SPE 151894

Increasing Propane Productivity by Changing the Operating Conditions without Adding any New Facilities Tamer Hamdy Riad, The Egyptian Natural Gas Co. Gasco

Copyright 2012, Society of Petroleum Engineers This paper was prepared for presentation at the North Africa Technical Conference and Exhibition held in Cairo, Egypt, 20–22 February 2012. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.

Abstract Gasco operates two NGL plants located in Alexandria; Amerya LPG plant and Western Desert Gas Complex (WDGC).

Recently, Gasco has started up a new project that integrates the two plants to maximize Ethane and Propane productivity.

The project design is based on adding new process facilities in Amerya plant to start producing C2+ that directed to WDGC,

while a new train is added in WDGC to increase the feed gas capacity and maximize C2+ recovery by applying the Gas

Subcooled Process (GSP) as Ethan mode of operation scheme.

This paper presents a study to increase the productivity of the two plants by using simulation software to help the decision

making for what the optimum conditions should be applied in different modes of operation to increase the production.

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1. Introduction Gasco operates two NGL plants Amerya LPG and Western Desert Gas Complex WDGC

Amerya LPG plant is designed to treat 300 MMSCFD of feed gas to extract LPG and condensate. The feed gas sources of

this plant are Badr 2,3 (Bapetco), Abu-Sanan, south dabah, petro-alm, (neag & sheba), west setra and septco fields. The plant

produces the following :

• 250 MT/Y LPG for local market

• 25 MT/Y condensate for the refineries.

Fig. 1 shows block diagram for Amerya LPG plant and its products

WDGC plant receives & treats 600 MMSCFD of western desert gases from Al-Obayed (Bapetco), Salam, Tarek and El-

Qaser (Khalda) fields, to produce the following products:

• 465 MT/Y of Ethane/Propane mixture used as a feed stock for petrochemical industry

(SIDPEC Company) to produce Ethylene

• 280 MT/Y & 59 MT/Y of LPG and condensate for the local market consumption

adding value for national economy by reducing the imported quantities of the same

products

• 210 MT/Y of Commercial Propane for export to the international market increasing

income from the hard currency to support the national economy.

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Fig. 2 shows block diagram for WDGC and its products

Recently, Gasco has started up a new project that integrates the two plants to maximize Ethane and Propane productivity.

The project design is based on adding new process facilities in Amerya plant to start producing C2+ that directed to WDGC,

while a new train is added in WDGC to increase the feed gas capacity to 900 MMSCFD and maximize C2+ recovery by

applying the Gas Subcooled Process (GSP) as Ethan mode of operation scheme.

Fig. 3 shows block diagram for the integration between Ameryal LPG & WDGC

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The aim of study how to maximize the C3 productivity and switch the plant to propane mode of operation there are many obstructs which constrain this change the study will take the new train in WDGC to change the mode of operation to maximize the production of propane.

Fig. 4 shows process flow diagram (PFD) for a new train in WDGC

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2. Design basis of new train in WDGC 2.1 New feed characteristic

Table 1: Design capacity 300 MMSCFD

Min Max

Pressure 70 kg/cm2 g 68 72

Temperature 14 30

Table 2: Feed gas composition

Components Lean case mol %

H2O 0

N2 0.81

CO2 3.7

H2S 0

C1 79.22

C2 9.9

C3 4.45

IC4 0.71

NC4 0.91

IC5 0.1

NC5 0.1

NC6 0.04

NC7 0.03

NC8 0.03

2.2 Product specifications from new train in WDGC

Table 3: C2/C3 mixture specifications

Specifications mol%

C1 max 0.5

C2 without CO2 92

C3 8-15

C4+ 0.1

CO2 Depends on CO2 in the feed

Table 4: LPG specifications

Specifications

Vapor pressure @ 50 0C 10 kg/cm2 g

C5+ LV% 2

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Table 5: Commercial propane specifications

