1

PROJECT REPORT

ON

ENHANCEMENT OF LPG RECOVERY

GAIL (India) Limited, LAKWA

SUBMITTED BY: GUIDED BY:

KUMAR SANU MAHATO MR. VENU BABU PULI

B.TECH, PRE-FINAL YEAR, CHEMICAL ENGINEERING DEPUTY MANAGER (OPERATION)

INDIAN INSTITUTE OF TECHNOLOGY, GUWAHATI GAIL (India), LAKWA

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ABSTRACT

This report is prepared at GAIL (India) Limited, Lakwa as a part of the industrial training and

contains a brief description of the LPG recovery process employed in the GAIL (India) Limited,

Lakwa. It mainly focuses on the process description of conversion of Natural Gas to LPG .The

details of the project undertaken in the same unit as a part of practical training along with the

methodology and the procedure adopted are also included in this report.

Project Guide,

Mr. Venu Babu Puli

Deputy Manager (Operation)

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ACKNOWLEDGEMENT

It has been an immense pleasure and truly enriching experience doing my vocational

training at GAIL (India) Limited, Lakwa.

I take this opportunity to thank all those people who have made this experience a

memorable one. I am heartily thankful to Mr. G.Ankaiah (CM, Operation), Mr. Anant Purohit

(SM, Operation), Mr. Venu Babu Puli (DM, Operation), and Mr. Nikunj Bhatnagar (DM,

Environment) for their co-operation and proper guidance during my training.

I would like to thank my guide Mr. Venu Babu Puli, DM (Operation) who has been the

guiding force behind the completion of this project. I am sincerely thankful to the entire team

of the Operation unit for their valuable help and guidance in the completion of my training.

I am also thankful to Mr. A.P Gogoi, SM, HR for giving me an opportunity to work with

GAIL (India) Limited. I would also like to thank Mrs. Elveena Isaac (DM, HR), who coordinated

my training extremely well.

Finally, I am grateful for the joint support from the GAIL Group as a whole for the

opportunity and assistance they provided me to do my training here.

Thanking You.

Kumar Sanu Mahato

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PREFACE

Any amount of theoretical knowledge is incomplete without exposure to industrial practice.

Practical knowledge means visualization and application of knowledge which we read in books.

Theoretical studies cannot be perfect without practical training. Hence, in-plant training is of

great importance for an engineering student. Teaching gives theoretical aspect of technology,

but practical training gives knowledge of industrial activities.

My aim for this industrial training was to enhance the LPG recovery by designing a heat

exchanger and decreasing the temperature of the feed gas using the lean gas, so that the

recovery of LPG could enhance. I have used excel sheet and generated a general function which

would give the design by changing few parameters.

This project report presents a detailed summary of my enriching industrial experience at the

GAIL (India), Lakwa.

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Table of Contents

1) GAIL Profile 6-7

2) Introduction to Plant 8-15

LPG Plant Overview 8

LPG Manufacturing Process Description 8-10

Process Flow Diagram 11

Product Quality Control 12

Fire Fighting And Protection Systems 12-15

3) Project 16-30

Introduction to Project 16

Introduction to Heat Exchangers 16-17

Design of Heat Exchanger 17-29

Cost Benefit Analysis 30

Result 30

4) Conclusion 31

5) Bibliography 32

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1) GAIL (India)-Profile

Formation of GAIL

GAIL (India) Ltd was incorporated in August 1984 as a Central Public Sector Undertaking (PSU)

under the Ministry of Petroleum & Natural Gas (MoP&NG). The company was initially given the

responsibility of construction, operation & maintenance of the Hazira – Vijaypur – Jagdishpur

(HVJ) pipeline Project. It was one of the largest cross-country natural gas pipeline projects in

the world. Originally this 1800 Km long pipeline was built at a cost of Rs 1700 Crores and it laid

the foundation for development of market for natural Gas in India.

