Hi, I am working on an air compr

[Process_Nerd]

Hi,

I am working on an air compressor inter-stage cooler. The cooler is S&T type with TEMA type BEW . Air on the shell side is cooled with cooling water on the tube side.Air contain water content which upon cooling from 160 deg.C to 45 deg C. condenses. Air enters the shell side from the top of rear head and leaves the shell from the top side of front head. A liquid outlet is provided at the bottom of shell. I have attached a sketch in an effort to give some clarity to my query. Now, the challenge is to separate the water content from air before it leaves the cooler and is further compressed in the compressor.

I would request the experts to please advise how the water content can be removed. It should be noted that the air moves with a velocity of 12 m/sec and I'm afraid the air will sweep out the moisture(water). Certainly, one way could be installing a filter downstream of this cooler, before it enters the 2nd stage compressor. but I am looking for any solution within the cooler. Can installing a longitudinal perforated plate below the bundle and 2) Providing space(compartment) for liquid separation at the shell bottom below the bundle help? I would appreciate if anyone could advise any practical solutions.

Process Parameters:

Shell Side Fluid: Air
Shell side mass flow: 54095 kg/hr
Moisture (water) content in air: 662 kg/hr. (0.012 mass fraction of total air flow)
Shell side inlet pressure/temp. : 3.7 kg/cm2.g/ 160 deg.C
Shell side outlet pressure/temp. : 3.0 kg/cm2.g/ 45 deg.C
Tube side fluid: Cooling Water
Tube side inlet pressure/temp. : 3.5 kg/cm2.g/ 33 deg.C
Tube side outlet pressure/temp. : 3.0 kg/cm2.g/ 42 deg.C

Regards,
Bilal

 

[LittleInch]

Is that 12m/sec inside the shell? I'm amazed that you can get such a large temp drop with what would seem to be 1 second contact time, but even if true that velocity is simply too big to allow the cooler to act like a separator. You probably need to lower velocity inside the shell by a factor of 10 to get any joy.

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[Compositepro]

Separating liquid droplets from a gas stream is a very common process. And the most common approach to accomplish this is is with a knock-out pot. A knock-out pot is basically a cylindrical pressure vessel with a tangential inlet, which creates a cyclone and adds residence time to allow for droplet separation. Air exits from the top and water drains out the bottom. With a knock-out pot you will also get additional cooling. The smaller you make to knock-out pot, the more pressure drop you will get, so sizing is a compromise between pot size and cost versus effectiveness and operating cost.

https://en.wikipedia.org/wiki/Vapor–liquid_separator

 

[LittleInch]

This is a massive air compressor - unless I've got my units wrong its coming out at 26,000 cfm. I think pushing that much air through one set of equipment is pushing it a bit or will need a large knockout pot....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

There were no interstage KODs' in these compressors in the air separations plant I used to work in. Cannot remember if there was wiremesh demisters installed into the exit nozzle, but that would seem one approach if you can enable an oversized nozzle. A liquid drainer is installed at the bottom of the shell. These being centrifugal compressors, some small amount of liquid entrainment is usually tolerated in the feedgas, since it is all in mist form.

Typically, for a regular wiremesh type separator, a Souder- Brown K value of 0.35fps (or 0.1035m/sec in SI units) is usual. In this case, since only coarse separation is required, a 100% exceedence may be okay ? - see also Perry Chem Engg Handbook, 7th edition, fig 14-124 and narrative, which indicates a superficial velocity of up to 4m/sec may be tolerated for vertical upflow of gas / mesh in horizontal plane for air /water systems with low liquid loading. Also talk to York to see if they would suggest an upper limit for the K value for coarse separation.

Using a max superficial velocity limit of 4m/sec (which corresponds to K = 0.7fps roughly), I get a 1200mm dia exit nozzle. Else an external wiremesh KOD or some kind of external cyclonic separator may be required.