Natural Gas Dehydration Processes Natural Gas GasDehydrationProcesses Petroleum Gas Technology

1. Koya University
Faculty of Engineering
Chemical Engineering Department
3rd Stage (2021-2022)
Instructor
Mr. Ribwar K. Abdulrahman
Prepared by
Safeen Yaseen Jafar
Rekar Hamza
Ibrahim Ali
Rekan Kazm
Submitted Date
5 Nov. 2021
Petroleum Gas Technology
Natural Gas Dehydration Processes

2. Table of Contents
Abstract ............................................................................................................................................................................1
1. Introduction..................................................................................................................................................................2
2. Literature Review ........................................................................................................................................................3
2.1 Hydrates and its formation...................................................................................................................................3
2.2 Hydrate Properties ................................................................................................................................................4
2.3 Structure of hydrate ..............................................................................................................................................4
3. Methodology.................................................................................................................................................................5
3.1 Gas Dehydration Methods. ...................................................................................................................................5
3.1.1 Absorption Process .........................................................................................................................................5
3.1.2 Adsorption Process .........................................................................................................................................7
3.1.3 Less common dehydration methods..............................................................................................................9
4. Results.........................................................................................................................................................................10
5. Discussion ...................................................................................................................................................................11
6. Conclusion ..................................................................................................................................................................12
7. List of References.......................................................................................................................................................13

3. LIST OF FIGURES
Figure 1 ............................................................................................................................. 2
Figure 2 ............................................................................................................................. 3
Figure 3 ............................................................................................................................. 4
Figure 4 ............................................................................................................................. 5
Figure 5 ............................................................................................................................. 6
Figure 6 ............................................................................................................................. 7
Figure 7 ............................................................................................................................. 8
Figure 8 ............................................................................................................................. 8
Figure 9 ............................................................................................................................. 9

4. 1
Abstract
Natural gas is the important source of energy and it can be converts and make it very useful
source to daily use by process it by several processing which called as Natural Gas Processing.
However, these processes of natural gas include important process. so, because of that during this
essay we talked about the most important process of the gases which called and it will be mention
in this report as Natural Gas Dehydration Process. Its main purpose to remove the water (in vapor
phase) content from the natural gas because of its harmful and poisons on the flowlines (pipelines).
In this report also we discuss about the hydrates, their properties and how we can select or use
them.

5. 2
1. Introduction
As we know the natural gas is the gas which obtained from natural underground reservoirs
(source of gases or gas well), it is generally contented huge quintiles of methane CH4 along with
heavier hydrocarbons for instance, ethane, propane, butane, etc. Because natural gas exists in
underground reservoirs it can contain various impurities in varying amounts for instance, carbon
dioxide and hydrogen supplied also water vapor. So, water vapor should be removed or reduced
to small quantity from raw gas pipelines to prevent any problems for example (hydrates). If water
vapor is permitted to stay in natural gas, it will: Decrease a pipeline's efficiency and capacity.
Corrosion will eat holes in the pipe or vessel that the gas goes through. In pipelines, valves, or
vessels, form hydrates or ice blocks. [1]
Humidity is generally present in natural gas from wells. When gas comes into touch with
an aqueous solution of a solvent, such as methyl diethanolamine, used to eliminate the acid gases
in the raw gas, it becomes wet in the sweetening unit of a gas processing plant. Dehydration is a
step in the natural gas processing process that must be completed in order to meet pipeline
specifications. Processing natural gas to meet pipeline requirements Water must be removed from
the gas handling system to avoid condensation of an aqueous phase, which can lead to hydrate
development and corrosion. The purpose of this paper is to review commercial natural gas
dehydration processes and recent developments which impact the installation and operation of
these facilities. [2]
In 1810, Sir Humphrey Day discovered Gas Hydrate. The oil and gas industry grew
interested in analyzing and exploring hydrate when Hamrnerschmidt identified the first pipeline
obstacle in 1934. The crystalline, non-flowing structure of hydrates was the reason behind this. By
Figure 1: Glycol Dehydration System