Wt %

C1 max 0.1

C2 max 1.8

C3 min 95

C4 5

Table 6: Condensate specifications

Specifications

Red vapor pressure 12 psi

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3. Process description The main areas of the new train are the following:

1- Gas dehydration through a molecular sieve dehydration package

2- Chilling trains

3- Turbo – expander package

4- Demethanizer systems

5- Fractionation, including deethanizer, depropanizer, debutanizer systems

6- Sales gas compression package

The new feed gas is directed to the WDGC firstly to dehydration molecular sieve package at 70 kg/cm2 and 27 0C (summer

case) in case of operating upsets leading to hydrate formation; provision has been made for methanol injection at a number of

positions within the cryogenic C2 recovery section of the plant which are most susceptible to hydrate formation.

The new feed gas from dehydration package entering to the cryogenic section is cooled by exchange heat with the

Demethanizer gas heat exchangers and propane package, further cooling to the dry gas happens by the expander for gases

and JT valves for liquids after that the cooled gas conditions becomes 22 kg/cm2 g and -93 0C.

The Demethanizer tower which separate methane from C2 and heavier C2+ it operated with a top pressure (21 - 21.5) kg/cm2

g and liquid bottoms are collected in a separate vessel which forms the liquid hold up capacity of the column

The Demethanizer bottom are pimped to the Deethanizer tower and

the overhead vapor from the Demethanizer first cools the feed gas and compress to the national grade by expander re-

compressor and residue gas compressor.

the fractionation zone including Deethanizer, Depropanizer, Debutanizer towers which separate the fractionate the gas and

produce the products C2/C3 mixture, LPG, Propane and condensate with earlier specifications. This mode of operation called

Ethan recovery to produce C2/C3 mixture, in case of no C2/C3 and switch to Propane recovery mode of operation the

operating conditions will change to extract the amount of C3 in sales gas and C2/C3 which added to propane final product with

acceptable specifications for all products.

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This paper take the deethanizer tower as a case of study, the main parameters will affect to increase the production of propane

are : -

1- Reflux ratio of the deethanizer tower

2- Deethanizer bottom Temperature

The main constrains affect on these parameters are:

• The design duty of the condenser and reboiler

• The specifications of the products like the minimum weigh percent of C3 and maximum weight percent of C2 and

C5+ in the propane product, the vapor pressure of the LPG @ 50 0C and so on. – all specifications are mentioned in

product specification part –

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So, the study will introduce three cases by using HYSYS 7.1 and recommend the optimum condition to obtain maximum

production & profit these cases are: -

Case (1) Changing in Deethanizer bottom temperature and reflux flow

Case (2) Changing in Deethanizer bottom temperature, reflux flow and operating pressure

Case (3) Changing in Deethanizer reflux flow, bottom temperature, operating pressure and Demethanizer bottom temperature

3.1 Define constrains of the design

Table 7: The Related Design Parameters

Equipment availability

Demethanizer reboiler duty, MMcal/hr 11.2

Deethanizer condenser duty MW 4.33

Deethanizer reboiler duty, MMcal/hr 12.96

Deethanizer reflux pump flow rate, m3/hr 85

Table 8: Products specifications and limitations according to the contract obligations

C1 in propane production, mole %  Max. 0.1 

C2 in propane production, wt %  Max. 1.8 

C3 in propane production, wt %  Min. 95 

LPG vapor pressure @ 50 0

C, kg/cm2

g 10 

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3.2 Case I, Changing in Deethanizer bottom temperature and reflux flow

Fig. 5 shows Deethanizer tower

In this case the paper study takes the deethanizer tower and changes both bottom temperature and reflux flow (decrease bottom temp. and increase the reflux flow) within the margin limites and constrains shown in above tables to reach for the optimum conditions to maximize the propane produttion. Firstly, study the effect of temp. only on the production rate

Fig. 6 The effect of decrease the de-ethnizer bottom temperature on C3 production This figure shows that the relation is reverse proportional so, we decrease the temp. with in the main constrain limits

