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Reciprocating Hydrogen Makeup Gas Compressor Troubleshooting

hydrogen compression reciprocating compressors

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#1 Phukan

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Posted 21 December 2018 - 01:24 AM

We are having a reciprocating compressor that is utilised for supplying hydrogen to a hydrotreater. The design condition of the compressor is as follows:

 

Suction pr: 19.81 Kg/cm2

1st stg Discharge Pr: 47.91 kg/cm2g

1st stg Discharge Temp:132.2 deg C

2nd stg discharge pr: 142 kg/cm2g

2nd stage dis Temp: 133.8

 

It is a double acting low RPM machine ( 1500) and the design feed composition is 86.5% H2, 6.3% C1, 2.3% C2, 1.6% C3 and small amount of C-4, C5 and 300 ppm H2S.

 

We have tried different feed into it, all of which basically are higher purity hydrogen gas. The operating parameters are attached in the excel sheet. I have simulated the compressors performance in Pro-II based on the operating parameters and feed composition. In almost all the cases the compressor first stage is shown to operate close to 80 % efficiency but the second stage showing 75% adiabatic efficiency. Does this compressor needs repair or is there anything that can be done to restrict the discharge temperature. Reducing the cooling water temperature is not an option and we cannot reduce the purity of feed hydrogen. What would be associated risks to increase the Compressor Trip point by another 10 deg C considering it is presently set at 154 deg C. 

 

I came to this forum after a long time and hope Art is still active with so much of compressing experience behind him.


Edited by Phukan, 21 December 2018 - 05:40 AM.


#2 Phukan

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Posted 21 December 2018 - 01:27 AM

The compressor operating parameters sent as an attachment

Attached Files



#3 Technical Bard

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Posted 21 December 2018 - 09:17 AM

A new reciprocating compressor on high purity hydrogen should achieve efficiencies well in to the 90%.   Pure hydrogen (99+%) can get close to 98% efficiency (if a big enough machine). 

 

Older machines designed for lower purities generally only get efficiencies around where you see your operating data (~80%).  One problem is that higher operating temperatures are reducing efficiency as well.

 

What is the suction temperature to each stage?  Can you reduce that through additional cooling? 



#4 Art Montemayor

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Posted 21 December 2018 - 11:26 AM

Phukan:

 

Please refer to the attached Rev1 of your workbook to see my comments and revisions of your tabular data.

 

Attached File  Hydrogen Compression Operating DataRev1.xlsx   59.42KB   29 downloads



#5 Bobby Strain

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Posted 21 December 2018 - 02:17 PM

Seems as though 1500 rpm is the motor speed, not the compressor speed. One would need the original performance to judge whether the compressor needs repair.

 

Bobby



#6 Phukan

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Posted 22 December 2018 - 02:01 AM

Dear Art,

 

I take the liberty to reproduce the contents of your reply in Excel sheet for benefit of all. Being a naive in the field of reciprocating compressors ( a lot of other things for that matter), I misjudged the 1500 RPM as that of the compressor , which in fact is the RPM of the driver. I misjudged the amount of data required too, again blame my ignorance.

The compressor as such has a RPM of 263, quite within the range you prefer. I have provided few more details in the attachments and also cleared some of the doubts in the reply below.

 

● The compression ratio of each stage is the product of the ABSOLUTE discharge pressure divided by the ABSOLUTE suction pressure - it does not relate to the gauge pressures.

● Note that when the 1st stage suction pressure of the 90% H2 flow is increased by 5 kg/cm2 (71 psi), the compression ratio increases dramatically. 

● No flow diagram, P&ID, or process description is given.  It is assumed that the feed stream is supplied evenly and in a controlled manner. The feed available is in abundance. in a sense the suction pressure is controlled by sending the excess to elsewhere, so no feed starvation is there.      

 

● No information is given on the capacity control(s) and it is assumed that the compressor is allowed to run at rated speed and capacity in each stage. There is no capacity control in place and the compressor works in 100% load all the time.    

