Aspen Plus Research Articles

Optimizing Hydrogen-Rich Biofuel Production: Syngas Generation from Wood Chips and Corn Cobs

This study investigates gasification using wood chips (WC) and corn cobs (CC) for hydrogen-rich syngas production. A simulation model developed in Aspen Plus was used to evaluate the performance of biomass gasification. The model incorporates a system of Fortran subroutines that automate the definition of input parameters based on the analysis of biomass composition. Furthermore, the model’s equilibrium constants were adjusted based on experimentally measured gas concentrations, increasing the precision of the variations. The numerical results predicted hydrogen yields of 65–120 g/kg biomass, with 60–70% energy efficiency for steam gasification (versus 40–50% for air gasification). The hydrogen concentration ranged from 34% to 40%, with CO (27–11%), CO2 (9–20%), and CH4 (<4%). The gasification temperature increased hydrogen production by up to 40% but also increased CO2 emissions by up to 20%. Higher biomass moisture content promoted hydrogen production by up to 15% but reduced energy efficiency by up to 10% if excessive. Steam gasification with wood chips and corn cobs shows promising potential for hydrogen-rich syngas production, offering benefits such as reduced emissions (up to 30% less CO) and sustainability by utilizing agricultural residues.

Experimental analysis and numerical simulation of biomass pyrolysis

AbstractFinding alternatives to fossil fuels is extremely important for economic and environmental considerations. Biomass pyrolysis stands out as an efficient method for generating fuels and chemical intermediates. This study explored the influence of wood particle size (ranging from 1 to 3 cm) and pyrolysis temperature (ranging from about 300 to 480 °C) on the process. Characterization of wood residues utilized energy-dispersive X-ray (EDX) and field emission scanning electron microscopy (FE-SEM) to comprehend surface morphology and resultant biochar structure. Results revealed a significant temperature-dependent impact on pyrolysis product concentrations. Biomass composition analysis indicates lignin, hemicellulose, extractive contents, and cellulose percentages at 11.23%, 39%, 2.15%, and 47.62% mass/mass, respectively. Reduction in particle size to less than 2 mm enhances heat transfer, elevating overall bio-oil production. Major bio-oil components comprise phenolics, acids, alcohols, aldehydes, and ketones. Optimal conditions are identified at a wood particle size of 1 cm and a heating temperature of 480 °C. For every 1.0 kg of wood biomass residues, bio-oil, syngas, and biochar yields are 0.38 kg, 0.22 kg, and 0.4 kg, respectively. Notably, the agreement between Aspen Plus simulation and experimental findings underscored the robustness of the study.

Impact of intermittent electricity supply on a conceptual process design for microbial conversion of CO2 into hexanoic acid

Combining intermittent renewable electricity (IRE) with carbon capture and utilisation is urgently needed in the chemical sector. In this context, microbial electrosynthesis (MES) has gained attention. It can electrochemically produce hexanoic acid, a value-added chemical, from CO2. However, there is a lack of understanding regarding how the intermittency of renewable electricity could impact the design of a MES plant. We studied this using Aspen Plus models.A MES plant that was powered by constant grid electricity could operate from 100% down to 70% of its nominal capacity, at which point the heat exchangers and the internal geometrical design of the distillation towers became bottlenecks. The levelised production cost of hexanoic acid (LPCC6A) was estimated at 4.0 €/kg. Switching to IRE supply increased LPCC6A to 5.3 €/kg (for wind electricity) and 4.7 €/kg (for hybrid renewable electricity).A battery energy storage system (BESS) was deployed. The lowest LPCC6A was found at a BESS installation of 29 GJ/h for wind electricity (5.1 €/kg) and at 12 GJ/h for hybrid renewable electricity (4.7 €/kg). In both situations, the volume flexibility of the MES plant was not improved. At the investigated market and operating conditions, coupling IRE to the MES plant was economically infeasible.

