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Ministry of Higher Education

& Scientific Research

University of Technology

Chemical Engineering Department

A study of the dehydration process of natural gas in Iraqi North Gas Company and the treatment methods of molecular

sieve problems

A Research Submitted to the Department of Chemical

Engineering University of Technology in Partial Fulfillment

of the Requirements for the Degree of Higher Diploma in

Chemical Engineering/Petroleum Refining and Gas

Technology

By

Farman Saeed Abd. Zangana (B.Sc. in Chemical Engineering 2004)

Supervised by

Assist.Prof. Dr.Anaam A.Sabri

2012

CERTIFICATE We certify that we have read this research entitled " A study of the

dehydration process of natural gas in Iraqi North Gas Company and

the treatment methods of molecular sieve problems " by Farman

Saeed Abd. Zangana and as an Examining Committee examined the

student in its contents and that in our opinion it meets the standard of a

research for the degree of Higher Diploma in Chemical Engineering

/Petroleum Refining and Gas Technology.

Signature:

Assistant Prof. Dr. Anaam A.Sabri

(Supervisor)

Date: / / 2012

Signature: Signature:

Assist. Prof. Dr.Mohammed F.Abid Prof. Dr. Mumtaz A. Zablouk

(Member) (Chairman)

Date: / / 2012 Date: / / 2012

Approved for the University of Technology

Signature:

Prof. Dr. Mumtaz A. Zablouk

Head of Chemical Engineering Department

Date: / / 2012

CERTIFICATION

This is to certify that I have read the research titled " A study

of the dehydration process of natural gas in Iraqi North Gas

Company and the treatment methods of molecular sieve

problems " and corrected any grammatical mistakes I found. The

research is therefore qualified for debate.

Signature:

Prof. Dr. Mumtaz A. Zablouk

University of Technology

Date: / / 2012

Acknowledgments First of all, praise is to Allah for every thing. Without his great

assistance the work wouldn't have been finished.

I would like to express my sincere appreciation and thanks to my

supervisor Assist.Prof. Dr.Anaam A.Sabri, for his constant guidance and

valuable comments, without which, this research would not have been

successfully completed.

My grateful thanks to Prof. Dr. Mumtaz A. Zablouk, the Chairman

of the Department of Chemical Engineering at the University of

Technology for the provision of research facilities.

My deep thanks go to Assist. Prof. Dr. Mohammed I. Mohammed,

the head of post graduate committee for all the help and encouragement,

also I wish to express my sincere gratitude to my family for them

encouragement and helpful.

Also I would like to convey my sincere appreciation to any one that

helped me in Iraqi North Cas Company.

Also I would like to convey my sincere appreciation to all staff of

Chemical Engineering Department in the University of Technology and the

workshops unit.

Finally, to all that helped me in one way or another, I wish to express

my thanks.

Farman

Abstract

The purpose of this research is to study the dehydration process of

natural gas by adsorption using molecular sieve as it is in the North Gas

Company. Dehydration of natural gas is needed to remove the water that is

associated with natural gas in vapor form. The natural gas industry has

recognized that dehydration is necessary to insure smooth operation of gas

transmission lines, dehydration prevents the formation of gas hydrates and

reduces corrosion. Unless gases are dehydrated, liquid water may condense

in pipeline and accumulate at low point along the line and reducing its

flow capacity. Several methods have been developed to dehydrate gases in

an industrial scale . The four major methods of dehydration are direct

cooling , indirect cooling , absorption and adsorption. This study focuses

on the adsorption method which is used to dehydrate the natural gas in

North Gas Company and also focuses on the problem of breaking up and

aging of the molecular sieve before ending its real life time .Some testing

were made on the aging and the new molecular sieve to show the difference

between them. Some suggestions are made to overcome the problem of

aging of the molecular sieve, like improve the efficiency of gas

separator,using antifoaming to prevent liquid carryover, choose the

regeneration conditions carefully, using multi bed technology and using

glycol dehydration unit with molecular sieve dehydration unit to reduce the

water content of natural gas.

Contents

Subject Page 1 Chapter One Introduction 1-3 1-1 Problem Statement 3 1-2 Scope of the Study 3 2 Chapter Two 4 Literature Review 4 2-1 Types of Dehydration of Natural Gas 4 2-1-1 Direct Cooling 4 2-1-2 Indirect Cooling 4-5 2-1-3 Dehydration by Absorption 5-9 2-1-4 Dehydration by Adsorption (Solid Desiccant) 10 2-2 Types of Adsorbents 11 2-2-1 Alumina 11 2-2-2 Silica Gel and Silica-Alumina Gel 11 2-2-3 Molecular Sieves 11-13 2-3 Some Types of Molecular Sieves 14 2-3-1 3A Molecular Sieve 14 2-3-2 4A Molecular Sieve 14-15 2-3-3 5A Molecular Sieve 15-16 2-3-4 13X Molecular Sieve 16 2-4 Solid Desiccant Adsorption Kinetics 16-17 2-5 Fundamentals of Adsorption 17-18 2-6 Development of Adsorption Isotherms 18-19 2-6-1 Freundlich Isotherms 19- 20 2-6-2 Langmuir Isotherm 20-21 2-7 Some previous Work on Dehydration of Natural Gas 3 Chapter Three 23 Design and Theoretical Considerations 23 3-1 Design Consideration 23

3-1-1 Solid Desiccant Dehydration 23

3-1-1-1 Allowable Gas Velocity 23-24 3-1-1-2 Bed Length to Diameter Ratio 24-25

3-1-1-3 Desiccant Capacity 25 3-1-1-4 MTZ Length 25 3-1-1-5 Breakthrough Time 25 3-1-2 Glycol Dehydration 25 3-1-2-1 Absorber (Contactor) 25-27 3-1-2-2 UStill (Stripper) 27 3-1-2-3 Reboiler 27 3-1-2-4 Surge Tank (Accumulator) 28 3-1-2-5 Heat Exchanger 28

3-1-2-5-1 Glycol/Glycol Exchanger 28

3-1-2-5-2 Dry Gas/Lean Glycol Exchanger

28

3-1-2-6 Phase Separator (Flash Tank) 28-29

3-1-2-7 Glycol Circulation Pumps 29

3-1-2-8 Filters

29

3-1-2-8-1 Fabric (Particulate) Filters 29

3-1-2-8-2 Carbon Filters 29 3-2 Operational Problems 30 3-2-1 Solid Desiccant Dehydration 30

3-2-1-1 Bed Contamination 30

3-2-1-2 High Dew Point 30-31

3-2-1-3 Premature Breakthrough 31

3-2-1-4 Hydrothermal Damaging 31-32

3-2-1-5 Liquid Carryover 32

3-2-1-6 Bottom Support

32

3-2-2 Glycol Dehydration 33

3-2-2-1 Absorber 33 3-2-2-1-1 Insufficient Dehydration Causes of insufficient

dehydration 33

3-2-2-1-2 Foaming 33 3-2-2-1-3 Hydrocarbon Solubility in TEG Solution 33 3-2-2-2 Still (Stripper)

33-34

3-2-2-3 Reboiler 34 3-2-2-3-1 Salt Contamination 34 3-2-2-3-2 Glycol Degradation 34-35

3-2-2-3-3 Acid Gas 35 3-2-2-3-4 Surge Tank 35 3-2-2-3-5 Heat Exchanger 35-36

3-2-2-3-6 Phase Separator (Flash Tank) 36 3-2-2-3-7 Glycol Circulation Pump 36 4 Chapter Four 37

Case Study 37 4-1 Dehydration Process 37-38 4-2 Regeneration Process 38-39 4-3 The Molecular Sieve Dehydrate 39-42 5 Chapter Five 43

5-1 Result and Discussion 43-49

5-2 Overcome the Breaking Up and Aging Problems of the Molecular Sieve

49-50

6 Chapter Six 51 Conclusions and Recommendations 51-53

6-1 Conclusions 51-52 6-2 Recommendations 53

Chapter One Introduction

Introduction

Today, natural gas is one of the most important fuel in our life and one

of the principle sources of energy for many of our day-to-day needs and

activities. It is an important factor for the development of countries that

have strong economies because it is a source of energy for household,

industrial and commercial use, as well as to generate electricity.

Natural gas, in itself, might be considered a very uninteresting gas - it

is colorless, shapeless, and odorless in its pure form, but it is one of the

cleanest, safest ,and most useful of all energy sources. Natural gas is a

gaseous fossil fuel. Fossil fuels are essentially, the remains of plants and

animals and microorganisms that lived millions and millions of years

ago. It consists primarily of methane but including significant quantities of

ethane, propane, butane, and pentane. Methane is a molecule made up of

one carbon atom and four hydrogen atoms, and is referred to as CH4.

Natural gas is considered 'dry' when it is almost pure methane, having

had most of the other commonly associated hydrocarbons removed. When

other hydrocarbons are present, the natural gas is 'wet'.The natural gas used

by consumers is composed almost entirely of methane .However, natural

gas found at the wellhead, although still composed primarily of methane, is

by no means as pure. Raw natural gas comes from three types of wells: oil

wells, gas wells, and condensate wells.

Natural gas that comes from oil wells is typically termed 'associated

gas'. This gas can exist separately from oil in the formation of (free gas),or

dissolved in the crude oil (dissolved gas). Natural gas from gas and

condensate wells ,in which there is little or no crude oil, is termed non

associated gas. Gas wells typically produce raw natural gas by itself, while

condensate wells produce free natural gas along with a semi-liquid

hydrocarbon condensate. Whatever the source of the natural gas, once


separated from crude oil it commonly exists in raw natural gas or sour

gas.The raw natural gas contains water vapor, hydrogen sulfide

(H2S),carbon dioxide, helium, nitrogen, and other compounds .In order to

meet the requirements for a clean, dry, wholly gaseous fuel suitable for

transmission through pipelines and distribution for burning by end users,

the gas must go through several stages of processing, including the removal

of entrained liquids from the gas, followed by drying to reduce water

content. In order to remove water content, dehydration process is used to

treat the natural gas. Dehydration is the removal of water from an object. In

Physiologic terms, it entails a relative deficiency of water molecules in

relation to other dissolved solutes. Gas dehydration is one of the most

prominent unit operations in the natural gas industry(1).

