Flowsheet Model Research Articles

Membrane Systems Engineering for Post-combustion Carbon Capture

This study proposes a strategy for optimal design of hollow fiber membrane networks for post combustion carbon capture from power plant multicomponent flue gas. A mathematical model describing multicomponent gas permeation through a separation membrane was customized into the flowsheet modeling package ASPEN PLUS. An N-stage membrane network superstructure was defined considering all possible flowsheeting configurations. An optimization formulation was then developed and solved using an objective function that minimizes the costs associated with operating and capital expenses. For a case study of flue gas feed flow rate of 298 m3/s with 13% CO2 and under defined economic parameters, the optimization resulted in the synthesis of a membrane network structure consisting of two stages in series. This optimal design was found while also considering feed and permeate pressures as well as recycle ratios between stages. The cost of carbon capture for this optimal membrane network is estimated to be $28 per tonne of CO2 captured, considering a membrane permeance of 1000 GPU and membrane selectivity of 50. Following this approach, a reduction in capture cost to less than $20 per tonne CO2 captured is possible if membranes with permeance of 2000 GPU and selectivity higher than 70 materialize.

Application of the flux number approach for the simulation of granulation processes by use of flowsheeting tools

The present work describes the study of a continuous fluidized bed granulation process involving a solution spray as binder. The study entails the employment of a flux number as an extension to an existing flowsheet model (SolidSim). The agglomeration kernel used here is based on the Equi-Kinetic Energy principle and has been derived and proven for fluidized bed granulation processes using reactive and melt binders, but not for solution binders. This kernel has been correlated in the past to the flux number, which contains the main characteristics of the fluidized solids and the spray-on, such as the binder flux, the particle density and the fluidization gas velocity, in combination with population balances. This correlation was derived for a few liquid/solids systems only, notably small scale batch processes with melt binders, and a first attempt to the generalization of this correlation is shown here by its application to a completely different system, notably a continuous large pilot using a solution binder. The validated SolidSim flowsheet is useful for parameter variations and sensitivity analyses, showing a strong effect of the flux number exponent and the cut size of the screen on the product size distribution and recycle rate. Such quantitative relations between process conditions and product quality allow for significant savings in cost and time for process and product development and optimization.

An integrated approach for dynamic flowsheet modeling and sensitivity analysis of a continuous tablet manufacturing process

Manufacturing of powder-based products is a focus of increasing research in the recent years. The main reason is the lack of predictive process models connecting process parameters and material properties to product quality attributes. Moreover, the trend towards continuous manufacturing for the production of multiple pharmaceutical products increases the need for model-based process and product design. This work aims to identify the challenges in flowsheet model development and simulation for solid-based pharmaceutical processes and show its application and advantages for the integrated simulation and sensitivity analysis of two tablet manufacturing case studies: direct compaction and dry granulation. The developed flowsheet system involves a combination of hybrid, population balance and data-based models. Results show that feeder refill fluctuations propagate downstream and cause fluctuations in the mixing uniformity of the blend as well as the tablet composition. However, this effect can be mitigated through recycling. Dynamic sensitivity analysis performed on the developed flowsheet, classifies the most significant sources of variability, which are material properties such as mean particle size and bulk density of powders.

Nitric Acid Extraction into TODGA

Advanced solvent extraction processes, namely DIAMEX, SANEX or GANEX, for the separation of the minor actinides (americium and curium) are under development within Europe. The tridentate diglycolamide ligand, TODGA, shows many interesting properties and is under investigation in conjunction with a variety of other extractants for the DIAMEX and SANEX processes as well as the GANEX process. In order to successfully demonstrate these processes, understanding the acid extraction into the organic phases is critical to process flowsheet design and modelling. Here nitric acid extractions into TODGA have been measured and models produced using an equilibrium based approach accounting for nitric acid activities in the aqueous phase.

Flow Sheet Model Evaluation of Nuclear Hydrogen Steelmaking Processes with VHTR-IS (Very High Temperature Reactor and Iodine-sulfur Process)

Nuclear hydrogen steelmaking (NHS) and nuclear hydrogen partial reduction steelmaking (NHPRS) systems were proposed using very high temperature reactor, and thermochemical hydrogen production iodine-sulfur process. Heat input and CO2 emissions of these systems were analyzed by heat and mass balance calculation. Total net heat input to the NHS system was 28.4 GJ/t-high quality steel (HQS), including material production, material transportation, and power generation. This value was much larger than that of a blast furnace steelmaking (BFS) system of 17.6 GJ/t-HQS. Reduction of hydrogen consumption in the shaft furnace and electricity consumption in the electric arc furnace were desired for lowering the heat input. Total net heat input of a NHPRS system was 31.9 GJ/t-HQS. Optimization of operation parameters such as the reduction ratio of partial reduced ore (PRO) and ratio of the PRO input to the blast furnace is desired to decrease the heat input. CO2 emissions of the NHS system and the NHPRS system were 9% and 50% of that from the BFS system. Substitution of coal by hydrogen and reduction of transportation weight contributed to the reduction. Steelmaking cost was also evaluated. When steelmaking scale of each system was unified to one million t-HQS/y, NHS was economically competitive to BFS and Midrex steelmaking. And NHS was advantageous at higher cost of resources.

