CDP FINAL REPORT

Optimization of a TEG
dehydration unit with
recent advances in tech-
nology CPD (3425)
Team 10
TechnischeUniversiteitDelft

Optimization of a TEG dehydration
unit with recent advances in
technology CPD (3425)
by
Team 10
Javier Leyva Rico - 4415027 - +31617370757
Agnes van Endhoven - 4174933 - +31627117687
Ameya Thakurdesai - 4411153 - +31617327604
Toon Nieboer - 4114965 - +31641317731
Assignment issued: 28-04-2015
Report issued: 26-06-2015
Appraisal: 30-06-2015
in partial fulfillment of the requirements for the course of
Design Project
in Chemical Engineering
at the Delft University of Technology,
Technical advisor: Dr. P. Hamersma, TU Delft
Creativity Coach: Prof. dr. B. Dam, TU Delft
Principals: Ir. A. Didden, Frames Group
Ir. A. Malhotra, Frames Group

Preface
For the conceptual design project of the master Chemical Engineering we, a group of four students,
have been put together to work on an assignment for M/s Frames. The main purpose of the project is
to decrease the size and costs of an offshore TEG gas dehydration unit, a widely used technique for gas
dehydration. This has been done by adding new technologies from industry. For the past 10 weeks,
literature studies were performed, contacts with professors and companies have been made and many
simulations and calculations were done.
After a study, some thorough & some brief, out of nine different technologies three were chosen to
be added to the conventional process in order to try to decrease the CAPEX, OPEX and weight of the
unit. Pervoparation membranes, a liquid turbochargers and injection of semi-lean TEG were included.
The conventionally used process has been simulated to set a benchmark and the impact of all
different techniques has been calculated. Thereafter the hybrid process was simulated. This resulted
in a reduction of OPEX of € 70,000 per year, but also an increase of 15 million €, which means the
CAPEX has doubled. The weight of the unit stayed more or less the same as is shown in the report.
In the end it is concluded that the addition of liquid turbochargers has a positive effect on the total
energy needed for the TEG transport throughout the plant. A reduction of 70% of energy consumption
is achieved. The pervaporation membranes decrease the energy needed for reboiling but turn out to
be very costly in capital expenses. As of now it is not yet beneficial to add these membranes as the
rate of return is too low. It is expected that after more research the price of these membranes can
drop however, as a larger surface area per unit can be achieved. This will cut down the capital costs of
the membranes and make them a viable option in the future. The addition of semi-lean TEG injection
proved a useful addition. It resulted in a size reduction of the still column, reboiler and surge vessel. To
implement this technology in the conventional process however the design of the still column needs to
be altered or the distillation needs to be done in two steps in order to provide a semi-lean TEG stream
to return to the contactor (absorption tower).
Team 10: Javier Leyva, Ameya Thakurdesai, Agnes van Endhoven & Toon Nieboer
Delft, June 2015
iii

Contents
1 Introduction and Project Charter 1
1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.3 Concept Stage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3.1 Process synthesis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3.2 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3.3 Plant capacity and location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.4 Database. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4.1 Component list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4.2 Component and thermodynamic properties . . . . . . . . . . . . . . . . . . . 5
2 Conventional Process 7
2.1 Process description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.1 Contactor (C101) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.2 Flash (V201). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.3 Filters (S201) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.4 Reboiler (V202) & Still column (C201) . . . . . . . . . . . . . . . . . . . . . . 9
2.1.5 Stripping column (C202) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.6 Surge (V203) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2 Mass and energy balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.1 Simulation on Aspen Hysys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3 Equipment sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.4 Total weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.5 Health, Safety & Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.5.1 Preliminary study of risks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.5.2 Dow’s Fire and Explosion Index (F&EI) . . . . . . . . . . . . . . . . . . . . . . 14
2.5.3 Waste. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.6 Bottlenecks and possible improvements . . . . . . . . . . . . . . . . . . . . . . . . . 17
3 Innovation Map 19
3.1 Description of alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.1.1 Improved TEG injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.1.2 Microwave heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.1.3 Super-X packing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.1.4 Liquid turbochargers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.1.5 Pervaporation membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.1.6 Molecular sieves + TEG unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.1.7 Addition of entrainer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.1.8 Vacuum operation in still column . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.1.9 Rotating packed beds (HiGee) . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.2 Selection of alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.2.1 Turbochargers and split-flow injection . . . . . . . . . . . . . . . . . . . . . . 25
3.2.2 Alternative 1: Process scheme with microwave heating . . . . . . . . . . . . 28
3.2.3 Alternative 2: Process scheme with pervaporation membranes and semi
lean injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.2.4 Alternative 3: Process scheme with hybrid system . . . . . . . . . . . . . . . 38
3.3 Selection of the optimized process scheme. . . . . . . . . . . . . . . . . . . . . . . . 39
v

vi Contents
4 Hybrid Process 41
4.1 Process description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.2 Material and energy balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.2.1 Energy demands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.3 Equipment sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.4 Total weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.5 Safety, Health & Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.5.1 Hazard and Operability study (HAZOP) . . . . . . . . . . . . . . . . . . . . . . 47
4.6 Process control and instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
5 Economic Analysis 51
5.1 CAPEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.1.1 Conventional . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
5.1.2 Hybrid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
5.1.3 Conclusions regarding CAPEX . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
5.2 OPEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
5.2.1 Pumping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
5.2.2 Heating. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
5.2.3 Cooling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
5.2.4 Conclusion regarding OPEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
6 Creativity & Group Process Methods 57
6.1 Team division, process tools and results . . . . . . . . . . . . . . . . . . . . . . . . . 57
6.2 Creativity tools and results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
6.3 Process planning and results. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
6.3.1 Overall planning and deadlines . . . . . . . . . . . . . . . . . . . . . . . . . . 61
6.3.2 Work division . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
7 Conclusions & Recommendations 63
List of Symbols 66
A Unit sizing 67
A.1 Contactor (C-101) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
A.2 Vessel sizing (V201, V202 & V203) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
A.3 Heat exchangers (E-201,202 & 203) . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
A.4 Still Column (C-201) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
A.5 Pumps (P-101 A/B and 202 A/B) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
A.6 Pervaporation membrane module (S-202) . . . . . . . . . . . . . . . . . . . . . . . . 70
B Used graphs 73
C Flow sheet conventional design 77
D Stream Summary - Conventional Design Case 79
E Stream Summary - Turndown Case 83
F Microwave heating model 87
G Split flow model 89
H Model used for hybrid system 91
I Stream Summary - Hybrid: Design Flow 93
J Stream Summary - Hybrid: Turndown Case 97
K Stream Summary - Hybrid: Max Flow Case 101
L HAZOP and FEI 105
M Equipment Summary 109
Bibliography 135