Study on the mechanism of extractive distillation separation of cyclohexane/ethanol azeotrope based on ionic liquid and molecular liquid mixed solvent as extractant

The development of high-performance new extractants is crucial for the separation of azeotropes by extractive distillation (ED). In this paper, an effective method for the separation of azeotropes by ED using IL mixed extractants (ILMEs) is proposed. Based on the COSMO-SAC thermodynamic model and relative volatility, the optimal extractants [Dmim][Ac] and DMSO were selected respectively. The structure–activity relationship between single extractant and ILMEs was analyzed by quantum chemistry (QC) calculations. Molecular simulation results showed that compared with single extractant, the addition of DMSO increased the interaction sites between ethanol and extractant, which made ILMEs ([Dmim][Ac] + DMSO) easier to combine with ethanol to form H-bond, thus facilitating the separation of cyclohexane/ethanol. H in DMSO mainly forms C2–H5…O3 hydrogen bonds with O in ethanol, and O in [Ac]− mainly forms C1–O4…H4 H-bond with H in ethanol. Through molecular dynamics (MD) simulation, the phase behavior and structural distribution of ILMEs and azeotropes under different mixed solvent ratios were explored from the microscopic mechanism, so as to determine the optimal mixing ratio. The MD results showed that the interaction between [Dmim][Ac]+DMSO and ethanol was enhanced with the addition of DMSO. When the amount of [Dmim][Ac] is reduced to DMSO:[Dmim][Ac] = 4:1, the interaction between ethanol and the mixed extractant in the quaternary system is the strongest, and the ethanol molecule is completely immersed in the mixed extractant, cyclohexane and ethanol are completely separated and the aggregation behavior is maximized, indicating that the mixed solvent ratio DMSO:[Dmim][Ac] = 4:1, the separation effect is the best. Finally, the separation of ILMEs and DMSO cyclohexane/ethanol azeotrope was simulated by Aspen Plus V12, and the feasibility of ILMEs as extractant was verified. The results show that compared with the traditional organic extractant DMSO, ILMEs have potential environmental and economic advantages. The total annual cost (TAC) is reduced by 13.65 % and the gas emission is reduced by 23.04 %. This study provides theoretical guidance for the study of ED mechanism and the determination of solvent ratio of mixed extractants.

Activated carbon production from algal biochar: Chemical activation and feasibility analysis

Chemical activation was employed to convert algal biochar obtained from hydrothermal carbonization of lipid-extracted algae (LEA) to activated carbon. Potassium hydroxide, previously utilized on cellulosic biomass but not on algal biomass, was employed as activating agent and the impact of the activation conditions, namely temperature, activation time, and amount of activating agent, were investigated. The yield of activated carbon from biochar ranged from 28 % to 52% and decreased as the temperature was raised from 400 to 600 °C, the residence time from 30 to 60 min, and the KOH/biochar mass ratio from 0.25 to 1.0. In contrast, surface area increased by 2.1-fold when the activation temperature was raised to 600 °C and by 1.5-fold when the KOH: biochar ratio was raised to 1.0. Maximum BET surface area of 847 m2/g was achieved at 600 °C after 30 min at a mass ratio of 1:1. The integrated hydrothermal carbonization and activation process of LEA was simulated in Aspen Plus® and the technoeconomic feasibility was assessed based on our experimental data at 1,000 and 10,000 acres of cultivation area. For the latter, net present value analysis determined a minimum selling price of $2,200/ton for algal activated carbon with a financial breakeven achieved in 3.5 years. This is cost-competitive with the current price of commercial fossil-derived activated carbon, which is $1,543-$2,645/ton. Sensitivity analysis showed that the minimum selling price is significantly affected by algal biomass yield during cultivation and is more sensitive to the operating expenses than to the capital investment.

Assessing the feasibility and sustainability of a surfactin production process: a techno-economic and environmental analysis.

