Supersonic Separation Research Articles

Effect of Supersonic Nozzle Structure on Vapor Spontaneous Condensation

To study the effect of the supersonic nozzle structure on the spontaneous condensation of water vapor, the wet steam model used to study the wet steam liquefaction of steam turbine was introduced into the numerical study of supersonic nozzle in supersonic cyclone separator, and the numerical results was in good agreement with the experimental data of the related literature. The supersonic nozzles, the contraction section with the Witozinsky curve and the bicubic curve, and the expansion section with conical curve and Foelsch curves, were designed. The influence of supersonic nozzle structure on water vapour liquefaction ability was investigated. And the following research results were obtained. When the structure of the supersonic nozzle was the same, the Witozinsky curve was selected for contraction section of the supersonic nozzle, and the nucleation rate of the droplet in the nozzle increased by 21.97 % and the number of droplets increased by 32.16 %, which was helpful to the gas liquefaction in the nozzle. When the contraction curve of the supersonic nozzle was consistent, and the expansion curve was Foelsch curve, the gas nucleation rate and the number of droplets in the nozzle were greatly improved. The distribution of nozzle humidity was related to the structure of expansion section, but not to the structure of contraction section. The maximum humidity in nozzle depended on the outlet diameter of nozzle. When the other structures of the nozzle were consistent, the cone angle of divergent section increased from 2° to 8°, the peak value of the nucleation rate increased by 493.15 %, the maximum of the droplet number increased by 246.12 %, the outlet humidity of the nozzle increased by 73.37 %, which greatly improved the gas liquefaction rate. In the case of gas liquefaction, increasing the cone angle of expansion section was conducive to liquefaction of water vapor.

Effect of the Wet Outlet Geometry on the Shockwave Position in Supersonic Separators

AbstractSupersonic separators (3Ss) are applied in gas separation processes. Two‐dimensional simulation is employed to investigate the effect of operational and thermophysical parameters on the shockwave position. In addition, the impact of the cyclonic part and wet outlet geometry is evaluated by proposing four cases. Increasing the length of the cyclonic part exerts positive and negative influences on the performance of the 3S and the pressure recovery coefficient, respectively. The optimum length is determined between 10 and 15 cm. To demonstrate negative effects of wasted air from the wet outlet, its flow has been increased from 3.6 to 8.1 % of the inlet flow. Improved performance of the 3S is obtained by reducing the flow disturbances around the wet outlet and moving the shockwave towards the outlet.

An efficient method for removing hydrogen sulfide from natural gas using supersonic Laval nozzle

A new method was proposed for hydrogen sulfide removal from natural gas through the utilization of supersonic flow in a Laval nozzle. For this purpose, a mathematical model was established for the supersonic non-equilibrium condensation flow of the binary methane-hydrogen sulfide mixture. The condensation parameters were numerically calculated and described in detail, and a sensitivity analysis was carried out to investigate the influence of the inlet parameters on the supersonic condensation flow. The results show that when the inlet temperature and pressure were 290K and 5MPa respectively, and the mole fraction of hydrogen sulfide was 15%, the removal efficiency of hydrogen sulfide was 64.83%, which indicates that the use of supersonic separation technology for this application is indeed feasible. It was also found that with the decrease of inlet temperature or the increase of inlet pressure, the nucleation site moved forward (i.e. closer to the throat), and the maximum droplet radius and liquid mass fraction of hydrogen sulfide increased. When the mole fraction of hydrogen sulfide was less than 5%, however, the liquid mass fraction of hydrogen sulfide was almost zero. Therefore, it appears that using a reasonable hydrogen sulfide fraction, a lower inlet temperature, and a higher inlet pressure can promote the supersonic condensation of hydrogen sulfide in the Laval nozzle and improve the efficiency of the removal process. These results suggest that supersonic separation technology can provide an efficient and environment-friendly way to remove hydrogen sulfide from natural gas, thereby reducing emissions.

