4 replies to this topic

[m42364236k]

Dear colleagues

I have two question about sure of compressor

Do we have any way to decrease the turn down  of the compressor to prevent the anti-surge valve open?

One vendor said the the turn down of their compressor is 75 % do we have any way to decrease the turn down to prevent the surge valve opening

Second question

Do we have any problem like surge in positive displacement type compressor? If yes is it common to use anti

 

surge valve for this type of compressor

 

 

Mike 

[ankur2061]

Hi,

 

Surge is not a phenomena for PD compressors, simply because PD compressors are constant volume and variable head machines.

 

Surge valve is provided and needs to open when a surge condition exists. So it is not clear why you want to prevent the anti-surge valve to open?

 

Volume flow control (increase or decrease) for centrifugal compressors can be achieved by various means. Some of the common methods employed are:

 

1. Variable Opening Inlet Guide Vanes

2. Variable Speed Drive

3. Suction Throttling (Control) Valve

 

Hope this helps.

 

Regards,

Ankur.

[m42364236k]

Hi,

 

Surge is not a phenomena for PD compressors, simply because PD compressors are constant volume and variable head machines.

 

Surge valve is provided and needs to open when a surge condition exists. So it is not clear why you want to prevent the anti-surge valve to open?

 

Volume flow control (increase or decrease) for centrifugal compressors can be achieved by various means. Some of the common methods employed are:

 

1. Variable Opening Inlet Guide Vanes

2. Variable Speed Drive

3. Suction Throttling (Control) Valve

 

Hope this helps.

 

Regards,

Ankur.

ANKUR thanks a lot for your quick and complete reply

 

Opening the anti-surge valve in long time will damage the compressor.

Vendor of compressor said that when flow rate reach the 75% normal flow rate anti surge valve will open, our plant turn down is 50 % and in  some months(two or three) of year plant work in turndown and in this condition anti surge valve will be open for two or three months

Does it have bad effect on performance of compressor or damage the compressor after log time time?

Or it is common

 

Mike

[ankur2061]

Mike,

 

I don't know who your vendor is, but I certainly can tell from what you have mentioned above that either he has no idea about what he is talking or he is hiding information from you. What is meant by "long time". What kind of damage can happen to compressor?

 

The one problem that I can foresee is that if gas is recycled through anti-surge valve or for that matter through any recycle mechanism, the temperature of the recycle gas will be higher than the fresh feed to compressor inlet. This is quite solvable. Just by having a properly designed air cooled heat exchanger in the recycle line you can avoid this problem.

 

However, one important point to be noted when specifying a compressor, specifically in process gas service, is to provide the compressor vendor the entire flow range including maximum turn-down and the maximum variation in gas composition, gas molecular weight, gas density etc. This is generally done by defining various cases or scenarios as permutation /combination of flow rate, gas composition / properties  or in a nutshell the entire performance envelope of the compressor

 

Most performance problems related to changed operating conditions with compressors arise because due diligence was not done in defining the entire performance envelope of the compressor during the engineering design stage.

 

Regards,

Ankur

[m42364236k]

Mike,

 

I don't know who your vendor is, but I certainly can tell from what you have mentioned above that either he has no idea about what he is talking or he is hiding information from you. What is meant by "long time". What kind of damage can happen to compressor?

 

The one problem that I can foresee is that if gas is recycled through anti-surge valve or for that matter through any recycle mechanism, the temperature of the recycle gas will be higher than the fresh feed to compressor inlet. This is quite solvable. Just by having a properly designed air cooled heat exchanger in the recycle line you can avoid this problem.

 

However, one important point to be noted when specifying a compressor, specifically in process gas service, is to provide the compressor vendor the entire flow range including maximum turn-down and the maximum variation in gas composition, gas molecular weight, gas density etc. This is generally done by defining various cases or scenarios as permutation /combination of flow rate, gas composition / properties  or in a nutshell the entire performance envelope of the compressor

 

Most performance problems related to changed operating conditions with compressors arise because due diligence was not done in defining the entire performance envelope of the compressor during the engineering design stage.

 

Regards,

Ankur

thanks a lot 

very useful