Gas Separation Systems Research Articles

A Steady-state Simulation Model of Gas Separation System by Hollow-filament Type Membrane Module.

A steady-state simulation model of the gas separation system using a hollow-filament type membrane has been proposed. The mass transfer coefficients in the non-porous thin layer, in the porous support layer of the membrane and in the boundary layer of the membrane surface are estimated in the model. The four types of flow patterns: cross flow, mixing flow, concurrent flow and counter current flow, are also considered in the model. The mass transfer through the non-porous thin layer of the membrane controls the overall mass transfer by ~99%. The experimental observations of TPL (Tritium Process Laboratory in JAERI) for N2–H2 and Air—H2 systems agreed with the calculated results of the cross flow under a set of typical conditions (disposal volume of 2.78×10−3 Nm3/s, feed-side pressure of 3.44×105Pa, and permeated-side pressure of 1.07×104 Pa). The validity of the simulation method was thus proved. For Air-H2-H2O system also, the recovery ratios calculated for H2 are in good agreement with the experimental observations. However, the calculated recovery ratios of water vapor were slightly smaller than the experimental observations. This discrepancy may result from the difference in separation mechanism between H2 and water vapor, or the construction change of membrane caused by the existence of water vapor.

A Steady-state Simulation Model of Gas Separation System by Hollow-filament Type Membrane Module

A steady-state simulation model of the gas separation system using a hollow-filament type membrane has been proposed. The mass transfer coefficients in the non-porous thin layer, in the porous support layer of the membrane and in the boundary layer of the membrane surface are estimated in the model. The four types of flow patterns: cross flow, mixing flow, concurrent flow and counter current flow, are also considered in the model. The mass transfer through the non-porous thin layer of the membrane controls the overall mass transfer by ~99%. The experimental observations of TPL (Tritium Process Laboratory in JAERI) for N2–H2 and Air—H2 systems agreed with the calculated results of the cross flow under a set of typical conditions (disposal volume of 2.78×10−3 Nm3/s, feed-side pressure of 3.44×105Pa, and permeated-side pressure of 1.07×104 Pa). The validity of the simulation method was thus proved. For Air-H2-H2O system also, the recovery ratios calculated for H2 are in good agreement with the experimental observations. However, the calculated recovery ratios of water vapor were slightly smaller than the experimental observations. This discrepancy may result from the difference in separation mechanism between H2 and water vapor, or the construction change of membrane caused by the existence of water vapor.

The design of membrane vapor–gas separation systems

Membrane vapor–gas separation systems are beginning to be applied to a number of gas separation problems in the petrochemical and refinery areas. In this paper, some of the factors that affect the design of these systems are described using, as an application example, the separation of propylene from nitrogen in polyolefin resin degassing vents.

Optimization-based design of spiral-wound membrane systems for CO2/CH4 separations

A systematic design strategy for spiral-wound gas separation systems is studied using a recently proposed algebraic permeator model (Qi and Henson, Approximate modeling of spiral-wound gas permeators, J. Membrane Sci. 121 (1996) 11–24). Nonlinear programming (NLP) is used to determine operating conditions which satisfy the separation requirements while minimizing the annual process cost. The design method is applied to the separation of CO2/CH4 mixtures in natural gas treatment and enhanced oil recovery applications. It is shown that a two-stage configuration with permeate recycle and a three-stage configuration with residue recycle are suitable for natural gas treatment, while a three-stage configuration with both permeate and residue recycle is appropriate for enhanced oil recovery. Parameter sensitivities are analyzed by changing operating conditions, membrane properties, and economic parameters. The optimization procedure is sufficiently robust to handle multi-stage configurations with very demanding separation requirements. The proposed NLP design method facilitates the development of mixed-integer nonlinear programming design strategies which allow simultaneous optimization of the permeator configuration and operating conditions.

Preparation and Evaluation of CO2-Permselective Membrane for High Temperature Gas Separation.

With the greenhouse effect in mind, we have been studying the CO 2 recovery thermal power generation system. In this system, it is necessary to recover CO2 from LNG reformed fuel gas using a high temperature gas separation system. By a trial calculation of the efficiency of a power generation plant with CO 2 recovery system, it is appeared that membrane separation offered low power and low cost. A homogeneous silica-base membrane was obtained by the advanced sol-gel method with a polymer-hybrid. The gas separation factor of H 2 to CO 2 and the factor of N2 to CO2 was larger than 100 at 673 K. H 2 permeability was on the order of 10 -7 mol/m 2 .s.Pa order. This performance remained almost constant for 720 hours.

