Study On Gas-solid Reaction Kinetics Of CO₂ Adsorption In Calcium Looping And The Whole Process Simulation Under Effects Of Sulfation

The large amount of CO₂ emitted by human industrial activities is considered to be the main cause of global climate change.As an effective method to capture CO₂ from large fixed carbon emission sources,CaL（calcium looping）has attracted extensive attention from researchers all over the world.However,the presence of SO₂ in industrial flue gas will lead to the side reaction of sulfation in the process of carbon capture,which will have a very adverse effect on the reaction process and sorption capacity of Ca-based sorbent.In this context,this paper has carried out the experimental and numerical research,aims to investigate the kinetics of cyclic carbonation of Ca-based sorbents under the action of sulfation,and build parallel coupling reaction,the structure evolution and heat/mass transfer process of numerical model,so as to reveal the competitive mechanism of carbonation/sulfation of Ca-based sorbent particles and provide a reference for the industrial application of CaL.In this paper,the sorbent which has undergone several calcination/carbonation cycles under the action of sulfation has been prepared firstly,and the effect of sulfation on carbonation kinetics has been studied.The apparent kinetics model and 3-D diffusion model were used to analyze the chemical reaction-controlled stage and diffusion-controlled stage in the multiple calcination/carbonation cycles.The results show that the carbonation rate constant decreases with the increase of the number of cycles.In the chemical reaction-controlled stage,the activation energy tends to rise,but in the diffusion-controlled stage,the activation energy tends to decline.In addition,the occurrence of sulfation will increase the activation energy of the sorbent and reduce its reaction rate constant.Secondly,a particle model coupling the whole process of parallel reactions,structural evolution and heat and mass transfer was constructed to illustrate the individual contribution and interaction behavior of each reaction in the carbonation/sulfation competition process at the particle scale.In the numerical study,by coupling the carbonation/sulfation reaction,the mass transfer process,the heat transfer process and the structural evolution of the adsorbent particles,the reaction characteristics and rules of the whole process of sorption of the sorbent materials under the action of sulfation were mastered.It is found that in the parallel reaction,sulfation and carbonation compete for adsorption,and the two reactions are divided into two stages:chemical reaction-controlled stage and diffusion-controlled stage.In addition,the carbonation reaction is weakened in the competition,resulting in the decrease of CaCO₃ content.In the radial direction,the solid products increase gradually from the inside to the outside;At the same position of the particle,the formation rate of solid products gradually slows down with time.The porosity is larger near the outside of the particle and smaller near the core of the particle.As time goes on,the porosity decreases slowly.Finally,the effects of reaction conditions and sorbent properties on CO₂ capture process were studied.The results show that the higher concentration of CO₂ and the lower concentration of SO₂ are favorable to the carbonation reaction and inhibit the sulfation reaction.The optimal temperature of carbonation reaction is about 923 K.In terms of particle properties,the initial particle size and porosity are the most important parameters affecting the parallel reaction,which is helpful to the parameter setting of the reactor and the development of Ca-based sorbents with superior performance in CaL.