Current Businesses – Domestic

GAIL, after having started as a natural gas transmission company during the late eighties, has

grown organically by building large network of Natural Gas Pipelines covering more than 10900

Km with a capacity of around 200 MMSCMD; two LPG Pipelines covering 2040 Km with a

capacity of 3.8 MMTPA of LPG; seven gas processing plants for production of LPG and other

Liquid Hydrocarbons, with a production capacity of 1.4 MMTPA; and a gas based integrated

Petrochemical plant of 410,000 TPA polymer capacity which is further being expanded to a

capacity of 900,000 TPA. The Company also has 70% equity share in Brahmaputra Cracker and

Polymer Limited (BCPL) which is setting up a 280,000 TPA polymer plant in Assam. Further, GAIL

is a co-promoter with 15.5% equity stake in ONGC Petro-additions Limited (OPaL) which is

implementing a green field petrochemical complex of 1.1 MMTPA Ethylene capacities at Dahej

in the state of Gujarat. GAIL has 32.86% stake along with NTPC as equal partner in JV Company,

RGPPL at Dabhol which is house to largest gas based power generation facility and an LNG

regasification terminal operated by GAIL. In 2013, GAIL commissioned 5 MMTPA Dabhol LNG

terminals and will remain its commercial operator for 25 years.

Keeping in mind the requirement of growth and consolidation as well as opportunities arising

out of New Exploration Licensing Policy (NELP) of Government of India, the company has

moved into upstream of gas value chain i.e. Exploration & Production and currently has stakes

in 20 E&P blocks including 2 blocks overseas (in Myanmar).

GAIL is a pioneer in City Gas Distribution (CGD) business in India, with Indraprastha Gas Limited

(IGL) in Delhi and Mahanagar Gas Limited (MGL) in Mumbai being its biggest success stories.

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Besides IGL and MGL, GAIL has set up several JVs for CGD to supply gas to households,

transport sector & commercial consumers in various cities including Hyderabad, Agartala,

Kanpur, Indore, Vadodara, Lucknow, Agra and Pune. In 2008, GAIL incorporated a wholly owned

subsidiary, GAIL Gas Ltd (GGL) to exclusively focus on city gas distribution business. GGL has

been authorized for implementation of CGD projects in four cities namely Kota, Dewas, Sonepat

& Meerut in the 1st round of bidding by Petroleum & Natural Gas Regulatory Board (PNGRB).

Leveraging on its pipeline network, GAIL has built a strong Optic Fibre Cable (OFC) network of

approximately 13,000 km for its own internal use and leasing of bandwidth as a carriers' carrier.

As a part of its initiative towards reducing carbon footprint and creating a path of sustainable

growth, GAIL is building a portfolio of renewable businesses. The company has successfully set

up wind energy power projects of 118 MW across states of Gujarat, Tamil Nadu and Karnataka.

Global Presence

As a strategy of going global and further expanding global footprint, GAIL has formed a wholly-

owned subsidiary company, GAIL Global (Singapore) Pte Ltd. in Singapore for pursuing overseas

business opportunities including LNG & petrochemical trading. In U.S, GAIL has 20% working

interest with Carrizo Oil & Gas Inc. in the Eagle Ford shale acreage, Texas through a wholly

owned subsidiary GAIL Global (USA) Inc. Subsequently, a wholly owned subsidiary of GAIL

Global (USA) Inc. was formed in order to explore LNG import/liquefaction capacity booking

opportunities from U.S.

GAIL is also an equity partner in two retail gas companies of Egypt, namely Fayum Gas Company

(FGC) and National Gas Company (Natgas). Besides, GAIL is an equity partner in a retail gas

company involved in city gas and CNG business in China – China Gas Holdings Limited (China

Gas). Further, GAIL and China Gas have formed a joint venture company – GAIL China Gas

Global Energy Holdings Limited for pursuing gas sector opportunities primarily in China.

GAIL is a part of consortium in two offshore E&P blocks in Myanmar and also holds participating

interest in the joint venture company – South East Asia Gas Pipeline Company Limited

incorporated for transportation of gas produced from two blocks in Myanmar to China.

Consistent track record

GAIL has been a leading public enterprise with a consistently excellent financial track record.

The Turnover and PAT have shown remarkable accomplishment with CAGR of 18% and 9%

respectively in the last decade.

