Detailed Process Simulation Research Articles

Stochastic modeling of integrated order fulfillment processes with delivery time promise: Order picking, batching, and last-mile delivery

To guarantee high customer service and short and accurate lead times, many e-commerce retailers have started to home deliver their customer orders within a few hours or even minutes, also known as quick-commerce order fulfillment. Quick-commerce order fulfillment consists of three main processes: order picking in the warehouse, order batching for delivery, and last-mile delivery. The ultimate delivery performance depends on managing all three processes, which are highly stochastic, and interdependent. We capture this stochasticity and interdependency in an integrated analytical framework and derive approximate analytical expressions for the mean and variance of the total order fulfillment time. We validate the analytical expressions with both in-house detailed process simulations and external-party output measures. We then analyze the delivery cost-service quality trade-offs using an optimization model that minimizes the expected order fulfillment cost with a delivery probability (DP) constraint, focusing on meeting delivery time deadlines. The optimization model determines the number of pickers, the optimal delivery batch size, and the number of vehicles required to deliver the customer orders. Achieving a high delivery reliability comes at a cost. In comparison to the model with DP constraints, we observe that the expected order fulfillment cost averaged over all data parameter settings obtained from the model without DP constraints is 8.9% lower; however, the mean and standard deviation of order fulfillment time increase by 44.1% and 18.6%, respectively, which results in low delivery reliability. We further demonstrate that an integrated analysis of the order fulfillment process is essential to set reliable fulfillment due times.

Entrained flow gasification-based biomass-to-X processes: A techno-economic assessment

In the pursuit of a successful energy transition, synthetic basic chemicals and fuels, alongside renewable energies, play pivotal roles. This study focuses on the utilization of biomass as a carbon source to replace conventional fossil feedstocks, conducting detailed process simulations and techno-economic analyses for various biomass-to-x pathways. Six key products—Methanol, Dimethyl Ether, Methane (SNG), Fischer-Tropsch syncrude, Hydrogen, and Ammonia—derived from entrained flow gasification of a representative biomass are systematically compared. The uniformity of simulation detail and economic methodology enables a direct and comprehensive comparison of these products. Notably, carbon-based products exhibit up to 34% lower average investment costs compared to their hydrogen-based counterparts, namely ammonia and hydrogen. This cost discrepancy is reflected in the levelized costs of manufacturing, with hydrogen-based products emerging as the most energy-expensive. The analysis identifies variable costs as the primary contributor to overall costs with around 50%, followed by fixed investment. The study underscores the critical impact of full load hours, plant lifetime, and feedstock costs on results. This emphasise the importance of detailed planning if alternative feedstock is used to balance fuel costs and enhance plant availability. Among the evaluated products, methanol emerges as the most promising across the evaluated KPIs with costs of 283.48 € MWh−1. However, regarding hydrogen-based products, it is suggested that, especially in the context of CO2 abatement costs, a comprehensive consideration of the long-term system effects is essential to prevent misinvestments during the early stages of the energy transition. This emphasizes the need for strategic planning to ensure a sustainable and economically viable shift towards biomass-derived synthetic fuels.

A systematic multicriteria-based approach to support product portfolio selection in microalgae biorefineries

This work proposes and applies a sequential approach of objective methods to aid the decision-making process for the deployment of microalgae biorefineries. The strategy combines Multicriteria Decision Analysis (MCDA) and weight assignment methods to simultaneously consider technical, economic, and environmental criteria to (1) outrank the best bioproduct options from different biomass fractions present in microalgae biomass at different ratios (namely carbohydrates, lipids, and protein) and (2) define the most suitable biorefining pathways associated with specific pairings of microalgae strains and cultivation conditions. The first part of the assessment identified succinic acid, acrylic acid, and citric acid as the top-ranked bioproducts from carbohydrates, polyurethane from lipids, and a thermoplastic extrusion co-feed from protein. The second step of the analysis determined that, when production of a hydrocarbon fuel is desired, the compositional profile of a strain is paramount in defining the biorefining setup that should be pursued. In summary, microalgae lipids should be sent to the production of hydrocarbon fuels if the ratio between neutral lipids and fermentable carbohydrates is higher than roughly 1, with the simultaneous conversion of carbohydrates and protein to the higher-value products noted above. Finally, this result was corroborated through process simulations, which indicated superior economic and environmental metrics when strains are paired with the most suitable conversion pathways as identified through MCDA. The outcomes of this work provide objective guidelines for establishing the best biorefining approaches for a large suite of biochemical compositions as a screening method prior to employing detailed process simulations alongside rigorous techno-economic and life-cycle assessments.