1
Introduction and Project Charter
In this first section of the project, it will be described the background of the process as well as the
objectives and requirements of the dehydration unit for the natural gas. Moreover, all relevant data
necessary for further understanding of the process and design will be also displayed.
1.1. Background
During the last 40 years, the production of natural gas has increased by more than a factor 3, resulting
in a fast increase of the amount and size of production plants. This, plus the on going scarcity of oil and
gas, forces companies to place drilling platforms on more remote and violent locations. These offshore
platforms, where huge feeds of oil and gas are processed, must operate with as few equipment as
possible to avoid the extra weight, trying to keep the production as cheap as possible.
In 2010, 4.359 billion (4395·10 ) cubic meters of natural gas were produced worldwide. Norway is
situated 2nd in the ranking of biggest natural gas producing countries with a production of 114.7 billion
cubic meters. In 2010, production of crude oil, Natural Gas and pipeline services accounted for 50%
of the export value of Norway and 21% of the GDP (gross domestic product). All of the oil and natural
gas fields in Norway are located subsea on the Norwegian Continental Shelf, being the Troll field the
largest single one, representing one-third of the country’s natural gas production. When natural gas is
taken out of the ground it needs to be processed before it can be used commercially. A conventional
gas sweetening process is displayed in figure 1.1.
Figure 1.1: Simplified liquid natural gas plant diagram. Here the purple block indicates the gas well,
the blue ones indicate process steps and the orange ones are the products of this industry.
1

2 1. Introduction and Project Charter
Natural gas that comes out of a well is saturated water. It often also contains other compounds
such as Hydrogen Sulfide, souring the gas. These components must be removed following the scheme
of figure 1.1. Moreover, several crucial reasons why water need to be taken out are presented below:
• It can trigger the production of hydrates and of crystals. When transport of the natural gas is
lead through long pipes, the chance of clogging becomes high and the removal of these plugs is
expensive.
• Water can cause corrosion to the pipelines.
• It can cause slugging flow conditions which increases the pressure drop over the pipeline.
• In presence of water, the heating value of gas decreases radically. [1] [2] [3]
One of the most used dehydration processes is Glycol dehydration, with about 30,000 units in
operation in the USA alone. This method can be performed with any Glycol solvent, but the mostly
tri-ethylene glycol (TEG) is used. This process started to be used in the 1970’s and has not changed
much since. In a contactor column of perforated trays or a packing, the wet gas stream and the TEG
stream will meet in counter current. After absorption the TEG rich in water goes to a regenerator,
where the water is taken out in a still column. The pressure difference between these two processes
is usually very high, going from 160-170 bar to atmospheric.
As mentioned before, the dehydration of Natural Gas using TEG has been used for over 40 years.
Not much has changed to the way this process works over all the years. However, with a growing
interest in process intensification and many developments in this field, it could be possible to decrease
the size of the TEG unit while maintaining or even increasing the effectiveness.
Parts of the system in which a potential weight loss can be significant are the TEG inventory and
the size of the regeneration system. Examples of techniques that will be looked into are pervaporation
membranes and microwave heating, among others, having the potential to reduce the size and price
of the unit significantly.
1.2. Objectives
The assignment, provided by Frames group, is to find and design a new dehydration unit by introducing
new innovations in order to lower the CAPEX, OPEX and weight of the conventional TEG dehydration
unit for an offshore platform using recent advances in science.
Therefore, the first task that needs to be done is the definition of the conventional process.Then,
the CAPEX, OPEX and weight of it will be set as benchmark. In the next stage, improvements will be
proposed and their impact will be estimated especially in terms of CAPEX, OPEX and weight. Finally,
conclusions and remarks will be posed about the proposed design of the unit.

1.3. Concept Stage 3
1.3. Concept Stage
1.3.1. Process synthesis
The typical process for dehydration of wet natural gas can be simplified by splitting it in two parts, as
shown in figure 1.2.
The first part is where the actual absorption takes place. Lean water-free Glycol is contacted with
wet Natural Gas in a contactor where the Glycol removes the water from the gas. Then, after this
absorption, the dry gas rich in Methane is sent for downstream processing, whereas the rich TEG
needs to be dehydrated and purified for reuse. From the regeneration subsystem also some overhead
and waste streams are formed, that then will be treated. However, this part is out of the scope of this
project.
Figure 1.2: Block diagram of the process. Orange blocks represent the battery limits of the
dehydration process whereas blue blocks represent steps taken in TEG dehydration.
Hence, the battery limits of the unit are represented by the four orange circles shown in figure 1.2.
There is only one inlet flow to the system, wet gas, and three outlet flows, dry gas product, drain and
overhead gases.
1.3.2. Requirements
The requirements for natural gas after dehydration are presented in table 1.1.
Table 1.1: List of requirements as provided by Frames group
Location Offshore fixed platform in Norway
Water specification 24 mg/Sm
Turndown 10%
Pressure drop ≤ 0.25 bar
Glycol losses contactor ≤ 10 l/MMNm (0.07 UGS/MMSCF)
Others No mercury
Notes. S= Standard Conditions of 1 bar and 15 °C
N= Normal Conditions of 1 bar and 0 °C.
(As agreed with Frames during Kick-off meeting)
Although the implementation will be on a Norwegian offshore oil plant, the host country regulations
will not be taken into account and the extra costs that come from the installation being on an offshore
location need not have to be considered as this difference works for both the conventional and the
suggested processes.