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2) Introduction to Plant

2.1) LPG PLANT OVERVIEW:

GAIL’s LPG Plant located at Lakwa, is designed to process 2.0 MMSCMD gas to

produce 85,000 TPA of LPG products and 30,000 TPA NAPHTHA as by product. The

Feedstock is Natural Gas supplied by M/s ONGCL from their Lakwa, Rudrasagar and

Gelaki Oil Fields.

The total plant is divided into two sections namely a) Process or Unit Area and b)

Utilities and off sites Areas. In the unit area, the actual processing or conversion of

Natural Gas to LPG is carried out. The Off sites area consists of a set of supporting

utilities such Power, Water, Flare, Inert Gas, Instrument Air etc., which are necessary

for the operation of the plant.

2.2) LPG MANUFACTURING PROCESS DESCRIPTION:

From the operational point of view, the Unit or Process area is divided into various

sections and each section is described below.

2.2.1) Feed Gas Compression (11-KA-001) Section:

Feed Gas at 8 Kg/cm2 g received from ONGCL, first passes through a Knock Out drum

(VV-001) to remove any free liquid carry over, in this drum, thereby protecting the

downstream Feed Gas Compressor. Water retained in this drum is drained manually

from the bootstrap, into oil water sewer. Liquid hydrocarbon collected, if any, is

dispatched to the lean gas header using Free Liquid Pumps (11-PA-007 A/B). The

feed gas then passes through feed gas compressor suction KOD (11-VV-002), to

knock out any final traces of liquid, before compression. The Feed Gas is compressed

from 8 Kg/cm2 g to 18 Kg/cm2 g in the first stage and then to 44 Kg/cm2 g in the

second stage. Two Air Cooled Inter Coolers, EA-001 and EA-002 are provided, after I

and II stages respectively, to remove the heat of compression from each stage. The

feed gas after I stage compressor is cooled in EA-001 and any liquid condensed is

collected II stage suction knock out drum VV-003. The feed gas from VV-003 is then

compressed in II stage of KA-001 from 18 Kg/cm2 g to 44 Kg/cm2 g. A part of the hot

gas from II stage discharge is used to re boil the Light End Fractionators, in the LEF

Re boiler. The other part of II stage discharge is cooled in the intercooler EA-002.

Any liquid condensed in this stage is collected in VV-004, III stage suction knock out

drum. The third stage compressor is achieved by, the Expander driven Compressor

(11-KA-002) where the gas is compressed to 64 Kg/cm2 g (presently 50-54 Kg/cm2 g).

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The hot gas from III discharge is cooled in air cooler EA-003, and the condensed

liquid is collected in III stage discharge KOD (11-VV-005). The compressed feed gases

are then passed through a Pre-Filter (11-GN-001) to remove any final liquid droplets,

mainly seal oil carry over from the compressor, thereby protecting the molecular

sieve driers located in the downstream. When this filter is fouled, the gas can be

bypassed till the time the cartridge is being replaced.

2.2.2) Feed Gas Drying (11-GN-002A/B) Section:

The compressed feed gas is then dried in Feed Gas Driers (11-GN-002A/B). Each drier

consists of a molecular sieve bed (type 4A), which reduces the moist content to as

low as 1ppm. Out of the two driers, one will be in service and the other one will be

in regeneration mode. Each drier after 24 hours of service cycle, is taken off line and

the standby regenerated drier is taken on service mode. During the regeneration

cycle, the moisture in the standby is expelled using hot lean gas.

The dried gas is passed through Dust filter (11-GN-003 A/B) to remove the fine

particles carried by the feed gas, from the drying bed. This is to safeguard the Plate

Exchanger of chilling section, located in the downstream.

2.2.3) Feed Gas Chilling (11-EP-004 & 11-EP-005) Section:

The drier feed gas is cooled to about -15:C in the chilling section. The section

comprises of a Gas-Gas exchanger (11-EP-004) and a Gas-Liquid Exchanger (11-EP-

005). The feed gas from dust filter outlet is split into two parallel streams, one

passing through the Gas-Gas exchanger where it exchanges heat with the Lean Gas

stream from LEF Condenser (11-EE-006). The other stream passes through the Gas-

Liquid Exchanger exchanging heat with the combined liquid from HP and LP

separator. The partly condensed feed stream, collected from both these exchangers,

is then routed to the HP separator (11-VV-06).