On the mechanism of initiation steam cracking of C6 hydrocarbons by hyperbranched poly(amidoamine) (PAMAM) initiator

Initiators with low bond dissociation energy can initiate the cracking of hydrocarbons, but the initiation effect on hydrocarbons with different molecule structures remains ambiguous. In this study, the steam cracking of three C6 hydrocarbons, namely n-hexane, iso-hexane and methyl-cyclopentane (MCP), initiated by hyperbranched poly(amidoamine) (PAMAM) were investigated experimentally in a stainless-steel tubular reactor, and the detailed kinetic reaction models and reaction process simulations were conducted by Reaction Mechanism Generator and Chemkin-pro software packages. The results confirm that the addition of PAMAM can significantly promote the cracking conversion and reduce the initial cracking temperature of hydrocarbons because the decomposition of PAMAM at relatively low temperature produces high concentration of active NH2 and CH3 radicals, which significantly increases the rate of hydrogen abstraction. Importantly, the promotion efficiency of the initiator can be highly dependent on the cracking behaviour of hydrocarbons. The initiator will show higher promotion efficiency for hydrocarbon that is more prone to undergo sustained hydrogen abstraction after initiation. Therefore, the promotion efficiency of PAMAM follows the order of n-hexane > iso-hexane > MCP. This study is helpful for a better understanding of the initiation mechanism and will guide the design and screening of effective initiators for naphtha with different compositions.

Assessing opportunities and weaknesses of green hydrogen transport via LOHC through a detailed techno-economic analysis

In the transition towards a more sustainable energy system, hydrogen is seen as the key low-emission energy source. However, the limited H2 volumetric density hinders its transportation. To overcome this issue, liquid organic hydrogen carriers (LOHCs), molecules that can be hydrogenated and, upon arrival, dehydrogenated for H2 release, have been proposed as hydrogen transport media. Considering toluene and dibenzyltoluene as representative carriers, this work offers a systematic methodology for the analysis and the comparison of LOHCs, in view of identifying cost-drivers of the overall value-chain. A detailed Aspen Plus process simulation is provided for hydrogenation and dehydrogenation sections. Simulation results are used as input data for the economic assessment. The process economics reveals that dehydrogenation is the most impactful cost-item, together with the carrier initial loading, the latter related to the LOHC transport distance. The choice of the most suitable molecule as H2 carrier, ultimately, is a trade-off between its hydrogenation enthalpy and cost.

Process Simulation Modeling of the Linear Low-Density Polyethylene Catalytic Pyrolysis in a Fluidized Bed Reactor

In this work, a comprehensive process simulation was developed to study and predict the pyrolysis of linear low-density polyethylene (LLDPE) in a fluidized bed reactor (FBR). The comprehensive simulation operated at 600 and 700 °C to investigate the pyrolytic oil and wax yields. These products were chosen as they mimic fuel range products available as a renewable fuel and energy source. The results showed that the oil yield decreased from 600 to 700 °C. This is because of an increase in the polyolefin polymer matrix’s vibration leading to an increase in temperature and absorbed thermal energy. In addition, there is a higher gas yield produced and negligible wax formation at 700 °C, which is beneficial in controlling accrued plastic waste (PW), of which polyethylene (PE) represents a vast proportion of via thermo-chemical conversion (TCC) technologies. The detailed process simulation was compared with experimental data under the same technology and operating conditions, and it was found that less than 10% discrepancy was observed between the two sets of data, suggesting a good validation between the two studies. Further studies showed that the diesel fuel lumped hydrocarbon (HC) range (C10–C19) was between 40 and 63% in the pyrolysis oil yield obtained. Moreover, the temperature profiles and fluidized bed distributor parameters were compared and investigated. The current simulation has proven that it can successfully predict the pyrolysis of LLDPE in an FBR.

