Techno-economic evaluation of stillage treatment with anaerobic digestion in a softwood-to-ethanol process

<p>Abstract</p> <p>Background</p> <p>Replacing the energy-intensive evaporation of stillage by anaerobic digestion is one way of decreasing the energy demand of the lignocellulosic biomass to the ethanol process. The biogas can be upgraded and sold as transportation fuel, injected directly into the gas grid or be incinerated on-site for combined heat and power generation. A techno-economic evaluation of the spruce-to-ethanol process, based on SO₂-catalysed steam pretreatment followed by simultaneous saccharification and fermentation, has been performed using the commercial flow-sheeting program Aspen Plus™. Various process configurations of anaerobic digestion of the stillage, with different combinations of co-products, have been evaluated in terms of energy efficiency and ethanol production cost versus the reference case of evaporation.</p> <p>Results</p> <p>Anaerobic digestion of the stillage showed a significantly higher overall energy efficiency (87-92%), based on the lower heating values, than the reference case (81%). Although the amount of ethanol produced was the same in all scenarios, the production cost varied between 4.00 and 5.27 Swedish kronor per litre (0.38-0.50 euro/L), including the reference case.</p> <p>Conclusions</p> <p>Higher energy efficiency options did not necessarily result in lower ethanol production costs. Anaerobic digestion of the stillage with biogas upgrading was demonstrated to be a favourable option for both energy efficiency and ethanol production cost. The difference in the production cost of ethanol between using the whole stillage or only the liquid fraction in anaerobic digestion was negligible for the combination of co-products including upgraded biogas, electricity and district heat.</p

LIGNOCELLULOSE CONVERSION VIA CONSOLIDATED BIOPROCESSING: HIGH SOLID LOADINGS, BIOREACTOR DEVELOPMENT, AND TECHNOECONOMIC ANALYSIS

Efficient deconstruction and conversion of inedible plant biomass, i.e., lignocellulose, is critical to decarbonizing the energy system in order to meet climate stabilization objectives. However, lignocellulose biomass is recalcitrant to deconstruction, and is often augmented by energy and capital intensive thermochemical pretreatment. Alternatively, Clostridium thermocellum is a thermophilic anaerobe capable of both deconstruction and conversion of lignocellulose without pretreatment. This thesis seeks to inform the deployment of cellulosic ethanol production by furthering our understanding of C. thermocellum mediated deconstruction, especially at industrially relevant conditions, i.e., solid loadings exceeding 100 g/L. In batch fermentations, it was observed that fractional deconstruction declines as solid loadings increase, which prompted diagnostic experiments and the inclusion of a second bacterium, Thermoanaerobacterium thermosaccharolyticum, to improve deconstruction. Ultimately, the bioreactors used to characterize this were unsuitable for work above 100 g/L, which necessitated a novel bioreactor system capable of high solids, semi-continuous fermentations. To our knowledge, this first-of-its-kind bioreactor will enable lab-scale characterization of lignocellulose deconstruction at high solid loadings not yet reported in literature. Lastly, a technoeconomic analysis adds another component to the thesis describing project economics and relative greenhouse gas (GHG) emissions for a 60-million gallon per year biorefinery. The impact of adopting emerging technologies such as carbon capture and storage (CCS) and biogas upgrading were evaluated in this context. Results indicate there are significant, i.e., up to 8-fold improvement, in net GHG benefits by adopting this approach, while simultaneously improving project economics

Integration of pulp and paper technology with bioethanol production

BACKGROUND: Despite decades of work and billions of dollars of investments in laboratory and pilot plant projects, commercial production of cellulosic ethanol is only now beginning to emerge. Because of: (1)high technical risk coupled with; (2) high capital investment cost relative to ethanol product value, investors have not been able to justify moving forward with large scale projects on woody biomass. RESULTS: Both issues have been addressed by targeting pulp and paper industry processes for application in bioethanol production, in Greenfield, Repurpose and Co-Location scenarios. Processes commercially proven in hundreds of mills for many decades have been tailored to the recalcitrance of the biomass available. Economically feasible cellulosic bioethanol can be produced in Greenfield application with hardwoods, but not softwoods, using kraft mill equipment. Both types of wood species can profitably produce ethanol when kraft mill or newsprint assets are Repurposed to a biorefinery. A third situation which can generate high financial returns is where excess kraft pulp is available at a mill which has no excess drying capacity. Each scenario is supported by laboratory simulation, engineering and financial analysis. While pretreatment is critical to providing access of the biomass to enzymes, capital investment per unit of ethanol produced can be attractive, even if ethanol yield is modest. CONCLUSIONS: Three guiding principles result in attractive economics: (1) re-use existing assets to the maximum extent; (2) keep the process as simple as possible; (3) match the recalcitrance of the biomass with the severity of the pretreatment

