Liquid-vapor Separation Research Articles

Techno‐Economic Analysis for Production of L‐Arabitol from L‐Arabinose

AbstractThe process design for synthesis of arabitol by hydrogenation of arabinose on a supported ruthenium catalyst is described. Aspen HYSYS software was used to design an arabitol production plant for subsequent generation of hydrogen through aqueous phase reforming (APR). The process design included hydrogen recycling requiring a flash drum and recompression. The total costs of arabitol were estimated to be substantially dependent on the feedstock costs and are closely related to arabinose feed cost. Feasible production of hydrogen using APR requires efficient extraction of hemicellulose from lignocellulosic biomass and subsequent hydrolysis.

Solar Desalination by Humidification-Dehumidification Using Aspen Plus simulation

Most of desalination processes require a large amount of energy derived from natural gas and oil, which are non-renewable energy, to supply heat and electric energy. So, this paper depends on solar energy as a source of renewable energy, and can be powered for producing fresh water. The new idea depends on using simulation ASPEN- PLUS. The solar collector and air cooler is replaced by heater in simulation program, absorber and cooler are used instead of humidification-dehumidification device, and flash drum to separate fresh water from air after cooling process, certainly pressure drop occurred so compressor is used to raise pressure, in order to doing recycle of air after drying it. Venting of air before recycle process at 0%, 25%, 50%, 75% and 100% is done. The simulation program is worked at Egyptian climate in summer and winter case. The maximum productivity of fresh water is at winter, when ratio of air to saline water is 3.47 with air temperature 250 oC

Technical and economic evaluation of triethylene glycol regeneration process using flash gas as stripping gas in a domestic natural gas dehydration unit

AbstractNatural gas from an underground reservoir is typically saturated with water vapor. Removal of this water vapor is required in the gas processing to avoid serious problems. This study investigated the technical and economic aspects of a triethylene glycol (TEG) regeneration unit in a domestic natural gas processing plant. This study aims to improve the performance of this dehydration unit to meet sales gas specifications while minimizing the Total Annual Cost (TAC). The important variables in this work are TEG circulation mass flow and rerouting the gas from TEG Flash Drum to TEG Regenerator as stripping gas. The flash gas, instead of discharged directly to the Flare system, is routed to the TEG Regenerator and serves as stripping gas agent to improve the TEG purity. The results revealed that utilizing flash gas as stripping gas has allowed lower TEG circulation mass flow rate and reduced the reboiler duty from 1.464 to 0.934 GJ/h (a 36.2% reduction). The TAC was reduced from $ 296 058/year to $ 236 890 /year (20.0% reduction). Through this work, a more economical design was obtained compared to the base case design.

Quantification on the Effects of Liquid-Vapor Separation in Air-Conditioning System by using Advanced Exergy Analysis

Air-conditioning system consumes a large amount of electricity in residential sections, and its efficiency has drawn extensive concerns in energy-conscious era. Liquid-vapor separation is a heat transfer enhancement technology that can effectively improve the performance of the heat exchanger as well as the system. In this paper, a regular air-conditioning system as the baseline (system-A) and other two air-conditioning systems with liquid-vapor separation heat exchanger (system-B and system-C) are comparatively studied. The component behaviors and system performances are deeply explored by using advanced exergy analysis with a focus on quantifying how much consequences come from the variants, i.e. liquid-vapor separation. The results indicate that the system-B has large reduced exergy destruction from the compressor and condenser at cooling mode relative to the system-A. The system-C has mainly diminished exergy destruction in the compressor caused by other components relative to the system-B. At heating mode, the system-C has an enhanced system exergy efficiency of 9.6% over the system-A, and it also has the decreased avoidable exergy destruction which is dominantly contributed by the compressor and evaporator. Furthermore, it is found that liquid-vapor separation mainly benefits the compressor and outdoor heat exchanger where it locates, leading to the system performance improvements.

