ASPEN-HYSYS Simulation of Natural Gas Processing
Plant & Analysis of Different Operating Parameters
Mohammad Hasibul Hasan*, Quazi Azizul Hassan, Sadat Kamal Amit, Dr. Md. Ruhul Amin
Department of Chemical Engineering,
Bangladesh University of Engineering and Technology
Dhaka-1000, Bangladesh
hhasiib@gmail.com*, sazim91@gmail.com, sadat018@gmail.com, amin@che.buet.ac.bd.
Abstract— In this time of energy crisis, low production rate
against the increasing demand of the gas production regularly
hampers both the domestic and industrial operations. Natural
gas is the major power source of this country. Unless other
power source is developed, natural gas is our only hope. So far
in Bangladesh 23 gas fields have been discovered with the rate
of success ratio 3.1:1 of which two of the gas fields are located in
offshore area. Bibiyana is a world class gas reservoir that has
the capacity to safely and efficiently deliver gas supply. Flow
sheet development of the natural gas processing plant having
capacity of 150 MMSCFD at Bibiyana in Moulavibazar district
of Bangladesh was undertaken using the Aspen HYSYS process
simulator. The steady state simulation of the gas processing
plant shall be performed based on both the design and physical
property data of the plant.
Index Terms— Natural gas; Aspen-Hysys; gas processing;
separation; simulation;
I. INTRODUCTION
Natural gas is playing a growing energy role. The scale of
its reverse and its environmental advantages favor its use, for
fast growing activities such as the precision industries and the
generation of electricity.
The natural gas produced into the mainline gas
transportation system must need specific quality measure in
order for the pipeline grid to operate properly. Consequently,
natural gas produced at the wellhead, which in most cases
contains contaminates and natural gas liquids, must be
processed, i.e. cleaned, before it can be safely delivered to
high pressure, long distance pipe lines that transport the
product to consuming public[1].
There are many different simulation programs used in
industry depending on the field of application and desired
simulation product. When used to its full capability ‘ASPEN
HYSYS’ can be very powerful tool for an engineer to achieve
major business benefits by
 Ensuring more efficient and profitability design.
 Improving plant control, operability.
 Eliminating process bottle necks and minimizing
process network.
 Reducing human error and time requirement.
The inherent flexibility contributes through its design,
combined with the unparalleled accuracy and robustness
provided by it, leads to represent a more realistic model. It
can be used for variety of field including gas production[2].
In order to reduce the operating costs of a plant, much effort
is put to find the optimal design condition of the process
though optimization studies.
Optimization of chemical and related processes requires a
process modeling and optimization along with control
characterizes the area of process systems[3].
The Bibiyana gas field represents one of the most
significant natural gas discoveries in Bangladesh in terms of
quality and quantity; the field is now the second largest in the
country [4]. Bibiyana gas field is discovered in 1998.
Bibiyana is the largest producing gas field in the country. It
is a world-class gas reservoir that is expected to supply
reliable, clean energy for the next 20 to 30 years. Total
estimated reserve of this gas field is 3144.5 BCF and
recoverable amount is 2400.8 BCF [5].
Flow sheet development provides a good insight into the
behavior of the actual system based on a mathematical and
scientific model. By proper simulation process, it has become
easy to fix design variables, particularly for complex systems
with several interacting variables. Simulation model responds
to adjustments or changes in design parameters as does a real
process. Flow sheet development provides a convenient,
inexpensive and safe method of gaining to adjust design
variables and optimize the natural gas processing plant. Flow
sheet simulation based approach implemented in Aspen
HYSYS is used to study the effect of design parameters.
In the study of performance analysis using flow sheet
development, the operation variables are changed. For flow
sheet development, simulation of the plant was carried out
using the design data and then the simulation work was
performed with the operating data to study the performance
of the plant. The simulation model consists of both
geometrical parameters like vessel dimensions, heat transfer
area, number of trays in a column etc. and operation variables
like temperature, pressure, feed ratio etc. [6].
II. NATURAL GAS PROCESSING
Natural-gas processing is a complex industrial process
designed to clean raw natural gas by separating impurities and
various non-methane hydrocarbons and fluids to produce what
is known as pipeline quality dry natural gas [7].
Natural-gas processing begins at the well head. The
composition of the raw natural gas extracted from producing
wells depends on the type, depth, and location of the
underground deposit and the geology of the area. Oil and
natural gas are often found together in the same reservoir. The
natural gas produced from oil wells is generally classified
as associated-dissolved, meaning that the natural gas is
associated with or dissolved in crude oil. Natural gas
production absent any association with crude oil is classified
as “non-associated” [8].