Baseline Flowsheet Model for IGCC with Carbon Capture

Integrated gasification combined cycle (IGCC) processes have the potential for high thermal efficiency with a low energy penalty for carbon capture. Many researchers have proposed various innovations to improve upon the efficiency of the IGCC process. However, the analysis methods of most publications are generally not transparent and these published results are exceedingly difficult to reproduce. The National Energy Technology Laboratory (NETL) report [Cost and Performance Baseline for Fossil Energy Plants: Bituminous Coal and Natural Gas to Electricity Final Report; U.S. Department of Energy, Office of Fossil Energy, NETL, DOE/NETL-2010/1397, 2010] is widely used as a reference by researchers and by industry. To enable researchers to have a consistent and transparent framework for analyzing IGCC flowsheets and potential innovations, a baseline model derived from the NETL report is described herein and the corresponding flowsheet model and its full documentation are available online from this journal for...

Optimal heat distribution in the internally heat-integrated distillation column (HIDiC)

The internally heat-integrated distillation column (HIDiC) is an interesting separation alternative to the conventional column or the vapor recompression distillation (VRC). In an HIDiC, the influence of heat distribution along the column section has a significant impact on the design and optimization in addition to the compressor pressure ratio. In this work, the optimization of heat distribution in the HIDiC is completely investigated through the application of flowsheet modeling and optimization solver in Aspen Plus. A commercial-scale propylene/propane splitter is used as a case study to illustrate the effect of heat distribution on energy or cost performance. A comparison of the optimum HIDiC structures obtained from different objective functions is discussed. Some optimum HIDiC structures could be evolved into Linde double columns with a side rectifier, which is a common application found in air separation process. This structure is potentially another interesting alternative to the conventional VRC.

Integrating anaerobic processes into wastewater treatment

Over the past decade, the concept of anaerobic processes for the treatment of low temperature domestic wastewater has been introduced. This paper uses a developed wastewater flowsheet model and experimental data from several pilot scale studies to establish the impact of integrating anaerobic process into the wastewater flowsheet. The results demonstrate that, by integrating an expanded granular sludge blanket reactor to treat settled wastewater upstream of the activated sludge process, an immediate reduction in imported electricity of 62.5% may be achieved for a treated flow of c. 10,000 m3 d−1. This proposed modification to the flowsheet offers potential synergies with novel unit processes including physico-chemical ammonia removal and dissolved methane recovery. Incorporating either of these unit operations can potentially further improve the flowsheet net energy balance to between +0.037 and +0.078 kWh m−3 of produced water. The impact of these secondary unit operations is significant as it is this contribution to the net energy balance that facilitates the shift from energy negative to energy positive wastewater treatment.

Flowsheet Development and Modeling of Hydrogen Production from Empty Fruit Bunch via Steam Gasification

Due to the availability of agricultural land and significant production of palm oil in Malaysia, there is abundance of biomass in the form of agricultural wastes. This work reports a mathematical model for the flowsheet developed for hydrogen production from empty fruit bunch from oil palm via steam gasification with in-situ carbon dioxide capture by CaO as sorbent. The flowsheet model incorporates the chemical reaction kinetics, mass and energy balances calculations. Parameter analysis on the influence of the temperature, steam/biomass and sorbent/biomass ratios are performed. It is predicted that more than 70 mole% hydrogen can be produced at 1150 K. In addition, CO2 are predicted to be fully absorbed from the system at sorbent/biomass ratio of 2.0. It is observed that the thermodynamic efficiency of the gasifier increases with temperature reaching a maximum efficiency of 84% at steam/biomass ratio of 2.0. It is shown that by using CaO as the sorbent in the gasifier, the efficiency can be increased by 10% compared to the conventional gasification method.

