Supersonic Separation Research Articles

Aerodynamic Characteristics of Supersonic Separator for Natural Gas Processing

Natural gas is a key energy source to achieve the carbon peaking and carbon neutrality goals in China. Dehydration and de-hydrocarbon process is crucial for pipeline transportation of natural gas since water and hydrocarbons in the natural gas would condense to cause corrosion and freeze-blockage in the pipeline. The supersonic separator is innovative low-temperature separation equipment characterized by a simpler equipment structure and higher refrigeration efficiency than the traditional device. In this paper, the numerical analysis is employed to predict the performance of the supersonic separator. The results show that this separator can reach an advanced level compared with others. The separator cannot start-up as the inlet-outlet pressure ratio is lower than1.29, and the minimum pressure ratio needed for normal work is 1.39. Under normal operating conditions, total pressure loss is about 25.4%, the minimum temperature is about 213K, and the mean rotation speed is about 170m/s.

Numerical simulation of supersonic condensation flows using Eulerian-Lagrangian and Eulerian wall film models

As a clean and energy-saving natural gas purification and separation device, the supersonic separator's internal gas-liquid separation mechanism needs to be explored. However, the complex three-field (gas, droplet, liquid film) two-phase (gas, liquid) supersonic condensation flow challenges the numerical modeling. Most studies are limited to tracking the gas phase and droplets and ignore the effects of liquid film and phase change on droplets and water vapor removal. In the present study, we established a novel Eulerian-Lagrangian method coupled with the Eulerian wall film model to study the three-field behaviors and phase change for the enhancement of separation efficiency in the supersonic separator. The accuracy of the proposed model was validated by three experiments. The gas, droplet, and liquid film behaviors and three-field heat and mass transfers in the supersonic separator are studied using the proposed three-field two-phase flow model. Then, the sensitivity analysis was carried out, which showed the inlet mass flow rate qp,in of the heterogeneous droplets determines the maximum film thickness. For qp, in = 0.001 kg/s, this value is about 85.2 μm. The result also showed a significant improvement in separation efficiency with a proper inlet droplet diameter dp,in, qp,in, and gas pressure pin. For dp,in, qp,in, and pin are selected as 2.2 μm, 0.0015 kg/s, and 3 atm, better separation efficiency can be obtained with droplet removal rate, water vapor removal rate, and dew point depression being optimized to 100%, 57.4%, and 29.1% respectively.

Justification of the use of a supersonic separator at the Yu. Kuvykin gas condensate field

The main trends in the advancement of technology for the development and operation of offshore fields can be called underwater production complexes, which are a system of technological blocks that allow the production and treatment of hydrocarbons on the seabed. This article covers the technology of gas condensate separation using a supersonic separator. This 3S separator is able to perform deep purification of gas condensate with the extraction of CO2 and H2S and can be installed on the shelf as part of an underwater production complex. We consider it possible to apply this technology at the Yu. Kuvykin gas condensate field, which has a positive impact on the realization of the field’s resource potentials.

Carbon-dioxide-to-methanol intensification with supersonic separators: Extra-carbonated natural gas purification via carbon capture and utilization

A novel carbon-capture-and-utilization route from extra-carbonated natural gas using low-cost/low-carbon chloralkali hydrogen is disclosed. Methanol and methane-rich gas are produced without direct carbon emissions and also with low indirect emissions assuming the local electricity-matrix as 87% non-emitting. Carbon dioxide removed from raw natural gas via cryogenic extractive distillation with methanol entrainer, feeds a new Carbon-Dioxide-to-Methanol hydrogenation route intensified by supersonic separators with liquid water injection for greater methanol conversion per pass in the synthesis-loop and greater methanol recovery in the separation system. Intensified Carbon-Dioxide-to-Methanol is designed economically optimizing water/methanol injection-ratios and maximum Mach numbers of supersonic separators. Extra-carbonated natural gas processing coupled to intensified Carbon-Dioxide-to-Methanol is techno-economically assessed, demonstrating that supersonic intensification entails 2% greater methanol production, 11% less power consumption and 7.5% greater net value comparatively to non-intensified counterpart. The intensified process removes 99.2% of CO2 from extra-carbonated gas and was analyzed at two methanol scales [8021.5 t/d, 1692.3 t/d] giving, respectively, [9.5, 41.5] payback-years, and [2896.4MMUSD, 41.37MMUSD] net values (60years). A critical feasibility factor is low-cost/low-carbon by-product hydrogen from chloralkali industries, for which the break-even prices were respectively evaluated for the two scales as [685USD/tH2, 358USD/tH2]. A third, better and safer, option is to couple intensified Carbon-Dioxide-to-Methanol to large-scale Carbon-Dioxide-to-Enhanced-Oil-Recovery providing hedging against insufficient offer of low-cost/low-carbon hydrogen while practically keeping the project net value (60years) despite twofold investment.

