| Bioenergy has been seen increasingly as a renewable and clean energy source.Fast pyrolysis-a rapid decomposition of organic materials in the absence of oxygen-has many advantages.It is a relatively simple process,rarely affected by the environmental conditions,has a high energy conversion rate,is CO2/GHG neutral without SOx emissions.To produce bio-oil as a renewable fuel replacement and as a source of chemical commodities,a fast pyrolysis reactor has to be designed and operated to meet the requirements for high yields of liquid fuels.And the research on mechanism of fast pyrolysis has drown much attention.In this study,a lab-scale catalytic pyrolysis unit with the feeding rate of 100-500 g/h was designed and manufactured with a fluidized bed reactor.The process and operation method of the unit were introduced in detail.Then,the effects of reaction temperature,the amount of catalyst and the location of catalyst on the pyrolysis products were investigated.Subsequently,the mechanism of biomass pyrolysis was studied.A commercial-scale biomass fast pyrolysis plant,based on downdraft circulating fluidized bed technology with biomass throughput of 1-3 T/h,has been developed for bio-oil production and its performance has been investigated.This work could provide a valid reference and technical support for biomass fast pyrolysis and bio-oil potential utilization.A lab-scale catalytic pyrolysis unit with the feeding rate of 100-500 g/h was designed and manufactured with a fluidized bed reactor.The feed rate of the lab-scale catalytic pyrolysis unit is 100-500 g/h.And the inner diameter of reactor is 40 mm and the height is 550 mm.The medium of fluidization is quartz sand.The quality of quartz sand is 150g and the bed pressure drop is 11.7 Pa.It consists of eight systems:feed system,reactor system,cyclone separation system,catalytic system,condensation system,gas detection system,gas collection system and control system.It has two-stage screw feeding system,three-stage condensing system?water cooling,electrostatic condensation and dry ice/acetone condensation?.The operation of the device is very simple.The feeding rate is accurate and continuous.The device can be used in conventional pyrolysis and catalytic pyrolysis experiment research.In the operation research of the lab-scale biomass catalytic pyrolysis unit,four temperature gradient?400oC,450oC,500oC and 550oC?were chosen to evaluate the effect of temperature on pyrolysis products.Then,the influence of catalyst on thermal cracking was investigated at 500oC,and three catalyst weight gradients?0 g,2 g and 4g?were selected.Finally,the influence of catalyst location on thermal cracking was investigated.The results showed that the zeolite catalyst had a great influence on thermal cracking,and the peak time and height of the Py-GC/MS spectrum have been changed.In conventional pyrolysis,the peak of Py-GC/MS spectrum was at 34.76 min?2,3-Dihydrobenzofuran?.In catalytic pyrolysis,the peak of Py-GC/MS spectrum was at 20.95 min?3-Methoxyphenol?.With the pyrolysis temperature increasing,the variation trend of water content and pH were identical,which decreases first and then increases.The variation trend of ash content,HHV,solid content and viscosity were identical,which increases first and then decreases.The minimum value of the water content of bio-oil samples was 13.39±0.22%under 550oC.The maximum value of the HHV was 23.95±0.55 MJ/kg under 450oC.The catalyst can significantly increase the water content of bio-oil and reduce the ash content,HHV,solid content and viscosity of bio-oil.The HHV was 23.61±0.3 MJ/kg under 500oC without catalyst.The HHV was 22.16±0.39 MJ/kg under 500oC with 2 g catalyst in fluidized bed reactor.The HHV was 18.97±0.40 MJ/kg under 500oC with 2 g catalyst in caltaytic fixed bed.The mechanism of biomass pyrolysis was studied.The biomass structure was dramatically changed after the process of torrefaction?a mild thermolysis process?.High temperature had more effects on sawdust than rice husk,for in 280-300°C the weight losses were 27.72%and 18.33%for sawdust and rice husk,respectively.In addition,energy yield of sawdust was more affected by the process of torrefaction for the energy yields were 77.63%and 