Fractionation of Natural Gas Liquids to Produce LPG

DEPARTMENT OF PETROLEUM ENGINEERING AND APPLIED GEOPHYSICS

TPG4140 NATURAL GAS

Fractionation of Natural Gas Liquids to produce LPG

Submitted To

Prof. Jon Steinar Gudmundsson

Submitted By

Ahmad, Rafiq

Malla, Majed A. Osama El-Majzoub Det

Hladky ,Maros

Shadman Far, Amir

Usman, Muhammad

Trondheim Nov 24, 2011

Table of Contents

Abstract .......................................................................................................................................................... i

1. Introduction ...................................................................................................................................... 1

1.1 Properties .................................................................................................................................. 1

1.2 Uses of LPG ............................................................................................................................... 3

1.3 The future for LPG ................................................................................................................. 3

2. Natural Gas Liquids Processing ............................................................................................................. 5

2.1 LPG Recovery Processes ................................................................................................................ 5

2.1.1 Recontacting-compression ................................................................................................... 6

2.1.2 Refrigeration ......................................................................................................................... 6

2.1.3 Lean oil absorption................................................................................................................ 6

2.1.4 Adsorption ............................................................................................................................. 6

2.2 LPG Manufacturing ....................................................................................................................... 6

2.2.1 Acid gas removal ................................................................................................................... 7

2.2.2 Extraction Unit ...................................................................................................................... 7

2.2.3 Fractionation Unit ................................................................................................................. 7

2.2.3.1 Deethanizer Section .......................................................................................................... 8

2.2.3.2 Depropanizer Section ........................................................................................................ 8

2.2.3.3 Debutanizer Section .......................................................................................................... 9

2.2.4 Product Treatment Plant ...................................................................................................... 9

2.3 Feed Specifications for NGL Fractionation .................................................................................. 10

2.4 Product Specifications ................................................................................................................. 10

3. Simulation ........................................................................................................................................... 12

3.1 Feed conditioning ....................................................................................................................... 12

3.2 Fractionation columns ............................................................................................................ 13

3.2.1 Deethanizer ................................................................................................................. 13

3.2.2 Debutanizer............................................................................................................. 14

3.2.3 Depropanizer .......................................................................................................... 15

3.2.4 Butane splitter .................................................................................................... 16

4. LPG Transport ..................................................................................................................................... 17

4.1 Continuous flow of LPG – Pipe system ....................................................................................... 17

4.2 Discrete (bulk) means of LPG transport .................................................................................. 18

4.2.1 Vessel tanker transport ................................................................................................... 19

4.2.2 Rail, truck, car transport ............................................................................................. 20

4.3 Economic analysis ....................................................................................................... 20

Conclusions and Discussions ....................................................................................................................... 23

References .................................................................................................................................................. 24

Appendix ..................................................................................................................................................... 26

List of Tables

Table 1: Typical Properties of LPG ................................................................................................................ 2

Table 2:Fractionator types for LPG Production (Abdel-Aal, H. K.et al 2003) ................................................ 9

Table 3:Different Contaminants in LPG (Abdel-Aal, H. K.et al 2003) ............................................................ 9

Table 4: Specifications of feed for NGL fractionation unit (Manley ,D.B.) .................................................. 10

Table 5:Product specifications for LPG (Manley ,D.B) ................................................................................ 11

Table A1:Simulation reults ......................................................................................................................... 27

List of Figures

Figure 1:Blockdiagram for LPG Manufacturing (Parkash ,Surinder ,2009) .................................................. 7

Figure 2: Typical Fractionator train for NGL (Parkash ,Surinder 2009) ........................................................ 8

Figure3: Feed conditioning alt.1 ................................................................................................................. 12

Figure 4: Feed conditioning alt.2 ................................................................................................................ 13

Figure 5:Feed conditioning alt.3 ................................................................................................................. 13

Figure 6: Deethanizer column ..................................................................................................................... 14

Figure 7: Debutanizer column ..................................................................................................................... 15

Figure 8: Depropanizer column................................................................................................................... 15

Figure 9: Butane splitter ............................................................................................................................. 16

Figure A1: Process Flow Sheet (Simulation sheet from Hysys) ................................................................... 26

Figure A2. Distribution Chain (World LP Gas Association 2009) ................................................................. 28

Figure A3: Mid-America Pipeline (Willbros Group, Inc. 2011) .................................................................... 29

Figure A4: Jamnanagar New Delhi ............................................................................................................. 29

Figure A5: SST,SSM ..................................................................................................................................... 30

Figure A6: amerigas Canister ...................................................................................................................... 30

Figure A7: World LPG gas consumption (Fundamentals of the World Gas Industry, 2008) ....................... 31

FigureA 8: World autogas consumption (Fundamentals of the World Gas Industry, 2008) ...................... 31

Abstract

Raw natural gas contains valuable heavier hydrocarbons such as ethane, propane, butane

and fraction of higher hydrocarbons. These associated hydrocarbons, known as natural gas

liquids (NGL), must be recovered from the gas in order to control the dew point of natural

gas stream and to earn revenue by selling these components as products for different

industries. Natural gas liquids are fractionated to produce LPG.

