4 replies to this topic

[keby9wtw]

Dear Experts,

I have encountered a problem while selecting an appropriate compressor for my plant design project. I am compressing 166 m3/h of hydrogen gas from 24 MPa to 200 MPa with inlet temperature of 38C. From the compressor selection chart, the appropriate compressor is multistage reciprocating compressor, However, reciprocating compressor works under intermittent condition. Does this condition has any effect on the overall plant process as the hydrgen gas should be transported continuously throughout the process? Second, is it possible for a centrifugal compressor to compress in such a low inlet volume?

Thank you

[ankur2061]

keby9wtw,

Refer the link below where an attachment provides a compressor selection chart:

http://www.cheresour...3854#entry43854

I don't know where you got the information that reciprocating compressors are for intermittent duty, because that is not correct. Reciprocating compressors can be used for continuous duty for a wide range of gas compression applications. In fact for small capacities and high compression ratios multi-stage reciprocating compressors would be the first choice.

Art Montemayor can give you a whole lot more information on why a multi-stage reciprocating compressor would be the prefered choice for your particular application.

As far as centrifugal compressor is concerned, the low flow rate and the high compression ratio does not favor its selection both due to the economics and operational flexibility.

Hope this helps.

Regards,
Ankur.

Edited by ankur2061, 12 February 2012 - 02:29 AM.

[keby9wtw]

in this case , can the outlet temperature in 1st stage of compressor be more than 150C?

[ankur2061]

No, certainly not in hydrogen service. I will quote on stage outlet temperatures from API STD 618

Special consideration shall be given to services (such as those with high-pressure hydrogen or applications requiring non-lubricated cylinders) where temperature limitations should be lower. Predicted discharge temperatures shall not exceed 135°C (275°F) for hydrogen-rich services( those with molecular weight of 12 or less).

Hope this helps.

Regards,

Ankur

Edited by ankur2061, 12 February 2012 - 08:32 AM.

[Art Montemayor]

keby9wtw:

I add my response and recommendations to your comments and queries as follows:

1) I am compressing 166 m³/h (100 Scfm) of hydrogen gas from 24 MPa (3,481 psig) to 200 MPa (29,008 psig) with an inlet temperature of 38 C (100 ^oF).
This is considered by industry to be a small capacity. The fluid is Hydrogen and, consequently, the immediate choice should be a reciprocating compressor. The molecular weight of Hydrogen is so small as to make a competitive centrifugal device both inefficient and exorbitant in capital costs. Additionally, the centrifugal compressor will be very difficult to control with respect to capacity. A reciprocating machine is much simpler and easier to control its capacity. Since this is a Student Problem, the suction pressure of 24 Mpa with a discharge of 200 Mpa is obviously a theoretical “dream”. Only experimental and research reciprocating compressors have been used to reach such high discharge pressures – and then, only on an intermittent basis. A centrifugal machine is completely out of the picture for this range of pressure service.

2) From the compressor selection chart, the appropriate compressor is multistage reciprocating compressor.
The logical choice is a reciprocating compressor – not because of a selection chart, but because of common sense and the limitations of a centrifugal with respect to design capacity, compression efficiency, capacity control, and availability.

3) However, reciprocating compressor works under intermittent condition.
As Ankur has inferred, where do you get this input or belief that a reciprocating compressor is designed to only work intermittently? Reciprocating compressors are designed and operated on a “24 – 7” (24 hours a day, 7 days a week) basis, continuously for at least 330 days per year. Practical, field experience with reciprocating compressors throughout the last century proves your statement to be erroneous.

4) Does this condition have any effect on the overall plant process as the hydrgen gas should be transported continuously throughout the process?
If the “condition” referred to is intermittent service, the prior response should resolve this issue.

5) Second, is it possible for a centrifugal compressor to compress in such a low inlet volume?
Yes, it might be feasibly possible – with enough money – to attract a centrifugal compressor manufacturer to develop and build such a low capacity machine for a one-time application. However, in the practical world that we live in, if is fair to state that the amount of capital money required for this “adventure” would not be attractive – nor practical – to a manufacturer. It is very difficult to gain pressure increases in a very light gas such as hydrogen in a centrifugal device and the inherent power inefficiencies of a centrifugal machine make it impractical to consider.