【機(jī)械類畢業(yè)論文中英文對照文獻(xiàn)翻譯】緊湊型管柱狀氣液旋流分離器技術(shù)目前的發(fā)展?fàn)顩r

【機(jī)械類畢業(yè)論文中英文對照文獻(xiàn)翻譯】緊湊型管柱狀氣液旋流分離器技術(shù)目前的發(fā)展?fàn)顩r,機(jī)械類畢業(yè)論文中英文對照文獻(xiàn)翻譯,機(jī)械類,畢業(yè)論文,中英文,對照,對比,比照,文獻(xiàn),翻譯,緊湊型,柱狀,旋流分離器,技術(shù),目前,發(fā)展,狀況,狀態(tài) 緊湊型管柱狀氣液旋流分離器技術(shù)目前的發(fā)展?fàn)顩r Ovadia Shoham Gene E. Kouba著 ，狄磊譯 摘要 石油行業(yè)主要依靠傳統(tǒng)的容器式分離器處理井口生產(chǎn)過程中的油/水/氣采出液。但經(jīng)濟(jì)性和操作壓力條件不斷要求其尋找新型高效、低成本的緊湊型分離器，特別是在海上油田上這種要求更加迫切。與容器型的分離器相比，緊湊型分離器，如管柱式氣液旋流分離器，不僅簡單，成本低，重量輕，需要很少的維護(hù)，而且易于安裝和操作。然而，無法預(yù)測的GLCC性能充分抑制了其廣泛的發(fā)展。目前研發(fā)的目的是研發(fā)必要的性能預(yù)測工具對GLCC分離器進(jìn)行適當(dāng)?shù)脑O(shè)計(jì)和操作。本文從最先進(jìn)的仿真和設(shè)計(jì)方面，介紹了GLCC目前成功的應(yīng)用，以及潛在的應(yīng)用方面的發(fā)展?fàn)顟B(tài)。 簡介 GLCC是帶有傾斜切向入口的氣體及液體出口的垂直管。切向液流從入口進(jìn)入GLCC后形成的漩渦產(chǎn)生了作用于液體的離心力和浮力，其數(shù)值要比重力高出許多倍。重力、離心力、浮力的聯(lián)合作用使氣體和液體的分離開。液體沿徑向被推向外側(cè)，并向下由液體出口排出，而氣體則運(yùn)動到中心，并向上由氣體出口排出。這一低成本、重量輕、緊湊型的GLCC分離器在替代常規(guī)容器型分離器方面具有很大的吸引力。GLCC和常規(guī)容器型立式和臥式分離器在尺寸方面的差別進(jìn)行了對比，在表壓力100 PSIG下，石油和天然氣的流速分別為100,000 B / D和70000Mscf/ D，這種情況下，所需的GLCC的直徑和高度尺寸分別為5和20英尺。相當(dāng)于同規(guī)模的常規(guī)立式分離器（9×35英尺）一半左右的尺寸，相當(dāng)于常規(guī)臥式分離器（19×75英尺）四分之一左右的尺寸。 GLCC的操作區(qū)域是指由兩個(gè)限制的現(xiàn)象：氣體流中遺留液體和液體流中攜帶氣體?，F(xiàn)在已經(jīng)確定液體遺留發(fā)生在氣流中的液體的第一跡線上。類似地，在液體下溢最早觀察到的氣泡與氣體攜帶的發(fā)生有關(guān)。 開發(fā)精確的性能預(yù)測工具中的困難大部分來源于可能發(fā)生在GLCC中的各種復(fù)雜流型。上方的進(jìn)氣口的流動模式可能包括泡狀流、段塞流、渦流、霧狀流和液體帶流。進(jìn)氣口下方的流型通常由液體渦旋與氣芯絲組成。在遠(yuǎn)低于入口的液位，液體在旋轉(zhuǎn)膜上從入口流向漩渦。 阻礙GLCC更廣泛的使用的最大原因是難以預(yù)測的水動力性能。即使沒有嘗試和測試性能的預(yù)測，GLCC幾個(gè)成功的應(yīng)用已經(jīng)有了報(bào)道?？煽康男阅茴A(yù)測工具的發(fā)展將通過硬件修改來提高GLCC的性能，最終會加快GLCC技術(shù)在現(xiàn)有的和新的領(lǐng)域應(yīng)用的發(fā)展。 硬件的發(fā)展 研究者已經(jīng)對GLCC幾個(gè)不同的機(jī)械功能配置進(jìn)行了研究。最近的實(shí)驗(yàn)室觀察和計(jì)算機(jī)模擬表明，硬件修改會對GLCC的表現(xiàn)產(chǎn)生深遠(yuǎn)的影響。以下是總結(jié)的幾個(gè)重要的硬件改進(jìn)。 進(jìn)氣口設(shè)計(jì)。入口部確定進(jìn)入的氣體/液體分布和GLCC的初始切向入口速度。由于GLCC性能強(qiáng)烈依賴于切向入口的速度，入口一直是最需要重新設(shè)計(jì)的GLCC組件。 傾斜的進(jìn)氣口。傳統(tǒng)的垂直分離器通常使用垂直進(jìn)氣口。最近的研究已經(jīng)表明，一個(gè)傾斜的進(jìn)氣口，減少氣相中的液體遺留通過兩個(gè)方面來提高GLCC的性能。首先,向下傾斜的進(jìn)口有利于形成分層流，實(shí)現(xiàn)了了氣液兩項(xiàng)的初步分離。其次，向下的傾斜結(jié)構(gòu)使經(jīng)過初步分離的液相在進(jìn)氣口下方旋轉(zhuǎn)一圈之后形成旋流場，避免了對氣相向分離器上方運(yùn)動的阻塞。 入口噴嘴。噴嘴是入口段最后一個(gè)影響進(jìn)入分離器氣液相流速分布和入口切向速度大小的因素。切向入口噴嘴的制造是GLCC制造中最昂貴的部分。幾種噴嘴配置已經(jīng)過測試，旨在優(yōu)化成本效益的水動力性能。薄的，矩形槽結(jié)構(gòu)是水動力性能的最佳配置，同時(shí)也是難以制造的。另一方面，同心圓形的切向入口是容易制造的，但性能較低。通過對具有相同截面積的三種不同的入口槽結(jié)構(gòu)（矩形，圓形，同心圓型和新月型）的初步試驗(yàn)，發(fā)現(xiàn)同心圓形噴嘴（異徑管）結(jié)構(gòu)表現(xiàn)最差，而月牙型的噴嘴（切向平板）的表現(xiàn)最接近矩形槽結(jié)構(gòu)。 雙入口。雙傾斜的進(jìn)氣口將入口流預(yù)分為兩股流動：低入口的富含液體的流動和高入口富含氣體的流動。雙入口的試驗(yàn)表明，在低到中等的氣體流量（在入口處段塞流轉(zhuǎn)為分層流）下，氣體攜帶液率有明顯的降低，而當(dāng)氣體流量較高時(shí)（在入口處為環(huán)狀流），無明顯的變化。 GLCC配置。盡管GLCC的設(shè)計(jì)簡單，但幾種可能的配置修改會影響其性能。 進(jìn)氣口位置。對于沒有液位控制的GLCC，將入口段定位于靠近液面上方是至關(guān)重要的。大多數(shù)測試表明，單入口GLCC的最佳液位是在約低于入口下方1-3個(gè)L / D處。液位遠(yuǎn)低于3個(gè)L/D的會導(dǎo)致切向進(jìn)氣的速度的顯著衰減，影響GLCC的性能。如果液位高于入口，氣體必然會穿過液體而溢出，造成更多的液體遺留。 最佳長徑比。長徑比是GLCC的長度和直徑之比。它的尺寸影響GLCC的性能和成本。對于一個(gè)給定的直徑，GLCC在進(jìn)氣口上方的長度提供液體擾動的容量，而在進(jìn)氣口下方的長度決定從液體中分離氣泡的滯留時(shí)間。此外，離心力和浮力的大小與直徑成反比，切線速度的衰減與長度成正比。由于這種現(xiàn)象的復(fù)雜性，最近才剛剛提出了一套決定最佳長徑比的基本標(biāo)準(zhǔn)。 旋流體錐度。在對反錐型、正錐型和圓柱型的旋流體的調(diào)查中得出，對于氣/液分離，圓柱型旋流體要稍優(yōu)于反錐形和正錐形結(jié)構(gòu)。 液位控制。GLCC液位控制在大范圍的流動條件下并不容易實(shí)現(xiàn)，是因?yàn)槠潴w積小。