Study On Gas Production From Nickel Loaded Biochar Catalyzed Sludge Steam Gasification By Mechanical Ball Milling

The efficient utilization of biomass has always been a hot issue for the majority of scientific researchers,among which sludge as a biomass resource is also concerned.Using sludge gasification to produce high-quality hydrogen-rich gas can not only reduce and harmless sludge,but also realize energy recovery.However,the tar produced by gasification will reduce the efficiency of biomass gasification,and will cause serious impact on the gasification system and environmental pollution.As a material with developed pore structure,biochar is not only a good catalyst carrier,but also can enhance tar cracking and promote gas production.In order to reduce the influence of tar and improve the efficiency of sludge gas production,a mechanical ball milling method was introduced to combine biochar with nickel base as catalyst to catalyze sludge gas production.In order to improve the quality of syngas,the effect of sludge on the formation of syngas was studied in the aspects of different biochar,gasification process parameters（milling time,gasification temperature）and material ratio（Ni based loading rate and water vapor flow）.The influence mechanism was analyzed by FTIR and XRD characterization of catalyst and solid residue after gasification.The main research contents and conclusions are as follows:（1）NiO loaded with coal char,straw char and sludge char can significantly promote sludge gasification,and the gas production effect is significantly improved.The volume fraction of H₂ in NiO loaded sludge char catalytic sludge gasification reaches 45.15%of the maximum,the total volume fraction of combustible gas reaches 79.97%,and the H₂/CO of syngas also reaches 1.98;that is to say,the quality of syngas is the best among three kinds of biochar,the hydrogen ratio（H₂/CO）and hydrogen yield increased by 209%and 54.5%respectively,and the volume fraction of H₂ increased by 15%.The functional groups on the surface of NiO loaded biochar synthesized by mechanical ball milling are helpful for sludge gasification and gas production.In the process of catalytic cracking,C in the carrier of bio coke participates in the reaction,CO and H₂ in the syngas form a reducing atmosphere,NiO is reduced to metal Ni,which in turn promotes tar cracking.（2）When the sludge coke is loaded with NiO,the treatment time of mechanical ball milling is 10min,the gasification temperature is 900℃,and the flow rate of water vapor is 1g/min,the effect of sludge gasification is the best,among which the gas yield,H2 yield,sludge low calorific value and carbon conversion rate are 0.76 m³·kg^-1、0.34 m³·kg^-1、8646.7 k J·kg^-1、64.69%,respectively.（3）With the increase of ball milling time,NiO can disperse evenly on the surface of sludge char,promote sludge decomposition and tar secondary cracking,increase gas production rate and H₂ production rate,and improve gas production effect and quality.However,if ball milling time is too long,the material in sludge char will be lost,and the carrier structure of sludge char,especially the crystal structure of Si O₂,will be damaged,which will affect the nickel based load When the gasification temperature of sludge increases（500-900℃）,the decomposition reaction of sludge such as deacidification and dehydroxylation is strengthened,which is beneficial to the reaction of refractory substances in sludge,volatile gas released.The gas production effect is obviously increased,and the indicators of gasified syngas are basically on the rise.（4）With the increase of NiO loading rate of sludge coke,the gasification gas yield,H2yield,low calorific value and H₂/CO of sludge increase first and then decrease.The main reason is that when NiO loading amount reaches a certain degree,with the increase of loading amount,excessive NiO will cover some active sites on the biochar,and may also block the sludge coke channel,resulting in particle agglomeration and impact The homogeneous dispersion on the surface of semicoke will weaken the catalytic effect of negative nickel semicoke,which will easily lead to serious carbon deposition and reduce the catalytic sludge effect of catalyst.The increase of water vapor flow has the obvious effect of strengthening sludge gas production.It continuously reacts with coke to generate gas and improve the carbon conversion rate of sludge.The gas production rate shows an upward trend.However,too much water vapor will consume the heat of the system.Excessive water vapor will cause the decrease of H₂ volume fraction.When the water vapor flow rate is 1 g/min,the H₂ volume fraction reaches the highest value of 45.14%.