Does increase in suction temp. cause failure ?

[Abualnassr]

Hi.

We have a centrifugal compressor (blower) that handles chlorine gas.
The process temperature at the suction is about 200C but when i looked in the manufacturer's manual i found that the design suction temperature is 138C.

So, is this can cause failures ?

Some of the failures are:
1 - Defected carbon seal.
2 - Unbalance in the impeller.
3 - Misalignment.


P.S. the process discharge temperature is less than the manufacturer's maximum discharge temperature. And also pressure at both sides is within the limits.

 

[pmover]

Unbalance is a manufacturing problem; unless mass is deposited onto the rotating assembly during operation. Balancing rotating assemblies are done at the end of the manufacturing process and before assembling into the blower housing.

Misalignment for a blower is again, likely a manufacturing problem. This really depends upon the setup of the blower; such as a rotating assembly, coupled to a motor via a coupling. Final alignment is generally done at the site prior to equipment commissioning.

"Defected carbon seal" - again, sounds like a problem with manufacturer. Further clarification is needed.

hope this helps!
-pmover

 

[JRLAKE]

Misalignment is a manufacturer's problem? I would think it is the end user's problem to check the alignment of their equipment.

Can you share more information? Differential pressure? Temperature rise? History? Does it fail on startup? Does it run for years? Can you post the curve? Is it definitely imbalance or is it vibration and imbalance was assumed?

It is certainly possible that the temperature is causing some problems. Misalignment and imbalance can also lead to seal failures. What is the cause and what is the effect is difficult to say without more information on the blower and system. Running a blower off its curve can cause these problems. Changing the inlet conditions can change the operating point, I think.

 

[Abualnassr]

Thanks guys for replying.

pmover, I don't know if imbalance and misalignment are manufacturing problems. But, we have 5 identical gas blowers in 5 identical lines and all are facing almost the same problems. I've tried to look for the blower curve in the manual but had no luck.

JRLAKE, Differential pressure = 0.5 bar
Temperature rise = 30C
And, it doesn't fail on startup and it's running 24/7.

But as i said the process suction temperature is much higher the design suction temperature. And i don't know if this can cause some of these failures.

 

[pmover]

ok Abualnassr,

balancing of a rotating assembly is typically done at the mfg shop (or subbed out) before final assembly. once the rotating assembly is balanced within acceptable industrial limits (or otherwise specified in purchase agreement), there should be no reason to suspect unbalance unless something changes to the rotating assembly. the change could be impeller cracks, deposits to rotating assembly, etc. if there are high vibration levels during operation, these can be attributed to several factors. one of which is operating the unit in an unstable region, whereby the rotating assembly becomes unstable in operation. this is not an unbalance problem.

as far as misalignment, no information is given about the blower. but i assume the blower to be completely assembled and cold aligned by mfg, electric motor driven w/ coupling, and installed in accordance with mfg procedures. final or hot alignment should be done at site before operation by mfg representatives. any maintenance activities resulting in disconnecting the driver from blower will require checking the alignment prior to operation. again, the mfg typically do provide services for start-up/commissioning of blowers, which includes alignment.

since you state a higher inlet temperature, yes this results in a less dense gas at inlet conditions. have the mfg analyze the design with the higher inlet temps as this may have an impact of rotor stability with higher temps.

perhaps having a skilled technician or engineer visit the site to collect vibrational/operational data will be useful to you in determining the problem.

hope this clarifies the matter for you.

good luck!
-pmover

 

[flexibox]

Check what the cold offset is for your alignment and it will interesting to know what type of coupling you have and what speed the compressor runs at. If you have an API671 gear coupling then what is the lubrication being used? do you have a lube oil system? is the coupling in good condition? Have you stripped the coupling if so check its design and if it is an API671 design then seek advice from the manufacturer

 

[JRLAKE]

I suspect not an imbalance (unless Abualnassr confirms that this was specifically checked) but rather vibration due to the operating conditions of which the blower was not sized. Changes in gas inlet conditions have been known to cause severe vibrations in centrifugal compressors/blowers, which could cause all of the problems listed above. However, without more details such as the blower curve, it is impossible to say.

The manufacturer or rep is in the best position to answer this question correctly.

But to answer the question, yes. The elevated inlet temperature COULD be the cause.

 

[Abualnassr]

The problem is that the blower performance curve is based on some parameters that the current process can't maintain (suction temp).

The coupling is John Crane's Mid Duty :

http://www.johncrane.co.uk/Prod_Pro...ctItemID=22&element=Prod_ProdPage_Couplings_1

And the impeller rpm is 5850 RPM.
And yes, the blower has it's own lube oil system.

Today we opened the case of the blower and i noticed there are some build-ups inside the casing just around the impeller and it looked really tough to remove so we used a hammer and a chisel to remove. So, maybe due to fluctuating the process these build-ups causes imbalance in the impeller.

Another point to mention, few months ago we've changed the original impeller (cost about 100'000$) to a cheaper one (about 48'000$). So, maybe the quality of the impeller is bad.

Regards,

 

[JRLAKE]

What accounts for the drop in price Abualnassr? Change in material?

 

[Abualnassr]

The quality of material and finishing

 

[TPL]

Quote:But, we have 5 identical gas blowers in 5 identical lines and all are facing almost the same problems.

Quote: i noticed there are some build-ups inside the casing just around the impeller and it looked really tough to remove so we used a hammer and a chisel to remove

Sounds to me like you have a case of compressor fouling. Something is deposited on the impellers in a unifom manner and comes off in random chunks, making the rotor unbalanced.

You really need to analyse the nature of the build-ups that you saw and work with your process people to see how it gets there and how you can stop it building up- could be related to different suction temperatures

How long has this problem existed - did its appearance coincide with the chang ein process conditions?

 

[Abualnassr]

TPL, i think that is the case.

The process people now are trying to increase the production. So, now the failures are becoming more and more. And my boss asked me to solve this problem without decreasing the production.
So, i have to either change the design of the blowers or buy new blowers with higher capacity.

So, do you have guys any suggestion ???

 

[TPL]

You really do need to understand the chemical composition of the build up that has been deposited on the impellers.
The you can figure out where it is coming from and address the root cause.

If could be some sort of reaction between chlorine gas and iron pipework producing iron chloride based compounds - alternatively, since you have gone for cheaper imnpellers, maybe you have the chlorine attacking the metallurgy.

Changing the design of the blowers or buying new ones is going to cost a lot of money - if you go down this route, how can you be certain that new/revamped machines will not experience exactly the same problems?