Recip Packing 1

[zdas04]

I'm reviewing some new proposed EPA air regulations (U.S.A) and one of them jumped out at me. For recips in natural gas service after the well site and before the city gate, operators of recip compressors will be required to replace (and document in submittals to the EPA) all compressor packing every 26,000 hours of operation (less than 3 years of continuous operation).

It doesn't mention an acceptable leakage rate or allow alternative methodologies to control emissions (just off the top of my head it seems like the emissions could be reduced to near zero by building a distance piece rated for 3-5 psig and porting the distance piece to a flare or VRU).

Does anyone have a feeling for how long packing is supposed to last? Also, what is the cost to replace the packing on a cylinder and how long would the machine be out of service?

Comments to the agency are due in a couple of weeks so any ideas need to come in pretty soon.


David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

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[pmover]

i'm surprise no response to this . . .

Dave, let me call someone tomorrow (employed by an P/L operator) and I'll post a response . . . that is if I remember to call. I've got CRS really bad lately . . .

-pmover

 

[pmover]

sorry for the delay . . .

we spoke today and there are variables that impact the longevity of packing (i.e. quality of gas, materials, rod surface, rod drop, material of packing used, etc.). the application/service even has a factor. he suggested contacting CECO (1-800-try-CECO) for further assistance.

btw, his first inquiry/response was whether or not the request had anything to do with the EPA. apparently, he is aware of these "proposed regs" . . . not too favorable either . . .

i've not read the proposed EPA regs - can you post a link (if available).

the distance piece and flaring or using a VRU will be $ - though not a bad idea.

good luck David.
-pmover

 

[zdas04]

The rule is at EPA Proposed Rule, it is 106 single spaced, three column pages of an 8 pitch font. You'll need something stronger than coffee to get through it in one sitting (the pre-release version was single column, double spaced, 10 pitch font and took 604 pages). The compressor stuff is just a few pages, but it mostly isn't together so you have to jump around and it can be fun to tell where the search took you.

David

 

[JJPellin]

We do not have any reciprocating compressors in natural gas service. The majority of ours are in Hydrogen service. I would expect pressure packing to last at least 5 years. With proper lubrication, 10 years would not be unreasonable. Some of our packing cases are cooled using the same circulating glycol system that cools the cylinders. Some of our packing cases are nitrogen purged. We do have distance pieces that are vented to flare to contain any packing leakage. However, pure hydrogen streams are usually exempted from emissions regulations. The main problem with allowing any pressure to build in the distance piece is a safety concern. If you have scrapper packing and wiper packing and an additional chamber between the flare vented section and the frame, you can be sure that you will never build-up process gas in the frame. Process gas in the frame (either natural gas or hydrogen) would pose an obvious safety risk.

Most of our reciprocating compressors have rods 3 inch diameter or larger. To replace the main pressure packing, I would expect the compressor to be out of service for 2 days or more. I would probably schedule the job for 5 days in case they found any other problems. Some compressors are very difficult to repack around the rod. If the piston and rod has to be pulled, this will obviously increase the time required.


Johnny Pellin

 

[zdas04]

Thank you for that. The new rule is all about carbon, so hydrogen compressors would be excempt.

David

 

[JJPellin]

I consulted with our recip compressor program engineer. He felt very strongly that you should never replace packing based on time alone. New packing has a break-in period when the leakage will be higher than it would be with older packing. And infant mortality based on installation problems or manufacturing defects is not uncommon. If you also account for the additional emissions that are likely to be released when preparing the machine for maintenance, a time-based replacement program would probably result in higher environmental emissions that a condition based program.

Johnny Pellin

 

[zdas04]

Thank you, I forwarded that to the guy preparing API's response to the compressor part of the rule.

David

 

[BNiessing]

Assuming you have spare packings rings on site, it should not take more than a couple hours to replace a cylinder packing. I've replaced all the rings on our manufacturing floor in 30 minutes or so.

Per my interaction with packing OEMs as a compressor engineer, a cylinder packing in good condition will leak approximately .1SCFM . Rod finish, case condition, gas properties and many more factors can influence the above rule of thumb rate.

Regarding methods to reduce emissions, several packing OEMs (CECO, Hoerbiger, COOK) offering static pack which seal both dynamically (during operation) and statically (during shut down). New low emission rings are available to reduce emissions (limited available data). Nitrogen purging is also a viable method to reduce packing leakage.

Brian
Dresser-Rand

 

[CaracasEC]

Usually replacing a packing for reciprocating compressor takes hours, the only time consuming is preparing the machine i.e blinding,purging and after maintenance is deblinding and drying.