1.3.3. Plant capacity and location
The capacity of the plant will be 380617 kg/h of wet natural gas which comes as feed stream to the
unit. Once the mass balance and streams study is completed, it results that the plant will produce
around 340000 kg/h of dry gas which includes small amount of water (24 mg/Sm3) coming out of the
unit. This means that 2594 kg/h (purity wt 99.4%) of lean TEG are needed to absorb the 131 kg/h of
water which needs to be removed. Given that the expected results are subject to 10% of turn down,
the capacity of the plant must hold these fluctuations too.
Figure 1.3: Norwegian geographical map,
green areas are open for petroleum and gas
platforms, red and orange are considered to
be opened for industrial uses [4]
The TEG dehydration unit will be located in the
European country Norway, specifically in an offshore
platform of its coasts situated in the North Sea. As
shown in figure 1.3 the whole western part of the Nor-
wegian coast in the North Sea is open for petroleum
and gas industry.
Norway is the world’s second biggest exporter of
natural gas and the fifth biggest exporter of oil, at
the same trying to become one of the world’s most
environmentally friendly industries in this field. This
country has high pollution standards and there is con-
tinued work on reducing emissions and avoiding ac-
cidents or spills. This sector is vital for the country’s
economy, representing about 25% of the gross do-
mestic product, 30% of the state income, more than
50% of export earnings and providing approximately
250,000 jobs, directly and indirectly. In addition, this
industry not only helps to its own wealth fare, but also
is a very important contributor for the innovation and
technological development in other related sectors.[5]
Norway has been producing gas for about 40 years,
but at this moment its production has lowered till 20%
of its highest peak. The development in natural gas
exports from facilities on the Norwegian Continental
Shelf (NCS) has drastically decreased as reported by
the Norwegian Petroleum Directorate (NPD) from 2006 to 2013. [6] The natural gas extraction has
reduced total sales gas volumes with around 4% relative to what was exported from the production
installations. In spite of this trend, optimism is present because of the discovery of new reserves, even
in mature areas. Together, these will amount to 400-600 million barrels of oil equivalents allowing new
projects in Norwegian waters in the next 10-15 years.
Although the production costs are relatively high in the North sea, the quality of the oil and gas,
the political stability of the region, and the close proximity to important markets in western Europe has
made it an important oil and gas producing region. The largest natural gas field in the North Sea, the
Troll gas field, lies in the Norwegian trench dropping over 300 metres. This required the construction
of the enormous Troll A platform to access it. Besides it, in the Ekofisk oil field, the Statfjord platform
is also notable as it was the cause of the first pipeline to span the Norwegian trench.
The average air temperature in summer is 17°C while it is 6°C during the winter. The average
temperatures have been trending higher since 1988, which has been attributed to climate change. Air
temperatures in January range on average between 0 to 4°C and in July between 13 to 18°C. The
salinity averages between 34 to 35 grams of salt per litre of water, having its highest variability where
there is fresh water inflow, such as at the Rhine and Elbe estuaries, the Baltic Sea exit and along the
coast of Norway.
With growing demand for improved gas technology, this field is suitable to process intensification.
As stated in the Petroleum White Paper, the Government has confirmed the strategy for developing the
petroleum and gas with a proactive, parallel commitment to increased recovery from production fields,
developing commercial/profitable discoveries, exploring in open acreage and opening up new areas.

1.4. Database 5
1.4. Database
In this section of the project, all relevant data of the compounds involved is tabulated. This is also the
data that is used in the simulations.
1.4.1. Component list
In this project only three different species are observed. TEG, natural gas and water. The natural gas
coming out of the well consist of the components shown in table 1.2. The properties of the different
species are discussed later in this section.
Table 1.2: List of components in Natural gas provided by Frames
Component name Mol. %
H O @saturation
N 0.18
CO 3.58
Methane (CH ) 86.49
Ethane (C H ) 5.33
Propane (C H ) 2.18
i-Butane (C H ) 0.49
n-Butane (C H ) 0.89
i-Pentane (C H ) 0.25
n-Pentane (C H ) 0.24
C + 0.33
1.4.2. Component and thermodynamic properties
Table 1.3: Component and thermodynamic properties of Triethylene Glycol and water
Property Value TEG Value water
Molecular Formula C H O H O
Molecular Weight 150.17kg/kmol [7] 18 kg/kmol
Boiling Point 285 °C[8] @ 1 atm 100 °C @1 atm
Melting Point -7 °C [8] 0 °C @ 1 atm
Density 1127.4 m @ 15 °C [8] 998.3 kg/m @ 200 °C[9]
Viscosity 0.00478 Pa.s @ 200 °C[8] 0.001003 Pa.s @ 200 °C [9]
Vapour Pressure <0.001 kPa [7] 2337 Pa @ 200 °C [9]
Heat of Vaporisation 61.04 kJ/mol @ 1 atm [8] 2257 kJ/kg @ 1 atm[10]
Triethylene Glycol (TEG)
TEG is the water absorbing species in this system. It is a colorless, viscous liquid, well known for
its hygroscopic properties and its ability for dehumidifying fluids. It is used especially as a desiccant
for dehydration of Natural gas. It will however degrade when the temperature rises above 204 °C,
this makes good temperature control important and hotspots should be avoided. It’s thermodynamic
properties can be found in table 1.3.
Water
Water is the universal solvent. Industrially, water has been used for many purposes, especially for
cooling. The natural gas obtained from wells is saturated with water which needs to be removed due

to the reasons mentioned in section 1. The thermodynamic properties of water are also listed in table
1.3
Natural gas
Table 1.4: Component and thermodynamic properties of natural gas
Property Value natural gas
Molecular Formula 86.49% CH
Molecular Weight 19.5 kg/kmol (Frames specified)
Density [11] 0.79-0.9 kg/m @ STP
Net Heating Value [11] 46054800 J/kg (11000 kcal/kg)
Natural gas, consisting of predominantly Methane, is a hydrocarbon gas formed due to fossilization
of buried plants and animals. For these species to become natural gas they were below the earths
surface for over a thousand years. It is a non-renewable source of energy and is typically used for
heating (industrial) and cooking (domestic). Some of the properties of Natural gas are given in table
1.4. The specification of the natural gas that comes from the specific well in Norway are given in table
1.2.

2
Conventional Process
In this chapter the conventional process currently used in the industry to dehydrate natural gas is
described. Firstly a process scheme is shown and later every step is explained into detail. A few
remarks on how this process is modelled in Aspen Hysys are given. All equipment sizing is explained
and a safety assessment is done. Lastly a few comments on bottlenecks and areas to improve will be
mentioned.
2.1. Process description
In this section the conventional process for dehydration using TEG widely used in industries is described
with all details taking into consideration the technical and feed requirements stated. These will be
used to define the conventional benchmark as well as rooms for improvement in the different pieces
of equipment. The conventional process is depicted in figure 2.1.
Figure 2.1: Flowsheet of currently used TEG dehydration process. In green the Absorption unit
(U100) and in purple the Regeneration unit (U200).
7