6. 3
following WW II, the natural gas transmission and processing industries flourished at a breakneck
pace. Dry desiccant was still used in most dehydration installations, although silica gel has
surpassed activated alumina as the most used desiccant. Silica gel had a larger water capacity and,
if required, could be used to extract heavier hydrocarbons from the gas. [3]
2. Literature Review
2.1 Hydrates and its formation
Gas hydrates can be defined as “the solid material which formed in the shape of crystal
because of the chemical mixture of N.G and H2O which pressurized at the temperature that above
the freezing point temperature of H2O.” they have many chemical formulas which combined with
water as we mentioned in the definition of it such as: Methane (+7 H2O), Ethane (+8 H2O), etc.
Hydrate formation: in the science of chemistry, we have reactions, reaction between hydrocarbons
with water and they cause to formation of the Hydrates. [4]
Why control the hydrate important?
Gas hydrates are unwanted substances that can occur during the production or
transportation of natural gas in petroleum technology. On the other hand, substantial deposits of
gas hydrates have been discovered in nature. These resources are currently being looked at as non-
traditional energy sources. [5]
Some hydrate controlling methods for subsea systems include:
➢ Pressure Control.
➢ Temperature Control.
➢ Remove Water.
➢ Inject Chemical Inhibitors.
Figure 2: Gas hydrate sample that formed by (Methane
and Water molecules)

7. 4
2.2 Hydrate Properties
They have a lot in common with regular ice in terms of look and qualities, with one notable
distinction. At temperatures over 32°F, which is the freezing point of water, hydrates develop. The
generation and dispersion of gas hydrates is regulated by pressure and temperature, gas
composition, reservoir water salinity, and the features of the permeable medium in which they
formed. They have a lot in common with regular ice in terms of look and qualities, with one notable
distinction. At temperatures over 32°F, which is the freezing point of water, hydrates develop. [6]
2.3 Structure of hydrate
Clathrates are crystal formations in which water molecules form a hydrogen-bonded
cage-like structure that is stabilized by 'guest' molecules within the lattice. The three hydrate
structures that have been found so far are Structures I, II, and H. [7]
Figure 3: Gas hydrate structure types a) Structure I, b) Structure II and c) Structure H in nature.

8. 5
3. Methodology
3.1 Gas Dehydration Methods.
Natural gas can be dehydrated by several methods. The two most method that we have here
are Absorption and Adsorption Processes.
1. Absorption: Glycol System.
2. Adsorption: in this process a hygroscopic substance used as a dryer (drying agent).
3. Condensation: Cooling with injection of hydrates inhibitors (glycols or methanol).
4. Membranes: Based on elastomer or glassy polymers.
Figure 4: Real dehydration process plant.
3.1.1 Absorption Process
Absorption process: is a method include gas processing, gas sweetening, and glycol
dehydration. A sufficiently pure liquid solvent stream absorbs and dissolves the water in a gas
stream. The process of stripping involves moving the water in the solvent to the gas phase. The
terms regeneration, reconcentration, and reclamation are also used to describe stripping since the
solvent is recovered for reuse in the absorption process. [8]

9. 6
Table 1: Properties for MEG, DEG, TEG, TREG and water
Process (Glycol System) Description:
If we want to know how the dehydration plant works, we need to look the diagram below
to understand as good. So, this is simple. The wet gas is introduced to dry glycol, which absorbs
water from the gas. Wet gas enters the tower at the bottom. So, dry glycol drips from the top of
the tower, by packing material or from tray to tray, to the bottom.
Absorption Process of the Water Process by Glycol – P&ID
Figure 5: Absorption by using dry glycol system

10. 7
Absorption of water from gas using glycol (Process Details)
The innovative bubble cap (as shown in Figure 5)
construction improves gas/glycol interaction while reducing
water levels to less than 5 lbm/MMcf. It is feasible to create
systems with values as low as 1 lbm/MMcf. The dehydrated
gas is channeled to the pipeline or other processing equipment
from the top of the tower. The water-rich glycol is routed to the
reconcentration system when it exits the bottom of the tower.
In the reconcentration system, the wet glycol is screened for
impurities and heated to 400 degrees Fahrenheit. The purified
glycol makes its way back to the tower, where it comes into
contact with moist gas once more, releasing the water as steam.
The entire system is self-contained and does not require human interaction. Pressures,
temperatures, and other aspects of the system are monitored by controllers to ensure proper
operation. [9]
Process Advantages:
▪ Pressure differences across the unit are relatively low
▪ Small working costs
▪ Capable of handling input gases containing high levels of particle contaminants, which can
destroy solid sorbents.
Process Limitation:
▪ The treated gas temperature has to be above 40° С
▪ Moderate level of dehydration.
▪ Possible foaming of sorbents. [10]
Glycol Dehydration Unit – PFD
In a TEG dehydration machine, natural gas drying stages were integrated with glycol
regeneration activities. To begin, a feed gas intake feeds natural gas mixed with water vapor into
the gas scrubber, which eliminates any free water. This method removes the bulk of the water
suspended in the gas stream, as well as particle pollutants and free hydrocarbons. However, the
natural gas is still considered "wet" at this point and must be dried further.
Figure 6: Glycol dehydration
system bubble cap

