Turn-Down Ration for Centrifugal Compressor?
Turn-Down Ration for Centrifugal Compressor?
(OP)
Hi All.
I am looking for a suitable turn down ratio for centrifugal compressors? Does it depend on compression ratio?
For a Centrifugal compressor with ratio of about 4 and a capacity of 350000 kg/hr ,what turn down ratio do you suggest?
I am looking for a suitable turn down ratio for centrifugal compressors? Does it depend on compression ratio?
For a Centrifugal compressor with ratio of about 4 and a capacity of 350000 kg/hr ,what turn down ratio do you suggest?





RE: Turn-Down Ration for Centrifugal Compressor?
"Turndown" has a lot of definitions, but if we use maximum mass flow rate at maximum compression ratios divided by minimum mass flow rate at minimum compression ratios then the answer for centrifugal compressors is so near to 1.0 as not to matter.
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.
RE: Turn-Down Ration for Centrifugal Compressor?
(referred to rated capacity) between the rated capacity and the surge point capacity at the rated head when the unit is operating at rated suction temperature and gas composition."
good luck!
-pmover
RE: Turn-Down Ration for Centrifugal Compressor?
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.
RE: Turn-Down Ration for Centrifugal Compressor?
RE: Turn-Down Ration for Centrifugal Compressor?
relax & thanks; the clarification for "1.5.51 turndown" is the definitions paragraph in API-617, 7th edition.
Sabergg1981,
with increasing compression ratio (Rc), the flow reduces in the centrifugal unit. due to decreasing inlet pressures, there comes a point at which the centrifugal unit can no longer increase the Rc due to speed limitations (variable unit) &/or the compressor is operating at or left of the surge control line. this then becomes an inefficient process/operation and it is time to re-wheel the centrifugal unit or add another compressor (+HP) designed for the lower inlet pressures. this is expensive.
if flow rate is relatively constant over the years, then seriously think about the recip compressor. have the ariel or DR folks send you some preliminary data (sizing) on recip compressors based on your predicted conditions. they may be able to configure a compressor unit with cylinders for single and 2-stage operation depending upon inlet conditions. you will need to be certain of sufficient HP (driver) for all conditions.
good luck!
-pmover
RE: Turn-Down Ration for Centrifugal Compressor?
RE: Turn-Down Ration for Centrifugal Compressor?
In the early days (71 bar to 91 bar) you are doing about 1.3 compression ratios and hp requirements are slightly less than 30 hp/MMSCF or 1700 hp. Late days you're doing about 3.5 compression ratios and your hp requirements go to 85 hp/MMSCF or 340 hp for the design MMSCFd. I'd do this with a single stage recip with something like 1400 hp (assuming you can tolerate 72-74 bar in the earliest days) and variable speed control (either a speed changer on an engine or a VFD). Late days you may need to put a backpressure regulator on the discharge to waste some hp to keep the driver on its performance curve
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.
RE: Turn-Down Ration for Centrifugal Compressor?
RE: Turn-Down Ration for Centrifugal Compressor?
with the reduction in capacity, are there economics to justify such a project?
good luck.
-pmover
RE: Turn-Down Ration for Centrifugal Compressor?
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.
RE: Turn-Down Ration for Centrifugal Compressor?
I think fewer capacity of recip compressors than centrifugals lead in more recip compressors in number.
Can you give me a gas busting compressor with recips details? name, location,....?
i am wondering can i find a reference about how to build a gas compressor station with reciprocating compressors? do they arrange in parallel? what about turn down ratio? and other design problem...
RE: Turn-Down Ration for Centrifugal Compressor?
I don't know what in the hell you are talking about when you say "gas busting compressor" and the term sounds kind of derogatory.
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.
RE: Turn-Down Ration for Centrifugal Compressor?
your reference is PHMSA 192.
based on your questions, it is apparent you do not have the expertise nor knowledge to build a gas compressor station yourself, much less determine HP size and type. I recommend you seek the expertise from reputable engineering firms.
good luck.
-pmover
RE: Turn-Down Ration for Centrifugal Compressor?
RE: Turn-Down Ration for Centrifugal Compressor?
RE: Turn-Down Ration for Centrifugal Compressor?
Can you reference me about criteria you mentioned above: "Change suction pressure by more than 5%, change suction temperature (in absolute units) by more than 2%, change discharge pressure more than 15%, change the required mass flow rate more than 5%, or change molecular weight of the gas by more than .05 SG units and the world starts getting really ugly really fast."
I appreciate your concern
RE: Turn-Down Ration for Centrifugal Compressor?
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.
RE: Turn-Down Ration for Centrifugal Compressor?
If you want to have a feeling on how large are operating curves of centrifugal compressor, I would suggest to pay much attention to the MW, knowing that Inlet Pressure and Temperature would also impact.
Hydrogen service have often wide and flat curves.
Wet gas, coker gas or other heavy MW compressor have very narrow curve range with steep curves.
Typically you want a good turndown to avoid recycle, if your turndown case is specified for which you want no recycle, situation might end up with the rated case being selected to the right of the curve with penalty on efficiency and even bigger driver sizing.
For typical natural gas 17 ~20 MW application, I would say if you set the design point on the rated case you may have around 30-35% turndown but really from the top of my head!
RE: Turn-Down Ration for Centrifugal Compressor?
Do you remember our discussion under this topic? we are starting basic engineering and i want to challenge our guys about change our minds to reciprocating compressors. Also some reservoir parameters change.
Here, we want to make up pressure drop of a gas reservoir by building a gas compressor station. capacity of this reservoir is 68 MSMPD. after 4 years this capacity falls down and in last years( 20 years) it reaches to 4 MSMPD. Suction pressure of this station is 74 barg at start and after 4 years drop to 21 barg and then remains constant. also molecular weight varies about 10% ( i dont know exactly, but our process guys calculated so).
you had told me about Ariel JGJ/6 with six 4-5/8 HJ cylinders for whole range of over the life of the field. but they only give about 1860 hp. from power approch for compressing of 68 MSMPD we need about 250 MW power for this station. considering a 2 MW ariel compressor we need a large amount of compressor. how it could be? or some concepts are mistaken here by me?
RE: Turn-Down Ration for Centrifugal Compressor?
RE: Turn-Down Ration for Centrifugal Compressor?
In the early days you are only doing 1.3 compression ratios, 30 hp/MMCF, or 72000 hp (54 MW). Late days you are doing less than 4 compression ratios and 85 hp/MMSCF, so for 141 MMSCF/day you would use something like 12000 hp or 9 MW.
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: Turn-Down Ration for Centrifugal Compressor?
RE: Turn-Down Ration for Centrifugal Compressor?
I want to know how many recip compressor can handle our field?
RE: Turn-Down Ration for Centrifugal Compressor?
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: Turn-Down Ration for Centrifugal Compressor?
As you know i am involved in construction of a gas compressor station but i think i have no much practical knowledge. Pmover gave me some references such as PHMSA but i want to have some detail references about compressors and also gas compressor stations. we both know there are to many references such as handbooks... exist in this subject that all of them are useful. and i know you as a experienced guy in this field. so i wanted you to introduce me the latest and useful source in subject of compressors and subject of gas compressor stations based on your experience and upstream guys you met and discuss.
thanks alot
RE: Turn-Down Ration for Centrifugal Compressor?
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"