CO<sub>2</sub> Rich Natural Gas Processing: Technical, Power Consumption and Emission Comparisons of Conventional and Supersonic Technologies

Supersonic separator is investigated via process simulation for treating CO2 rich (>40%) natural gas in terms of dew-points adjustment and CO2 removal for enhanced oil recovery. These applications are compared in terms of technical and energetic performances with conventional technologies, also comparing CO2 emissions by power generation. The context is that of an offshore platform to treat raw gas with 45%mol of CO2, producing a lean gas stream with maximum CO2 composition of ≈20%mol, suitable for use as fuel gas, and a CO2 rich stream that is compressed and injected to the oil and gas fields. The conventional process comprises dehydration by chemical absorption in TEG, Joule-Thomson expansion for C3+ removal, and membrane permeation for CO2 capture. The other alternatives use supersonic separation for dew-points adjustment, and membranes or another supersonic separation unit for CO2 capture. Simulations are carried out in HYSYS 8.8, where membranes and supersonic separation are modeled via unit operation extensions developed in a previous work: MP-UOE and SS-UOE. A full technical and power consumption analysis is performed for comparison of the three cases. The results show that the replacement of conventional dehydration technology by supersonic separators decreases power demand by 8.5%, consequently reducing 69.66 t/d of CO2 emitted to the atmosphere. The use of supersonic separation for CO2 capture is also superior than membranes, mainly due to the production of a high-pressure CO2 stream, that requires much less power for injection compression than the low-pressure permeate stream from membranes. Therefore, the case with two supersonic separator units in series presents the best results: lowest power demand (-23.9% than conventional case), directly impacting on CO2 emissions, which are reduced by 2598 t/d (-27.82%).

CO<sub>2</sub> Emission and Energy Assessments of a Novel Pre-Purification Unit for Cryogenic Air Separation Using Supersonic Separator

Thermal power plants with oxy-combustion CO2 capture are featured by large scale oxygen demand, where cryogenic air separation is most suitable. In such context, a Pre-Purification Unit (PPU) is required, prior to air fractionation, to remove hazardous air contaminants – H2O, CO2 and several trace-species – preventing ingress into the Cold Box. The conventional PPU – named FULL-TSA – remove those contaminants by means of Temperature Swing Adsorption (TSA), ordinarily using double-layered bed with activated alumina for adsorbing H2O and zeolitic molecular sieve for adsorbing CO2 and further trace-species, which implicates in relatively high demand of low-pressure steam for impurities desorption. A novel pre-purification concept (SS-TSA) embraces a Supersonic Separator (SS) performing the bulk of separation service, abating nearly 98.5% of H2O, followed by a finishing single-bed molecular sieve (MS) TSA step, which is featured by its relatively small size, for removing CO2 and remaining impurities. This work presents the energy analysis, as well as the related indirect CO2 emissions, of such a novel concept (SS-TSA) comprising air compression, cooling, SS dehydration and finishing MS-TSA against the conventional method fully based in TSA purification (FULL-TSA). Process simulation in HYSYS 8.8 assisted technical evaluation and comparison of alternatives, which included the use of two Hysys Unit Operation Extensions – SS-UOE and PEC-UOE – for rigorous thermodynamic SS modeling with phase equilibrium sound speed. SS was designed to impose only 1.4% of head loss, while shrinking TSA service to about 10% of FULL-TSA counterpart, also recovering super-cooled aqueous condensate that reduces water make-up and N2 consumption for cooling. Changing from FULL-TSA to SS-TSA the average demand of low-pressure steam reduced from 1.37 to 0.16 MW. In terms of electricity demand the difference was quite small, referring to a tiny increase of 0.07 MW in SS-TSA comparatively to total power demand of 14.97 MW in FULL-TSA. Assuming a natural gas combined cycle cogeneration plant matching requirements to air compression and pre-purification process, equivalent reduction in CO2 indirect emission was 20 kg/h for SS-TSA. These results point superiority of SS-TSA.