There are five major reasons for natural gas treating from water contents: • Liquid water and natural gas can form hydrates which causes plug the

pipelines and other equipments such as valves, collectors etc. (Gas

Hydrate: are solids formed by the physical combination of water and other

small molecules of hydrocarbons. They are icy hydrocarbon compounds of

about 10% hydrocarbon and 90% water).

• Natural gas containing H2S and/or CO2 is corrosive when liquid water is

present (corrosion often occurs when liquid water is present along with

acidic gases, which tend to dissolved and disassociate in the water phase,

forming acidic solutions).

• Water content of natural gas decreases of it is heat value.

• Liquid water in natural gas pipelines potentially causes slugging flow

conditions resulting in lower flow efficiency of the pipelines.

• In most commercial hydrocarbon processes, the presence of water may

cause side reactions, foaming or catalyst deactivation(2).


There are several methods of dehydrating natural gas. The

refrigeration (direct cooling and indirect cooling). liquid desiccant (glycol)

dehydration and solid desiccant dehydration, the first two methods employ

cooling to condense the water molecules to the liquid phase with the

subsequent injection of inhibitor to prevent hydrate formation. The other

two methods utilize mass transfer of the water molecular into a liquid

solvent (glycol solution) or a crystalline structure (dry desiccant). However,

the choice of dehydration method is usually between glycol and solid (3).

1-1 Problem Statement

Gas dehydration is a common process in gas treatment plant because

water and hydrocarbons can form hydrates ,which may block valves and

pipelines .Also water can cause corrosion in present of acid compounds in

natural gas .In Iraqi North Gas Company, the molecular sieve of type 4A is

used to remove water from the natural gas, the main problem is the

breaking up and aging of the molecular sieves (1.5-2 year) before ending its

service life time (3years).

1-2 Scope of the Study

The aim of this research is

1.To conduct literature survey of different methods for dehydration of

natural gas .

2.To describe the process of dehydration of natural gas using molecular

sieve as it is in Iraqi North Gas Company and try to study the problem of

breaking up and aging of the molecular sieve which is used in the

dehydration process .

3.Suggesting solutions for this problem (aging of molecular sieve) .

Chapter Two Literature Review

Literature Review

2-1 Dehydration Methods of Natural Gas

Dehydration of natural gas is the process removal of the water that is

associated with natural gases. The natural gas industry has recognized that

dehydration is necessary to ensure smooth operation of gas transmission

lines. Several methods have been developed to dehydrate gases on an

industrial scale.

2-1-1 Direct Cooling

The ability of natural gas to contain water vapor decreases as the

temperature is lowered at constant pressure. During the cooling process, the

excess water in the vapor state becomes liquid and is removed from the

system. Natural gas containing less water vapor at low temperature is

output from the cooling unit. The gas dehydrated by cooling is still at its

water dew point unless the temperature is raised again or the pressure is

decreased. It is often a good practice that cooling is used in conjunction

with other dehydration processes. Glycol may be injected into the gas

upstream ahead of the heat exchanger to reach lower temperatures before

expansion into a low temperature separator(5).

2-1-2 Indirect Cooling

Expansion is a second way of natural gas cooling. It can be achieved

by the expander or Joule-Thomson valve. These processes are

characterized by a temperature drop to remove condensed water to yield

dehydrated natural gas. The principal is similar to the removal of humidity

from outside air as a result of air conditioning. Gas is forced through a

constriction called an expansion valve into space with a lower pressure. As

a gas expands, the average distance between molecules increase. Because

of intermolecular attractive forces, expansion causes an increase in the

potential energy of the gas. If no external work is extracted in the process

and no heat is transfered, the total energy of the gas remains the


same. The increase in potential energy thus implies a decrease in kinetic

energy and therefore in temperature(5).

2-1-3 Dehydration by Absorption

The basis for gas dehydration using absorption is the absorbent; there

are certain requirements for absorbents used in gas treating.

● Strong affinity for water to minimize the required amount of absorbent

(liquid solvent).

● Low potential for corrosion in equipments, low volatility at the process

temperature to minimize vaporization losses.

● Low affinity for hydrocarbons to minimize their loss during the process.

● Low solubility in hydrocarbons to minimize losses during treating.

● Low tendency to foam and emulsify to avoid reduction in gas handling

capacity and minimize losses during regeneration.

● Good thermal stability to prevent decomposition during regeneration and

low viscosity for easily pumping and good contact between gas and liquid

phases. Off course, the major critical property for a good absorbent is the

high affinity for water. The others are used to evaluate potential absorbents

practical applicability in the industry (2) .

There are numbers of liquids that can be used to absorb water from

natural gases such as calcium chloride, lithium chloride and glycols. Glycol

dehydration is a liquid desiccant system for the removal of water from

natural gas. It is the most common and economic means of water removal

from these streams .Glycol, the principal agent in this process, has a

chemical affinity for water. The liquid glycol will absorbs the water content

in the natural gas. This means that, when in contact with a stream of natural

gas that contains water, glycol will serve to 'steal' the water out of the gas


stream. This operation is called absorption (1) . There are a few types of

glycol usually used in industry with their advantages and disadvantages

like ethylene glycol (EG), diethylene glycol (DEG), triethyleneglycol

(TEG), and tetraethylene glycol (TREG). Glycols typically seen in industry

include monoethylene glycol (MEG) Table( 2-1) shows the properties of

the glycols (1) .The commonly available glycol and their uses are described

as follows.

1. Monoethylene glycol (MEG);high vapor equilibrium with gas so tend to

lose Monoethylene glycol to gas phase in contactor. Use as hydrate

inhibitor where it can be recovered from gas by separation at temperature

below 50ºF.

2. Diethylene glycol (DEG); high vapor pressure leads to high losses in

contactor. Low decomposition temperature requires low reconcentrator

temperature (315 to 340ºF) and thus cannot get pure enough for most

applications.

3.Triethylene glycol (TEG); most common. Reconcentrate at 340-400ºF,for

high purity. At contactor temperatures in excess of 120ºF, there is a

tendency to high vapor losses. Dew point depressions up to 150ºF are

possible with stripping gas.

4. Tetraethylene glycol (TREG); more expensive than TEG but less loss at

high gas contact temperatures. Reconcentrate at 400 to 430ºF.

TEG is by far the most common liquid desiccant used in natural gas

dehydration. It exhibits most of the desirable criteria of commercial

suitability listed here.

1.TEG is regenerated more easily to a concentration of 98-99% in an

atmospheric stripper because of its high boiling point and decomposition

temperature.

2. TEG has an initial theoretical decomposition temperature of 404ºF,

whereas that of diethylene glycol is only 328ºF.


Table( 2-1) Shows the properties of the glycols


3. Vaporization losses are lower than monoethylene glycol or diethylene

glycol. Therefore, the TEG can be regenerated easily to the high

concentrations needed to meet pipeline water dew point specifications.

4. Capital and operating costs are lower (3) .

The rational of using TEG or advantages of TEG is ease of

regeneration and operation, minimal losses of drying agent during

operation, high affinity for water (this may be attributed to hydrogen-

oxygen bonds which are set up between atoms of the hydroxyl groups

and those of water), chemical stability, high hygroscopicity and low vapor

pressure at the contact temperature (1) . TEG, or triethyleneglycol is a

colorless, odourless viscous liquid with molecular formula C6H14O4 and

molecular structure as shown in Figure (2-1).

Figure (2-1): Molecular structure of triethylene glycol (TEG)

Essentially, Dehydration of natural gas by TEG is first outlined by

summarizing the flow paths of natural gas and glycol . Then the individual

components of a typical TEG unit are described in detail. shown in Figure

(2-2), wet natural gas first typically enters an inlet separator to remove all

liquid hydrocarbons from the gas stream. Then the gas flows to an absorber

(contactor) where it is contacted countercurrently and dried by the lean

TEG. TEG also absorbs volatile organic compounds (VOCs²) that vaporize

with the water in the reboiler. Dry natural gas exiting in the absorber

passes through a gas/glycol heat exchanger and then into the sales line.


The wet or "rich" glycol exiting the absorber flows through a coil in

the accumulator where it is preheated by hot lean glycol. After the glycol-

glycol heat exchanger, the rich glycol enters the stripping column and

flows down the packed bed section in to the reboiler . Steam generated in

the reboiler strips absorbed water and VOCs out of the glycol as it rises up

the packed bed. The water vapor and desorbed natural gas are vented from

the top of the stripper. The hot regenerated lean glycol flows out of the

reboiler into the accumulator (surge tank) where it is cooled via cross

exchanger with returning rich glycol; it is pumped to a glycol/gas heat

exchanger and back to the top of the absorber. Glycol unit decreases the

water content to 60 ppm (3) .

Sweet gas

inlet


2-1-4 Dehydration by Adsorption (Solid Desiccant)

Adsorption (or solid bed) dehydration is the process where a solid

desiccant is used for the removal of water content from a gas stream. The

solid desiccants commonly used for gas dehydration are those that can be

regenerated and, consequently, used over several adsorption-desorption

cycles. The mechanisms of adsorption on a surface are of two types;

physical and chemical. The latter process, involving a chemical reaction, is

termed "chemisorption". Chemical adsorbents find very limited application

in gas processing. Adsorbents that allow physical adsorption hold the

adsorbate on their surface by surface forces. For physical adsorbents used

in gas dehydration, the following properties are desirable(1) .