Biosurfactants have been profiled as a sustainable replacement for chemical-based surfactants since these bio-based molecules have higher biodegradability. Few research papers have focused on assessing biosurfactant production to elucidate potential bottlenecks. This research aims to assess the techno-economic and environmental performance of surfactin production in a potential scale of 65m3, considering different product yields and involving the European energy crisis of 2021-2022. The conceptual design, simulation, techno-economic, and environmental assessments were done by applying process engineering concepts and software tools such as Aspen Plus v.9.0 and SimaPro v.8.3.3. The results demonstrated the high economic potential of surfactin production since the higher values in the market offset the low fermentation yields, low recovery efficiency, and high capital investment. The sensitivity analysis of the economic assessment elucidated a minimum surfactin selling price between 29 and 31 USD/kg of surfactin, while a minimum processing scale for economic feasibility between 4 and 5kg/h is needed to reach an equilibrium point. The environmental performance must be improved since the carbon footprint was 43kg CO2eq/kg of surfactin. The downstream processing and energy demand are the main bottlenecks since these aspects contribute to 63 and 25% of the total emissions. The fermentation process and downstream process are key factors for future optimization and research.

Biogas Production Optimization in the Anaerobic Codigestion Process: A Critical Review on Process Parameters Modeling and Simulation Tools

Many operational parameters, either discretely or collectively, can influence the biodegradation performance towards enhancing biogas yield and quality. Among the operating parameters, organic loading rate (OLR), inoculum-substrate ratio, and carbon-nitrogen ratio (C/N) are the most critical parameters in the optimization and enhancement of biogas yield. Optimization of the biogas production processes depends on the ability of anaerobic microorganisms to respond to variations in operational parameters such as pH, redox potential, and intermediate products to enhance the biogas yield. This review article focuses on the role of process parameters, kinetic models, artificial intelligence, Aspen Plus (AP), and anaerobic digestion model no. 1 (ADM1) in optimizing biogas yield via an anaerobic codigestion (AcoD) process. The review showed that biomaterials codigestion upgraded biogas yield to the extent of 400%, and organic removal efficiency reached up to 90% compared to a single substrate. In addition, the current work has verified that the kinetic model is the most effective tool for signifying that the hydrolysis phase is the rate-limiting step, whereas AP is the most effective tool in the design and optimization of the AcoD process parameters. The reviewed kinetic and AI models show strong correlation values ranging from 0.931 to 0.9991 and 0.8700 to 0.9998, respectively. The AcoD system involves complex chemical reactions, but AP might have limitations in representing such complex chemical processes with nonideal behavior and complicated reaction mechanisms. The design and optimization of AcoD with reliable input parameters are highly limited or nonexistent. The AcoD process design with AP opens fresh research opportunities, including improved efficiency, finding appropriate retention time, and saving time, as well as finding the optimum biogas yield. This review article gives an insightful understanding of AcoD process parameter optimization and valuable strategies for policy development enhancing sustainability in the biogas sector.

Conceptual design of a fixed bed N2O decomposition reactor with a heat pipe heat exchanger

Abstract This paper introduces a novel process for decomposing N2O through interstage cooling utilizing a heat pipe heat exchanger. The reactor design involves segmenting the fixed bed reactor into multiple layers and integrating heat pipe heat exchangers between these layers to efficiently dissipate the high heat generated by the upper fixed bed reactor. This innovative approach facilitates the direct decomposition of N2O feedgas with high concentrations, obviating the need for gas dilution. The study conducted in this paper employed Fluent and ASPEN PLUS to investigate N2O decomposition with interstage cooling using heat pipe heat exchangers, as well as decomposition after dilution. A comparison between the two methods was made based on catalyst dosage, temperature uniformity, and reactor energy consumption. The results demonstrate that the proposed method for N2O decomposition via interstage cooling with a heat pipe heat exchanger is a viable option, offering the desired temperature control and enhanced efficiency. Furthermore, this reactor design effectively reduces both catalyst usage and energy consumption, providing substantial advantages over traditional approaches.