Scenario assessment of introducing carbon utilization and carbon removal technologies considering future technological transition based on renewable energy and direct air capture

Carbon capture and utilization (CCU) and carbon dioxide removal (CDR) technologies have the potential to significantly contribute to GHG reduction. Numerous studies have evaluated the CO2 reduction effects and economics of CCUs and CDRs; however, uncertainties in these evaluations due to various regional characterizations and future technological transitions are of high importance. In this study, four synthetic fuels (fuels produced from captured CO2 and H2), methanol, methane, gasoline, and diesel, were evaluated by life cycle assessment (LCA) and techno-economic assessment (TEA). Five representative countries with different regional characteristics were selected for the study. A bottom-up integrated LCA/TEA approach was used, involving detailed process simulations to avoid uncertainties and to evaluate future technological transitions based on direct air capture (DAC) and renewable energy. The overarching objective of this study was to provide a transparent framework with a common dataset generation methodology to determine the countries that have the advantages/disadvantages in synthetic fuel production and sale, considering the local operational parameters and large-scale introduction of DAC/renewable energy. Such multiple synthetic fuel analyses across various jurisdictions have not been conducted in previous studies. The results showed that the highest and lowest CO2 reductions were achieved by diesel (average 6.33 kg-CO2·kg−1) and methanol (average 3.43 kg-CO2·kg−1), respectively, whereas the highest and lowest product costs were of gasoline (average 2.96 USD·kg−1) and methanol (average 0.82 USD·kg−1), respectively. The technological transition using DAC and renewable energy showed average CO2 emission reductions of 47% (methanol), 99% (methane), 545% (gasoline), and 621% (diesel). Moreover, in the future, the lowest CO2 emission reduction costs are expected in Germany for methanol and diesel, Australia for methane, and Canada for gasoline. These findings can contribute to improving international collaboration to promote CCU and CDR technologies.

Process simulation for enhanced p-xylene production via aromatics complex integrated toluene methylation with low-cost methanol feedstock

Enhancing the p-xylene (PX) yield for the process of direct crude to chemicals will keep more technological competitiveness and sustainable economics. However, the enhancement would be limited by the ratio of benzene ring to methyl groups in the feedstock. To maximize the PX capacity, the toluene methylation unit is integrated to the traditional aromatic complex with the low-cost methanol as additional feedstock. The detailed process modeling and simulation are presented for the mass balance, energy consumption and technoeconomic analyses. The results show that the PX yield is significantly improved by integrating toluene methylation unit and the additional methanol feedstock to break the limitations of ratio of benzene ring to methyl groups in the original feedstock. By comparing with the traditional aromatic complex, the PX product increases with a growth of 31.24% from 869.70 kmol·h−1 to 1140.92 kmol·h−1 for the methylation integrated process, and the effective utilization rate of benzene ring in the feedstock enhances from 65.74% to 86.23%. Under the minimum temperature difference of 10 °C, the integrated process reduces the unit energy consumption by 5.59% equaling 7.55% of standard oil. Besides, the integrated process needs less total capital investment but produces more annual sales revenues due to the high PX yield and low energy consumption, which exhibits more sensibility to the prices of feedstock and products and greater techno-economic performance than that of traditional aromatic complex.

Conceptual carbon-reduction process design and quantitative sustainable assessment for concentrating high purity ethylene from wasted refinery gas

The direct emission of waste refinery gas after combustion will cause a severe greenhouse effect. Recovering high-value-added ethylene from wasted refinery gas has fundamental economic and environmental significance. Due to the complexity of the composition of refinery waste gas, designing and optimizing the whole recovery process is still a challenging task. Herein, a novel process (SCOAS) was proposed to obtain polymer-grade ethylene from wasted refinery gas through a direct separation process, and heat pump-assisted thermal integration optimization (HPSCOAS) was carried out. The unique feature of the novel approach is that a new stripper and ethylene reabsorber follow the dry gas absorber to ensure ethylene recovery and methane content. An industrial model, shallow cooling oil absorption (SCOA), and concentration combined cold separation system of ethylene unit using wasted refinery gas was established to analyze the technology and environment. Based on the detailed process modeling and simulation results, the quantitative sustainability assessment of economy and environment based on product life cycle process is carried out. The results show that compared with the traditional process when the same product is obtained, the total annual cost of the HPSCOAS process is the lowest, which is 15.4% lower than that of the SCOA process and 6.1% lower than that of the SCOAS process. In addition, compared with the SCOA process and the HPSCOAS process, the SCOAS process has more environmental advantages. The non-renewable energy consumed by SCOAS is reduced by about 24.8% and 6.1%, respectively. The CO2 equivalent is reduced by about 38.6% and 23.7%.