1. Large surface area for high capacity. Commercial adsorbents have a

surface area of 500-800 m² /g.

2. Good "activity" for the components to be removed and good activity

retention with time/use.

3. High mass transfer rate or high rate of removal.

4. Easy, economic regeneration.

5. Small resistance to gas flow, so that the pressure drop through the

dehydration system is small.

6. High mechanical strength to resist crushing and dust formation. The

adsorbent also must retain enough strength when "wet".

7. Cheap, non-corrosive, non-toxic, chemically inert, high bulk density, and

small volume changes upon adsorption and desorption of water(1)ℓ(6).

The most widely used adsorbents today are activated alumina, silica

gel, molecular sieves (zeolites) (1) .


2-2 Types of Adsorbents

2-2-1 Alumina

A hydrated form of aluminum oxide (Al2O3), alumina is the least

expensive adsorbent. It is activated by driving off some of the water

associated with it in its hydrated form ((Al2O3.3H2O) by heating. It

produces an excellent dew point depression values as low as -100 ºF, but

requires much more heat for regeneration. Also, it is alkaline and cannot be

used in the presence of acid gases, or acidic chemicals used for well

treating. The tendency to adsorb heavy hydrocarbons is high, and it is

difficult to remove these during regeneration. It has good resistance to

liquids, but little resistance to disintegration due to mechanical agitation by

the flowing gas (6) .

2-2-2 Silica Gel and Silica-Alumina Gel

Gels are granular, amorphous solids manufactered by chemical

reaction. Gels manufactured from sulfuric acid and sodium silicate reaction

are called silica gels, and consist almost solely of silicon dioxide (SiO2).

Alumina gels consist primarily of some hydrated form of Al2O3. Silica-

alumina gels are a combination of silica and alumina gel. Gels can

dehydrate gas to as low as 10 ppm, and have the greatest ease of

regeneration of all desiccants. They adsorb heavy hydrocarbons, but release

them relatively more easily during regeneration. Since they are acidic, they

can handle sour gases, but not alkaline materials such as caustic or

ammonia. Although there is no reaction with H2S, sulfur can deposit and

block their surface. Therefore, gels are useful if the H2S content is less than

(5-6%) (6) .

2-2-3 Molecular Sieves

Molecular Sieves are crystalline alkali metal alumino silicates

comprising a three dimensional interconnecting network of silica and

alumina tetrahedral (3). These tetrahedras are the basic building blocks for


various zeolite structures, such as zeolites A and X, the most common

commercial adsorbents (figure.2-3). (7)

Molecular sieve is the most versatile adsorbent because it can be

manufactured for a specific pore size, depending on the application. It is:

● Capable of dehydration to less than 0.1 ppm water content.

● The overwhelming choice for dehydration prior to cryogenic processes

(especially true for LNG ).

● Excellent for H2S removal, CO2, dehydration, high temperature

dehydration, heavy hydrocarbon liquids, and highly selective removal.

● More expensive than silica gel ,but offers greater dehydration.

Figure (2-3): Zeolite structure

● Requires higher temperatures for regeneration, thus has a higher

operating,cost(3). .

The water adsorption in zeolites functions on the basis of physisorption. the

main driving force for adsorption is the highly polar surface within the

pores. This unique characteristic distinguishes zeolites from other

commercially available adsorbents, enabling an extremely high adsorption

capacity for water and other polar components even at very low

concentrations (figure 2-4) (7) .

The structure of molecular sieve is an array of cavities connected by

uniform pores with diameters ranging from about 3 to 10ºA, depending on


the sieve type. In addition, the pore size plays a significant role, allowing or

prohibiting the entrance of molecules to the pore system (3) .Some types of

molecular sieves and it application in table (2-2).

Figure( 2-4) Water adsorption curve versus relative humidity.

Table(2-2) Technical data & application of some kind of molecular

sieve.

Type Bulk

density (kg/m3)

Water adsorption

(%)

Loss on abrasion

(%) Application

3A 0.60-0.70 19-20 0.3-0.6 Drying agent for pyrolysis gas and

alkene

4A 0.60-0.70 20-21 0.3-0.5 Drying agent for natural gas and

absorbent for paraffin separation

5A 0.65-0.70 21-21 0.3-0.5

Dehydration, desulfurization and purification of air, natural gas and oil during oxygen making and hydrogen making by PSA processes

10X 0.50-0.60 23-24 0.8

High-pow absorbents for removal of H2O, H2S and CO2, in liquid and gas, as well as for paraffin separation

13X 0.55-0.65 23-24 0.4 Drying, desulfurization and purification

of oil and gas


2-3 Some Types of Molecular Sieves

2-3-1 3A Molecular Sieve

The pore size of 3A molecular sieve is 3A. It does not adsorb any

molecular larger than 3A. According to the industrial application

specialties, 3A molecular sieves have the characters of higher adsorption

speed, stronger crushing and anti-contaminative resistance, more cyclic

times and longer work-span. All these advantages have made it come to be

the most essential and necessary desiccant in the fields of the deep drying,

refinery polymerization for cracked gases (pyrolysis gas), ethylene,

propylene and any other non-acidic gasses of liquids in petroleum and

chemical industrials.

Formula

0.4K2O · 0.6Na2O · Al2O3 · 2.0SiO2 · 4.5H2O

Molecular Sieve type 4A is an alkali alumino silicate, obtained

through synthesis of type A zeolite in sodic form. It is the sodium form of

Type A crystal structure. 4A molecular sieve has an effective pore opening

of about 4 angstroms (0.4nm). Galaxychem type 4A molecular sieve will

adsorb most molecules with a kinetic diameter of less than 4 angstroms and

exclude those larger. Regeneration: Molecular sieve 4A can be revived

for reuse and the required factors for revival are temperature and pressure.

To remove the adsorbed moisture and other materials, the revival condition

Applications

Dehydration of many kinds of liquids (such as ethanol), dehydration

of air, dehydration of refrigerant, dehydration of natural gas or methane,

dehydration of cracked gas (pyrolysis gas), ethylene, propylene or

butadiene(8). .



is set up considering the features of target material and processing

environment.The general revival temperature of Molecular Sieve 4A is

about200-300℃(8).

Formula

Na2O . Al2O3 . 2SiO2 . 4.5 H2O

Applications

Deep drying of air, Natural gas, alkane and refrigerant. Generation and

purification of argon. Static dehydration of electronic element,

pharmaceutical and unstable materials. Desiccant for paint, dope and foul

etc. Type 4A molecular sieve is typically used in regenerable drying systems

to remove water vapor or contaminants which have a smaller critical

diameter than four angstroms.


Molecular Sieve type 5A is an alkali alumino silicate; it is the calcium

form of the Type A crystal structure. The pore size of 5A molecular sieve is

about 5 Å . It can adsorb all kinds of molecular smaller than this size, it is

mainly used in separation of the normal and isomerous alkane,pressure

swing adsorption (PSA) for gases,co-adsorption of moisture and carbon

dioxide.Regeneration: molecular sieve Type 5A can be regenerated by

pressure swing or purging, usually at elevated temperatures. The purge gas

temperature must be sufficiently high to bring the molecular sieve to a level

of 200°C - 350°C (8) .

Formula

0.75 CaO . 0.25 Na2O . Al2O3 . 2 SiO2 . 4.5H2O

Applications Oxygen/hydrogen PSA (Pressure Swing Adsorption) process

for removal of water and carbon dioxide from air. Type 5A separates normal


paraffins from branched-chain and / cyclic hydrocarbons through a selective

adsorption process. Ethanol refinement (moisture, CO2, etc.).

2-3-4 13X Molecular Sieve

Molecular Sieve 13X is the sodium form of the type X crystal and has a

much larger pore opening than the type A crystals.The pore size 13X

molecular sieve is about 10 Å . It can adsorb any molecular smaller than 10

Å , mainly used as catalyst carrier, co-adsorption of CO2 and H2O, H2O and

H2S, as desiccant for medical and air compressor system, and can also be

adjusted to fit other various applications. Regeneration : molecular sieve

Type 13X can be regenerated by evacuating or purging, usually at elevated

temperatures. The purge gas temperature must be sufficiently high to bring

the molecular sieve to a level of 250°C - 350°C (8) .

Formula

Na2O . Al2O3 . (2.8±0.2) SiO2 . (6~7)H2O.

Applications

Air refining (removing CO2 and H2O) removal of mercaptans and

hydrogen sulphide from natural gas, removal of mercaptans and hydrpogen

sulphide from hydrocarbon liquid streams (LPG, butane, propane etc.) ,

oxygen PSA (Pressure Swing Adsorption) process special double glass

(removing solvent and grease).

2-4 Solid Desiccant Adsorption Kinetics

Figure (2-5) illustrates the movement of an adsorption zone front as a

function of time. In a dry desiccant bed, the adsorbtcate components are

adsorbed at different rates. A short while after the process has begun, a series

of adsorption zones appear, as shown in Figure (2-5)b. The distance between


successive adsorption zone fronts is indicative of the length of the bed

involved in the adsorption of a given component. Behind the zone, all of the

entering component is removed from the gas; ahead of the zone, the

concentration of that component is zero. Note the adsorption sequence: C1

and C2 are adsorbed almost instantaneously, followed by the heavier

hydrocarbons, and finally by water that constitutes the last zone. Almost all

the hydrocarbons are removed and dehydration begins. Water displaces the

hydrocarbons on the adsorbent surface if enough time is allowed. At the start

of dehydration cycle, the bed is saturated with methane as the gas flows

through the bed. Then ethane replaces methane, and propane is adsorbed

next. Finally, water will replace all the hydrocarbons. For good dehydration,

the bed should be switched to regeneration just before the water content of

outlet gas reaches an unacceptable level. The regeneration of the bed consists

of circulating hot dehydrated gas to strip the adsorbed water, then circulating

cold gas to cool

the bed down (6). SAT ADSORBATE BED SATURATION 1 2 3 direction OF FLOW 5 0 t1 BED LENGTH (a) SAT ADSORBATE BED H2O C6+ C5 C4 SATURATION

0 1 BED LENGTH (b)

Figure (2-5) Schematic representation of the adsorption process (6)

2-5 Fundamentals of Adsorption

The adsorption process, takes place in four more or less definable steps.