正在研究的幾種不同的液位控制方法，包括氣腿的流量控制，液體的腿流量控制，以及兩條腿的共同流量控制。同時(shí)也正在考慮氣腿背壓控制和液體腿液位控制的結(jié)合。其他值得關(guān)注的問題包括能量要求，穩(wěn)定性和成本。 GLCC液位控制的幾個(gè)備選方案已付諸實(shí)施。例如，一個(gè)商業(yè)的多相流測量系統(tǒng)使用傳統(tǒng)的控制設(shè)備，通過控制出氣流率來控制液位的試驗(yàn)已經(jīng)在GLCC上取得成功。另一個(gè)項(xiàng)目探討的用低功耗替代傳統(tǒng)的電平控制，通過GLCC的靜壓頭差來操作控制裝置。最近的GLCC的性能研究調(diào)查表明，帶有被動控制系統(tǒng)的GLCC，只是使用流量能而沒有使用外部能量。 未來至關(guān)重要的工作是發(fā)展穩(wěn)定，有效的液位控制技術(shù)。由于較小的緊湊型的分離器的滯留時(shí)間和控制閥嚴(yán)格的響應(yīng)時(shí)間的要求，這不是一個(gè)簡單的容器式分離器控制技術(shù)的擴(kuò)展問題。這些技術(shù)應(yīng)該使GLCC能夠處理段塞流、喘流、及廣泛的流速，從基本上符合充滿氣體液體流量條件下的工作要求。 集成分離系統(tǒng)。迫使行業(yè)擺脫傳統(tǒng)的重力分離器轉(zhuǎn)移到小巧的分離系統(tǒng)上存在巨大的經(jīng)濟(jì)誘因。GLCC根據(jù)不同的應(yīng)用，可用于完全或部分分離。部分的氣體分離允許下游設(shè)備的更?。ㄒ虼烁阋耍┖透行?。當(dāng)在結(jié)合多相流量計(jì)，分離系統(tǒng)和液/液水力旋流器時(shí)，GLCC非常有效。無論是單獨(dú)使用或與其它設(shè)備相結(jié)合的配置，GLCC可以顯著的降低成本和重量。這在設(shè)計(jì)或改造海上平臺上是特別重要的，平臺的建設(shè)成本的節(jié)省可能比分離設(shè)備的成本高許多倍。 另一種GLCC的組合是兩個(gè)GLCC的串聯(lián)使用。 一個(gè)商業(yè)測量系統(tǒng)已經(jīng)開發(fā)出來，使用第二級臥式分離器可以去除任何可能從GLCC下面溢出的小氣泡。這使得擴(kuò)展系統(tǒng)的操作范圍超出了“正常”運(yùn)行的GLCC的完整的氣/液分離范圍。 其他硬件的改善。已經(jīng)在考慮的其他幾個(gè)潛在的改善，但是，我們在這里還沒有討論他們是因?yàn)楹苌倩蚋緵]有性能信息可用。這些包括一個(gè)可變的入口槽區(qū)配置和氣體液體出口的配置。 模擬 過去，在經(jīng)驗(yàn)法則和經(jīng)驗(yàn)關(guān)系式的基礎(chǔ)上，進(jìn)行了GLCC分離器的性能預(yù)測的試驗(yàn)。這些方法僅限于GLCC的能力外推到不同的流體條件和未經(jīng)考驗(yàn)的應(yīng)用方面。目前，正在努力發(fā)展GLCC的機(jī)械模型和進(jìn)行計(jì)算流體動力學(xué)（CFD）模擬。 機(jī)械模型提供了一個(gè)實(shí)用的進(jìn)行GLCC的設(shè)計(jì)和性能預(yù)測的途徑。簡化了假設(shè)，但是，在理想情況下，該模型仍然能夠采集足夠的基本物理問題，進(jìn)而內(nèi)插和外推到不同的流體流動情況。CFD可以預(yù)測GLCC中的復(fù)雜的流體動力流動特性的細(xì)節(jié)，包括流場、含率分布、分散相的離散顆粒的軌跡。同時(shí)適用于單相局部模擬或稀的分散流的模擬，目前CFD還不能模擬復(fù)雜的全方位的多相流。此外，CFD模型的大型管道系統(tǒng)，包括通常GLCC過于笨拙的無法實(shí)用的設(shè)計(jì)目的。 由于機(jī)械模型的大大簡化，沒有CFD模擬的詳細(xì)、嚴(yán)謹(jǐn)、準(zhǔn)確。然而，機(jī)械模型具有很多優(yōu)點(diǎn)：快速的設(shè)置和計(jì)算，整個(gè)系統(tǒng)建模的能力，并且適合PC操作。因此，機(jī)械模型比CFD模擬更容易成為工程師的設(shè)計(jì)工具。 機(jī)械建模。到今天為止建模工作的最終目的，是預(yù)測GLCC的操作區(qū)域液體遺留在氣體流和氣體攜帶在液體流。每個(gè)流體流動路徑有其自己特定的一組計(jì)算。任一計(jì)算路徑的起點(diǎn)是GLCC中氣體和液體的球分布，即平衡液面。 均衡液位。GLCC的平衡中液面是由氣體和液體出口之間的壓力降決定的。由于GLCC中摩擦損失低，平衡液位是GLCC中的液體的量的合理指示。 旋渦的形狀和位置。旋渦的形狀和位置是液體遺留和氣體攜帶很重要的預(yù)測。旋渦模型假設(shè)為剛體的轉(zhuǎn)動。平衡液面和渦形耦合的計(jì)算，使得測定的旋渦的位置和旋渦冠的高度成為可能。這種模式的球狀分布，為氣體和液體的性能模型的建立提供了基礎(chǔ)。 液體遺留。在氣流中的液體殘留物在很大程度上依賴于GLCC上部的流動模式。溢流可能發(fā)生在GLCC高液位和低氣率的地方，會導(dǎo)致產(chǎn)生泡狀流。不穩(wěn)定的液體振蕩，在適度氣率下渦流的特征，可能使飛濺的液體進(jìn)入出氣口。在高氣率的情況下發(fā)生環(huán)形霧流時(shí)，液體也可能以液滴的形式被帶出。在非常高的氣體速率下，旋流氣體的離心力將液體推到管壁上，在那里可以形成一個(gè)的螺旋形上升的連續(xù)的帶狀流。 DISTINGUISHED AUTHOR SERIES 58 JULY 1998 ? STATE OF THE ART OF GAS/LIQUID CYLINDRICAL-CYCLONE COMPACT-SEPARATOR TECHNOLOGY Ovadia Shoham, SPE, U. of Tulsa, and Gene E. Kouba, SPE, Chevron Petroleum Technology Co. SUMMARY The petroleum industry has relied mainly on conventional, vessel- type separators to process wellhead production of oil/water/gas flow. However, economic and operational pressures continue to force the industry to seek less expensive and more efficient separa- tion alternatives in the form of compact separators, especially for offshore applications. Compared with vessel-type separators, com- pact separators, such as the gas/liquid cylindrical cyclone (GLCC), are simple, low-cost, low-weight separators that require little main- tenance and are easy to install and