Liquid-vapor Separation Research Articles

Integration of rich and lean vapor recompression configurations for aqueous ammonia-based CO2 capture process

Post-combustion carbon capture (PCC) using a chemical solvent is the most mature and well-proven technology to mitigate carbon dioxide (CO2) emission. However, substantial energy consumption for solvent regeneration is still a critical challenge for widespread deployment of this PCC. In this study, a novel low-energy, combined rich and lean vapor recompression (RLVR) process for the CO2 capture process using dilute aqueous ammonia (NH3) solvent was developed and optimized by integrating of rich vapor recompression (RVR) and lean vapor recompression (LVR) approaches. A parametric study showed that the minimum total equivalent work can be obtained when CO2 loading and NH3 concentration of lean solution are 0.275 mol CO2/mol NH3 and 5.0 wt%, respectively and the pressures of stripper, rich and lean solvent flash drums are maintained at 10.5 bar, 4.62 bar and 6.93 bar, respectively. Under such operation conditions, the total equivalent work required for a CO2 capture plant was remarkably reduced to 0.123 kW h/kg of CO2 captured, which is equivalent to about 10% energy penalty. This amounts to 26–54% reduction from recent literature reports. Furthermore, this combined RLVR process can completely eliminate the need of reboiler, leads to improving the flexibility of the capture plant since it can be separated from power plant steam systems.

Simulation and Capacity Evaluation of Refinery Flare System and Comparative Analysis of Carbon Capture Technologies

In refinery flare system is the last defense line for controlling over-pressurization of process vessels. Mostly power failure is the worst contingency in the refinery, and the flare capacity is evaluated for this case. The data of pressure safety vessels (PSVs), header network, knockout drums, flare stack and flare tip is to utilize for simulating the flare system of oil refinery complex (ORC-II). Carbon dioxide (CO2) is a significant benefactor in the global warming stances a severe hazard to environment. The procedure was conveyed using 30 wt. % monoethanolamine (MEA) dissolvable and Hollow-fiber cellulose acetic membrane framework. This research consists of two sections. The initial segment the capacity evaluation of the flare framework was finished utilizing Aspen Flare System Analyzer V8.4 and rating of flare framework was conveyed in which to break down the necessary parameters like Mach number and back weight in the system and the adjustments in the flare framework were made as per API 520. In the second part chemical absorption and membrane separation innovations were looked at for post-combustion carbon catch. The research focuses on conveying relative investigation of above-expressed methods for flow rate of vent gas runs between 1 to 200 MMSCFD. The goal is to accomplish 90% recuperation of CO2 with carbon decrease from 10.66 mole % to 2 mole %. The absorption technique is simulated by ASPEN HYSYS V8.4 and program for membrane framework is created by connecting values from ASPEN HYSYS to Microsoft EXCEL. For membrane separation the operating expense is seen as lower than absorption process, yet from the results it was concluded that the absorption technique is superior to membrane technique until the problems concerning degradation of membrane and high capital expense would be settled.

Numerical simulation and structure optimization of a liquid–vapor separation plate condenser

Based on innovative design, a liquid–vapor separation plate condenser with excellent heat transfer performance is invented. It takes less time to discharge condensate from the refrigerant channel and get a thinner liquid film in condensing channel with the new-type condenser than with the conventional one. The evaluation of the heat transfer performance of the liquid–vapor separation plate condenser and the optimization of its structure design is realized with a validated mathematical model. In this numerical simulation, the performance evaluation criterion and penalty factor are used to assess the refrigerant side performance, while the exergy efficiency is used to evaluate the overall performance, which includes the water-side performance. According to the simulation results, the optimal structure of the liquid–vapor separation plate condenser is achieved when altitude ratio is equal to 0.6 and length ratio is equal to 0.5. In this structure, when the condensation temperature of refrigerant R410A is 20 °C, the heat flux is kW m−2, the mass flux is 50 kg m−2 s−1, the performance evaluation criterion is at 1.13, the penalty factor is at 0.89, and the exergy efficiency is at 0.34. All these values outperform those of conventional plate condenser. Compared with conventional one, the heat transfer coefficients of refrigerant of liquid–vapor separation plate condenser increase by 15.98%, and its the pressure drop increases by 16.45% under the setting conditions.