Hydrothermal Gasification of Waste Biomass: Process Design and Life Cycle Asessment

A process evaluation methodology is presented that incorporates flowsheet mass and energy balance modeling, heat and power integration, and life cycle assessment Environmental impacts are determined by characterizing and weighting (using CO2 equivalents, Eco-indicator 99, and Eco-scarcity) the flowsheet and inventory modeling results. The methodology is applied to a waste biomass to synthetic natural gas (SNG) conversion process involving a catalytic hydrothermal gasification step. Several scenarios are constructed for different Swiss biomass feedstocks and different scales depending on logistical choices: large-scale (155 MW(SNG)) and small-scale (5.2 MW(SNG)) scenarios for a manure feedstock and one scenario (35.6 MW(SNG))for a wood feedstock. Process modeling shows that 62% of the manure's lower heating value (LHV) is converted to SNG and 71% of wood's LHV is converted to SNG. Life cycle modeling shows that, for all processes, about 10% of fossil energy use is imbedded in the produced renewable SNG. Converting manure and replacing it, as a fertilizer, with the process mineral byproduct leads to reduced N20 emissions and an improved environmental performance such as global warming potential: -0.6 kg(CO2eq)/MJ(SNG) vs. -0.02 kg(CO2eq)/MJ(SNG) for wood scenarios.

Parametric study of large-scale production of syngas via high-temperature co-electrolysis

Abstract A process model has been developed to evaluate the potential performance of a large-scale high-temperature co-electrolysis plant for the production of syngas from steam and carbon dioxide. The co-electrolysis process allows for direct electrochemical reduction of the steam/carbon dioxide gas mixture, yielding hydrogen and carbon monoxide, or syngas. The process model has been developed using the UniSim system-analysis code. Using this code, a detailed process flow sheet has been defined that includes all the components that would be present in an actual plant such as pumps, compressors, heat exchangers, turbines, and the electrolyzer. Since the electrolyzer is not a standard UniSim component, a custom integral co-electrolysis model was developed for incorporation into the overall UniSim process flow sheet. The integral co-electrolysis model assumes local chemical equilibrium among the four process-gas species via the water-gas shift reaction. The electrolyzer model allows for the determination of co-electrolysis outlet temperature, composition (anode and cathode sides); mean Nernst potential, operating voltage and electrolyzer power based on specified inlet gas flow rates, heat loss or gain, current density, and cell area-specific resistance. The integral electrolyzer model was validated by comparison with results obtained from a fully three-dimensional computational fluid dynamics model developed using FLUENT, and by comparison with experimental data. This paper provides representative results obtained from the UniSim flow sheet model for a 300 MW e co-electrolysis plant, coupled to a high-temperature gas-cooled nuclear reactor. The co-electrolysis process, coupled to a nuclear reactor, provides a means of recycling carbon dioxide back into a useful liquid fuel. If the carbon dioxide source is based on biomass, the overall process, from production through utilization, would be climate-neutral.

Investigation of hydrocarbon reforming processes for micro-cogeneration systems

Hydrogen is the lightest chemical element and offers the best energy-to-weight ratio of any fuel. Hydrogen is colorless, odorless and its only by-product is water. It offers cost-effective solutions to reduce greenhouse gas emissions (in accordance with the Kyoto Protocol), improve air quality, diversify energy supply and reduce noise. The use of hydrogen with the practical application of household fuel cells such as micro-cogeneration and fuel-cell vehicles signifies a paradigm shift from a society that burns fossil fuels, to a society based around hydrogen. In the short term, hydrogen could be used in urban vehicles, which would reduce emissions in city centers. In the long term, it could be used in combined heat/power generation, in industry, in residential applications and in every form of transport like ships, trains and airplanes. There are several methods of producing hydrogen from fossil resources such as natural gas or naphtha, for example, steam reforming, partial oxidation and autothermal reforming. Among these, steam reforming of natural gas is a widely used method of extracting hydrogen by a process in which natural gas and steam are caused to react in a reactor filled with a catalyst. In this article, the effects of reforming operation parameters on the product distribution and conversion efficiency of hydrocarbon mixtures were discussed. The investigated reforming options are autothermal reforming (ATR), steam reforming (SR) and partial oxidation (POX). The ASPEN-HYSIS 3.2 process simulation software code has been utilized for the calculations of the whole fuel processing systems. Natural gas fuel has been simulated and applied to the flow-sheet model. It is desired to produce hydrogen-rich reformate gas with as low as possible CO formation. Different parametric process simulation studies have been studied such as reactor temperature affects the steam to carbon (S/C) and oxygen to carbon (O 2/C) ratios. Net electrical and fuel processing efficiencies of all selected options have been investigated as well. The results indicate that these selected operation parameters are very important for the appropriate selection of the most efficient system approach.

