Steady-state Process Simulation Research Articles

Integrated biomass thermochemical conversion for clean energy production: Process design and economic analysis

In this study, conversion of Napier grass bagasse into biofuel was carried out through steady state process modelling and simulation using Aspen Plus software. An integrated thermochemical system consisting pyrolysis, gasification and combustion section for pyrolytic oil production and upgrading, non-condensable gas/syngas and bio-char valorisation was developed in a single flowsheet with capacity of 49 kg/h feedstock. Aspen process economic analyser was used to generate both capital and operating costs estimates, and other investment analysis following first quarter 2016 pricing basis. The simulation result showed that about 68 wt% of the feedstock could be processed into pyrolytic oil at 480 °C with corresponding liquid biofuel yield of 5.35 kg/h, which is equivalent to about 11 wt% of the initial feedstock through in-situ hydrodeoxygenation process. The result of economic evaluation of the entire process plant indicated that a total capital cost of $2.13 M and operating cost/year of $0.3 M is required for 25-year economic life of the project with net present value of $15.18 M at 8% internal rate of return. The standalone biomass refining plant is expected to produce fuel at minimum fuel selling price of $5.81/gallon ($1.45/L) gasoline equivalent, mainly driven by the capital cost. This work presents a systematic combination of process units that will be needed to produce advanced cellulosic biofuels in the near future.

Techno-economic analysis of microalgae-based liquid fuels production from wastewater via hydrothermal liquefaction and hydroprocessing

In this work, a conceptual process design of wastewater-based algal biofuels production through hydrothermal liquefaction and hydroprocessing is proposed. Then a steady-state process simulation is performed to calculate the mass and energy analysis of the whole process for the production of hydrocarbons such as diesel, jet, gasoline, and H2. A discounted cash flow analysis is used to calculate a minimum selling price (MSP) of the hydrocarbon fuels. The MSP of the hydrocarbon fuels is found at US$4.3/GGE. This value is comparable with the previously reported value in the literature. In addition, the sensitivity study is carried out to study the influence of both processes and economic parameters on the minimum selling price (MSP) of the hydrocarbon fuels.

Co-production of hydrogen and power from black liquor via supercritical water gasification, chemical looping and power generation

Abstract An integrated system to harvest efficiently the energy from the waste of pulp mill industry, which is black liquor (BL), is proposed and evaluated. The proposed system consists of the supercritical water gasification (SCWG) of BL, syngas chemical looping, and power generation. To minimize the exergy loss throughout the system and to optimize the energy efficiency, process design and integration is conducted by employing the principles of exergy recovery and process integration methods. Hydrogen is set as the main output, while power is produced by utilizing the heat generated throughout the process. Process simulation is conducted using a steady state process simulator, Aspen Plus. Energy efficiency is defined into three categories: hydrogen production efficiency, power generation efficiency, and total energy efficiency. From process simulation, both of the integrated systems show very high total energy efficiency of about 73%.

Co-production of hydrogen and power from palm mill wastes

An integrated system to harvest efficiently the energy from palm mill wastes, which are empty fruit bunch (EFB) and palm oil mill effluent (POME), is proposed and evaluated. The proposed system adopts the supercritical water gasification (SCWG) of mixed EFB and POME, which is integrated with also with chemical looping and power generation. To minimize the exergy loss throughout the system, and therefore, optimize the energy efficiency, process design and integration is conducted by employing the principles of exergy recovery and process integration technologies. Hydrogen is set as the main output, while power is produced by utilizing the heat generated throughout the process. Process simulation is conducted using a steady state process simulator Aspen Plus V8.8. Energy efficiency is defined into three categories: hydrogen production efficiency, power generation efficiency, and total energy efficiency. From process simulation, the integrated systems show high total energy efficiency. Further study should be performed to investigate the effect of EFB/POME ratio, gasification temperature, SCL pressure condition on the system performance including total energy efficiency.