Numerical simulation on the header-orifice structure-based liquid-vapor separator used in liquid-separation condenser

Liquid-vapor separation process is a widely used process in many industrial and domestic applications. Liquid-separation condenser using header-orifice as liquid-vapor separator has been widely studied, confirming its superiority of higher heat transfer coefficient and lower pressure drop simultaneously over the conventional condenser. However, research on flow and separation mechanism of the header-orifice liquid-vapor separator is rarely found in existing literatures. Herein, we propose a numerical simulation model based on Volume of Fluid for the header-orifice liquid-vapor separator. The model is verified and applied to study the liquid-vapor separation mechanism of the header-orifice. The major parameters that influence the liquid-separation efficiency are analyzed, including the diameter of a liquid-separation hole, header height and inlet mass flow rate. Multi-factor analysis is also performed to investigate the synergetic effects of the parameters on the liquid-separation efficiency. A correlation of liquid-separation efficiency as a function of cross-section area, two-phase Reynolds number, and modified Weber number is obtained based on the orthogonal experimental method.

Tamagawa hyper-acidic hot spring and phreatic eruptions at Mt. Akita-Yakeyama: Part 1. The isotopic and chemical characteristics of the hot spring water

Isotopic (D, 3H, 18O, and 34S) and chemical studies on the hyper-acidic hot spring waters (Obuki; pH 1.1), other hot spring waters, and fumarolic gases taken in 1990–1992 at Tamagawa Hot Spring, Akita, Japan were undertaken to investigate the source and behavior of sulfur compounds. The Obuki hot spring water discharges after mixing of magmatic gas with meteoric water and underground vapor–liquid separation. SO42− and H2S was formed by the disproportionation reaction of SO2 at around 220 °C. Tritium concentration indicated that the subsurface residence time of the Obuki hot spring water is 13–25 years. In the downstream of the Obuki hot spring, there are many hyper-acidic hot springs that are diluted by meteoric water and flow as a river (Yukawa).

Regeneration of CO2 absorbent with membrane contactor via pressure swing

A new method to regenerate high pressure CO2 absorbent is presented in this paper, where PTFE hollow fiber membrane contactor was used as a gas–liquid separator in pressure swing process. CO2 desorption happened in the membrane contactor at the same time. The two mass transfer mechanisms were analysed through calculation of viscous flux and mass transfer coefficients. Experimental results showed that CO2 loading in regenerated absorbent increased with absorbent flow rate. This was due to decrease in membrane area available for CO2 desorption, as most of the membrane area was utilized for gas-liquid separation. Co-current configuration exhibited higher CO2 desorption driving force compared to counter-current configuration, hence its CO2 loading in regenerated absorbent was lower. When integrated with membrane contactor for CO2 absorption, stable and consistent performance was observed. Unlike conventional flash drum, membrane contactor did not have requirement on flashed gas velocity, because the membrane itself functioned as a screen to prevent fine liquid droplets from escaping the system along with flashed gas. Results from this study show that vessel size reduction up to 2.5 times could be achieved when PTFE membrane contactor was used, with absorbent regeneration energy as low as 0.94 GJ/ton CO2.