Offshore Natural Gas Conditioning and Recovery of Methanol as Hydrate Inhibitor with Supersonic Separators: Increasing Energy Efficiency with Lower CO<sub>2</sub> Emissions

The oil and gas industry represents an important contributor to CO2 emissions as offshore platforms are power intensive for producing, processing and transporting hydrocarbons. In offshore rigs CO2 emissions mainly come from on-site gas-fired power generation for heat and electricity production. The accumulation of atmospheric CO2 is one of the main causes of the planetary greenhouse effect, thus CO2 emissions should be minimized. To achieve that, more energy efficient processes for natural gas (NG) conditioning are needed in order to minimize platform power consumption and thus lowering the associated generation of CO2. In addition, in offshore scenarios gas-hydrate obstructions are a major concern in flow assurance strategies, since thermodynamic conditions favoring hydrate formation are present, such as high pressure, low external temperature and gas contact with free water. To avoid hydrate issues, hydrate inhibition is carried out by the injection of a thermodynamic hydrate inhibitor (THI) in well-heads such that it flows along with production fluids, thus removing the thermodynamic conditions for hydrate formation and ensuring unimpeded flow. Therefore, the three-phase high-pressure separator (HPS) is fed with production fluids, where the HPS splits the feed into: (i) an upper gas phase, (ii) hydrocarbon condensate, and (iii) a bottom aqueous phase. The gas phase goes to NG conditioning for hydrocarbon dew point adjustment (HCDPA) and water dew point adjustment (WDPA) so as to make NG exportable. The hydrocarbon condensate (if present) is collected for stabilization and the bottom aqueous phase consisting of water, salts and THI is sent to a THI recovery unit (THI-RU) for THI re-concentration and reinjection. In conventional plants, WDPA and HCDPA are done by glycol absorption and Joule-Thomson expansion respectively. Moreover, the HPS gas carries some THI such as methanol that is lost in the processing. This work analyses a new process – SS-THI-Recovery – where HPS gas feeds a supersonic separator (SS) with injected water and compares it to the conventional processing. As a result, SS ejects a cold two-phase condensate with almost all water, THI and C3+ hydrocarbons, discharging exportable NG with enough HCDPA and WDPA grades, while the condensate gives aqueous THI returned to the THI-RU and LPG with high commercial value. Thus, SS-THI-Recovery not only avoids THI losses as well as exports NG and LPG. Both conventional gas plant and SS-THI-Recovery alternative coupled to THI-RU were simulated in HYSYS 8.8 for a given NG field and targeting the same product specifications. SS-THI-Recovery presented lower power consumption and thus less associated CO2 emissions, while potentially increasing the gas plant profitability, as THI losses are significantly reduced and higher flow rate of LPG with higher commercial value is produced in comparison with the conventional alternative. Hence, the higher efficiency of SS-THI-recovery makes it not only more environmentally friendly with lower CO2 emissions, but also a potential alternative for improving process economics and thus providing an economic leverage that could justify investments in carbon capture technologies, contributing to avoid CO2 emissions even more with cleaner NG and LPG production.

Supersonic separator for cleaner offshore processing of supercritical fluid with ultra-high carbon dioxide content: Economic and environmental evaluation

Offshore gas processing presents challenges, especially when high flow rates, high-pressure and high carbon dioxide contents are involved. The present scenario comprehends offshore processing of high flow rate of high-pressure natural gas with 68%mol carbon dioxide, which results from oil production and behaves as a dense supercritical fluid. The processing goals with this fluid comprise: [A] water dew-point adjustment; [B] hydrocarbon dew-point adjustment; [C] decarbonation of a small part to 20%mol carbon dioxide fuel-gas for power production; and [D] compression/pumping of the remaining fluid enriched with carbon dioxide from decarbonation for enhanced oil recovery. For these tasks the industry considers traditional well established processes such as molecular-sieves adsorption for water dew-point adjustment, Joule-Thompson expansion for hydrocarbon dew-point adjustment and membrane-permeation for carbon dioxide removal. However, conventional technologies can become cumbersome in such awkward conditions. Thus, unconventional solutions are sought for reliability, lower equipment size/weight, and better power consumption, emissions and environmental sustainability. Recently, supersonic separators have been analyzed in proof-of-concept researches for natural gas processing. In this regard, this work quantitatively proves that goals [A],[B],[C] are achievable using only supersonic separators, attaining 33% higher net value, 40% greater oil production, 10% lower investment and economic leverage to reach lower carbon emission relatively to conventional counterparts.