A generalized disjunctive programming framework for the optimal synthesis and analysis of processes for ethanol production from corn stover

The aim of this study is to analyze the techno-economic performance of process configurations for ethanol production involving solid-liquid separators and reactors in the saccharification and fermentation stage, a family of process configurations where few alternatives have been proposed. Since including these process alternatives creates a large number of possible process configurations, a framework for process synthesis and optimization is proposed. This approach is supported on kinetic models fed with experimental data and a plant-wide techno-economic model. Among 150 process configurations, 40 show an improved MESP compared to a well-documented base case (BC), almost all include solid separators and some show energy retrieved in products 32% higher compared to the BC. Moreover, 16 of them also show a lower capital investment per unit of ethanol produced per year. Several of the process configurations found in this work have not been reported in the literature.Financial support granted to F. Scott by CONICYT's scholarship program (Comisión Nacional de Investigación Científica y Tecnológica, grant 21100634) is gratefully acknowledged. This work was funded by Innova Chile Project 208-7320 Technological Consortium Bioenercel S.A

Techno-economic analysis of biochemicals and biofuels production via thermal and electrochemical processes

Climate change is leading to concerning fluctuations in weather patterns mainly due to anthropogenic activities such as deforestation and burning of fossil fuels which are and will affect different sectors such as food chains, wildlife and most importantly the human life. The upcoming generations must be left with an environment worth to live in thus humans must intervene to reduce the emissions of greenhouse gases and that is why sustainable means must be used to provide clean energy and renewable-based chemicals. For the U.S., the USDOE and USDA proposed a 25% and 20% vision for biomass-based chemicals and fuels respectively by the year 2030. The different chapters of this dissertation are: 1) introduction, 2) literature review, 3) “more than ethanol: a techno-economic analysis of corn stover-ethanol biorefinery integrated with hydrothermal liquefaction (HTL) process to convert lignin into biochemicals”, 4) “techno-economic analysis of 2,5-dimethylfuran (DMF) production using an electrolyzer/electrochemical reactor”, 5) “electrochemical production of 2-methylfuran (MF) from furfural: a techno-economic analysis”, and 6) “electrochemical processing of CO2 into Fischer Tropsch (FT) fuels using renewable electricity: a techno-economic analysis”, 7) general conclusions, and 8) recommendations for future work. The project of integrating corn stover biorefinery with HTL evaluates a 2000 metric tonne per day (MTPD) corn stover biorefinery producing 61 MMgal/yr. of ethanol and different yields of lignin-based biochemicals. A minimum ethanol selling price (MESP) of $1.03ñ0.19 per gal was estimated considering the production of lignin-derived catechol, phenol, cresols, acetic acid, formic acid, furfural, and acetaldehyde. The most influential factors on MESP are fixed capital investment, internal rate of return, feedstock price, cresols, catechol, and acetic acid prices. In terms of costs, the total purchased equipment cost is$114.5 million (MM), total installed cost (TIC) is $345.7 MM, and total capital investment is$624.5 MM. Producing lignin-derived biochemicals using hydrothermal liquefaction (HTL) is in the early stages of development thus more research is needed to establish its commercialization potential. The 2,5-dimethylfuran (DMF) project evaluates the techno-economic feasibility of producing DMF using an electrolyzer/electrochemical reactor. A 300-metric ton per day (MTPD) fructose biorefinery was considered producing 34 MTPD levulinic acid as a byproduct and 174 MTPD of hydroxymethylfurfural/5-hydroxymethylfurfural (HMF). The HMF is further converted to DMF through an electrochemical process producing 95 MTPD of 2,5-dimethylfuran (DMF) and the byproducts being 59 MTPD 2,5-bis(hydroxymethyl)furan and 21 MTPD 5-methylfurfuryl alcohol. A minimum product-selling price (MPSP) of $12.51/gal of DMF was estimated. The sensitivity analysis results showed that DMF yield, fixed capital investment, internal rate of return (IRR), 2,5-bis(hydroxymethyl)furan price, and fructose feedstock price are the most influential parameters on the MPSP. The biorefinery considered in this analysis requires a total purchased equipment cost (TPEC) of$146 MM, $442 MM of total installed cost (TIC), and$799 MM as the total capital investment. Using an electrolyzer/electrochemical reactor process to produce bioproducts is promising though in the early stages of development thus more research should be done to enable commercialization of the electrochemical process. The 2-methyfuran project investigated the techno-economic feasibility of producing 2-methylfuran (MF) from furfural using an electrolyzer that utilizes renewable electricity. Furfural flowrate assumed was 300 MTPD producing over 239 MTPD with byproducts of furoic acid (30 MTPD) and furfuryl alcohol (30 MTPD). MPSP is $9.07/gal and its mostly influenced by MF yield, fixed capital investment, furfural price, and acetonitrile price. The different cost are$79 MM, $240 MM, and$433 MM for total purchased equipment cost, total installed cost, and total capital invest cost respectively. The CO2 project, analyzed a 2000 MTPD biorefinery producing Fischer Tropsch biofuel gasoline gallon equivalent (GGE). The electrochemical conversion of CO2 into biofuels is an alternative to carbon sequestration and/or its release into the atmosphere that causes global warming. The biorefinery considered produces 70.7 MM gal/yr GGE (1236 MTPD, C8 and C16 hydrocarbons) and 253 MTPD of propane (CH4 – C3 hydrocarbon mixture). The estimated investments are $388 MM as total purchased equipment cost (TPEC),$1.2 BB for total installed costs (TIC), $1.8 BB as fixed capital investment (FCI) and$2.1 BB as the total investment cost. The estimated MPSP is $4.69/gal GGE and is mostly influenced by F-T GGE yield ($3.91 – 5.86/GGE), fixed capital investment ($3.86 – 5.53/GGE), IRR ($4.11 – 5.28/GGE), and income tax rate ($$4.51-4.91/GGE). Electrochemical conversion of CO2 is a promising technology to combat global warming though more research is needed to ascertain the electrolyzer functionality in converting CO2. The overall conclusion is that techno-economic analysis (TEA) is a good method to evaluate the feasibility of a project before being scaled-up from a laboratory to a pilot scale and then to a commercial facility. The evaluation provides insights of the minimum product selling price(s) and the factors that affect it most. This helps in comparison of biomass-based verses fossil-based products. Also, TEA provides estimates of total purchased equipment costs, total installation cost, and total capital investment. Overall, to have a bioeconomy, biofuels must be produced with biochemicals and CO2 capture and conversion into useful products will minimize and/or eliminate global warming

