UNIVERSITY OF PORT HARCOURT GRADUATE SCHOOL OF ENGINEERING AND

TECHNOLOGYMASTERS PETROLEUM AND GAS ENGINEERING

A THESIS PROPOSAL

ON

OPTIMIZATION OF CONDENSATE PRODUCTION IN AN LNG PLANT

Submitted by

OKORO MATTHEW IFEBADIOFUG2014/MENG/PNG/FT/1013

Supervisor: Prof. G. J. IGWE

Co-Supervisor: Dr. EMEKA OKAFOR

IN PARTIAL FULFILLMENT OF MASTERS IN ENGINEERING DEGREE,PETROLEUM AND GAS ENGINEERING

SEPTEMBER 2015

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INTRODUCTION

Natural gas is a naturally occurring gaseous mixture of hydrocarbons and non-

hydrocarbon gases found in underground reservoir rocks either as associated gas,

that is natural gas in contact or co-existing with crude oil in reservoirs, non-

associated gas which are free gases not in contact or exists without crude oil in the

reservoir and as gas condensate(dissolved gas) which are gases in solution with

crude oil or exist in gaseous form in the reservoir but liquefy on production as a

result of reduction in pressure and a change in temperature. Though of these three,

gas condensate is of a higher quality and therefore has more economic value. There

is no one composition or mixture of hydrocarbons and impurities that can be

referred to as natural gas. Whether it’s associated, non-associated or dissolved in

solution, each gas stream that is produced has its own composition. The principal

hydrocarbon gases found in natural gas are methane, ethane, propane, butanes,

pentanes and heavier hydrocarbons, the impurities include Nitrogen, water vapour,

hydrogen sulphide, carbon-dioxide, mercury and helium.

Natural gas processing is basically done for two main purposes which are; for the

use of natural gas as fuel which is mainly methane and a small percentage of

ethane (LNG) and as feed stock for other petrochemical processes which are

usually natural gas liquids (NGL) with a composition of ethane, propane, butanes,

pentanes and heavier hydrocarbon fractions. In the processing of natural gas, NGL

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recovery is done as an additional process through a fractionation train or unit,

consisting of three distillation columns in series; a de-ethanizer, a de-propanizer

and a de-butanizer. The overhead product of the deethanizer is ethane (C2) and

bottom products which are propane (C3), butane (C4) and heavies are fed into the

depropanizer whose overhead product is propane (C3) and bottoms butane (C4)

and heavies are fed to the debutanizer. The overhead product from the debutanizer

gives a mixture of iso-butane (iC4) and normal-butane (nC4), while the bottom

product is a mixture of pentane plus which will be our focus in this project.

Natural gas condensate can be defined as a low density, high API gravity liquid

hydrocarbon mixture that is present in raw natural gas as gaseous component. They

have a specific gravity ranging from 0.5 to 0.8 and normally has a composition of

mainly butane, pentane plus and other non-hydrocarbon gases as impurities.

Natural gas condensate can also be known as simply condensate or gas condensate

or sometimes as natural gasoline and drip gas. It is produced mainly at an oil and

gas surface production facility (wellhead), where it is been separated or at a gas

processing plant (LNG plant) where it is produced as one of the by-products.

Therefore because of its economic value different operators process their

condensate in different ways based on their commercial considerations and

operational preference. As a result of this, the demand for gas condensate in

Nigeria and around the world has become increasingly important due to the need

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for additional liquid recovery and an increase in the demand for light oil and

natural gas

In the processing of Natural gas liquids, which is an additional process of the LNG

process train, condensate as the last by-product of the fractionation unit requires

careful process analysis with which to exploit and optimize its recovery.

Condensate as mention earlier is produced at several stages during natural gas

processing and often contains lighter hydrocarbons which can make it dangerous to

store and transport by increasing its vapor pressure. Therefore it should further be

processed through stabilization in order that it meets the required standards for

storage, transportation and sales. The process of stabilization is simply separating

lighter hydrocarbon gases from the heavier hydrocarbon liquid component in order

to reduce its vapor pressure as the produced condensate would be stored in tank or

transported in a pressure vessel which has a definite pressure limits with their Reid

Vapor Pressure range of 10psia-12psia maximum. There are basically two methods

of stabilization: flash vaporization and fractionation (distillation), which would be

reviewed further in this study.

There are many different simulation programs used in the industry, depending on

the field of application and desired simulation. ASPEN HYSYS Simulation

package would be used in this project for the optimization of condensate

production in an LNG plant since it is a tool that can be used to improve plant

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control and operability, ensure a more efficient and profitable design and it

represents a more realistic model.

STATEMENT OF PROBLEM

In the industry today, condensate has many uses but it’s primarily used as a diluent

in heavy crude blending and processed for its individual components. Condensate

as it is known is lighter than crude oil but heavier than natural gas liquids and one

major issue associated with it is that in its natural form it contains lighter

hydrocarbons that increases its vapor pressure to the point that it is not saleable ,

dangerous to store and transport. It is therefore required to accurately anticipate the

quality of condensate produced (that it meets the required standard) before it is

sold to consumers, sent to storage or transported

OBJECTIVE OF THE STUDY

The primary objectives of this study are

To model and simulate the production of condensate from the NGL

fractionation unit and its stabilization in an LNG Plant with the use of

ASPEN HYSYS.

To identify the optimal operational conditions in the units mentioned above

to predict the quality of condensate produced.

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To know the effect of heat duty, pressure temperature variations and column

design to the production of condensate with respect to the fractionation unit

and the stabilization unit.

SCOPE OF THE STUDY

This work will be focused on the optimization of condensate production from the

NGL fractionation unit and its stabilization with the use of ASPEN HYSYS.

Various methods of stabilization will be reviewed and this study will also focused

on finding the best operational conditions for the production of condensate to meet

the required standard for sales, storage and transportation.

METHODOLOGY

Relevant data on condensate production and its stabilization in an LNG Plant

would be collected. Existing literatures on condensate production process would be

reviewed especially in the area of its stabilization. ASPEN HYSYS simulation

software would be used for simulations and optimizations that would be carried out

in this study.

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REFERENCE

1. A.Rahman, K. Kirtania, “Simulation Study Of A Fractionation Column With

Varying Parameters” department of chemical engineering, Bangladesh University

of Engineering and Technology, Dhaka-1000, Bangladesh. Engineering e-

transaction(ISSN 1823-6379) 1, June 2011 pp 43-49.

2. Navid Moghadam and Masoud Samadi, “Gas Condensate Stabilization Unit:

Different Design Approach” international journal of chemical Engineering and

Application. Volume 3, No 6. December 2012.

3. Partho S. Roy and Ruhul Amin M., “Aspen-HYSYS Simulation of Natural Gas

Processing plant”. department of chemical engineering, Bangladesh University of

Engineering and Technology, Dhaka-1000, Bangladesh. Journal of chemical

engineering. IEB Vol. ChE. 26, No 1, December 2011

4. Ikoku, Chi U. “Natural Gas Production Engineering”. New York: John Wiley and

Sons, 1984

5. Ikoku, Chi U. “Natural Gas Reservoir Engineering”. New York: John Wiley and

Sons, 1984

6. Henri Parodowski et al, “Compare the different options for NGL Recovery from

Natural gas”. Gas processing Department, Technip, 92973 Paris La Defense,

CEDEX, France.

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