Experimental Study On The Preparation Of Shaped Charcoal By Pyrolysis And Gasification Of Pine Wood Chips Under N₂/CO₂/O₂ Atmosphere

In order to produce high quality biochar briquette with advantage of higher surface area,higher porosity,higher energy density,higher relaxed density and higher durability,the best molded pine sawdust briquettes were selected to conduct pyrolysis experiments in N₂/O₂/CO₂ atmosphere.The experimental results indicated that:?1?The molding process of pinewood sawdust was a physical process.The relaxed density and durability of biochar increased firstly and then didn't change a lot with increasing pressure and temperature.Considering the factors of production cost,the optimum temperature and pressure were respectively 150?and15MPa.?2?In N₂/CO₂ atmosphere,CO₂ can promote the release of volatile and increase the yield of H₂,CH₄ and CO by enhancing pine sawdust briquette pyrolysis and tar cracking.The presence of CO₂ can also reduce the biochar briquette relaxed density and durability,as well as increased the specific surface area and pore structure.Besides,the introduction of CO₂ promoted the fractures of hydroxyl,methyl,methylene,C=C bonds,carbonyl?C=O?,C-O of aliphatic ether bond and ring.The intensity of CO₂ promoting briquette pyrolysis increased with the increase of temperature and CO₂ concentration.At low temperature?400?⁶00??and low CO₂concentration?10%⁶0%?,the promoting effects were not obvious,but were very obvious at high temperature?600?⁸00??and high CO₂ concentration?100%?.According to the comprehensive analysis of energy consumption,CO₂ conversion efficiency and biochar briquette physicochemical properties,it was concluded that the optimal introducing CO₂ concentration and pyrolysis temperature were 10%and600?,respectively.?3?Under condition of N₂/O₂,oxidative pyrolysis can be described as the sum of volatile oxidation,tar oxidation and char combustion.Introducing O₂ can promote the volatile release,tar cracking and char combustion,which reduced the relaxed density and durability,as well as increased the specific surface area and pore structure of biochar briquette.In addition,the increase of O₂ can also reduce the ratios of carbon element content,ash content and oxygen content,which resulted in the decrease of higher heating value and functional groups.An accurate control of pyrolysis temperature and O₂ concentration was good for reducing tars yield and improving biochar briquette surface area.According to the comprehensive analysis of energy consumption,char properties,500?and 6%O₂ were the optimal condition for biochar production.?4?Under condition of 4%CO₂/10%N₂/10%O₂ with 500?and 600?,H₂yield was higher than other atmospheres at the same temperature.However,the yield of tar and biochar briquette were reduced.The comprehensive effects of CO₂ and O₂accelerating pine sawdust pyrolysis and tar cracking were greater than the other condition.In addition,the relaxed density,durability and high heating value of biochar obtained at 500?were higher than that obtained at 600?.However,the specific surface areas of the two chars were very similar.Considering the energy consumption and biochar briquette quality,500?was more suitable for biochar briquette production under mixed pyrolysis atmosphere.