The hydrodynamics of multiphase flow in a Liquid-Liquid Cylindrical Cyclone (LLCC) compact separator have been studied experimentally and theoretically for evaluation of its performance as a free water knockout device. In the LLCC, no complete oil-water separation occurs. Rather, it performs as a free water knockout, delivering a clean water stream in the underflow and an oil rich stream in the overflow. A total of 260 runs have been conducted for the LLCC for water-dominated flow conditions. Four different flow patterns in the inlet have been identified, namely, Stratified flow, Oil-in-Water Dispersion and Water Layer flow, Double Oil-in-Water Dispersion flow, and Oil-in-Water Dispersion flow. For all runs, an optimal split ratio (underflow to inlet flow rate ratio) exists, where the flow rate in the water stream is maximum with 100% water cut. The value of the optimal split ratio depends upon the existing inlet flow pattern, varying between 60% (for Stratified and Oil-in-Water Dispersion and Water Layer flow patterns) to 20% for the other inlet flow patterns. For split ratios higher than the optimal one, the water cut in the underflow stream decreases as the split ratio increases. A novel mechanistic model has been developed for the prediction of the complex flow behavior and the separation efficiency in the LLCC. The model consists of several sub-models, including inlet analysis, nozzle analysis, droplet size distribution model, and separation model based on droplet trajectories in swirling flow. Comparisons between the experimental data and the LLCC model predictions show excellent agreement. The model is capable of predicting both the trend of the experimental data as well as the absolute measured values. The developed model can be utilized for the design and performance analysis of the LLCC.

Summary Gas/Liquid Cylindrical Cyclone (GLCC, copyright, the U. of Tulsa, 1994) separator performance can be improved considerably by adopting a suitable control strategy to reduce liquid carry-over into the gas stream or gas carry-under into the liquid stream. A dynamic model for control of GLCC liquid level and pressure with classical control techniques is developed in this paper for the first time. Detailed analysis of the GLCC control-system stability and transient response indicates that liquid-level control can be achieved effectively by a control valve in the liquid outlet for gas-dominated systems or by a control valve in the gas outlet for liquid-dominated systems. Based on the proposed linear-control system model, the system performance is simulated with a suitable software design tool. Experimental investigations have been conducted to evaluate the liquid-level and pressure-control systems. The novel control-system design approach presented in this paper forms a framework for the GLCC active control-system optimization. Introduction The petroleum industry has traditionally relied on conventional vessel-type separators, which are bulky, heavy, and expensive in capital, installation, and operation. Compact separators, such as the GLCC, are now becoming increasingly popular because they are simple, compact, lightweight, inexpensive, low-maintenance, and easy to install and operate. The development ranking of the various separation-technology alternatives1 shows that conventional vessel-type separators have reached their maturity, except for some minor improvements that are being incorporated, such as new developments of internal devices and control systems. Potential applications of GLCC include performance enhancement of multiphase meters, multiphase flow pumps, and desanders through control of gas/liquid ratio, partial processing, portable well-testing equipment, flare gas scrubbers, slug catchers, downhole separators, preseparators, and primary separators.2,3 The GLCC separator has a simple construction with neither moving parts nor internal devices. It is a vertically installed pipe mounted with a downward-inclined tangential inlet, with outlets for gas and liquid provided at the top and bottom of the pipe. The two phases of the incoming mixture are separated owing to the centrifugal/ buoyancy forces produced by the swirling motion and the gravity forces acting on the phases. The liquid is forced radially toward the wall of the cylinder and is collected from the bottom, while the gas moves to the center of the cyclone and is taken out from the top. Applications to date have been for GLCC loop configurations in which the gas and liquid outlets are recombined, such as in a multiphase metering loop. This configuration is self-regulating for small flow variations. However, many field applications other than metering are characterized by separate gas and liquid outlets. GLCC's used in such configurations must have liquid-level and pressure control so as to prevent, or delay, the onset of liquid carry-over into the gas stream or gas carry-under into the liquid stream. Also, the GLCC loop operation could be improved for large flow variations through suitable liquid-level control. Different GLCC control-system strategies are briefly discussed by Wang4 and Mohan et al.5 This paper presents, for the first time, a dynamic model for control of GLCC liquid level and pressure using classical control strategies. The dynamic model is especially significant for GLCC's operating under slug flow conditions. The results of a detailed system-stability analysis performed with the dynamic model are also discussed. This analysis showed that system stability could be ensured by appropriately designing the controller and control valve. It is concluded that the liquid-level control could be achieved effectively by a control valve in the liquid outlet for gas-dominated systems or by a control valve in the gas outlet for liquid-dominated systems. A control valve in the gas outlet for any inflow condition could achieve GLCC pressure control. Based on the proposed linear control-system model, a sample control-system design is performed and the system-transient response is simulated with suitable software. A design framework for implementation of the GLCC control system using a dedicated simulator is finally presented. Literature Review Arpandi et al.6 and Marti et al.7 have conducted detailed reviews of the literature on separation technology, revealing that very little information is available about the optimum design and performance of the GLCC. Most of the investigations are based on experimental correlation. The existing mathematical models for cyclone separators have been limited to single-phase flow with low concentration of a dispersed phase. Also, no reliable models are available for cyclones8 (conical or cylindrical) that are capable of simulating a full range of multiphase flows entering and separating in a cyclone. Several investigators3,4,5,9 have realized that the performance of compact separators could be improved by incorporating suitable control systems. Kolpak9 developed a hydrostatic model for passive control of compact separators in a metering loop configuration. This model provides the sensitivity of the liquid level to the gas and liquid inflow rates. For gas/liquid two-phase flow separators that operate under slug flow conditions, the system dynamics are crucial, especially when a control system is added to the separator. Genceli et al.10 developed a dynamic model for a slug catcher. The system response of slug catchers was found to be quite slow because of the large residence time of the big vessel. Roy and Smith11 discussed the control algorithms in digital controllers to meet the goal of averaging level control for a single-phase surge tank system. These control algorithms are a primary concern in chemical processes, where smooth outlet flow from the tank is very important. Galichet et al.12 presented the development of a fuzzy-logic controller that maintains a floating level in a tank (single-phase flow) on top of an atmospheric distillation unit of a refinery. The authors of this paper4,5 have developed a steady-state model for GLCC control and performed a sensitivity analysis. Detailed experimental investigations on a newly developed GLCC passive control system demonstrated that the passive control system improved the GLCC operational envelope in a restricted range of flow conditions.

