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NATURAL GAS PROCESSING – DESIGNING AND SIMULATION
SARTHAK VAIDYA
Datta Meghe College of Engineering, University of Mumbai, Airoli, Mumbai, India
ABSTRACT
Natural Gas is an important, non-renewable gas which is obtained along with crude oil extraction. Raw Natural gas
contains a high amount of impurities and acidic gases. It is extremely important to remove these gases for efficient
combustion of products. Natural gas processing is the term used for the separation of Natural gas stream into
commercially viable products such as LNG, LPG, and NAPTHA. This paper emphasizes on design and simulation of the
processing of natural gas to yield maximum productivity of LNG and LPG. It also focuses on reducing acid gas content
from the "Raw natural gas" stream. Simulation is performed by using DWSIM software. Effect on LPG production by
varying the operating parameters such as Reflux Ratio, operating pressure, and Number of trays is also studied. Around
96% of LNG and 95% of LPG were produced when the process flowsheet was simulated. Also, the developed process is
found to be energy efficient as only two fractionating towers are required to obtain the optimum production yield.
KEYWORDS: Simulation, Natural Gas Processing, Process Design, LPG, LNG, & DWSIM
Received: Sep 19, 2020; Accepted: Oct 09, 2020; Published: Oct 23, 2020; Paper Id.: IJCPTDEC20201
INTRODUCTION
Natural gas, sometimes also called as fossil gas, is naturally occurring gas inside Earth's crust. It is a non-renewable
source of energy containing low molecular weight hydrocarbons. Natural gas is widely used for cooking, heating
and electricity generation. It is found deep inside the earth's crust, underground rock formations, or associated with
other hydrocarbon reservoirs in coal beds and as methane clathrates. Primarily, Natural gas is found along with
crude oil. The primary source for formation of the oil and gas is microscopic marine organisms, also known as
Plankton. The formation of Oil and gas will start proceeding only when the marine life above sea bed is sufficient
enough to accumulate on seabed along with sediments coming off the land. As more sediments are accumulated
over the years, they start to pressurize the organic matter beneath them. This results in rising the temperature of that
layer to a point that it breaks down the organic matter and releases the accumulated oil and gas.
The Raw Natural gas, which is extracted from source rock or oil well, contains high amount of impurities
including water, carbon dioxide, and Hydrogen sulphide. Hence, Natural gas processing is an extremely important
step before its commercial utilization. Natural gas processing is a complex industrial process which is designed to
purify the raw natural gas extracted from field source by removing impurities, acidic gases and separating heavier
hydrocarbons and fluids to pipeline-quality dry natural gas [1]. Depending upon the source, the composition of
natural gas can vary. Usually, it contains about 75-80% of Methane, 5-10 % of ethane and propane, and 0-5% of
heavier hydrocarbons. Mainly, every source contains about 1-2 % of Carbon dioxide (CO2) and Hydrogen sulphide
(H2S). These gases are also called as "Acidic Gases". These gases are highly corrosive, hence their presence in final
products can corrode the pipelines and also affect the calorific values. The presence of CO2 content can cause
undesired hydrate formation and severe problems in the cryogenic process. It is extremely important to reduce the
Orig
ina
l Article
International Journal of Chemical &
Petrochemical Technology (IJCPT)
ISSN(P): 2277–4807; ISSN(E): 2319–4464
Vol. 10, Issue 2, Dec 2020, 1–12
© TJPRC Pvt. Ltd.
2 Sarthak Vaidya
Impact Factor (JCC): 5.5342 NAAS Rating: 3.56
acid gas content from the Natural gas stream. This process is termed as "Gas Sweetening". Once the Acidic gases are
removed, Natural gas is further processed and separated into Liquefied petroleum gas (LPG), Liquefied Natural Gas
(LNG), and NAPTHA as products. The natural gas is also extracted from coal reservoirs and coal mines (coal bed
methane), which usually contains a mix of mostly methane and about 10 percent carbon dioxide (CO2) [2]. The processing
of Natural gas is easier, less complicated and more efficient than crude oil and is equally important before it is used by
consumers [3]. LPG burns cleaner with octane number closer to 105 and is used as fuel in vehicles as an alternative to
petrol and diesel [4].
Flowsheet development and its simulation is an important step in process development and modification.