Effects of the Operating Parameters of Supersonic Separators on the Supersonic Liquefaction Characteristics of Natural Gas

In this study, a mathematical model for the supersonic condensate flow of natural gas to understand its condensation process in a supersonic separator has been proposed. The effects of export back pressure, inlet temperature, and inlet pressure on the condensation parameters were investigated. The results indicate that the condensation position moves forward with the increase in the inlet pressure and the decrease in the inlet temperature. A method for determining the optimal range of operating parameters (export back pressure, inlet temperature, and inlet pressure) for the supersonic separator is proposed. Within the optimal back pressure range, the region of extreme Mach number in the device should be at the inlet of the straight pipe section after the separation gap, and extreme value distribution areas of low temperature, condensation nucleation, and humidity should be between the nozzle expansion section and the inlet of the straight pipe section. It is important to choose a higher temperature among the optimal values as the inlet temperature and also ensure that the optimal inlet pressure is not higher than the pressure corresponding to the humidity inflection point. At the optimal inlet pressure, the maximum humidity distribution area should be behind the supersonic nozzle expansion section and in front of the inlet of the straight pipe section.

Sustainable offshore natural gas processing with thermodynamic gas-hydrate inhibitor reclamation: Supersonic separation affords carbon capture

Dew-point adjustments and reclamation of thermodynamic gas-hydrate inhibitors injected in subsea flowlines are common operations in offshore natural gas rigs characterized by high costs, power consumption and carbon emissions. Typically, offshore plants employ triethylene-glycol absorption for water dew-point adjustment and Joule–Thomson expansion for hydrocarbon dew-point adjustment, while hydrate inhibitor reclamation is applied only on aqueous-inhibitor streams for re-concentration. To implement economically sustained post-combustion carbon capture on offshore rigs, a more efficient gas processing is necessary. This work contemplates a new process – supersonic separator inhibitor-reclamation – which recovers inhibitors from saturated raw-gas via supersonic separation with liquid-water injection additionally yielding exportable liquefied-petroleum-gas and natural gas with adjusted dew-points. This process dramatically improves profitability for thermodynamic inhibitors methanol, ethanol and monoethylene-glycol, creating an economic leverage that affords a post-combustion capture plant avoiding about 43% of carbon emissions. Even including post-combustion capture penalties, the supersonic separator inhibitor-reclamation process achieves a higher net value than the conventional gas processing without carbon capture. A multi-criteria sustainability assessment, based on quantitative metrics and qualitative aspects over all sustainability dimensions, evinces the supersonic separator inhibitor-reclamation process with carbon capture as more sustainable than the conventional counterpart for all inhibitors, whereas among the three inhibitors, the gas processing with monoethylene-glycol was ranked as the more sustainable for offshore rigs.

Evaluation of influential parameters for supersonic dehydration of natural gas: Machine learning approach

The supersonic dehydration of natural gas is gaining more attention due to its numerous advantages over the conventional natural gas dehydration technologies. However, supersonic separators have seen minimal field applications despite the multiple benefits over other gas dehydration techniques. This has been mostly attributed to the uncertainty in ascertaining the design and operating parameters that should be monitored to ensure optimum dehydration of the supersonic separation device. In this study, the decision tree machine learning model is employed in investigating the effects of design and operating parameters (inlet and outlet pressures, nozzle length, throat diameter, and pressure loss ratio) on the supersonic separator performance during dehydration of natural gas. The model results show that the significant parameters influencing the shock wave location are the pressure loss ratio and nozzle length. The former was found to have the most significant effect on the dew point depression. The dehydration efficiency is mainly dependent on the pressure loss ratio, nozzle throat diameter, and the nozzle length. Comparing the machine learning model-accuracy with a 1-D iterative model, the machine learning model outperformed the 1-D iterative model with a lower mean average percentage error (MAPE) of 5.98 relative to 15.44 as obtained for the 1-D model.

