm,along with the best desulfurization performance.With the increase of calcination temperature from450°C to 600°C,the pore structure parameters of desulfurization sorbent continue decreasing,while the sulfur content increased firstly and then decreased.Combined with the desulfurization performance,the best calcination temperature under microwave for desulfurizer preparation of is 500°C,with the best desulfurization performance and strength stability of sorbent.The calcination time also plays an important role in the calcination process of desulfurizer.The specific surface area,pore volume and average pore size of sorbent calcined for 0 min were 27.846 m2/g,0.0771 cm3/g and 13.522 nm,which respectively reduced to 25.814 m2/g,0.0683 cm3/g and 12.648 nm of sorbent calcined at 30 min,however,the mechanical strength of sorbent was found increased with the extend of calcination time.Through the comprehensive analyses,it is concluded that when the microwave calcination time is 10 min,the sorbent has the best desulfurization performance.In summary,the optimum conditions under microwave solid state method are 30%of active component,500°C of calcination temperature and 10 min of calcination time.?2?The differences have been compared in two methods under the same conditions that were measured before:the desulfurizer prepared by microwave showed better mechanical stability time and longer breakthrough time than that of conventional prepared sorbent;for the sorbent prepared by microwave heating,XPS analyses showed that the percentage of lattice oxygen was higher than that of conventional sorbent,which is beneficial for the adsorption and reaction of H2S;SEM and BET results exhibited that the sorbent under microwave heating has smaller particle size and the pore structure is more abundant with uniformly dispersed active components;XAS results implied that the desulfurizer prepared by microwave has a larger degree of desulfurization along with smaller particle sizes before and after desulfurization.The desulfurization kinetics showed that pre-exponential factor ks00 of reaction rate constant upon desulfurizers by microwave and conventional preparation is2.20×10-2,1.60×10-2 m2/s,the chemical reaction activation energy Ea is 12.64,13.72 kJ/mol;the effective diffusion coefficient of the pre-exponential factor De0is 3.46×10-3,8.63×10-4 m2/s,the diffusion activation energy Ep is 19.28,24.28kJ/mol,respectively.The activation energies of chemical reaction and internal diffusion of microwave calcination desulfurizer both are lower and the diffusivity of internal diffusion is higher,impling that it has higher activity for removing of H2S.?3?The regeneration conditions?regeneration temperature,oxygen concentration and space velocity?of iron oxide desulfurizer for high temperature gas were investigated,and the cyclic performance of iron oxide desulfurizer was tested.When the regeneration temperature was in the range of 550-700°C,the regeneration rate first increased and then decreased with the increment of temperature,and the regeneration rate of 550°C was the lowest,which was about 94.8%,and the highest regeneration rate was 99.1%at 650°C.Kept on increasing regeneration temperature,the regeneration rate of desulfurizer decreased to 97.7%.In this experiment,the increase of space velocity led the regeneration rate and the second sulfur capacity climbed up initially and second decreased.When the gas velocity was 1000 h-1,the regeneration rate was 93.7%;while the velocity was 3000 h-1,the regeneration rate reached 99.1%and the sulfur capacity up to 11.06 g sulfur/100 g sorbent;when the space velocity was greater than 3000 h-1,the regeneration rate and the sulfur capacity decreased.The regeneration reaction is exothermic,the runaway of bed temperature and the probability of desulfurizer sintering will be greatly improved along with the increment of oxygen concentration.The combined analyses of regeneration rate and penetration performance showed that the optimum concentration of oxygen for regeneration is 4%.In summary,the best regeneration temperature,O2content and space velocity for iron oxide desulfurizer is 650°C,3000 h-1 and4%,respectively.In the process of multiple desulfurization regeneration cycles,although the desulfurization performance gradually decreased,iron oxide desulfurizer showed good reusability.It is found that the decreased desulfurizer performance can be attributed to the decrased reactivity of active component and deterioration of pore structure as well as the accumulation of by-product Fe2?SO4?3.The regeneration kinetics implied the reaction rate was limited via surface chemical reaction at first,and then transferred to internal diffusion control at later stage.The chemical reaction rate constant of the pre-exponential factor ks0 and the activation energy Ea is 1.10×10-2 m/s and 12.89 kJ/mol,respectively;the effective diffusion coefficient of the pre-exponential factor De0is 3.57×10-3 m2/s,the diffusion activation energy Ep is 61.19 kJ/mol.?4?Through the establishment of multi-physical field coupled numerical calculation model,the desulfurization and regeneration process of high temperature gas desulfurization sorbent under actual conditions were simulated and compared.The results showed that:COMSOL Multiphysics transient simulation showed that the desulfurization and regeneration of iron oxide sorbent fitted the unreacted shrinking core model from the angle of theory,which is a process that is“outside to inside”and a substitution between iron oxide and sulfide.Numerical results from the simulated model showed that COMSOL Multiphysics can accurately predict the desulfurization and regeneration process,which has the power to provide a convenient alternative process for some chemical processes that are complicated,time-consuming and high cost,and is of great help to save time and cost of scientific research. |
PDF Full Text Request