Flowsheet provides a safe and inexpensive method to obtain and validate the designed process. 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. [5]. Many simulators available in the market which are used
by industry and academic professionals. Here, DWSIM is used for modelling and simulation of the process. It is a
multiplatform, CAPE-OPEN compliant chemical process simulator for Windows, Linux, Android, macOS, and iOS. Built
on the top of the Microsoft .NET and Mono Platforms and featuring a rich Graphical User Interface (GUI). DWSIM can
understand the behaviour of their chemical systems and solve the processes by using rigorous thermodynamic and unit
operations models.
Numerous experiments were performed and studied for the processing of Natural gas. Various processes for
separation into LPG, LNG, and NGL are suggested by Industry engineers and academic researchers, depending upon the
requirements of the products. Housam Binous and Ahmed Bellagi, studied and simulated, five different cases for
separation of industrially relevant hydrocarbon mixture [6]. Their main agenda was to show that complex separations can
be handled by computer algebra Mathematica© and compare the results with those obtained in Aspen-HYSYS. The five
cases were: separation of natural gas, using Furfural as entrainer, fractionate C4 to separate 1,3-butadiene, producing
methyl tert-butyl ether (MTBE) from methanol and i-butene, decomposition of MTBE to methanol and i-butene, and the
equilibrium-limited metathesis of cis-2-pentene to cis-2-butene and cis-2-hexene. Shuaib A. Khan et al. developed a
process for efficient recovery of LPG and Natural gas liquids (NGL) [7]. In their process, they cooled the vapour stream
obtained as top product form Deethanizer column and then mixed it with gaseous feed stream. This contact between two
streams took place inside the heat exchanger which results in large fraction of Methane and small traces of Ethane, which
constitutes of NGL. Ali I. Shehata et al. studied the simulation of the Natural gas process using Aspen-HYSYS, to yield
optimum results for NGL production with minimum power consumption [8]. They identified that number of trays in the
Distillation column plays an important role in separation of the feed stream. By increasing the number of trays from 10-40,
mole fractions of ethane, propane, and butane in the LNG product stream was increased by 2%, 4.5%, and 21%
respectively. Also, heat duties from Deethanizer, Depropanizer, and Debutanizer columns werereduced by 1.5%, 1.7%, and
29%. Khaled M. ElBadawy et al. studied the design and simulation of LPG plant to minimize the heat consumption of each
of fractionation towers used [9]. To obtain individual products such as methane, ethane, propane, and butane, different
fractionation towers like Demethanizer, Deethanizer, Depropanizer, and Debutanizer were used. Simulation was performed
using Aspen HYSYS software. They studied LPG production by varying the feed tray and operating pressure of the
Depropanizer column. The heat duty was found to be lowest when the feed tray was in the exact centre of the Depropanizer
column. Also, they found that heat duty was reduced by 45.9% when operating pressure was decreased from 10 bar to 8
bar. Many other studies were performed to improve the purity and productivity of LPG, NGL, and LNG as well as
Natural Gas Processing – Designing And Simulation 3
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reducing the energy consumption, by studying parameters like reflux ratio, and the number of trays inside each tower [10-
16].
This paper focuses on the development of a process to obtain high production yield, at a lower cost. This paper
also emphasizes the effect on productivity when parameters such as Reflux Ratio, Pressure, and Number of trays for LPG
column are varied.
METHODS
Process Description
As the main commercial products of Natural Gas are LNG and LPG, this process focuses on cumulative production of
LNG (Methane and Ethane), and LPG (Propane, n-Butane, iso-Butane, etc.).
Gas Sweetening
Natural gas feed stream maintained at 330K, 60 atm pressure, and a molar flowrate of 5000 Kmol/h. The feed stream is
passed through a vapour-liquid separator, also called as Flash Drum or Knockout Drum (KOD).
