| The biorefining technology converting the lignocellulosic biomass into biofuels or bulk chemical has been entered the commercialization stage.While,there is still huge space for its large-scale industrialization production.Dry dilute acid pretreatment and biodetoxification(DryPB)biorefining process is a high-efficiency biochemical conversion technology with the advantages of extreme low usage of fresh water and energy as well as low wastewater generation.A series of "dry" technologies,which including dry dilute acid pretreatment(DDAP),solid-state biodetoxification,high solids loading enzymatic hydrolysis and fermentation,are applied in the DryPB process.In this dissertation,flowsheet simulation and process models of DryPB process were set up on Aspen Plus chemical process simulation software based on actual experimental data and engineering experience,including the production of cellulosic ethanol,L-lactic acid and sodium gluconate.Modeling deduction of high enzyme cost,high process cost and low conversion yield,which affect the industrialization of biorefining was executed with the goal of reducing the biorefining cost and improving feasibility of industrialization.Systemic and thorough research was performed on factors closely related to the industrialization including process design and optimization,concept of innovation and validation,as well as technical feasibility evaluation and analysis,based on flowsheet simulation and process modeling on Aspen Plus platform.Significant improvement on the DryPB technology and product cost was achieved.This dissertation thus provides necessary tools and essential methodology for industrialization design and scaleup.In the first part of this dissertation,whole process models of the DryPB process,including the production of cellulosic ethanol,L-lactic acid or sodium gluconate,were established on Aspen Plus platform based on the characteristic of DryPB process.The designed biorefining plant contains ten process areas:feedstock handing,pretreatment,biodetoxification,enzymatic hydrolysis and fermentation,cellulase production,product recovery,wastewater treatment,lignin residue combustion,storage,and utilities system.The strict technol-economic evaluation models that are applicable to the national conditions were developed based on the Aspen Plus models.The economics of DryPB process was then rigorously calculated from aspects of fixed capital investment,variable operating cost and fixed operating cost.With the minimum selling price of cellulosic products as objective function,stringent assessment of DryPB process economy was carried on.In the second part of this dissertation,commercial potentials of cellulosic ethanol were maximizied by minimizing of energy input and wastewater generation in lignocellulose biorefining.High ethanol yields were obtained using five lignocellulose biomasses(corn stover,wheat straw,rice straw,poplar sawdust and sugarcane)with low enzyme loading(10 or 15 mg/g cellulose).Ethanol titers as high as 11.4%(v/v)for corn stover and 12.8%(v/v)for wheat straw with the MESP of $2.05/gal and $1.93/gal were achieved respectively,which is close to that of corn ethanol production(12-15%,v/v).Significantly,current DryPB process cuts the energy and water balance to the similar level of dry mill process for corn ethanol production,while the close conversion efficiency to corn ethanol is maintained:8.63 GJ vs.7.83 GJ of steam consumption,262.95 kWh vs.34.46 kWh of electricity consumption,and 7.71 tons vs.8.33 tons of wastewater generation for producing on metric ton of cellulosic ethanol vs.corn ethanol in the core step of biorefining process.The higher electricity consumption of cellulosic ethanol is easily balanced by lignin residue combustion.Both the conversion efficiency and the energy and water balance of present DryPB process for cellulosic ethanol production has reached the competing level of the dry mill process for corn ethanol production.MESP could be less than $1.50/gal with the consideration of electricity price subsidies,straw subsidies and by-product of ash.In the third part,high titer L-lactic acid fermentation was studied from dry dilute acid pretreated and biodetoxified corn stover feedstock using an engineered Pediococcus acidilactici strain.Current optimal L-lactic acid production reached a titer of 104.5 g/L and overall yield of 71.5%from pretreated corn stover by overcoming several technical barriers.A rigorous Aspen Plus model for L-lactic acid production from corn stover was developed based on the dry milling biorefinery process Flowschart and the fermentation results obtained.The techno-economic analysis(TEA)show that the minimum L-lactic acid selling price(MLSP)was $ 0.559 per kg,which was close to that of the commercial L-lactic acid produced from starch feedstock,and 24%less expensive than that of ethanol from corn stover,even though the xylose utilization was not considered.In the fouth part,high titer gluconic acid and xylonic acid were simultaneously generated by Gluconobacter oxydans DSM 2003 using corn stover feedstock after dry dilute sulfuric acid pretreatment,biodetoxification and high solids content hydrolysis.Maximum sodium gluconate and xylonate were produced at the titer of 118.13 g/L and 64.27 g/L,respectively.The techno-economic analysis based on the rigorous Aspen Plus modeling was performed and the minimum 50%(w/w)sodium gluconate/xylonate product selling price(MGSP)was calculated as $0.182/kg,which is highly competitive as cement retarder additive to the commercial product from corn feedstock with excellent performance and low cost.In the fifth part,super large-scale biorefinery plants was constructed by decentralizing dry dilute acid pretreatment(DDAP)operation with minimum energy input and wastewater generation.In this DDAP based biomass supply system,the agricultural crop residues are pretreated in the biomass producing locations,stored,and transported to central biorefinery plant for conversion into ethanol and biochemicals.The unique properties of low energy input,zero wastewater generation,high tapped accumulative density,long-term storage,and easy miniaturization with low capital cost in the DDAP provides an ideal pretreatment for the distributing pretreatment into regional locations.The Aspen Plus model and discounted cash flow analysis show that DDAP-based distributing pretreatment operation significantly reduced transportation cost and the MESP was reduced by 14%when comparing to the traditional centralized biomass supply system.Using current DDAP-based biomass supply system,the biomass densely accumulating regions in China and USA have potentials to set up super large biorefinery plants with the competing capacity of daily 10,000 metric ton biomass processing to the modern oil refining factories.Conclusively,this dissertation established a set of rigorous whole process models of the DryPB process on Aspen Plus platform.High product yield and titer were achieved by applying the DryPB process technology.The characteristics of low energy consumption and wastewater discharge resulted in high industrialization feasibility from the view of environment and society,and the low production cost increased the market competitiveness of DryPB process.Distribution of dry dilute acid pretreatment technology that makes it possible to set up super large scale biorefining plant.The results of this dissertation provide theoretical basis for the industrialization design of realistic biorefining process. |
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