89.38%for sawdust and rice husk at 280-300°C,respectively.After torrefaction in 280-300°C,HHV of the sawdust increased from20.84 to 22.38 MJ/kg and that of the rice husk increased from 17.07 to 18.68 MJ/kg.The significant mass loss was associated with the decomposition of hemicellulose.Through Py-GC/MS analysis,the pyrolysis mechanism of biomass to bio-oil was summerized as follows.The cellulose,hemicellulose and lignin were firstly pyrolyzed to monomers:glucose,galactose,mannose,xylose,arabinose,guaiacol,hydroquinone and eugenol.Then some chemicals were produced from these monomers through a series of reactions:isomerization reaction,dehydration reaction,retro-aldol reaction,esterification,carbonyl reaction and so on.In catalytic pyrolysis,the active site of catalyst acts as deoxidizer.Hydrocarbon radicals'pool was formed through monomers thermal cracking.Then some relatively stable chemicals were formed through reactions among those radicals.A commercial-scale biomass fast pyrolysis plant,based on downdraft circulating fluidized bed technology with biomass throughput of 1-3 T/h,has been developed for bio-oil production and its performance has been investigated.The commercial-scale biomass fast pyrolysis plant consists of six parts:a feeding system,a heat carrier system,a reactor system,a cyclone system,a condensation system and a carbon separating system.The plant has four circulation systems:circulation of a heat carrier,quenching materials?bio-oil?,cooling water and non-condensable gas.The exhaust gas from a vertical bed was used as drying gas to remove moisture from the rice husk under the temperature of 180oC to meet the pyrolysis requirement with the exhaust gas flow rate of 18,000 m3/h.The biomass throughput was 1-3 T/h.The consumption rate of bio-oil was 400 kg/h.The consumption rate of non-condensable gas was 350 m3/h.The bio-oil,raw material?rice husk?,char and non-condensable gas samples were analyzed using GC-MS,FTIR and SEM to characterize the physical properties and chemical composition.Results showed that the operation of the plant was stable.At 550oC,the highest yield of bio-oil obtained was 48.1%with char,and non-condensable gas yields of 26.0%and 25.9%,respectively.GC-MS results revealed that the composition of the bio-oil was complicated and the most abundant compound category was phenolics?14.92%?.The char had complex pore structure by SEM analysis,which can be collected as a resources for further comprehensive utilization.The operation stability of the commercial-scale fast pyrolyzers was investigated.Bio-oils from 27 independent runs under 550oC were analyzed.The thermal properties of the feedstock?rice husk?,dust?separated from feedstock?,char and heat carrier were analyzed and the bio-oil properties such as water content,pyrolytic water content,viscosity,density,pH,heating value,solid content and ash content were analyzed and presented.The thermal resistance of the heat carrier?ceramic balls?was 481.7±0.5 oC·cm/W which is much lower than that of rice husk?796.6±6.5 oC·cm/W?.The specific heat capacity of the heat carrier?1.363±0.023 MJ/?m·K??was nearly twice of that of rice husk?0.755±0.017 MJ/?m·K??,which proves that the ceramic balls are excellent heat transfer medium.The quality of the produced bio-oil meets the pyrolysis liquid biofuels standards in ASTM D7544-12 for Grade G biofuels,except for the water content of the bio-oil,which is slightly higher than that of Grade G biofuels.In energy balance analysis,the potential recovered energy of the three main products was 8.0±1.1,2.1±0.1 and 5.3±0.7 MJ/kg for bio-oil,char and non-condensable gas,respectively,which shows that the largest portion of the energy in biomass was recovered in the bio-oil.In summary,two biomass pyrolysis process were established in this study:a lab-scale catalytic pyrolysis system with the feeding rate of 100-500 g/h and a commercial-scale biomass fast pyrolysis plant with biomass throughput of 1-3 T/h.The two system can be operated in stable with high quality bio-oil production.This work could provide a valid reference and technical support for biomass fast pyrolysis and bio-oil potential utilization. |
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