A mass- and energy balance-based process modelling study for the pyrolysis of cotton stalks with char utilization for sustainable soil enhancement and carbon storage

Thermal conversion of ligno-cellulosic agricultural waste inside a pyrolysis reactor and soil-storage of pyrolysis char is discussed as a low-tech negative emission technology. Cotton stalks are a typical agricultural residue with little economic value and there is no direct competition to food or feed provision. Currently, the stalks are often burnt on the fields. The investigated rotary kiln pyrolysis process has already been successfully applied at industrial scale before. In the investigated scenario, the pyrolysis char is returned to the soil for long-term carbon storage while the volatile pyrolysis products are used energetically. The steady-state process simulation environment IPSEpro was used to assess a virtual conversion plant. The mass- and energy flows are determined based on earlier measurements at a 500 kg/h test plant. The results show that 52.8% of the carbon contained in the biomass accumulate in the biochar, whereas 38% of the input energy can be exported as heat energy at temperature levels suitable for electricity generation or industrial heat supply. The pyrolysis char shows a low molecular O/C ratio of 0.07 and an H/C ratio of 0.26. The expected half-lives of biochar in soil are in the order of 1000 years for O/C ratios below 0.2. This makes the presented approach an interesting low-tech negative emission option. The predicted net negative emissions through stored carbon amount to 2.42 t CO2 per hectare and year. The overall CO2 emission avoidance effect can be increased if fossil fuel is substituted by the energy exported from the pyrolysis process.

Energy-saving performance of reactive distillation process for TAME synthesis through multiple steady state conditions

We have previously reported the existence of steady-state solutions where reaction conversion is improved within multiple steady states, which appear in the reactive distillation column for tert-amyl methyl ether (TAME) synthesis. In the present study, we examined the energy-saving performance of a reactive distillation process that comprises a reactive distillation column and two recovery distillation columns for multiple steady state conditions using steady-state process simulation. Bifurcation analysis revealed that the multiple steady state did not exist under a reflux ratio of 1, but existed under reflux ratios of 2, 3, and 4. The reboiler duty required to obtain high-purity TAME increased with increase in reflux ratio. The evaluation of energy consumption revealed that the reboiler duties of the second recovery column at the steady-state solutions in the multiple steady state were lower than that at the steady-state solution of reflux ratio 1. Due to the high reaction conversion and reduction of the reboiler duty in the second recovery column, the energy inputs per mole of TAME product at steady-state solutions of the multiple steady state with reflux ratios of 2, 3, and 4 reduced by 17, 12, and 6%, respectively, compared to that for reflux ratio 1.

Flexible heat pump or chiller with hybrid water/LiBr absorption/compression cycle

The concept and general considerations for the design of a hybrid absorption/compression cycle are presented. An electrically driven high-speed turbo compressor which is directly integrated in a single-stage water/LiBr absorption heat pump cycle provides a pressure lift for the refrigerant vapor transmitted from the evaporator to the absorber or from the desorber to the condenser, resulting in increased flexibility of the cycle for operation under non-standard boundary conditions. By detailed steady-state thermodynamic process simulation, three main operation modes are investigated concerning the required temperature level of the cooling water and the driving heat source as well as the increase of the chilled water capacity. Characteristic data for compression ratios between 1 and 3 are presented. Depending on the specific electrical input a significant change of the operating limits is observed. In order to assess the influence on the overall system efficiency, selected key figures such as driving power of the compressor, temperature lift, driving heat temperature level, as well as thermal and mechanical COP, are determined and discussed.As preparation for implementation of the concept with maximum flexibility, the required characteristic of the turbo compressor — governed by refrigerant vapor flow and pressure ratio — is deduced from the targeted operating envelope.Based on a fundamental physical model a preliminary design of the turbo compressor is found. This design has been further elaborated by a detailed fluid-dynamic and structural modeling of the compressor, allowing for a precise prediction of its performance and technical feasibility.

