5 replies to this topic

[raxza]

Anybody knows about NGL extraction from gas pipeline? The situation is like this:
We have a gas pipeline running about 450 km (32", 275 MMSCFD), we've got a proposal from Company (say it Company A). Company A want to take our gas and extract the NGL (heavy hydrocarbon fraction, C2-C7+) . The gas will be routed to their plant (the tapping point is located in km-350) and they extract the NGL with cascade refrigeration and the residue gas will be sent back to the pipeline. I think it will be the first NGL extraction from the pipeline in my country. I want to ask anybody who have experience in this kind of project...
(Note that we don't sell the C2-C7 in liquid form)

1. Is it common to extract NGL from the pipeline because all I know that the NGL extraction usually occur in the gas processing plant before sent to the pipeline. What about the continous supply of the pipeline for our customer downstream this NGL plant?
2. What about the pricing of the NGL, is it the same with the gas price or is it difference regarding to the substance (not the energy), e.g C3 price is higher than C2, and C2 price is higher than the natural gas pipeline.

Thank You.

-Raxza-

[Art Montemayor]

Raxza:

I have participated in the development and design of NGL (Natural Gas Liquids) plants. I can answer your questions. However, if this thread is to continue, I think it best if you fully identify as much background information and data as possible in order to better address and answer your queries in a manner that is best understandable to you. For example,

1) Are you a Chemical Engineer; are you familiar (experienced) in hydrocarbon processing?
2) Will the NGL’s be further processed to make downstream products or will they be simply distributed as liquid fuel (propane, butane) to remote or underdeveloped areas of your country?
3) Are the natural resources (the hydrocarbons) nationalized in your country? I presume they are.
4) Does your country presently process or produce other hydrocarbons – such as crude oil?
5) What part of the world is your country in? Mid-East? Far East?
6) What is the size of the NGL plant in capacity? Or, better yet, what is the composition of the natural gas?

Now to answer your questions.
1) It is very common to extract NGLs from natural gas (NG) pipelines prior to distributing the NG to sales markets where it is used as a fuel – principally for domestic and commercial residences. Natural gas is composed of Methane, Ethane, Propane, Butane, and other heavier hydrocarbons. Water and other impurities such as CO2, H2S, COS can also be in it, but these are removed prior to transporting the NG through major pipelines in order to avoid corrosion and other operating problems.
From a fuel application standpoint, it is more desirable to sell the NG as essentially pure Methane and dedicate the heavier hydrocarbons (especially ethane, ethylene, propylene) to sales as feedstock for further processing and conversion into other chemicals. The pricing for fuel is based on the BTU CONTENT of the fuel itself. The pricing of fuel is based worldwide principally on the OPEC pricing for crude oil. However, chemical feedstocks demand a higher price usually because of the market demand for such stuff. Therefore, this is the incentive to remove the NGLs from the natural gas and market them separately. It is considered wasteful and uneconomic to literally burn such unsaturates as ethylene and propylene when they can be used as feedstock to make plastics and other chemicals.

2) The NGL is usually priced as a chemical commodity – not as a fuel. Therefore, the market demand and the availability set the price. This, as I stated previously, is different from the pricing for fuel stock – which is based on world energy prices dominated by OPEC. But a lot of other factors enter into the pricing question. If you have a socialist government, then there is probably a locally subsidized price for fuels. Of course, I’m assuming a truly serious socialist government; I’ve been in -and lived in- socialist countries where the natural resources were being stolen or pilfered by corrupt government officials, so that local prices were set to please them – not to serve the national interest. But that’s a political problem, not an engineering problem. My point is that your government sets the pricing rules in place and I can’t speculate without knowing where you live and what government you answer to. When a local government undertakes to socialize the natural resources and imposes a monopoly on their production and sale, then obviously you and I have very little to say about it. However, if that same government intends to sell or deal with outside entities or countries, then they have to negotiate the pricing of their national products if they intend to compete on an international level. I know this because I’ve served as consultant to the World Bank on energy projects in the past.

