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.
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
Original Article Original
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
www.tjprc.org [email protected] 2 Sarthak Vaidya 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
Impact Factor (JCC): 5.5342 NAAS Rating: 3.56 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
www.tjprc.org [email protected] 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
Impact Factor (JCC): 5.5342 NAAS Rating: 3.56 Natural Gas Processing – Designing And Simulation 5
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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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
Impact Factor (JCC): 5.5342 NAAS Rating: 3.56 Natural Gas Processing – Designing And Simulation 7
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.
Impact Factor (JCC): 5.5342 NAAS Rating: 3.56 Natural Gas Processing – Designing And Simulation 9
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, (20, 5) (20, 10) (30,10) (30,15) (30, 25) (50,10) (50,25) (50,40) Feed Tray) 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 0.00014053 0.000319 4.48E-05 0.000117 0.000874 9.06E-07 1.65E-05 0.000315 sulphide 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 (20, 5) (20, 10) (30,10) (30,15) (30, 25) (50,10) (50,25) (50,40) Tray) 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 www.tjprc.org [email protected] 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 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).
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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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