8 2. Conventional Process
2.1.1. Contactor (C101)
Streams in: Wet gas <102>, Lean TEG <103>. Streams out: Dry gas, Rich TEG <104>.
The absorption column, also called the contactor in this process, is the main piece of equipment of
a TEG dehydration process. In the absorption process, a liquid is used to contact wet gas and remove
the water vapor. With absorption, the water content in the gas stream is dissolved in a relatively pure
liquid solvent stream. To achieve this it is necessary to create a surface area as large as possible
between the two phases. This can be achieved using several pieces of internal equipment, such as:
• Division into trays.
• Random packing.
• Structured packing.
Trays
Figure 2.2: Typical
bubble cap plate
column for TEG
dehydration
contractor[12]
One way to achieve a high surface area between the two phases is to divide
the column into trays as displayed in figure 2.2. Gas flows from below each tray
through bubble caps, which ensures the formation of small bubbles of gas. Each
tray is filled with liquid glycol which accumulates due to an overflow wall at the
tray. The small gas bubbles provide a large surface area which is needed for
the mass transfer. Because the bubbles rise relatively fast the contacting time is
short. Hence equilibrium is not reached. Therefore several trays are needed to
reach the dehydration specifications for gas transport, usually 6 to 20 trays are
used, spaced approximately 61 cm apart.[13]
Random packing
Various types of random packing are also used in glycol contactors to achieve a
high surface area for mass transfer. The total height of the packing in the vessel
can be calculated from the number of theoretical stages used in the design.
Typically suppliers of the packings have correlations for packing height needed
per theoretical stage.
Structured Packing
Structured packing is to load the column with arrangements of steel internals
over which the glycol flows downward. The gas flows upward through the pack-
ing and has a large contact area with the glycol. This provides a very efficient way for mass transfer to
occur and is therefore used the most throughout offshore dehydration[13]. Just as in random packing,
suppliers have developed a relationship between the packing height needed and the number of theo-
retical stages. When designing the column it is essential that the glycol is distributed evenly over the
top of the packing, to ensure a good mass transfer area. A typical structured packing is displayed in
figure 2.3.
Usually a structured packing is used as it provides the best mass transfer surface area compared to
random packing and tray columns. A larger surface area provides a better mass transfer and therefore
a smaller column. The wet gas is fed at the bottom of the column and dry gas leaves the top. At the
top the lean glycol is fed and the rich glycol will be returned below the wet gas feed.

2.1. Process description 9
Figure 2.3: Typical structured packing used in the industry[14]
2.1.2. Flash (V201)
Streams in: From HX (E201) <203>, Streams out: Drain, OVHD & to filters (S201) <205>.
(The stream numbers depicted refer to Figure C.1 in Appendix C)
Due to the high pressure used in the contactor some gas is physically dissolved in the liquid glycol. The
higher the pressure in the contactor, the more gas dissolves in the liquid. A flash tank is needed to take
that portion of gas out of the liquid. The liquid first gets heated in the still column and afterwards it is
depressurised in the flash tank. With these changes the gases evolve from the glycol in the gas tank.
It is designed as a three-phase separator to help remove any condensate in the liquid and therefore
increase the lifetime of the downstream filters.
2.1.3. Filters (S201)
Streams in: From flash (V201) <205>, Streams out: to HX (E202) <206>.
To prevent clogging and optimal conditions for glycol it is very important to keep the glycol as clean
as possible. Impurities might also cause foaming in the still or contactor. Therefore filters are installed
to take out impurities. Particle filter are usually in operation all the time to take out any condensate in
the liquid. Carbon filters can be bypassed most of the time and will be installed on stream, if there are
no hydrocarbons in the stream.
2.1.4. Reboiler (V202) & Still column (C201)
Streams in: From HX (E202) <207> & OVHD, Streams out: to OVHD & to Surge <208>.
The rich glycol is preheated through heat exchange with the lean glycol leaving the reboiler and
enters the top of the still column. By taking the temperature near the boiling point of glycol the glycol
release the absorbed water and any other compounds until a purity of 99.4% is reached. The reboiler
is heated through a fire tube in which natural gas, sometimes from the flash, is burned. The reboiler
and the still run at near atmospheric pressures.
2.1.5. Stripping column (C202)
Streams in: From reboiler (V202), Streams out: To Surge (V203).
A stripping column is inserted between the reboiler and surge to achieve the highest purity possible.
As stripping gas the gas phase from the flash vessel is used. A part of the water will dissolve in the
gas phase and be taken out to overhead treatment. The opposite happens from what is happening in
the contactor.

2.1.6. Surge (V203)
Streams in: From Stripping (C202), Streams out: To booster pump (P201) <210>.
Due to the fluctuations in the gas feed, the circulation might not always be even. A surge drum is
installed to allow for these fluctuations and to achieve a constant recirculation of TEG. An additional
benefit is the fact that it can be used as a check to see if everything is still working correctly. When
the level is significant lower then the needed of the vessel either a leak or holdup is present in the
system.
2.2. Mass and energy balance
The inlet wet Natural gas flow for the design case is given to be 380617 kg/hr at 156.5 bar(a) and 35 °C
, the outlet dry gas water fraction and the glycol loses must be lower then 24 mg/Sm , as described in
Table 1.1. From the above information, the quantity of water required to be removed in the design case
and in the turndown case were calculated. For systematic design of the Dehydration unit,a step-wise
method given by Campbell [15] was used. It consists of following steps:
• Calculation of TEG concentration: The minimum concentration of lean TEG required for dehy-
dration of natural gas was calculated by first estimating the dew point of the outlet dry gas at
given conditions from the water content in natural gas v/s water dew point graph available in
[15] and figure B.2. From the calculated dew point, the concentration of lean TEG required was
calculated from the equilibrium dew point v/s inlet gas temperature graph available in [15] and
figure B.1.From this procedure, we find that the minimum concentration of the lean TEG required
for our case is 99.2% wt.
• Calculation of lean TEG circulation rate: From the knowledge of the water content in and targeted
water content out of the contactor, the TEG circulation rate was calculated by considering a ratio
20 kg TEG/ kg water removed for a number of theoretical stages of N=1.5. This ratio was agreed
upon during the BOD meeting with Frames. The number of stages were chosen taking into
account that most TEG contactors work with 6 actual trays (tray efficiency is considered to be
0.25). The circulation rate for TEG was calculated to be around 2594 kg/hr for the design case
using this method.
In the regeneration section, the stripper column was assumed to have 3 stages.This was assumed
taking into consideration that normally the stripper column(or still column) has a lower number
of stages than the contactor.
The exhaust gas from the flash is also diverted to the stripping column so as to aid in removing water
from rich TEG.It enters the stripping column via the reboiler. Before it enters the reboiler, it is contacted
with outgoing hot TEG. For determining the pressure of the flash drum,the still top was assumed to
be at 1 bar and subsequently heat exchanger pressure drops(0.5 bar each) were added. This gave
around 4 bar operating pressure for the flash drum including some margin.
2.2.1. Simulation on Aspen Hysys
Using the background calculations as basis, the process was simulated for design and turndown case
in Aspen Hysys platform using the Glycol Package for thermodynamic calculations. This package was
chosen as it is highly recommended for systems involving dehydration of gas with TEG. The following
observations were made during simulation:
• The concentration of TEG from the regeneration increased to 99.4% on simulation and so to be
consistent, the lean TEG concentration of 99.4% was used for the complete simulation. The total
stream summary can be found in appendix C.
• It was argued that by decreasing the TEG flow proportionately for a 10% turndown would cause
cavitation in pumps and may even lead to weeping in the regeneration column. Therefore, the
lean TEG flow for the turndown case was maintained at 33% (which corresponds to 877 kg/hr).
The total stream summary can be found in appendix E.

