Efficiency of Centrifugal Vortex Separators

 
If the liquid load is greater than 20% or if occasional “slugs” of liquid need to be removed it requires a slightly more complex design.
 
The “T” style operates on the same principles with the vessel body oriented 90° to the horizontal pipeline to which it is installed.  This design utilizes an angled deflector plate to create the centrifugal vortex and due to the location of the outlet nozzle pipe, gravity assists with the removal rate.  The lower portion of the vessel is also a built-in sump with a vortex containment plate preventing re-entrainment of the separated liquid.  Only droplets finer than 10 microns can be drawn out through the low velocity area of the vortex where the outlet nozzle pipe is located.
 
The Type “T” gas/liquid separator has a separation capacity equivalent to 40% of its maximum mass flow capacity.

If we elongate the body of a Type “T” by approximately 25% it becomes what we refer to as a Type “TS” and is now capable of a liquid separation rate equivalent to 60% of its maximum mass flow capacity.
 
Applications having a very high liquid load, or more commonly an upset condition resulting in a large “slug” of liquid may require the “Receiver” style centrifugal separator, simply referred to as a Type “R”.
 
The internal complexity of the Type R is slightly more than the Type T due to the addition of a secondary vortex.  Instead of the gas exiting through the low velocity (center) of the initial centrifugal vortex, the gas travels to the topside of the vessel and must pass through angled vanes; the outlet nozzle pipe is located in the low velocity (center) of this secondary vortex. The Type “R” centrifugal separator has a liquid separation capacity equivalent to 90% of its maximum mass flow capacity.

All of the aforementioned centrifugal separators maintain 99% efficiency for removal of droplets and particulate greater than 10 microns without any moving or serviceable components.  They are considered self-cleaning due to the constant centrifugal vortex forces and require zero maintenance.
 
To accommodate applications requiring separation of droplets >5 microns an additional coalescing stage is added prior to the centrifugal vortex stage.
 
We can separate even finer droplets, as fine as 0.3 microns with 99% efficiency, by installing a “polishing stage” after the centrifugal vortex. Specially designed borosilicate microglass filter cartridges are used to channel these fine droplets to a coalescing drain point.
 
The addition of a coalescing or polishing stage increases the vessel complexity periodically the internal elements require cleaning or replacement.
 
How to you select the “best” centrifugal separator design for your application?
We have created the only known publically available, Internet based centrifugal separator sizing tool and it is designed to help you compare your options.
 
After inputting just (4) design criteria the “separator size” is calculated; we show two different values, one for the Type “R” (receiver style) and the highlighted size applicable to all of the other “standard” separator designs.
 
To simplify the selection process, “size” is referring to the maximum inlet connection ID as relates to the vessel diameter and length.  This is a nuanced delineation that I will explain further with our example.

Our example application therefore would require a 2.5” centrifugal separator or a 3” receiver style separator as both 2.5” and 3” are standard pipeline sizes.
 
Inputting “3” for the size calculates the maximum capacity (volumetric and mass flow), the differential pressure and chart of maximum liquid removal rates.
 
Additional factors that affect sizing include the liquid load to be removed and differential pressure.
 
If the calculated differential pressure is too high for your application, increase the size of the separator until it meets your requirement.
 
Likewise use the liquid removal capacity chart to determine which separator design is required; this is where things can get interesting.
 
If keeping the vessel size to a minimum is critical, moving up the chart to the 90% (receiver style) might make sense, however if you have “extra space” it might be less expensive to use a larger size “L” or “T” style because they are not as complex to manufacture.
 
Size Matters!
You cannot “oversize” a separator; the 99% efficiency will be retained, however you can certainly “undersize” a separator.  Technically what happens when a centrifugal separator is undersized is that the velocity around the outlet nozzle pipe is high enough to prevent the droplets from impinging to the vessel walls where coalescing and gravity take-over.  So we can easily “oversize” a centrifugal separator and attach to it smaller inlet and outlet connections to match your piping to handle your liquid load or differential pressure requirements.  Remember the “minimum size” of 2.29” in our example is also related to the minimal internal diameter and length of the vessel, so anything larger increases the separation efficiency.
 
It is not recommended to install a separator having an inlet size smaller than the pipeline it will be attached to, even if the design criteria indicates a smaller size would be sufficient.  The thought behind this is that there is likely an engineering reason for the existing pipeline size and it’s usually not a good idea to unnecessarily restrict it.
 
The sizing tool is available to assist you with a better understanding of your options. We typically prompt you for the applicable design criteria and an overview of your application to provide a proposal, however you can use this tool to approximate the physical dimensions of the required separator and to have a better feel for the performance vs. pressure drop as compared to vane and mesh pad style separators which typically are physically larger (expensive) and have higher pressure drops (not to mention require periodic maintenance and lose efficiency at low flow rate conditions).