9 replies to this topic

[procengsas]

t

Edited by procengsas, 16 February 2010 - 11:58 AM.

[procengsas]

Hi All,

Is there anyone out there with compressor experience that can help me? Can anyone give me a starting point?

Thanks

[ankur2061]

Hi All,

Is there anyone out there with compressor experience that can help me? Can anyone give me a starting point?

Thanks

procengas

As far as practical experience is concerned, I may not be able to help you much but you certainly can refer two books for guidance on your specific problem:

1. Compressor Handbook by Paul C. Hanlon

2. Compressors- Selection & Sizing by Royce N. Brown

These are amongst the top books for compressors.

Hope this helps.

Regards,
Ankur.

[Art Montemayor]

procengsas:

If you want to compress hydrogen to 30 bara (435 psia) – presumably from atmospheric, then you are dealing with a reciprocating machine. I have accumulated many years dealing with compressors and have compressed just about every conventional known gas (both hydrogen and oxygen many times), so I am confident that what you are dealing with is a RECIPROCATING COMPRESSOR – and multi-stage.

I have done the REVERSE of what you are proposing. I would never recommend you try to convert a hydrogen reciprocating compressor into oxygen compression service. An oxygen reciprocating compressor is a very special and specific machine designed to do a very hazardous and specific duty. I have compressed oxygen from atmospheric to 3,000 psig (206.8 barg) on a routine basis, but I can assure you that you need a special machine dedicated to that service – and ONLY THAT SERVICE.

The basic problem in trying to run one reciprocating machine in both hydrogen and oxygen service is that it involves a very dangerous and hazardous operation. You would be well ahead in your design if you simply forgot about that idea. I realize that with today’s “wonder” materials – like Teflon, carbon, PEEK, stainless steels, and others – that the idea of having a perfectly “non-lubricated” cylinder leads to the idea that since no lubricants (hydrocarbon oils) are required for the piston rings and valves, then one could simply use the same basic compressor for both hydrogen and oxygen service (since the oxygen service is the strictest and most conservative due to the potential for instantaneous oxidation (otherwise known as an EXPLOSION). There are other factors to take into consideration for the successful, safe operation of an oxygen compressor and the two gases simply are not compatible.

You are probably dealing with an electrolytic cell production of both hydrogen and oxygen at relatively low pressure and want to compress both gases for sale or transfer. I would seriously recommend you to install two, separate and independent compressors – in separate locations – for each of the two gases.

From the nature and type of queries that you present, I assume that you are not experienced in designing (process), installing, and operating such machines. There have been many text books written on reciprocating machines. Unfortunately, few of them deal with the practical aspects of operating and controlling them from the point of view of varying capacities and discharge pressures. For this, I have always relied on my 50 years of field experience. The GPSA is an excellent source of basic knowledge, but it lacks the “hands-on”, key information that is vital for field operations. If you have to vary the capacity of the machines you are describing, then I recommend you apply either one of two methods:

• Clearance pockets; or,
• Gas recycle from discharge to suction.

The first method is the premium, most efficient method. The second is the simplest and cheapest method, but wastes the energy recyled.

I hope this helps you out.

[AZIZ_MN]

HI PROCENGSAS'

IF YOUR H2 COMPRESSOR IS DIAPHARM TYPE THEN U CAN NOT USE IT FOR OXYGEN B'COZ THERE IS POSSIBLITY OF DAMAGE OR LEAKING DIAPHARM AND IF OXYGEN MIX WITH LUBE OIL IT WILL CUASE EXPLOSION, IF YOUR COMPRESSOR IS CYLINDER-PISTON TYPE THEN YOU HAVE TO GIVE NITROGEN PURGE BETWEEN GEARBOX AND CYLINDER TO AVOID ANY EXPLOSIVE MIXTURE (INCASE OXYGEN LEAK FROM CYLINDER SIDE AND MINOR OIL EMMISION ALWAYS THERE FROM GEARBOX OIL SEAL), OTHER THAN THAT COMPRESSOR SUCTION AND DISCHARGE PIPE LINE MATERIAL OF CONSTRUCTION (MOC) AND FLANGES GASKETS TO BE TAKEN IN CONSIDRATION. NORMALLY FOR OXYGEN SERVICE PIPELINE MOC IS STAINLESS STILL AND GASKET IS GALVENIC TYPE SPECIAL GASKET IS BEING USED

THANKS AND REGARDS

[procengsas]

T

Edited by procengsas, 16 February 2010 - 11:59 AM.