Technoeconomic Analysis of Biofuel Production and Biorefinery Operation Utilizing Geothermal Energy

A technoeconomic study is conducted to assess the feasibility of integrating geothermal energy into a biorefinery for biofuel production. The biorefinery is based on a thermochemical platform that converts low-value lignocellulosic biomass into biofuels via gasification and fuel reforming. Geothermal energy is utilized in the refinery to generate process steam for gasification and steam-methane reforming in addition to providing excess electricity via the organic Rankine cycle. A process simulation model is developed to simulate the operation of the proposed biorefinery, and corresponding economic analysis tools are utilized to predict the product value. The biorefinery uses 2000 metric tons of corn stover per day, and the products include gasoline, diesel fuel, hydrogen, and electricity. Implementation of geothermal energy into the proposed biorefinery is analyzed through two studies. In the first study, process steam at 150 °C with a flow rate of approximately 16 kg/s is assumed to be generated through a heat exchanger process by utilizing the heat from geothermal resources, producing a geothermal liquid at 180 °C and a total flow rate of 105 kg/s which is used to provide steam for gasification and steam-methane reforming within the biorefinery. In the second study, additional geothermal capacity of 204 kg/s is assumed to be available and is separated into two phases (liquid and steam) via a flash column. The steam produced is utilized in the same manner as the initial study while the geothermal liquid is used for electricity production via the organic Rankine cycle to add to the profitability of the biorefinery. This analysis considers that the technology is feasible in the near future with a high scope of technology development and the end products are compatible with the present fuel infrastructure. The total capital investment, operating costs, and total product values are calculated considering an operating duration of 20 years for the plant, and the data are reported based on the 2012 cost year. Simulation results show that the price of the fuel obtained from the present biorefinery utilizing geothermal energy ranges from $5.17 to$5.48 per gallon gasoline equivalent, which is comparable to $5.14 using the purchased steam. One important incentive for using geothermal energy in the present scenario is the reduction of greenhouse gas emissions resulting from the combustion of fossil fuels used to generate the purchased steam. Geothermal energy is an important renewable energy resource, and this study provides a unique way of integrating geothermal energy into a biorefinery to produce biofuels in an environmentally friendly manner

TECHNO-ECONOMIC AND LIFE CYCLE ASSESSMENTS OF BIOFUEL PRODUCTION FROM WOODY BIOMASS THROUGH TORREFACTION-FAST PYROLYSIS AND CATALYTIC UPGRADING