1.Bulk solution transport.

2.Film diffusion transport.

3.Pore transport.

4.Adsorption (or sorption).

Bulk solution transport involves the movement of the organic material

to be adsorbed through the bulk liquid to the boundary layer of fixed film of

liquid surrounding the adsorbent, typically by advection and dispersion in

adsorbent contactors. Film diffusion transport involves the transport by

diffusion of the organic material through the stagnant liquid film to the

entrance of the pores of the adsorbent. Pore transport involves the transport

of the material to be adsorbed through the pores by a combination of

molecular diffusion through the pore liquid and/or by diffusion along the

surface of the adsorbent. Adsorption involves the attachment of the material

to be adsorbed to adsorbent at an available adsorption site. Because the

adsorption process occurs in a series of steps, the slowest step in the series is

identified as the rate limiting step. In general, if physical adsorption is the

principal method of adsorption, one of the diffusion transport steps will be

the rate limiting, because the rate of physical adsorption is rapid. Where

chemical adsorption is the principal method of adsorption, the adsorption

step has often been observed to be rate limiting. When the rate of sorption

equals the rate of desorption, equilibrium is achieved and the capacity of the

adsorbent is reached. The theoretical adsorption capacity of the molecular

sieve for a particular contaminant can be determined by developing its

adsorption isotherm as described below (9).

2-6 Development of Adsorption Isotherms

The quantity of adsorbate that can be taken up by an adsorbent is a

function of both the characteristics and concentration of adsorbate and the


temperature. The amount of material adsorbed is determined as a function of

the concentration at a constant temperature, and the resulting function is

called an adsorption isotherm. Adsorption isotherms are developed by

exposing a given amount of absorbate in a fixed volume of liquid to varying

amounts of molecular sieve. At the end of the test period, the amount of

absorbate remaining in solution is measured. The absorbent phase

concentration after equilibrium is computed using Eq.(2-1). The absorbent

phase concentration date computed using Eq. (2-1) are then used to develop

adsorption isotherms as described below(9).

qe = (𝐶𝐶𝑜𝑜−𝐶𝐶𝐶𝐶)𝑉𝑉𝑚𝑚

(2-1)

where qe= adsorbent (i.e., solid ) phase concentration after equilibrium, mg

adsorbate/g adsorbent

Cо=initial concentration of adsorbate, mg/L

Ce=final equilibrium concentration of adsobate after absorption has occurred,

mg/L

V= volume of liquid in the reactor,L

m= mass of adsorbent, g

2-6-1 Freundlich Isotherms

Equations that are often used to describe the experimental isotherm

date were developed by Freundlich, Langmuir , and Brunauer, Emmet, and

Teller (BET isotherm) . the Freundlich isotherm is used most commonly to

describe the adsorption characteristics of the adsorbent used in water

treatment. The Freundlich isotherm is defined as follows:

𝑥𝑥𝑚𝑚

= Kƒ𝐶𝐶𝐶𝐶1𝑛𝑛 (2-2)


Where 𝑥𝑥𝑚𝑚

= mass of adsorbate adsorbed per unit mass of adsorbent, mg

adsorbate/g molecular sieve

Kƒ = Freundlich capacity factor, (mg absorbate/g adsorbent)(L water/mg

adsorbate)(L water/mg adsorbate) 1𝑛𝑛

Ce = equilibrium concentration of adsorbate in solution after

adsorption,mg/L

1/n = Freundlich intensity parameter

The constants in the Freundlich isotherm can be determined by plotting

log(x/m) versus log Ce and making use of Eq. (2-2) rewritten as(9) :

Log ﴾ 𝑥𝑥𝑚𝑚﴿ = log Kƒ + 1𝑛𝑛 log Ce (2-3)

2-6-2 Langmuir Isotherm

Derived from rational considerations, the Langmuir adsorption isotherm

is defined as:

𝑥𝑥𝑚𝑚

= 𝑎𝑎𝑎𝑎𝐶𝐶𝐶𝐶1+𝑎𝑎𝐶𝐶𝐶𝐶

(2-4)

a, b = empirical constants

The Langmuir adsorption isotherm was developed by assuming:

1. A fixed number of accessible sites are available on the adsorbent surface,

all of which have the same energy,

2. Adsorption is reversible.


Equilibrium is reached when the rate of adsorption of molecules onto

the surface is the same as the rate of desorption of molecules from the

surface. The rate at which adsorption proceeds is proportional to the driving

force, which is the difference between the amount adsorbed at a particular

concentration and the amount that can be adsorbed at that concentration. At

the equilibrium concentration, this difference is zero correspondence of

experimental data to the Langmuir equation does not mean that the stated

assumptions are valid for the particular system being studied, because

departures from the assumptions can have a canceling effect. The constants

in the Langmuir isotherm can be determined by plotting Ce /(x/m) versus Ce

and making use of eq.(2-5)rewritten as: (9) .

𝐶𝐶𝐶𝐶(𝑥𝑥 𝑚𝑚 )⁄

= 1𝑎𝑎𝑎𝑎

+ 1𝑎𝑎 Ce (2-5)

2-7 Some Previous Work on Dehydration of Natural Gas

Theoretical and experimental works on dehydration of natural gas have

been extensively reported. Ahmad (1)Studied pressure and volumetric

flowrate of natural gas on the effect of operating the removal of water from

natural gas by using triethylene glycol (TEG). And he focused on the effect

of operating pressure and volumetric flowrate of natural gas. From the result

of experiments he found that, the highest amount of water was removed

when the operating pressure at lowest and the volumetric flowrate at

highest. Pezhman and Roya (2) presented a comprehensive study of software

simulator and investigate the effectiveness parameters in a TEG-dehydration

plant in Persian Gulf region. Henry and Julie (19) developed molecular sieve

uI-94 adsorbent to overcome the problems of accelerated particle break-

up. So uI-94 adsorbent increase the operational life of molecular sieves in

natural gas dehydration units and doubled it compared to standard 4A-type

molecular sieve by minimizing pressure drop increase over the life of the


adsorbent. Siti (4) studied, the dehydration of natural gas by adsorption using

silica gel as a solid desiccant and he focuses on designing, fabrication,

hydrostatic test and experimental part . Lukás (5) focused on dehydration of

natural gas by absorption drying using triethylene glycol (TEG) its benefits

and disadvantages. Then the dehydration is simulated with Aspen Hysys

software. The minimum glycol mass flow and specific glycol circulation rate

is calculated. Mohamadbeigy (20) presented a comprehensive study on gas

drying unit and investigated the effectiveness parameters such as glycol flow

rate, stages number of absorption tower and stripping gas rate on water

content in glycol dehydration units. Mohamadbeigy,et al (7) investigated

effectiveness parameter of water adsorption on molecular sieve to find

optimum operating condition. The obtained experimental breakthrough

curves were fitted to theoretical models in order to establish the main

mechanisms of mass transfer. Mohamadbeigy , Kasir and Hormozdi (21)

investigated the effect of some influential factors such as temperature and

flow rate of TEG entering the tower number of equilibrium stages and liquid

fractional entrainment in gas phase on performance of absorption tower in

natural gas dehydration process. Vincente et. Al. (22) studied the effects of

varying the glycol flow rate, number of stages in the contactor, reboiler

temperature, and stripping gas rate on water content in glycol dehydration

units and presented the effect of high carbon dioxide composition in the feed.

Gholaml (23) developed a comprehensive mathematical model to investigate

the simplifying assumptions in modeling of natural gas dehydration by the

adsorption process. Axens company (11) used multi bed technology in the

drying of natural gas by combination of activated alumina with molecular

sieve .This technology improved adsorption capacity , purification capability

and life time of the adsorbent.

Chapter Three Design and Theoretical Consideration

Design and Theoretical Considerations

3-1 Design Considerations

3-1-1 Solid Desiccant Dehydration

The following considerations are a good approximation for estimation

of the solid desiccant dehydration behavior. This information serves only as

a basis for performing preliminary design calculations based on a given cycle

length, number of vessels and their configuration, and a given desiccant.

Therefor, it is highly recommended to refer to desiccant vendors. For

designing a solid desiccant dehydration unit, as the useful capacity of a

desiccant is highly dependent on its aging behavior. To take aging into

account, experience is very important and no published correlations exist

intellectual property and know how. To use only literature data will result in

either uneconomical units or potentially nonworking units (3) .

3-1-1-1 Allowable Gas Velocity

Generally, as the gas velocity during the drying cycle decreases the ability of

the desiccant to dehydrate the gas increases. Low velocities require towers

with large cross sectional areas to handle a given gas flow and allow the wet

gas to channel through the desiccant bed with incomplete dehydration. In

selecting the design velocity, therefore,a compromise must be made between

the tower diameter and the maximum use of the desiccant. Smaller velocities

may be required due to pressure drop considerations. An alternative method

for determining superficial gas velocity in a molecular sieve bed is using the

Ergun equation (12), which relates ∆P to V sG , µ, p,and desiccant size, as

follows(3) .

∆P/L = Bµ VsG +C pG V²sG (3-1)

Where ∆P/L is pressure drop per length of bed ,psi/ft.