The purpose of this report is to see the method to fractionate different NGL’s to produce

LPG. Different processes for LPG production and recovery from natural gas are discussed.

Further, process has been described for LPG production from NGL by fractionation.

Simulation for fractionation columns has been done in order to investigate the material and

energy balance.

An overview of LPG transportation through canisters and pipeline, which is a new thing, has

been highlighted in the report.

Economic analysis and future market for LPG has been highlighted to see whether this

product can be an alternative to high fuel consumption and demands or not.

Fractionation of NGL to produce LPG

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1. Introduction

Natural gas is one of the world’s favorite and promising fuels. Transportation of gas is not

something easy therefore converting this gas into liquid simplifies and eases the

transportation process. Liquefied Petroleum Gas, which is a super pressurized gas stored in

a liquid form in tanks or canisters, is a known type of Natural gas that we are going to look

very close into.

LPG is a flammable mixture of hydrocarbon gases used as a fossil fuel

closely linked to oil, almost two third of the LPG that is used is extracted

directly from the Earth in the same way as Natural gas. The rest is

manufactured indirectly from petroleum drilled from the Earth in wells.

(Crude oil)

LPG is considered to be a mixture of two flammable nontoxic gases known as propane (C3H8)

and butane (C4H10). Propylene and butylenes are present in small concentrations too.

Mainly the LPG gas is of no odor which makes it hard for people to detect the leakage if it

happens, so a small amount of a pungent gas such as ethanethiol are added to help people

smell potentially dangerous gas leaks.

1.1 Properties

LPG is as twice as heavy as air and half as heavy as water and it is colorless and odorless.

LPG can be compressed at a ratio of 1:250 which enables it to be marked in portable

containers in liquid form as mentioned above. LPG also produces less air pollutants and

carbon dioxide than most other fuels; it helps to reduce the emissions of the typical house


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by almost 1.5 tones of CO2 a year. LPG reduced black carbon emissions as well which are the

second biggest contributor of global warming and causes serious health hazards.

LPG has a high heating (the amount of heat released during combustion of a specified

amount of it) of 12,467 kcal/m³ which is much higher than the average heat value of most

Natural gas (9350 kcal/m3). Also LPG has a very high Wobbe index (an indicator of the

interchangeability of fuel gases: GrossHeatValue

WISpecificGravity

) of 73.5-87.5 MJ/Sm3 which is a

high combustion energy output.

LPG can be used as an alternative fuel to natural gas (methane) in residential, commercial

and industrial applications, as an alternative to gasoline for automotive fuel purposes, and

as a feedstock in petrochemical applications. Both propane and butane are gaseous

hydrocarbons at normal temperatures (15 degrees Celsius) and atmospheric pressure.

However, they can be stored and distributed in liquid from at temperatures of under -42

degrees and -2 degrees Celsius for propane and butane respectively. The Fig below shows

the typical properties of LPG.

Table 1: Typical Properties of LPG

Property Propane Butane

Liquid Density 0.50-0.51 0.57-0.58

Conversion(Ltr per ton) 1968 1732

Gas Density/air 1.40-1.55 1.90-2.10

Boiling Point (C) -45 -2

Latent Heat of Vaporization 358 KJ/Kg 372 KJ/Kg

Specific Heat(as liquid) 0.60 Btu/deg 0.57 Btu/deg

Sulfur Content 0-0.02% 0-0.02%

Calorific Value 2,500 Btu/ft3 3,270 Btu/ft3


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1.2 Uses of LPG

LPG is used as fuel, especially for vehicles such as cars and motorcycles, also as an aerosol

propellant and refrigerant to avoid damage to the ozone. It is an advantage to use LPG as a

fuel for vehicles because it burns cleaner than petrol and diesel.

Another use is as a refrigerant. Propane gas and butane gas are used to make hydrocarbon

refrigerants. Hydrocarbons are known to be more energy efficient and cheaper than other

chemicals, which is why it is suitable to be used as refrigerants.

Another popular use is as a cooking fuel. LPG is very popular, especially among countries like

India and other Asian countries. LPG is used as a cooking fuel for households and even

businesses such as restaurants. As for propane, it is more popularly being used as fuel for

barbeques and portable stoves. This is because propane has a low boiling point, so it will

vaporize once it is released from the container. Butane, on the other hand, is famously

bottled as fuel for lighters and deodorants. When propane and butane combine together,

they become LPG.

LPG can be used as a back-up or secondary fuel in generating the energy for the household.

For example, in order to heat water in winter, LPG is used alongside a solar panel to provide

enough energy for this purpose.

1.3 The future for LPG

LP Gas has played a valuable role in meeting the world’s energy needs. In the future, LPG

has the opportunity to enhance this role by also helping to combat climate change. By

releasing fewer harmful pollutants when used as a domestic and automotive fuel source

LPG is not only a cleaner alternative but also a healthy one.