Table 1: Feed Stream Composition
Mole Fractions
Methane 0.815
Ethane 0.079
Propane 0.068
N-Butane 0.0047
Isobutane 0.0033
Isopentane 0.002
N-pentane 0.003
N-Hexane 0.002
N-Heptane 0.0018
Carbon-dioxide 0.012
Hydrogen sulphide 0.008
Nitrogen 0.0012
Table 2: Feed Stream Conditions
Temperature 330K
Pressure 60 atm
Molar Flowrate 5000 Kmol/hr
When the feed is flashed, vaporized feed is passed through the upper part, and liquid feed is collected at the
bottom of KOD. The vapour feed is further sent to Acid-Gas absorber (C-1201). The corrosive acidic gases in the feed
stream are absorbed here. The solvent used here is a blend of Monoethylamine (MEA), Diethylamine (DEA), and water in
mole ratio of 0.4 : 0.4 : 0.2. The number of stages in absorber is 45, with feed stage being 1, and the solvent stage being 45
respectively Top product consisted of less than 0.02% of CO2 and H2S, 5% of the solvent mixture, and 94.88% of
Hydrocarbon gases. The top product is sent to KOD (V-1202) where the top product stream from the absorber is flashed
and the top product from this KOD is called "Sweet Gas". This is because the stream S-09, is in complete gaseous form
and free from acidic gases. This stream is further sent for Natural gas processing. The Bottom product comprises of a large
amount of solvent with absorbed acidic gases and small traces of hydrocarbon gases. This stream is mixed and combined
with the bottom stream of KOD (V-1202), in mixture (MIX-01). As the prices of solvents are very high, it is extremely
4 Sarthak Vaidya
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important to recover them. The product stream of MIX_01, is passed through the regenerator column for solvent
regeneration. The regenerator is nothing but a simple stripping column with a number of stages equal to 30, and the feed
stage equal to 1. Inside the column, acidic gases are stripped off from the solvent mixture yielding regenerated solvent as a
bottom product, and Acidic gases are eliminated as top product.
LPG Production
Due to the Absorption column, the sweet gas stream (S-09), was having an extreme temperature of 590K. It was necessary
to drop down the temperature in order to condense heavier hydrocarbons. Thus, the stream is passed through a series of
heat exchangers (propane chiller) and a cooler (Cool-06), which drops the temperature to around 247K. This temperature
proved to be favourable for condensation of heavier hydrocarbons. The stream is then flashed onto a series of vapour-
liquid separators or KOD. Two separators in series are used such that the vapour stream (top product) from 1st KOD (V-
103) is the inlet stream to 2nd KOD (V-104). The vapour product stream from 2nd KOD (S-29) consisted of 90% of
Methane, and 5.5% of Ethane. This product is also called as "supersaturated vapours". These super-saturated vapours are
commercially called as LNG.
The liquid product or bottom product from both the KOD (V-103, V-104) is heated using a heat exchanger from
263 K to 310 K. These heated product streams (S-31, S-32), are mixed and combined into a single product stream (S-33)
using a mixture (MIX-02). The stream (S-33), is further sent to glycol dehydration unit (C-1203), having 20 stages and
maintained at a constant pressure of 206843 N/m2, for removal of excessive water. It is just a simple stripping column, in
which water is extracted from the feed using Tetraethylene Glycol as solvent. The top product is cooled to 300K and fed to
LEF column (C-101), for separation of low and high molecular weight hydrocarbons. Here, LEF column is a simple
distillation unit with a total condenser and partial reboiler. It consists of 20 trays with feed tray equal to 10 and maintained
at a constant pressure of 2242322 N/m2. The distillate obtained from C-101, contains 88% of Methane and 9% of Ethane.
This stream (S-39) is also a supersaturated vapour stream, and is further processed to manufacture LNG. The Bottom
product form C-101 contains majority ofheavier Hydrocarbons and small amounts of lighter hydrocarbons such as
Methane and Ethane. This bottom product stream (S-40), is heated from 316K to 340K and fed as an inlet stream to LPG
column (C-102). LPG column is a complex distillation column with a total condenser and partial reboiler. Number of trays
= 30, feed tray =15, and maintained at a constant pressure of 1029698 N/m2. The Distillate from the column consists of
60% of propane and 35% of n-Butane. The product obtained in this distillate stream (S-42), is called as "LPG". Also, the
bottom product of C-102 consists of 28% of N-Hexane, 19% of N-Pentane, and 19% of Isopentane. The components of the
bottom stream (S-43) is called as "NAPTHA".
Table 3: Operating Conditions for Absorber, Regenerator and Dehydration Columns
Parameters Acid-Gas Absorber Regenerator Glycol Dehydration Column
Pressure (N/m2) 6080000 192581 206843
No. of stages 45 30 20
Feed stages 1,45 1 1,20
Condenser Type None None None
Reboiler Type None Partial None
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Table 4: Operating Conditions for Distillation Columns.
