Compressor process control
Compressor process control
(OP)
All,
Is it okay to design a moto compressor centrifugal type handling clean natural gas without any control method provided (No by-pass, NO IGV nor throttling device, NO speed variation). The decision to not implement any control method is dictated by process.
Whatever can be the arguments to justify such approach, I beleive this is not a sound practice because there is no flexiblity.
In your opinion what can be the implications to go this way ?
Thank you
Is it okay to design a moto compressor centrifugal type handling clean natural gas without any control method provided (No by-pass, NO IGV nor throttling device, NO speed variation). The decision to not implement any control method is dictated by process.
Whatever can be the arguments to justify such approach, I beleive this is not a sound practice because there is no flexiblity.
In your opinion what can be the implications to go this way ?
Thank you





RE: Compressor process control
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
RE: Compressor process control
I agree. The application is pure downstream, does it change something?
The argument I received is that downstream compressor somewhere in the process there is a control valve that could adjust the system curve. I have never faced such situation before for compressors that's why I am a bit puzzled.
In the upstream, nobody can predict the behavior of a reservoir and we might end up with huge variations, especially at the compressor inlet, MW changes and are never as expected. In the downstream, the process variables are generally better under control, but still I believe process upset may occur: fouling can happen in equipment, equipment performance might be altered etc.
In your opinion, what can go wrong if the design I have mentioned will be finally adopted.
Could you please illustrate with some example or scenario to figure out ?
Thanks
RE: Compressor process control
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
RE: Compressor process control
Johnny Pellin
RE: Compressor process control
Are you aware of any reference (code, engineering practice, book) where I can find a table that links between SIL level of the application and the minimum safeguard protection required to be implemented? I know some compressors manufacturers have minimum requirements on Discharge Temperature, Discharge pressure and Vibrations such as Voting rule for trip (2oo3) to match a given SIL level (as a minimum for OEM). If something is said on controllers it would be good.
In addition, with regard to the point of JJPellin related to automatic trip. I suppose that if the compressor is shutdown on emergency trip without damage or failure it does not mean that the rest of the process is not at risk. I deem this may (or may not) lead to unexpected behavior somewhere else in the plant. Which incidentally would lead to a risk of loss of containment elsewhere despite the compressor has been tripped without failure or damage. Is such assumption correct ?
RE: Compressor process control
Is it a good idea - definetly not. One key qestion to ask "process" is how do they intend to start and stop the whole system?? Many times people seem to think a system just magically runs at steady state without working out how to start and stop this thing, even if is a continuous process it needs to start at least once in tis lifetime and probably more during commissioning.
You may not use the bypass line very often, but if there is any possibility of a no flow situation occuring, no matter how remote or needing manual intervation (an isolating valve for instance) then your compresor will only last a very short time before suffering some major damage. Often these scenarios are not properly considered until the final HAZOP when you then need to go and add a reycle line into the design at the last minute.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Compressor process control
But, if a compressor is running to destruction, it is going to shut down anyway. I can trip it off and bring it down safely. Or, I can let it wreck and wait for the driver to trip off on overload after the rotating parts start to weld themselves to the stationary parts. In some scenarios it comes down to a question of timing. Do you want to trip sooner or trip later?
Johnny Pellin
RE: Compressor process control
Your point is clear. I would not design anything not in accordance to API617 and therefore stick to the trip setting on high vibrations aligned with API. By the way if the trip is initiated on high vibrations or on axial thrust, the trip sequence will be automatic. How much can you do to influence the timing then, no idea. Otherwise are we talking about operator action that will override the automatic sequence ?
LittleInch,
I noted (on the other parallel thread) that in some cases (reformer) with no closed valve in the loop, anti-surge protection via by-pass line can be omitted. Consider the type of gas being compressed. Hydrogen gas leads to very gentle, flat and wide performance curves. Something going wrong in a context where the turndown to surge is typically as high as 40% may allow you to buy some time. It is not like having steep curves with high molecular weight. With narrow curves, especially if continuous operation were already on a point close to surge at 100% speed, chances exist that the compressor will surge during trip, even a by pass protection may not suffice. So I can hardly imagine the situation where, on top of that, nothing has been envisaged to safeguard the machine. Not sure it will get better because the application involves in particular a reformer, or not?
Regards
RE: Compressor process control
RE: Compressor process control
Independent events are seldomly independent.