Comparative study of heat transfer enhancement on liquid-vapor separation plate condenser

AbstractBasic structures of liquid-vapor separation cooling plates (LSCPs) and a liquid-vapor separation plate condenser (LVSPC) are innovatively designed. Strengthening heat transfer principle of the LSCPs is demonstrated by theoretical analysis. The average condensation heat transfer coefficients (ACHTCs) of the LSCPs are calculated and compared with conventional cooling plate (CCP). Results show that for a laminar flow, the ACHTCs of 2-parts liquid-vapor separation cooling plate and 3-parts liquid-vapor separation cooling plate are respectively 19% and 32% higher than the ACHTCs of the CCP in the same conditions. The ACHTC ratio of N-parts liquid-vapor separation cooling plates (NLSCP) to CCP is $\sqrt[4]{N}$in the same conditions. For a turbulent flow, results show the smaller the height of condensation area, the greater the ACHTCs of cooling plate. In the LVSPC study, operation conditions include the refrigerant R134a mass flux ranging from 22 to 32 kg/(m2.s) and inlet vapor quality from 0.5 to 1 for the saturated temperature of 40∘C. Calculation results showed that the ACHTCs of the LVSPC are 6–24% higher than the ACHTCs of the given common plate condenser (CPC), and similar to the CPC, the ACHTCs of the LVSPC increases with the increase of mass flux and vapor quality.

Wettability of ultra-small pores of carbon electrodes by size-asymmetric ionic fluids.

Recently, we studied the phase behavior of ionic fluids under confinement using the classical density functional theory within the framework of the restricted primitive model. The theoretical results indicate that narrowing the pore size may lead to a drastic reduction in the electric double layer capacitance, while increasing the surface electrical potential would improve the ionic accessibility of micropores. In this work, we extend the theoretical investigation to systems containing size-asymmetric electrolytes that may exhibit a vapor-liquid like phase transition in the bulk phase. The effects of pore size and surface electric potential on the phase diagram and microscopic structures of the confined electrolytes were studied over a broad range of parameters. We found that decreasing the pore size or increasing the surface potential could destabilize the liquid phase in micropores, and capillary evaporation could occur regardless of the size asymmetry between cations and anions. Compared to that in a symmetric ionic system, the vapor-liquid phase separation is more likely to take place as the size asymmetry becomes more pronounced. The phase transition would alter the "accessibility" of ions to micropores and lead to coexisting micropores with different surface charge densities as identified by Monte Carlo simulation.

Flash Distillation Control Using a Feasible Operating Region: A Sliding Mode Control Approach

The aim of this work is to develop a sliding mode control scheme to keep the operation of a flash distiller in the feasible operating region. Flash distillation is characterized as a simple single-phase separation system but operationally complex because it has a strong nonlinear behavior due to the thermodynamic equilibrium, obligatory to reach the required component separation. Control of flash distillation processes must guarantee a good performance and robustness to achieve preseparation quality before entering to next fractional distillation processes. A phenomenological-based semiphysical model is used here to represent the flash distillation process. The proposed control structure tries to avoid the biggest problem of the flash distiller: its recurrent restart due to temperature disturbances in the feed flow. The suggested control schemes, applied to a given separation, allow regulation of the pressure and the liquid level of the flash drum, keeping also the concentration of propylene glycol at the flash vapor outlet near its set point, rejecting temperature disturbances. The simulation results show the features of the proposed controllers, which overcome some of the disadvantages of typical flash distiller controllers operating in design conditions.

An experimental analysis over phase separators applied to household refrigerators

The objective of this study was to experimentally evaluate the influence of liquid-vapor separators in the performance of a novel dual-evaporator cycle architecture for household refrigerators. A refrigerator prototype was designed and constructed and two T-separators with vapor branches of 10 mm and 28 mm in diameter were tested with compressor speeds from 2000 to 3500 rpm and duty cycle from 10% to 45%. A visualization section was installed to capture the refrigerant flow through the acrylic T-separators. Cooling capacity and coefficient of performance were measured and photographs of the refrigerant flow in the separators were used to gain a better understanding of the results. The study concluded that the liquid entrainment in the separator of 10 mm increased the freezer coefficient of performance up to 55% and the system performance for the same duty cycle in 11%, in average, when comparing to the system with 28 mm separator with no liquid drag. The liquid entrainment also compromised the compressor reliability and decreased the fresh food COP up to 29%. The separator of 28 mm increased the fresh food performance and provided a reliable system during the entire tested range. Also, with the use of this separator, liquid was able to accumulate at duty cycles of 40% and 45% and, at 45%, the system reached its maximum cooling capacity and COP at 16 °C and 3500 rpm, around 6% higher than the average global COP of the reduced diameter separator. Finally, pull down tests were performed to verify the systems performance during transient conditions. It was shown that the liquid entrainment tended to increase the pull down time.