When Bigger Is Not Greener: Ensuring the Sustainability of Power-to-Gas Hydrogen on a National Scale.

As the prices of photovoltaics and wind turbines continue to decrease, more renewable electricity-generating capacity is installed globally. While this is considered an integral part of a sustainable energy future by many nations, it also poses a significant strain on current electricity grids due to the inherent output variability of renewable electricity. This work addresses the challenge of renewable electricity surplus (RES) utilization with target-scaling of centralized power-to-gas (PtG) hydrogen production. Using the Republic of Korea as a case study, due to its ambitious plan of 2030 green hydrogen production capacity of 0.97 million tons year-1, we combine predictions of future, season-averaged RES with a detailed conceptual process simulation for green H2 production via polymer electrolyte membrane (PEM) electrolysis combined with a desalination plant in six distinct scale cases (0.5-8.5 GW). It is demonstrated that at scales of 0.5 to 1.75 GW the RES is optimally utilized, and PtG hydrogen can therefore outperform conventional hydrogen production both environmentally (650-2210 Mton CO2 not emitted per year) and economically (16-30% levelized cost reduction). Beyond these scales, the PtG benefits sharply drop, and thus it is answered how much of the planned green hydrogen target can realistically be "green" if produced domestically on an industrial scale.

A Detailed Process and Techno-Economic Analysis of Methanol Synthesis from H2 and CO2 with Intermediate Condensation Steps

In order to increase the typically low equilibrium CO2 conversion to methanol using commercially proven technology, the addition of two intermediate condensation units between reaction steps is evaluated in this work. Detailed process simulations with heat integration and techno-economic analyses of methanol synthesis from green H2 and captured CO2 are presented here, comparing the proposed process with condensation steps with the conventional approach. In the new process, a CO2 single-pass conversion of 53.9% was achieved, which is significantly higher than the conversion of the conventional process (28.5%) and its equilibrium conversion (30.4%). Consequently, the total recycle stream flow was halved, which reduced reactant losses in the purge stream and the compression work of the recycle streams, lowering operating costs by 4.8% (61.2 M€·a−1). In spite of the additional number of heat exchangers and flash drums related to the intermediate condensation units, the fixed investment costs of the improved process decreased by 22.7% (94.5 M€). This was a consequence of the increased reaction rates and lower recycle flows, reducing the required size of the main equipment. Therefore, intermediate condensation steps are beneficial for methanol synthesis from H2/CO2, significantly boosting CO2 single-pass conversion, which consequently reduces both the investment and operating costs.

Preliminary feasibility study for hydrogen storage using several promising liquid organic hydrogen carriers: Technical, economic, and environmental perspectives

Liquid organic hydrogen carriers (LOHC) are promising alternatives to conventional H2 media owing to their novelty in the storage and transportation of H2. Herein, a comprehensive feasibility study is reported for hydrogenation processes using several promising LOHC systems: N-ethylcarbazole (NEC)–perhydro-NEC (12H-NEC), dibenzyltoluene (DBT), perhydro-dibenzyltoluene (18H-DBT), toluene (TOL)–methylcyclohexane (MCH), and CO2–methanol (MeOH). Detailed process simulation using Aspen Plus® reveals a considerable amount of stored H2 for DBT–18H-DBT (7.20 kmolH2 h−1) and the lowest unit cost of H2 storage (7.00 $ kgH2-1) by itemized cost estimation. In addition, the effects of operating temperature, recycle ratio of unreacted H2, and scale of H2 storage on economic feasibility are investigated, and the expected cost reductions to 2.83, 4.21, 3.84, and 2.37 $ kgH2-1 are evaluated for NEC–12H-NEC, DBT–18H-DBT, TOL–MCH, and CO2–MeOH, respectively. The sensitivity analysis quantifies the variation in the total unit cost of H2 storage and identifies the costs of the H2 reactant and labor as key economic parameters in LOHC hydrogenation. Furthermore, 0.16–0.43, 0.78–1.72, 1.25–1.73, and 1.12–5.52 kgCO2 kgH2-1 of unit CO2 emissions are evaluated by integrative carbon footprint analysis.