Flexible Green Ammonia Production Plants: Small-Scale Simulations Based on Energy Aspects

The conventional Haber–Bosch process (HBP) for NH3 production results in CO2 emissions of almost 400 Mt/y and is responsible for 1–2% of global energy consumption; furthermore, HBP requires large-scale industrial equipment. Green or e-ammonia produced with hydrogen from alkaline water electrolysis using renewable energy and nitrogen from the air is considered an alternative to fossil-fuel-based ammonia production. Small-scale plants with the distributed on-site production of e-ammonia will begin to supplant centralized manufacturing in a carbon-neutral framework due to its flexibility and agility. In this study, a flexible small-scale NH3 plant is analyzed with respect to three steps—H2 generation, air separation, and NH3 synthesis—to understand if milder operating conditions can benefit the process. This study investigates the aspects of flexible small-scale NH3 plants powered by alkaline electrolyzer units with three specific capacities: 1 MW, 5 MW, and 10 MW. The analysis is carried out through Aspen Plus V14 simulations, and the primary criteria for selecting the pressure, temperature, and number of reactors are based on the maximum ammonia conversion and minimum energy consumption. The results show that: (i) the plant can be operated across a wide range of process variables while maintaining low energy consumption and (ii) alkaline electrolysis is responsible for the majority of energy consumption, followed by the ammonia synthesis loop and the obtention of N2, which is negligible.

Enhanced downstream processing of NGL using intensified fluid separation technologies

Downstream processing of natural gas liquids (NGL) provides feedstock needed for plastic production, upgraded fuels and heating, but it is one of the largest high-pressure and energy intensive processes. This original study is the first to integrate novel process intensification options from a holistic viewpoint for the full process covering all sections: 1) NGL recovery, 2) NGL fractionation, and 3) isomerization. Intensified fluid separation technologies (e.g. complex columns, thermal coupling, and heat pumps) are explored and integrated into a full NGL process to improve the energy efficiency and mitigate GHG emissions, and to establish the limits of operation, utility usage, and specific product costs. All NGL processes are rigorously simulated in Aspen Plus, and evaluated based on a fair economic and sustainability analysis.The enhanced recycle split vapor process for NGL recovery results in a full heat recovery for the reboiler of the demethanizer (2.9 MW energy savings), while the enhanced gas subcooled process results in 17.9% reduction of the refrigerant duty, 20.2% reduction of the electrical duty, and 19.9% reduction of the total utility cost. For the NGL fractionation section, heat pump assisted double dividing wall process improves energy intensity for a fraction of the utility cost although requiring external incentives (e.g., carbon tax) to become commercially viable. The total utility costs as well as GHG emissions are reduced up to 30% and 49%, respectively, while the specific product cost reduces to $23.45/t or $24.38/t with carbon tax. The heat pump assisted recycled isomerization process for the last section increased AKI from 65.3 to 89.6, with 19.1% reduction of utility usage and 42.4% reduction of carbon emission.

Olive leaves upgrading applying a novel two-stage organosolv pretreatment: Techno-economic and environmental assessment

This research study evaluates the techno-economic and environmental performance of an olive leaves based biorefinery to produce antioxidants, bioethanol, and organosolv lignin. The biorefinery comprises processes such as organosolv extraction, organosolv pretreatment and simultaneous saccharification and fermentation, which were simulated in Aspen Plus v9.0. Experimental data were used to simulate the process, assuming a linear up-scaling. The techno-economic evaluation was carried out considering financial indicators such as net present value (NPV) and internal rate of return (IRR). The environmental assessment was done applying the life cycle assessment methodology. The results shows that 100 g olive leaves can produce 16.58 g antioxidant extract, 11.12 g organosolv lignin, and 2.85 g bioethanol. The proposed biorefinery was feasible at a processing scale of 30,000 t/y with a NPV of 47.9 million USD and an internal rate of return of 27.8%. The proposed biorefinery can be implemented in Jaén (Andalusia-Spain) based on the high amount of olive leaves produced in this region. Stillages are the most polluting waste stream of the process. The carbon footprint of the biorefinery was 1.13 kgCO2-eq/kg olive leaves. The application of the biorefinery concept revealed that olive leaves could be transformed into value-added products from a techno-economic and environmental perspective.