µ is gas viscosity, cP.

pG is gas density,Ib/ft³. and VsG is superficial gas velocity,ft/min. Constants


for Equation (3-1) given in Table (3-1) for molecular sieve materials.

Table (3-1) Parameters used in Equation (3-1)

The design pressure drop across the entire bed should be about 5 psi;

values higher than approximately 8 psi are not recommended. Most designs

are based on ∆P/L of about 0.31 -0.44 psi/ft , and typical superficial gas

velocities of 30-60 ft/min(3).

3-1-1-2 Bed Length to Diameter Ratio

After superficial gas velocity is determined, then the diameter and

length of the bed can be calculated from geometry of the adsorber. The

adsorber is normally a cylindrical tower filled with a solid desiccant. The

depth of the desiccant may vary from a few feet to 30 ft or more. The

minimum bed internal diameter for a specified superficial gas velocity is

given by the following equation (Ergun,) (12).

D²= 25(QG)(T)(Z)/(P)(VsG) (3-2)

Where D is bed diameter,ft, QG is gas flow rate, MMscfd;T is inlet gas

temperature, ºR; P is inlet gas pressure, psia; Z is compressibility factor and

VsG is superficial gas velocity, ft/min.

Also, the bed length, can be determined by the following equation (Collins,)

(13) .

LB= 127.3(W)/(pb)(D²)(X) (3-3)

Where LB is bed length, ft; W is weight of water adsorbed, Ib per cycle,pb is

bulk density of desiccant,Ib/ft³;and X is maximum desiccant useful capacity,

Particle type coefficients

B C 1/8-in. beads 0.0560 0.0000889 1/8-in. extrudate 0.0722 0.000124 1/16-in. beads 0.152 0.000136 1/16-in. extrudate 0.238 0.000210


Ib water/100 Ib desiccant. A bed length to diameter ratio of higher than 2.5 is

desirable.

3-1-1-3 Desiccant Capacity

The maximum desiccant useful capacity can be calculated as equation.

(X)(LB) = (Xs)( LB) –(0.45)(Lz)(Xs) (3-4)

Where X is desiccant useful capacity, Ib water per 100-Ib desiccant;Xs is

dynamic capacity at saturation, Ib water per 100-Ib desiccant; Lz is MTZ

length, ft;and LB is bed length, ft (3) .

3-1-1-4 MTZ (Mass Transfer Zone) Length

The MTZ length, LMTZ , depends on gas composition, flow rate,RS

For silica gel the MTZ length may be estimated from the following equation

(simpson and cummings) (14) .

LMTZ = 375 [mw^0.7895 / VsG^0.5506 (RS)^0.2646] (3-5)

Where LMTZ is MTZ length, inch; mw is water loading, Ib/(hr.ft²);VsG is gas

superficial velocity, ft/min; RS is percentage relative saturation of inlet gas.

The relevant equation for calculation of the water loading (mw ) can be

written as follows (Ledoux) (15) .

mw = 0.053[QG(W)/D²] (3-6)

where QG is gas flow rate , MMscfd; D is bed diameter, ft; and w is water

content of gas, Ib/MMscf.

3-1-1-5 Breakthrough Time

The breakthrough time for the water zone formed, tb in hours, can be

estimated as follows (3) (McCabe et al) (16) .

tb = (0.01)(X)(pb)(LB)/mw (3-7)

3-1-2 Glycol Dehydration

More detailed information about each equipment operation and

design used in a TEG dehydration unit is described as follow.

3-1-2-1 Absorber (Contactor)

The incoming wet gas and the lean TEG are contacted countercurrently


in the absorber to reduce the water content of the gas to the required

specifications (3) .

The water removal rate, assuming the inlet gas is water saturated, can be

determined as:

Wr = QG (Wi –wo)/24 (3-8)

Where Wr is water removed, Ib/hr; Wi is water content of inlet gas,

Ib/MMscf; Wo is water content of outlet gas, Ib/MMscf; and QG gas flow

rate,MMscfd.

The glycol circulation rate is determined on the basis of the amount of

water to be. Higher circulation rates provide little additional dehydration

while increasing reboiler fuel and pumping requirements. Problems can arise

if the TEG circulation rate is too low (3) .

The minimum glycol circulation rate can then be calculated as

QTEG,min = G * Wr (3-9)

Where QTEG,min is the minimum TEG circulation rate (gal TEG/hr) and G is

the glycol-to-water ratio (gal TEG/Ib water removed).

The diameter of the contactor (absorber) can be estimated from the

Souders and Brown (17) . correlation as follows.

Vmax = KSB [pL – pG/ pG] = [4QG/∏D²] (3-10)

Where D is internal diameter of glycol contactor,QG is gas volumetric flow

rate,ft³/hr;Vmax is maximum superficial gas velocity,ft/hr; KSB is Souders

and Brown coefficient, ft/hr; pL is glycol density, Ib/ft³; and pG gas density at

column condition, Ib/ft³. Traditionally , the glycol absorber contains 6-12

trays. The standard tray spacing in glycol contactors is 24 inches;closer

spacing increases glycol losses if foaming occurs because of greater

entrainment. The total height of the contactor column will be based on the

number of trays required plus an additional 6-10 ft to allow space for a vapor


disengagement area above the top tray and an inlet gas area at the bottom of

the column (3).

3-1-2-2 Still (Stripper)

The still or stripper column is used in conjunction with the reboiler to

regenerate the glycol. The diameter of the still is based on the liquid load

(rich glycol and reflex) and the vapor load (water vapor and stripping gas).

(Caldwell,; Sivalls) (18). Alternatively, the following approximate equation is

used:

D = 9(QTEG)º·⁵ (3-11)

Where QTEG is TEG circulation rate, gal/min ;and D is inside diameter of

stripping column,inch. Smaller diameter towers (less than 2 ft in diameter)

are often packed with ceramic intalox saddles or stainless steel pall rings

instead of trays. Larger-diameter towers may be designed with 10 to 20

bubble cap trays or structured packing.

3-1-2-3 Reboiler

The reboiler and still are typically a single piece of equipment. The

reboiler supplies heat to regenerate the rich glycol in the still by simple

distillation. Reboiler duty can be estimated by the following equation

(Sivalls,) (18).

QR = 900 + 966(G) (3-12)

Where QR is regenerator duty,Btu/Ib H2O removed; and G is glycol-to-

water ratio,gal TEG/Ib H2O removed.

The reboiler normally operate at a temperature of 350 to 400 ºF for a

TEG system. This temperature controls the lean glycol water concentration.


3-1-2-4 Surge Tank (Accumulator)

Lean glycol from the reboiler is routed through an overflow pipe or weir

to a surge tank or accumulator. Because this vessel is not insulated in many

cases, the lean glycol is cooled to some extent via heat loss from the shell.

3-1-2-5 Heat Exchanger

Two types of heat exchangers are found in glycol plant: glycol/glycol and

gas/glycol.

3-1-2-5-1 Glycol/Glycol Exchanger

A Glycol/Glycol exchanger cools the lean glycol while preheating the

rich glycol. It may be an external exchanger or may be located within the

surge tank (an integral exchanger). For small standard designs, the integral

exchanger is economical to fabricate but may not heat the rich glycol above

200 ºF. (3) .

3-1-2-5-2 Dry Gas/Lean Glycol Exchanger

This type of exchanger uses the exiting dry natural gas to control the

lean glycol temperature to the absorber. High glycol temperature relative to

the gas temperature reduce the moisture absorption capacity of TEG (3) .

3-1-2-6 Phase Separator (Flash Tank)

Many glycol dehydration units contain an emissions separator and a

three-phase vacuum separator. An emissions separator removes dissolved

gases from the warm rich glycol and reduces VOC emissions from the still.

The wet or rich glycol is flashed at 50-100 psia and 100-150ºF.

A three-phase vacuum separator is desirable if liquid hydrocarbons are

present. This allows the liquid hydrocarbon to be removed before it enters

the still, where it could result in emissions or cause excess glycol losses from


the still vent. Because the hydrocarbons are collected under a vacuum,they

are stable and no vapor losses or weathering occurs. The design of the three-

phase separator is similar to that of two-phase separator except that it has a

second control valve and liquid level controller to drain the accumulated

hydrocarbon phase.

3-1-2-7 Glycol Circulation Pumps

A circulation pump is used to move the glycol through the unit. A wide

variety of pump and driver types are used in glycol systems, including

gas/glycol-powered positive displacement or glycol balance pumps (e.g.,

kimray pumps) and electric motor-driven reciprocating or centrifugal pumps.

3-1-2-8 Filters

Two types of filters are commonly used in glycol system.

3-1-2-8-1 Fabric (Particulate) Filters

The suspended solids content of glycol should be kept below 0.01 wt%

to minimize pump wear,plugging of exchangers,fouling of absorber trays and

stripper packing,solids deposition on the firetube in the reboiler, and glycol

foaming. Solid filters are selected to remove particles with a diameter of 5

µm and larger. A common design is a 3-inch diameter by 36-inch-long

cylindrical element in housing,sized for a flow rate of 1 to 2 gallon per

minutes per element. The filters are sized for a 12 – to 15-psi pressure drop

when plugged. This filter will remove any foreign solid particles picked up

in the absorber before entering the glycol pump.

3-1-2-8-2 Carbon Filters

Activated carbon filters are used to remove dissolved impurities in the

glycol, such as high-boiling hydrocarbons,surfactants,well-treatin

chemicals,compressor lubricants,and TEG degradation products.


3-2 Operational Problems

3-2-1 Solid Desiccant Dehydration

Operational problems that may occur because of poor design,

operation, and maintenance in a solid desiccant unit are described in this

section.

