NATURAL GAS PROCESSING DESIGNING AND SIMULATION

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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


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


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



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.

6 Sarthak Vaidya


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



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

8 Sarthak Vaidya


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.



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

10 Sarthak Vaidya


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


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


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).



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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NATURAL GAS PROCESSING DESIGNING AND SIMULATION

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