Investigation on New Innovation in Natural Gas Dehydration Based on Supersonic Nozzle Technology

Abstract

According to growing of demand for natural gas in global markets, it causes to modify and intensify its process. Indisputably, the existance of water in natural gas has so long been a controversial issue in gas industry and removing water from NG becomes a big deal, indeed. Gas dehydration is the most essntial and important way to solve this problem and there are several approaches to attain this aim. Among these methods, dehydration of natural gas with supersonic nozzle is an effictive method which is more efficient way than other methods. The main advantages of this method are its small size that is big deal for off-shore units because of limitation of location and also low operating costs with no deleterious environmental impact. In this study at first we examined some important methods for gas dehydration and then we proceed the details of supersonic nozzle method, and finally we compare it with other methods and conclude its unique advantages as abest method for gas dehydration.

Full text

Abstract
According to growing of demand for natural gas in global markets, it causes to modify and intensify its process. Indisputably,
the existance of water in natural gas has so long been a controversial issue in gas industry and removing water from NG
becomes a big deal, indeed. Gas dehydration is the most essntial and important way to solve this problem and there are

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deal for off-shore units because of limitation of location and also low operating costs with no deleterious environmental
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
method for gas dehydration.
*Author for correspondence
Indian Journal of Science and Technology, Vol 8(S9), 450–454, May 2015
ISSN (Print) : 0974-6846
ISSN (Online) : 0974-5645
Investigation on New Innovation in Natural
Gas Dehydration Based on Supersonic Nozzle
Technology
Saeed Jamali Ashtiani1*, Athareh Haghnejat2, Mehdi Sharif2 and Ali Fazli1
1Department of Polymer Engineering, Sahand University of Technology, Tabriz, Iran; Ashtiani.saeed@yahoo.com m
2Department of Polymer Engineering, Shiraz Branch, Islamic Azad University, Shiraz, Iran; a_fazli@sut.ac.ir
1. Introduction
Dehydration process is an essential part of gas process-
ing in oshore units which avoid several important
problems in gas processing. e problems encompass
erosion, fouling, gas hydrate and such like. ere are the
varity of methods for gas dehydration in gas industry but
some them are most important compare to others like
adsobrtion, adsorbtion and direct cooling for instance,
due to absorption preocess the amin part is uing di-eth-
ylene and glycoles that are used for withdrawing water
content in gas. One of the modern high technology
intersted to developed target ingredients from natural
gases supersonic-technology. If we using a convergent-
divergent Laval nozzle, the supersonic ow is produced.
e components of C3+ are heavy and when mixed with
condensed drops, they are separated from the natural gas
ow in the supersonic nozzle.
Under action of centrifugal forces, we can separated
the condensate drops with target ingredients condensed
in the supersonic nozzle is carry out. is means that ow
swirling at the supersonic nozzle entry.
e supersonic-high technology have many advan-
tages as compared with old technologies. Some of these
dierences are list in below:
• Small size of the hydrocarbons separation from
natural gas.
• Decreased space requirements.
• High portability.
• Decreased handling.
• Decreased installation costs.
• Decreased costs of operating.
• No harmful environmental impact.
Keywords:

Saeed Jamali Ashtiani, Athareh Haghnejat, Mehdi Sharif and Ali Fazli
Indian Journal of Science and Technology 451
Vol 8 (S9) | May 2015 | www.indjst.org
• No demand for routine maintenance1.
2. Gas Dehydration
Natural gas can carry certain amounts of water in the
vapour form. Water is a contaminant in natural gas and its
concentration increases with temperature or equally with
reduced pressure. Physical appearance of gas hydrates is
like packed snow. e conditions at which hydrates start
to solidify, and become a cause for trouble, depend on
many factors including but not limited to gas temperature,
pressure, composition, and the water content. erefore
it is very important to develop techniques to prevent
hydrate formation. e following methods have been
conventionally used for hydrate prevention like identi-
fying the temperature at which hydrates formation and
keeping the gas above this temperature, reducing pressure
and therefore reducing the possibility of hydrate forma-
tion, adding hydrate inhibitors to the gas, which in tum
will either reduce the temperature at which hydrates are
likely to form or the rate at which they form and reducing
the water content of the gas and therefore reducing the
possibility of hydrate formation. is process is called gas
dehydration which is reported by Michalnetusil et al2 in
their article.
2.1 Problems with Water in the Gas
As mentioned before there are some amount of water in
gas which is named water content and in the cold region
as the ambient temprature of fell down and decrease
under the dew point temprature of water, the small mol-
culars of water which are in vapor phase in pip,beging
to condence and aggregate to big one and cause to form
methane hydrate that is in solid form and this small solid
particle which are crystal, beging to make large partile
and if they be in the way of natural gas which consist of
H2S and CO2 can cause several serious problems like cor-
rosion and erosion.
3. Supersonic Separation
We can use the 3S technology to exploit target component
from natural gases. Basis of this high technology, is realted
to the cooling of natural gas in a supersonic swirling gas
ow. Following thermodynamics devices is similar to the
supersonic separator:
• Turbo expander.
• Combining expansion.
• Cyclonic gas/liquid separation.
• Tubular device.
For transforing the pressure to sha power, we can
used the turbo expander. Also, using of the supersonic
systems in industry is one of the best methods to remove
compressible vapours like as natural gas liquids or water
from a gas stream.
In the 3S-technology, under action of centrifugal
forces, separation of condensate drops with target ingre-
dients condensed in the supersonic nozzle is carry outed.
e two phase mixture continues its supersonic swirling
now and under the inuence of the strong inertial force,
the droplets will collide with the wall and merge. A thin
lm of water will form around the swirling gas which
then will be separated by means of a vortex nder as in
cyclones. e gas is now dry, and will slow down in the
diverging part of the nozzle, regaining almost 70% of its
original pressure.
e concept of supersonic separators was introduced
to the oil and gas industry in 1990s. ese separators were
immediately identied as reliable devices with no rotat-
ing pans that required no chemicals and were capable of
unmanned operation. It has been the purpose of a few
studies since then to optimize the performance of super-
sonic separators and to expand their functionality from a
dehydration device to a more sophisticated hydrocarbon
dew•pointing and NGL recovery device. e following is
a quick review of the achievements of these studies. eir
study of supersonic separators is tracked back to 1997
and their rst full scalc tcst unit became operational in
1998 and in 2003, supersonic separator used in gas con-
ditioning technology. eir proposed design consisted
of a supersonic nozzle that incorporated a small blade
(supersonic wing) in the supersonic region to create
the swirling motion of thc gas and henee benet from
the centrifugal separation of the heavier particles. is
design was later improved to include a swirl generator
(ring wing) upstream of the nozzle and in the subsonic
region. Another group known for their extensive work on
the supersonic separators is a group of Russian specialists
who named their separator 3-S.
e design of the 3-S separator was similar to the
improved Twister design, incorporating a swirl generator
upstream of the nozzle. A third Chinese group has also
performed studies on supersonic separators. ey built a
pilot scale test which used wet gas as process uid which
was capable of attaining a dewpoint depression of about