Most natural gas extracted from earth contains, to varying
degrees, low molecular weight hydrocarbon compounds
including methane (CH4), ethane (C2H6), propane (C3H8)
and butane (C4H10). The natural gas extracted from coal
reservoirs and mines (coal bed methane) is the primary
exception, being essentially a mix of mostly methane and
about 10 percent carbon dioxide (CO2) [9].
III. SIMULATION OF THE GAS PROCESS PLANT
In this proposed plant there are five major units which will
process the raw natural gas. These are: (1) separation unit, (2)
dehydration unit & heat exchanger, (3) de-ethanizer and (4)
final purification & CO2 removal units.
A. Separation Unit
In simulating the processing plant, gas is drawn from three
wells: Well-1, Well-2 and Well-3 respectively. This data are
chosen randomly. Due to limitation and industrial visit the
used data are assumed. If the industrial data are obtained the
simulation can be done with real plant data can be compared
with ‘Bibiyana’ gas processing plant industry. Composition
of the feed can be found in datasheet. Then the gas is passed
through the pressure control valve to relief some pressure &
then fed into three ‘3 phase separators’ (H-110A, H-110B, H110C) to separate each valve out stream in heavy liquid, light
liquid & vapor streams. Most of the liquids are separated at
this separation unit.
The three heavy liquid streams (mostly H2O) are removed
& the three light liquid streams are mixed together in a mixer
& then entered into a distillation column (D-320) through an
expansion valve, the bottom liquid product is liquefied
petroleum gas (LPG) & is stored in a tank(F-210). The
overhead product of D-320 is mixed with refined gas stream
to prepare the very final product.
B. De-hydration Unit & Heat-Exchanger Unit
The three vapor streams of the separators are mixed in a
mixer & passed through the dehydration unit for water
removal. The dehydration unit consists of an absorption
tower (D-310) where TEGlycol is used as absorbent of water.
The overhead vapor product (dehydrated hydrocarbons) of
(D-310) is passed through two heat exchangers (E-230) & (E250) & temperature is decreased. The tube out of E-250 heat
exchanger is then entered into a separator (H-140). Then
expander (G-152) lowers streams temperature using JouleThomson principle of pressure relief & then three phase
separator separates the remaining water in the mixed inlet
more precisely. Heavy liquid is removed & light liquid (H150 liquid out) and vapor (H-150 vapor out) is used for
further processing.
On the other hand, bottom product of the absorption
tower(D-310) is passed through an expansion valve (K-131)
& a two phase separator(H-130) ,bottom product of which is
used as a tube side inlet of heat exchanger (E-240). The tube
side outlet is then entered into a column (D-330) whose
bottom product is make-up Glycol solution & is entered into
the shell side of the heat-exchanger (E-240) & heatexchanger (E-230). Between the heat-exchangers a pump is
used to increase the pressure. The shell outlet of E-230 is
mixed with TEGlycol feed to use in the absorption tower (D310).
C. De-ethanizer Unit
The liquid stream of the three phase separator(H-150) is
then used in the de-ethanizer(distillation column D340).Bottom product of the column(D-340) is LPG & passed
through the heat-exchanger(E-101) to prepare ‘Final LPG’ at
low temperature. Stream (H-150 vapor out) is mixed with the
over-head vapor product of (D-340). Mixed stream (M-231
out) is entered into the shell side of the heat exchanger (E250) to increase the temperature.
D. Purification & CO2 removal Unit
Stream (M-251 shell out) is then gone through CO2
removal process. In this stage we used principles of
liquefaction to separate CO2. Using cooler, heat-exchanger,
compressor & separator, CO2 from natural gas has been
highly decreased(less than 0.03%). CO2 can also be removed
using absorption process where ME-Amine solution is used
to absorb CO2. We can also use selexol for physical
absorption of CO2..
IV. PROCESS FLOW DIAGRAM (PFD)
V. RESULTS AND DISCUSSIONS
A. Product Composition
Flow sheet development and design of natural gas
processing plant using the Aspen HYSYS was undertaken.
Flow sheet development was performed based on the design
and operating data of the plant. The sales gas & LPG
composition obtained from this processing plant are shown in
Table 1 & Fig. 1 respectively.