The droplets and film behaviors in supersonic separator by using three-field two-fluid model with heterogenous condensation

Supersonic separator is a kind of natural gas dehydration device with great potential, but its internal mass and heat transfer process has not been fully studied. In this study, a novel three-field two-fluid model described by Eulerian-Eulerian approach for supersonic separator considering the heat and mass transfer between gas, liquid droplets, and liquid film was developed and validated. The interphase slip, latent heat, film heat flux, and film phase change rate were studied. It revealed that the maximum centrifugal slip velocity of droplets can reach 24.9 m s−1. The maximum latent heat is 5.3 × 108 J m−3 from droplets to gas phase during condensation, and the minimum latent heat is -3.4 × 108 J m−3 during evaporation. The thickness of swirling liquid film at wet gas outlet is 21 μm, 47 μm, 74 μm and 89 μm, respectively. The liquid film temperature decreases to a minimum 304.1 K due to droplets deposition, where the maximum heat flux is 0.74 MW m−2. Besides, the frequency and velocity of the interfacial wave of liquid film were obtained by using the cross-correlation algorithm, and their maximum values was 11.07 Hz and 1.49 m s−1, respectively. In addition, for achieving higher dehydration efficiency, the optimal value of the foreign droplet mass concentration should be 0.01 kg m−3. The maximum separation efficiency and dew point depression of separator A are 85.11% and 40.32 °C, respectively. The model without considering the liquid film over-predicts the separation efficiency.

A novel strategy for comprehensive optimization of structural and operational parameters in a supersonic separator using computational fluid dynamics modeling

In this study, the effects of several structural and operational parameters affecting the separation efficiency of supersonic separators were investigated by numerical methods. Different turbulence models were used and their accuracies were evaluated. Based on the error analysis, the V2-f turbulence model was more accurate for describing the high swirling turbulent flow than other investigated turbulence models. Therefore, the V2-f turbulence model and particle tracing model were selected to optimize the structure of the convergence part, the diffuser, the drainage port, and the swirler. The cooling performance of three line-type in the convergent section were calculated. The simulation results demonstrated that the convergent section designed by the Witoszynski curve had higher cooling depth compared to the Bi-cubic and Quintic curves. Furthermore, the expansion angle of 2° resulted in the highest stability of fluid flow and therefore was selected in the design of the diffuser. The effect of incorporating the swirler and its structure on the separation performance of supersonic separator was also studied. Three different swirler types, including axial, wall-mounted, and helical, were investigated. It was observed that installing the swirler significantly improved the separation efficiency of the supersonic separator. In addition, the simulation results demonstrated that the separation efficiency was higher for the axial swirler compared to the wall-mounted and helical swirlers. Therefore, for the improved nozzle, the swirling flow was generated by the axial swirler. The optimized axial swirler was constructed from 12 arced vanes each of which had a swirl angle of 40°. For the optimized structure, the effects of operating parameters such as inlet temperature, pressure recovery ratio, density, and droplet size was also investigated. It was concluded that increasing the droplet size and density significantly improved the separation efficiency of the supersonic separator. For hydrocarbon droplets, the separation efficiency improved from 4.6 to 76.7% upon increasing the droplet size from 0.1 to 2 µm.