2.3. Equipment sizing 11
Energy demands
From the Aspen Hysys simulations the energy demands in pumping and heating can be found.
Table 2.1: Energy demands per type
Location Type Energy duty [kW]
P101 Electrical energy 13.4
P202 Electrical energy 0.155
Reboiler Gas heating 191.5
Total 205.055
Cooling
E203 Sea water cooler -103.5
C201 TEG Condenser -49.85
Total -153.35
Heat exchanger
E201 HX 88.5
E202 HX 168.5
2.3. Equipment sizing
All sizing presented in this section has been done following the methods described in appendix A. Every
size is reported tabulated and with equipment name. Vessel weight estimation have been preformed
using the method described in Sieder et al[16]. There it is estimated that vessel weight depends on
wall thickness of the shell, assuming the shell to be evenly thick throughout the vessel.
𝑊 = 𝜋(𝐷 + 𝑡 )(𝐿 + 0.8𝐷 )𝑡 𝜌 (2.1)
With:
L = length of vessel [m]
𝐷 = Diameter of the vessel [m]
𝜌 = Density [kg/m ]
𝑡 = Wall thickness [m]
Heat exchanger weights are estimated using Aspen Hysys. Only motor weights have been used to
estimate weight of pumps[17].
Contactor
Table 2.2: Size and weight comparison of the conventional contactor column
Name Type Diameter [m] Height [m] Wall Thickness [mm] Weight [kg]
C-101 Column 2.04 12.2 190 143135

Vessels
Table 2.3: Vessel volumes
Name Type Volume Diameter Length Wall Thickness Weight
[m ] [m] [m] [mm] [kg]
V-201 Flash 0.535 0.554 2.217 6 221
V-202 Reboiler 0.465 0.529 2.117 6 202
V-203 Surge 1.16 0.719 2.875 6 371
Heat exchangers
Table 2.4: Total surface area needed per heat exchanger
Heat exchanger Surface area [m ] Weight [kg]
E-201 28.45 1253
E-202 147.0 3390
E-203 17.3 800
Basis and method of calculation of the area of heat exchanger is given in Appendix A Section
Still column
Table 2.5: Size of the conventional still column
C-201 Still column 0.28 6.5 10 476
Stripping Column
Table 2.6: Size of the conventional stripping column between the reboiler and the surge
C-202 Stripping column 0.25 0.5 6 32
Pumps
Table 2.7: Power requirement per pump
Pump Head [mlc] Power [kW] Weight [kg]
P-101A/B 1370 13.4 564
P-202A/B 20 0.155 22
2.4. Total weight
Adding all the weights of the separate pieces of equipment together, a total weight for the whole unit
can be estimated. In the case of the conventional process, this weight is estimated to be 150466 kg.
This is the dead weight of the unit without the weight of piping and the weight of the framework where
the unit is build.

2.5. Health, Safety & Environment 13
2.5. Health, Safety & Environment
2.5.1. Preliminary study of risks
One of the major points of the project is the analysis of risks and dangers arising from the unit. In
order to reduce them from a process design point of view the Dow’s Fire and Explosion Index (FEI)
has been performed on the absorber unit in the process. In addition, an analysis of the hazards of the
compounds present in the system as well as the possible waste generated was also carried.
The two major two flows present in the system are triethylene glycol and natural gas, described
below.
Triethylene Glycol
Figure 2.4: Safety of TEG
Some of the most important properties of triethylene glycol
(TEG) regarding safety are stated in table 2.8, where one
can appreciate that the boiling point is really high as well
as the auto-ignition temperature, reducing its risk.
Furthermore, there will be no explosion danger and
there is little toxicity danger, as shown in figure 2.4. Re-
lease of TEG into in the environment should be avoided as
much as possible, because the products of its biodegrada-
tion are more toxic than TEG itself. Moreover, in the case
of leak, the TEG should be diluted with water and absorbed into an inert material, whereas in the case
of fire, the fire should be extinguished with powder, water spray or foam. No water jet should be used.
Contact with heat sources should be avoided. Finally, direct contact with TEG should be avoided. When
in contact with eyes or digested a doctor should be contacted.
Table 2.8: List of properties for TEG [18]
Properties of TEG Value
Boiling point 285 C
Auto-ignition temperature 371 C
Flash point Closed cup 177 C
Open cup 165 C
Flammable limit Upper limit 0.9 %
Lower limit 9.2 %
LD (oral) 4700 mg/kg
TLV 10 ml/m
Natural gas
Figure 2.5: Safety of natural gas
Natural gas is highly flammable, creating the risk of explo-
sions, as can be seen in figure 2.5. Table 2.9 shows the
explosion limits of methane, which is a key component of
natural gas. A fire can not be extinguished unless the source
of the gas has been closed. So, it is advisable to let all the
gas burn up and then extinguish the fire with dry chemicals,
foam or CO .
In addition, when the gas is kept under pressure it can lead to the risk of frostbite, which occurs
when high-pressure gas is released, expanding and cooling down. This is however more dangerous
when handling liquefied gas, but in this system the natural gas remains in the gas phase. The gas is
not toxic but when released can be highly dangerous because it can cause asphyxiation by drawing
out all the oxygen. It has been found that up to concentrations of 10 000 ppm no physical changes
occur when a human is exposed. Studies have shown that there are some physical complications in
test animals who are exposed to high concentrations of methane (up to 70%) while having enough