Gasification of New Zealand Coals: A Comparative Simulation Study

The aim of this study was to conduct a preliminary feasibility assessment of gasification of New Zealand (NZ) lignite and sub-bituminous coals, using a commercial simulation tool. Gasification of these coals was simulated in an integrated gasification combined cycle (IGCC) application and associated preliminary economics compared. A simple method of coal characterization was developed for simulation purposes. The carbon, hydrogen, and oxygen content of the coal was represented by a three component vapor solid system of carbon, methane, and water, the composition of which was derived from proximate analysis data on fixed carbon and volatile matter, and the gross calorific value, both on a dry, ash free basis. The gasification process was modeled using Gibb's free energy minimization. Data from the U.S. Department of Energy's Shell Gasifier base cases using Illinios No. 6 coal was used to verify both the gasifier and the IGCC flowsheet models. The H:C and O:C ratios of the NZ coals were adjusted until the simulated gasifier output composition and temperature matched the values with the base case. The IGCC power output and other key operating variables such as gas turbine inlet and exhaust temperatures were kept constant for study of comparative economics. The results indicatedmore » that 16% more lignite than sub-bituminous coal was required. This translated into the requirement of a larger gasifier and air separation unit, but smaller gas and steam turbines were required. The gasifier was the largest sole contributor (30%) to the estimated capital cost of the IGCC plant. The overall cost differential associated with the processing of lignite versus processing sub-bituminous coal was estimated to be of the order of NZ $0.8/tonne. 13 refs., 9 tabs.« less

Operability and Flexibility of a Milk Production Line

The operability and flexibility of an existing milk treatment process are investigated through flowsheet modelling and simulation method. From the flowsheet simulation, a process operating region is determined using incoming milk flow viscosity and heat exchanger pressure drop as characteristic parameters. The operability and flexibility of the nominal operating points are evaluated with a minimization of the process pasteurization and cooling temperatures through vertex enumeration method. The milk treatment process simulation and process analysis provide a quantitative analysis method for the development of a flexible process in dairy industrial applications. The established process operability and flexibility analysis framework and flowsheet simulation can be adapted to other liquid food productions.

Flowsheet Modeling and Testing of Pseudohydroxide Extraction from Aqueous Sodium Hydroxide Solutions with 3,5‐di‐tert‐Butylphenol in Isopar® L Modified with Exxal® 8

A conceptual counter‐current process flowsheet was developed for sodium hydroxide recovery from alkaline solutions via pseudohydroxide extraction (PHE). PHE relies on a simple sodium ion/proton exchange mechanism at elevated pH using a weak organic acid extractant. The contact of the sodium‐loaded organic phase with water results in the reconstitution of the extractant in the organic phase and sodium hydroxide in the aqueous phase. In this work, the 3,5‐di‐tert‐butylphenol (35‐DTBP) cation exchanger was used in the Isopar® L diluent modified with isooctyl alcohol Exxal® 8. Equilibrium isotherms determined for PHE from pure sodium hydroxide solutions and simulated radioactive waste leachate were used to develop a semi‐empirical model that could be used for designing PHE process flowsheets. Using this model, a conceptual PHE flowsheet was developed for recovering NaOH from solutions generated by caustic leaching of radioactive tank sludges. The flowsheet consists of the extraction, scrub, and strip processes, each employing four equilibrium stages. The modeling of this flowsheet indicates 97% recovery of the sodium hydroxide from the waste leachate feed solution. An experimental demonstration, performed with a simulated radioactive waste leachate using batch contacts in a co‐current analog of the counter‐current flowsheet, confirmed the potential for practical application of PHE technology.

A Process Synthesis Approach To Investigate the Effect of the Probability of Chain Growth on the Efficiency of Fischer−Tropsch Synthesis

To evaluate a process at the early stage of its development, one must be able to perform simple calculations to compare all the alternatives. This must be done on a reasonably realistic basis, so that one can make credible decisions; however, the process should not be so detailed and laborious that it becomes too “expensive” to perform for alternatives that can ultimately be discarded. A methodology for performing these calculations has been developed, and this will be illustrated with a case study on Fischer−Tropsch synthesis (FTS). The effect of designing a Fischer−Tropsch (FT) process targeting a particular value of the probability of chain growth (α) on the overall carbon efficiency has been studied using simplified FTS flowsheet models. Two process configurationsnamely, the once-through and recycle processeshave been compared, and it is observed that, for a fixed production rate of liquid fuels at 100% CO conversion, the carbon efficiency for the process with a recycle stream is higher than that of t...