3-2-1-1 Bed Contamination

The most frequent cause is incomplete removal of contaminants in the

inlet gas separator. Also, if the regeneration gas leaving the separator is

commingled with the feed gas to the dehydrators,then a separator

malfunction can dump liquid hydrocarbons and water onto the desiccant

regenreration separators should usually be equipped with filtration levels

similar to the inlet gas to prevent recontamination (3) .

3-2-1-2 High Dew Point

High dew point is one of the two common problems that can cause

operating trouble. Possible causes include the following.

1."wet" inlet gas bypasses the dehydrator through cracks in the internal

insulation. Cracks in a liner or in sprayed-on insulation can be detected by

"hot spots" and peeling paint on the outer shell. Other symptoms are fast

water breakthrough and an unusually rapid rise in the effluent gas

temperature during regeneration.

2.Leaking valves also permit wet gas to bypass the dehydrators. Even a

slight leak of hot gas usually produces a detectable temperature rise in what

should be the cold side of the valve. Ultrasonic translators are also useful.

3.Incomplete desiccant regeneration will lead to a sudden loss in adsorption

capacity and a significantly premature breakthrough. To be sure to well

Chapter Three Design and Theoretical consideration

regenerate the adsorbents the inlet and outlet temperatures of the adsorber in

regeneration should be analyzed. At the end of the heating step the outlet

temperature should be almost contact during a certain time (30 minutes to 2

hours) depending on the design of the adsorber,and the temperature

difference between inlet and outlet should not be more than 59-68ºF

depending on the quality of the heat insulation.

4.Excessive water content in the wet feed gas due to increased flow

rate,higher temperatures,and lower pressure. It is very important to respect

the inlet temperature (feed temperature) of the adsorbers in case of saturated

gas. Small variations in temperature will lead to significant increases in the

water content (3) .

3-2-1-3 Premature Breakthrough

Satisfactory dew points are observed at the beginning but not for the

entire duration of the drying cycle. Desiccant capacity should decrease with

use but should stabilize at 55-70% of the initial capacity Ballard,

(24).However, premature symptoms of "old gas" are caused by an

unrecognized increase in inlet water loading, an increase in heavy

hydrocarbons (C4+) in feed gas, methanol vapor in feed, desiccant

contamination, or incomplete regeneration.

3-2-1-4 Hydrothermal Damaging

Heating up the adsorber without using a heating ramp or an

intermediate heating step leads to a strong temperature difference in the

vessel. At the bottom, the molecular sieve will be very hot and will desorb

rapidly the adsorbed water while the layers at the top of the adsorber will be

still at adsorption temperature. The water desorber in the bottom layer will

condense in the top layer. Hydrothermal damaging will appear in

consequence, which is different depending on the type of molecular sieve. In


order to prevent hydrothermal damaging of molecular sieves it is not only

important to choose the right formulation of the molecular sieve (binder and

zeolite) but the operating conditions; the regeneration conditions should be

determined carefully. In fact, the higher the regeneration temperature and the

higher the amount of liquid water present on the sieves, the heavier the

damaging of the molecular sieves. In an industrial unit it is also important to

limit the quantity of water appearing in liquid phase (condensing water due

to oversaturation of the gas phase), as this decreases the temperature where

hydrothermal destruction may occur with water acting as a stabilizer for

intermediates formed by dissolution of the zeolites.

3-2-1-5 Liquid Carryover

Liquid (particularly amines) carryover in the molecular sieve bed has a

bad effect on the drying process. In order to reduce the liquid carryover in

adsorbers, separators must be modified to improve their efficiency. The

regeneration procedure should also be changed so as to have a moderate

temperature increase to avoid water recondensation. Although on-site

mechanical changes of the drying unit can improve the performance,

however, the right corrective action can be found by using a more resistant

molecular sieve, SRA. The SRA adsorbent offers a better mechanical

resistance than the regular one to severe operating conditions simulating the

thermal regeneration step of a natural gas purification unit.

3-2-1-6 Bottom Support

Sometimes operators have problems with the support grid and leakage

of molecular sieves through the support grid. As a result, they have to

replace the whole bed. Important point here is the good mechanical design of

the support bed, putting three wire mesh on the support grid (4, 10,20 mesh)

and installing the correct quantity and size of ceramic balls.


3-2-2 Glycol Dehydration

The operating problems associated with each equipment in the TEG

dehydration unit are described individually in the following sections.

3-2-2-1 Absorber

The main operating problems associated with the absorber are

insufficient dehydration, foaming and hydrocarbon solubility in glycol,

which are discussed next.

3-2-2-1-1 Insufficient Dehydration Causes of insufficient dehydration (i,e,

wet sales gas) include excessive water content in the lean glycol, inadequate

absorber design, high inlet gas temperature, low lean glycol temperature, and

overcirculation /undercirculation of glycol (3) .

3-2-2-1-2 Foaming

Foaming causes glycol to be carried out of the absorber top with the

gas stream, resulting in large glycol losses and decreased glycol unit

efficiency. Foaming can normally be traced to mechanical or chemical

causes. High gas velocity is usually the source of mechanical entrainment.

Chemical foaming is caused by contaminants in the glycol, liquid

hydrocarbons, well-treating chemicals, salts, and solid. Adequate inlet

separation and filtration system (cartridge filter and activated carbon bed) are

therefore needed to prevent foaming due to chemical contamination.

3-2-2-1-3 Hydrocarbon solubility in TEG solution Aromatic hydrocarbon

solubility in glycol is a significant issue in gas dehydration technology due to

the potential release of aromatics to the atmosphere at the regenerator.

3-2-2-2 Still (Stripper)

Excessive glycol vaporization is more of a problem for finned

atmospheric condensers than for water-cooled or glycol-cooled condensers.


Although finned atmospheric condensers are simple and inexpensive,

they are sensitive to extremes in ambient temperature. For example, during

cold winter periods, a low temperature at the top of the still column causes

excessive condensation and floods the reboiler. This prevents adequate

regeneration of the glycol and reduces the potential dew point depression of

the glycol causing insufficient dehydration in the absorber. Also, excessive

glycol losses may occur as the reboiler pressure increases and blows the

liquids out the top of the column. During the summer months, inadequate

cooling may allow excessive glycol vaporization losses.

3-2-2-3 Reboiler

Operational problems associated with the reboiler include salt

contamination,glycol degradation, and acid gas-related problems.

3-2-2-3-1 Salt Contamination

Carry over of brine solution from the field can lead to salt

contamination in the glycol system. Sodium salt(typically sodium chloride,

NaCl) are a source of problems in the reboiler, as NaCl is less soluble in hot

TEG than in cool TEG; NaCl will precipitate from the solution at typical

reboiler temperature of 350-400ºF. The salt can deposit on the fire tube,

restricting heat transfer. If this occurs,the surface temperature of the fire tube

will increase,causing hot spots and increased thermal degradation of the

glycol. The deposition of salt may also result in corrosion of the fire tube.

Dissolved salt cannot be removed by filtration. As a general rule, when the

salt content reaches 1%, the glycol should be drained and reclaimed. If the

level of salts is allowed to increase beyond 1% both severe corrosion and

thermal degradation threaten the system.

3-2-2-3-2 Glycol Degradation

Glycol degradation is caused primarily by either oxidation or thermal


degradation. Glycol readily oxidizes to form corrosive acid. Oxygen can

enter the system with incoming gas, from unblanketed storage tanks or

sumps, and through packing glands. Although oxidation inhibitors [such as a

50-50 blend of monoethanolamine (MEA) and 33% hydrazine solution] can

be used to minimize corrosion, a better approach to controlling oxidation is

blanketing the glycol with natural gas, which can be applied to headspace in

storage tank and any other area where glycol may contact oxygen. Thermal

degradation of the glycol results from the following conditions: high reboiler

temperature, high heat flux rate, and localized overheating. The reboiler

temperature should always be kept below 402ºF to prevent degradation, and

a good fire tube design should inherently prevent a high heat flux rate. In

addition, thermal degradation of the glycol produces acid degradation

products that lower the PH and increase the rate of degradation, creating a

destructive cycle.

3-2-2-3-3 Acid Gas

Some natural gas contains H2S and/or CO2, and these acid gases may

be absorbed in the glycol. Acid gases can be stripped in the reboiler and still.

Mono-,di-, or triethanolamine may be added to the glycol to provide

corrosion protection from the acid gases(3) .

3-2-2-3-4 Surge Tank

When surge tanks also serve as glycol/glycol heat exchanger, the level

must be monitored to ensure that the lean glycol covers the rich glycol coil.

Otherwise, inadequate heat exchange will occur, and the lean glycol will

enter the absorber at an excessively high temperature.

3-2-2-3-5 Heat Exchanger

The primary operational problem with heat exchangers is poor heat

transfer, which results in lean glycol that is too warm. When this occurs,


poor dehydration and insufficient dew point depression can result. Also,

glycol vaporization losses to the product gas may be higher with increased

lean glycol temperature. Poor heat transfer and the resulting high lean glycol

temperature are usually caused by fouled heat exchangers. Exchangers may

be fouled by deposits such as salt, solids,coke,or gum. Corrosion of the coil

in surge tank heat exchangers can also present operating problems, as it can

lead to cross-contamination of rich and lean glycol.

3-2-2-3-6 Phase Separator (Flash Tank)

Inadequate residence time in the phase separator may result in a large

quantity of glycol being included in the hydrocarbon stream and vice versa.

3-2-2-3-7 Glycol Circulation Pump

Major problems associated with the circulation pump and rates are

related to reliability,pump wear, and overcirculation or undercirculation(3) .