Gas-Liquid Cylindrical Cyclone (GLCC) separator performance can be considerably improved by adopting a suitable control strategy to reduce liquid carry-over into the gas stream or gas carry-under into the liquid stream. A dynamic model for control of GLCC liquid level and pressure using classical control techniques is developed in this paper for the first time. Detailed analysis of the GLCC control system stability and transient response indicates that liquid level control could be achieved effectively by a control valve in the liquid outlet for gas dominated systems or by a control valve in the gas outlet for liquid dominated systems. Based on the proposed linear control system model, the system performance is simulated using a suitable software design tool. The novel control system design approach presented in this paper forms a framework for the GLCC active control system optimization. P. 545

The deployment of the new technology of gas-liquid compact separators such as Gas Liquid Cylindrical Cyclone (GLCC©1) requires dedicated control systems for field applications. The control strategy implementation is crucial for process optimization and adaptation, especially when GLCCs are operated at wide range of liquid and gas flow conditions. In this study, a unique and simple control strategy, which is capable of optimizing the operating pressure and adapting to liquid and gas inflow conditions, has been developed. Detailed simulations and experimental investigations have also been conducted to evaluate the performance of the proposed control systems. The significant advantages of this strategy are: the system can be operated at optimum separator back pressure; the system can adapt to the changes of liquid and gas flow conditions; and the strategy can be easily implemented using simple PID controllers available in the market. This provides the oil and gas industry a simple, robust compact separator control technique which has the potential for offshore and subsea applications. Introduction Compared to conventional separators, compact separators, such as the Gas-Liquid Cylindrical Cyclone (GLCC) are simple, compact, possess low weight, low-cost, require little maintenance, and are easy to install and operate. GLCCs have been used to enhance the performance of multiphase meters, multiphase pumps, de-sanders, slug catchers, partial separators, portable well testing equipment, pre-separators and primary separators for offshore and onshore operations. They also have the potential for applications as flare gas scrubbers, down-hole separators and subsea processing. Presently, more than a hundred and fifty GLCC units have been installed and put into use in the field for various applications. The size of these GLCCs varies from 3-in. to 5-ft in diameter and 7-ft to 30-ft in height. Figure 1 shows the largest GLCC in the world, a 5-ft diameter, 20-ft tall GLCC field unit operating in Minas, Indonesia, in a bulk separation/metering loop configuration1. The GLCC separator is a vertically installed pipe/vessel mounted with a downward inclined tangential inlet, with outlets for gas and liquid provided at the top and bottom, respectively. It has neither moving parts nor internal devices. The two phases of the incoming mixture are separated due to the centrifugal/buoyancy forces caused by the swirling motion and the gravity forces. The heavier liquid is forced radially towards the walls of the cylinder and is collected from the bottom, while the lighter gas moves to the center of the cyclone and is taken out from the top. GLCC in a metering loop configuration, where the gas and liquid outlets are recombined, is capable of self-regulating the liquid level for small flow variations. However, for large flow variations, it is essential to have a control sytem for proper operation. Also, GLCCs for other applications such as bulk separation, must have suitable control systems so as to prevent the liquid overflow through the gas leg and gas blow out through liquid leg. There is an increasing need to develop appropriate control strategies, design tools and simulators for GLCC control, as its residence time is very small and its applications could be different. Also, the performance of compact separators could be enhanced considerably by incorporating suitable control systems. Development of control systems for GLCC technology can have a tremendous impact in improving the optimization and productivity of the petroleum industry.

The liquid carry-over phenomenon in Gas-Liquid Cylindrical Cyclone (GLCC(c)1) compact separators has been studied experimentally and theoretically. Experimental data have been acquired including the operational envelope for liquid carry-over and percent liquid carry-over beyond the operational envelope. The data show that at low gas and high liquid flow rates, under churn flow conditions in the upper part of the GLCC(c), large amount of liquid can be carried over relatively easily. On the other hand, at high gas and low liquid flow rates, under annular flow conditions, one should exceed the operational envelope significantly in order to have large amount of liquid carry-over. A mechanistic model has been developed for the prediction of the percent liquid carry-over beyond the operational envelope, for churn flow conditions. An existing model for the prediction of the operational envelope for liquid carry-over has been extended to high-pressure conditions, including improved models for zero-net liquid flow holdup, droplet region and blowout and critical velocities. Comparisons between the new mechanistic model predictions for percent liquid carry-over with the experimental data, under churn flow conditions, show a good agreement. Also, in the lack of experimental data, the predictions of the operational envelope for liquid carry-over at high-pressure conditions show reasonable trends. 1 GLCC(c) - Gas-Liquid Cylindrical Cyclone - copyright, The University of Tulsa, 1994