It seems that the portable nature of bottled LPG, combined with its clean burning

characteristics, presents an immediate winning solution to rapidly expand the availability of

modern energy to those that have been without it.

LPG can claim to be ahead of its time, for its clean-burning, low-carbon advantage is

available at once, so that even using today’s technology, most industries can exceed Kyoto

greenhouse gas reduction targets by switching to LPG. LPG produces lower greenhouse gas


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emissions compared to conventional energy supplies in every application it is used, from

stationary applications such as water heating, space heating, cooking and industrial boilers

to transportation applications.


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2. Natural Gas Liquids Processing

Raw natural gas contains valuable heavier hydrocarbons when extracted from the well

head. The heavier hydrocarbons which are associated with the raw natural gas are ethane,

propane, butane and natural gasoline (condensate from). These associated hydrocarbons

are called natural gas liquids. These NGL components must be recovered to control the dew

point of natural gas stream and also to earn revenue by selling out the separated

components. Following are the different processes used to separate impurities:

Oil and condensate removal

Water Removal

Separation of natural gas liquids

Sulfur and carbon dioxide removal

Our aim/objective of this report is to study the fractionation of natural gas liquids to

produce LPG, (Abdel-Aal, H. K et.al 2003). We will discuss first different LPG manufacturing

processes.

2.1 LPG Recovery Processes

Natural gas mainly contains methane and smaller amounts of ethane, propane, butane and

heavier hydrocarbons along with varying amount of water vapors, carbon dioxide, sulfur

compounds and other non-hydrocarbons. Ethane, propane, butane and propane are known

as associated gases. The removal of these gases from raw natural gas is necessary to meet

the desired consumer specifications of natural gas and to extract valuable products such as

LPG from natural gas. Various techniques are used to recover LPG from natural gas/oil.

1. Recontacting-compression

2. Refrigeration

3. Absorption

4. Adsorption

5. A combination of above


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2.1.1 Recontacting-compression

This process is normally used for the recovery of LPG from crude oil fractionator. This

technique is hardly used in gas industry. The top product from a crude oil fractionator

consists of lighter fractions namely methane, ethane, propane and butane. This top product

stream is compressed, combined with top liquid product, cooled and fed to the separator.

The liquid phase from separator is passed through Deethanizer and the vapor phase

containing some LPG fractions is used as fuel gas. Liquid product of Deethanizer is LPG. The

recovery of LPG by this technique is 75% (Elvers , Barbara 2008).

2.1.2 Refrigeration

This technique is more common for recovery of LPG from gas streams. The principle behind

this technique is to refrigerate the gas stream and LPG fractions are obtained. Recovered

fractions are fractionated to get the LPG components.

The technique is employed in three different processes:

Low temperature separation

Expander Plants

Combined Processes

2.1.3 Lean oil absorption

This method employs the hydrocarbon oil to recover lighter fractions. This process is used in

refineries and also in gas processing plants. LPG recovery by this process is 98%.

2.1.4 Adsorption

Adsorbents are used in this process so that gas molecules are bonded to the surface.

Normally silica gel, activated carbon and alumina are used as adsorbent. The LPG recovery

by this process is significantly lower than other two processes.

2.2 LPG Manufacturing LPG is produced by fractionation of natural gas liquids and from crude oil by distillation,

catalytic cracking, delayed cokers and hydrocrackers. LPG manufacturing process starts with

acid gas removal and extraction unit, then fractionation unit and ends with the product

treatment plant. The simple process is described in the following block diagram. (Parkash

,Surinder ,2009)


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Fig1:Blockdiagram for LPG Manufacturing 1 (Parkash ,Surinder ,2009)

2.2.1 Acid gas removal

Raw gas from the well head is received in knock out drums to separate gas and liquid

phases. The oil field gases contain corrosive acid gases like CO2 and H2S.Removal of these

gases is necessary to further process the gas for LPG production or more products. These

acid gases are removed by amine treatment or Benfield processes .After this, acid gases free

natural gas is sent to extraction unit.

2.2.2 Extraction Unit

The feed of extraction unit is the combination of associated gases and condensate. The

product streams are divided into three steps .One having the liquid stream rich in propane,

butane, and gasoline is sent to the fractionation tower for LPG production and other two

streams to the product gas unit for further processing.

2.2.3 Fractionation Unit

Liquid stream consisting of ethane, propane, butane and pentane is treated in the

fractionator trains to separate them and sold as LPG. Complete process flow sheet is shown

in figure 2. Fractionation tower consists of three columns: Deethanizer, Depropanizer and

Debutanizer. The whole process description is as follows.

Raw Natural Gas

from gas well

Fractionation Unit

Product

Treatment Unit

Acid Gas Removal

Finished Product

LPG

Extraction Unit


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Figure 2: Typical Fractionator train for NGL (Parkash ,Surinder 2009)

2.2.3.1 Deethanizer Section

Raw gas containing associated gases is fed from the top of the Deethanizer. Deethanizer

operated at approximately 390lb/in2. We separated out ethane from this column. The

overhead product is ethane in the form of vapors, which is partially condensed in the

condenser by using propane at 20oF and collected in the reflux drum. Condensed product is

recycled to the Deethanizer tower and non-condensed vapors (mainly ethane) are sent to

the fuel gas system. Temperature inside tower is maintained by supplying heat from

reboiler. The bottom product from Deethanizer enters into the next columns, depropanizer.

