32 replies to this topic

[Art Montemayor]

Snorm:

 

I have in the past accumulated many years of experience in the compressed gas industry and, consequently have dealt with gas compressors.  I have compressed most – if not all – of the recognized industrial gases including most gaseous hydrocarbons.  In doing so I had to size, specify, select, install, operate, and in some cases convert compressor gas service between gases.  It is difficult to be specific in addressing your application because you don’t identify:

 

• If the compressor is oil lube or non-lube;
• If the pistons are single or double acting;
• If the pistons are conventional or trunk type;
• The compressor speed or rpms;
• If the drive is an engine or an electric motor;
• If the driver is connected via V-belt or direct;
• How you intercool between the first & second stage.
• What type of valves are used on both stages.

 

I’m forced to assume:

 

• The compressor uses trunk type pistons;
• The compressor crank, connecting rods, and piston rings are splash oil lubricated;
• The compressor crankcase and cylinders are lubricated with DTE-40 or similar oil;
• You have no capacity controls and the compressor runs at constant speed.

 

The compression ratio per stage is limited for any compressor by the need to limit the discharge temperature.  As the ratio per stage increases, the discharge temperatures also increase.

 

Discharge Temperature

The discharge temperature for any single stage of compression can be calculated from:

 

Td = TS (Pd/PS)^(k-1)/k

 

Where:

T_d = Stage discharge temperature, K (°R)

T_S = Stage suction temperature, K (°R)

P_d = Stage discharge pressure, kPa (psia)

P_S = Stage suction pressure, kPa (psia)

k = Ratio of gas specific heats, C_P/C_V = 1.4

C_P = Specific heat at constant pressure

C_V = Specific heat at constant volume

 

When applying reciprocating air compressors, the basic, iron clad rule is to limit all cylinder discharge temperatures to below 250 – 275 °F to ensure adequate piston rod packing life and to avoid lube oil degradation.  At temperatures above 300 °F, eventual lube oil degradation is very likely, and if oxygen is present, ignition is possible.  Under no circumstances should the discharge temperature be allowed to exceed 350 °F.

 

This rule is not based solely on common sense; previous serious compressor cylinder explosions have proven the veracity of the rule.  I personally have visited two explosion sites and the resulting damage was not pretty.  One involved two deaths.  So, if you are presently compressing air from 12.5 psia (at 4,500 ft above sea level) to 45 psig, you have a compression ration for your first stage of 3.8.

 

With this lengthy explanation of how a reciprocating compressor’s discharge temperature is estimated and why it is limited, I think your first stage discharge temperature is in the vicinity of 340+ ^oF and your second stage is around 430+ ^oF – both well above anything I would operate a lubricated air compressor cylinder under.  I would refuse to operate the compressor under these conditions.  You can verify my explanation with any reliable air compressor manufacturer.

 

I hope I have clearly explained what I believe to be factual and actual information regarding the compression of air in reciprocating compressors.  Major operating companies – like Exxon oil for one – will back up what I stated.  I also hope you are successful in working safely with the proper air compressor.

 

P.S. - go to: https://qa.oges.info...perature-normal

and you will find I'm not the only one with the bad news.

[breizh]

Hi,

To add to this topic:

https://www.detechti...t is,C (300°F).

 

Good luck

Breizh 

[Art Montemayor]

Snorm:

 

I hate to extend the length of this thread with yet another post, but such is the importance that I have always given to safe gas compressor operations that I felt obligated to supply you with further details and background regarding the comments and recommendations I offered in my last post.  Basically, my last words were that I do not recommend the operation of the air compressor that you defined as giving you problems.

 

I have gone back and further read what you describe as the LeRoi model you have and I believe it resembles the type I submit in the attached drawing below.  I am very familiar with this type of machine.  I used this type in some refrigerating projects that I designed and operated.  I’ve never used a LeRoi compressor.  By the specifications you furnish, I never would recommend – much less employ – the model you describe.  I’ve gone thru the Internet looking for the LeRoi model you describe and can’t find it.  But what you describe fits a direct-driven, high-speed machine with trunk-type pistons (no cross head) and splash oil lubrication direct from the connected crankcase.  This type of description, when applied to air compression, is an application I would never contemplate or consider for field, steady operation.

 

To reinforce what I consider as a high-risk, hazardous air compressor design, I am attaching also a .pdf document from the U.S. government discussing exactly what I have mentioned and detailed.  After reading about your situation and field application I cannot refrain from trying to give you some of the hard, actual field experience I’ve accumulated regarding safety in this type of application.  I think it is my duty to share this experience with you.  You will note that I have made extensive notes in the .pdf document because it is a product issued exactly when I graduated as an engineer in 1960.  Since that time the industry has improved tremendously in know-how.  However, it is not presently against the law to manufacture and sell what I consider inherently hazardous equipment to ill-advised or economy-minded engineers.  Consequently, there are some gas compressor designs that, in my opinion, should never be regarded as safe to operate in the field – especially in relatively remote sites.  I hope this information helps you out in remaining safe and productive in all your field operations.  If you have further doubts or questions on this application, please feel free to express them in this Forum.  Our members are serious professionals and we all are, I believe, dedicated to foster and promote safe field engineering applications.

 

 

 U.S. Govmnt on Air Compressor Safety - 1960.pdf   1.03MB   9 downloads

 

 Vilter Model 4416 Compressor.jpg   68.28KB   0 downloads

[Bobby Strain]

Snorm,

   I must defer to Art's advice. So, for now, ignore any suggestions that I provided. And don't increase the operating pressure! I will, however, contact Siemens for more information on your compressor.

 

Siemens Energy Global GmbH & Co. KG
Siemens Energy
Customer Support
Tel.: +49 911 6505 6505
E-Mail: support@siemens-energy.com

 

They asked for the following information:

 

Technical Data:
       Serial-/ Fabrication-/ Machine- / Contract Number:
       Equipment Number:
       Project Name and Location:
       Photo of the Equipment / Equipment Name Plate:
 
End Customer's Contact Information:
       Company:
       Country:

 

I'll ask for information about compressor expected performance. Provide what information you can. Meanwhile, you should contact whomever supplied your compressor and ask their advice. I will do a bit of research, too. Something to look at is superior lube oil. Synthetic for instance.

 

Bobby

bobby@bobby-strain-group.com

 

30 CFR § 56.13010 - Reciprocating-type air compressors.

• CFR

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§ 56.13010 Reciprocating-type air compressors.

(a) Reciprocating-type air compressors rated over 10 horsepower shall be equipped with automatic temperature-actuated shutoff mechanisms which shall be set or adjusted to the compressor when the normal operating temperature is exceeded by more than 25 percent.

( However, this standard does not apply to reciprocating-type air compressors rated over 10 horsepower if equipped with fusible plugs that were installed in the compressor discharge lines before November 15, 1979, and designed to melt at temperatures at least 50 degrees below the flash point of the compressors' lubricating oil.

Edited by Bobby Strain, 28 May 2022 - 05:22 PM.

[Bobby Strain]

Art,

 Maybe you should send Snorm an email to be sure he looks at your comments.

 

Bobby

[Snorm]

I have read and understand your posts I will keep you posted I will provide model numbers etc.
Thanks for your concern

[Snorm]

https://ndsdrillings...compressors.pdf

[Snorm]

That link is the same manual I have