11. 8
Figure 7: Process of Dehydration by TEG system.
3.1.2 Adsorption Process
Adsorption is a physical phenomenon in which some of a gas's molecules condense when
they come into contact with a solid surface. The adsorption process of dehydrating a gas with a
dry desiccant involves the desiccant absorbing and removing water molecules from the gas stream.
Adsorption is a sort of adhesion that occurs between the surface of a solid desiccant and the water
vapor in a gas. Water leaves a thin layer on the desiccant surface that is held in place by
gravitational forces rather than chemical reaction. A desiccant is a granular, solid drying medium
with a large effective surface area per unit weight (a large number of tiny holes). Desiccants such
as alumina, silica gel, and molecular sieves are commonly utilized.
Figure 8: PFD of the typical adsorption process

12. 9
A slipstream (usually ten percent – twenty percent of the R.G/Raw Gas) is used as
regeneration gas in the process arrangement indicated in Figure 4. The regeneration gas is
removed upstream of the control valve and reinjected into the adsorption circuit downstream of
the control valve to provide the driving power required to cycle the gas through the regeneration
loop. This control valve provides the complete driving force for the regeneration gas circulation.
[12]
Advantages of Adsorption Method:
▪ Exceptional service life of adsorbent
▪ High depression of the low water dew point level can be reached across a wide process
parameters scenario
▪ The quality of dehydration is hardly affected by changes in temperature and pressure of
the feed gas
▪ Simple and reliable process
Adsorption Method Limitations:
▪ Large capital expenses
▪ High operational expenses
▪ Adsorbent is prone to contamination which requires frequent cleaning and may lead to a
replacement
▪ Failure to reliably provide an uninterrupted production cycle. [13]
3.1.3 Less common dehydration methods
While condensation, membranes, and other methods may clean complicated gases, they
are most typically utilized to remove a large number of impurities from raw supply gas.
Adsorption is a terrific approach to handle gas in this respect, although condensation and
membranes are crude methods. Condensation is commonly utilized when low water and
hydrocarbon dew point values 0-20 °C are required; membranes are similar but have the ability
to remove some of the acid gas component. [14]
Figure 9: Natural gas dehydration by
membrane technology

13. 10
4. Results
Now we know there are a several methods can apply on natural gas to remove water content
from it. So, we need to choose a best method for save and require less cost and give us a more
availability of safety.
Absorption is the most important and best method of dehydration because usually in this
method we use glycol system as we mentioned during this report such as Triethyleneglycol. TEG
while absorption require less temperature and pressure to proceeds. Because of its high boiling
point and decomposition temperature, TEG is more readily regenerated in an atmospheric stripper
to a concentration of 98-99.95 percent. Temperature losses during vaporization are smaller than in
EG or DEG. The cost of capital and the cost of operation are both cheaper.

14. 11
5. Discussion
Now we know that which method is best or give us low cost to produce the sale gas. So,
we learned all process requirements which need to choose the water remover in our gas
processing plant. So, finally we can summarize and enumerate advantages of the absorption
process as well as follow points:
1. Absorption process by glycol system is less expensive than adsorption operation.
2. Anytime we can change the glycol by another glycol without shutdown the process.
3. Glycol changing is cheaper than adsorbents.
4. Regeneration of the adsorbent is hard and need a lot of the energy.