2.2.3.2 Depropanizer Section

The pressure of Deethanizer bottom product is reduced to 290 lb/in2 and then entered into

the depropanizer. The overhead product of this column is propane rich and is condensed in

the condenser by using cooling water. The condensed product is collected in the reflux

drum. Some amount of this is refluxed back to the column. Heat is supplied through direct

fired heater.


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2.2.3.3 Debutanizer Section

Depropanizer bottom product is expanded to a pressure of 110 lb/in2 and fed to the top of

the tower. Propane is separated as top product and condensed further in condenser by

using cooling water. Bottom products are the heavier hydrocarbons. Fractionators of

different types are commonly used in gas plant. Commonly used fractionators for LPG are

listed in the table below.

Table 2:Fractionator types for LPG Production (Abdel-Aal, H. K.et al 2003)

Type of fractionator Feed Top product Bottom product

Demethanizer C1/C2 Methane Ethane

Deethanizer LPG Ethane Propane plus

Depropanizer Deethanizer bottoms Propane Butanes plus

Debutanizer Depropanizer bottoms Butanes Natural gasoline(pentanes plus)

Deisobutanizer Debutanizer top Isobutane Normal butane

2.2.4 Product Treatment Plant

Propane and butane products separated from the fractionation plant contain some

impurities as residual water, H2S, Carbon disulfide and sulfur compounds. These impurities

should be removed in order to meet the desired product specifications. The contaminants

and their reasons for removal have been listed in the table below.

Table 3:Different Contaminants in LPG (Abdel-Aal, H. K.et al 2003)

Numerous processes are available to remove contaminants but two of them are the most

important and commonly used.

Contaminants Reasons for Removal

Hydrogen sulfide

Carbon dioxide

Carbonyl sulfide

Carbon disulfide

Mercaptans

Organic sulfides

Nitrogen

Water

Safety and Environmental

Corrosion control

Product specification

Prevention of freeze out

at low temperatures

Prevention of catalyst

poisoning in downstream facilities


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a. Absorptive Purification

b. Adsorptive Purification

2.3 Feed Specifications for NGL Fractionation Feed for NGL (Natural gas liquid) fractionation plants comes from upstream processing

plants, which receives feed directly from gas reservoirs. Feed composition is different from

different reservoirs. Feed composition is important for design considerations. The feed for

NGL fractionation trains contain methane, ethane, propane, butane and heavier ones. The

feed composition for NGL fractionation column is shown in the table below.

Table 4: Specifications of feed for NGL fractionation unit (Manley ,D.B.)

Liquid

volume%

Feed Ethane Propane Iso-Butane N-Butane Gasoline

Methane,C1 0.5 1.36

Ethane,C2 37.0 95.14 7.32

Propane,C3 26.0 3.50 90.18 2.0

Isobutane,iC4 7.2 96.0 4.50

N-Butane,C4 14.8 2.0 95.0

Butanes, 2.50 3.0

Iso-pentane,iC5 5.0 33.13

Pentanes 3.5 0.50 23.52

N-pentane,NC5

N-hexane,NC6 4.0 26.90

N-heptane,NC7 2.0 13.45

2.4 Product Specifications The product specification for LPG plant is shown in the following table. This data has been

provided by the US Gas Processors Association. The products specifications must be met to

sale the qualitative gas. Vapor pressure and temperature are the most important

parameters which should be controlled during operation.


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Table 5:Product specifications for LPG (Manley ,D.B)

Product

characteristics

Commercial

propane

Commercial

butane

Commercial propane –

butane mix

Propane HD-

5 a

Composition mainly propane

and propene

mainly butane

and butene

mainly mixes of

propane – propene and

butane – butene

not less than

90 % propane;

not more than

5 % propene

Vapor pressure

(max.) at 100°F,

psig b

208 70 208 208

Temperature of

volatile residue: °F b

– 37 36 36 – 37

Butane and heavier,

vol%

2.5 2.5

Pentane and

heavier, vol%

2.0 2.0

Residual matter, ,

mL

0.05 0.05

Oil stain observation pass c pass c

Volatile

sulfur,grains/100 cu

ft

15 15 15 10

Moisture content pass d pass d

Free water content none none

http://onlinelibrary.wiley.com/doi/10.1002/14356007.a15_347.pub2/tables#a15_347-note-0002








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3. Simulation

The modelling of LPG extraction from fractionation of NGL is done using Aspen Hysys as

simulation tool. The process is divided into 5 sections. These sections are feed conditioning,

Deethanizer, depropanizer, debutanizer and butane splitter. Each section is described as

under.

3.1 Feed conditioning

The feed streams are NGL and their compositions are given in appendix. The first feed

stream is coming from separation unit from well stream and the second feed from

dehydration unit. The temperature and pressure of the feeds are given to be 25°C and 30

bar but they have different flow rates.