EFFECT OF LIQUID-VAPOR SEPARATION ON THE THERMAL-HYDRAULIC PERFORMANCE OF AN AIR-COOLED CONDENSER

This work characterizes the use of liquid-vapor separation inside air-cooled condensers and its effect on thermal-hydraulic performance. A series of 3 mm inner diameter U-tubes were installed in the condenser for the liquid-vapor separation with 6 mm inner diameter and 215 mm long-finned condenser tubes. R134a was used as the working fluid. During operation, condensed R134a was separated by the liquid-vapor separation device to significantly improve the heat transfer compared to that of a serpentine condenser without liquid-vapor separation. In addition, fewer tubes were required inside the air-cooled condenser due to its high heat transfer rates, which indicated a potential for reducing the condenser size. This study investigated the key factors affecting the liquid-vapor separation process, such as the number of liquid-vapor separation devices, the wind velocity, and the total mass flow rate. The results indicated that in-tube pressure drop is the dominant parameter affecting separation efficiency. This liquid-vapor separation condenser design had better thermal-hydraulic performance than a serpentine condenser due to the enhanced heat transfer. Adding an additional liquid-vapor separation structure changed the separation conditions of the previous separation structure and made the condensation heat transfer more uniform.

Performance of rich solvent flashing for MEA-based post-combustion CO<SUB align="right">2 capture

High energy demand has led to the increased power production from the fossil power plants which are the largest source of CO2. Monoethanolamine-based post-combustion CO2 capture is a developed technology to mitigate CO2, however, it still needs attention towards process modification concerning energy requirements. Rich solvent flashing is the suggested modifications which is discussed in the present work and is used to minimise the overall energy. The minimum reboiler duty was observed at 20%, 30% and 40% split of the lean solvent at certain approach temperatures. The reboiler duty of 3.201 MJ/kg CO2 was observed at the approach temperatures of 5°C and 10°C with the split fraction of 40%. The system is also modelled using single, double and three flash drums where three flash drums indicates the minimum duty with 5% decrease from the base case model.

Performance of rich solvent flashing for MEA-based post-combustion CO<SUB align="right">2 capture

High energy demand has led to the increased power production from the fossil power plants which are the largest source of CO2. Monoethanolamine-based post-combustion CO2 capture is a developed technology to mitigate CO2, however, it still needs attention towards process modification concerning energy requirements. Rich solvent flashing is the suggested modifications which is discussed in the present work and is used to minimise the overall energy. The minimum reboiler duty was observed at 20%, 30% and 40% split of the lean solvent at certain approach temperatures. The reboiler duty of 3.201 MJ/kg CO2 was observed at the approach temperatures of 5°C and 10°C with the split fraction of 40%. The system is also modelled using single, double and three flash drums where three flash drums indicates the minimum duty with 5% decrease from the base case model.

Multi-stage Depressurization Analysis of Subsea Production System Based on LedaFlow Software

This paper briefly summarizes that during the depressurization operation in subsea pipeline for maintenance or prevention of hydrate formation, because the flare knock-out drum pump is designed for ambient temperature, and cannot deal with the low temperature fluid in the depressurization process. Therefore, the low temperature fluid needs to be heated in the knock-out drum to meet the temperature requirement of pump. In order to avoid the volume of low temperature fluid exceeding the surge volume of the flare knock-out drum, the concept of multi stage depressurization is innovatively proposed in this paper, which meets both the requirements of pump temperature and the surge volume of flare drum. Taking a gas field project in the South China Sea as an example, the simulation analysis of depressurization temperature and pressure is carried out by using different size of the blowdown valve. It provides a good reference for the similar project in future.

Design and CFD Simulation of Knockout Drum

Recently, the emission of black smoke over local area of Basra Oil Company from flare system represents a big problem facing the company and causing huge pollution in the surrounding environment. The main reason of emission black smoke is carryover of droplets of the rest hydrocarbons such as condensate and droplets of crude oil by gases which are came from degassing stations facility in the north Rumelia field, southern Iraq. In this study, a design methodology was developed for designing the knockout drum, and different design criteria were used in sizing and selecting the drum based on the specification of the inlet fluid mixture. Three designs of knockout drums with respect to the gas conditions were performed. The horizontal knockout drum with a diameter of 2.5 m and length of 5.5 m was simulated using a Computational Fluid Dynamics (CFD) model (ANSYS FLUENT 15.0). The CFD model predicted very well the two-phase flow behavior and proved the need for a vortex breaker at the liquid outlet. The CFD simulation revealed quantitatively that the design configuration of the knockout drum performed the separation of condensate droplets from natural gas with excellent efficiency.