oxygen, but not much has been documented on these phenomenon and it seems unlikely that these
circumstances will occur on the plant.[19]
Table 2.9: Explosion limits of methane (key component in natural gas)[20]
Properties of methane Value
Explosion limits Lower 5%
Upper 15%
Health, Safety and Environment assessment
In conclusion, both components in the system are not extremely toxic. Good ventilation is important
to prevent a build up of natural gas in closed spaces because this can lead to asphyxiation.
Then, natural gas should not end up in the environment, hence if natural gas needs to be disposed
of, it should be burned, leading to mostly H O and CO . A danger of high concentrations of CO is that
it is heavier than oxygen and can therefor accumulate at the surface. This can cause asphyxiation.
Also, although TEG is not very toxic, the products of the degradation are. The liquid TEG needs to get
diluted with water and then absorbed into an inert and collected. When this is done, what remains can
be diluted again and disposed of through the waste water system.
Finally, the conditions at which the system operates are relatively mild. The highest temperature
reached will be around 200 °C. Only one recorded incident has been found. In may 2013 in Spain a
fire occurred after TEG was added via the TEG inlet. The TEG inlet was aimed at a hot spot and the
TEG vapor caught fire. It was only reported as a level 1 emergency shut down. [21]
If TEG or natural gas leak from the system, the chance of it reaching a hot surface or an ignition
spot should be decreased as much as possible. Another big risk comes with the high pressure in the
absorption tower. When the vessel or piping at high pressure breaks, it can result in an explosion
and both TEG and Natural gas can be released. The sudden expansion of the natural gas can cause
frostbite. Also the chance of an explosion of natural gas will increase in these conditions, resulting in
big amount of natural gas released in a very short time.
In addition to the HSE assessment, a bow tie diagram has been made, shown in figure 2.6. For this,
it was selected that the high pressure of 156.5 bar in the contactor is the most hazardous condition
present in the process and the selected top event is a rupture in the wall of the contactor. The bow tie
can be used to identify threats that increase the chance of the top event happening. It also contains
the consequences of that top event. Also barriers to decrease the treats and the consequences of the
top event are added.
2.5.2. Dow’s Fire and Explosion Index (F&EI)
In order to classify the risk of the dehydration process, a fire and explosion index has been made. The
tabel with assigned values and the final F&EI can be found in appendix L
The two species in the system that are capable of creating a fire or explosion are TEG and natural
gas. Because natural gas exists of multiple species, the properties of methane have been used, since
the largest part of natural gas consists of this. The information needed for the F&EI is in table L.1.
For the F&EI the material with the highest Material Factor(MF) needs to be used for the calculations.
In this case this will be the natural gas because the methane has an MF of 21. Also the unit which
will be looked at needs to be specified, in this case the contactor. The species present in this unit are
natural gas, TEG and water.
Base factors
This subject is cut into multiple items. The only items which get a penalty are: Material Handling
and Transfer, Access and Drainage and Spill Control. These items get penalties because of the highly
flammable nature of natural gas, the inaccessibility of an offshore platform and the difficulty in im-

2.5. Health, Safety & Environment 15
Figure2.6:Bowtie

Table 2.10: List of properties of TEG and Methane for determining the F&EI
Properties TEG Methane
Material Factor 4 21
H 9.3·10 21.5·10
N 1 1
N 1 4
N 0 0
Flash point 350 °F Gas
Boiling point 546 °F -258 °F
plementing a draining system and prevention measures for spills. The total penalty adds up to be
2.70.
Special process hazards
Some of the items that got a penalty in this subject were the pressure, which is high in the contactor,
which receives a penalty of 0.48. Also the quantity of flammable material got a high penalty, 3. The
total penalty for Special Process Hazards adds up to 5.18.
Conclusion
The final Fire & explosion index turns out to be 294 which categorizes this unit in the severe degree of
hazard region. The exposure radius for this F&EI will be 70 m. This will mean that a large part of the
platform will be affected by an explosion. There are no structures around the platform which makes
the consequences for second parties minimal.
Loss control credit factors
The fire and explosion index can be reduced when measures against fire and explosions are present.
Therefor a few thinks need to be present in the final design of the unit itself and the surrounding plant
• Emergency power
In case of an emergency there can be a power outage, it can be possible to automatically go to
emergency energy. If we have a power outage there will be no drying of the gas anymore but
there will be no possibility for for instance a runaway reaction or agitation for which it might be
necessary to have a big emergency supply of energy.
• Cooling
Our system does now only have one cooling device and no backup, but because there is no
chemical reaction in our system but only separation the consequences of losing a cooler will not
directly cause a fire or explosion.
• Emergency shutdown
If something abnormal happens the entire system should be shut down completely. If this hap-
pens automatically than the reduction of the F&EI is bigger than when it only sounds an alarm.
• Computer control
The bigger part of the system is controlled via computers, the more reduction is given to the
system. The more advanced the system the better.
Material isolation credit factor
In this section items that prevent the build up or spilling of material to places where they should not
be, both within or outside the system.

2.6. Bottlenecks and possible improvements 17
• Remote Control Valves
These are valves that can isolate different sections of the process. This can prevent spreading of
hazardous material or fire.
• Dump/Blow-down
This means that there is a vent with flair present in case the natural gas present needs to be
released. Also a way to remove the TEG from the system should be present.
• Drainage
On land the ground has to have a slope of 2% that leads to a drainage trench. This will be more
difficult on a platform since we will not have much space for draining reservoirs.
• Interlocks
Thee prevent incorrect material flows within the system.
Fire protection credit factors
These are things that should be present on a plant in case a fire breaks out.
• Leak detection
Gas detectors should be present on the plant. These need to sound an alarm, and even better
would automatically start the protective system to prevent a fire or explosion.
• Structural steel
The weight bearing steel steel needs to be fireproofed.
• Fire extinguishing
On the offshore plant enough water will be present. Only thing extra needed are pumps that can
create enough water pressure. If the fire is burning on TEG it should be extinguished with CO
or foam. This requires a special system. There should be an automatic water or foam sprinkler
system present.
• Hand extinguishers/monitors
There should be an adequate supply of hand extinguishers present on the plant. These will have
no effect when the fire is from a big spill.
• Cable protection
The cables needed for the equipment are vulnerable to fire and need extra protection. These
should not be forgotten when the plant is set up.
2.5.3. Waste
There are two waste streams leaving the TEG dehydration system, both from the regeneration unit.
One is a liquid outflow from the flash equipment which will prevent buildup from unwanted species.
The second one is a combination of the vapour gas outflow from the flash and the water rich outflow
from the separation units (still column and pervaporation membranes). Because this specific unit is on
an offshore gas platform, using a flair to burn the waist would be too dangerous. Therefore, all waste
streams will be incinerated.
2.6. Bottlenecks and possible improvements
The requirement in offshore engineering is striving for the lightest and smallest equipment as a gain
in weight will have an effect on the total investment for a platform. The biggest piece and heaviest
piece of equipment is the absorption column (C101). As only approximately 40% of a typical contactor
column consist of the packing and transfer area and the rest is filled with equipment and spargers it is
not expected that a large weight gain can be achieved there.