These feeds are to be processed in order to extract LPG products that are propane, iso-

butane and n-butane. The products were selected based on demand in LPG market. Before

the Deethanizer column the feeds are to be conditioned. There are three alternatives for

conditioning.

First alternative is to mix both feeds before Deethanizer column and then expand the mixed

feed. A separator is used to remove the lighter hydrocarbons that are methane and ethane.

An illustration of this alternative is shown in figure (3)

Figure3: Feed conditioning alt.1

The second alternative is to expansion and separation of methane in each stream. The

bottom stream from the separators in each stream are mixed in mixer and then sent to

deethanizer as shown in figure (4).


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Figure 4: Feed conditioning alt.2

The third alternative is to mix both feeds, expand the mixed feed and let it into the

Deethanizer column as shown in figure (5). In this project the third alternative was

considered to be the best choice.

Figure 5:Feed conditioning alt.3

3.2 Fractionation columns

3.2.1 Deethanizer

In this project no refrigeration is used in order to minimize the cost. The first column is deethanizer

where no condenser is used and the top product gases (methane and ethane) are withdrawn from

top if gas phase. The feed is fed to the column from top. See Figure (6).


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The condition inside the column is set such as 26 bar pressure and number of trays to be 15 trays.

The specification in the deethanizer is selected in order to converge the column. Since there is no

condenser, only one specification would be enough to converge the column. In this column the

bottom product rate was used since both methane and ethane are light and would be difficult to

stay in the bottom stream. Other specifications such as component recovery and component

fraction were used but it was difficult to converge the column.

The number of trays in the column is very important, since the more the number of stages the

higher the column will be and the more expensive expensive the cost will be but in the same time

the purer the product will be. The optimum number of stages in this project is 15 stages.

Figure 6: Deethanizer column

3.2.2 Debutanizer

Here the debutanizer was used before depropanizer for economic reason so that the next

separation will be easier and the depropanizer will be smaller. In debutanizer the butane

and lighter hydrocarbons are withdrawn as top products and condensed in condenser while

heavier hydrocarbons are withdrawn from bottom as bottom products. A debutanizer

model is shown in figure (7).

In modelling the debutanizer two specifications are required in order to converge the

column since both condenser and reboiler are present. In this case both distillate rate and

component recovery of both propane and butane in top are selected. In modelling the


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debutanizer, specification has an influence of the purity of the top products as it is expected

over 99.9% of propane and 966% of butane recovered in the top product.

The number of stages were 15 and top and bottom pressure were 16 and 17 bar

respectively.

Figure 7: Debutanizer column

3.2.3 Depropanizer

Depropanizer separates propane from butane with a similar modelling to debutanizer. Propane is

withdrawn from top as top product after condensing and butane as bottom product. Figure (8)

shows depropanizer column. Since there are only butane and propane in the feed, the modelling is

easier. Both component recovery and component ratio are selected as specification. With thses

specifications over 99.8% of propane was recovered in the top product. The condition inside the

column is as follow: 15 stages, top and bottom pressure 9 and 10bar respectively.

Figure 8: Depropanizer column


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3.2.4 Butane splitter

The last column is butane splitter in which butane is separated in iso-butane as top product and n-

butane as bottom product. In butane splitter distillate rate and component recovery are selected as

specification. The separation of iso and n-butane is more difficult and therefore the number of

stages is higher than in depropanizer.

With this specifications and manipulating the pressure in the column an iso-butane recovery of

96.6% was achieved. A model of butane splitter is shown in figure (9).

Figure 9: Butane splitter

Note: All simulation results have been pasted in table A1 in appendix.


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4. LPG Transport

Demand for LPG is growing constantly. It is used in all energy requiring areas, particularly

residential and commercial sectors of developed or developing countries. It is expected, that

with population growth bonded with energy demand, the use of clean liquid and gaseous

fuels will continue to increase. At the same time, the historic levels of oil prices are pushing

the transportation demands of LPG. New transportation projects are expected to come,

alongside with many already in planning stage. With increasing access to LPG and many new

market possibilities, complex and innovative solutions for transport problems will play

important role in those projects. The LPG distribution chain can be seen in fig 2A in

appendix. Due to the fact, that LPG in normal conditions (1 bar, 20°C) has gaseous form,

unequal distribution in area, seasonal consumption and static, highly localized production,

many problems had to be overcome and wide network of transport systems was developed.

To fulfill certain pressure and market requirements, two main types of LPG distribution was

introduced:

Continuous flow of gas characterized by all types of pipe technologies, providing cheap,

constant and simple access to LPG at the expense of high preliminary investments,

localized storage terminals and additional extended network of delivery.

“Discrete” (bulk) means of transport characterized by moving certain amount of LPG in

pressurized canisters carried by cars, trains, ships.

Each of those two branches contains special types of transport and is described by different

safety measures and precautions. Due to their complexity it’s necessary to describe that in

few paragraphs bellow.