Technoeconomic Evaluation of Multiple Mixed Suspension-Mixed Product Removal (MSMPR) Crystallizer Configurations for Continuous Cyclosporine Crystallization

Continuous crystallization using Mixed Suspension-Mixed Product Removal (MSMPR) crystallizers has been demonstrated as a feasible method for implementing continuous separations in pharmaceutical manufacturing processes. This work conducts a steady-state process modeling and simulation study of the continuous cooling crystallization of cyclosporine, comparing processes with and without solids recycle for their technoeconomic viability. The model describes population balance equations, crystallization kinetics, and process mass balances to compare attainable crystallization and plantwide yields of different process configurations. Total cost components using an established economic analysis methodology are compared for varying numbers of crystallizers, operating temperatures, total crystallizer cascade residence times and API feed concentrations. Economic analyses and the calculation of normalized cost components with respect to total crystallizer volumes identify the process without recycle as the most economically viable option, achieving the lowest total costs and low E-factors for pharmaceutical processes. The sensitivity of total costs to the selected total residence times for economic analyses highlights the need for rigorous comparison methodologies. This work identifies the need for technoeconomic optimization studies of continuous crystallization processes to establish the optimal design of manufacturing campaigns prior to further development.

Modeling, simulation and analysis of a process for the production of crotonaldehyde

Crotonaldehyde is an important intermediate in the chemical industry and usually produced from acetaldehyde in aqueous solution. Recently, new results on the reactions which yield crotonaldehyde from acetaldehyde have become available. It was shown that the formation of aldoxane from acetaldehyde and acetaldol, as well as the oligomer formation in the system acetaldehyde and water have to be taken into account. In the present paper, the established process for the production of crotonaldehyde is analyzed based on that new information. A model for the physico-chemical properties of the relevant mixtures is developed as well as an equilibrium stage based process model. The models are implemented in a steady state process simulation tool which is used for numerical studies of the process. The results provide unexpected insights in the process which contains distillations in which complex reactions occur. A conceptual process design is carried out applying a structured approach. The performance of the process is analyzed and potential for its optimization is discussed.

Simulation-based techno-economic evaluation for optimal design of CO2 transport pipeline network

For large volumes of carbon dioxide (CO2) onshore and offshore transportation, pipeline is considered the preferred method. This paper presents a study of the pipeline network planned in the Humber region of the UK. Steady state process simulation models of the CO2 transport pipeline network were developed using Aspen HYSYS®. The simulation models were integrated with Aspen Process Economic Analyser® (APEA). In this study, techno-economic evaluations for different options were conducted for the CO2 compression train and the trunk pipelines respectively. The evaluation results were compared with other published cost models. Optimal options of compression train and trunk pipelines were applied to form an optimal case. The overall cost of CO2 transport pipeline network was analyzed and compared between the base case and the optimal case. The results show the optimal case has an annual saving of 22.7M€. For the optimal case, levelized energy and utilities cost is 7.62€/t-CO2, levelized capital cost of trunk pipeline is about 8.11€/t-CO2 and levelized capital cost of collecting system is 2.62€/t- CO2. The overall levelized cost of the optimal case was also compared to the result of another project to gain more insights for CO2 pipeline network design.

Heat and mass transfer modeling for multicomponent multiphase flow with CFD

Heat and mass transfer take place in a large number of processes. These phenomena are encountered in systems comprised of two or more phases, in which at least one of them is a mixture of many chemical species. The predictability of such multiphase and multicomponent systems plays a major role in the efficient design and operation of equipment and processes, where CFD has been frequently applied successfully over the past decade. Modeling multicomponent flow remains a challenge in relation to both micro or macro systems. In this study, simulations were carried out with the commercial code ANSYS® CFD (FLUENT®), version 14.0, and customized functions developed to predict the equilibrium compositions and temperature of a vapor–liquid system. A preliminary study on a binary mixture (water/air) was conducted in order to validate the results obtained with the commercial code using the data obtained from a standard psychrometric chart. In addition, simulations were carried out for a mixture of four pure hydrocarbons (methane, n-pentane, n-hexane and n-octane). Thus, a complete multicomponent mass transfer theory, based on Maxwell–Stefan’s equations, was applied as a customized function code, which can be used to calculate high flux corrections and the convective mass flux. The results were verified with predicted values obtained using the steady-state process simulator PRO/II®, version 8.2.