2.2.4) Expander (11-KA-002) Section:

The chilling feed stream from the chilling section is separated in the HP Separator

(11-VV-006) between the vapor and the liquid phases. The vapor stream is expanded

in the expander section from 50-54 Kg/cm2 g to 12.7-13 Kg/cm2 g, thereby chilling it

to -65:C. It is then joined with the vapors from the LEF overhead condenser, which

are at about -25:C. The combined vapors are used as cooling medium in Gas-Gas

exchanger (11-EP-004). Here they are heated to ambient temperature and exported

from the plant as lean gas through a PCV 1008. A slipstream from this control valve

runs through the regeneration circuit for the Dryers.

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The liquid stream from the LP separator is pumped by LP liquid pumps (11-PA-001

A/B) to about 25 Kg/cm2 g and joins the HP Separator liquids. The combined liquids

at about -38:C serve as the chilling medium in the Gas-Liquid exchanger (11-EP-005),

before being routed to the LEF column as feed at about 20-30:C.

A slipstream of the heated lean gas, from the Gas-Gas exchanger is used for the drier

regeneration. A part of this is used as feed in the Regeneration Gas Heater (11-FF-

002) and another part is used as Fuel gas in the same heater. The heated gas is

routed through the drier to expel the moisture. It is then cooled using Regeneration

Gas cooler (11-EA-010) to condense the carried moisture. Finally this gas joins the

lean gas header and leaves the plant to the downstream consumers, ONGCL,ASEB

and Lakwa-TE.

2.2.5) Light End Fractionating, LEF (11-CC-001) Section:

The combined liquid from the HP-LP separators, heated in Gas-Liquid exchanger, is

routed as feed to the LEF column for removal of light ends (C1 & C2). LEF column

separates the light ends, mainly Methane (C1), Ethane (C2), and CO2 from the feed

as overhead product. The column bottom products rich in propane (C3) and butane

(C4) is sent as feed to the LPG column.

The LEF bottom product is routed to the LPG column (11-CC-002) where they are

separated into LPG.

2.2.6) LPG Column (11-CC-002) Section:

The feed comes from the LEF column, where they are separated into LPG (C3, C4) as

top product and NAPHTHA (C5 & higher fraction) as bottom product. The column

has 47 trays.

LPG is sent to the permanent bullet storage using LPG Reflux cum Transfer pumps.

LPG from the storage area is pumped to truck loading gantry where it is dispatched

into LPG tankers. The column bottom product NAPHTHA is sent to Temp Bullet

storage using transfer pumps. There is also provision to spike this product into the

lean gas header using the same pump.

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2.4) PRODUCT QUALITY CONTROL

The LPG Recovery Plant is equipped with most modern equipment and automatic digital control

system to produce LPG of desired quality. Presently the LPG is produced to meet IS: 4576

standard at continuous monitoring and controlling of various process parameters (viz.

temperature, pressure, flow, level etc.), is the key for achieving the desire quality of LPG.

The LPG product from the Unit is analyzed by the laboratory during LPG production. In case the

production quality does not meet the specified standards (presently IS: 4576), then the process

parameters are readjusted to produce the LPG of desired amount. This way online LPG product

quality is controlled. Also before the delivery of LPG from the storage bullet, the final inspection

of stored LPG is again carried out by Laboratory for confirming the quality. Once the LPG is

declared conforming, the final product is released for delivery. This way LPG product quality is

strictly controlled to meet desired specifications.

2.5) FIRE FIGHTING AND PROTECTION SYSTEMS:

The fire detection and protection system mainly covers the plant area, offsite, the LPG road

loading facilities. The various fire protection facilities provided are:

Fire water networking system with hydrants and monitors

Fixed Water Sprinkler system.

Fire alarm system.

LEL Gas Detector Alarm System.

Fire detection and INERGEN protection system.

First Aid Fire Fighting equipment.

Mobile free fighting equipment.

Emergency Action Plan.