Uncertainty quantification of real gas models in [formula omitted] supersonic flow

Carbon dioxide (CO2) is an undesirable component present in natural gas composition. The supersonic separator is a new and potential technology for natural gas treatment, which expands the gas through supersonic velocities until a shock wave formation. The modeling capacity to predict the shock wave position inside the device is analyzed considering parametric uncertainties. Results from four real gas models were compared in computational fluid dynamic modeling. Uncertainties that affect coefficients in the real gas models were propagated through the carbon dioxide flow solver using the Latin Hypercube Sampling approach. It was observed that the shock wave introduces non-linearity in the local standard deviation. Soave–Redlich–Kwong and Aungier–Redlich–Kwong are slightly affected by input parametric uncertainties. On the other hand, the Peng–Robinson model results are strongly affected.

On the sustainability of small-scale expansion-based natural gas liquefaction: Supersonic separator, Joule-Thomson, and turbo-expander

Expansion-based liquefaction technologies are prime candidates for small scale offshore natural gas liquefaction, aiding in reducing NG chain logistical costs, due to their compactness. This study assesses the sustainability and profitability of three expansion-based small-capacity natural gas liquefaction technologies: the rigid-geometry supersonic separator, the Joule-Thomson valve and the turbo-expander. The rigid-geometry supersonic separator was simulated for liquefaction of nearly pure methane via a thermodynamically rigorous steady-state modeling. Supersonic separator inlet conditions were optimized via a response-surface predictor of its critical flowrate in terms of temperature and pressure. Such optimum inlet conditions were found to be T = -15.79°C, P = 80 bar for a maximum 2.5 Mach. With these conditions a multi-criteria analysis was conducted combining sustainability metrics to heuristic criteria into a single one-dimensional index, the Sustainability Degree. Turbo-expander was unveiled as the most sustainable process as it has the highest SD = 11.39 due to its lowest power intensity (0.78 kWh/kgLNG), highest net present value (15.89 MMUSD) and minimal carbon emissions. Single unit supersonic separator has a medium performance (SD = 3.5), weighed down by the large natural gas recycle needed, while Joule-Thomson is the worst process due to the largest power consumption (1.66 kWh/kgLNG) and the lowest net present value (4.4 MMUSD).

Energy separation and condensation effects in pressure energy recovery process of natural gas supersonic dehydration

Pressure energy recovery is one of the main advantages of a supersonic separator. However, the pressure energy recovery process can cause droplet evaporation in the divergent section, which will reduce the liquefaction efficiency of the nozzle. This paper aims to clarify the shock wave/boundary layer interaction and liquefaction efficiency of wet natural gas in the process of pressure energy recovery. A mathematical model of methane-water vapor condensation was established to study the energy separation and condensation characteristics of wet natural gas in the nozzle. The results show that shock wave/boundary layer interaction leads to the energy separation phenomenon. When pressure energy recovery efficiency is reduced from 78.6% to 57.1%, the Mach number and liquid mass fraction at the outlet of the nozzle increase from 0.368 to 0.683 and 0 to 0.73%, respectively. In addition, the counterclockwise vortex region increases, and the energy separation phenomenon becomes more obvious. In actual gas processing, the pressure energy recovery efficiency at the range of 57.1%–64.2% can effectively improve energy recovery efficiency and ensure high liquefaction efficiency of natural gas in the nozzle.

Upgrading exergy utilization and sustainability via supersonic separators: Offshore processing of carbonated natural gas

Offshore processing of natural gas with 44%mol carbon dioxide at remote deep-water oil-and-gas fields is invariably characterized by low-efficiency power generation via gas-fired turbines releasing hot flue-gas and entailing high degradation of resources, high carbon emissions and low sustainability. This work demonstrates how to upgrade exergy utilization and consequently process sustainability by using supersonic separators in some gas processing steps; namely: (i) water dew-point adjustment; (ii) hydrocarbon dew-point adjustment; and (iii) carbon dioxide abatement to 20%mol. To accomplish this, the exergy performance of two supersonic separator gas processing alternatives are compared with conventional gas processing comprising triethylene-glycol absorption for water dew-point adjustment, Joule-Thomson expansion hydrocarbon dew-point adjustment and membrane-permeation carbon dioxide removal. Since exergy is measured relatively to a reference environmental reservoir, two such reference reservoirs are used: RER-1: standard atmosphere with 2%mol water containing hydrocarbons at combustion chemical equilibrium with air species; and RER-2: 1atm water-saturated raw natural gas in equilibrium with liquid water. Aspen-HYSYS simulations are used to solve mass/energy balances and thermodynamic property calculations. With RER-2 the conventional gas processing conserves 63.3% of the inlet exergy, while the two alternative supersonic separator processes attain 66.5% and 72.4% of exergy conservation, proving the associate gains of exergy efficiency and sustainability.

