Study On Process Simulation Of Producing Polyol Fuel Via Oriented Pyrolysis Of Biomass And Full Life Cycle Carbon Footprint

Biomass is the only source of organic carbon,and the only multi-functional renewable resource that can be converted into fuels,chemicals and functional materials to replace the fossil resources.Biomass fast pyrolysis is regarded as one of the most potential options to convert biomass into the liquid fuels.However,the poor physicochemical properties of bio-oil seriously hinder the application of bio-oil.At present,most of the research focuses on the microcosmic aspects of biomass pyrolysis reaction mechanism,the catalyst design for upgrading bio-oil,the reaction mechanism of catalysts,the deactivation and the modification of catalysts.There is a lack of comprehensive and systematic research on the macroscopic aspects including the overall process system design of bio-oil upgrading,the system performance and the environmental benefits of the bio-based products.Under the framework of the technology of producing the oxygen-containing liquid fuels via biomass thermochemical conversion from our research groups,a polygeneration process system of biomass thermochemical conversion has been developed taking hydrogen gas and the bio-based polyol fuel as the target products.This system integrates biomass fast pyrolysis,the iron-based oxygen carrier chemical-looping hydrogen production?CLHP?using non-aqueous phase bio-oil?NAPB?as fuel with supercritical methanol esterification?two-stage low and medium temperature catalytic hydrogenation of aqueous phase bio-oil?APB?.This research focuses on the macroscopic aspects of the optimization of the chemical process system integration,the system function realization and the environmental performance assessment of the process system.Its aim is to objectively evaluate the comprehensive performance of the biomass thermochemical conversion system,optimize the design of the key technologies and provide the necessary basis and information for the future engineering demonstration.Based on the theory of the energy cascade utilization,the layouts and the key parameters of the entire process system have been designed optimally.On the basis of the identification of the characteristics of the key reaction processes and the determination of their process models,the whole process simulation and the optimized configuration of the process parameters have been implemented using Aspen Plus software.The self-balance of the thermal load of the fast pyrolysis reactor of biomass and the fuel reactor of the CLHP subsystem have been respectively achieved by means of the heat carrier circulation,meanwhile the self-heating and the partial electricity replacement of the process system have been realized by optimizing the waste heat utilization of the whole system.Under the conservative assumption conditions,a detailed set of parameters of the mass flow,the energy flow and the thermal conditions have been obtained.The carbon metabolism analysis of the process system taking the product flow as the main line indicates that the conversion ratio of the APB to the polyol fuel is a key factor affecting the performance of the entire process system.According to the calculation models of the system evaluation indicators established,some important parameters have been obtained,including 55.8 wt%of the anhydrous bio-oil yield,16.4 wt%of the polyol yield and 11.5 wt%of the esters yield based on the dry basis of corn stover,56.8%of the hydrogen thermal efficiency,58.1%of the total thermal efficiency and about 99.9%of the CO₂ capture efficiency in the CLHP subsystem,and 35.5%of the total system energy utilization efficiency.Even under the condition of the lower yield of the polyol fuel?16.4 wt%?,the polygene ration system of biomass thermochemical conversion still has a significant competitive advantage over the industrialized biomass direct-fired power generation technology.Besides H₂ and the polyol fuel,there is also a by-product of bio-based esters replacing the petroleum-based chemicals to reduce the consumption of the fossil raw materials,and the high-efficient capture of CO₂ in the CLHP subsystem brings significant environmental benefits of reducing greenhouse gas?GHG?emission.Based on the method of life cycle assessment?LCA?and the localization basic data of China,the calculation models of the LCA indicators for the means of production,the energy sources and the target products of the product system have been established in turn and the complete life cycle data inventories for the target product have been compiled.The hybrid allocation methods are utilized to deal with the intricate multi-product co-production of the biomass thermochemical conversion system and the quantitative research on the life cycle fossil energy input intensity?FEI?and the carbon footprint for the target products have been performed.The life cycle FEI and the net carbon footprint of H₂ are 0.575 MJ/MJ H₂ and-97.5 gCO_2,eq/MJ H₂,respectively and those of the polyol fuel are respectively 0.626 MJ/MJ energy output and 26.3 gCO_2,eq/MJ energy output.As for H₂,the electricity consumption of NAPB production and biomass pretreatment and the nitrogen fertilizer consumption are the main factors causing GHG emission,and CO₂ capture during H₂production is a key factor determining the carbon footprint.Concerning the polyol fuel,the factors resulting in GHG emission mainly include the electricity consumption of APB production and biomass pretreatment,the methanol consumption,the catalyst loss and the energy consumption used for the organic wastewater treatment during the polyol production,while the carbon credit caused by the consumption of H₂ from the CLHP technology plays a role in reducing the carbon footprint of the polyol fuel.Sensitivity analysis on the carbon footprints of H₂ and the polyol fuel are separately performed via changing the parameters within a prescribed range?±25%?.The sensitivity analysis results indicate that the change in the electricity consumption for NAPB production obviously influences on the carbon footprint of H₂,meanwhile the polyol yield and the electricity consumption of APB production have a greater impact on the carbon footprint of the polyol fuel.It indicates the data uncertainties of the electricity consumption of bio-oil production and the polyol yield significantly influence the results of LCA.It also means that the carbon footprint of the polyol fuel will obviously go down if reducing the electricity consumption of bio-oil production and increasing the polyol yield.Compared to the technologies of natural gas steam reforming?SMR?and coal gasification?CG?for H₂production,the iron-based oxygen carrier CLHP technology using NAPB as fuel makes the net carbon footprint of the polyol fuel reduce by 70.5%and 77.5%,respectively.The obvious GHG emission reduction is mainly due to the bio-based fuel used and high-efficient CO₂ capture in the CLHP subsystem.From the perspective of the polyol fuel,the energy credit and the carbon credit generated by the surplus H₂ substituting for H₂ from SMR can make the fossil energy consumption and the carbon footprint of the polyol product decrease by 66.3%and 325.9%,respectively,two life cycle indicators of which are separately 0.211 MJ/MJ energy output and-59.4 gCO_2,eq/MJ energy output.Based on 1MJ energy replaced,the substitution of the polyol fuel for the petroleum-based gasoline and petroleum-based diesel can respectively lower the fossil energy consumption by 82.0%and 83.8%,and the GHG emission by 163.9%and 155.8%,respectively.The LCA research cases of the bio-based liquid fuels from the different technologies show that the polygeneration process system of biomass thermochemical conversion designed in this study has comprehensive competitive advantages in the multi-purpose utilization of the biomass carbon element,the target product yields,and the GHG emission reduction.In summary,this process designed for producing the polyol liquid fuel via biomass oriented pyrolysis has the characteristics of the mild reaction conditions,the controllable hydrogenation depth and hydrogen gas self-sufficiency,and the multi-product conversion has been realized from biomass to the polyol fuel,hydrogen gas and the esters chemicals.In the perspective of the product life cycle,the process system has lower fossil energy input and significant GHG emission reduction,which accords with the sustainable and low-carbon development requirements in the conversion and utilization of biomass.