Modelling and Simulation of Co-Gasification of Chlorella Vulgaris and High-density Polyethylene Using Aspen Plus

A technical innovation that holds promise for producing renewable fuel and decreasing waste disposal is the production of syngas from the co-gasification of waste materials and biomass. In this present study, a new simulation model for co-gasifying high-density polyethylene (HDPE) and microalgae using Aspen plus V10 was built. Several operating parameters, including operating temperature, air equivalence ratio (ER), biomass blending ratio, steam-to-biomass ratio (S/B), and air/steam ratio, were investigated for their influence on the yield and composition of H2, CO, CO2, and CH4. Results indicated that these operating parameters had significant impacts on the gaseous products. High gasifier temperatures (1000°C) for the co-gasification process favored the formation of H2 and CO and increased their yields. Also, the yield of H2 significantly decreased when the value of the equivalence ratio was increased. According to simulation results, increasing the steam-to-biomass ratio favored the synthesis of H2 and CO up to a point. In addition, waste plastic (HDPE) in the feedstock should be kept at a minimum to favor the production of hydrogen-rich gas. The findings show that the model results agree with previous experimental studies. This research study has proven the air-steam co-gasification of microalgae and HDPE as a suitable process for the production of syngas rich in hydrogen.

Process Design for the Directly Coupled Production of Methanol and Formaldehyde Based on CO2

AbstractSustainable hydrogen generation is preferred over production from fossil sources in the context of a carbon‐neutral economy. As a result, production costs for CO2‐based products are estimated to be much higher than those of their fossil equivalents. Hence, it is essential to optimize process chains regarding their hydrogen efficiency. In this study, a concept for the directly coupled production of CO2‐based methanol and formaldehyde in a modified silver catalyst process is evaluated regarding the utilization of H2. Detailed simulations in Aspen Plus allow the comparison to the separately operated synthesis of green methanol and formaldehyde. By directly connecting both production steps, utilization ratios of introduced H2 and CO2 could be improved, reaching values of 98 % and 99 %, respectively.

Thermodynamic Feasibility Evaluation of Alkaline Thermal Treatment Process for Hydrogen Production and Carbon Capture from Biomass by Process Modeling

Hydrogen is attracting attention as a low-carbon fuel. In particular, economical hydrogen production technologies without carbon emissions are gaining increasing attention. Recently, alkaline thermal treatment (ATT) has been proposed to reduce carbon emissions by capturing carbon in its solid phase during hydrogen production. By adding an alkali catalyst to the conventional thermochemical hydrogen production reaction, ATT enables carbon capture through the reaction of an alkali catalyst and carbon. In this study, a thermodynamic feasibility evaluation was carried out, and the effects of the process conditions for ATT with wheat straw grass (WSG) as biomass were investigated using Aspen Plus software V12.1. First, an ATT process model was developed, and basic thermodynamic equilibrium compositions were obtained in various conditions. Then, the effects of the process parameters of the reactor temperature and the mass ratio of NaOH/WSG (alkali/biomass, A/B value) were analyzed. Finally, the product gas compositions, process efficiency, and amount of carbon capture were evaluated. The results showed that the ATT process could be an efficient hydrogen production process with carbon capture, and the optimal process conditions were a reactor temperature of 800 °C, an A/B value of three, and a flow rate of steam of 6.9 × 10−5 L/min. Under these conditions, the maximum efficiency and the amount of carbon dioxide captured were 56.9% and 28.41 mmol/g WSG, respectively.

Economic, environmental, energy, exergy (4E) analysis and simulated annealing algorithm optimization of dividing-wall column-intensified heterogeneous azeotropic pressure-swing distillation process

This work presents an approach for the recovery of high purity cyclohexane (CYCLO) and tertiary butyl alcohol (TBA) from wastewater. After thermodynamic analysis, a heterogeneous azeotrope-pressure swing distillation process (HAPSD) with a decanter is proposed. The heterogenous azeotrope distillation with a high-pressure column and a dividing-wall column process (HADWC) is also being developed to propose a green and sustainable process. The novel processes are optimized using simulated annealing algorithm (SAA). Those processes are optimized by simulated annealing algorithm by linking Aspen Plus and MATLAB via taking the total annual cost (TAC) as objective function. Three energy-efficient HADWC processes are proposed based on the process intensification approach of heat pump and heat integration technologies. All processes are evaluated for multi-criteria performance including economy, energy consumption, gas emissions and thermodynamic efficiency. As the result, HADWC-HP-HI process shows the best performance with 31.79%, 53.46%, 50.69%, and 57.94% reducing over the conventional HAPSD process in terms of TAC, energy consumption, gas emissions and thermodynamic efficiency, respectively.