5626166 Temperature control valve without moving parts

This paper reports the results from the application of various methodologies to generate and analyse process flowsheets with novel separation units. Novel separation processes in this paper include supercritical extraction (SCE), melt crystallization (MC) and gas adsorption (GA). Application of a newly developed process synthesis technique has allowed the identification of processes where mixtures to be separated show azeotropic behaviour and, therefore, are candidates for a SCE-based process. Design and optimization studies have revealed the feasibility of ‘pressure-swing’ distillation as well as SCE-based separation as promising alternatives for these separations. In the case of MC, processes requiring separation/purification of compounds having specified limits of viscosity and melting point have been identified as candidates for MC-based separation. In the case of GA, a knowledge-based analysis is currently being developed for identification of potential candidate adsorbents and the corresponding gas-separation systems. Melt crystallization could be identified as a substitute for distillation in acrylic acid production. In acrylic acid production distillation resulted in an energy demand of 2.659 × 106 kJ/ton acrylic acid. Six different cases of incorporation of melt crystallization as a partial or total substitute for distillation were analysed, and melt crystallization gave energy reductions in the range from 7.7 × 104 to 1.86 × 106 kJ/ton acrylic acid. In a phenol production plant [9], the energy consumption may be reduced from 8.68 × 106 kJ/ton phenol to 8.00 × 106 kJ/ton phenol by employing melt crystallization as a substitute for distillation. For methylacetate production, novel separation schemes reduce the energy costs 1.4 times compared to the conventional separation schemes [9].

Computer-aided process design and optimization with novel separation units

This paper reports the results from the application of various methodologies to generate and analyse process flowsheets with novel separation units. Novel separation processes in this paper include supercritical extraction (SCE), melt crystallization (MC) and gas adsorption (GA). Application of a newly developed process synthesis technique has allowed the identification of processes where mixtures to be separated show azeotropic behaviour and, therefore, are candidates for a SCE-based process. Design and optimization studies have revealed the feasibility of ‘pressure-swing’ distillation as well as SCE-based separation as promising alternatives for these separations. In the case of MC, processes requiring separation/purification of compounds having specified limits of viscosity and melting point have been identified as candidates for MC-based separation. In the case of GA, a knowledge-based analysis is currently being developed for identification of potential candidate adsorbents and the corresponding gas-separation systems. Melt crystallization could be identified as a substitute for distillation in acrylic acid production. In acrylic acid production distillation resulted in an energy demand of 2.659 × 10 6 kJ/ton acrylic acid. Six different cases of incorporation of melt crystallization as a partial or total substitute for distillation were analysed, and melt crystallization gave energy reductions in the range from 7.7 × 10 4 to 1.86 × 10 6 kJ/ton acrylic acid. In a phenol production plant [9], the energy consumption may be reduced from 8.68 × 10 6 kJ/ton phenol to 8.00 × 10 6 kJ/ton phenol by employing melt crystallization as a substitute for distillation. For methylacetate production, novel separation schemes reduce the energy costs 1.4 times compared to the conventional separation schemes [9].

Gas Separation Using Membranes. 1. Optimization of the Separation Process Using New Cost Parameters

This is the first in a series of papers presenting new concepts for the development of membranes for gas separation. In this paper two new cost parameters, which are useful for costing and optimization of membrane gas separation systems, are described. The new parameters, cost permeability and effective selectivity, can be used to show the direction to be taken in membrane research and development. The new parameters are shown to predict accurately the cost of membrane separation plant by correlating bids from membrane plant suppliers using the new parameters with cross-flow design equations. The parameters are used to optimize the membrane gas separation of hydrogen and carbon monoxide for two commercially available membrane systems in a process to manufacture acetic acid. The membrane separation is compared with the currently used method, cryogenic flash distillation. Economic evaluation methods are developed to compare different separation methods so that the process as a whole can be optimized. The ev...

96/05983 A preliminary design study of a multicomponent PSA gas separation system

96/05983 A preliminary design study of a multicomponent PSA gas separation system

Passive CO 2 removal using a carbon fiber composite molecular sieve

Manufacture and characterization of a carbon fiber composite molecular sieve (CFCMS), and its efficacy as a CO 2 gas adsorbent are reported. The CFCMS consists of an isotropic pitch derived carbon fiber and a phenolic resin derived carbon binder. Activation (selective gasification) of the CFCMS creates microporosity in the carbon fibers, yielding high micropore volumes (>0.5 cm 3/g) and BET surface areas (>1000 m 2/g). Moreover, the CFCMS material is a rigid, strong, monolith with an open structure that allows the free-flow of fluids through the material. This combination of properties provides an adsorbent material that has several distinct advantages over granular adsorbents in gas separation systems such as pressure swing adsorption (PSA) units. The results of our initial evaluations of the CO 2 adsorption capacity and kinetics of CFCMS are reported. The room temperature CO 2 adsorption capacity of CFCMS is >120 mg of CO 2 per g of CFCMS. A proposed project is described that targets the development, over a three-year period, of a demonstration separation system based on CFCMS for the removal of CO 2 from a flue gas slip stream at a coal-fired power plant. The proposed program would be conducted jointly with industrial and utility partners.

