Research On Catalytic Gasification Of Charcoal For Syngas And Syngas Reforming

Syngas is combustible gas with H2 and CO as its main components.At present,coal gasification or natural gas reforming is the most predominant method to produce syngas.However,coal gasification and natural gas reforming have problems with high pollution and high cost.Charcoal is a solid residue of biomass pyrolysis with low volatile content,and producing syngas from charcoal gasification is a technology that has the potential to replace the existing technology for syngas.In this paper,using charcoal as raw material,steam and CO2were used as gasification agents respectively and gasification characteristics of charcoal were studied.The experimental research on charcoal gasification and syngas reforming were carried out based on a two-stage fixed-bed gasification unit.1.Using charcoal as raw material,syngas from charcoal steam catalytic gasification was studied.The effects of catalyst types?KOH,K2CO3,KHCO3,KNO3?,catalyst dosage,steam flow rate and gasification temperature?750°C?950°C?on carbon conversion rate,hydrogen yield,gas composition and H2/CO were also investigate.The method of char absorbing catalyst was used to load catalyst in this paper.The experimental results showed that the four catalysts could improve the gasification efficiency,and the catalytic activity sequence was KOH>K2CO3>KHCO3>KNO3.Both the carbon conversion rate and the hydrogen yield increased with the increase of the concentration of the catalyst solution,when the concentration of catalyst solution was 4 wt%,the carbon conversion rate reached 88%,but the increasing tendency gradually slowed down,so the mass concentration of the catalyst solution was suitably from 4 wt%to 6wt%.Increasing the steam flow rate enhanced the volume fraction of H2 in syngas and boosted the H₂/CO value.When the steam flow rate increased from 0.10g/?min·g?to 0.3g/?min·g?,the volume fraction of H2 rose from 57.17%to 61.03%,and the carbon conversion rose from 53.69%to 97.35%,the CO2 volume fraction grew from 10.54%to 16.96%.When the steam flow rate exceeded 0.20g/?min·g?,the increase of carbon conversion and hydrogen yield tended to be gentle,and the excess steam would consume heat in the furnace,so 0.2g/?min·g?was a suitable amount of water vapor.Increasing the temperature could promote the gasification reaction,and improve the CO composition in syngas and reduce H2 composition.The carbon conversion and hydrogen yield at 950°C were 98.7%and 145.23g/kg,respectively.The H2/CO ratio of produced syngas ranged from 1.53 to 4.09.2.With the usage of the thermogravimetric analysis method,the charcoal CO2 gasification experiment was carried out using asynchronous thermal analyser,and the charcoal CO2 catalytic gasification experiment was carried out in a fixed bed furnace.The effects of experimental temperatures?850??1000??,types of catalyst?KOH,KHCO3,KNO3,K2CO3?on the gasification reaction characteristics and the volume fraction of syngas obtained from gasification were investigated.The experimental results showed that the reaction rate increased rapidly with the increase of temperature.The temperature increased from 850?to 1000?,the volume fraction of CO rose from 25.88%to 56.49%,and the gas production increased from 1.08L to1.89L,and the H2 volume fraction remained at around 8%.The four K metal compound catalysts could improve the CO2 gasification of charcoal and increase the volume fraction of CO in syngas.The catalytic activity sequence was KOH>K2CO3>KHCO3>KNO3.The mixed reaction model was used to describe the catalytic gasification reaction process of charcoal and CO2,from which could derive kinetic reaction parameters.The catalysts of KOH,KHCO3,KNO3,and K2CO3could greatly reduce the activation energy,and the catalytic activity of KOH was the strongest.The activation energy Ea of KOH-impregnated charcoal was 71.90KJ/mol,the pre-exponential factor A was 8.98×10²min^-1,in contrast to 133.63KJ/mol and 4.96×10⁴ min^-1 of blank carbon.The activation energy of the reaction reduced by half.3.A two-stage gasification device was built to investigate charcoal gasification and syngas reforming.The first stage is steam catalytic gasification of charcoal,where the gasification conditions is constant,the temperature was at 850?,and the steam flow rate was 0.2g/?min·g?,2 g charcoal impregnated with 6 wt%KOH solution as material.The second stage of furnace was placed with charcoal,the effects of catalyst types,catalyst dosage,charcoal dosage and temperature on syngas reforming were studied.Experiments showed that C+CO2?2CO was a method to reduce CO2 composition in syngas effectively and converted CO2 into CO.KOH,KHCO3,KNO3,K2CO3 can catalyse effectively the syngas reforming,in which the catalytic performance of KOH is the strongest.When charcoal impregnated with 6wt%KOH solution was used as the reforming raw material,the volume fraction of H2+CO was 96.2%,and the volume fraction of CO2 is 2.71%in produced syngas.The larger the amount of charcoal,the better the reforming effect.Under the experimental conditions,when the amount of charcoal was 16g,the syngas with?H2+CO?volume fraction above 95%and CO2 volume fraction below 3%can be obtained.C+CO₂?2CO is an endothermic reaction,so temperature can promote the reaction to a positive direction.When the reforming temperature was 1000?,the reforming effect was the best,and the CO2 volume fraction could arrive at 2.03%,.?H2+CO?%was 96.91%,and the gas production increased to 8.03L.In this paper,charcoal was used as raw material with K metal compound as catalyst,and the charcoal steam gasification,charcoal CO2 gasification characteristics were studied.Finally,high-quality syngas was produced by two-stage method of catalytic gasification and reforming.The CO2 volume fraction can be reduced to 2%,H2 is about 59%and CO is about 38%,and the calorific value is above 11MJ/Nm³.