LEF Column LPG column
Pressure (N/m2) 2242322 2242322
No. of trays/stages 20 50
Feed tray 10 25
Condenser type Total Total
Reboiler type Partial Partial
Reflux Ratio 2 2
Enthalpy-Thermodynamic Model Peng-Robinson 76 Peng-Robinson 76
The natural Gas processing studied by [10-16], consisted of separate distillation columns called Demethanizer,
Deethanizer, Depropanizer, etc. However, in this process, only two distillation columns are used (LEF and LPG columns),
reducing significantly the number of distillation columns required.
Flow Sheet
Figure 1: Process Flow Diagram for LPG and LNG Production from Natural Gas using DWSIM.
RESULTS AND DISCUSSIONS
From the table (5) below, it is clearly seen that this process yields 88% of Methane and around 9 % of Ethane, from the
Distillate stream of LEF column. As both Methane and Ethane are the main components of LNG, this process is highly
efficient for LNG production. The propane and N-butane content constitutes to around 96% of the Distillate stream of LPG
column. Hence LPG production yield is also high and optimum.
The acidic gas content is largely reduced from the natural gas stream, making the process more efficient in terms
of the product quality of LPG and LNG. The solvent used for absorption is also regenerated completely in the regeneration
column. The above Table also shows that Water content is negligible in the final product streams. Thus, the designed
process is efficient in obtaining optimum LNG and LPG production.
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Impact Factor (JCC): 5.5342 NAAS Rating: 3.56
Table 5: Product Streams for LEF and LPG Columns, Dehydrated Natural Gas Stream from Glycol
Dehydration Unit, Sweet Gas Stream after Elimination of Acidic Gases.
Note: MF = Mole Fraction of the particular component in the mixture
Effect on LPG Production by Varying Reflux Ratio of LPG Column.
Table 6: Molar Compositions of Top Product (S-42) of LPG Column, with Number of
Trays =30, Feed Tray = 15, Operating Constant Pressure = 2242322 N/m2
Reflux Ratio 0.5 0.75 1 1.5 1.75 2 2.5
Carbon dioxide 0.0073703 7.37E-03 0.00737 0.00737 0.00737 0.00737 0.00737
Hydrogen sulphide 0.034608936 0.03676686 0.037595 0.03793 0.037903 0.037939 0.037945
Methane 4.27E-07 4.27E-07 4.27E-07 4.27E-07 4.27E-07 4.27E-07 4.27E-07
Ethane 0.012891891 0.00263454 9.11E-05 4.70E-07 1.46E-06 1.97E-07 5.59E-08
Propane 0.56088646 0.57570241 0.585095 0.586315 0.586318 0.586312 0.58631
N-butane 0.36837303 0.36837305 0.368373 0.368373 0.368373 0.368373 0.368373
Isobutane 0.015865557 0.0091524 0.001476 1.10E-05 3.36E-05 4.65E-06 1.31E-06
Isopentane 2.61E-06 7.66E-09 9.56E-11 4.37E-13 1.34E-12 1.88E-13 5.66E-14
N-pentane 7.54E-07 2.12E-09 2.82E-11 1.49E-13 4.47E-13 6.53E-14 2.02E-14
N-hexane 7.63E-17 1.77E-19 1.74E-21 9.28E-24 2.55E-23 1.44E-23 1.62E-24
N-heptane 3.75E-24 0 4.90E-22 0 1.16E-23 0 1.81E-17
As shown in figure (2), and Table (6) above, comparisons are done for the top product of the LPG column, by
varying its reflux Ratio. Methane and Ethane, are already eliminated in LEF column. It is important to obtain minimum
NAPTHA content in bottoms stream of LPG column, to optimize LPG production. As shown below in Table (8), the total
NAPTHA content is minimum for the Reflux Ratio of 1.75. Hence, Reflux Ratio of 1.75 is most suitable to yield optimum
LPG
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Figure 2: Mole Fractions of Propane and Butane (LPG) with Varying Reflux Ratio.