Basically, when liquid hydrocarbons are extracted from a natural gas pipeline nothing happens to interrupt or affect the availability of the basic (Methane) NG to its national fuel market. The supply of NG continues nevertheless. In some developing countries it is far wiser and more efficient to undertake the distribution of LPG (propane + butane) in compressed, liquid cylinders to those remote and underdeveloped areas of a country in order to give people there the facilities of having a reliable and economic fuel supply for cooking, bathing, and other needs. The pipelined NG (mostly methane) is then routed to the more densely populated and affluent areas of the country that can economically justify a pipeline. This system of energy distribution is actively practiced even here in the USA. Remote farm and rural communities cannot justify a pipeline and normally are supplied their energy needs by using LPG cylinder distribution. This LPG normally originates in an NGL plant located on a near-by main natural gas system. The same may apply to your country or local situation.

Depending on the “wetness” of the feed NG (the content of NGLs), normally a cryogenic type of process plant is employed to remove the NGL from the parent NG. This is the current state-of-the-art. A “cascade” type of refrigeration process may be used or a turbo-expander process may also be incorporated. The capacity, the feed analysis, the location, and the economics all play a factor in determining the design and selection of the NGL plant. If you are interested in reading further about the removal of NGLs, I recommend you read John M. Campbell’s book – “Gas Conditioning and Processing”.

I hope this answers your questions.

[gvdlans]

Just to prevent any confusions:

Natural gas does not contain unsaturates such as ethylene or propylene. Natural Gas Liquids contain mainly ethane and propane that can subsequently be converted to mainly ethylene and propylene in an Ethylene (Olefins) Cracker. Ethylene and propylene are of course important feedstocks for e.g. polyethylene, polypropylene or (poly) styrene plants.

[Art Montemayor]

Raxza:

Thanks to Guido for kicking my cage and setting me straight. After having the website down for over a week, it took time for me to wake up and note the obvious error I typed in my response.

Guido's close scrutiny and watchful eye keeps me honest and awake. He points out the obvious and common sense description of natural gas: coming from a long, long stay under the earth, it wouldn't be "natural" for natural gas to be unsaturated after such a long time lingering under so much pressure and reaction opportunities under the earth. It is the 2+ carbon molecules of the high boilers that are valuable raw material for the plastics and chemical industries - ethane, propane, etc. and the ones that are sought after in a NGL plant.

I forgot to add that your gas should be coming from an associated gas field if it is expected to be rich in the condensable liquids that can be extracted.

I hope I did not confuse you and others with my writing words that were not in the same wave length as my thinking and knowledge. Sorry.

[gvdlans]

Art,

I read about your illness on the eng-tips forum, and just want to say that I am glad you are back and recovering well. It was getting a bit quiet around here... I hope to see many more of your valuable contributions to the industrial safety and chemical engineering society. Your recent post on the filling of a hot oil tank in Sudan showed that you did not loose any of your sharpness.

About the unsaturates, this was a typical slip of the pen. I just wanted to prevent confusions.

[raxza]

Thanks for all your replies.......

Art, to answer your questions

1) Are you a Chemical Engineer; are you familiar (experienced) in hydrocarbon processing?
Yes, I'm famiiliar but not well experienced

2) Will the NGL’s be further processed to make downstream products or will they be simply distributed as liquid fuel (propane, butane) to remote or underdeveloped areas of your country?
The NGL will be further processed (esp. C2) to ethylene by OTHERS. The rest NGL will be distributed as liquid fuel.


3) Are the natural resources (the hydrocarbons) nationalized in your country? I presume they are.
Yes

4) Does your country presently process or produce other hydrocarbons – such as crude oil?
Yes

5) What part of the world is your country in? Mid-East? Far East?
My country is in far-east

6) What is the size of the NGL plant in capacity? Or, better yet, what is the composition of the natural gas?
The size (feed gas is 275 MMSCFD) with composition : C1 81%, C2 4%, C3 3.5%, iC4 0.7%, nC4 0.94% iC5 0.3%, nC5 0.16%, CO2 4%, H2O 0.015%, the rest are N2 and C6+.

Remember that this gas composition is sales gas quality so to remind you that the gas pipeline will be extracted in the middle of the pipeline not in the beginning (prior to) gas pipeline. I know that NGL extraction usually occur in the gas plant (wellhead gas processing into the NG pipeline)--and I familiar with this type of plant but what about my case.

Thanks for the explanation about pricing--I'll inform this to my marketing colleague.