10 replies to this topic

[chemiboy11]

Hi all.
I have my final year project entitled "LPG separation from light naphtha"
I have been looking for this topic on the internet as literature survey but it has not been fruitful.
Can anyone please guide me where to read about this topic from?
Basically my concern is "where do I start from?"
Awaiting replies.

Thanks in advance.
Haris

[ankur2061]

Haris,

LPG is a mixture of C3 & C4 whereas my understanding about light naphtha is that it is mostly a mixture of C5 and paraffinic C6 with traces of lighter paraffins (C3, C4). So trying to recover trace amounts from light naphtha doesn't make economic sense.

Regards,
Ankur

[sheiko]

Hi,

Separation of butane and propane from naphtha can be done in saturates gas processing plants.

First, a naphtha range liquid is used to absorb propane and butane from the gas streams coming from the refinery processing units (containing methane, ethane, propane, butane and maybe hydrogen).

After that, propane and butane are separated from the liquid naphtha in a debutanizer.
The split is relatively easy given the difference in boiling point between naphtha and butane/propane. For example, butane starts to boild at 31°F while naphta starts at about 180°F.

Downstream the debutanizer there can be a depropanizer (to separate propane and butane) and maybe a deisobutanizer (to separate normal butane and isobutane).

As far as I know, the naphtha range liquid used in sat gas plants is not light naphta (wich is mostly pentane and hexane as pointed out by Ankur) but rather heptane or octane. But it shall depends on product availability in a given refinery...To be checked in your library or best: try to contact and meet professionals (process engineers preferably) from a refinery of your country to have more clue, your teachers will appreciate!

Edited by sheiko, 03 July 2012 - 05:20 AM.

[kkala]

Cracked gasoline, wild natural gasoline, similar stocks, contain dissolved gaseous hydrocarbons that tend to escape during storage. Gaseous or very low boiling materials are removed in stabilizers, columns with numerous fractionating plates. These are mentioned in Nelson, Petroleum Refinery Engineering, 4th edition (McGraw-Hill, 1958), stabilization, p. 242 - 248).
Other forms of stabilization can be applied in natural gas treating or in gas plants, e.g. http://books.google....ization&f=false '> http://books.google....ization&f=false , or http://sourcing.indi...what-gas-plant/ '> http://sourcing.indi...what-gas-plant/ .

[ankur2061]

Haris,

Recovery of C3 & C4 from Natural Gas Liquids (NGL) is a common operation in a Gas Plant which is a down-stream operation in the entire chain of upstream oil & gas processing. The NGL recovered from the treated gas (acid gas / water removed) is fractionated using a series of fractionators such as De-ethanizer, De-Propanizer and De-Butanizer to recover C2, C3 and C4.

However, in this entire treatment and recovery of C3/C4 (LPG) the term used is NGL and not Naphtha. Should your project be titled as:

"LPG Separation from NGL"

Also refer the link below for a gas-processing and gas-to-liquid plant:

http://www.fwc.com/p...PETER ALDER.pdf

Regards,
Ankur.

[sheiko]

Just to fix the OP's ideas:
NGLs consist of ethane, propane, butane, and natural gasoline (which basic constituents are pentane and hexane).

Edited by sheiko, 03 July 2012 - 05:16 AM.

[Padmakar Katre]

Hi all.
I have my final year project entitled "LPG separation from light naphtha"
I have been looking for this topic on the internet as literature survey but it has not been fruitful.
Can anyone please guide me where to read about this topic from?
Basically my concern is "where do I start from?"
Awaiting replies.

Thanks in advance.
Haris

Hi,
The only reference I could see with this topic is Crude Distillation Unit main fractionator overhead stream contains C1 to naphtha end point say ~ 170 C (purposely not specifying end point as every refinery has different product slates, range of naphtha). The lighters such as C1,C2 and some C3 are sent to fuel gas headers and the ovhd product is essentially unsaturated naphtha i.e. it has some lighters C4 and minus which need to be removed before naphtha is sent to storage. The same are recovered from Naphtha stabilizer which has ovhd vapors (balance C1/C2), LPG as distillate and stabilized Naphtha as bottom product.

[chemiboy11]

I am in agreement with Kkala and Padmakar S Katre.
As discussed with one of my teachers, I have found that what we are going to deal with is basically straight-run-gasoline/naphtha drawn from the top of an atmospheric column. We may be calling it light naphtha because it has lighter ends with it. So we need to strip out these lighter fractions from the top product to collect a distillate containing C1 through C3 (which will then be compressed to produce LPG) and a bottom product (almost) free from the lighter ends (this may be called medium naphtha or stabilized naphtha).

Now I am left with precisely two questions right now:
1. Can it be called condensate stabilization? (I am asking this because another group of students in my class has the project named as "condensate stabilization")
2. Do we need to use steam to strip out the C1, C2, and C3 components or is it only separation at elevated pressure?

Edited by chemiboy11, 06 July 2012 - 05:30 AM.

[kkala]

- We called it naphtha stabilization in a hydro desulfurisation unit (2005). This stabilizer was located just downstream of naphtha desulfurization and did not use stripping steam.
-Book by Nelson (most probably found in the library, reference in post No 4), page 246 / Fig 7-14 (*), treats wild gasoline through a combination of "natural gas stabilizer" (no tripping steam) and "stripping still" (using stripping steam).
Page 244 / Fig 7-13 of same book presents a stabilization scheme of raw natural gasoline with depropanizer, debutanizer, etc (without stripping steam); but this seems to aim at polymer grade butane (high purity).
Starting with a simple distillation scheme and trying to specify trays / conditions according to requirements and to assumed feed specification might be a way out (adding something more, if necessary).
However advice from someone having actual experience on crude distillation processing would be appreciated. I do not have such, having dealt with other refinery topics.

(*) Titled : Gas recovery and stabilization system.
I think a similar title would be OK (condensate may not be a good term) for your project.

Edited by kkala, 06 July 2012 - 07:49 AM.

[Padmakar Katre]

I am in agreement with Kkala and Padmakar S Katre.
As discussed with one of my teachers, I have found that what we are going to deal with is basically straight-run-gasoline/naphtha drawn from the top of an atmospheric column. We may be calling it light naphtha because it has lighter ends with it. So we need to strip out these lighter fractions from the top product to collect a distillate containing C1 through C3 (which will then be compressed to produce LPG) and a bottom product (almost) free from the lighter ends (this may be called medium naphtha or stabilized naphtha).

Hi,
In a naphtha stabilizer, mainly C1 and C2 with some C3 are withdrawn as the overhead gas and C3 and nearly total C4 as distillate product or LPG product. Bottom product is termed as stabilized naphtha which can be further used as gasoline blending component, feed to aromatic complex.

Now I am left with precisely two questions right now:
1. Can it be called condensate stabilization? (I am asking this because another group of students in my class has the project named as "condensate stabilization")

Condensate stabilization term is mainly used for separation of C5 and heavies from gas stream. If I start from the basics the gas/oil well will produce gas, oil and water. The condensate constituents are C5 and heavies can be termed as light naphtha. The terminology is different for gas plants and refinery. You will understand these terms in details once you will be a practicing process engineer.

2. Do we need to use steam to strip out the C1, C2, and C3 components or is it only separation at elevated pressure?

As I stated above, there is single column which operates at ~10 bar pressure, with a partial condenser at the top and a reboiler at the bottom and not the steam stripping.

[chemiboy11]

Yes, I get your point.
Now I am in search of feed data from a refinery operating here in Karachi. Once I get it, I will be working towards designing a real column. And the auxiliary equipment.