Investigation on New Innovation in Natural Gas Dehydration Based on Supersonic Nozzle Technology
Indian Journal of Science and Technology
Vol 8 (S9) | May 2015 | www.indjst.org
452
20°C. eir design used a cyclonic swirl generator in the
supersonic region. Another study was performed by a
group in Newfoundland, Canada on which the current
study is based. ey performed CFD based predictions
of the ow characteristics inside a converging. Diverging
nozzle and showed that this method is a valid tool for
this type of study by comparing their results with similar
published experimental data. ey moreover developed a
soware that linked to a process simulator (HYSYS), was
capable of predicting the performance of a supersonic
separator under certain operating conditions with much
less computational resources than a CFD package which
is reported by Bart prast et al3 in their article. A super-
sonic dehydration unit may be consisted of several parts,
the most important of which is a converging - diverging
supersonic nozzle. It is in this nozzle where the condensa-
tion or as it may be in some cases, solidication occurs as
well as the separation itself. Since the gas mixture is ow-
ing at supersonic velocities, residence time is extremely
low in this type of separators and hydrate has no time to
deposit along the device. e unit is considerably smaller
than conventional dehydration units and therefore suit-
able for oshore applications. Moreover, the nozzle has
no moving parts and is simple to operate which makes
it a very good candidate for unmanned operations for
subsea application is also important to note that the gas
temperature is reduced based on gas expansion principles
and requires no external refrigerant. is brings another
major advantage over conventional dehydration units in
that intensive water dew points, down to 60°C, can be
achieved without any use of external cooling. e selectiv-
ity of separation is another asset when water is removed
Figure 1. Schematic of suppersonic nozzle separator.
Figure 2. Supersonic nozzle body.

Saeed Jamali Ashtiani, Athareh Haghnejat, Mehdi Sharif and Ali Fazli
Indian Journal of Science and Technology 453
Vol 8 (S9) | May 2015 | www.indjst.org
without the removal of hydrocarbons. is is bene-
cial in that presence of heavier hydrocarbons increases
the gas gravity and reduces the compressibility factor,
which results in increased pipeline mass ow capac-
ity. Malyshkina developed mathematical simulations for
velocity components, pressure and other parameters as
functions of radius for ow within the supersonic sepa-
rator using the two dimensional Euler model. Qingfcn,
Depang, and other colleagues investigated the perfor-
mance of supersonic separators incorporating a method
of particle enlargement to reduce the length of the device.
Brouwer, J. M. et al4,5 used air-ethanol as their medium
and water droplets as nucleation centers.
Figure 1 display the shematic design of a supersonic
nozzle and Figure 2 shows the schematic of the super
sonic nozzle body6. ese examples which is oered
Qingfen Maa et al7 the probability of increasing the prof-
itability of gas processing plants by means of an cheap
modernization gure.
e picture of a supersonic dehydration line working
on the essential described which is reported by Wen C et
al8 and also with Okimoto Fa and Brouwer J. M.9 here is
pictured in Figure 3.
4. Conclusions
ere are several processes involved in processing the
reservoir uid into oil, gas andwater. One of the most
important processes oshore is gas dehydration, because
wet gas increases corrosion and can course plugs from ice
or gas hydrate.
5. Acknowledgement
I would like to thank of Dr. Khosravi Niko for his invalu-
able support and guidance throughout this article, my
parents and my friends at the Petroleum University of
Technology for making my stay, a wonderful and memo-
rable experience.
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Figure 3. Schematic representation of a supersonic
dehydration line.

Investigation on New Innovation in Natural Gas Dehydration Based on Supersonic Nozzle Technology
Indian Journal of Science and Technology
Vol 8 (S9) | May 2015 | www.indjst.org
454
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