A preliminary design study of a multicomponent PSA gas separation system

A model for the design of a PSA system in which hydrogen is recovered is proposed. It is found that mass transfer between the gas phase and adsorbent phase during blow-down can be omitted, while this is not the case during the repressurization step. The change in interstitial gas velocity during adsorption and desorption also needs to be considered. A basis design for a two-column system is presented and compared to results obtained by using a short-cut method. It is concluded that rigorous models are needed in order to determine exactly the important effects of interactions among the components in the gas mixture and the interactions between the different steps in the cycle.

Gas separation using polymer membranes: an overview

AbstractThis overview article discusses fundamental principles of gas sorption and transport in rubbery and glassy polymers and material selection guidelines for gas separation membranes. Comparisons between the performance of membrane‐based gas separation systems and more conventional technologies in key commercial applications are provided. Companion articles in this special edition focus on state‐of‐the‐art reviews and descriptions of theoretical and experimental developments important in the technology of gas separations using polymeric membranes.

Insights into the design of optimal separation systems using membrane permeators

Using a new robust design model, parametric studies have been performed to investigate the behaviour of gas separation systems based on membrane permeators. The existence of a maximum for permeate purity as a function of membrane pressure ratio is observed for simple permeators without recycle. It is found that overpurification of the permeate stream, followed by mixing (a by-pass configuration) may be profitable in cases where membrane area is expensive compared to compression, and purity requirements are modest. Retentate recycle is found to be detrimental to product purity and recovery in both retentate and permeate streams. It is shown that permeate recycle may significantly reduce compressor duty, even in cases where recycle is not required to obtain the specified permeate purity.

Combating Global Warming—Reducing CO2 Emissions from Coal-Fired Power Plant

The threat of global warming is sufficient to warrant ‘least regrets’ measures to reduce emissions of greenhouse gases, in particular through increased efficiency in energy production and use. British Coal has set up a programme to contribute to the international responses to the threat. It is concentrating on investigating options for removing carbon dioxide from fossil-fuelled power plants in case expensive fallback options become necessary. Screening of the options commenced with flowsheeting studies which estimated the thermal efficiency of a number of process schemes. These screening studies concluded that carbon dioxide (CO2) control could be retrofitted to existing coal-fired power stations, but that the new generation of gasification-based systems is more promising. CO2 separation could be more easily integrated into advanced power plants as they operate at high pressure, resulting in increased CO2 partial pressure which reduces the energy penalty associated with the separation. The CO2 would need to be exported as a liquid stream for storage in exhausted oil or gas fields. Costs of such power plants and CO2 disposal options have been developed. These studies suggest that, using proven technology, the cost of electricity would rise by about 42 per cent. If novel gas separation systems based on membranes can be developed, the increase in electricity cost could be limited to around 34 per cent. This paper discusses the options and presents the results of costing studies.

Development of a transportable thermal separation process

A new process for remediation of organics-contaminated soils and sludges has been developed. The process consists of a soil dryer and a gas separation system. The dryer heats the soil indirectly to 200–450°C in a rotary kiln, volatilizing the water and organic contaminants. No oxygen is present, and no organic destruction or incineration occurs. The dry treated soil discharged from the dryer is used for backfill at the site. The gas separation system condenses and collects the volatilized contaminants. The vapors are first sent to a water spray scrubber to remove the dust, then are cooled with heat exchangers to about 4°C to condense the water and organics. The water is treated and used to wet the cleaned soil or discharged, as appropriate, while the organics are shipped offsite for later treatment. Most of the remaining gas is reheated and recycled to the dryer. The gas not recycled is cleaned and vented. Development has progressed from laboratory and pilot units to a full commercial scale unit capable of processing 115 metric tons per day of soil with 20% moisture. Soil contaminants effectively removed include polychlorinated biphenyls (PCBs), petroleum hydrocarbons and chlorinated hydrocarbons.

Necessary protection for sensitive separation equipment

Colin Billiet, Engineering Director of domnick hunter filters looks at the role played by compressed air filters in protecting sensitive Gas Separation and Pressure-swing Adsorption systems. Particular reference is made to the company's OIL-X range of filters, associated technology and the quality class standards under which they operate.

Octyl salicylate

Helium is regarded as a vital gas to various industries such as medicine, aircraft manufacturing, electronics and fiber optics fabrication. Currently, natural gas reserves are considered the only viable resource for this rare element. When processing (helium-rich) natural gas, helium is generally recovered in the most downstream stage in conjunction with the nitrogen rejection unit (NRU). The feed to this unit is a nitrogen rich stream, and the product is either crude helium (50–70 mol% purity) or purified helium (99.99 mol% purity). Currently, the cryogenic distillation method is a common technology for a crude helium extraction unit (HeXU). The alternative method for this purpose is a membrane gas separation system, which is successfully used in other applications. This study aims to propose an energy-integrated scheme for each of the two helium separation technologies with a single-column NRU and to evaluate and compare them for different applications. Matlab programming has been used to model the membrane system and incorporate it into Aspen Hysys, which is used to simulate the rest of the process flowsheet. Next, the energy consumption of the systems was optimized using the particle swarm optimization method. An economic analysis was adopted to compare the two technologies for different applications in order to suggest a comprehensive map for HeXU technology selection.