Biofuel production through fast pyrolysis of biomass is a promising conversion route in the production of biofuels compatible with existing technology. The bio-oil produced from fast pyrolysis is a versatile feedstock that can be used as a heating oil or upgraded to a transportation hydrocarbon biofuel. Comparative study of a one-step, fast pyrolysis only pathway and a two-step torrefaction-fast pyrolysis pathway was carried out to evaluate the effect of torrefcation on (i) the minimum selling price of biofuel and (ii) the potential life cycle GHG emissions of the biofuel production pathway. To produce bio-oil which can serve as a substitute for heating oil from loblolly pine biomass feedstock, torrefaction at three different temperatures of 290, 310 and 330°C were investigated while fast pyrolysis occurred at 530°C. Three scenarios of producing process heat from natural gas, internal by-products biochar or torrefaction condensate were also investigated. Economic assessment showed more favorable economics for the two-step bio-oil production pathway relative to the one-step bio-oil production pathway. The lowest minimum selling price of $1.04/gal was obtained for a two-step pathway with torrefaction taking place at 330°C. The environmental impact assessment also showed more the two-step bio-oil production pathway to be more environmentally friendly. The lowest GWP of about -60g CO2eq was observed for the two-step pathway at torrefaction temperature of 330°C while GWP of about 36g CO2eq was observed for the one-step pathway. Relative to heavy fuel oil, the one-step and two-step pathways are more environmentally friendly with lower GWP. To produce hydrocarbon biofuel by the catalytic upgrade of bio-oil derived from fast pyrolysis of loblolly pine, three torrefaction temperatures of 290, 310 and 330°C were investigated with fast pyrolysis taking place at 530°C. Three scenarios of producing process heat from natural gas, internal by-products biochar or torrefaction condensate were investigated. The effect of heat integration was also examined. The economic assessment showed equal minimum selling price for the one-step hydrocarbon biofuel production pathway and a two-step pathway with torrefaction occurring at 290°C. A minimum selling price of$4.82/gal was estimated while higher torrefaction temperatures showed less favorable economics. The environmental impact assessment however showed the two-step pathway to be more environmentally friendly when compared with the one-step pathway. GWP of about -66g CO2eq was observed for the two-step pathway with torrefaction taking place at 330°C compared to a GWP of about 88g CO2eq obtained for the one-step. Further reduction in minimum selling price and GWP were observed with heat integration. A minimum selling price of about $4.01/gal was estimated for the one-step and two-step pathway with torrefaction taking place at 290°C while GWP of about -144 g CO2eq was observed for the two-step hydrocarbon biofuel with torrefaction temperature of 330°C

OPTIMAL USES OF BIOMASS RESOURCES IN DISTRIBUTED APPLICATIONS

Biomass production is spatially distributed resulting in high transportation costs when moving dedicated biomass crops and crop residues. A multifaceted approach was taken to address this issue as the low bulk and energy density of biomass limits transportation efficiency. Two systems were analyzed for the conversion of biomass into a denser feedstock applicable to on-farm use. Pelletization was able to densify the material into a solid fuel. Using a pilot scale flat ring pellet mill, the density of the material was able to be increased to at least 4.4 times that of uncompressed material. Pellet durability was found to be strongly related to the moisture content of the material entering the mill. Unlike with ring roller pellet mills, a higher durability was typically seen forbiomass materials with a preconditioned moisture content of 20% (w.b.). From a liquid fuel standpoint, the conversion of lignocellulosic material into biobutanol on-farm was the second method investigated. For the pretreatment of biomass, alkaline hydrogen peroxide spray was demonstrated to be an effective enhancer of saccharification. The viability of on-farm biobutanol preprocessing bunker facilities within Kentucky was analyzed using Geographic Information systems (GIS) to specifically address transportation related factors. The spatial variability of corn field production, size, and location were resolved by utilizing ModelBuilder to combine the various forms of data and their attributes. Centralized and Distributed preprocessing with Centralized refining (DC) transportation systems were compared. Centralized was defined as transport of corn stover directly from the field to a refinery. Distributed-Centralized was specified as going from the field to the biobutanol bunker with corn stover and from the bunker to the refinery with a dewatered crude biobutanol solution. For the DC design, the location of the field and refinery were fixed with the biobutanol bunker location being variable and dependent upon differing maximum transportation (8-80 km) cutoffs for biomass transport from the field to biobutanol bunkers. The DC designs demonstrated a lower (38 - 59%) total transportation cost with a reduced fuel use and CO2 emissions compared to the centralized system