Simulation research on the flow field performance of the supersonic separator for natural gas

The separation of natural gas dehydration and de-heavy-hydrocarbons is an important part of natural gas treatment, the main purpose of which is to prevent liquid water in the later processing, transportation and storage of natural gas, and to prevent acidic gas dissolving in free water which will cause the corrosion of pipelines and equipment. This paper introduces a new type of natural gas separation technology— supersonic gas-liquid separation technology. Based on the working principle of supersonic gas liquid separator, using relevant theories such as fluid mechanics, gas dynamics and thermodynamics, the structure of Laval nozzle was mainly optimized and the flow field of the separator was simulated through ANSYS software, the distribution of the characteristic parameters such as pressure, velocity, temperature of shrink segment, throat, expansion segment of the supersonic cyclone separator nozzle were studied in this paper. The results show that the design of the nozzle structure meets the needs of low temperature, can make the water vapor in natural gas condense into small droplets and separate out, so as to achieve the goal of natural gas dehydration. Then, comparing the different design methods of Laval nozzle, the most reasonable design scheme is selected to improve the separation efficiency of the separator.

Comparative Study of the Combined Supersonic Separator and Vortex Tube Performance for Hydrocarbon Gas Drying

AbstractExperimental investigation of the combined supersonic separator (CSS) characteristics was carried out and the results were compared with those from the vortex tube. The separator is a counter‐flow vortex tube with an energy separation chamber in the shape of a Laval nozzle; it can be used for hydrocarbon gas transportation preparation and power plant fuel gas drying. Numerical modeling was carried out to confirm the flow specifics in the examined separator structure. Although the cooling capability of the CSS is 30–50 % less than that of the vortex tube, its efficiency of moisture removal is twice as large, as is shown by the experimental research. The maximal cooling power corresponds to a cold flow fraction level of 0.39, while the range of optimal values for the moisture separation is 0.4–0.6.

Supersonic refrigeration performances of nozzles and phase transition characteristics of wet natural gas considering shock wave effects

Laval nozzle is the critical part of supersonic separator to provide refrigeration environment. Due to the back pressure at the outlet of supersonic separator in dehydration process, the condensation characteristics of water vapor and the refrigeration performances of the nozzles are affected by the shock wave. Herein, mathematical models for the supersonic condensation and flow of the methane-water two-phase flow model were established, which were verified by the experimental data. The effects of different divergent angles on the refrigeration and condensation behavior in the Laval nozzle were studied considering shock wave. The results show that the refrigeration performance of the nozzle will be worsen under the presence of shock waves. With the divergent angle of the nozzle increased from 2° to 8°, the lowest temperature was decreased from 304.4 K to 291.8 K, the liquid mass fraction at the nozzle outlet was decreased from 0.84% to 0.133%, the maximum droplet radius that can be obtained was reduced from 2.54 × 10−7 m to 1.69 × 10−7 m due to the forward movements of the shock waves. The divergent angle of the nozzle is recommended to be designed to 4°–6° in consideration of the refrigeration performance.

Supersonic separation technology for carbon dioxide and hydrogen sulfide removal from natural gas