● It is assumed that the 2nd stage discharge pressure of the compressor is held constant by a back-pressure control valve on the discharge stream. IT is rather controlled by system pressure of hydrotreater it is supplying to, which infact is controlled.    

● No information is given on the cylinder lubrication feature - lubed or non-lubed; it is not known if this compressor is a new purchase or used (from another application?). It is a lube cooled compressor and in use for last 17 years which is due for overhauling as reported by maintenance guys.

 

● Although the service is not severe, it is taxing on a machine that is double-acting (on both stages?) and running at 1,500 rpm.  This is considered as an excessive,  high speed - especially for Hydrogen, a very small molecule.   RPM is 263, double acting in both cylinders.                   

 

● A manufacturer's detailed data sheet (such as API 618 Data Sheet) is needed to evaluate the compressor's rated operation and present results. Could manage the detail Engg consultant's datasheet and few details from manufacturer's installation guide. hope this suffices.    

 

● A discharge temperature on an oil-lubricated cylinder should be around 300 °F (148 °C) as recommended by API standards.   This temperature is normally used as    an alarm point and 350 °F (175 °C) is the shutdown temperature.  These alarm points are related to the limits of the lubricating oil used - not to the machine itself.     The potential hazards are oil ignition and explosion (in air service) or oil coking and sludge creation.              

 

● The capacity or size of the compressor and driver are not given. Capacity is 188 Kg/hr    

             

● I would normally specify a 3-stage, oil lubricated compressor for this application running a conservative 300-400 rpm.  This would reduce discharge temperatures (and wear).

 

● Depending on the type and present condition of the piston rings on this double acting machine, there might be ring wear - particularly in the 2nd stage - that is      causing some re-compression and elevating the discharge pressure(s).  This is hard to speculate without past compressor operating records and history.         Certainly, a super-high rpm of 1,500 rpm is going to favor fast piston ring wear as well as bearings and valves.   That is the price you pay when you specify a cheaper,    fast rpm machine.  This type of machines are not meant for application as dependable process compressors.  They are designed and employed out in the oil patch    where they are depreciated at a very fast rate just as everything else in the oil patch.  They are not meant for the usual 10-15 year operating life.      

 

● More information is needed on the compressor: Make, model, type, cylinder sizes, rod size, configuration, capacity control, driver specifications, etc., etc.  Its a Dresser Rand make

 

In addition to above, we intend to improve the jacket, bearing housing and seal cooling system of the compressor by means of providing Deminaralised water/ steam condensate with ethylene glycol in 50:50 ratio in a closed loop tempered water system. The makeup in the jacket cooling tempered water system is presently from cooling water which tends to choke frequently. We assume this would help improve the discharge temperatures.

Attached Files


Edited by Phukan, 22 December 2018 - 02:11 AM.


#7 Bobby Strain

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Posted 22 December 2018 - 05:56 PM

Wow! 17 years service is remarkable. Time to give it a thorough overhaul.

 

Bobby



#8 Art Montemayor

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Posted 22 December 2018 - 06:34 PM

Phukan:

 

First of all, don’t feel you’ve been naive; a lot of engineers have not been around gas compressors to know enough about them.  It takes a very sage and experienced engineer - such as Bobby Strain - to immediately detect a questionable basic data and identify it as an induction electric motor driver running at 50 Hertz frequency.  The majority of USA engineers who have not battled foreign projects would probably be unaware of the fact that unlike the USA where 60 Hertz is “universal”, 50 Hertz speeds abound in foreign lands.  Bobby correctly hit on the error because, like some of our members, he is very astute and experienced.  So don’t feel bad.

 

Thank you for the additional data.  It helps, as demonstrated in my attached Rev3 version of your workbook.  However, a lot of the data is merely scribblings and the scanned product is blurred in many places and difficult to read legibly.  I’ve included a lot of the data in transcribed form within the workbook for you to check and correct if needed.