operate. However, the inability to predict GLCC performance adequately has inhibited its wide- spread deployment. Current R however, we have not dis- cussed them here because little or no performance information is available. These include a variable inlet-slot area and the config- urations of the gas and liquid outlets. SIMULATION In the past, performance predictions of GLCC separators have been carried out on the basis of experience, rules of thumb, and empirical correlations. These methods are limited in their ability to be extrapolated to different flow conditions and untried appli- cations. Currently, efforts are under way to develop mechanistic models for the GLCC and conduct computational fluid dynamic (CFD) simulations. Mechanistic modeling offers a practical approach to GLCC design and performance prediction. Simplifying assumptions are used, but, ideally, the models still capture enough of the fundamental physics of the problem to allow interpolation and extrapolation to different fluid-flow conditions. CFD simulations predict details of the com- plex hydrodynamic-flow behavior in the GLCC, including flow field, holdup distribution, and trajectories of discrete particles of the dis- persed phase. While well-suited for local simulation of single-phase or dilute dispersion flows, current CFD simulators cannot yet handle the complexities of the full range of multiphase flow. Furthermore, CFD models of large piping systems that include the GLCC typical- ly are too unwieldy to be practical for design purposes. Because mechanistic models are greatly simplified, they are not as detailed, rigorous, or accurate as CFD models. However, mech- anistic modeling has many advantages: speed of setup and compu- tation, ability to model an entire system, and suitability for PC operation. Consequently, these models are more accessible to engi- neers as a design tool than are CFD models. Mechanistic Modeling. The ultimate aim of modeling work to date has been to predict the operating envelope for the GLCC with respect to liquid carry-over in the gas stream and gas carry-under in the liquid stream. Each fluid-flow path has its own particular set of calculations. The starting point for either calculation path is the global distribution of gas and liquid in the GLCC, namely, the equilibrium liquid level. Equilibrium Liquid Level. The equilibrium liquid level in the GLCC is determined by the pressure drop between the gas and liq- uid outlets. Because the frictional losses in the GLCC are low, the equilibrium liquid level is a reasonable indication of the amount of liquid in the GLCC. The model is based on a pressure balance on the gas and liquid legs. Ref. 2 gives details of this model. Vortex Shape and Location. The shape and location of the vortex are important for prediction of both liquid carry-over and gas carry- under. The vortex model assumes rigid-body rotation (i.e., a linear tangential-velocity profile in the radial direction). 