Thus, it was identified that the majority of changes according to the objectives of the project can
be done in the regeneration subsystem, because it contains more pieces of equipment, almost all the
TEG stored and the conditions on the TEG are more strict in this section (i.e. 150-200 °C). For these
reasons the focus of the alternative technologies will be in this unit of the system.
Furthermore, the TEG inventory and regeneration loop can provide also some weight loss. By using
a more effective separation in the contactor the TEG circulation rate can be lowered. This leads then
to a reduction of TEG inventory, which leads to smaller equipment especially in the form of the reboiler
and the surge (V-202) & (V-203), with volume of respectively 0.667 m and 1.16m . This will lead to
a weight reduction as less steal is needed. Also different techniques of TEG dehydration need to be
considered to reduce the size and costs of the total regeneration loop.
Finally, the biggest energy demand is identified from the reboiler which requires 194 kW to run
efficiently. Also the injection pump of 13.4 kW contributes to the total energy demand. By reducing
both, the total operational costs can be cut down and more efficient and cheap operations can be carried
out. This reduction in energy demands can also be achieved using a completely different technique of
TEG dehydration, as mentioned before.
In the next chapters recent advances from science will be discussed and reviewed in order to check
its usability in this process. From these concepts, a new system will be then proposed and the possible
optimization and improvements achieved will be calculated and reviewed.

3
Innovation Map
All innovation and improvement opportunities are described in this chapter. First all considered alterna-
tives are described in a technological and more qualitative way and their beneficial effects are touched
upon. After that a preliminary cut will be made to discard technologies which have too many down-
sides. Later different process schemes are proposed and studied quantitatively and then researched for
beneficial effects on this system, regarding CAPEX, OPEX & weight. Here calculations and simulations
are tried upon the new technologies which were earlier proposed. Lastly the final system is chosen
which will be modeled and designed in the rest of this report.
3.1. Description of alternatives
Carrying out an analysis on the different parts of the TEG dehydration unit, it is clearly observed that
improvements can be implemented in every piece of equipment such as the contactor, reboiler, still
column, heat exchangers, flash vessel and/or pumps. A change of solvent for the dehydration process
was also considered, but it was decided to continue the optimization of the process with TEG, because
it is the most used solvent used in the natural gas dehydration industry. Therefore, taking into account
new advances and approaches in process engineering, an extensive research was made based on
different criteria (feasibility, applicability, cost, experience, effectiveness, weight and size), leading to
the descriptions and final selection of the more appropriate alternative for this process.
3.1.1. Improved TEG injection
This technology basically splits the TEG inlet stream introducing the lean solvent in different stages
of the contactor column instead of only one. Hence, as there are multiple TEG injection points, lean
TEG contacts wet gas earlier in the column, increasing the effectiveness of the water removal due to a
better mass transfer.
This option will not reduce too much the size of the contactor, because the packing (mass transfer
zone) only represents about 25% of the piece of equipment, but it might reduce the necessary inventory
of TEG and, therefore, the energy consumption, weight and costs.
An alternative TEG injection method is to use semi lean TEG out the reboiler, before the stripping
column. Injecting this semi lean TEG halfway the column, where there already is a lot of oxygen
absorbed in the TEG. This can lower the size and energy needed for reboiling and it will lower the size
needed for the surge. An extra injection pump however is needed to pressurise this semi lean TEG.
3.1.2. Microwave heating
Microwaves are electromagnetic waves with a wavelength between 1 mm to 1 m. These microwaves
affect the dielectric molecules, which start re-orienting themselves and try to follow the direction of
the field created by the waves. The friction that occurs because of this movement generates heat.
19

20 3. Innovation Map
Advantages of this technique are that there is no heat transfer zone so the heating occurs in the entire
volume that is being irradiated. The waves are selectively being absorbed and a rapid heating can
occur.
The dielectric component in the TEG regenerator is water, this is the species that needs to evaporate
out of the TEG. This will also be the target specie of the microwaves generating the heat, which means
that the water in the mixture can become warmer than the TEG, which will lead to faster evaporation.
TEG however has an interaction with water molecules as it contains alcohol groups. This can lead to
the TEG heating up as well. No test regarding this specific process to check if only the water heats has
been done as of now. The molar fraction of water molecules of the feed stream is 32 mol%. Regarding
this high molar concentration it can be expected that there is a lot of contact between water and glcyol
and therefor energy transfer. A different benefit is however, while there is no heat transfer area, the
total volume of TEG and water can be heated at once and uniformly.
Figure 3.1: Microwave heating[22]
Experiments showed that only heating up the liquid will not benefit the separation of the binary
mixture[22] and the stirring will also create a uniform temperature in the liquid phase which takes
away the advantages of the selective heating. However, when also the surface is irradiated with
microwaves the separation of the more volatile species is more effective than in a separation without
microwave heating. One explanation of this is that very locally high temperatures will occur, resulting
in a smaller column with fewer trays. These so called ”hot-spots” can lead to a fouling in TEG, as TEG
thermally degrades at temperatures above 210 C.[7] Discussion with professor Stankiewicz and Dr.
Guido Sturm however provided a different outlook as they mentioned new ways of heating which was
very controllable an predictable and therefor those hot-spots can be avoided.
The uniformity of microwave heating however is debatable. In literature it is described that by
absorption in the medium the intensity of the field will drop quickly. This leads to a large part of the
volume not heated and parts of the volume overly heated [23]. Dr. Guido Sturm mentioned however
that this effect can be reduced a lot, because the behaviour of microwaves can be described quite
good. By altering the field and radiation techniques these hot spots can be minimized. This is not done
on a larger scale then lab, but shows good promise.
The currents hurdles in the use of microwaves in industry are the yet unreliable scale up of the
process, which can be helped by modeling the field and design it that way. Another hurdle is the
implementation of microwave equipment into conventional chemical equipment.
3.1.3. Super-X packing
The Super X-pack packing is an innovation which is fabricated to mimic fractal structures. These fractal
structures, shown in figure 3.2, are known to enhance transfer rates, leading to a decrease in TEG
inventory. This packing could be beneficial in both the regenerator as well as in the absorber.