Simulation of Underground Coal-Gasification Process Using Aspen Plus

In order to study the underground coal-gasification process, Aspen Plus software was used to simulate the lignite underground gasification process, and a variety of unit operation modules were selected and combined with the kinetic equations of coal underground gasification. The model can reflect the complete gasification process of the coal underground gasifier well, and the simulation results are more in line with the experimental results of the lignite underground gasification model test. The changes in the temperature and pressure of oxygen, gasification water, spray water, and syngas in pipelines were studied, and the effects of pipe diameters on pipeline conveying performance were investigated as well. The effects of the oxygen/water ratio, processing capacity, and spray-water volume on the components of syngas and components in different reaction zones were studied. In addition, the change tendency of gasification products under different conditions was researched. The results indicate that: (1) The depth of injection and the formation pressure at that depth need to be taken into account to determine a reasonable injection pressure. (2) The liquid-water injection process should select a lower injection pressure. (3) Increasing the oxygen/water ratio favors H2 production and decreasing the oxygen/water ratio favors CH4 production. (4) The content of CO2 is the highest in the oxidation zone, the lowest in the reduction zone, and then increases a little in the methanation reaction zone for the transform reaction. The content of CO is the lowest in the oxidation zone and the highest in the reduction zone. In the methanation reaction zone, CO partially converts into H2 and CO2, and the content of CO is reduced. (5) The injection of spray water does not affect the components of the gas but will increase the water vapor content in the gas; thus, this changes the molar fraction of the wet gas.

A study on integrated HTR-PM driven hydrogen production using thermochemical cycles

This present study aims to design a nuclear-based hydrogen production system by using the three- and four-step magnesium-chloride cycles, and compares the three-step magnesium-chloride cycle integrated nuclear-based system and the four-step magnesium-chloride cycle integrated nuclear-based system. Within the scope of this study, four units of high-temperature gas-cooled-pebble bed modular nuclear reactor are employed, where a total of 1 GW thermal energy (heat) is secured from these four reactors. All of the heat generated by the reactors is used to drive the power generation and hydrogen production cycles. The proposed system, along with its cycles and processes, are examined by using mass, energy, entropy, and exergy balance equations. The modeling and simulations for the three- and four-step magnesium-chloride cycles are carried out via the Aspen Plus software package. The results are compared for two hydrogen production methods, and sensitivity analysis is assessed for various steam/MgCl2 ratios, as well as different reactor temperatures and pressures for each reaction in the cycles. While the three-step magnesium-chloride cycle integrated nuclear-based system produces 2.43 kg/s hydrogen, 2.13 kg/s hydrogen is produced by the four-step magnesium-chloride cycle integrated nuclear-based system. As a consequence of this present study, energy and exergy efficiencies are calculated as 54.2% and 60.9% for the three-step magnesium-chloride cycle, while these values are 48.0% and 54.0% for the four-step magnesium-chloride cycle. Additionally, while the energy and exergy efficiencies of the three-step magnesium-chloride cycle integrated overall system are 29.2% and 40.3%, these values are 25.6% and 35.2% for the four-step magnesium-chloride cycle integrated system, respectively.

Design and hydraulic study of double‐partition dividing‐wall column

AbstractDividing‐wall column (DWC) provides tremendous advantages in terms of energy savings and capital costs for three‐component and even multi‐component separations. With increasing industrial application of three‐component DWCs, DWCs for separation of four‐component have received considerable research attention. The aim of this work is to investigate the design of the two‐staggered wall region and gas–liquid two‐phase flow behavior on the tray in a double‐partition DWC (DPDWC). The Aspen Plus was applied to simulate the steady state to obtain the gas–liquid‐phase flow rate in each region to serve as the basis for the tray design. In different task regions, the gas‐ and liquid‐phase flow varied in some ways. The drag models have variability for the study of fluid flow, and the Tomiyama model is more appropriate. Moreover, high‐velocity gradients and recirculating phenomenon can be discovered owing to the existence of multiple partitions in DPDWC.