Table 7: Molar Compositions of Bottom Product (S-43) (NAPTHA) of LPG Column, with
Number of Trays =30, Feed Tray = 15, Constant Operating Pressure = 2242322 N/m2
Reflux Ratio 0.5 0.75 1 1.5 1.75 2 2.5
Carbon dioxide 3.72E-12 2.67E-13 3.83E-14 9.10E-16 2.67E-15 3.52E-16 7.22E-17
Hydrogen sulphide 0.003337126 0.0011792 0.000351 1.65E-05 4.30E-05 6.77E-06 1.41E-06
Methane 1.86E-22 4.72E-22 1.31E-21 2.76E-22 2.34E-22 1.22E-20 1.10E-18
Ethane 2.01E-08 2.56E-09 6.31E-10 6.72E-11 1.20E-10 4.21E-11 2.13E-11
Propane 0.01703128 0.01703388 0.017034 0.017034 0.017034 0.017034 0.017034
N-butane 0.036590899 0.04684826 0.049392 0.049482 0.049481 0.049483 0.049483
Isobutane 0.021745652 0.02845881 0.036135 0.0376 0.037578 0.037607 0.03761
Isopentane 0.15105114 0.13623518 0.126843 0.125622 0.125619 0.125626 0.125627
N-pentane 0.021610889 0.02161164 0.021612 0.021612 0.021612 0.021612 0.021612
N-hexane 0.005338876 0.00533888 0.005339 0.005339 0.005339 0.005339 0.005339
N-heptane 0.001055806 0.00105581 0.001056 0.001056 0.001056 0.001056 0.001056
Table 8: Molar Compositions and Summation of NAPTHA Content with Varying Reflux Ratio
Reflux Ratio 0.5 0.75 1 1.5 1.75 2 2.5
Isopentane 0.15105114 0.13623518 0.126843 0.125622 0.125619 0.125626 0.125627
N-pentane 0.021610889 0.02161164 0.021612 0.021612 0.021612 0.021612 0.021612
N-hexane 0.005338876 0.00533888 0.005339 0.005339 0.005339 0.005339 0.005339
N-heptane 0.001055806 0.00105581 0.001056 0.001056 0.001056 0.001056 0.001056
Summation 0.179056711 0.1642415 0.154849 0.153629 0.153626 0.153632 0.153634
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Effect on LPG Production by Varying Number of Trays of LPG Column
Table 9: Molar Compositions of Top Product (S-42) of LPG Column, with Reflux
Ratio = 1.75 and Constant Operating Pressure = 2242322 N/m2
(No. of trays, Feed tray) (20, 5) (20, 10) (30,10) (30,15) (30, 25) (50,10) (50,25)
Carbon dioxide 0.0073703 0.00737 0.00737 0.00737 0.007369 0.00737 0.00737
Hydrogen sulphide 0.03780553 0.037627 0.037901 0.037829 0.037072 0.037945 0.03793
Methane 4.27E-07 4.27E-07 4.27E-07 4.27E-07 4.27E-07 4.27E-07 4.27E-07
Ethane 0.00335774 0.000384 0.000382 4.18E-05 5.31E-07 0.000382 4.70E-07
Propane 0.57763077 0.585083 0.584815 0.586136 0.587451 0.584772 0.586315
N-butane 0.36837289 0.368367 0.368373 0.368373 0.368092 0.368373 0.368373
Isobutane 0.00519123 0.001167 0.001155 0.00025 1.38E-05 0.001155 1.10E-05
Isopentane 0.00014162 1.12E-06 1.12E-06 8.33E-09 4.71E-13 1.12E-06 4.37E-13
N-pentane 0.00012857 7.92E-07 7.89E-07 4.60E-09 1.59E-13 7.89E-07 1.49E-13
N-hexane 9.03E-07 5.48E-11 5.45E-11 3.09E-15 7.74E-16 5.45E-11 9.28E-24
N-heptane 1.27E-08 2.97E-14 2.95E-14 6.42E-20 0 2.95E-14 0
Water 9.14E-09 7.23E-10 7.21E-10 5.52E-11 3.29E-13 7.21E-10 3.06E-13
As shown in table (9) and figure (3), the maximum propane content is obtained when number of trays are 30 and
feed tray is 25 for an LPG column. Also, from table (11), NAPTHA content in minimum in bottoms stream of LPG column
when, Number of trays are 30 with feed tray at 25. Hence, (No. of trays = 30, feed tray = 15) are most suitable for optimum
production yield of LPG.
Figure 3: Mole Fraction of Propane with Varying Number of Trays.