4.1 Continuous flow of LPG – Pipe system

LPG flow in certain time of its migration to consumers through pipelines. Although the initial

construction expanses ale high, the result if are build and correctly maintained is significant.

This way of LPG transport is most economic and safe, and moreover, has some other

advantages such as :

Better availability of LPG in hardly accessible areas

Significant LPG transport reduction costs


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Environmental impact in terms of reducing exhaust emissions and energy

consumptions

LPG pipeline system is not as wide as NG and oil pipeline system, however, it still follows all

“LP gas production – consumer” steps. Also, it is not evenly spread over the globe and

differs by continents and final usage.

Most widespread network is in Europe, where LPG is mainly used in residential areas for

water heating. The pipes are mostly made from carbon steel and are 1” to 6” wide.

Different situation occurs on USA, where LPG is used for distributed power generation. As a

result, pipe network is not so wide, but the existing pipes are larger, and generate higher gas

flow to Gas plants. One example is double pipeline from New Mexico to Minnesota and

Wisconsin – Mid-America Pipeline. First system devoted only for LPG. It is 3540 km ANSI900

system of 4”to 10” pipeline, was constructed in 1960, and includes 6 delivery, 2 operating

terminals, 14 pumping stations and underground storage. The pipeline map is shown in fig.

A3 in appendix .

Similar example with different goal was established in India, where 33.6 million Indian

households in 2001 were using LPG for cooking. Primary cooking usage, lack of developed

infrastructure, and vast unsupplied areas had lead to building 1900 km LPG mostly 12” to

16” pipeline network. 1300 km branch connects Jamnagar on the west with New Delhi area

on the north. And 600 km of network is connecting Vizag on the east coast with midlands

Secenderabad. The LPG transmission system has a capacity 3.8 MMTPA LPG. The Jamnagar –

New Delhi branch can be seen on figure A4 in appendix.

4.2 Discrete (bulk) means of LPG transport

The discrete transport system is completely opposite than Continuous system. Where pipe

system was rigid in delivery, the discrete system is flexible, in the terms of place, amount

and time. The same works for price, initial investments are lover in comparison, but overall

expenses are higher in order. As a result, other than pipeline systems are used whenever

the pipes would be economically unjustifiable. Detailed view to each type can be read

below.


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4.2.1 Vessel tanker transport

Provide the vast majority of LPG discrete transportation, and major amount of transported

LPG is transported by sea. There is a fleet of more than 1000 tankers around the globe.

Those tankers are not single-function vessels dedicated only for LPG. By the nature of LPG,

every ship capable of carrying pressurized, semi-pressurized or refrigerated LPG can work as

a LPG tanker. Due to the fact that it is safer to transport huge amounts under low

temperature, rather than high pressure, there are three types of LPG vessels, divided by

size, derived from system of keeping the gas in liquid form.

Pressurized tankers (18 bar, ambient temperatures) used in short to medium haul

trades. Carrying capacity differs from 3 000 – 10 000 m3.

Semi-pressurized tankers (5-8 bar, -15 ± 5°C) for medium haul trades, with capacity 10

000 – 30 000 m3.

Fully refrigerated vessels (ambient pressure, -43°C for pure propane) are used for long

haul trades, with high LPG demand, e.g. Japan. Those carrying capacity varies from 30

000 to 100 000 m3.

There is also considerable fleet of very small vessels used mainly for coastal, short sea and

inland-river trades.

Because the LPG vapors are highly flammable, without scent and unrecognizable by naked

eye, some safety precautions was introduced to avoid leakage or any disaster. The

containers for LPG have usually strong walls, and are shielded from outside area by inner-

wall layer of inert gas, mostly nitrogen. Also, because of possibility to carry other gases,

before loading are cleaned by CNG vapors blow.

Vessel transport itself can be considered as simple and safe in comparison to on-loading and

offloading. There are two main systems of transfer nowadays, static shore terminal (SST),

and single point mooring system (SPM).

SPM consist of onshore LPG storage facility and LPG offshore buoy, connected by flexible

pipelines. Thanks to the pipeline connection, SPM can be considered as middle-step

between pipe and vessel transport. Floating buoy allows connection of all types of tankers,

360° movement grants tanker possibility to moor from all sides depending on bathymetry


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and environmental condition at given time. In comparison with SST, SPM grants much

quicker transfer, independent of weather and lower maintenance costs. Both SST and SPM

are illustrated in Fig.A5, SST-SPM.

After vessels offload the cargo, other types of distribution come to play.

4.2.2 Rail, truck, car transport

Rail with truck transport fulfills the role of ship on the land. Following receipt at terminals

from ships, LPG is transported to localized storage stations for further distribution by

smaller cars, or to the consumers directly, mostly Industry. For instance in Italy is LPG

exclusively transported by trains, where no pipeline network was developed.

