Condensation?? in compressor suction lines 5

[krsmani77]

We find condensate downstream of the separator ( K.O.Pot)in the suction line even upto the suction snubber. This leads to repeated failures of the machine. Anybody faced/solved such problems?

 

[TD2K]

I seen at least 2 companies that specify the suction lines downstream of the knock-out pots up to the compressor inlet will be insulated and heat traced to ensure the gas does not cool off with resulting condensation.

 

[kbander]

I agree with TD2K. In addition to this I would check the sizing of the knockout drum, review the need for a coalescing pad (although this won't help if the drum diameter is too small) and for new installations ensure that the ko drum is as close to the compressor as possible.


Regrds,


Bob

 

[pmover]

i trust you are referring to centrifugal compressors?

in addition to td2k & kbander:

typically, ko drums and/or seperators have a drain system + instrumentation to remove collected condensate. if system has drain system, suggest investigating them and its operation.

also, i trust the surge control piping is connected somewhere upstream of the ko pot/drum. there is the jt effect across the surge valve.

also, is there a mechanical seal system that can potentially allow for liquids to enter the process stream?

-pmover

 

[krsmani77]

Thanks guys. But the compressor is actually a twin lobe blower, which does not tolerate the liquid carry over. The K.O.Pot is a narrow vertical NO INTERNALS TANGENTIAL Compact Cyclone separator, for which there does not seem to be any reference in Separator Literature.Any ideas how to check its adequacy? The liquid is hexane carrying waxy low MW polymer and when dry, tends to plug wire mesh and packings. We constantly drain the separator bypassing the LCV so there is no chance of liquid level build-up and carry-over. We tried a bigger dia (3 times the original) gravity separator but failed miserably as it ended up as an unintended supersonic vortex(??) separator pulling vacuum in the separator preventing the liquid drainage ( Resulting in a catastrophic failure of the blower after an agonising wait of 12 hours). Due to space and time limitations, the new inlet nozzle became totally tangential and made the new separator supersonic cyclone(??)separator. How does one control the pressure drop across a cyclone(no internals- only tangential entry) separator? -- Mech seal -- yes but we have not found the heavy lube/seal oil inside the failed blowers.Pl continue this thread on the separators handling condensing liquid carry-overs

 

[longeron]

What I know about cyclone separators is generally applied to solid separation, so take this with a grain of salt.

1. The Reynolds Number at the inlet needs to be above 2,000, but you’ll see better efficiencies closer to 10,000. In general cyclones are more sensitive to the densities of the media than to the pressure differentials.

2. To achieve the highest efficiency (about 95%) you want the discharge pressure of the dirty fluid to equal the discharge pressure of the clean fluid at the top of the separator. You can use whatever combination of piping, valves, orifice plates, whatever in the dirty flow obtain this (assuming that you can with this set-up).

I'm interested to learn what kind of seal and flush plan you are using with this blower. When I hear blower I am used to thinking of packing not a mechanical seal.

 

[longeron]

It looks like I contradicted myself.
When dealing with solids, the particle size that can be separated from the flow is more affected by the density of the solids in the process than changes in pressure.

 

[krsmani77]

The inlet/oulet Re No is around 275000. So that should not be a problem from what you say. The mech seal is a standard gas mech seal known as "emission controlled non-contact externally flushed mech seal"( pure Nitrogen gas flushing- Mode GF200), supplied by Duromaetallic. It is similar too liq mech seals except that the gap between seal faces is slightly larger and maintained by external flushing gas pressure.
Anything on liquid cyclone separators?? Anybody??

 

[unitradingco]

what is the inlet velocity ? It seems very high based on the Re# you given. I designed a cyclone before. The maximum velocity should be exceeded 135 ft/s. >135 ft/s, particle or liquid droplet will re-entrain.

 

[25362]

It is good you continuously remove bottom-collected liquids off the KO pot since horizontal velocities tend to induce waves spraying drops into high vertical velocity regions.

If the KO pot cannot be modified, have you checked the possibility of making changes at the source of the liquid entrainment, or of adding in-line coalescers available in the market ?

By the way, when making calculations of maximum allowable vertical velocities to reduce entrainment, it is recommended to use the geometric mean of both actual horizontal and vertical velocities, rather than the vertical velocity alone, for comparison, as a safer conservative approach.

 

[krsmani77]

Thanks guys. The inlet velocity is around 20Meters/sec. Much less than yr 135ft/sec limit and so should not be a problem.
Still all of you are talking about gravity separation. How about the centrifugal separation? It is 30 times more than "g".