Vapor–liquid separation of mixtures R134a/R600a at horizontal branch T-junctions

Abstract As a promising separator, T-junction can be easily incorporated into the thermodynamic systems. Previous researches have investigated the phase separation of air-water and pure refrigerants but here the separation performance of mixtures at horizontal branch T-junctions is reported. Experiments were conducted to explore the effects of the flow conditions, the mass fractions and the geometric structures on the phase separation of R134a/R600a. During the experiments, the flow parameters including the inlet mass flux, the vapor quality and the mass flow ratio of the branch to the inlet, were varied. Three mixtures with R134a mass fraction 0.3030, 0.5202 and 0.7053 were employed. Furthermore, for the configurations of branching T-junction, the diameter ratio of the branch to the inlet was set to be 0.75 and 1.0, and three branch angles (45°, 90° and 135°) were considered. From the generated data, it was found that the branch outlet quality is always higher than the inlet quality, and the vapor fraction of branch outlet decreases with the increase of inlet vapor quality. The higher the mass flow ratio is, the larger the vapor fraction of R134a/R600a is. Under the experimental conditions, the mixtures with R134a mass fraction 0.3030 and 0.5202 have lower vapor fraction than R134a at inlet quality 0.1–0.5. As for the geometric effects, when the mass flow ratio is relatively large, more vapors usually prefer to flow into the branch with the smaller diameter, and vapor fraction for the angle 45° is lower than those for angles 90° and 135°

Non-equilibrium phase behavior in gas condensate depletion experiments

Full diameter core depletion tests are performed in this study to investigate the influence of depletion rate on the production of gas and condensate. Experimental results confirm that the gas recovery of the fast-depletion test is lower than that of the slow-depletion test. On the contrary, without the consideration of the fluid flow in porous media, the condensate recovery of the fast-depletion test is higher than that of the slow-depletion test.Non-equilibrium phase behavior is claimed to explain this abnormal behavior. The non-equilibrium model is adopted in this paper based on the components’ transfer rates between oil and gas phases. In addition, with the consideration of the compositional change in gas-condensate production, a numerical model is built to simulate the depletion process. Based on the comparison between the simulation and experimental results, the influence of non-equilibrium phase behavior on gas-condensate production is analyzed. If the depletion rate is relatively high, the heavy components of the gas-condensate system tend to be produced within the gas phase instead of condensing inside the core due to incomplete vapor-liquid separation. As a result, more condensate is acquired from the fast-depletion test.

Lattice theory for binding of linear polymers to a solid substrate from polymer melts. II. Influence of van der Waals interactions and chain semiflexibility on molecular binding and adsorption.

The polymeric Langmuir theory, developed in Paper I [J. Dudowicz et al., J. Chem. Phys. 151, 124706 (2019)], is employed to investigate the influence of van der Waals interactions and chain rigidity on the thermodynamics of the reversible molecular binding to interfaces in one component polymer fluids (polymer melts). Both van der Waals interactions and chain stiffness are found to influence the temperature variation of the surface coverage Θ, the binding transition itself, and the cooperativity of molecular binding. Re-entrancy of the surface coverage Θ(T) is found to arise when the intermolecular interactions are sufficiently attractive to cause a liquid-vapor like phase separation in the interfacial region, a phenomenon that can occur in the binding of both small molecules and polymer chains to surfaces.

An Intensified Reactive Separation Process for Bio-Jet Diesel Production

An intensified three-step reaction-separation process for the production of bio-jet diesel from tryglycerides and petro-diesel mixtures is proposed. The intensified reaction-separation process considers three sequentially connected sections: (1) a triglyceride hydrolysis section with a catalytic heterogeneous reactor, which is used to convert the triglycerides of the vegetable oils into the resultant fatty acids. The separation of the pure fatty acid from glycerol and water is performed by a three-phase flash drum and two conventional distillation columns; (2) a co-hydrotreating section with a reactive distillation column used to perform simultaneously the deep hydrodesulphurisation (HDS) of petro-diesel and the hydrodeoxigenation (HDO), decarbonylation and decarboxylation of the fatty acids; and (3) an isomerization-cracking section with a hydrogenation catalytic reactor coupled with a two-phase flash drum is used to produce bio-jet diesel with the suitable fuel features required by the international standards. Intensive simulations were carried out and the effect of several operating variables of the three sections (triglyceride-water feed ratio, oleic acid-petro-diesel feed ratio, hydrogen consumption) on the global intensified process was studied and the optimal operating conditions of the intensified process for the production of bio-jet diesel were achieved.