Novel areas and future trends of computational fluid dynamics software applications in chemical engineering

The paper presents a brief overview of advanced novel applications and future trends of Computational Fluid Dynamics software in Chemical Engineering. Among the cases of major importance, single phase turbulent flow, as well as multiphase flow models are reviewed. Referring to single phase flows, the LES and RANS approaches are described and illustrated. The RANS approach is revealed as the most popular and inexpensive method for the analysis and solving of technical tasks. The paper reports on two recent modeling applications, namely, the CFD facilitated design of a new mixing impeller and the CFD characterization of impeller mixing efficiency. Multiphase models of increased sophistication describing solid, liquid and gas flows with simultaneous mass transfer between the phases are summarized with emphasis on their applications to describe evaporation, condensation, as well as chemical reactions in process equipment such as distillation columns and fluidized beds. The future trends and directions in Computer Aided methods for the analysis of Chemical Engineering processes incorporate developments, such as the integration of various pieces of software including flow sheet modeling CFD modeling and complex reaction and thermodynamic models.

Incorporating uncertainty in chemical process design for environmental risk assessment

AbstractThe effects of uncertainty in thermophysical properties on the evaluation of the environmental performance is demonstrated with a chemical process to recover toluene and ethyl acetate by absorption from a gaseous waste stream of a cellophane production plant. In this case study, the environmental performance is defined as the estimation of the volatile organic compounds (VOCs) and total emissions of the plant and of several environmental risk indexes. We found that estimations of VOCs are very sensitive to uncertainty in thermophysical properties such as infinite‐dilution activity coefficients, and vapor pressures (through uncertain temperature variations). Additionally, we concluded that calculation of the total emissions can be very sensitive to fuel content factors such as those used to estimate greenhouse gases. This can have such an impact on the emission calculations that a detailed model of the given chemical process might not be required for the estimation of the total emissions. In other words, a simpler process flowsheet model can perform the same task just as well, with the results within the variations caused by uncertainty in the thermophysical properties. We demonstrate a Monte Carlo approach that allows the detection of such uncertainty characteristics in a design, providing a rational basis for prediction of the associated environmental risks. This procedure also enables the deconvolution of various sources of uncertainty, and the estimation of physical property uncertainty through a similarity approach. We concluded that our framework can be used to enhance decision making by uncovering uncertainties and sensitivities in chemical process simulation. © 2004 American Institute of Chemical Engineers Environ Prog, 2004

Dynamic simulation of grinding circuits

A flexible and powerful dynamic simulation approach to grinding circuit simulation has recently been developed in CSIRO Minerals. The MATLAB/SIMULINK graphical programming environment has been used to construct a library of dynamic mathematical models of a number of key grinding and separation devices and to link them into various complex dynamic grinding circuits. True real-time dynamic simulation and visualisation of interlinked unit process operations in grinding circuits of arbitrary complexity can readily be achieved. The application of the dynamic simulation approach can help greatly in understanding the sometimes complex, nonlinear behaviour and dynamic interactions in various grinding circuits. Dynamic simulation can be used to test “what-ifs” in grinding process operations such as circuit response to variations in feed and unit operation characteristics. It is a cheap and effective means of investigating circuit optimisation without the risk of possible damage to operating units or production of a large amount of unwanted product during a physical optimisation process. Dynamic simulation is also extremely useful in developing and testing new ideas for process soft-sensors and control. The experience and knowledge gained in dynamic simulation of grinding circuits is directly applicable to other dynamic flowsheet modelling and optimisation problems in the minerals and process engineering industries. The advantages of building flowsheet models within the MATLAB/SIMULINK programming environment include the ability to readily develop and modify continuous, discrete and/or hybrid models of individual unit operations, with solution of the flowsheet system by a powerful in-built suite of equation solvers and analysis of results utilising extensive existing graphical capabilities. Flowsheet models of arbitrary complexity can easily be graphically developed, while individual unit models can be developed in terms of graphical block diagrams and/or customised block models written in computer code.

Group contribution based process flowsheet synthesis, design and modelling

In a group contribution method for pure component property prediction, a molecule is described as a set of groups linked together to form a molecular structure. In the same way, for flowsheet ”property” prediction, a flowsheet can be described as a set of process-groups linked together to represent the flowsheet structure. Just as a functional group is a collection of atoms, a process-group is a collection of operations forming an ”unit” operation or a set of ”unit” operations. The link between the process-groups are the streams similar to the bonds that are attachments to atoms/groups. Each process-group provides a contribution to the ”property” of the flowsheet, which can be performance in terms of energy consumption, thereby allowing a flowsheet ”property” to be calculated, once it is described by the groups. Another feature of this approach is that the process-group attachments provide automatically the flowsheet stream properties, which serves as very good initial estimates for convergence of mass/energy balance calculations.