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Heavy Hydrocarbon Recovery From Natural Gas




Heavy Hydrocarbon Recovery From Natural Gas I have had several questions asked by entry level process engineers and even chemical engineering students studying petroleum engineering, about the various methods employed for heavier hydrocarbons recovery from natural gas and which one is better. While mentioning that there are many older methods which are gradually being phased out and newer methods being developed by technology licensors in the upstream oil and gas business, it is important to note that the method selected is governed by the type of hydrocarbon recovery that is desired by the operator of the gas plant and the end specifications of the lean gas after the recovery.

The purpose of today's blog entry is to provide a brief description of the most common methods for heavy hydrocarbon recovery from natural gas and what these methods are capable and their limitations:

The most common methods employed for hydrocarbon recovery in Gas processing plants are as follows:

1. Mechanical Refrigeration plants (using propane for refrigerant)

2. Lean Oil Absorption Plants / Refrigerated Lean Oil Absorption Plants

3. Turboexpander plants

Let us understand the application and / or limitation of each of these methods:

1. Mechanical Refrigeration Plants:

If the major purpose of a plant is to condition rich gas to meet certain pipeline specifications, the mechanical refrigeration plant may be the proper selection. Refrigeration is used to condition produced gas to meet pipeline hydrocarbon (HC) dew point specification, heating value specification, limited gas liquids recovery of heavier hydrocarbons such as C5+, or a combination of these objectives. The straight refrigeration plant is limited to chilling the gas stream to the range of -34°C (-29°F) to -40°C (-40°F). This limits product recovery to about 60 percent of the propane content at typical plant operating pressure

2. Lean Oil Absorption Plants:

The most efficient lean oil absorption plants recover only about 40 percent of the ethane, 90 percent of the propane, and 100 percent of the butane and heavier hydrocarbons from the gas. Additional heat is required to separate the products from the lean oil, and additional cooling is required in order to reliquify the raw products before fractionation. Lean oil absorption plants usually have higher operating costs than either refrigeration plants or turboexpander plants.

3. Turboexpander Plants:

Turboexpander plants can recover from 60 to 90 percent of the ethane, 90 to 98 percent of the propane, and 100 percent of the butane and heavier hydrocarbons from the gas. These plants are compact and relatively simple to install and operate, if designed properly. The inlet gas to a turboexpander plant must have essentially all of the water removed (to 1 ppm or less) to prevent hydrate formation. Turboexpander plants have less process equipment (towers and external heating) than lean oil absorption plants, but they have more mechanical equipment (gas exchangers and re-compressors). If ethane recovery is the objective, the expander process is the most economical means for recovering a high percentage of ethane and heavier hydrocarbons from a gas stream.

The above mentioned guidelines are very general in nature and there can be specific instances where a particular method with certain adaptations may be more suitable for a particular heavy hydrocarbon recovery in contradiction to the guidelines provided above. Many technology licensors today are providing state-of-the-art technology for selective and optimum heavy hydrocarbon recovery from natural gas and readers of this blog entry are well advised to search for more efficient and economical methods offered by some of these technology licensors.

A flow scheme for a turboexpander and refrigeration plant is provided as an attachment,

Readers are also advised to read through the chapter titled:

Section 16, Hydrocarbon Recovery, GPSA Engineering Databook, 11th Edition (SI units)

Looking forward to comments from the readers of "Cheresources".

Regards,
Ankur,

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Appreciate your sharing, please would you tell me more about "split vapor", sub-cooled processes in Gas processing and any update? as far as I know, the 3 methods mentioned above will be sometime applied for a gas processing process.

Thank you.
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Mainak Sarkar
Apr 10 2012 10:40 AM
What are the recent technologies for using Natural Gas condensate?
What do you mean by "using" natural gas condensate? Your question is very vague.
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Mainak Sarkar
Apr 11 2012 10:47 AM
Is there any particular use of Natural gas condensate or it is sent to steam reforming unit? I am asking this question since, somebody form GAIL has said me that they are looking for some technology to convert Natural gas condensate to some value added product. As I know, Natural gas condensate is a low value product, since it has low octane number to blend it in the MS pool.
I don't know who told you that NGL products are low value products because by fractional distillation of NGL you can directly obtain hydrocarbons such as ethane, propane an butane which are precursors to most petrochemical plants. Try having a look at the following link:

http://en.wikipedia....-gas_processing

Regards,
Ankur
Could I suggest two more technologies: J-T Valve and adsorption?
The J-T valve plant uses the adiabatic cooling created by simply depressurising a high-pressure gas across a valve. As for the refrigeration and turbo-expander plant, the balance of the plant uses gas-gas heat exchange and separators.

Adsorption processes use beds of silica gel or mol-sieve adsorbent to remove the heavier hydrocarbons and other components from the gas (including water). Regeneration of the bed using a pulse of heat reduces the regeneration time and increases the effective capacity of the bed. This technique works best on gas where the dewpoint is dependent on the removal of small quantities of heavier components (C7+) - typical of underground storage systems

What about LPG extraction?

Dear Sir,

It's very nice of you to introduce all the listed methods.

We are producers of Membranes for hydrocarbons recovery.

Let me say that the marketing of the project is rather complicated.

i\m aware of the negative aspects of the methods, but still there are and positive as well.

 

Shall appreciate if you find possible to share your knowledge or experience with related Membranes, sure if you have any 

 

Thank you in advance. 

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