Investigation of the Liquid–Vapor Separator Efficiency on the Performance of the Ejector Used as an Expansion Device in the Vapor-Compression Refrigeration Cycle

Abstract Ejector expansion refrigeration cycle with reference to the constant pressure mixing theory is investigated to display the effects of the liquid–vapor separator efficiency on the performance, entrainment ratio, and area ratio at various operation conditions. Reversible ejector assumption is used for the highest theoretical performance limit, whereas efficiency of the liquid–vapor separator and all ejector components is added to the model to calculate more realistic performance improvement potentials. R1234yf and R1234ze(E) having low global warming potential values are used in the analyses. Zero-dimensional thermodynamic models are constructed applying the conservation equations between the inlets and outlets of the refrigeration cycle and ejector components. Percentage performance decrease is higher when the mixing section and the separator efficiency is added to the model at higher condenser temperatures compared with the lower evaporator temperatures according to the investigated operation ranges. Vapor and liquid separation efficiency affects not only the performance but also the design of the ejector although it is an external component since it has influence on the area ratio and entrainment ratio. Finally, the difference between the percentage performance improvement of the reversible ejector cycle and the realistic ejector cycle including the separator and ejector components efficiencies is as high as 35% at the highest investigated condenser temperature for R1234yf.

Analysis of the heat transfer characteristics of the liquid-vapor separation condenser based on a condensate growth model in horizontal tube

A theoretical model for horizontal tubes was proposed to analyze heat transfer performance of the condenser with liquid-vapor separation device in this paper. The model was on basis of convection boundary condition and effects of gravity and shear force to express the feature of the condensing film growth inside a horizontal smooth circular tube. In order to validate the model, a set of relevant experiments were carried out to gauge the heat transfer coefficients of condensers with liquid-vapor separation device. The predicted heat transfer coefficients showed a nice agreement with these experimental results. The refrigerant circuitry of a condenser with liquid-vapor separation device was designed according to the principle of equal mass flux with predicted results. Besides, the heat transfer performance of a condenser unit with liquid-vapor separation device in actual operating condition was calculated and analyzed. The influences of refrigerant vapor mass flux and saturation temperature on the performance were investigated and the enhancement of the liquid-vapor separation device on heat transfer was verified.

Numerical simulation of multi-pass parallel flow condensers with liquid-vapor separation

Liquid-vapor separation is an advanced technology recently developed enabling significant further heat transfer enhancement for condensers. This paper reports a distributed parameter model, using the ε-NTU method, to numerically simulate heat transfer performance of multi-pass parallel flow condensers with liquid-vapor separation (referred to as MPFCs-LS). For achieving higher accurate results and lower computational time, a segment self-subdivision method is used to locate the positions of onset and completion of condensation. Furthermore genetic algorithm is adopted to determine the refrigerant flow rates through tubes in a flow pass. Relevant empirical correlations are selected for heat transfer and frictional pressure drop in different flow regimes during condensation in microfin tubes. The predictions of the model agree well with the experimental data within ±20%. The model and numerical methods developed in this work for MPFCs-LS are of important value in design and performance optimization of these new advanced condensers.

Separation of BTX chemicals from biomass pyrolysis oils via continuous flash distillation

Partially deoxygenated pyrolysis oils, such as those produced by tail gas reactive pyrolysis (TGRP), show promise for use in biorefineries if they can integrate into standard refinery operations, one of which is distillation. A feasible method for modeling the process and for removing aqueous components will advance progress. This study investigated the potential of continuous flash distillation for fractionating partially deoxygenated bio-oil component chemicals benzene, toluene, and xylene (BTX), which are critical feedstocks for producing many refinery products. A model bio-oil mixture was used to evaluate process performance, and process conditions were investigated with respect to separation efficiency (temperature = 120, 130, and 140 °C; input flow rate = 2 or 3 mL min−1). Mean BTX yield (gout gin−1) for an oil flow rate of 2 mL min−1 ranged between 0.134 and 0.222 gout gin−1, while for 3 mL min−1 yields ranged from 0.135 to 0.400 gout gin−1. In all treatments, the measured amounts of BTX from model bio-oil were less than those from ASPEN simulations. From the distillates, aqueous fractions phase separated while sequestering acetic acid from the organics. Residence time within the drum was positively correlated with concentration of BTX in the distillates. At no point did solid residues form within the flash drum. When compared with analogous experiments at optimal conditions, BTX yields from real TGRP oil were comparable but less than the analogous model experiment. These results suggest that continuous, atmospheric pressure distillation of low-oxygen bio-oils can be used for separating commodity, refinery-grade chemicals such as BTX from biomass pyrolysis-derived bio-oils.