Because of the highest number of single transports and high concentration of population in

comparison to pipe or ship, certain precautions were taken. The LPG is mostly kept liquefied

by pressure, therefore canisters of all types must be robust, able to keep high internal

pressure and sustain significant damage without leakage. Next, canisters never can be

fulfilled more than 40% of water equivalent capacity. This is necessary because of high

differences of external temperature changes. So the gas inside the canister is allowed to

evaporate, without significant increase on pressure. As well, canisters must be equipped

with overpressure valves and mechanical safety cover around valve. In terms of visual

recognition, international regulations demands white or red color, and exact signs on visible

places, showing the content of canister. Example of unified canister can be seen on fig.A6 in

appendix.

4.3 Economic analysis

Supplies of LPG are continually rising, closely followed by prices. And, the estimations show,

that it will have positive future.

The demand for LPG on market over years is stable, that in combination with rising supply

would for commonly thinking mind signalize, easing of prices. However, the situations on

markets looks different. For illustration, the price of propane rose during last few years from

500 dollars/tone to 900 d/t in late 2007 and 1500 d/t in 2011. This increase is however

inevitable. It is caused by many factors, one of the biggest, is close link to price of crude oil

and constantly weakening dollar. Quick rise of prices choke the demand for LPG few times in


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the past. Recovery came hand to hand with rising prices mainly thanks to constant

petrochemical demand and never-ending rising of petrol prices.

Main sources of LPG

Refinery production – increasing

Crude oil associated gases processing – moderate increase

Non-associated natural gas processing – significant increase due to new started up

discoveries and large volumes originated from Qatar, Iran, UAE and Nigeria.

In the past was estimated, that petrochemical industry will not be able to consume these

increasing amounts, resulting in LPG price moderation. Unfortunately, as actual prices show,

it didn’t happen. Future estimations in this direction are unwise.

Demand

Petrochemical industry in western Europe and Middle East - rising

Middle East, Asia and Africa domestic sector – rising

Transport sector (autogas) in Europe and Asia – Pacific – rising

North America - falling around 2,3m t/year

The increase in demand is highly fractionated, by timescale, geographically or by sector. See

Fig.A7 in appendix.

In domestic sector, the increase is stable thanks to easy access to LPG cylinders, growing

infrastructure, substitution of other types of fuel by LPG etc. Also, domestic market in Asia

shows positive numbers. Population and income are rising quicker than grid based energy

sources, resulting in higher demand for flexible LPG.

Similarity with natural gas is next key reason for rising LPG demand. For industry, possibility

to relative easy switch from natural gas to LPG means high valued advantage, mainly in long

term NG prices predictions. LPG is used also as a backup plan for NG using industry, and not

surprisingly, for large-scale capital investors.

Autogas sector was rising in last years probably in highest pace from all sectors. Over year

growth in consumption is app. 6%. Two thirds of this consumption is located in only 7


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countries. This trend is not caused only by usual gasoline and diesel rising prices, but by cars

manufacturers. Their new introduced cars running on autogas, are another key for demand.

This boom is illustrated on South Korean example. Where, almost 80% of autogas

consuming cars, was introduced by domestic manufactures. Similar picture occur in Turkey,

where government – car manufacturers cooperation led to 16% growth in LPG

consumption. See Fig.A8 in appendix.

Despite the continuously rising prices, the clean burning LPG remains a growing source of

energy. And future estimations, although was wrong sometimes, confirms its rising role in

energy-demanding world.


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Conclusions and Discussions

LPG can be an alternative fuel for vehicles as it burns cleaner and greenhouse gas

emissions can be controlled. So, it can help us to combat climate change.

LPG can be recovered from natural gas liquids by different methods. Refrigeration

method is more common of all because recovery from this process is 98%.

There are three alternatives to condition the feed stream for fractionation unit. It

has been found to be the best choice to mix the two feed streams from the wells

having different compositions and feeding it to deethanizer first.

Cost for fractionation operation can be reduced by adapting refrigeration of ….

Debutanizer has been used before depropanizer in order to become it more

economical and to make separation easy at next stage.

The separation of iso and n-butane is more difficult and more number of stages are

required in order to do the separation which in turn increases the overall cost.

LPG transportation cost can be reduced by employing the pipeline technology.

Although these projects are underway but it would be proved as a safe and

economic.


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References

[1] Abdel-Aal, H. K. , Aggour ,Mohamed, Fahim, M. Al. (2003) “ Petroleum and Gas Field

Processing”, Marcel Dekker INC, New York Basel, pp- 317-329

[2] Asian development bank “PROJECT COMPLETION REPORT ON THE LPG PIPELINE PROJECT (Loan

1591-IND) IN INDIA “;(2003)

[3] Bahnassi ,Essam , Khouri,Abdul Rahman , Alderton,Peter , Fleshman ,James “Achieving

product specifications for ethane through to pentane plus from NGL fractionation plants”,

(AIChE Fall Conference, Foster Wheeler); 2005

[4] Elvers ,Barbara (2008) “ Handbook of fuels: energy sources for transportation”, Wiley-

VCH-Verlag GmbH & Co, pp-142-149

[5] Fundamentals of the World Gas Industry, 2008,

http://91.121.21.64/page_attachments/0000/0330/Petroleum_Economist.pdf

[6] Gail India Limited, 2011, http://gail.nic.in/gailnewsite/businesses/lpgpipeline.html