2 Coupling the cal- culations for equilibrium liquid level and vortex shape makes deter- mination of the location of the vortex and the height of the vortex crown possible. This model of the global distribution of gas and liq- uid provides the groundwork for the performance models. Liquid Carry-Over. Liquid carry-over in the gas stream is largely dependent on the flow pattern in the upper part of the GLCC. Flooding may occur in the GLCC at high liquid levels and low gas rates, produc- ing bubbly flow. The unstable liquid oscillations, characteristic of churn flow at moderate gas rates, may splash liquid into the gas outlet. Liquid can also be carried out in droplets at the onset of annular mist flow at high gas rates. At very high gas rates, the centrifugal force of the swirling gas pushes the liquid to the wall of the pipe, where it may form an upward-spiraling continuous ribbon of liquid. At present, the onset of liquid carry-over is predicted for low to moderately high gas rates. The key to onset of liquid carry-over has been to predict accurately the maximum liquid holdup (volume frac- tion) occurring in the upper part of the GLCC under zero-net-liquid- flow conditions and its effect on the pressure balance between the gas and liquid legs. Fig. 2 compares model predictions with experimen- tal results in plots of the maximum liquid holdup in the upper GLCC region (i.e., zero-net-liquid-flow holdup, y L0 , vs. the superficial gas velocity, v gs , in the GLCC). 2 Additional data collected for a range of liquid viscosities from 1 to 10 cp showed negligible effect on the zero-net-liquid-flow holdup. 6 Once the maximum liquid holdup Fig. 2—Zero-net-liquid-flow holdup in air/water system. 2 Fig. 3—Operational envelope for liquid carry-over in a 3-in. GLCC operated with air and water. 2 v gs , ft/sec y L0 v gs , ft/sec v Ls , ft/sec ? JULY 1998 61 allowed in the upper part of the GLCC is known for a given gas rate, the pressure-balance calculation is used to determine the liquid rate required to achieve this holdup and initiate liquid carry-over. Fig. 3 compares the experimental and predicted operational envelopes for a 3-in. laboratory GLCC in a loop configuration, operated with air and water at low pressures. 2 The operational envelopes are presented in terms of superficial liquid velocity, v Ls , vs. superficial gas velocity, v gs , in the GLCC. The agreement of model predictions with the data is very good. Comparison with data from Ref. 6 showed that the model seems to capture the phys- ical phenomena and predict well the reduction of the operational envelope with increasing liquid viscosity. Future improvements to liquid-carry-over modeling will include expansion to different operational conditions (e.g., high gas rates) as well as prediction of the quantity of liquid carry-over and dynamic responses to flow-rate surges. Gas Carry-Under. Three mechanisms have been identified as possi- ble contributors to gas carry-under in the liquid stream: (1) shallow bubble trajectories prevent small bubbles from escaping to the gas-core filament, (2) rotational-flow instability causes helical whipping and breaking of the gas-core filament near the liquid exit, and (3) liquid- rate surges can produce a concentrated cloud of bubbles that hinders bubble migration to the gas core. Currently, attempts to predict gas carry-under have focused only on the first mechanism, discussed next. Bubble-Trajectory Analysis. This analysis is carried out by assuming successive steady-state force-balance calculations on a bubble. The forces acting on the bubbles are centrifugal, buoyancy, and drag. Recent work compared bubble trajectories predicted by the mechanistic model and CFD simulations for the same flow con- ditions. 