Firewater network system:

A firewater network has been designed to fight against possible occurrence of two

major fires at a time. The firewater network pressure is always maintained at a

minimum of 9 Kg/cm2 g fighting fire at all points at all times. The system consists of the

following:

2 no. of fire water reservoirs each with a capacity of 3500 m3. The tank receives

water from the service water pumps.

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Fire water pumps – 2 no. Jockey, 3 no. Diesel, 3 no. Electric HT Motor pumps to

maintain the fire water header pressure at 9 Kg/cm2 g.

67 nos. of hydrants and 16 no. of fire monitors.

During normal operation one jockey pump runs to maintain the firewater network pressure. All

the pumps are provided with auto start switches. When the network pressure falls below the

desired level, one after the other pump takes auto start immediately. The details regarding

these pumps are given below.

Pump type Quantity Drive Rating (KW) Capacity(m3) Head (m)

Jockey pumps 2 Electric 22 50 95

Diesel pumps 3 Diesel 172 410 88

Electric pump 3 Electric 140 410 88

Fire Water Sprinkler System:

LPG storage bullets and loading gentry are provided with automatic water sprinklers system.

Each bullet is fitted with a number of heat sensitive Quartzoid bulbs distributed equally at the

surface of the billets. The bulb senses heat (which may be due to fire) at 79 :C and melt off. This

causes air bleeding to atmosphere there by reducing air pressure of the network. A pressure

switch of the deluge valve senses this reduction of air pressure and water spray system starts

automatically. The spray system can be operated manually by pressing emergency lever, or by

opening the bypass valve.

Fixed Water spray system:

Fixed water spray system with medium velocity has been provided around all LPG bullets, road

loading gantries, and 4 no of pumps in unit area are protected with medium velocity water

protection spray system. A Quartzoid bulb provided bursts whenever the temperature in the

area increases and this activates the water spray system. This water spray system can be

activated locally.

Fire Alarm system:

BGUs (Break Glass Unit) are provided at several points in the plant to facilitate people for

feeding information to MCR in the event of occurrence of a fire without any delay. In the event

of fire or emergency the nearest BGU may be broken. This sounds an alarm in the Fire control

room & MCR immediately. This also activates the Main siren located at substation-2, so that all

personnel in the plant reach the nearest assembly point. Once the area is cleared of emergency

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an all-clear alarm may be activated from MCR so that people can reach back their areas of

work.

LEL Gas Detector Alarm:

An LEL gas detector alarm system is installed in the LPG plant. Electronic sensors are provided

for determining the concentration of combustible gases at a number of locations in the plant.

The system is designed to alarm in the MCR when the level of combustible gas exceeds

predetermined limits at any of the locations. It should be noted that LEL gas detectors do not

initiate any actions except to raise an alarm in the MCR. The only exception to this is that

sometimes gas detectors on the air inlet to the control room air conditioning system. The

following guidelines may be adhered to incase the system sounds an alarm in MCR.

Acknowledge the alarm on the LEL alarm panel located in MCR.

Identify the area of the alarm.

Inform F&S and ensure that always two persons, one from operations and the other

person from F&S with a walkie-talkie and LEL detector must reach the alarm area as

quickly as possible.

Determine the presence of hydrocarbons using the LEL meter. If leak is present, the

source should be identified and isolated as soon as possible.

If smoke or flames are present, initiate the fire alarm to initiate Emergency action

measures from MCR.

Fire Detection and INERGEN extinguishing system:

Automatic fire detection cum INERGEN extinguishing system has been provided at following

places:

Main control room (MCR).

Loading control room.

UPS room at Main C.R.

At each zone pair of detector smoke detectors, Ionization and Photoelectric type (or Optical

type), are located at strategically. There will be two fire monitoring and detection circuits

for each zone linked to each detector in the INERGEN system. Whenever a smoke or fire is

sensed in any zone, by any one of the two types of detectors then a fire alarm starts glowing

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along with audible alarm but without giving any signal to INERGEN releasing module. When

the second detector also detects the fire then the following system will be activated.

The external alarm hooter of that zone gets energized for warning to personnel to

evacuate the premises.