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Table 10: Molar Compositions of Bottom Product (S-43) (NAPTHA) of LPG Column,
with Reflux Ratio = 1.75 and Constant Operating Pressure = 2242322 N/m2
(No. of Trays,
Feed Tray) (20, 5) (20, 10) (30,10) (30,15) (30, 25) (50,10) (50,25) (50,40)
Carbon dioxide 3.17E-11 4.96E-09 1.63E-13 2.81E-11 8.57E-07 5.19E-22 9.10E-16 4.90E-09
Hydrogen
sulphide 0.00014053 0.000319 4.48E-05 0.000117 0.000874 9.06E-07 1.65E-05 0.000315
Methane 1.16E-22 2.70E-18 6.76E-19 6.04E-23 7.47E-14 3.55E-20 1.44E-22 2.70E-18
Ethane 1.63E-07 6.29E-06 3.09E-09 1.38E-07 0.000281 7.44E-16 6.72E-11 6.22E-06
Propane 0.01689227 0.017033 0.017033 0.017034 0.017034 0.017033 0.017034 0.017034
N-butane 0.04612505 0.049099 0.0491 0.049441 0.049482 0.049101 0.049482 0.049483
Isobutane 0.03241998 0.036444 0.036456 0.037361 0.037597 0.036456 0.0376 0.037611
Isopentane 0.13430682 0.126855 0.127122 0.125802 0.124486 0.127166 0.125622 0.125307
N-pentane 0.02148307 0.021611 0.021611 0.021612 0.021612 0.021611 0.021612 0.021612
N-hexane 0.00533797 0.005339 0.005339 0.005339 0.005339 0.005339 0.005339 0.005339
N-heptane 0.00105579 0.001056 0.001056 0.001056 0.001056 0.001056 0.001056 0.001056
Water 6.48E-07 6.57E-07 6.57E-07 6.57E-07 6.57E-07 6.57E-07 6.57E-07 6.57E-07
Table 11: Molar Compositions and Summation of NAPTHA Content with Varying
NO. of Trays and FEED Tray, of LPG Column.
(No. of
Trays, Feed
Tray)
(20, 5) (20, 10) (30,10) (30,15) (30, 25) (50,10) (50,25) (50,40)
Isopentane 0.13430682 0.126855 0.127122 0.125802 0.124486 0.127166 0.125622 0.125307
N-pentane 0.02148307 0.021611 0.021611 0.021612 0.021612 0.021611 0.021612 0.021612
N-hexane 0.00533797 0.005339 0.005339 0.005339 0.005339 0.005339 0.005339 0.005339
N-heptane 0.00105579 0.001056 0.001056 0.001056 0.001056 0.001056 0.001056 0.001056
Summation 0.16218366 0.154861 0.155128 0.153808 0.152492 0.155171 0.153629 0.153313
Effect on LPG Production by Varying Operating Pressure and Condenser Pressure of LPG Column
Table 12: Molar Compositions of Top Product (S-42) of LPG Column, with Reflux Ratio = 1.75
and Number of Trays = 30, Feed Tray = 25
Condenser Pressure 2242322 4000000 1765500 800000 1765500 2765500
Pressure 2242322 4000000 1029698 1029698 800000 1029698
Carbon dioxide 8.57E-07 1.47E-05 3.36E-06 1.41E-19 7.29E-18 1.97E-16
Hydrogen sulphide 0.000874 0.0031716 0.0023703 3.81E-07 2.35E-05 1.69E-05
Methane 7.47E-14 8.79E-12 2.81E-14 3.07E-22 6.81E-22 1.36E-22
Ethane 0.0002807 0.0023013 0.0006122 4.00E-14 2.37E-13 1.34E-11
Propane 0.0170339 0.0170299 0.0170339 0.0170339 0.0170339 0.0170339
N-butane 0.0494823 0.0463979 0.0494795 0.0494828 0.0494828 0.0494827
Isobutane 0.0375974 0.0296986 0.0372738 0.0376112 0.0376112 0.0376084
Isopentane 0.1244862 0.1311437 0.1229823 0.1256271 0.1256039 0.1256135
N-pentane 0.0216116 0.0216092 0.0216116 0.0216116 0.0216116 0.0216116
N-hexane 0.0053389 0.0053389 0.0053389 0.0053389 0.0053389 0.0053389
N-heptane 0.0010558 0.0010558 0.0010558 0.0010558 0.0010558 0.0010558
Water 6.57E-07 6.51E-07 6.57E-07 6.57E-07 6.57E-07 6.57E-07
As shown in table (12), the maximum Propane and Butane content was obtained for a condenser pressure of
1765500 N/m2, and constant operating pressure of 1029698 N/m2. From Table (14), the NAPTHA content is found to be
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Impact Factor (JCC): 5.5342 NAAS Rating: 3.56
minimum at this operating and condenser pressure. Hence, Condenser pressure of 1765500 N/m2, and constant operating
pressure of 1029698 N/m2 is most suitable for yielding maximum LPG production.