9 Fig. 4, where x/d and r/R are the dimensionless axial and radial coordinates below the GLCC inlet, respectively, provides an example of such a comparison. The figure shows good agreement with respect to the trend and absolute value. Bubble-trajectory analysis 10 was used to predict the onset of gas carry-under and separation efficiency for different sized bubbles in a manner similar to the liquid/liquid analysis carried out for hydro- cyclones. 11 The minimum diameter of the bubble that always migrates from the GLCC wall to the gas core and thus is separated (i.e., d 100 ) was predicted. Fig. 5 shows the effect of the ratio of the tangential velocity at the inlet slot to the axial velocity in the GLCC (namely, v tis /v z ) on d 100 . The continuous line represents the regres- sion curve of the simulation results. For these conditions, d 100 decreases with increasing v tis /v z ratio up to about 100 and remains approximately constant for larger values of this ratio. The region from the bottom of the vortex to the liquid exit is where small bubbles are separated and captured by the gas-core fil- ament. Because vortex height is a strong function of tangential-inlet velocity and bubble-trajectory length diminishes with vortex height, an optimum tangential-inlet velocity must exist that mini- mizes gas carry-under. A tangential-inlet velocity that is too low produces insufficient centrifugal and buoyancy forces, whereas the available length for bubble trajectory is too short with a tangential- inlet velocity that is too high. As yet, a general scheme to determine optimum velocity has not been presented. Work is now in progress to develop the methodology to predict overall separation efficiency in a GLCC. This requires two addition- Fig. 4—Bubble-trajectory comparison of mechanistic model and CFX simulations with v Ls = 0.25 ft/sec, v gs = 10 ft/sec, v tis /v z = 34, d= 3 in., and d b = 20 μm. 9 Fig. 5—Effect of tangential-/axial-velocity ratio on d 100 for a 3-in. GLCC operated with air and water at atmospheric conditions. 10 v Ls = 0.05 ft/sec v Ls = 0.1 ft/sec v Ls = 0.5 ft/sec 100 80 60 40 20 0 d 100 , μ m v tis /v z 62 JULY 1998 ? al pieces of information: the amount of gas entrained and the bub- ble-size distribution. Coupling these to the bubble-capture efficien- cy ultimately will enable prediction of overall separation efficiency. CFD Simulation. Verifying mechanistic models with real data is not always practical or possible. CFD simulations are used to validate and improve the mechanistic models. CFD simulations for the GLCC can be lumped into two broad categories: single- phase flow with particle tracking and two-phase flow. Single-Phase Flow and Particle Tracking. The simplest and most widely used approximation for CFD simulation of two-phase flow is to consider single-phase flow populated with particles (bub- bles) that neither interact with each other nor influence the flow. This, in effect, is simply solving for a single-phase-flow field and superimposing particle-trajectory tracking. CFD and bubble-trajectory analysis were used to investigate the sensitivity of gas separation to bubble-size distribution. 