Signal to HVAC to shut down. The exhaust fan below false floor void and above false

ceiling to start automatically after 90 seconds.

Signals to INERGEN release module to open the INERGEN cylinders after present time of

60 seconds.

A manual release pull level is also provided at a suitable location in case of necessity manual

release of INERGEN.

First aid Fire Fighting Equipment:

Fire should be extinguished at the incipient stage before it can cause any major damage. For

this purpose, portable fire extinguishers of different types are provided at all strategic location

inside the plant areas. Depending upon the types of fire, suitable fire extinguisher will be used

for fighting in the initial stages by the operation persons trained for operation of Fire

Extinguisher. The different types of extinguishers provided are:

Dry Chemical Powder Extinguisher (10 Kg & 75 Kg)

CO2 Extinguisher (4.5Kg & 6.5Kg)

Mobile Types Fire Fighting Equipment (Dry Chemical powder cum Foam/water tender-

2no. and DCP trolley).

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3) PROJECT ON

ENHANCEMENT OF LPG RECOVERY THROUGH PRE COOLING OF FEED

GAS BY UTILISING THE AVAILABLE CHILL LEAN GAS.

3.1) INTRODUCTION TO PROJECT:

The feed gas temperature has a significant effect on the recovery of LPG as the liquefaction of

the natural gas decreases with increase in feed gas temperature thus affecting LPG recovery.

Problem faced: High feed gas temperature resulting in low production of LPG.

Aim: Installation of Gas-Gas Exchanger for cooling Feed Gas below 35 :C, not at the battery limit

but between the feed gas coming out of the Filter (11-GN-003 A/B) at temperature 40 :C and

the Lean gas going out of the Gas-Gas exchanger (11-EP-004) at temperature 15 :C.

Present scenario: Average monthly loss of LPG Production is 130 M.T due to higher Feed Gas

Temperature.

Goal setting: Gain in LPG production by approx. 8% during summers.

3.2) INTRODUCTION TO HEAT EXCHANGER:

Transfer of heat from one fluid to another is an important operation for most of the chemical

industries. The most common application of heat transfer is in designing of heat transfer

equipment for exchanging heat from one fluid to another fluid. Such devices for efficient

transfer of heat are generally called Heat Exchanger.

Amongst of all types of exchangers, shell and tube exchangers are most commonly used heat

exchanger equipment. The Fixed-tube sheet exchanger is the simplest and the cheapest type of

shell and tube exchanger. In this type of exchanger the tube sheet is welded to the shell and no

relative movements between the shell and tube is possible. We have used Fixed-tube sheet

exchanger.

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FIGURE: FIXED-TUBESHEET HEAT EXCHANGER

3.3) DESIGN OF HEAT EXCHANGER:

Problem statement: We need to design a heat exchanger to sub-cool the feed gas from 40 :C

to 35 :C. Flow rate of feed gas is 0.65 MMSCMD. Lean gas will be used as coolant which is at a

temperature 15 :C and flow rate of lean gas is 0.48 MMSCMD.

Solution:

Physical properties of gases at different temperature and pressure: (B.A Younglove&Ely)

Properties C1 C2 C3 C4 C5 C6 CO2 N2 Units

Cp(37:C,50bar) 2.563 6.12 2.763 2.484 2.4 1.7 1.468 0.556 kJ/kg.K

Cp(15:C,12.5bar) 2.290 1.934 2.67 2.401 2.319 1.6511 0.953 0.531 kJ/kg.K

Density(37:C,50bar) 31.03 58.19 85.36 112.5 139.6 166.8 85.35 54.31 kg/m3

Density(19:C,12.5bar) 8.238 15.44 22.65 29.86 37.07 44.28 22.65 14.41 kg/m3

Viscosity( 37:C,50bar) 12.51 14.4 93.6 145.5 180 240 16.91 19.18 10-

6Ns/m2

Viscosity(19:C,12.5bar) 11.13 9.44 107.4 168.5 220 - 14.78 17.72 do

Ther.Cond.(37:C,50bar) 0.039 0.059 0.091 0.094 0.1 0.11 0.023 0.029 W/m:C

Ther.Cond.(19:C,12.5bar) 0.033 0.021 0.097 0.099 - - 0.016 0.026 W/m:C

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Composition:

C1 C2 C3 C4 C5 C6 CO2 N2

Rich Gas 0.8075 0.077 0.0529 0.0292 0.0091 0.0028 0.0199 0.0016

Lean Gas 0.8724 0.0843 0.0173 0.0021 0 0 0.0221 0.0018

Physical Properties of Feed and Lean gas:

Thermal Conductivity

Flow rates Cp Density Viscosity

Rich Gas .04598 W/m:C 7.51941 kg/s 2816.4 J/kg.K 40.870 kg/m3 2.30904 E-05 Ns/m2

Lean Gas .033505 W/m:C 5.54919 kg/s 2234.7 J/kg.K 9.4705 kg/m3 1.30831 E-05 Ns/m2

We have only considered thermal design and used the Kern’s method.

The feed gas is at a pressure of 50 bar, so it is allocated tube side. Since, high pressure tubes

will be cheaper than a high pressure shell.

Heat capacity (feed) = 2.81 kJ/kg.K

Heat load = 7.51941 × 2816.4 × (40-35) = 105889.4 W

Heat capacity (lean) = 2.23 kJ/kg.K

Cooling water final temperature = (105889.4/ (2234.7 × 5.54919)) +15 :C

= 23.5389 :C

LMTD (∆Tlm) = 18.17316 :C by using the formula

We are using one shell pass and two tube passes, so by using the formula

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R=0.585555

S=0.341556

By using the formula

Ft = 0.978027

By using the formula,

(∆Tm) = 0.978027 × 18.17316 = 17.77383 :C

From book Coulson and Richardson

U(guess) for gas gas = 20 W/m2 :C

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Provisional area

A = 297.8799 m2

Choose 0.0381 m (1.5 inches) Outer Diameter, 0.034798 m (1.37 inch) Outer

Diameter, 3.65 m long tube, cupro-nickel.

Allowing for tube sheet thickness, take

L = 3.60 m

Area of one tube = 0.430682 m2

Number of tubes = 691.6463 = 692

As the shell-side fluid is relatively clean use 1.25 triangular pitch.

Bundle diameter Db = 1.383845 m

Using a fixed tube head type,

From the figure given in next page, we can find the bundle diameter clearance

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Bundle diametrical clearance = 0.017 m

Shell diameter = 1.400845 m

Tube-side coefficient

Mean feed temperature = 37.5 :C

Tube cross-sectional area = 0.000951 m2

Tube per pass = 346

Total flow area = 0.328417 m2

Feed mass velocity = 22.89589 kg/s m2

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Density feed = 40.87082 kg/m3

Feed linear velocity = 0.560201 m/s

Re = 34504.8

Pr = 1.41385

Jh = 0.001 from the figure below

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By using the formula

We get

hi = 36.5005 W/m2 :C

Shell-side coefficient (Lean gas)

Choose baffle spacing = Ds/3 = 0.466948 m

Tube pitch = 0.047625 m

Equivalent diameter,

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From formula above,

de = 0.027053 m

By using the formula for cross flow area

We get,

Cross flow area, As = 0.130824 m2

Mass velocity, Gs = 42.41706 kg/s m2

Mean shell side temperature = 19.26 :C

Density Lean = 9.470533 kg/m3

Viscosity = 1.31E-05 Ns/m2

Heat capacity = 2234.707 J/kg :C

Thermal conductivity = 0.033505 W/m :C

Re = 87708.97

Pr = 0.872602

Jh = 0.003 (25% baffle cut) , from figure below

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By using the formula

We get,

ho = 305.3245 W/m2 :C

We are neglecting the viscosity term because for low viscous fluid it is not significant.

Overall co-efficient

Thermal conductivity of cupro-nickel alloy = 50 W/m :C

Taking fouling factor for light hydrocarbon from table below and putting it in the

formula

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We get,

Uo = 29.65134 W/m2 ⁰C

Well above assumed value of 20 W/m2 :C was taken.