 

[25362]

Dear Krsmani77, got the message! Velocities lower than 30 m/s are OK for cyclones. Literature says that centrifugal deposition is, however, not very effective on particles smaller than about 5 micrometers in diameter. In any case the top outlet nozzle should protrude into the KO pot to avoid liquid collected on the walls to escape.

Some kind of impact or intercept collection may be added ahead of the KO pot to increase size of droplets. Inertial impaction may be effective especially for droplets of less than 1 micron in diameter.

Fibrous (plastic, steel or glass) packings with a large void fraction (up to 99%) are very effective collectors by inertial impaction. Since they may be susceptible to plugging a set of two in parallel could be used to keep the unit running while cleaning or replacing.

There are quite a few in the market and makers would gladly give you advice on the best option for the purpose.

 

[unitradingco]

If your velocity is 20 meters/sec or 60 ft/sec, it is at low side of the limit. It is acceptable. One thing you should do is to add an annular ring above the inlet nozzle to prevent the lquid re-entrainment. I believe this will help. but I am not sure it is good enough to completely solve the liuid entrainment problem.

centrifugal force is only 30 times the "g". it's a kind of low. 75 is my magic number.

 

[longeron]

Just thought of something... As I read your reply to my post it came to me...

Is there a coalecer on the N2 line to the mechanical seal?
If so, when was it last replaced? If no one remembers, it is time to do that. I think that most folks reccomend replacing the coalecer every quarter or so.

After talking to a guy in the know, the leakage rates on the GF200 brochure are low....

Josh

 

[krsmani77]

Thank you all for the sustained interest.
Dear unitradingco, Actually, the centrifugal force (V**2/R)is 160 G but When compared with the new large dia gravity KO pot which we tried, the inertial forces dropped due to lower velocities and so in comparison, the ratio was 30. But since we have gone back to the original compact Cyclone separator, the ratio is now back to 160.
There is a small amount of very fine Polymer powder coming with the gas and is likely to choke any fibrous impact collector.Now it is being removed along with the liquid from the bottom of the separator. Annular ring -- like a skirt OR a tray support ring?
Longeron, The Nirogen is from a Liquid Nitrogen vaporiser, situated offsite - so there is no coalescer.

 

[syed69]

STRATEGIES.
1.TO CHECK THE SEPERATION EFFICIENCY OF THE EQUIPMENT DEALING WITH MOISTURE OR THE LIQUID DROPLETS REMOVAL.
2.INSULATING THE SUCTION LINES AND HEAT TRACING EITHER ELECTRICAL OR STEAM,TO AVOID CONDENSATION OF THE LIQUID ON THE WAY TO COMPRESSOR.
HOPE U WILL ANSWER BACK AND ALSO CONCLUDE AFTER THE PROBLEM IS SOLVED AS THIS WILL BE A LEARNING FOR US ASWELL.
rEGARDS

KHALEEL

 

[unitradingco]

please provide all the process information and cyclone information(dimensions). thanks

 

[krsmani77]

Dear Unitradingco,
The compact cylindrical cyclone separator(CCCS), is just a cylindrical vessel with no internals. The feed inlet is tangential and the vessel dia is double that of inlet nozzle. Inlet dia is 250mm. Feed is Nitrogen gas saturated in hexane( not pure) solvent vapours( Boiling range 65 - 400Deg C)having dissolved low molecular weight polyethylene wax. Flow of gas is around 4000NM3/hr and pressure at exit of vessel is of the order of 300mm H2O. The service is for polyethylene powder conveying from the Drier to Powder Silos.The vessel has LG and Hi level alarms at the bottom. Hope it is detailed enough. Thanks for the interest.

 

[krossview]

krsmani77, in your 2nd mail you mentioned that the Cyclone is a Compact Cyclone Separator.

My assumption maybe a shot in the dark, but if you mean with Compact the manufacturer of the cyclone, then you may be happy to know that they are still around.

COMPACT stands for Complete Package Technology
and address of Head Office/Manufacturing Facility is

Complete Package Technology, Ltd.
2887 Parsons Road
Edmonton, Alberta
Canada,T6N 1A3
Phone: (780) 465-4200
Fax: (780) 465-1001
E-Mail: compact@telusplanet.net

They should be able to help you, if they are the orginal manufacturer.

Hope this helps

Krossview/OK

 

[krsmani77]

Sorry, it is a generic name. Thanks anyway.