MOLE FRACTION OF METHANE IN
PRODUCT
0.9652845
0.965284
0.9652835
0.965283
0.9652825
0.965282
0.9652815
TABLE 1. COMPOSITION OF SALES GAS
0.965281
Composition
Name of
Components
Composition
Water(H2O)
5.9×10-6
n-Heptane
7.09×10-5
N2
2.1×10-3
n-Octane
1.2×10-5
CO2
2.6×10-4
n-Nonane
2.8×10-6
-7
Methane
0.9957
n-Decane
5.3×10
Ethane
-4
9.2×10
n-C11
1.3×10-7
Propane
2.6×10-4
n-C12
5.2×10-8
i-Butane
1.2×10-4
n-C13
1.5×10-8
n-Butane
1.6×10-4
n-C14
9.8×10-9
i-Pentane
1.7×10-4
TEGlycol
4.05×10-23
n-Pentane
1.03×10-4
MEAmine
0
n-Hexane
6.8×10-5
LPG Composition
7%
24%
14%
10%
14%
6%
9%
16%
Propane
i-Butane
n-Butane
i-Pentane
n-Pentane
n-Hexane
n-Heptane
Others
0.9652805
0
20
40
60
NO OF STAGES
Fig. 2. Graph of mole fraction of CH4 vs No of stages
From Fig. 2 it is shown in the graph that as the no of
stages get increased the mole percentage of CH4 gets
increased. Usually greater the no of stages, more the
contact between vapor and liquid phase and more the
separation can be done. But in case of building distillation
column the point that should be in consideration is the
cost of building and maintenance.
So, for minimizing the cost of production and optimizing
the amount of CH4 produced the design parameter need
to be determined.
PRESSURE IN G-152 COMPRESSOR (KPA)
Name of
Components
6000
5000
4000
3000
2000
1000
0
0.963 0.9635 0.964 0.9645 0.965 0.9655
MOLE FRACTION OF METHANE IN PRODUCT
Fig. 3. Graph of pressure in compressor vs mole fraction of CH4
Fig. 1. Composition of LPG
B. Graphical Representation
For the process described, varying the value of different
variable their corresponding data were generated and relevant
curves were plotted.
It is noted from the Fig. 3 that as the pressure of the
compressor G-152 get increased the composition of
methane in product got decreased. But it is required to
compress the gas to separate the other components from
the stream. The compressed gas is later sent to 3-phase
MOLE FRAACTION OF PROPANE IN LPG
separator in which the pressure impact is resulting the
separation of desired product from other elements.
MOLE FRACTION OF METHANE IN
PRODUCT
0.965285
0.965284
0.965283
0.965282
0.965281
0.96528
0.2375
0.237
0.2365
0.236
0.2355
0.235
0.2345
0.234
0.2335
0.233
0
0.965279
5
10
15
FEED STAGE OF DISTILLATION COLOUMN D-340
0.965278
0
5
10
NO OF FEED STAGE IN D-340 DISTILLATION
COLOUMN
15
Fig. 4. Graph of mole fraction of CH4 vs feed stage no. in distillation column
From Fig. 4 it is noticed from the curve that mole fraction
of CH4 get increased as the no of feed stage get increased. At
some point some consistency is shown. As the no of feed stage
becomes larger the contact time for liquid and vapor phase in
distillation column get increased thus the output percentage get
larger.
MOLAR FLOW OF CO2 IN PRODUCT
(KGMOL/HR)
12
10
Fig. . Graph of C3H8 in LPG vs feed stage in distillation column D340
From the Fig. we can see that with the increased number
of feed stage in D-340 distillation column, the propane recovery
in LPG becomes higher. This is because the less the feed stage
number is, the more the efficiency of the column will be as there
will be increased amount of contact and heat transfer. As a
result propane becomes more in liquid form. This curve justifies
theoretical curve.
C. Product Comparison between Our Simulated Plant data &
Different Natural Gas Processing Plants
Methane composition, Carbon-Di-Oxide content & specific
gravity of our simulated sales gas product & existing different
gas processing plants are shown comparatively in Fig. 6, 7 and
8 respectively. Here, the term, ‘experimental’ represents our
simulated data.