[Art Montemayor]

Your query is very strange and lacks details as to what you are trying to do, at what stage do you find yourself (in a presumed project), what are your objectives (scope of work), and what are your constraints. Without these data and further details it is very difficult to contribute a meaningful comment.

Example: You seem to lack experience in compressing gases, but yet are trying to compress hydrogen, oxygen, & "plant" air from 1 bara to 30 bara in the same compressor. Are all 3 gases required at the same final pressure? As I remarked earlier, you are looking at a multi-stage machine(s) for the gases. Your capacity - 300 m3/h - is relatively small and you will have problems finding a a small, multi-stage machine. This becomes exceedingly harder when you then come back with additional, piece-meal data like the requirement for non-lubrication. You can´t expect specific answers or comments if you don't supply ALL of the story.

Please define your compression requirements for each of the gases - flows, pressures, temperatures, turn-downs, continuous/batch operation, etc., etc. and then we can have an idea of what you are trying to do. Also supply all the above requested information - as well as your experience level. Otherwise, we'll all go around in circles.

Await your reply.

[procengsas]

Please define your compression requirements for each of the gases - flows, pressures, temperatures, turn-downs, continuous/batch operation, etc., etc. and then we can have an idea of what you are trying to do. Also supply all the above requested information - as well as your experience level. Otherwise, we'll all go around in circles.


Hi Art,

I am a junior design engineer and my initial query was to determine whether a compressor can compress two gasses of varying molecular weights. My concern also is the safety around working with one compressor to do both hydrogen and plant air. I have used oxygen as an extreme case. In fact, in the process that i am working on plant air will be used and not oxygen.

In terms of flows: Plant air to process varies from 5m3/hr act to 150m3/hr act and hydrogen from 5m3/hr act to 300m3/hr act. The pressure to process varies from 1bara to 30bara. Discharge temperature of compressor; 120 deg.C. It is a continuous operation. In addition, the compressed gas cannot be contaminated with any oils.

I hope this helps.

Thanks

[akslzf]

For such a small quantity of gas, only some positive displacement compressor is suitable.

If you are trying to salvage one of the existing compressors and that happens to be a recip, two crucial items need to be checked
1) Motor power (MW of 2 Vs MW of ~30)
2) Suc & Dis valves need to be changed every time you swap the gas, as no valve I know of, can handle gases with such a big differnce in MW.

You may look for a Roots blower or small screw compressors, with elaborate recycle loops.

Whatever be the case, you need a motor sized to the highest flow & heaviest gas.

A better description of the scheme will help.

[Art Montemayor]

procengsas:

As I stated previously, when you are not specific and furnish ALL the necessary basic data & background, we all tend to go around in circles and you get a bunch of comments that don't apply. For example, a Roots blower is certainly not applicable in what you describe. A Roots is nothing more than a lobe-type of blower - not a compressor.

Now that you have identified your level of engineering, I can understand your situation and your concern better. I also have been in similar situations many years ago. Allow me to give you some learned advice and recommendations:

Compressed hydrogen gas when handled in carbon steel (& other alloys) will, with time, become absorbed in the parent metal. This is a field-learned and experienced phenomena and is such because the hydrogen molecule is the smallest in the universe - or close to it. I have personally disassembled and modified hydrogen piping systems where I have had to wait for days to allow the absorbed gas to permeate out of the metal in order to start cutting and welding into the system. Hydrogen is so small that it actually permeates through metal walls. What I am telling you is that you have to take a large degree of precaution when dealing with such a flammable and explosive gas. As I stated before, DO NOT ATTEMPT TO MIX HYDROGEN COMPRESSION SERVICE WITH OTHER GASES - PARTICULARLY THOSE CONTAINING AN OXIDANT (SUCH AS OXYGEN).

There are other, important reasons for not doing what you are proposing or thinking about. However, I presently do not have the time nor the resources to go into the details and am not prepared to give a seminar on compressed gases on this Forum. Our Forums are not structured nor designed to educate engineers. The basic engineering education starts in universities and is finalized in the field. We can only give advice and comments on what we know and have experience on. A lot of the knowledge on gas compressors is in the hands and minds of those engineering mentors that are your supervisors or leaders in your organization. I realize that times have changed and there are fewer and fewer of those still around and who are willing/available to help you out, but you must make every effort to seek out information with specific and detailed explanations of what you need. We can try to help you out, but it is difficult when we don't receive ALL of the story.

I hope this helps you out and that you continue seeking out enrichment in your early engineering career.

Good Luck.