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Pressure drop

Tube side

From figure below, for Re = 34504.8

jf = 0.0035

Neglecting the viscosity correction term and by using the formula

∆Pt = 69.21996 N/m2

= 0.006922 bar (negligible)

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Shell side

From figure below, at Re = 87708.97

jf = 0.032

Neglecting the viscosity correction and

By using the formula

∆Ps = 9707.927 N/m2

= 0.970793 bar (acceptable)

29

Material of construction: Cupro-Nickel alloy

Heat duty 105.8894 kW

Overall heat transfer coefficient 29.65134 W/m2 :C

Heat transfer area 298 m2

Tube outer diameter 1.5 inch

Tube inter diameter 1.37 inch

Tube length 3.60 m

Number of tubes 692

No. of tube passes 2

No. of shell passes 1

Bundle diameter 1.383845 m

Shell diameter 1.400845 m

Baffle spacing 0.466948 m

Tube pitch 0.047625

Inlet feed temperature 40 :C

Outlet feed temperature 35 :C

*all formulae are taken from the book Coulson and Richardson

30

3.4) COST BENEFIT ANALYSIS

The Product rate at 40 :C A 3.541 MT/HR

The Product rate at 35 :C B 3.958 MT/HR

Increase in Hourly Production X = B-A 0.417 MT/HR

Increase in Production on daily basis 10.008 MT/DAY

Considering the temperature remains 40 ⁰C for 5 months in a year

Estimated increase in production (annual basis) Y = X*150 1501.2 MT/YEAR

Financial Benefit

Average cost of LPG L 54901.00 Rs/MT

Average cost of Production M 27000.00 Rs/MT

Financial Benefit (excluding taxes/duties subsidy) N=L-M 27901 Rs/MT

Total Benefit N*Y 4,18,84,981 Rs

4.18 Crore/ Year

Pay Back Period Less than 3 months (if Exchanger cost Rs 1 crore)

3.5) RESULT

Theme: Enhancement of Productivity of Liquefied Petroleum Gas (LPG)

Achievement: Additional LPG Production = 10 MT/Day during summer

Sources of LPG Production Maximization

Decrease in Feed Gas

Temperature

Higher Butane

content

Higher yield

of LPG

31

4) CONCLUSION

The feed gas is coming at a temperature of 28 :C during summers and my plan is to put

a heat exchanger between the gas coming out of the drier (40 :C) and the gas coming

out of the Gas-Gas heat exchanger, 11-EP-004 (15 :C) so that before the feed gas goes

into the LEF column, the temperature decreases resulting in more production of C4

(butane) thereby increasing the production of LPG and enhancing the recovery of LPG by

approx. 8 % during summers.

If we could implement the above idea of heat exchanger, we can save an amount of Rs 4

crores per year. It could be beneficial during the summers when the temperature of the

feed gas is high.

During winters the production of LPG is high and we don’t need to decrease the

temperature further.

Installing heat exchanger generally costs around one crore rupees and this money could

be recovered in around three months.

The pressure drop coming out after the calculation is also acceptable.

We will be using a fixed tube-sheet shell and tube heat exchanger with a heat duty of

105 kW. One shell pass and two tube passes (1, 2 heat exchanger) with number of tubes

692 and shell diameter of around 1.4 meters.

32

5) BIBLIOGRAPGY

Fourth edition Coulson & Richardson’s CHEMICAL ENGINEERING SERIES , Chemical

Engineering Design, Volume 6 , R.K SINNOTT

Thermophysical Properties of fluids. II. Methane, Ethane, Propane, Isobutane, and

Normal Butane, B.A Younglove and J. F. Ely, Thermophysical division, National

Engineering Laboratory, Nation Bureau of Standards, Boulder, Colorado 80303.

Indian Standards, Specification for Shell and Tube Heat Type Heat Exchanger, Bureau

of Indian Standards.

Standards of Tubular Exchanger Manufacturers Association (TEMA), Eighth edition

http://www.peacesoftware.de/einigewerte/co2_e.html

http://www.peacesoftware.de/einigewerte/stickstoff_e.html

http://www.peacesoftware.de/einigewerte/methan_e.html

Perry’s Chemical Engineering Handbook 6.

Process Heat Transfer by Donald Q. Kern