8
Methane Composition
Comparison
6
4
2
0
-185
-165
-145
-125
-105
OUTLET TEMPERATURE OF HEATER E-
-85
100
98
96
94
92
90
ᴼC
Fig. . Graph of molar flow rate of CO2 vs heater outlet temp
Fig. . Comparison of Methane composition
Due to cooling by unit E-100 the percentage of CO2 along
with CH4 get increased in product as shown by the plot. It’s
because the separation process of CH4 from CO2 can’t be attain
by varying temperature. Thus using some adsorbent to absorb
the amount of CO2 need to be removed can be a better approach
shows that the methane composition of our
Figure
experimental sales gas product is higher than that of different
gas processing plants of our country. We know, natural gas is
mainly methane [11]. Methane composition is a parameter
which denotes natural gas product quality [12]. In this regard
ours’ is better.
Carbon Di Oxide Content
Comparison
0.6
0.4
0.2
0
0.6
0.47
0.0003
0.07
0.11
0.15
processing plant is developed in this paper. Different process
can be used to meet the specification required for processing of
natural gas. Environmental constraints and the need to reduce
cost require innovative processes. The process used here
derived from earlier processes, but tend to offer significant
reductions in investment and operating costs. In the longer term,
new concepts such as gas permeation can be expected to play a
growing role and the natural gas processing will keep changing.
In these plan, the composition of sales gas satisfactory. The
percentage removals of unwanted elements are good enough to
run the process.
ACKNOWLEDGMENT
Fig. . Carbon-Di-Oxide content comparison
CO2 removal is another pre-requisite in natural gas
processing plant [13]. Presence of CO2 content can cause
corrosion, undesired hydrate formation and severe problem in
cryogenic process [14]. So, the lesser the CO2 content, the
better. From Fig. we find the CO2 content of experimental
value is less than other NG processing plants of our country.
Specific Gravity
Comparison
0.62
0.6
0.58
0.56
0.54
Fig, . Specific gravity comparison
From Fig. it is found that, the specific gravity of the
product natural gas of our experiment is similar to the different
gas processing plants of our country. All of them range between
0.54 & 0.60.
VI. CONCLUSION
At present time natural gas is a major source of energy. Most
of the industries are run by energy using natural gas as their
main source. Near about 95% of the natural gas is used as fuel
gas. So, it is a major prospect to focus on and develop for the
betterment of energy utilization. The model for natural gas
The work is supervised by Dr. Md. Ruhul Amin. We are very
grateful for his kind assistance. The technical and administrative
backup given by the Department of Chemical Engineering,
BUET is highly valuable and we are very thankful to the
department also.
REFERENCES
1
Arthur J. Kidnay, W.R.P., Fundamentals of Natural Gas
Processing. 2006, USA: CRC Press. 418.
2
M., P.S.R.a.R.A., Aspen-HYSYS Simulation of Natural Gas
Processing Plant. Journal of Chemical Engineering, IEB, 2011.
Vol. ChE. 26(1): p. 4.
3
Saeid Mokhatab, W.A.P., Handbook of Natural Gas
Transmission and Processing. 2nd ed. 2006, UK: Elsevier science
limited.
4
Zahir Ahmed, M.R., Fatem Bashar and Katy Gardner, Bibiyana:
Local Livelihoods, Poverty and the Gas Fields Some Initial
Findings.
5
Chowdhury, Z., , Natural Gas Reserve Estimate of Bangladesh.
6
Chandra, V., Fundamentals of Natural Gas: An International
2006, USA: PennWell Corporation. 169.
7
Kelkar, M., Natural Gas Production Engineering. 2008, USA:
PennWell Corporation.
8
Gene Whitney, C.E.B., Energy: Natural Gas: The Production and
Use of Natural Gas, Natural Gas 2010, USA: The Caitol.Net,Inc.
9
Robert Hubbard, U.o.O., The Role of Gas Processing in the
Natural-Gas Value Chain. 2009: p. 7.
10 Saeid Mokhatab, J.Y.M., Jaleel V. Valappil, David A. Woo,
Handbook of Liquefied Natural Gas. 2014, UK: Elsevier Inc.
[11] Salvo, J.M., DETERMINING NATURAL GAS QUALITY
PARAMETERS EXPRESSED IN VOLUME.
[12] Biruh Shimekit, H.M., Natural Gas Purification Technologies –
Major Advances for CO2 Separation and Future Directions, in
Advances in Natural Gas Technology, D.H. Al-Megren, Editor.
2012, In Tech: Malaysia. p. 542.
[13] Kumar, S., Gas Production Engineering. Vol. 04. 1987, Houston
Texas: Gulfs Publishing company.