The Twister SwirlValve™ improves the HC dew pointing performance of existing JT-LTS plants by:
Control valves are used in the oil & gas industry to control pressure, temperature and flow. In many cases these control valves operate at choked conditions, once sufficient pressure drop is created over the control valve. The pressure reduction over a valve causes the temperature to drop without extracting heat or work from the gas. This isenthalpic expansion process is also known as Joule-Thomson (JT) cooling. This JT cooling effect over a valve is used to condense part of the natural gas stream, such that the liquefied fraction can be separated in a vessel, the LTS or Low Temperature Separator.
The prime function of a JT valve then is flow rate control, but is also used to create a separable liquid phase. The mean droplet size resulting from isenthalpic expansion over a JT valve is difficult to determine, hence the separation efficiency of downstream separators is generally also unknown.
Twister SwirlValve enlarges the mean diameter of the dispersed phase
Since most separators – such as gravity separators, cyclone separators and filter separators – can be characterized by a typical separable diameter (i.e. cut-off diameter), the improvement of the SwirlValve in conjunction with a separator is illustrated below.
Twister SwirlValve working principle
Tangential slots in a cage valve trim forces the choking flow into a strong rotation causing small droplets to concentrate and agglomerate along the perimeter of the pipe wall.
Gas is expanded isenthalpically across the valve, and a swirling flow is imposed by an engineered geometry of the valve trim and/or valve stem. The kinetic energy is then mainly dissipated through dampening of the vortex along an extended pipe length downstream of the valve.
The advantage of creating a swirling flow in the valve is twofold:
The flow is normally throttled over a perforated cylinder (cage). These perforations – slots or holes – normally have a radial orientation i.e. rectangular to the cylinder surface. The Swirl modified cage forces the flow into a swirling motion.
It can be expected that the flow pattern in a cage valve with radial openings has a highly disordered shear force, whereas the cage with the tangential openings forces the droplets to move to the outer circumference of the flow area, where they easily agglomerate into larger droplets.