Carbon Footprint of Bleached Softwood Fluff Pulp: Detailed Process Simulation and Environmental Life Cycle Assessment to Understand Carbon Emissions

Carbon Footprint of Bleached Softwood Fluff Pulp: Detailed Process Simulation and Environmental Life Cycle Assessment to Understand Carbon Emissions

Controlling local overheating in topology optimization for additive manufacturing

A novel constraint to prevent local overheating is presented for use in topology optimization (TO). The very basis for the constraint is the Additive Manufacturing (AM) process physics. AM enables fabrication of highly complex topologically optimized designs. However, local overheating is a major concern especially in metal AM processes leading to part failure, poor surface finish, lack of dimensional precision, and inferior mechanical properties. It should therefore be taken into account at the design optimization stage. However, including a detailed process simulation in the optimization would make the optimization intractable. Hence, a computationally inexpensive thermal process model, recently presented in the literature, is used to detect zones prone to local overheating in a given part geometry. The process model is integrated into density-based TO in combination with a robust formulation, and applied in various numerical test examples. It is found that existing AM-oriented TO methods which rely purely on overhang control do not ensure overheating avoidance. Instead, the proposed physics-based constraint is able to suppress geometric features causing local overheating and delivers optimized results in a computationally efficient manner.

Experiment and optimization of a large scale xenon/krypton cryogenic distillation system

A highly efficient cryogenic distillation system has been designed, developed and assessed to remove radioactive krypton-85 (85Kr) from xenon (Xe), which is commonly used as a valuable medium for dark matter detectors. By using the self-designed distillation system, the concentration of krypton (Kr) in a commercial xenon product can be reduced from 10−9 to 10−12 mol/mol with 99% xenon collection efficiency at maximum flow rate of 5 kg/h. Over 1000 kg of xenon has been purified and employed as the detection medium in project Panda X, the first dark matter detector developed in China. In this present paper, detailed process simulation was conducted to refine the working parameters and to define the optimum operating conditions for the cryogenic distillation system. The predicted results were compared with those of experimental data obtained from the distillation system. The influence of comprehensive factors was investigated. Simultaneously, a dynamic model for the cryogenic distillation system was established to provide an in depth analysis of the dynamic characteristics of the system.

Performance assessment of biogas-fed solid oxide fuel cell system for municipal solid waste treatment

An enormous amount of municipal waste is produced globally and a large proportion of this waste is dumped into the landfill that is now about to reach the maximum capacity and makes it obligatory to investigate alternative methods for waste treatment. This study proposes a novel design to treat the organic fraction municipal solid waste (OFMSW) to generate electricity using solid oxide fuel cells (SOFC). The detailed process simulation is conducted using the standard chemical process simulator Aspen Plus which predicts the electricity that is generated using the OFMSW as feedstock. The biogas from the system is employed to the reformer that produces syngas and this mixture of hydrogen and carbon monoxide is fed to the SOFC with air to generate electricity. The detailed characterization of the proposed system is conducted and numerous sensitivity analyses are performed to investigate the system performance. The study also employs a detailed technical and economic feasibility of the biogas-fed SOFC system for municipal solid waste treatment. The proposed design employs 1,000 Nm3/hr of biogas flow rate that produces 3,633 kW of DC power using SOFC. The thermal management of the designed system is also performed to recover the additional heat within the designed system. A detailed techno-economic feasibility study is conducted for the proposed system and the capital and operating expenditures, income and depreciation costs are also evaluated. The economic and cash flow analyses show that the plant is suitable for a long-term scenario. It has been predicted that if the electricity price increase to 130 $/MWh, it will take 5 years as a payback period for the long-term scenario. Furthermore, the results obtained from the sensitivity studies and techno-economic analysis are presented and discussed.