 

I have worked with, operated, installed, specified, and bought many ESH model compressors - since 1960 when they were the original Ingersoll Rand product through the Dresser Rand years and ultimately they have been purchased by Siemens of Germany.  The design is a very sound and good one that has been proven for over ¾ of a century.  I have operated and managed as many as 5 Hydrogen ESH compressors in the field in one plant alone.  There have been updated modifications to the design as the years have gone by and these have been such items as non-lube design and poppet valves.  I have detected that you have “mini-lube” in your compressor and unless I am totally wrong, you have non-metallic piston rings and piston rider bands in your cylinders.  Since you are working with engineering consultant specifications and data (which was generated prior to purchase of the equipment) you have some faulty information.  You should be working only with “as-built” information and not consultant data that was issued for proposals.

 

If this compressor was purchased in 1996 (as the driver data indicates) it should have undergone a complete inspection for wear at least by 2006.  I doubt that it has and I believe that your piston non-metallic rings and rider bands are probably worn.  This would certainly correspond to internal leakage in double-acting cylinders and cause a natural “re-compression” by the piston leakage inside the cylinder.  This would certainly raise the discharge temperatures as witnessed today.  You haven’t furnished any historical operating data on this machine, so we can’t categorically prove what I state.  But I doubt you would have subjected the machine to a piston ring wear analysis in the past 22 years.  Such an analysis is difficult to do in the field due to the critical cylinder and piston re-alignment required during the re-assembly of cylinders and piston - especially in an “in-tandem” compressor (which is what I believe your machine is).  And any non-lube compressor cylinder should certainly require it.  This is the main trade-off suffered by users of non-lubricated compressors.  It’s great to eliminate or reduce the oil lubrication in compressor cylinders - but there is a price to pay: rings and bands have to be inspected and replaced as needed on a strict schedule.  Your engineering consultant should have known this and made this an issue to confront prior to purchase.

 

I hope that I’m wrong, but I doubt it.  If the data that you’ve sent is correct, then it indicates that you are starting to exceed the maximum discharge temperatures allowed for the machine.  If indeed you have plastic, composite rings and bands, then the situation is even worse.  This is all assuming that you have historically had better compressor performance with much lower discharge temperatures - until now or recently.

 

Your maintenance people are correct in making this machine due for an “overhaul”.  If indeed, you have non-metallic rings and bands in your pistons, they should prepare for a formal disassembly of the cylinders in order to gain access to the pistons and their rings.  There is no other way to ensure continuous, reliable operation from what is basically a good machine.  If you decide to take the machine down for a complete piston inspection and repair, I recommend you obtain the services of a certified Siemens Rand field engineer that is experienced in doing this type of job.  Unless your maintenance personnel have done this successfully before, I wouldn't do it any other way.  This is not a job for the faint of heart.  It requires experience, the correct tools, and excellent mechanical abilities.

 

I hope this helps you out.

Attached File  Hydrogen Compression Operating DataRev3.xlsx   12.36MB   14 downloads



#9 Phukan

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Posted 24 December 2018 - 06:58 AM

Dear Art,

 

I really get amazed by the amount of effort you always put in to guide engineers around the world fighting their daily challenges in this forum and elsewhere too. Whenever, I come to forums looking for some guidance, I tend to quickly scroll down to see if you are replying to; among few other practicing/retired veterans and more often than not your replies give me the impetus to dive deeper and look for a solution. Considering its time for festivities/ holidays especially at US, I thought I would get a late response. But BANG ON !!! you replied on the same day and I didn't even care to check, my bad. I haven't been able to see the details in excel sheet as I am in bit of hurry to perform a little gig on the Christmas eve party at my local club today. So Sorry to sound unprofessional. 

 

The compressor overall is planned through authorized vendor but for other details I must discuss with maintenance guys to give you a true picture. 

 

Until then Wish you a Merry Christmas and greetings for upcoming new year. I hope and wish you will keep enlightening our thoughts for many more years to come.



#10 Bobby Strain

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Posted 25 December 2018 - 01:13 PM

I keep only the best references in my library. Here you can find one for reciprocating compressors.

https://kupdf.net/do...5f723687054_pdf

 

Bobby



#11 Phukan

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Posted 25 December 2018 - 11:48 PM

Thanks Bobby.. This would be of great help






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