Finite Element Based Determination and Optimization of Seam Weld Positions in Porthole Die Extrusion of Double Hollow Profile with Asymmetric Cross Section

Finite elemente analysis (FEA) allows to reduce development time during the die design stage as well as costly extrusion trials with prototypes. Therefore, it is essential that FEA computation provides reliable results. Among other output quantities such as temperature, load, or die stress, the prediction of material flow is one of the most essential ones. Especially in porthole dies, the material flow can be very complex and thus the position of the seam welds in the profile may be uncertain. In this study the particle tracing method was utilized to determine and finally adjust the seam weld positions in a double hollow profile with varying wall thicknesses over the cross section. The seam weld positions resulting from the original die design were determined by Eulerian FEA computation in the first step. Subsequently, the seam weld positions were adjusted by changing the die geometry. The simulation results were verified by means of extrusion tests, which were conducted under industrial conditions. In addition, Lagrangian and Eulerian FEA was utilized to analyze the evolution of the seam weld positions by evaluation of material flow as well as pressure distribution during the transient initial stage and the steady-state stage of the extrusion process. It was demonstrated that steady state process simulation and the particle tracing method can be used for the prediction of seam weld positions in complex hollow cross sections.

Coal-CO2 Slurry Feed for Pressurized Gasifiers: Slurry Preparation System Characterization and Economics

Gasification-based plants with coal-CO2 slurry feed are predicted to be more efficient than those with coal-water slurry feed. This is particularly true for high moisture, low rank coal such as lignite. Nevertheless, preparation of the CO2 slurry is challenging and the losses associated with this process have not been accounted for in previous analyses. This work introduces the Phase Inversion-based Coal-CO2 Slurry (PHICCOS) feeding system, in which coal-CO2 slurry is prepared at ambient temperature via coal-water slurry. Steady-state process simulation is used to estimate the performance of the proposed slurry preparation and feeding system for bituminous coal and lignite. An Integrated Gasification Combined Cycle (IGCC) power plant with carbon capture is used here as a potential application, but this concept is applicable to any high-pressure coal feeding process. The economic attractiveness of the PHICCOS feeding system is assessed through calculation of its capital costs and resulting levelized cost of electricity, relative to competing commercial technologies. The findings of this work show that the PHICCOS feeding system offers a good tradeoff between overall process performance and costs. It is the most cost-effective method for feeding lignite and the second most attractive for bituminous coal, for which the competing technology is marginally cheaper. The PHICCOS feeding system is hence the only feeding system which is consistently cost-effective across the entire coal rank spectrum and is increasingly so for high-moisture and high-ash coal.

Dynamic modeling of CO2 absorption from coal-fired power plants into an aqueous monoethanolamine solution

Among carbon capture and storage (CCS), the post-combustion capture of carbon dioxide (CO2) by means of chemical absorption is actually the most developed process. Steady state process simulation turned out as a powerful tool for the design of such CO2 scrubbers. Besides steady state modeling, transient process simulations deliver valuable information on the dynamic behavior of the system. Dynamic interactions of the power plant with the CO2 separation plant can be described by such models. Within this work a dynamic process simulation model of the absorption unit of a CO2 separation plant was developed. For describing the chemical absorption of CO2 into an aqueous monoethanolamine solution a rate based approach was used. All models were developed within the Aspen Custom Modeler® simulation environment. Thermo physical properties as well as transport properties were taken from the electrolyte non-random-two-liquid model provided by the Aspen Properties® database. Within this work two simulation cases are presented. In a first simulation the inlet temperature of the flue gas and the lean solvent into the absorber column was changed. The results were validated by using experimental data from the CO2SEPPL test rig located at the Dürnrohr power station. In a second simulation the flue gas flow to the separation plant was increased. Due to the unavailability of experimental data a validation of the results from the second simulation could not be achieved.