Supersonic separator for cleaner offshore processing of natural gas with high carbon dioxide content: Environmental and economic assessments

Supersonic separators offer a cleaner offshore processing of natural gas with carbon dioxide content from deep-water oil-gas fields. Conventional offshore gas processing comprises water dew-point adjustment via glycol-absorption, hydrocarbon dew-point adjustment via Joule-Thomson expansion, and carbon dioxide removal via membrane-permeation. Alternative processing contemplates the use of supersonic separators for adjusting gas dew-points followed by carbon dioxide capture via membrane-permeation (so-called SS-MP scheme); or for adjusting gas dew-points and also accomplishing carbon dioxide abatement (so-called SS-SS scheme). The conventional process is environmentally and economically compared with SS-MP and SS-SS for application in offshore rigs treating raw gas (44%mol carbon dioxide) to produce exportable fuel-gas (≈20%mol carbon dioxide), while dispatching carbon dioxide rich fluid (≈75%mol carbon dioxide) for enhanced oil recovery in the oil-gas field. Results show that SS-MP requires 7.8% less power than the conventional process. Moreover, implementing SS-SS deepens the advantage against the conventional operation because SS-SS produces carbon dioxide rich fluid at high-pressure, requiring much less compression power for enhanced oil recovery than the low-pressure permeate from membrane-permeation. SS-SS has lowest carbon emission (−28.3%), lowest power consumption (−21.3%) and best economic performance: lowest manufacturing cost and lowest compressor investment. Thus, SS-SS is the overall best and cleanest solution, with highest 20 years net value (+860 MMUSD) and lowest environmental impact.

Low-emission offshore Gas-To-Wire from natural gas with carbon dioxide: Supersonic separator conditioning and post-combustion decarbonation

Gas-To-Wire is a solution for remote offshore oil-gas fields with high gas-oil ratio and high carbon dioxide content, as it requires minimum natural gas upgrade and is feasible for long-distance transportation. Additionally, combining offshore Gas-To-Wire with carbon capture enables abatement of emissions while providing revenues from enhanced oil recovery. This work investigated offshore Gas-To-Wire comprising processing of natural gas with high carbon dioxide content, power generation, post-combustion carbon capture and enhanced oil recovery. Supersonic separator is proposed for three applications: fuel-gas conditioning, fuel-gas decarbonation and pioneering dehydration of supercritical carbon dioxide. Economic analysis, including offshore rig and electricity transmission, results in positive Net Present Value with 20% of return-on-investment, besides a Levelized Cost of Energy comparable to onshore power plants with carbon capture and storage. Sensitivity analysis shows high impact of electricity-price and oil recovery yield on profitability, as well as better economic performance when carbon dioxide is not removed from fuel-gas; i.e., all carbon capture should be post-combustion capture. Thus, despite effectiveness of supersonic separator for fuel-gas decarbonation, the 612 MW optimized Gas-To-Wire with carbon capture plant should have 100% of carbon removal via post-combustion, resulting in 38.3% return-on-investment and even better Levelized Cost of Energy similar to onshore power plants without carbon capture.

Improvement of recovery of gaseous fluids using the replacement of supersonic separator instead of Joule–Thomson valve in dehydration/NGL recovery unit with computational fluid dynamic modeling

In this study, we employed the computational fluid dynamic (CFD) technique in conjunction with a thermodynamic EOS package to investigate the liquid hydrocarbon recovery of dehydration/NGL recovery unit. The effect of modification in dehydration/NGL recovery unit using the supersonic separator was studied. The Peng–Robinson equation of state in conjunction with the thermodynamic process modeling package were used to simulate the heavy hydrocarbon separation in the supersonic separator. The κ–ε turbulence model was used to simulate the natural gas flow in supersonic separator and the behavior of gas pressure reduction on refrigeration performance was studied under the conditions of specified boundary layers. The CFD modeling results revealed a satisfactory agreement with the measured data reported in literature. The results showed that cooling performance was improved for this system compared to J–T valve and turbo-expander. The performance of this system can be further intensified by comparing the refrigeration effect in the same pressure difference. Furthermore, the condensation process of natural gas stream was investigated with the modification of design of dehydration/NGL recovery unit. Compared to the Joule–Thomson valve, this new method derives about 2.85 time higher of C3+. The results showed that, when the pressure reduction of this device is equal to that of Joule–Thomson valve, the supersonic separator has a better cooling and separation performance.