Abstract A cleaner approach was proposed for removing CO2 and H2S from highly acid natural gas by supersonic separation technology. For this purpose, different structures of Laval nozzles and supersonic swirling separation devices were designed. The mathematical models of gas flow in the nozzle were established, and the supersonic flow characteristics of CH4–H2S–CO2 ternary mixture were accurately predicted by adding the real gas state equation and the transport equation to describe the rotational and irrotational flow field. The effects of nozzle structure, swirl angle of static vanes and inlet parameters on the refrigeration performance of the nozzle and the separation characteristics of the swirl device were systematically investigated. The results show that the average temperature at the nozzle outlet can be as low as 135.2 K under the condition of inlet temperature 293.15 K, inlet pressure 4 MPa and 20 mol % acid gas. It indicates that the refrigeration effect produced by high speed expansion of acid natural gas in the supersonic nozzle can provide a favorable liquefying environment for the acid components, which confirms the feasibility of capturing acid components by supersonic separation device. Better refrigeration performance can be achieved in the nozzle with higher outlet Mach number, but the pressure recovery capacity of the device will be suppressed accordingly. As swirl angle increases from 73.90° to 81.79°, the maximum tangential velocity in the nozzle rises from 119.6 m/s to 212.5 m/s, the separation performance of the swirl device increases, while the pressure and temperature at the same location decrease slightly. However, the increase of swirl intensity will restrict the flow capacity of the separator. For the given supersonic swirling separation device, it shows a good adaptability in separation performance when changing the inlet parameters.

Numerical study on the influence of supersonic nozzle structure on the swirling condensation characteristics of CO2

Compared with other natural gas processing methods, supersonic separation technology has the advantages of small floor space, no internal moving components, and no chemical additives. At present, the research on supersonic separation technology mainly focuses on dehydration and heavy hydrocarbon removal, and there is little research on the use of supersonic separator to separate CO2 from natural gas. In order to study the influence of nozzle structure on the supersonic swirling condensation characteristics of CO2, a CO2–CH4 mixed gas condensation flow model was established, and the swirling condensation process of CO2 in the supersonic nozzle was simulated by the Fluent software. The results show that the liquefaction efficiency and separation efficiency of the separator increase with the increase of the nozzle expansion section length. When there is no back pressure at the nozzle outlet, increasing the nozzle expansion angle will increase the liquefaction efficiency but decrease the separation efficiency. The nozzle designed with Witoszynski curve has the highest CO2 liquefaction efficiency. Considering the above factors, the nozzle expansion length and angle are finally determined to be 100 mm and 3°.

Experimental and numerical research on the effect of the inlet steam superheat degree on the spontaneous condensation in the IWSEP nozzle

The spontaneous condensation process takes place in many power engineering machines and devices, such as steam turbines, supersonic separators, ejectors etc. In the paper, the effect of the inlet steam superheat degree in steam condensing flow through the IWSEP (International Wet Steam Experimental Project) nozzle was investigated experimentally and numerically. The experiment was conducted for the low inlet pressure values under different inlet superheat conditions. The static pressure on the nozzle walls as well as the liquid phase properties in the three positions along the nozzle centreline were measured. The paper delivers new experimental data desirable for validation of the numerical models. For the numerical simulations, a condensation model using the Benson surface tension model was employed, and its accuracy was checked by comparing with the experimental data of SUT. The results state clearly that the condensation model using the Benson surface tension model can predict the spontaneous condensation process accurately, and the error is less than 5%. With the inlet steam superheat degree increasing, the condensation process moves downstream and the condensation strength weakens, and the nucleation zone range increases about 36mm. The presented results provide a good reference for further research in the field of condensing steam flows and for the improvement of both experimental and numerical methods and models.

Study on supersonic swirling condensation characteristics of CO2 in Laval nozzle

Supersonic swirl separation technology has been widely used in natural gas processing and has achieved good results. However, there are few studies on the application of supersonic separation technology to the removal of CO2 from natural gas, and the condensation rule of CO2 under supersonic swirling flow condition is still unclear. In order to study the supersonic swirling condensation characteristics of CO2 in Laval nozzle, the Euler mathematical model of the condensation flow of CO2–CH4 two-component mixed gas was established, and the feasibility of CO2 removal by supersonic separation technology was verified by numerical simulation. The results show that, in the process of axial flow and swirling flow, the variation trend of CO2 condensation parameters is basically the same along the axial direction of the nozzle, but the distribution of parameters is significantly different along the radial direction. The increase of swirl intensity will increase the nozzle's liquefaction efficiency and reduce the working flow of the nozzle. The inlet temperature and inlet pressure had a significant influence on the liquefaction efficiency of the nozzle, while the inlet CO2 content had little influence on the liquefaction efficiency.