Chapter Four Case Study

Case Study

4-1 Dehydration Process

In the north gas company the treated gas stream from the sweetening

unit is cooled to approximately 38ºC through EA-1305 to condense out

excess water.This cooling reduces significantly the required amount of

molecular sieve .The water condensate ,after separation from the gas stream

in the K.O.(knock-out) drum which is a vapor-liquid separator. It is a vertical

vessel used in several industrial applications to separate a vapor-liquid

mixture. There is a barrier inside K.O drum to separator the gas by bang to

it .Gravity causes the liquid to settle to the bottom of the vessel ,where it is

withdrawn and there is a clip upper the drum to prevent crossing of the liquid

with gas . (FA-1304), is returned to the sweetening unit for re-use. The gas

is normally not cooled enough to condense hydrocarbons. Any condensed

hydrocarbons ,if present in the K.O. drum, are sent to the Burning pit (BT-

0603). The gas from K.O. drum flows to the charge-Gas Dryer (FF-1301

A/B) before proceeding to the downstream , low-temperature separation

section. The gas is dried to prevent plugging due to freeze-ups and hydrate

formation at low temperatures . Two vessels containing molecular sieve

(type 4A) desiccant are provided ; these alternate between on-stream drying

service and regeneration , on an 8-hour cycle (cycle length will be longer

with new desiccant and progressively decline with time). An inter-bed

moisture probe monitors operation and detects water break-through from the

bed .The dried gas is sent to the activated carbon Bed (FA-1305), where any

trace amounts of mercury in the gas stream are removed .The gas then flows

through the filter (FD-1301 A/B), to remove desiccant dust and other solids

which may cause plugging in the down-stream equipment. Then the gas is

sent to section drum (surge drum)(FA-1302) where its given enough time to

process. The gas is then compressed to approximately 46 kg/cm²G with


a sidestream draw off at about 32.6 kg/cm²G for dryer regeneration

gas.Before entering the chilling section, the compressor (GB-1301)

discharge is cooled to 40ºC with cooling water. The vapor, separated in the

compressor discharge Drum (FA-1303), is sent to the chilling section, while

the hydrocarbon condensate is directed to the Deethanizer (DA-1501). figure

(4-1) illustrates this process.

Figure (4-1) Dehydration process of natural gas in North Gas Company.

4-2 Regeneration Process

The sidestream from the charge-Gas compressor (GB-1301) , is first

heated in the fired heater (BA-1301) to 343ºC and then used as the

regeneration gas for all the dryers in the plant. The regeneration gas, after

dryer regeneration , is cooled with cooling water to 38ºC where it is used for

cooling the dryer to 38 ºC after heating. The regeneration gas is then sent to


the K.O. drum (FA-1308) where water is removed . The water separated

from the K.O. (knock-out) drum is degassed in the degassing Drum (FA-

1306) before being discharged to the waste water treatment . The

regeneration gas from the K.O. (knock-out) drum (FA-1308) is recycled

back to the Absorber in the sweetening unit , for acid gas removal (DA-

1201) (10) . Anti surge out from the top of the vessel FA-1303 and enter the

path to enter the gas to the compressor GB-1301. Figure (4-1) illustrates this

process, and table (4-1) shows the composition of natural gas in dehydration

unit.

Table (4-1) The composition of natural gas in dehydration unit

4-3 The Molecular Sieve Dehydrator

In the North Gas Company, the molecular sieve bed for dehydration of

natural gas as shown in figure (4-2) consists of the following:-

1. The upper ceramic balls layer used as a support to the molecular sieve

and facilitates the passage of gas to the molecular sieve. The diameter of

single ball is (19mm) and the height of ceramic balls layer is (250mm) .


2.The wire mesh layer is used to isolated molecular sieves from ceramic

balls and keeps the molecular sieves from coming up with gas.

4700 mm I.D

Sweet gas inlet

1. Ceramic balls

250mm

4800mm

2. Wire mesh

6800mm

3. Molecular sieves

4. Ceramic balls 100mm

Dry gas outlet

5.Bottom support grid

Figure (4-2) Molecular sieve bed


3.The molecular sieves layer of type 4A represents the main part for adsorbing the water from the inlet gas. The height of the molecular sieve layer is (4800mm).

4.The lower ceramic balls layer is used to support the molecular sieve and

facilitates the passage of gas to the molecular sieve passage of gas to the

molecular sieve. The diameter of single ball is (6.2mm) and the height of

ceramic balls layer is (100mm) .

5.Bottom support grid, used to support the heavy weight of molecular sieve

(53.325ton).

Two beds are used in cyclic operation to dry the natural gas on a

continuous basis , one bed operates in adsorption , while the second operates

in desorption , and both beds are switched periodically. For dehydration , of

natural gas 4A type of molecular sieve is used in the North Gas

Company.This is a good choice because of its high selectivity and affinity

for water but the problem is after a certain number of cycles , molecular

sieve beds show broken particles and dust ,leading to aging of the molecular

sieve after (1.5-2) years instead of three years (the real life time of the

molecular sieve).

Many tests are made for the aging molecular sieve and the new

molecular sieve to show the difference between them.

1.(XRD) (X-ray Diffraction) tested in the state company of Geological

Survey and Mining.

2. (FT-IR) (Fourier Transform Infra Red) (BRUKER . TENSOR 27) tested

in Chemical Engineering Department at the University of Technology.

Figure (4-3) shows the FT-IR device.

3. Crystal structure analysis was carried out by microscope at the Materials


Engineering Department at the University of Technology.

4. The surface area and the pore volume of the aging and the new molecular

sieve were measured at the Petroleum Research and Development Center.

Figure (4-3) FT-IR device

Chapter Five Results and Discussion

5-1 Results and Discussion

The results of testing the aging and the new molecular sieve are shown

in figure (5-1) and figure (5-2) . The results of X-ray Diffraction test showed

no large and influential different between the new and the aging molecular

sieve as shown in figures (5-1) and (5-2). The results of (FT-IR) (Fourier

Transform Infra Red) as in figure (5-3) showed no difference between the

new and the aging of molecular sieve. The crystal structure of the aging and

the new molecular sieve were tested by microscope with magnification

power (100X ) (BEL. Italy ) and a picture was taker for the result of the

tested samples, the microstructure of each sample is different as shown in

figures (5-4) and (5-5).From these figures, it can be seen that the dark

regions in the aging molecular sieve are less than in the new molecular

sieves. This means that most of the pores (dark regions) in the aging

molecular sieve are blocked by contaminants which causes the decreasing in

the adsorption capacity of the molecular sieves. Also the surface area and the

pore volume of the aging and the new molecular sieve were measured as

shown in table (5-1). It can be seen that the surface area and the pore volume

for the aging molecular sieve are lower than for the new molecular sieve.

This confirms the above result about the blocking of the molecular sieve.

Table (5-1) Values of Surface Area and Pore volume as means the new

and aging molecular sieve

NO

Test New molecular sieve

Aging molecular sieve

1 Surface Area (m²/gm) 46.2643 7.3170

2 Pore volume (cm³/gm) 0.0569 0.0184

Chapter Five Result and Discussion

Figure (5-1) New molecular sieve


Figure (5-2) Aging molecular sieve


Figure (5-3) FT-IR of new and aging molecular sieve


Figure (5-4) New molecular sieve

Figure (5-5) Aging molecular sieve


So the most frequent cause of the aging , blocking and breaking up of

the molecular sieve may be the following :-

1.The incomplete removal of free liquid water in the inlet gas separator , so

the natural gas enters the dehydrator with a large amount of water

(2800ppm). This is a very important part of the system because free water

can cause the adsorbent materials to break down.This leads to higher

pressure drop and channeling , reducing the overall performance of the unit.

2. Liquid (particularly amines from sweetening unit) may carry over in the

molecular sieve bed which has a negative impact on the drying process (i.e.

poor gas flow distribution due to fines formation as a consequence of

chemical attack causing an increase of the pressure drop and a decrease of

adsorption time).

3. Hydrocarbons are adsorbed on molecular sieve just as water is but less

preferentially. That portion of the bed at a given time which is not

dehydrating gas is retaining hydrocarbons. The heavier hydrocarbon are

retained preferentially over the light hydrocarbons, where dehydration stops

short of the break through point , the portion of the bed not used for

dehydration will have retained hydrocarbons. Many dehydration units

produce hydrocarbon liquid in the regeneration condensate. So aging of

molecular sieve may be caused by coal sorption of hydrocarbons and coke

formation on the active surface of the adsorbent. This phenomenon is not

completely reversible, and carbon deposits increase with each

regeneration.This will block the pores of molecular sieve.

4. The aging of molecular sieve may be hydrothermal aging which is an

irreversible change of adsorbent structure caused by hydrothermal damaging

during regeneration. At the bottom of the bed , the molecular sieve will be

very hot and will desorb rapidly the adsorbed water while the layers at the


top of the a desorber will be still at adsorption temperature (38ºC) . The

water adsorbed in the bottom layer will condense in the top layer . This

phenomenon is called refluxing . The heating going on will heat up the liquid

water and boil the molecular sieves in liquid water. So certain components of

the binders used in standard 4A molecular sieve are some what soluble in

liquid water . Some of the soluble components can ion exchange with the

zeolite and /or combine with anions in the liquid water to form solid salts

(i.e.N2CO3,CaCO3, MgCO3 , NaNO3 , etc ) when the water evaporates . This

condition leads to hydrothermal damaging. Also the intimate contact of

molecular sieve with the rapidly vaporizing liquid water in the liquid reflux

zone results in accelerated particle break-up ; leading to(non – uniform )

pressure drop build-up through the molecular sieve bed and ultimately

channeling and premature water break through. on inspection , such

molecular sieve beds have shown broken particles and dust that has

compacted in a layer that can very in depth from several tens of centimeters

to, in extreme case , the majority of the bed.