Carbon capture and high-capacity supercritical fluid processing with supersonic separator: Natural gas with ultra-high CO2 content

Some deep-water offshore fields produce oil with high gas/oil ratios and ultra-high %CO2 (>60%mol) with the onus of processing low-grade gas simultaneously handling huge CO2 dispatch goals. Thus, processing solutions are needed to make feasible such high-capacity gas rigs hundreds of kilometers offshore. Feasibility relies on the choices for CO2 capture and adjustment of water and hydrocarbon dew-points of such high flow rate gas. This problem was approached adopting supersonic separators for dew-point adjustments and for CO2 capture on a floating-hub processing 50 MMsm³/d of CO2 ultra-rich gas, reinjecting 96% of treated CO2-rich gas for enhanced oil recovery, while reserving 4% as fuel-gas after CO2 abatement to 20%mol for power production. Process alternatives were assessed in terms of power demand and profitability comparing supersonic separator with membrane-permeation for CO2 removal. Results show that 1st supersonic separator for dew-point adjustments of raw gas recycling condensate to the oil-gas-water separator and 2nd supersonic separator for CO2 removal avoiding CO2 freeze-out, give optimum net present value and minimum CO2 emissions. On one hand, these facts are consequences of less compressor investment as 2nd supersonic separator ejects pressurized CO2 condensate requiring 5% less compression power for enhanced oil recovery relatively to the power required by the low-pressure CO2-rich permeate from the membrane-permeation alternative. On the other hand, the best net value of supersonic separator alternative also reflects its highest revenues derived from recycling condensate from 1st supersonic separator entailing 18% higher oil production.

Shortcut modeling of natural gas supersonic separation

Supersonic separation combines concepts from aerodynamics, thermodynamics, physical separation and fluid-dynamics resulting in an innovative gas conditioning process. It is used to condition the gas by removing condensable vapors and natural gas liquids. In the supersonic separation process, undesired components form liquid condensates, as a result of temperature drop, that are centrifugally removed through side collection streams. This article presents a shortcut one-dimensional numerical model that presents great potential as a fast and accurate tool that enables the simulation of supersonic separators. This model would best fit the category of preliminary conceptual design tools. The developed model is validated through several cases with air, 3-component natural gas and 13-component natural gas mixtures as working fluids at different conditions and nozzle area ratios. Tests included nozzles with and without side streams. Computational loads were decreased by reducing the number of locations tested in the diverging nozzle to locate the side streams and the shockwave. Simulation time and number of locations tested in the nozzle are reduced by 75%–97%. depending on the nozzle geometry and conditions.

Structure improvements and performance study of Supersonic Separation device with reflux channel

A new supersonic separator with reflux channel has been proposed to obtain better refrigeration and separation performance. However, the specific structure of the new separator has not been reported so far. Moreover, the length of the conical drainage structure is too short to allow sufficient time to discharge the condensate. Therefore, in the paper, a new hybrid two-stage drainage structure is designed by adding additional side drainage structure after the conical drainage structure. Effect of the above structure changes on separation performance are investigated with three-dimensional numerical simulation. The results show that the increasing of reflux can greatly optimize the flow field. As the reflux flow increases, the shock wave position moves backwards and the condensation area is expanded. At the same time, the centrifugal acceleration decreases which can be overcome by optimizing the exit angle of swirler blades. The hybrid two-stage drainage structure extends the condensation area and prolongs the time of the condensate through the outlet. Moreover, the insertion depth of 30mm, the diameter of the reflux outlet of 7mm and the diameter of the reflux channel of 24 mm are recommended based on the comprehensive consideration of good expansion characteristics and the location of the shock wave.

Effect of groove configurations on the swirling intensity of a supersonic separator

In the downstream process of an energy plant, a supersonic separator is a new technology that dehydrates natural gas with pressure and temperature differences using centrifugal force. Compared to other separating devices, a supersonic separator has the advantage of low cost in maintenance and its compatibility. In this study, the effect of the number of grooves on the swirling intensity of a supersonic separator was studied by numerical analysis using RNG turbulence model. Commercial CFD code ANSYS CFX 17.1 was used to determine and display a result of temperature and velocity distribution of the flow characteristics of a supersonic separator. Numerical results showed that the swirling intensity was proportional to the number of groove shapes but decreased when the number of grooves exceeded a certain number. As a result, a supersonic separator including the number of grooves with the highest swirling intensity deduced.