12,13 Two- and three-dimensional (2D and 3D) simulations 14 were carried out with CFX, a commercially available CFD code. 15 The authors con- cluded that the axisymmetric simulations (2D) gave good results compared with the 3D simulations. Fig. 6 compares single-phase CFD simulations with experimental data. 16 Both the data and CFD simulations demonstrated that the tangential-velocity distribution is dominated by a forced vortex, confirming this assumption in the mechanistic models. Furthermore, the CFD simulations also veri- fied the mechanistic model with respect to axial decay of tangen- tial-velocity distribution (5 to 7% L/d decay). The simulations in Ref. 14 also predicted the existence of an axial-flow-reversal region where the flow is downward near the wall and upward in the center core. The bubble-capture radius, R cap , is defined as the radial location where the axial-velocity component is zero as the flow reverses from downward to upward. Bubbles that migrate into the capture-radius area are separated and pushed upward into the upper part of the GLCC. Fig. 7 shows the capture radius as a function of the tangential-/axial-velocity ratio, v tis /v z , and axial location below the inlet. The results indicate a rapid decline of the capture radius as the velocity ratio decreases below 10. The cap- ture radius and the reversal in the axial-velocity profile recently have been incorporated into the mechanistic model. 9 Two-Phase Flow. Actual two-phase-flow CFD simulation is still in its infancy. Such simulations should predict the influence of the dis- persed phase on the flow of the continuous phase and the interface between the two phases. Recent two-phase-flow CFD simulation work has proceeded on two fronts: with CFX 14,17 and through development of a dedicated internal code. 17 The two-phase simula- tions provided details of the velocity field and gas-void-fraction dis- tribution. The simulations also provided the free interface between the gas and liquid phases (vortex), which compared favorably with experimental data. Fig. 8, which shows the gas-void-fraction distri- bution in the GLCC, gives an example of the results obtained. The figure reveals that the gas-void-fraction values at the top and bottom of the GLCC are nearly unity and nearly zero, respectively, indicat- ing efficient separation. For the first time, results have predicted the gas-core-filament diameter accurately and provided insight into the mechanism for its formation (continuous entrainment and radial migration of small gas bubbles into the gas core).* Fig. 6—Axisymmetric-tangential-velocity prediction vs. data for a 7.5-in. GLCC operated with air and water at atmospheric con- ditions. 14 Fig. 7—Variation of capture radius with tangential-/axial-veloci- ty ratio. 14 v tis /v z R cap /R 6 in. 12 in. Fig. 8—Void-fraction distribution for a 7.5-in. GLCC operated with air and water at atmospheric conditions. 