Liquid Liquid Cylindrical Cyclone (LLCC)

The production of water with oil continues to be a problem for the oil industry. Oil and gas companies are constantly searching for more effective ways to handle produced water and to increase oil production. Innovations over the years have led from the skim pit to installation of the stock tank, to the gun barrel, to the free water knockout device and most recently to compact separators. Most of the studies on compact liquid-liquid separation have been focused on conical liquid–liquid hydrocyclones (LLHC). The main application of the hydrocyclone is to clean produced oily water for disposal, reducing oil concentrations to the order of 20 or less ppm in the effluent. This equipment is suitable only for water with very low oil content. During the development of the conical hydrocyclone, attempts were made to utilize cylindrical geometries.


Schematic of LLCC Compact Separator

A schematic of the LLCC separator is shown in the figure above. The LLCC is a vertically installed pipe mounted with a horizontal inlet pipe. The oil-water mixture is introduced through a tangential slot at the inlet. It has two exits, the upper outlet that is oil rich stream, and the lower outlet, that is clear water stream. It has neither moving parts nor internal devices. Separation occurs due to the centrifugal forces caused by the swirling motion and the gravity forces. The heavier water is forced radially towards the cyclone wall and is collected from the bottom, while the lighter oil moves towards the center of the cyclone and is taken out from the top. Thus, it provides an efficient alternative for oil-water separation in the form of a free water knockout device.


LLCC compact separator performs the same function as its conventional counterpart, but it does so in a smaller shell. So, LLCC technology can have a tremendous impact in improving the optimization and productivity of the petroleum industry. By increasing the speed of separation, the need for long retention time within the vessel is eliminated. Considering field applications, LLCC has two possible configurations. It can be used either in a metering loop configuration or in a separation configuration. In a metering loop configuration, the oil and water streams are measured separately and recombined at the outlet. In a separation configuration, LLCC acts as a free water knockout device and the oil and water outlets are separated as explained in the earlier discussion. However, the operation of LLCC can be limited by two phenomena, namely, oil carry-under in the underflow (clear water) stream and water carry-over in the overflow (oil rich) stream. Water carry-over can be minimized by making appropriate design changes to the LLCC. Oil carry-under can be eliminated by implementing suitable control strategy in the underflow.


The performance of LLCC strongly depends upon the split of oil rich and clear water streams. Thus, the control system becomes an essential part in a separation configuration in order to maintain maximum underflow and at the same time obtaining clear water in the underflow.







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