Economic leverage affords post-combustion capture of 43% of carbon emissions: Supersonic separators for methanol hydrate inhibitor recovery from raw natural gas and CO2 drying

Offshore oil/gas productions are power intensive and CO2 emitters from gas-fired power generation. This work investigates supersonic separator as a strategy for affording post-combustion capture backed up by cost reductions. Conventional offshore gas processing usually loses thermodynamic hydrate inhibitor methanol in processing and exported gas. This work analyses a supersonic separator variant gas processing simultaneously reducing methanol losses. Such process dramatically improves gas-plant profitability via cost-reduction of methanol make-up and power-consumption, simultaneously increasing revenues from liquefied-petroleum-gas by-product. This economic leverage affords post-combustion carbon capture, including subsequent CO2 dehydration and compression for exportation of high-pressure liquid CO2. This corresponds to abate 43% of CO2 emissions boosting revenues via enhanced oil recovery. Moreover, CO2 is dehydrated via another supersonic separator operating with minimum head-loss, minimizing compression costs. Despite its much higher investment, the new process with carbon capture presents higher net value (865.63 MMUSD) than the conventional processing without carbon capture (829.31 MMUSD), being economically feasible and more environmentally adequate with cleaner natural gas production and successful CO2 management. The new process is superior in several scenarios and particularly favored by oil prices above 55 USD/bbl. Rising oil price from 40 to 100 USD/bbl, the new process net value rises 29%, whereas the conventional counterpart rises only 7.5%. In addition, as a plausible future scenario, CO2 taxation favors the new process, which always has superior economic performance, even without CO2 taxation. In summary, implementing supersonic separators in offshore natural gas processing aiming at anti-hydrate recovery and CO2 dehydration for enhanced oil recovery creates economic leverage sustaining Carbon Capture & Storage without loss of competitiveness. This result, backed up by rigorous thermodynamic simulations and economic-environmental assessments, configure an original achievement to the literature.

A new concept of air pre-purification unit for cryogenic separation: Low-pressure supersonic separator coupled to finishing adsorption

In commercial cryogenic manufacturing of oxygen, air to the Cold-Box must pass through a Pre-Purification Unit (PPU) to remove water, CO2 and other impurities. The conventional PPU – FULL-TSA – comprises compression, cooling pre-dehydration and temperature-swing adsorption (TSA) for dehydration and CO2 removal, supplying treated air at 3.1 bar. This work discloses a new PPU concept – SS-TSA – prescribing a supersonic separator (SS) upstream to TSA handling 98.5% of dehydration, greatly lowering TSA costs. SS-TSA comprises compression, cooling pre-dehydration, SS dehydration and a smaller TSA for finishing dehydration and CO2 removal. A SS-TSA variant – TSA-HI – additionally recovers compression heat lowering heating costs. SS-TSA, FULL-TSA and SS-SS-TSA-HI were analyzed. Flowsheets were simulated in HYSYS with full thermodynamic SS modeling via a new HYSYS Unit Operation Extension – SS-UOE – rigorously calculating the multiphase sound speed. SS was designed for only 3.5% of head-loss, recovering 98.5% of water as super-cooled liquid, lowering make-up and chilled-water costs, while shrinking the TSA service to 10% of the FULL-TSA counterpart. For commercial-scale PPU considering 20 years of operation at 10% interest rate, the purified 3.1 bar air breakeven prices reached 5.28, 5.19, and 5.18 US$/kNm3, respectively for FULL-TSA, SS-TSA and SS-TSA-HI, establishing superiority of SS alternatives over the conventional FULL-TSA.

