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Topic: Compressor Suction Throttling  (Read 17633 times)

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Offline technologist

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Compressor Suction Throttling
« on: May 03, 2006, 03:22:52 AM »
We have a centrifugal compressor in MEG plant which is recycling gas flow thru the system. Makeup is added at suction & product is removed from the loop.

Compressor is a constant speed machine. Which is giving higher pressure at discharge say 19 Kg abs. We dont need 19 Kg in the system so there is a pressure killing device which is reducing it to 17 Kg abs. Further system drop is 3 Kg. So at compressor suction it is 14 Kg.

Now somebody proposed to install IGV i.e. instead of dischrge throttle it should be suction throttle.

I am not able to understand how this is going to reduce the power consumtion in the compressor.

Because,
1. Will the pressure ratio change in this case, I suppose so bcoz suction pressure is different now.

2. If it changes, it will increase or decrease. My opinion - it will increase mathematically.

3. IGV control will reduce flow or not, bcoz we dont want to reduce flow. (My plant capacity will go down.)

4. How to calculate suction pressure and power consumption in this case.

Thanx

Offline eugenedakin

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Re: Compressor Suction Throttling
« Reply #1 on: May 03, 2006, 10:08:21 PM »
Hello technologist,

You have a very good question.  In my opinion, there will be a decrease in power consumption, BUT, it is going to be small.  I'll answer your questions first, and then provide an explanation:

1.  the pressure ratio will change.  Instead of the pressure going from 14(intake)-19(post compressor)-17(post throttle)-14(back to intake), it will go 14 (intake)-12(post throttle-*guess*)-17(post compressor)-14 (back to intake).
2. when the throttle is on the intake side, the pressure will decrease post-throttle.
3. I am not sure... it would depend where the gas is removed from the system.  Could you draw a very basic flow diagram and post it?  It really depends on a few critical factors ...
4. Most programs are able to determine the suction pressure (given a pipe size, restrictor (throttle valve) opening, etc.  The power consumption will decrease.... albeit -very very slightly .. my guess, close to the 2nd decimal point.  The reason is that less pressure (less atoms being moved and allowed to have friction), whereas more atoms (higher pressure, more atoms to create friction) has more friction.  If the system has an overall pressure differential which is lower after the modifications, then the pump efficiency should increase.

I have about 10 years experience on refrig plants.  They rank as one of my many favorite plant types.

I hope that I explained this well.  Feel free to comment on the parts which do not make sense ...

Sincerely,

Eugene


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Offline mbeychok

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Re: Compressor Suction Throttling
« Reply #2 on: May 30, 2006, 04:47:41 PM »
technologist:

I am a bit confused by your pressure units of "Kg".  Did you mean kilograms per square centimeter (i.e., kg/cm2) ? 

Usually, the clearer you can be when asking a question, the better will be the answers you receive.

Regards,

Milt Beychok
(Visit me at www.air-dispersion.com)
Milton Beychok
(Visit me at www.air-dispersion.com)

Offline eugenedakin

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Re: Compressor Suction Throttling
« Reply #3 on: May 30, 2006, 10:33:48 PM »
Hi technologist,

Ah yes, you noticed me using oilfield slang terms.  I was using the terms in which you originally asked your question, to minimize the confusion.  Slang terms for pressure in psi is commonly referred to as pounds or lbs, whereas Kg/cm2 should be referred to as Kgf/cm2 (Kilograms force per square centimeter), and not the slang term, Kg.

I'll try to not use 'technology slang' in the future.

Thanks for pointing that out to me Milt.

Sincerely,

Eugene
There are 10 kinds of people in this world: Those who understand binary, and those that do not.

Offline technologist

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Re: Compressor Suction Throttling
« Reply #4 on: May 31, 2006, 06:49:20 AM »
Thanks Eugene & Milt.

Kg was not used as technical slang. It was just to make life simpler & faster. I know what "Pressure" units are & how they are used.

Anyway Would like to thank you Eugene for very reasonable points.

1. Yes, U r right in your guess also. ( I hope now u wont mind SM slangs). Suction will reduce somehwhere close to 12 Atm. (Ya U noticed it again).

2. Well Now would like to ask U if u have already predicted that change will be at second decimal point, what do you expect if I Use IGV in place of suction throttle.

Thanks Again, I was looking for this kind of expertise level.

Offline eugenedakin

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Re: Compressor Suction Throttling
« Reply #5 on: June 04, 2006, 12:42:51 AM »
Hi technologist,

Hmm... I'll have to ask you to write out the long term for the abbreviation IGV .. Chuckle .. there are waaaayyyy too many abbreviations in technology (I want to make sure that I answer your question properly).

Thanks for your complements (Its nice to get those once-in-a-while).

Sincerely,

Eugene
There are 10 kinds of people in this world: Those who understand binary, and those that do not.

Offline technologist

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Re: Compressor Suction Throttling
« Reply #6 on: June 05, 2006, 12:08:31 AM »
Ha Ha... ;D
Inlet Guide Vanes.

Yes, I admit that we should respect & pay it to the expertise of each member.

Bcoz none of us is TOTALLY perfect in any of the fields which are discussed on net. It Can't be.
So, I seriously consider any suggestion & advice.
(Its not difficult to isolate Experts & Time Pass surfers).

I posted this question on many forums, none of them was able to think beyond "textbook lines". Without understanding the question & system they will answer in a more "Professional way".

Anyway, I make friends rarely but when I do I obey serious long term friendship.
Would you like to be my friend?

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Offline eugenedakin

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Re: Compressor Suction Throttling
« Reply #7 on: June 05, 2006, 10:50:59 PM »
Hi technologist,

In my opinion, I don't believe that there will be any measurable difference when exchanging a suction throttle with Inlet Guide Vanes from a 'normally-operating' power-consumption perspective.

One area that may be improved by using an Inlet Guide Vane (IGV) is that the IGV (depending on the model) may be able to have a more sensitive adjustment to compressor pulsing.  The flow would be more 'evenly distributed',  than a throttle valve. This would help prevent the compressor from surging.  If the system is working well, there would not be a difference between the two.

This is just my $0.02

I always welcome new friends !!!!

Your website looks great.  Keep up the great work !

Sincerely,

Eugene
There are 10 kinds of people in this world: Those who understand binary, and those that do not.

Offline technologist

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Re: Compressor Suction Throttling
« Reply #8 on: June 05, 2006, 11:38:16 PM »
Thats exactly I told my management that in case of discharge throttle vs IGV there will not be any significant power gain.

Thanks for Website.

I invite all members of this forum to comment on technology issues.

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