14 α=0.98 α=0.00 V t , ft/sec *Unpublished results, F.M. Erdal, U. of Tulsa, Tulsa, Oklahoma (1998). ? JULY 1998 63 APPLICATIONS A variety of GLCC applications have requirements that may vary from partial to complete gas/liquid separation. Recent technologi- cal development has helped increase deployment of GLCC separa- tor systems in the industry. Successful Applications. The GLCC modeling effort to date has resulted in successful deployment of the GLCC in a variety of selected applications, as discussed next. Multiphase Measurement Loop. Most of GLCC’s deployed to date (approaching 100) have been configured in a multiphase metering loop. Fig. 9 is a schematic of the GLCC in a multiphase metering loop, first introduced by Liu and Kouba, 18 and Fig. 10 shows a GLCC field prototype operated by Chevron in Oklahoma. This type of measurement-loop configuration affords several advantages over either conventional separation with single-phase measurement or nonseparating multiphase meters. The loop con- figuration is somewhat self-regulating, which can reduce or even eliminate the need for active level control. The compactness of the GLCC allows the measurement loop to weigh less, occupy less space, and maintain less hydrocarbon inventory than a conven- tional test separator. The advantages of a GLCC metering loop over a nonseparating three-phase meter include much improved meter- ing accuracy of individual phases over a wider range of flow rates and significantly lower cost. For flow conditions where gas carry-under cannot be prevented, a three-phase metering system is required on the liquid leg. In gen- eral, the accuracy of a multiphase meter on the liquid leg benefits significantly from removal of some of the gas. Most multiphase meters have an upper limit on the gas volume fraction allowed through the meter to maintain their accuracy specifications. Apart from improved accuracy, partial gas separation provides the addi- tional benefit of a smaller, less expensive multiphase meter. For multiphase meters (whose price scales directly with size), the cost savings of using a smaller meter in conjunction with a GLCC can be four times the cost of the GLCC. Partial Processing (Separation). A compact GLCC is often very appropriate for applications where only partial separation of gas from liquid is required. One such application is the partial separa- tion of raw gas from high-pressure wells to use for gas lift of low- pressure wells. The GLCC was a central feature in an offshore raw- gas-lift system designed by Chevron that allowed elimination of gas compressor and lift-gas pipelines. 19 Compact Separation Systems. Compact separation systems are a key element in reducing cost of production operations through reduction of size and weight. Furthermore, separating a significant Fig. 10—Chevron-operated GLCC field prototype. Fig. 9—GLCC in a multiphase metering loop configuration. 