Study On Activity And Life Of Char Catalyst For Tar Removal

Biomass gasification is one of the most effective ways of biomass energy utilization.However,the tar produced in the process of biomass gasification is regarded as the main bottleneck in the thermochemical utilization of biomass energy,which restricts the commercialization of biomass gasification technology.Among the methods of tar removal,catalytic cracking is considered to be the most promising one in large-scale applications because of its rapid reaction speed,high reliability and increasing the amount of available gas.The char catalyst has been widely concerned because of its low price,high resistance and good catalytic effect.Based on the technology of char catalyst for tar removal,the selection of typical char catalysts and the deactivation characteristics of active char catalysts are studied.The mechanism of char physical and chemical properties to tar removal activity in inert atmosphere and the formation law of coke deposition in the process of activated char deactivation are revealed.The relationship between char combustion characteristics and tar removal activity is discussed.The specific research content and conclusions are as follows:(1)Straw were used as the tar raw material,graphite,Zhundong coal char and sawdust biochar were used as the catalyst,and the key factors affecting the activity of char catalyst for tar removal in inert atmosphere in a fixed bed/fluidized bed reactor were studied.It was found that the best removal effect was 800? sawdust biochar.The effect of tar removal at low temperature char-making sawdust biochar was reduced in varying degrees in 800?,but the 700? sawdust biochar with better reaction activity and low preparation cost,which was considered more promising in the paper.The influence of the physicochemical properties of char catalyst on its tar removal activity is the result of joint action.In this paper,it was found that the pore structure and the degree of aromatizationhas were the most critical influence on the tar removal activity of char catalyst in the inert atmosphere.(2)The improvement of sawdust biochar were activated by 15 vol.% H2 O.The tar removal experiment under the condition of 800? and Ar atmosphere was carried out with the active sawdust biochar at different gasification time.The results show that the improvement of H2 O gasification time on the sawdust biochar first increases and then decreases.This process is from activation to overgasification,with the loss of mass.The best removal effect came to 30 min.The activity of active sawdust biochar was continuously declining during the continuous contact with tar,and the rate of decline decreased from slow to fast.After 75 min,the activitied sawdust biochar was completely inactivated.The process of deactivation mainly manifests in the deposition of coke on the surface area of the sawdust biochar.Firstly,the reforming and adsorption of tar are carried out at the same time,then only the adsorption of tar.The deposition mode of coke begins to accumulate on a single particle,eventually covering the surface of the whole sawdust biochar particles,and the structure of coke deposition is gradually moving toward graphitized structure.(3)The combustion characteristics of char catalysts in the microfluidized bed reaction system were studied.The results showed that different types of char catalysts exhibited the same pattern in terms of combustion activity and tar removal activity,ie sawdust biochar > Zhundong coal char >Graphite.The adsorption of tar causes the coke surface to initially form a carbonaceous material with high combustion activity.As the adsorption amount of tar increases,the degree of graphitization gradually increases as coke accumulation increases.It was found that combustion activity can be used to approximately characterize the tar removal activity of different types of coke catalysts and the deactivation characteristics of coke catalysts of the same kind.