Kinetics of domain growth and aging in a two-dimensional off-lattice system.

We have used molecular dynamics simulations for a comprehensive study of phase separation in a two-dimensional single-component off-lattice model where particles interact through the Lennard-Jones potential. Via state-of-the-art methods we have analyzed simulation data on structure, growth, and aging for nonequilibrium evolutions in the model. These data were obtained following quenches of well-equilibrated homogeneous configurations, with density close to the critical value, to various temperatures inside the miscibility gap, having vapor-"liquid" as well as vapor-"solid" coexistence. For the vapor-liquid phase separation we observe that ℓ, the average domain length, grows with time (t) as t^{1/2}, a behavior that has connection with hydrodynamics. At low-enough temperature, a sharp crossover of this time dependence to a much slower, temperature-dependent, growth is identified within the timescale of our simulations, implying "solid"-like final state of the high-density phase. This crossover is, interestingly, accompanied by strong differences in domain morphology and other structural aspects between the two situations. For aging, we have presented results for the order-parameter autocorrelation function. This quantity exhibits data collapse with respect to ℓ/ℓ_{w},ℓ, and ℓ_{w} being the average domain lengths at times t and t_{w} (≤t), respectively, the latter being the age of a system. Corresponding scaling function follows a power-law decay: ∼(ℓ/ℓ_{w})^{-λ} for t≫t_{w}. The decay exponent λ, for the vapor-liquid case, is accurately estimated via the application of an advanced finite-size scaling method. The obtained value is observed to satisfy a bound.

Discussion on Water Condensation in Membrane Pores during CO2 Absorption at High Temperature.

Water condensation is a possible cause of membrane wetting in the operation of membrane contactors, especially under high-temperature conditions. In this study, water condensation in pores of polytetrafluoroethylene (PTFE) hollow fiber membranes was investigated during high-pressure CO2 absorption around 70 °C. It was found that the liquid accumulation rate in the treated gas knock-out drum was constant during continuous operation for 24 h when all experimental conditions were fixed, indicating a stable degree of membrane wetting. However, as the operating parameters were changed, the equilibrium vapor pressure of water within membrane pores could change, which may result in a condensation-conducive environment. Water condensation in membrane pores was detected and proven indirectly through the increase in liquid accumulation rate in the treated gas knock-out drum. The Hagen–Poiseuille equation was used to correlate the liquid accumulation rate with the degree of membrane wetting. The degree of membrane wetting increased significantly from 1.8 × 10−15 m3 to 3.9 × 10−15 m3 when the feed gas flow rate was reduced from 1.45 kg/h to 0.40 kg/h in this study due to water condensation in membrane pores. The results of this study provide insights into potential operational limitations of membrane contactor for CO2 absorption under high-temperature conditions.

Nonlinear Model for the Globally Optimal Design of Vertical Vapor Liquid Separation Vessels

Separation vessels are traditionally designed based on rules of thumb that guide the designer to a feasible solution. Despite its widespread use, this approach presents important limitations, which...