Effect of linetype of convergent section on supersonic condensation characteristics of CH4-CO2 mixture gas in Laval nozzle

The Laval nozzle is an important part of the supersonic separator, which structure determines the separation efficiency of supersonic separator. In order to study the flow and condensation process in Laval nozzle with different convergent section, convergent section is designed by Bicubic parametric curve, Quintic polynomial curve, Witoszynski curve and Translation of Witoszynski curve, respectively. The numerical model for the supersonic condensing flow process of CH4-CO2 mixture gas is established and the User Define Function is invoked for numerical simulation. The effects of different linetypes of convergent section on the flow and condensation parameters in nozzle were investigated. The results confirm the Laval nozzle designed by Translation of Witoszynski curve has strengths such as the most stable pressure change, the best refrigeration effect, the most intense spontaneous condensation, and the nucleation rate is 1.610×1022m−3s−1, the number of droplets is as high as 2.023×1015m−3 at the nozzle outlet far better than the other nozzles. Therefore, Translation of Witoszynski curve is recommended to design the convergent section of Laval nozzle in supersonic separator.

Supersonic liquefaction properties of natural gas in the Laval nozzle

In view of the excellent performance of the supersonic separator for natural gas dehydration, a new type of natural gas liquefaction process using the Laval nozzle is proposed in this paper. Theoretical and numerical studies of the supersonic flow and liquefaction process of the methane-ethane binary system in this nozzle are carried out. The effects of the inlet temperature, inlet pressure, back pressure and component composition on the liquefaction process are analyzed. The results show that the critical liquefaction temperature and pressure of the methane-ethane binary system decrease under low inlet temperature or high inlet pressure conditions and the range of the liquid phase region increases, which promotes the liquefaction process. With the increase of the back pressure of the nozzle, the position of the shock wave moves forward and the liquefaction environment is more completely destroyed. For a multi-component natural gas, in which the heavy hydrocarbon content is high, natural gas is more easily liquefied using the Laval nozzle. The liquefaction efficiency range of the newly designed liquefaction process with the Laval nozzle are 0.0795–0.1321 (HYSYS results) and 0.0718–0.1505 (MATLAB results) when the inlet pressure of the process is 2–5 MPa. The nozzle more easily achieves liquefaction compared with a throttle under the same conditions.

Optimal operation of refrigeration oriented supersonic separators for natural gas dehydration via heterogeneous condensation

Refrigerative supersonic separators (3S's) have found extensive applications in natural gas industry, especially for dew point corrections of water vapor and heavier hydrocarbons. Previous studies indicated that even at heavy refrigeration duties and staggering radial acceleration values (>500,000 g) generated inside 3S units, the condensed water (or hydrocarbon) droplets should have a minimum diameter of 2 µm to provide sufficiently large dehydration efficiencies. To promote the overall condensation rate and facilitate the separation of condensed phase from natural gas streams, certain rates of edible salt particles are assumed in the present article to be injected into the gas flow at the 3S unit entrance. The plenum chamber static vanes are also positioned after the throat location to enjoy the full swirling effect. Our simulation results indicate that by using the optimal structure of the 3S unit for a typical case study, the minimum solid particle injection rate is around 2.4 wt% to achieve almost complete overall separation efficiency of the condensed water droplets. Moreover, the overall pressure recovery of the entire 3S unit can be boosted up to 83% for such optimal structure.

Numerical investigation of water droplets trajectories during natural gas dehydration inside supersonic separator

Reliable estimation of the condensed water droplets trajectories inside Supersonic separators (3Ss) during the dehydration process is essential for proper design and safe operation. Most of previous researches ignored the actual sizes of condensed droplets and predicted the particles trajectories for pre-specified diameters. In this article and for the first time, real trajectories are computed by considering the actual particle size distribution (PSD) of the condensed droplets in the presence of swirl, nucleation and growth processes during the dehydration of methane rich natural gas (MRNG) inside Laval nozzle for various diffuser angles. Furthermore, the injection of water droplets to facilitate the condensation process has not been addressed previously.Our simulation results indicate that even for the most optimal geometry and at extremely large centrifugal accelerations of 500,000 g, the condensed particles from MRNG are exceedingly small and can't reach the 3S walls for practical straight tube lengths. Our findings are verified with several previously reported experimental measurements and theoretical investigations results, borrowed from literature. To ensure proper dehumidification, sufficiently large water droplets are assumed to be injected preferably after the throat location. The computed results indicate that by injecting 5 μm diameter particles into MRNG of Khangiran refinery sweet gas stream and increasing its wetness fraction up to 0.12, the dehydration process is successfully achieved in an optimally designed supersonic separator.