Gas/liquid separators (‘Scrubbers’)
ASCOM designed scrubbers guarantee very high performance because of application of state-of-the-art design rules based on empirically verified CFD design models and use of the proprietary range of high peformance ASCOM HiPer internals.
Design philosophy: the 4 sections of a scrubber
Generally, in the mostly vertically orientated gas/liquid separators (‘scrubbers’), the incoming multiphase mixture flows into the vessel through an ‘inlet device’. The inlet section (1) ensures: a) preliminary gas/liquid(s) separation and b) a good flow distribution across the vessel.
The design of scrubbers generally include subsequently a gas/liquid gravity separation section (2), that ensures the creation and fall out of large liquid droplets.
The gravity separation section can include a coalescer stage (either a mesh type or vane type coalescer). After the fall out of the bulk liquids the demisting section (3) ensures the separation of finer mist particles.
The clean gas exits the vessel after this final stage. Separated liquids are degassed in the degassing section (4). Generally it consists of a liquid hold up that provides sufficient residence time for gas bubbles to escape from the liquids.
1) Inlet section
In vertically orientated gas/liquid separators (‘scrubbers’), the incoming multiphase mixture flows into the vessel through an inlet device, or inlet cyclone (1). In the processing industry a wide range of inlet devices are being used ranging from inlet baffles, half open pipes to more elaborate vane type inlet devices and cyclonic inlet devices. Irrespective of the service, only vane type inlet devices and properly designed cyclonic inlet devices will handle the fluids at the inlet nozzle adequately and will maximise the separation performance. All other inlet devices will result in a very poor gas distribution AND in an increase of the liquid content entrained in the gas due to the high shear forces exerted by these devices.
2) Gravity separation section
As can be seen, the HiPer Vane Diffuser is essential to evenly distribute the gas and therewith allowing the liquid entering the vessel in bulk to separate at the inlet nozzle. The liquid in mist form will travel further with the gas. From the vane diffuser to the mist eliminating equipment, the gas travels through the gravity separation section (2), which allows smaller droplets to coalesce into larger ones and drop out due to the gravity. In situations where the liquid load to the vessel is simply too high, under demanding process conditions, in retrofit situations where the size of the existing vessel/equipment is limited or in high pressure applications where the mean droplet size is small, the downstream mist eliminating equipment potentially may be overloaded with liquid and the downstream equipment, may be experiencing an excess of liquid carryover from this vessel.
In clean services, i.e. no presence of wax or fouling tendencies, the HiPer Mesh Coalescer can be used to increase the liquid handling capacity of the gravity separation section. The wire mesh structure is designed to coalesce small liquid droplets into larger ones. The specific arrangement of the HiPer Mesh Coalescer ensures very good drainage of the liquid accumulated within the mesh. It is particularly highlighted that this device has excellent turndown properties as the mode of operation changes from a flooded mode to a demisting mode once the gas velocity is reduced to below the transition point. In situations where the fluids do have a fouling tendency, alternatively a HiPer Vane Coalescer or HiPer Cyclone Coalescer can be considered.
3) Demisting section
The third section is the mist eliminating section (3) which ensures the separation of finer mist particles. Essentially, the overall gas-liquid separation efficiency of a scrubber depends on the fraction of liquid entrained as mist in the gas, the droplet size distribution, the volumetric amount of the liquid in mist form and the efficiency of the mist eliminating equipment under those conditions.
Summary
The advantages of the ASCOM HiPer internals are:
• Maximise droplet coalescence
• Maximise overall liquid separation efficiency from gas
• Excellent turndown characteristics
• Low pressure drop
• Clean & fouling service possible
• No maintenance due to robust design
• Removable through Man Way
• No welding required for installation
• Easily replaces existing older internals
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