Performance of an IGCC Plant with Carbon Capture and Coal-CO2-Slurry Feed: Impact of Coal Rank, Slurry Loading, and Syngas Cooling Technology

The high heat capacity and latent enthalpy of vaporization of water lead to a low gasification efficiency in gasifiers fed with coal-water slurry. Liquid carbon dioxide, CO2(l), has been suggested as an alternative slurrying medium to improve the efficiency of low-rank coal gasification in integrated gasification combined cycle power plants with carbon capture. Steady-state process simulation is used in this work to confirm published findings and present a comprehensive assessment of the impact of the coal rank, gasifier cooling technology, and CO2 slurry loading uncertainty on the performance advantage of CO2 slurry-fed plants. A power generation efficiency improvement of up to 25% (5%-points) is predicted, which is shown to increase with decreasing coal rank and to be highest for full-quench gasifier cooling technology; the latter is a significant source of capital cost savings and is especially attractive when combined with CO2 slurry feed. Using CO2(l) instead of water slurry reduces the performance penalty of low-rank coal gasification by half, thus substantially improving the feedstock flexibility of the plant. With a single exception, the performance benefit of coal-CO2 slurry was found to be outside the uncertainty range of the slurry loading, which is still one of the key unknowns of this alternative feed system.

Study of Direct Compression Heat Pump Energy-saving Technology

Abstract Analyzed the feasibility and necessity of the application of heat pump distillation in the gas separation unit. Through the comparison of the results of different heat exchanger, this paper verified the advantages of the heat exchanger with aluminum porous surface tube. Calculated the power consumption of the compressor by Aspen Plus steady-state process simulation, then the value of COP of the heat pump is obtained, and analyzed the economy of the heat pump distillation, the result shows that utilities and operating cost could be decreased by using heat pump distillation in gas separation unit, and the energy utilization efficiency economic benefits and energy-saving effects could be enhanced.

Performance Characterization of Hydrogen Isotope Exchange and Recombination Catalysts for Tritium Processing

AECL’s hydrogen isotope exchange catalyst and recombination catalysts have been successfully applied to a wide range of industrial tritium-removal applications. The catalysts are used for Liquid Phase Catalytic Exchange (LPCE) and for gas-phase and trickle-bed recombination of hydrogen isotopes and have led to process simplification, improved safety and operational advantages.Catalyst performance design equations derived from laboratory testing of these catalysts have been validated against performance under industrial conditions. In a Combined Electrolysis and Catalytic Exchange (CECE) demonstration plant analyses of LPCE and recombiner efficiency were carried out as a function of catalyst activity over a wide range of operation. A steady-state process simulation used to model and design the hydrogen-water isotopic exchange processes, such as the CECE detritiation plant, was validated using the results of this demonstration.Catalyst development for isotope-exchange and recombination applications has continued over the last decade. As a result, significant improvements in catalyst performance have been achieved for these applications. This paper outlines the uniqueness of AECL’s specialized catalysts and process designs for these applications with examples from laboratory and industrial case studies.