Carbon dioxide utilization in methanol synthesis plant: process modeling

Abstract The conversion of CO2 to methanol holds great promise, as it offers a pathway to reduce CO2 level in the atmosphere and also produce valuable components. In this study, a typical methanol synthesis plant for CO2 conversion was numerically modeled. Effect of fresh feed to plant parameters (i.e., pressure and CO2 concentration) as well as the influence of recycle ratio on the reactor performance was investigated. Hence, all essential equipment, including compressor, mixer, heat exchanger, reactor, and liquid–vapor separator were considered in the model. Then, at the best operating conditions, thermal behavior and components distribution along the length and radius of the reactor were predicted. Finally, the effect of inert gases was investigated in the methanol production process and the results were compared with the conventional route (CR), which uses natural gas for methanol synthesis. The results revealed that in the absence of inert gases and by employing a recycle stream in the process, CO2 hydrogenation leads to 13 ton/day production of methanol more than CR. While in the feedstock containing 20% inert gases, which is closer to the realistic case, methanol production rate is 45 ton/day lower than CR. These findings prospect a promising approach for the production of green methanol from carbon dioxide and hydrogen.

Improved two-phase flow boiling in a minichannel heat sink for thermal management of information and communication technology (ICT) equipment

Thermal management systems play a significant role in dissipating heat and guaranteeing the safety of facilities. For information and communication technology (ICT) systems, a highly reliable operation depends on accurate thermal control, including the maximum temperature attained and the uniformity of temperature of the semiconductor devices. In the literature, two-phase flow boiling devices have been proposed as an efficient solution for addressing this concern; however, the application of such devices is still fraught with serious challenges owing to the unstable flow boiling. This study aims at solving the problem of undesired heat transfer deterioration triggered by two-phase flow instability in ICT systems. Based on our previous proposed radial expanding minichannel heat sink (REMHS), we tested the effects of a cut-off structure and a gap structure on further stabilizing the flow boiling and enhancing heat transfer performance. The cut-off structure is employed in the flow direction to relieve the rapid expansion of vapor slugs in the minichannels. This elevated the heat transfer coefficient of the REMHS by nearly two-fold under high heat flux conditions and effectively eliminated the local hotspot on the heat sink. The overheating at the downstream of the REMHS, in terms of temperature, decreased by 55% from 29 to 13 K at a heat flux of 220 kW/m2. Moreover, a better wall temperature uniformity was obtained. The gap structure was found effective in liquid–vapor separation that maintains the temperature fluctuations below 0.6 K. By suppressing the detrimental reversal flow with the two proposed techniques, the REMHS achieved a high flow boiling heat transfer capability over a wide range of operating conditions and met the requirement of the ICT equipment thermal management system.

Levelized Cost of CO2 Captured Using Five Physical Solvents in Pre-combustion Applications

Aspen Plus v8.8 was used to perform techno-economic analysis (TEA) of a CO2 capture process from a typical fuel gas stream in a 543-MW pre-combustion power plant using five different physical solvents (Selexol, PEGPDMS-1, NMP, [aPy][Tf2N] and [hmim][Tf2N]). The process included a countercurrent packed-bed absorber operating under high-pressure over a wide range of temperatures and three pressure-swing flash drums for solvent regeneration. Two packings, Mellapak 250Y and IMTP50, were used and the Levelized costs of CO2 captured (LCOC) were calculated.The simulation results indicated that using Mellapak 250Y exhibited lower LCOC values than those when using IMTP50 for the five solvents under all conditions used as it offered better mass transfer. The CO2 capture process carried out at low temperatures showed lower LCOC values than those at higher temperatures due to the increased CO2 solubility in the solvents at lower temperatures, requiring smaller absorber diameter and lower solvent circulation rates, which offset the cooling requirements. Comparing the lowest LCOC values for the five solvents, the hydrophobic PEGPDMS-1 solvent was the most promising one compared to the other four solvents, due to its lowest capital and operating costs and noncorrosive, which enabled using less expensive materials for the process equipment.