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Secondly, study the effect of reflux ration only on the production rate

Fig. 7 The effect of increase the de-ethnizer bottom temperature on C3 production This figure shows that the relation is direct proportional so, we increase the reflux ration with in the main constrain limits So that in this case the study makes a compination between the two parameters (decrase bottom temp. and increase reflux ratio). The effect of this compination increases the C3 production, the results showns in a below table

Table 9: Case I, Changing in Deethanizer bottom temperature and reflux flow

  Design operating C2

recovery figure  Proposed figure 

Operating parameters    Deethanizer Reflux flow rate, m3/hr 68.54 84.79  Deethanizer bottom temperature,o C 57.8 56.4  Deethanizer operating pressure kg/cm2 15 15  Equipment availability  Condenser, Duty MW  3.51 4.326  Reboiler Duty, MMcal/hr  9.04 9.68  Measures  C2 in propane production, wt %  0.3 1.13  C3 in propane production, wt %  99.44 99.71  C3 in salse gase, mol %  0.7 0.4  Propane production, ton/d  569.8 629.8 

C3 recovery, % 87.8 93.4 

Added value ton/d  60  * In this case the production of propane increased by 60 ton /d

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3.3 Case II, Changing in Deethanizer bottom temperature, reflux flow and operating pressure

In case II we add operating pressure factor by increasing the pressure plus the case I and it’s the effect of that about increasing the production The effect of changing these parameters shown in a below table: Table 10: Case II, Changing in Deethanizer bottom temperature, reflux flow and operating pressure

  Design operating C2

recovery figure  Proposed figure 

Operating parameters    

Deethanizer Reflux flow rate, m3/hr  68.54  84.97 

Deethanizer bottom temperature, C  57.8  57 

Deethanizer operating pressure kg/cm2  15  15.5 

Equipment availability

Condenser, Duty MW  3.51  4.21 

Reboiler Duty, Mmcal/hr  9.04  9.425 

Measures

C2 in propane production, wt %  0.3  1.79 

C3 in propane production, wt %  99.44  98 

C3 in salse gase, mol %  0.7  0.4 

Propane production, ton/d  569.8  633.8 

C3 recovery, % 87.8  93.6 

Added value ton/d 64

* In this case the production of propane increased by 4 ton /d over the case I

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3.4 Case III, Changing in Deethanizer reflux flow, bottom temperature, operating pressure and Demethanizer

bottom temperature

Fig. 8 shows Deethanizer tower

In case III we Demethanizer bottom temperature add operating pressure factor by increasing the pressure plus the case I and it’s the effect of that about increasing the production The effect of changing these parameters shown in a below table:

Design operating C2 recovery figure Proposed figure

Operating parameters

Deethanizer Reflux flow rate, m3/hr 68.54 84.9

Deethanizer bottom temperature, C 57.8 57.1

Deethanizer operating pressure kg/cm2 15 15.5

Demethanizer operating temperature 4.5 0

Equipment availability

Condenser, Duty MW 3.51 4.21

Reboiler Duty, Mmcal/hr 9.04 9.404

Measures

C2 in propane production, wt % 0.3 1.62 C3 in propane production, wt % 99.44 98.17 C3 in salse gase, mol % 0.7 0.36 Propane production, ton/d 569.8 636.8

C3 recovery, % 87.8 94

Added value ton/d 67 * In this case the production of propane increased by 3 ton /d over the case II

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4. Summary Case III is the recommended case because we can recover about 24,000 Ton/Y from 38,000 which means profit

equal to 21 Million $/ Y

Fig. 9 the added values of C3 production in the three cases

So, to determine the optimum operating condition of swithching the plant from ethan to propane mode of operation you must take care about the dynamics of the change inputs and plant response inbetween the design parameters and costrains of the equipments so this study just a study of the effect of switching to propane mode of the respose of the plant between the design conditions.

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Referances 1- Enppi process design manual for WDGC and Amerya LPG plant

2- HYSYS 7.1 manual guide