Enhancement in NGL production and improvement in water dew point temperature by optimization of slug catchers’ pressures in water dew point adjustment unit

The water dew point adjustment is one of the most important processes in all gas refineries which reduces the water content of gas to some allowable limit and separates the heavy hydrocarbons from gas. In Sarkhun gas refinery, natural gas dehydration and hydrocarbon dew point adjustment are performed by cooling method. Diethylene glycol (DEG) is injected to gas–gas heat exchanger and chiller to absorb water from wet gas and act as a freezing inhibitor. Hydrate formation in filter elements was observed in this gas refinery which has been investigated in this research. The pressure difference between slug catchers and well streams were optimized by steady state process simulation software in order to decrease the mole percentage of C 6+ exited along with the outlet gas stream from slug catcher and maximize the separation of liquid hydrocarbons. The pressure difference between the slug catcher unit and well streamlines was adjusted at optimized conditions and the experimental sampling was performed during modifications. The experimental results showed a considerable decrease in the mole percentage of C 6+ exited along with the outlet gas stream from slug catcher and the simulation results showed 16500 bbl/year increase in NGL production rate. Operating under optimized pressure in the dew point adjustment unit of Sarkhun gas refinery decreased the water dew point temperature to −26 °C and improved the hydrocarbon dew point temperature to −9 °C. Moreover, NGL and LPG production rates increased annually about 18672 ton and 6365 ton after modifications which results in $11million extra annual income for company.

Toward Novel Hybrid Biomass, Coal, and Natural Gas Processes for Satisfying Current Transportation Fuel Demands, 1: Process Alternatives, Gasification Modeling, Process Simulation, and Economic Analysis

This paper, which is the first part of a series of papers, introduces a hybrid coal, biomass, and natural gas to liquids (CBGTL) process that can produce transportation fuels in ratios consistent with current U.S. transportation fuel demands. Using the principles of the H2Car process, an almost-100% feedstock carbon conversion is attained using hydrogen produced from a carbon or noncarbon source and the reverse water-gas-shift reaction. Seven novel process alternatives that illustrate the effect of feedstock, hydrogen source, and light gas treatment on the process are considered. A complete process description is presented for each section of the CBGTL process including syngas generation, syngas treatment, hydrocarbon generation, hydrocarbon upgrading, and hydrogen generation. Novel mathematical models for biomass and coal gasification are developed to model the nonequilibrium effluent conditions using a stoichiometry-based method. Input−output relationships are derived for all vapor-phase components, char, and tar through a nonlinear parameter estimation optimization model based on the experimental results of multiple case studies. Two distinct Fischer−Tropsch temperatures and a detailed upgrading section based on a Bechtel design are used to produce the proper effluent composition to correctly match the desired ratio of gasoline, diesel, and kerosene. Steady-state process simulation results based on Aspen Plus are presented for the seven process alternatives with a detailed economic analysis performed using the Aspen Process Economic Analyzer and unit cost functions obtained from literature. Based on the appropriate refinery margins for gasoline, diesel, and kerosene, the price at which the CBGTL process becomes competitive with current petroleum-based processes is calculated. This break-even oil price is derived for all seven process flowsheets, and the sensitivity analysis with respect to hydrogen price, electricity price, and electrolyzer capital cost, is presented.

A novel multi-effect methanol distillation process

Crude methanol distillation is an energy-intensive separation process and contributes significantly to the cost of methanol production. Although a number of energy-efficient distillation systems have been proposed, there is potential for energy savings in methanol distillation. To further reduce the energy consumption of methanol distillation, a novel five-column multi-effect distillation process is proposed in this work, which is essentially an improved version of an existing four-column scheme. The four-column scheme is made up of a pre-run column, a higher-pressure column, an atmospheric column and a recovery column. The new five-column scheme adds a medium-pressure column after the original higher-pressure column. In this way, the load of the original higher-pressure and atmospheric columns can be decreased by about 30%. The five-column arrangement creates a multi-effect distillation configuration involving efficient heat integration between higher-pressure and medium-pressure columns, atmospheric and recovery columns, and recovery and pre-run columns. Steady-state process simulation results indicate that temperature differences at two sides of each heat exchanger are appropriate, allowing effective heat transfer. Economic analysis shows that the energy consumption of the five-column scheme can be reduced by 33.6% compared to the four-column scheme. Significant savings in operating costs can therefore be achieved, resulting in an economically viable process for methanol distillation.