Simulation of Olive Pomace Gasification for Hydrogen Production Using Aspen Plus: Case Study Lebanon

Biomass is a renewable energy source gaining attention for its potential to replace fossil fuels. Biomass gasification can produce hydrogen-rich gas, offering an environmentally friendly fuel for power generation, transportation, and industry. Hydrogen is a promising energy carrier due to its high energy density, low greenhouse gas emissions, and versatility. This study aims to develop a hydrogen generation plant using a dual fluidized bed gasifier, which employs steam as a gasifying agent, to convert olive pomace waste from the Lebanese olive oil industry into hydrogen. The process is simulated using Aspen Plus and Fortran coding, and it includes a drying unit, gasification unit, gas cleaning unit, steam methane reformer unit, water–gas shift reactor unit, and a pressure swing adsorption unit. The generated gas composition is verified against previous research. Sensitivity analyses are conducted to investigate the impacts of the steam-to-biomass ratio (STBR) and gasification temperature on gas composition, demonstrating a valid STBR range of 0.5 to 1 and a reasonable gasification temperature range of 700 °C to 800 °C. Further sensitivity analyses assess the impact of reformer temperature and the steam-to-carbon ratio (S/C) on the gas composition leaving the steam methane reformer.

Comparative techno-economic and life cycle assessments of single and intercropped-mixed feedstocks-based biorefineries for profitable and cleaner production of energy

The role of intercropped mixed feedstocks (IMF) in advancing biorefineries is rarely studied. However, as opposed to conventional single feedstocks (SF) from monocropping systems (MCS), IMFs could potentially enhance the economic profitability of biorefineries by reducing the cost of feedstock transportation and overall operations due to high feedstock yield/ha and fewer inputs e.g., diesel. In addition, IMFs could improve environmental performance by minimizing emissions associated with feedstock farming inputs (e.g., fertilizer), transportation (e.g., diesel, and tear & wear), and overall operational requirements. Furthermore, intercropping systems (ICS) could mitigate feedstock yield uncertainties and ensure stable feedstock supply because legumes (e.g., pigeon peas) are drought-resistant and inhibit pests & diseases when intercropped with maize. Nonetheless, the actual benefits of IMFs must be quantified. Therefore, techno-economic and life cycle assessments were done, using the Malawian economic context, to evaluate IMFs of maize stover (MS) and pigeon pea stalks and leaves (PPSL) for ethanol, electricity, and biogas production in varying biorefinery capacities of 156 000 and 2184 000 mt/y. Four scenarios were investigated; MS from MCS (S1), MS from ICS (S2), MS and PPSL from ICS (S3), where PPSL was dedicated for combined heat & power (CHP), and MS and PPSL from ICS where MS was dedicated to CHP (S4). The biorefinery systems were simulated in Aspen Plus ® to obtain mass and energy balances (MEB) which were used in assessing economic performance via biorefinery gate feedstock cost (BGFC), net present value (NPV), and minimum product selling price (MPSP). BGFC was evaluated by aggregating the cost of buying feedstocks, labor, milling, baling, and transportation. Transportation cost was computed via summation of the cost of fuel, driving labor, depreciation, and maintenance influenced by transportation distance and feedstock yield/ha. MEBs were also used as input and output data in SimaPro software to estimate emissions in terms of fossil resource depletion (FRD), global warming potential (GWP), terrestrial acidification (TA), and freshwater eutrophication (FWE). The IMFs improve biorefineries' economic performance by reducing feedstock logistical cost and MPSP, and environmental performance by reducing FRD, GWP, TA, and FWE. For example, BGFC, MPSP & FRD for IMF's S3 were $228 million/t, $2.28/L & 135 kg oil eq/mt, respectively, compared to $258 million/t, $2.37/L, and 146 kg oil eq/mt respectively for MSF's S1 at 2184 000 mt/y. Thus, IMF improved BGFC, MPSP, and FRD by 12, 5, and 8%, respectively. Therefore, utilization of the IMFs can boost the economic and environmental performances of biorefineries.