[7] Manley.D.B. “Thermodynamically efficient distillation: NGL fractionation”; Department of

chemical engineering, university of missouri – rolla, Rolla, Missouri

[8] Naturalgas.org 2011, http://naturalgas.org/naturalgas/transport.asp

[9] Parkash ,Surinder (2009) “Petroleum Fuels Manufacturing Handbook: including Specialty

Products and Sustainable Manufacturing Techniques ” McGraw-Hill Professional Publishing,

pp-4-10

[10] René Raaijmakers, “Offshore terminals for the transportation of Liquefied Petroleum

Gas”, Bluewater Offshore Production Systems (USA), Inc., http://www.bluewater-

offshore.com/downloads/PT26_LPG%20SPM_bluewater.pdf

http://91.121.21.64/page_attachments/0000/0330/Petroleum_Economist.pdf

http://gail.nic.in/gailnewsite/businesses/lpgpipeline.html

http://naturalgas.org/naturalgas/transport.asp

http://www.bluewater-offshore.com/downloads/PT26_LPG%20SPM_bluewater.pdf

http://www.bluewater-offshore.com/downloads/PT26_LPG%20SPM_bluewater.pdf


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[11] Stellman ,J.M. (1998) “Encyclopaedia of Occupational Health and Safety”, International

Labor Office, Geneva

[12] Stopford ,Martin (2009) “Maritime economics”, 3rd edition, Rutledge

[13] Total 2011,

http://www.totalgaz.com/Gaz/International.nsf/VS_OPM/8AFAE12EA35EC563C125718100509959?

OpenDocument

[14] Willbros Group, Inc. 2011, “LPG pipeline system”; http://willbros.com/About/Areas-of-

Operation/United-States-398.html

[15] World LP Gas Association 2009, http://www.worldlpgas.com/what-is-lp-gas/interactive-

maps/

http://www.totalgaz.com/Gaz/International.nsf/VS_OPM/8AFAE12EA35EC563C125718100509959?OpenDocument

http://www.totalgaz.com/Gaz/International.nsf/VS_OPM/8AFAE12EA35EC563C125718100509959?OpenDocument

http://willbros.com/About/Areas-of-Operation/United-States-398.html

http://willbros.com/About/Areas-of-Operation/United-States-398.html

http://www.worldlpgas.com/what-is-lp-gas/interactive-maps/

http://www.worldlpgas.com/what-is-lp-gas/interactive-maps/


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Appendix

Figure A1: Process Flow Sheet (Simulation sheet from Hysys)


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Table A1:Simulation Results (Material Streams)

Feed1 Feed2 Feed Feed in C1.C2 C3+ C3+ in C5+

Vapor

Fraction

0.0000 0.0000 0.0000 0.0000 0.9985 0.0000 0.3064 0.0000

Temp. C 25.0 25.0 24.87 25.06 37.54 246.7 235.2 251.7

Pressur

e

KPa 3000 3000 3000 2600 1800 2600 1700 1700

Molar

Flow

Kgm

ol/hr

225.9 122.2 348.1 348.1 62.09 286.0 286.0 242.0

Mass

Flow

Kg/h

r

2.500e+

004

8000 3.300e+

004

3.300e+

004

1487.0 3.151e+

004

3.151e+

004

2.916e+

004

Liquid

Volume

flow

M3/h

r

36.00 13.38 49.39 49.39 4.119 45.27 45.27 41.02

Heat

Flow

kJ/hr -

5.499e+

007

-

1.986e+

007

-

7.485e+

007

-

7.485e+

007

-

5.203e+

007

-

5.016e+

007

-

5.016e+

007

-

4.524e+

007

C3.C4 C3.C4 in C4 C3 C4 in iC4 nC4

Vapor

Fraction

0.0000 0.2062 0.0000 0.0000 0.2392 0.0000 0.0000

Temperature C 76.67 56.50 74.71 22.82 46.17 5.095 50.93

Pressure KPa 1600 1000 1000 900 500 190 500

Molar Flow Kg

mol

/hr

44 44 29.19 14.81 29.19 10.07 19.12

Mass Flow Kg/

hr

2356 2356 1702 653.1 1702 583.2 1119

Liquid flow M3

/hr

4.243 4.243 2.954 1.289 2.954 1.038 1.916

Heat Flow kJ/

hr

-

5.499e+00

7

-

1.986e+0

07

-

7.485e+0

07

-

7.485e+0

07

-

5.203e+0

07

-

5.016e+0

07

-

5.016e+0

07


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Figure A2. Distribution Chain (World LP Gas Association 2009)


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Figure A3: Mid-America Pipeline (Willbros Group, Inc. 2011)

Figure A4: Jamnanagar New Delhi


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Figure A5: SST,SSM (René Raaijmakers)

Figure A6: amerigas Canister


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Figure A7: World LPG gas consumption (Fundamentals of the World Gas Industry, 2008)

FigureA 8: World autogas consumption (Fundamentals of the World Gas Industry, 2008)

Fractionation of Natural Gas Liquids to Produce LPG

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