Performance Evaluation of KBH4 as Energy Carrier for Shipping Applications

AbstractNon‐fossil fuels are urgently needed for maritime and inland shipping applications to mitigate the sector's adverse impact on the global climate. This study investigates the performance of potassium borohydride (KBH4) as an alternative, carbon‐free energy carrier on the basis of detailed process simulations of the overall energy storage cycle in Aspen Plus®. After optimizing the individual on‐board and off‐board process steps, the feasibility of installing a KBH4‐based energy supply system on board of an inland‐waterway cargo vessel is evaluated and critical process steps are highlighted along with current research challenges.

Demand response scheduling using derivative-based dynamic surrogate models

When assessing demand response to solve optimal scheduling problems, the optimization algorithm needs to be coupled with the process model in order to quantify the behavior of the monitored variable. For negligible transients, a first approximation consists of applying the steady state correlation between input and output variables. On the contrary, when dynamics show a relevant bias with respect to the estimated steady state response, a more accurate model is required. When coupling dynamic models of entire chemical processes with the optimization algorithm, the computational effort drastically increases. In those cases, the model should be simplified without losing its accuracy.In this research work, we propose a derivative-based approach for dynamic surrogate modeling applied to an ethylene oxide production scheduling problem. Thanks to its general validity, once derived, it can be applied to any setpoint trajectory. This approach allows to reduce the computational time of the optimization algorithm by orders of magnitude, providing results with the same accuracy as the detailed process simulation.

Fuelling power plants by natural gas: An analysis of energy efficiency, economical aspects and environmental footprint based on detailed process simulation of the whole carbon capture and storage system

In view of the low-carbon transformation of the power sector, natural gas-fired power generation is the only technology, among fossil resources, that will continue to provide an important source of flexibility for the power system in the coming years. However, the carbon dioxide emissions produced by the operation of such plants call for carbon capture and storage equipment, whose deployment needs to be assessed and compared with the main renewable technologies: wind power and photovoltaics. This work uses process simulation in order to assess two different carbon capture processes: a traditional one, based on monoethanolamine, and an innovative one, based on hot potassium carbonate. Process simulation is also used for the transportation of carbon dioxide to the sequestration site. Mass and energy balances from the simulations are then used for the calculation of the Energy Return on Energy Invested, the Levelized Cost of Energy and as inputs for the Life Cycle Assessments of both alternative designs. The life cycle analyses of the considered power technologies exhibited higher contributions due to fossil-based power plants towards climate-related impact categories, while renewable sources were revealed to be more burdensome for the exploitation of mineral resources. The calculated Energy Return on Energy Invested for gas-fired power plants with carbon capture and storage is between 5.2 and 12.4, comparable with the values of photovoltaics and wind power. On the other hand, their Levelized Cost of Energy is between 10.2 and 20.0 eurocent per kilowatt-hour, much higher than that of renewables. The conclusion is that, at present, the sustainability of gas-fired power stations equipped with carbon capture and storage should be carefully considered and not taken for granted.

Systematic Approach for Synthesizing Carbon–Hydrogen–Oxygen Networks Involving Detailed Process Simulations

Carbon–hydrogen–oxygen symbiotic networks (CHOSYNs) provide a systematic multiscale framework for integrating multiple hydrocarbon processing plants. Earlier approaches have focused on high-level performance benchmarking using atomic and stoichiometric targeting techniques, which are subsequently detailed to identify the implementation strategies for allocation and processing. These sequential approaches are very powerful for the cases involving benchmarks that are independent of the system details (e.g., minimum usage of raw materials, minimum discharge of wastes, maximum revenue). For objectives involving detailed process information (e.g., capital cost minimization), there is a need to include the system details early enough in optimization. This paper proposes a systematic approach for incorporating detailed process simulations throughout the various stages of synthesizing a CHOSYN. The proposed approach involves the use of computer-aided process simulators and simultaneous optimization for synthesizing a CHOSYN. Critical data are generated and used at each design stage. For existing facilities, targeting uses the simulated data on available resources and sinks (e.g., flow rate, composition, pressure, and temperature). Process synthesis is used to generate a set of candidate new units and plants to be added, while detailed simulation is used to size these plants and identify the specific needs for flows and compositions. The proposed approach is implemented for a case study that involves five existing plants and a set of seven candidate plants that can induce symbiosis. The results show final configurations with the selection of new plants, the reduction of raw material, the allocation of internal and external sources, and the details of process information, capital and operating costs, and flow rate, pressure, and temperature of the exchangeable streams across the network.