Centrifugal vs reciprocating ng compressors 1

[megero]

Hello everybody!

I am not a turbine machinery specialist and I would like some advice on the following issue: we need to feed a gas turbine with natural gas (approx. 65.000 Nm3/h) but the pressure of the ng system is relatively low. For this reason we need to install a natural gas compressor, to boost a bit (approx. 5 bars, from 40 barg to 45 barg) and keep the pressure at the inlet of the gt burner at a sufficiently high point. We are currently considering two types, centrifugal vs reciprocating. Since the no1 target is the minimization of the energy consumed in the compressor, what would be the suggested type?

Thanks in advance!

 

[nickelkid]

This paper should help you. It has been prepared by Centrifugal and Reciprocating experts.

 

[BigInch]

Generally the lower pressure boosts 2.5:1 or less can be accomplished nicely with centrifugal units. Higher pressures (and lower volumes) are more convenient to reach with recips.

I have not failed. I've just found 10,000 ways that won't work."-Edison “If Edison had a needle to find in a haystack, he would proceed at once to examine straw after straw until he found the object of his search. I was a sorry witness of such doings, knowing that a little theory and calculation would have saved 90% of his work.- Tesla

 

[toothless]

Wouldn't a reciprocating unit produce pressure undesirable pulsations in the fuel line to the GT?

 

[BigInch]

Pulsation bottles can mitigate those undesirable effects.

I have not failed. I've just found 10,000 ways that won't work."-Edison “If Edison had a needle to find in a haystack, he would proceed at once to examine straw after straw until he found the object of his search. I was a sorry witness of such doings, knowing that a little theory and calculation would have saved 90% of his work.- Tesla

 

[zdas04]

The document that RCHandy posted is a very good comparison. If you don't want to read all the words (there are a bunch of them) jump to the tables with the case study results.

If your goal is lower cost and your gas is reasonably light, then a recip fits that goal far better than a centrifigul almost all of the time. Considerations of pulsation, surge, oil caryover, etc. can all be engineered out of either machine through competent packaging.

In my practice, I say that the only time you want a centrifigul compressor is when energy density is the key design consideration (e.g., on an offshore platform). You can mate a centrifigul to a turbine and move a bunch of gas with very little deck space. Other than that, there are better ways to solve most problems.

I can't emphisise enough that a great package can get rid of most inherent disadvantages while a poor package can get rid of all inherent advantages.

David

 

[BigInch]

zdas,

Interstate gas transmission is virtually all done by centrifugals. In fact, I can't think of one recip I know of installed in an interstate transmission system (outside a liquid extraction plant), on a liquid or gas pipeline. I've only used gas recip compressors for gathering systems where relatively low volumes, small diameter pipe and high pressure ratios were the optimal solution, with little liquids and for very low volume and high pressure injection of blown down and interface fluids on crude oil and product lines.

I have not failed. I've just found 10,000 ways that won't work."-Edison “If Edison had a needle to find in a haystack, he would proceed at once to examine straw after straw until he found the object of his search. I was a sorry witness of such doings, knowing that a little theory and calculation would have saved 90% of his work.- Tesla

 

[zdas04]

Interesting, virtually all of the gas leaving the San Juan Basin for California (I think the number is around 6 BCF/d) leaves through a recip. A couple of years ago I visited several plants on South Kalimantan, Indonesia and the hp was about half recip and half centrifigul but when they idled a machine it was the less effecient centrifugal.

I know there are a lot of centrifugals onshore, but I've never seen the economic or technical analysis that put them there. Every time I've done that analysis onshore, the centrifugal comes up way short. I'm probably missing something when I run the numbers.

David

 

[BillBirch]

What about screw compressors?

 

[BigInch]

I find that surprizing as well. No argument. I obviously haven't worked everywhere.

A wider range of flowrates, much higher reliability, faster repairs and overall lower maintenance costs are supposedly the greatest advantages of centrifugals for transmission service.

I have not failed. I've just found 10,000 ways that won't work."-Edison “If Edison had a needle to find in a haystack, he would proceed at once to examine straw after straw until he found the object of his search. I was a sorry witness of such doings, knowing that a little theory and calculation would have saved 90% of his work.- Tesla

 

[zdas04]

Billbirch,
Pressures are too high for screws to be an option.

David

 

[dcasto]

pressures to HIGH for a screw, 850 psig at 10,000 ACM isn't big enough.

http://www.kocoa.com/Second page oil injected.htm

25,000acm/h at 60 BARG here too.

http://www.howden.com/NR/rdonlyres/...0-4B8300F22F2A/0/BrochureCompressorsScrew.pdf

The transmission companies got away from turbine centrifugal packages when gas was deregulated. Fuel became the KING and not a "rate base and the whole fuel cost could be passed on to the consumer" based industry imurged.

 

[zdas04]

I give. There are obviously screws out there that will handle the pressure. At 1.2 compression ratios, you might have a hard time getting enough temperature rise to cook off water, but there is certainly a way to solve that one (maybe run jacket water through the coalescing filter?) if the packager is savy enough to know there is a potential problem on the horizon.

Those are interesting machines, last time I got a quote from packagers who carry Kobelco and Howden, the packager was claiming long lead times (on the order of 56 weeks) for 350 psig MAWP machines, I'd hate to think how far out these beasts would be.

David

 

[dcasto]

zdas, you still need to get up here for that beer I owe you!

http://www.durangomountainresort.com/index.cfm?fa=feature.display&feature_id=208

 

[zdas04]

I went to the street fair you told me about, but I got there just after they closed. I looked for your booth, but it must have gotten torn down quickly.

What are the hours of the deal in Purgatory? I may have to go to Albuquerque on Saturday, but if I don't I'll be there.

David

 

[dcasto]

zdas, its downtown Durango this year

Other events are coming up soon. On August 23, United Way supporters in Archuleta County can play in the annual charity golf tournament. Also on August 23, residents of La Plata County can attend the 10th annual San Juan Brew Fest in downtown Durango. This event has been held at Purgatory at Durango Mountain Resort for the last nine years, but this year is moving to downtown Durango from 1:00 pm to 4:00 pm. The 10th annual San Juan Brew Fest will bring 20 brewers from all parts of the Southwest to Durango, and this year proceeds will benefit United Way.


Rats sorry we missed ya, we took first place in the fish cooking catagory for our blacken Talapia.