64 JULY 1998 ? portion of the gas reduces fluctuations in the liquid flow and may result in improved performance of other downstream separation devices, such as a wellhead desanding hydrocyclone. Chevron is investigating the series combination of a GLCC with a free-water- knockout hydrocyclone and a deoiling hydrocyclone in an effort to improve discharge-water quality. The GLCC was used to control gas/liquid ratio of a two-phase- flow mixture entering a multiphase pump to improve pumping effi- ciency. 20 Another study showed several combinations of GLCC and jet pumps that could be used to extract energy from high-pressure multiphase wells to enhance production from low-pressure wells. 21 Enhancement of Existing Separators. Cyclone separation already has proved useful in internal separation devices for large horizontal separators. The GLCC may also function as a useful external preseparation device to enhance performance of existing horizontal separators (Fig. 11). By separating part of the gas, the separator level might be raised to increase residence time without encountering the mist-flow regime in the vessel. Petrobrás Brazil has retrofitted an existing separator in one of its fields with a GLCC preseparator. 1 Another company is evaluating enhancement of their existing test separators with GLCC preseparation. Commercial GLCC Products. Most GLCC’s to date have been field fabricated for relatively straightforward applications. Applications of and demand for GLCC’s are growing rapidly. Several vendor compa- nies are in the process of incorporating the GLCC into their com- pact-separator product line. Also, as mentioned before, a commercial multiphase metering system that uses a GLCC and a second-stage horizontal separator is now available. Greater commercialization will be needed to meet the growing industry demand. Future Applications. Current successful GLCC applications lend confidence to future potential GLCC configurations. This requires enhancement of the existing models and is currently under way. The following are two of the most compelling applications. Subsea Production. The biggest impact to the petroleum industry from GLCC technology may be in subsea separation applications. Conclusions in Ref. 22 state that “wellhead separation and pumping is the most thermodynamically efficient method for wellstream transfer over long distances, particularly from deep water.” In a recent study, Prado et al. 23 argued that this is applicable to shallow and moderately deep waters. Undoubtedly, development of marginal offshore fields will depend on development of efficient and economical technologies. Subsea applications require a high degree of confidence in separator design and performance while demanding that the equipment be sim- ple, compact, robust, and economical. Here again, the virtues of the GLCC should place it in good standing among competing technologies. Production Separation. Vertical separators with tangential inlets are fairly common in the oil field. These predecessors of the GLCC are often big and bulky, with perpendicular low-velocity tangential pipe inlets. The tangential velocities are usually so low that gravi- tational, centrifugal, and buoyancy forces contribute approximate- ly equally to separation. Technological developments in both GLCC hardware and software should reduce the size and improve the performance of vertical separators. One challenge in optimiz