Ferromagnetism-induced phase separation in a two-dimensional spin fluid.

We study the liquid-gas phase separation observed in a system of repulsive particles dressed with ferromagnetically aligning spins, a so-called "spin fluid." Microcanonical ensemble numerical simulations of finite-size systems reveal that magnetization sets in and induces a liquid-gas phase separation between a disordered gas and a ferromagnetic dense phase at low enough energies and large enough densities. The dynamics after a quench into the coexistence region show that the order parameter associated with the liquid-vapor phase separation follows an algebraic law with an unusual exponent, as it is forced to synchronize with the growth of the magnetization: this suggests that for finite size systems the magnetization sets in along a Curie line, which is also the gas-side spinodal line, and that the coexistence region ends at a tricritical point. This picture is confirmed at the mean-field level with different approximation schemes, namely, a Bethe lattice resolution and a virial expansion complemented by the introduction of a self-consistent Weiss-like molecular field. However, a detailed finite-size scaling analysis shows that in two dimensions the ferromagnetic phase escapes the Berezinskii-Kosterlitz-Thouless scenario and that the long-range order is not destroyed by the unbinding of topological defects. The Curie line thus becomes a magnetic crossover in the thermodynamic limit. Finally, the effects of the magnetic interaction range and those of the interaction softness are characterized within a mean-field semianalytical low-density approach.

Operational safety of chemical processes via Safeness-Index based MPC: Two large-scale case studies

This work presents two applications of Safeness Index-based model predictive control to improve process operational safety in safety critical chemical processes. In the first case study, a high-pressure flash drum separator together with pressure relief valve as safety system is used to analyze the benefits of integrating Safeness Index-based considerations in model predictive control (MPC). In the second case study, four units in an ammonia process are simulated to demonstrate the application of Safeness Index-based MPC to handle significant disturbances.

Experimental study of condensation heat transfer in a condenser with a liquid-vapor separator

The condensation heat transfer and the separation efficiency of R134a in a condenser with a liquid-vapor separator were studied experimentally. The condenser had 33 parallel horizontal rectangular channels each100 mm long and 1.5 mm in hydraulic diameter divided into three channel passes. The liquid-vapor separator was a 2 mm diameter U-type tube installed at the junction between the first and second channel passes. The experiments used a saturation temperature of 25 °C with refrigerant mass fluxes of 74–212 kg/m2 s and cooling water mass fluxes of 25–250 kg/m2 s. The results showed that the condensation in the second channel pass was influenced by the liquid-vapor separator in the outlet of the first channel pass with the inlet vapor quality improved significantly by the removal of the condensate from the first channel pass. The heat transfer coefficient in the second channel pass was increased by 20% to 40% with the overall heat transfer coefficient in the condenser with the liquid-vapor separator improved by 10% to 20%. Increasing the cooling water mass flow rate slightly increased the condensate separation rate, but the separation ratio decreased. Both the amount of separated condensate and the separation ratio increased with increasing vapor mass flux. The condensate separation capacity was limited by the liquid-vapor separator tube diameter.

Flash Distillation of Bio-Oils for Simultaneous Production of Hydrocarbons and Green Coke

Fast pyrolysis bio-oils from biomass can potentially integrate with petroleum refinery infrastructure for production of renewable fuels and chemicals. Besides hydrodeoxygenation, few feasible options exist for entry points. When considering advanced pyrolysis techniques such as catalytic and/or tail-gas reactive pyrolysis (TGRP), distillation for using both light and heavy ends becomes possible. Our goal was to demonstrate and optimize continuous production of liquid organic distillates and residual solids coke, both in appreciable yields for downstream conversion into renewable products. We fabricated a flash drum for continuous one-step distillations of four oils of varying oxygen content (ranging from 5 to 32 wt %). While a mesh demisting screen enhanced separation, removal of the screen ultimately improved overall yields. The flash drum proceeded to distill lower-oxygen oils (∼10 wt %) with 80 wt % time-on-stream yields over several hours; steady state was reached within 30–40 min. Bio-oils with moder...