5-2 Overcoming the Breaking Up and Aging Problems of the Molecular

Sieve

1. Gas separator must be modified to improve their efficiency to maximize

water droplet removal. Also a filter separator is required if the adsorption

unit is downstream from an amine unit. Although there is a K.O drum , some

time amine cross with the natural gas.

2. Liquid (particularly amines) carry over in the molecular sieve bed must be

prevented by using antifoaming material, in the previous unit , and the gas

flow rate must be controlled carefully because at excessive velocities, amines

can be lifted up of the sweetening unit with the gas to the molecular sieve

bed.


3. It is important to choose the regeneration conditions carefully. In fact , the

higher the regeneration temperature and the higher amount of liquid water

present on the sieves, the heavier the damaging of the molecular sieve . This

leads to shorter desiccant life , and lower regeneration temperatures lead to

insufficient dehydration capacities.

4. A layer of less expensive desiccant (activated alumina) in the upper

section of the molecular sieve dehydrator will catch contaminants, such as

amines, this is called multi bed technology (11) . The results of this technology

are improved adsorption capacity , purification capability , life time of the

adsorbent and extend the bed life . Figure (5-6) shows the applications of the

multi bed technology.

5. Solid desiccant dehydrators are typically more effective than glycol

dehydrators , as they can dry a gas to less than 0.1 ppm v (0.05 Ib/MMCF).

However , in order to reduce the high amount of water in the inlet natural gas

and the size of the solid desiccant dehydrator , it is better to use glycol

dehydration unit to reduce the water content to around 60 ppm v and then

use solid desiccant for final drying.

Figure (5-6) Applications of the Multibed™ Technology(11)

Chapter Six Conclusions and Recommendations

6-1 Conclusions

From this research it can be concluded that the reason for breaking

up,blocking and aging the molecular sieve, is one or more of the following:

1. Amine carry over.

2. Water condensed.

3. The temperature of regeneration.

4. Inlet gas velocity.

So the problem can be treated by one or more of the following:

1. Gas separator must be modified to improve their efficiency to maximize

water droplet removal.

2. Filter separator is required if the adsorption unit is downstream from an

amine unit.

3. Liquid (particularly amines) carry over in the molecular sieve bed must be

prevent by using antifoaming material.

4. It is important to choose the regeneration conditions carefully. Where the

higher the regeneration temperature and the higher amount of liquid water

present on the sieves, the heavier the damaging of the molecular sieve.

Which lead to shorter desiccant life and lower regeneration temperatures

lead to insufficient dehydration capacities.

5. A layer of less expensive desiccant (activated alumina) in the upper

section of the molecular sieve dehydrator will catch contaminants, such as

amines, this is called multi bed technology. The results of this technology

improve adsorption capacity , purification capability , life time of the


adsorbent and extend the bed life.

6. It is better to use glycol dehydration unit to reduce the water content to

around 60 ppm v and then using solid desiccant for final drying.


6-2 Recommendations

After finishing this study there are some recommendations that may

be useful for research in the future work.

1. An experimental study of the problem of breaking up, blocking and

therefore the aging of molecular sieve must be done on-site of molecular

sieve dehydration unit of the Iraqi North Gas Company in order to

investigate the real variables that may affect the aging of molecular sieve and

try to treat it. Some of these variables which may have effects, are the inlet

gas velocity to molecular sieve dehydrator, the composition of the inlet and

the outlet of the natural gas, the temperature of regeneration ,and then try to

find a way to treat it .

2. Study the feasibility when glycol dehydration unit is used at the first to

reduce the water content of natural gas to around 60 ppm v and then use

molecular sieve for final drying in steal of using only molecular sieve for

dehydration of natural gas . In this case , molecular sieve problems which

may occur because of high water content of natural gas.

References

1. Ahmad Syahrul Bin Mohamad "Natural gas dehydration using

triethyleneglycol (TEG)" Faculty of Chemical & Natural Resources

Engineering University Malaysia Pahang . April 2009.

2. Pezhman Kazemi and Roya Hamidi "Sensitivity analysis of a natural

gas triethylene glycol dehydration plant in Persian gulf region" Received

November 9, 2010, Accepted February 1, 2011.

3.Saeid Mokhatab William A. Poe James G. Speight "Hand Book of natural

gas transmission and processing".

4. Siti Suhaila Bt Mohd Rohani "natural gas dehydration using silica gel"

fabrication of dehydration unit. APRIL 2009.

5. Luká Polák "Modelling absorption drying of natural gas" May 2009

Trondheim.

6. Chapter 7. The dehydration and sweetening of natural gas. From the

internet (the dehydration of natural gas).

7. Kh. Mohamadbeigy , Kh.Forsat , R.Binesh. Experimental studying on

gas dewatering by molecular sieve. Available online at Uwww.vurup.sk/pcU

Petroleum & Coal 49 (1), 41-45, 2007. Received December 21, 2006;

accepted June 25, 2007.

8.From the internet (the chemical structure of molecular sieve types).

9.Metcalf and Eddy., "wastewater engineering treatment and reuse" 4th

edition. 2003.

10.Iraqi North Gas project process plant operating manual vol 1.

11.Activated alumina &Molecular Sieves. Quality and advanced

technology.Company Axens , Procatalyse Catalysts & Adsorbents.

12. Ergun, S ., Fluid flow through packed column. Chem. Eng. prog. 48, 2

1952. Cited in reference (3).

13. Collins,J.J., AIChE Symp. Ser., No. 74, 63: 31, 1967. Cited in

reference (3).

http://www.vurup.sk/pc�

14.Simpson,E.A., and Cummings, W.P., A practical way to predict silica

gel performance."chem. Eng. Prog. 60(4), 57-60 ,1964. Cited in reference

(3).

15. Ledoux, E., Chem. Eng. (March 1948). Cited in reference (3).

16. McCabe, W.L., Smith, C.J., and Harriott, P., "Unit Operations of

Chemical Engineering," 4th Ed. McGraw-Hill, New York (1985). Cited in

reference (3).

17. Souders, M., and Brown, G.G., Fundamental design of absorbing and

stripping columns for complex vapours Ind. Eng. Chem. 24, 519. Cited in

reference (3).

18. Caldwell, R.E., "Glycol Dehydration Manual,"NATCO Group,

Tulsa,OK (Jan 30, 1976) (Sivalls, C.R., "Glycol Dehydration Design

Manual." Sivalls, Inc., Odessa, TX (June 1976). Cited in reference (3).

19 . Abu Phabi "Middle east adsorbents and gas processing Technology

conference" uAE , 2008.

20. Kh. Mohamadbeigy"Studying Of The Effectiveness Parameters On Gas

Dehydration Plant" Received December 15, 2007, accepted May 15, 2008.

21. N.Kasiri , Sh .Hormozdi "Improving performance of absorption tower

in natural gas dehydration process .

22. Vincente n. Hernandez-Valencia and et al"design glycol units for

maximum efficiency".

23. M. Gholaml and et al. Ind . engineering. Chemical .Res. 2010 , 49(2) ,

pp838-846 ).

24. Ballard, D., "How to Improve Cryogenic Dehydration."petroenergy,

83,Houston, TX (sept. 12-16, 1983). Cited in reference (3).

U اخلالصة

عن طريق االمتزاز باستخدام املناخل التجفيف للغاز الطبيعي اهلدف من هذا البحث هو دراسة عملية

اجلزيئية كما هو احلال يف شركة غاز الشمال .جتفيف الغاز الطبيعي ضروري إلزالة املاء املصاحب للغاز

الطبيعي على شكل خبار.صناعة الغاز الطبيعي أدركت ان التجفيف هو ضروري لضمان التشغيل السهل

يف حالة عدم اجراء خلطوط نقل الغاز, التجفيف مينع تكوين هيدرات الغاز, ويقلل عملية التأكل .

قد يتكثف املاء السائل يف األنبوب ويتجمع يف نقطة منخفضة على طول اخلط ويقلل من عملية التجفيف

.وهناك اربعة وقد وضعت العديد من الطرق لتجفيف الغازات على مستوى صناعي.قدرتا على التدفق

وتركز هذه الدراسة على ,امتصاص, امتزاز.التربيد املباشر, والتربيد غري املباشرطرق رئيسية للتجفيف هي

طريقة االمتزاز والذي يستخدم لتجفيف الغاز الطبيعي يف شركة غاز الشمال، ويركز أيضا على مشكلة

بعض التجارب اجريت للمناخل تفتيت وانتهاء كفاءة املناخل اجلزيئية قبل أن ينتهي عمره التشغيلي .

بعض املقرتحات وضعت للتغلب على مشكلة انتهاء كفاءة .اجلزيئية للجديد والتالف ألظهار الفرق بينهما

وعاء فصل الغاز , استخدام مانع الرغوة لتجنب عبور األمني مع مثل تحسين كفاءة املناخل اجلزيئية ,

الغاز,اختيار ظروف اعادة التنشيط بدقه , استخدام تكنولوجيا ثنائي املادة واستخدام وحدة التجفيف

بالكاليكول باألضافة اىل وحدة التجفيف باملناخل اجلزيئية خلفض حمتوى املاء من الغاز الطبيعي.

وزارة التعليم العالي والبحث العلمي

الجامعة التكنولوجية

قسم الهندسة الكيمياوية

دراسة عملية التجفيف للغازالطبيعي في شركة غاز الشمال العراقية وطرق معالجة مشاكل المناخل الجزيئية

مقدمة الى رسالة

قسم الهندسة الكيمياوية في الجامعة التكنولوجية كجزء من متطلبات

تصفية النفط في الهندسة الكيمياوية / الدبلوم العالينيل درجة

وتكنولوجيا الغاز

إعداد

فرمان سعيد عبداهللا زه نكنه

)2004(بكالوريوس هندسة كيمياوية

بإشراف

أ.م.د. أنعام أكرم صبري

2012ه شباط 1433صفر

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