Theoretical analysis of a novel liquid-vapor separation condensation ejector refrigeration cycle with zeotropic mixtures

This paper presents a novel liquid-vapor separation condensation ejector refrigeration cycle (LERC). The zeotropic mixture (R245fa/R134a) is used as the working fluid. And the fluid composition of primary and secondary flow are controlled by a heat exchanger and liquid-vapor separator. A constant pressure ejector model is established to evaluate the influence of fluid composition, vapor quality and other parameters on the cycle performance. Then the cycle performance is compared with the traditional ejector refrigeration cycle (ERC). It is found that COP achieves a maximum of 0.13 with mixture R245fa/R134a (0.5/0.5), and the exergy efficiency achieves a maximum of 10.53% with mixture R245fa/R134a (0.6/0.4). As the vapor quality increases from 0.1 to 0.2, the cycle COP increases from 0.08 to 0.19, the exergy efficiency increases from 7.78% to 12.49% and the area ratio decrease from 5.18 to 4.53 with mixture R245fa/R134a (0.5/0.5). The parametric analysis shows that the cycle performs better in higher vapor quality, lower generating temperature and lower condensing temperature.

Recovery and usage of [formula omitted] produced in the Fischer-Tropsch synthesis employing Gibbs energy minimization

This paper proposes a process to recover and recycle the carbon dioxide produced during Fischer-Tropsch synthesis (FTS) through thermodynamic analysis. Thus, it may avoid the release of large amounts of CO2 to the atmosphere. We investigated the chemical and phase equilibrium of Fischer-Tropsch reaction using CO2 as a reactant. Also, the chemical equilibrium of reverse water-gas shift (RWGS) reaction was considered as an alternative to obtaining carbon monoxide overall process. The effects of temperature, pressure, and the molar ratio of reactants were evaluated at thermodynamic equilibrium using Gibbs energy minimization. The Gibbs energy minimization problem is formulated as mathematical optimization (objective function), and to represent the non-ideality of the system, we used the cubic equation of state (Soave-Redlich-Kwong) as constraints. Non-negativity of the number of moles and stoichiometric balances were considered as constraints, using the reactions that take into account the effect of the catalyst. The software GAMS with solver CONOPT is employed to solve this nonlinear programming problem. In FTS, adding CO2 as co-reactant decreased the hydrocarbons production and has not presented an effective CO2 conversion. Alternatively, RWGS showed a higher CO2 conversion. Hence, it was possible to achieve a process in which CO2 generated in FTS could be recovered from liquid hydrocarbons using a flash drum, and then converting it in carbon monoxide by RWGS reaction at high temperatures. The proposed process operate at the same pressure in all vessels, and only heat exchangers and flash drums are used to separate and recover CO2 from the other compounds.

Experimental study of a liquid desiccant regeneration system: performance analysis for high feed concentrations

Liquid desiccant air-conditioning is an energy-efficient alternative to conventional vapor compression systems due to its ability to handle sensible and latent heat loads independently. Membrane-based processes are prevalent in desalination research due to their superior abilities to separate fluids. The membrane-assisted separation process is also suitable for use in liquid desiccant air-conditioning systems as it can minimize the problems of corrosion, which has so far prevented the widespread use of liquid desiccant systems. In this study, we have utilized the flat-sheet polytetrafluoroethylene membranes for liquid–vapor separation and combined multieffect design with vacuum conditions, for enhanced liquid–vapor separation across the membrane. Preliminary experiments and literature surveys indicate that the conventional vacuum multieffect membrane distillation system exhibits poor performance when the feed concentration is above 26%. Therefore, efforts are made to enhance its performance when operating at higher concentrations (30% and 34%) by employing flat-plate-type heat exchangers to preheat the liquid desiccant and by maintaining high air-side vacuum. The regeneration process can be optimized based on increase in concentration (ΔC) and performance ratio (PR), by controlling the operating conditions. The evaluations of the regenerator performance for different operating parameters including heat source temperature, circulation cross-flow rate are presented along with analysis. Preheating the LiCl solution before regeneration resulted in improved performance; PR of 0.58 and ΔC of 2.4% are achieved for 34% LiCl concentration. Schematic representation of the membrane-assisted LDAC test bed