15. 12
6. Conclusion
As we talked about one of the natural gas processes which is very important process to
save our economy, to avoid environment pollution and human’s health. So, we can conclude this
report to below points:
✓ Dehydration process is one the important offshore of the gas processing.
✓ We have many processes that include processing the impurities (fluids). One of them is water
include dehydration.
✓ We done the dehydration process to remove water amounts from the natural gas because of the
reaction between it and the hydrates.
✓ Corrosion occurs with plug flowlines by reaction wet gases with ice or gas hydrates.
✓ Both absorption and adsorption are the two effective natural gas dehydration processes.
✓ Water is eliminated from the body during dehydration via absorption by a liquid having a
high affinity for water.

16. 13
7. List of References
1. Christensen, D. (2009). LNG Dehydration (Drying of Natural Gas). [pdf] Available at:
https://projekter.aau.dk/projekter/files/17059482/Gas_Dehydration.pdf [Accessed 4 Nov.
2021].
2. glossary.oilfield.slb.com. (n.d.). dehydrate. [online] Available at:
https://glossary.oilfield.slb.com/en/terms/d/dehydrate. [Accessed 4 Nov. 2021].
3. Productions, C. (n.d.). Why Should You Dehydrate Natural Gas? [online]
https://www.croftsystems.net/. Available at: https://www.croftsystems.net/oil-gas-blog/why-
should-you-dehydrate-natural-gas/. [Accessed 4 Nov. 2021].
4. Arnold, K. and Stewart, M. (2011). Gas Dehydration Field Manual. 1st ed. [eBook] USA:
Gulf Professional Publishing, p.260. Available at:
https://books.google.iq/books?id=Kl9TqbcjI9UC&dq=natural+gas+dehydration+by+adsorpti
on&source=gbs_navlinks_s. [Accessed 3 Nov. 2021].
5. Gas hydrate control. (2015). Petroleum Engineer’s Guide to Oil Field Chemicals and Fluids,
pp.405–443. Available at: https://doi.org/10.1016/B978-0-12-803734-8.00013-8 [Accessed 3
Nov. 2021].
6. Aregbe, A.G. (2017). Gas Hydrate—Properties, Formation and Benefits. Open Journal of
Yangtze Oil and Gas, 02(01), pp.27–44. Available at:
https://doi.org/10.4236/ojogas.2017.21003 [Accessed 3 Nov. 2021].
7. Ribeiro, C.P. and Lage, P.L.C. (2008). Modelling of hydrate formation kinetics: State-of-the-
art and future directions. Chemical Engineering Science, 63(8), pp.2007–2034. Available at:
https://doi.org/10.1016/j.ces.2008.01.014 [Accessed 3 Nov. 2021].
8. gazsurf.com. (2021). GAS DEHYDRATION. [online] Available at:
https://gazsurf.com/en/gas-processing/articles/item/gas-dehydration [Accessed 3 Nov. 2021].
9. Aisyah, R. (2018). Several Natural Gas Dehydration Methods and Range of Application.
[online] Chemical Engineering Portal. Available at: https://missrifka.com/gas-processing-
plant/several-natural-gas-dehydration-methods-and-range-of-application.html. [Accessed 4
Nov. 2021].
10. Netusil, Michal & Ditl, Pavel. (2012). Natural Gas Dehydration. [Online] Available at:
https://www.researchgate.net/publication/279063450_Natural_Gas_Dehydration [Accessed 4
Nov. 2021].
11. Gasprocessingnews.com. (2019). The natural gas dehydration process. [online] Available at:
http://www.gasprocessingnews.com/features/202012/the-natural-gas-dehydration-
process.aspx. [Accessed 3 Nov. 2021].
12. Pall. (n.d.). Adsorbent Dehydration - Oil & Gas | Pall Corporation. [online] Available at:
https://www.pall.com/en/oil-gas/midstream/adsorbent-dehydration.html [Accessed 3 Nov.
2021].

17. 14
13. www.petroskills.com. (n.d.). Adsorption Dehydration: Two-Tower vs. Three-Tower System.
[online] Available at: https://www.petroskills.com/blog/entry/adsorption-
dehydration#.YYRfgGBBzrc [Accessed 4 Nov. 2021].
14. Salamat, R. (2009). Choose The Right Gas Dehydration Method and Optimize Your
Design. International Petroleum Technology Conference. Available at:
https://onepetro.org/IPTCONF/proceedings-abstract/09IPTC/All-09IPTC/IPTC-13321-
MS/151866 [Accessed 4 Nov. 2021].