Table 13: Molar Compositions of Bottom Product (S-43) (NAPTHA) of LPG Column,
with Reflux Ratio = 1.75 and Number of Trays = 30, Feed Tray = 25
Condenser Pressure 2242322 4000000 1765500 800000 1765500 2765500
Pressure 2242322 4000000 1029698 1029698 800000 1029698
Carbon dioxide 8.57E-07 1.47E-05 3.36E-06 1.41E-19 7.29E-18 1.97E-16
Hydrogen sulphide 0.000874 0.0031716 0.0023703 3.81E-07 2.35E-05 1.69E-05
Methane 7.47E-14 8.79E-12 2.81E-14 3.07E-22 6.81E-22 1.36E-22
Ethane 0.0002807 0.0023013 0.0006122 4.00E-14 2.37E-13 1.34E-11
Propane 0.0170339 0.0170299 0.0170339 0.0170339 0.0170339 0.0170339
N-butane 0.0494823 0.0463979 0.0494795 0.0494828 0.0494828 0.0494827
Isobutane 0.0375974 0.0296986 0.0372738 0.0376112 0.0376112 0.0376084
Isopentane 0.1244862 0.1311437 0.1229823 0.1256271 0.1256039 0.1256135
N-pentane 0.0216116 0.0216092 0.0216116 0.0216116 0.0216116 0.0216116
N-hexane 0.0053389 0.0053389 0.0053389 0.0053389 0.0053389 0.0053389
N-heptane 0.0010558 0.0010558 0.0010558 0.0010558 0.0010558 0.0010558
Water 6.57E-07 6.51E-07 6.57E-07 6.57E-07 6.57E-07 6.57E-07
Table 14: Molar Composition and Summation of NAPTHA Content, with Varying Operating
and Condenser Pressure of LPG Column
Condenser Pressure 2242322 4000000 1765500 800000 1765500 2765500
Pressure 2242322 4000000 1029698 1029698 800000 1029698
Isopentane 0.1244862 0.1311437 0.1229823 0.1256271 0.1256039 0.1256135
N-pentane 0.0216116 0.0216092 0.0216116 0.0216116 0.0216116 0.0216116
N-hexane 0.0053389 0.0053389 0.0053389 0.0053389 0.0053389 0.0053389
N-heptane 0.0010558 0.0010558 0.0010558 0.0010558 0.0010558 0.0010558
Summation 0.1524925 0.1591476 0.1509886 0.1536334 0.1536103 0.1536198
We can conclude, that operating parameters of LPG column for maximum LPG production are Reflux Ratio =
1.75, Number of Trays, Feed Tray = 30, 25 and operating pressure = 1029698 N/m2, condenser pressure = 1765500 N/m2.
Using these optimum operating conditions, the designed process is simulated and results are mentioned in Table (15).
Natural Gas Processing – Designing And Simulation 11
www.tjprc.org [email protected]
Using the above process and optimum operating parameters for LPG column, molar compositions for product
streams are tabulated below:
Table 15: Molar Compositions of Product Streams of LPG and LEF Columns,
using Optimum Operating parameters for LPG Column
CONCLUSIONS
The developed process focuses on obtaining high productivity of commercially used Natural gas products, such as LNG
and LPG. The process is simulated using DWSIM software. It is clearly visible, that the process has turned out to be
extremely efficient in terms of LPG and LNG manufacturing. Different parameters that would enhance the LPG production
such as the Reflux ratio, Number of trays, and operating pressure Of LPG column were also studied. The results showed
that, for the developed process, the LPG production was optimum and maximized for a reflux ratio of 1.75, the number of
trays = 30 with feed tray = 15, condenser pressure = 1765500 N/m2 and operating pressure of 1029698 N/m2. After
simulating the process flowsheet, LNG produced was 97% (Methane = 88%, Ethane = 9%) and LPG yield was 95%
(Propane = 59%, N-butane = 36%). The process uses a different approach for LNG and LPG production. Rather than using
different columns for obtaining individual products, only two fractionating columns are used for the separation of Natural
Gas. This method not only reduces the equipment cost but also reduces total energy consumption to obtain pure products.
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