3.1. Description of alternatives 21
Figure 3.2: Nagaoka Corp. Super-X packing
The Nagaoka International Corporation, which
developed the Super X-pack packing, made very
interesting claims with the development of this
technology. The company claimed a reduction of
the pressure drop by a factor of 3, while the pack-
ing reduced the height of the column by a factor
of 5 compared to conventional column, achieving
up to 80% energy saving [24].
However, despite these advantages, severe
operational problems were encountered, mostly
due to the packing getting clogged and fouled,
which eventually lead to the stopping of the com-
mercialisation of the packing.
3.1.4. Liquid turbochargers
A turbocharger, is an induction device used to al-
low more power to be produced by an engine of
any given size. A engine with a turbocharger can
be more efficient than a naturally aspirated en-
gine, because the turbine forces more air, and proportionately more fuel, into the combustion chamber
than atmospheric pressure alone. [25]
Applied to process engineering it can be used to transfer pressure using kinetic energy. A high-
pressure fluid or gas is used to drive a turbine which pressurises a low pressure liquid. Within TEG
dehydration it can be used to pressurise the lean glycol heading for the contactor, by transferring the
energy available in the rich Glycol.
Figure 3.3: Liquid Turbocharger [26]
As 50% of the total cost of gas refining is represented by energy costs, the addition of a turbocharger
can provide a significant cut down in operational costs. By using a liquid charger less investments
need to be done regarding pressurising the glycol, therefore a cut down in capital expenditure is also
expected. The company Energy Recovery claims an energy efficiency of up to 80%. On the other
hand, this technology reduces the degrees of freedom of the system, as it combines different streams
of the process. These Glycol powered pumps are currently sold skid mounted by companies such as
Kimray and Rotor-Tech.
3.1.5. Pervaporation membranes
This technology is itself a combination of two others. On the one hand it there is a permeation,
transport through a membrane, on the other there is evaporation, changing its phase from the liquid

to the vapour phase (see figure 3.4). Therefore, the water of TEG-water mixture in our regeneration
system might be taken out using a hydrophilic membrane as a selective barrier between the liquid
phase feed and the vapour phase permeate allowing the desired molecules to diffuse through it by
vaporization.
Figure 3.4: Pervaporation membrane for dehydration
One of its main benefits is not being a pressure driven process. Instead, the driving force is due
to a higher chemical potential on the feed side than on the permeate side. The gradient in chemical
potential is then maximized by using high feed temperatures and low pressures on the permeate side
as well as combining polymer properties for membrane. [27].
By replacing distillation by the pervaporation membranes for the Glycol regeneration subsystem,
according to Pervatech company savings up to 75% on regeneration equipment and 30 to 50% reduc-
tion on energy usage can be achieved. However, membrane units, including the need for vacuum, are
currently relatively expensive. Also, if the supply contains suspended matter or dissolved salts mem-
brane pollution may be encountered. In this case, an effective pretreatment must be implemented.
e.g. filtration.[28]
3.1.6. Molecular sieves + TEG unit
Molecular sieves are usually installed in applications in which very low residual water content is required,
such as ahead of a low temperature hydrocarbon extraction process. They are suitable for drying very
sour natural gas that also contains aromatic compounds. However, heavier hydrocarbons might be
difficult to remove from the silica gel during the regeneration step. These solid compounds (silica gel
or zeolites) used as molecular sieves are prepared as round or slightly elliptical beads having a diameter
of about 4 to 6 mm. Each of these compounds has its own characteristic affinity and adsorptive capacity
for water, so a good selection is crucial in the process.[29]
While dehydration with Glycol is the most common process used to meet the water dew point
specification for sale the gas, under certain conditions solid adsorbents are also used for this purpose.
i.e. Molecular sieves are used for many offshore applications such as floaters (FPSO’s). The positive
side of molecular sieves is that they can handle wave-motions very well. The downside is the scale
and weight of the units.
A molecular sieve dehydration unit after a TEG dehydration unit, will be used for polishing and
increasing water removal efficiency. It will be able to achieve very low dew points which are required
for cryogenic plants. Additionally, molecular sieve units can also handle large flow variations as well as
higher inlet gas temperatures. However, they have higher initial capital investments, are way bigger
and heavier than comparable Glycol units.

3.1. Description of alternatives 23
Figure 3.5: Molecular sieve for water adsorption
3.1.7. Addition of entrainer
Heterogeneous azeotropic distillation is a widely used technique to separate non-ideal mixtures. The
procedure is incorporating a new component (entrainer) in the system such as toluene or octane. The
entrainer will form a heterogeneous azeotrope with water of the initial mixture. Then, the azeotrope
having minimum boiling point goes to a decanter and splits in two liquid phases. The stream rich in
the entrainer is recycled back to the azeotropic column and the other water rich goes to treatment.
This azeotropic distillation has various advantages such as a high efficiency of separation, low reflux
ratio and a reduced heat energy and it can be a suitable solution for the regeneration part. However,
adding a third component always increases the complexity of the separation. The gas-liquid composition
distribution in the column is much more complicated than that in the usual one, and a stable operation
of a distillation column is very difficult. It is also necessary to add more pieces of equipment for the
entrainer recovery, resulting in a bigger and heavier unit.[30] [31]
3.1.8. Vacuum operation in still column
At vacuum conditions the concentration of TEG obtained in the still column will be higher for the
same reboiler temperature used for atmospheric operation, as the boiling point decreases for the same
rich solvent. Another possibility of vacuum operation, if not so pure TEG is required, is reducing the
temperature in the reboiler. In addition, it helps extend the useful life of the system Glycol.
However, reboilers are operated under vacuum conditions in rare cases due to its complexity, vacuum
generation equipment and the fact that any air in the process may result in degradation of the TEG.
Hence, it is usually cheaper to use stripping gas. [32]
3.1.9. Rotating packed beds (HiGee)
Firstly described by Ramshaw and Mallinson[33], rotating bed reactors or HiGee (short for high gravity)
distillation, have taken a large role in offshore oil dehydration. It is used widely in China and the benefits
were readily recognized by the American market and is currently being introduced there. The European
industry however lacks behind regarding HiGee distillation.
By rotating the reactor the gravitational field increases 100-1000 times and therefore the shear flow
is enhanced. The high centrifugal speeds allows for packing with relatively higher specific surface area
and achieves order(s) of magnitude higher gas liquid throughput and possible mass-transfer rates.[34]
These factors lead to a significant reduction in size of conventional mass-transfer equipment such as
absorption and distillation towers. Ramshaw and Mallinson [33] claim achieving an up to 100-fold
reduction in equipment size. Later experimental studies however tempered these claims and found an
5-10 fold reduction in HETP [35] which is still an significant decrease in size.
The main downsides however are that moving parts are introduced which are more maintenance
sensitive than conventional techniques. The inside rotating bed has a dynamic seal, which prevents
the gas from bypassing the rotor, but compromises the reliability and longevity due to its contact with

working fluid. Also, one unit can not be competent for continuous distillation owing to incapability of
feeding the rotor at radial position, equivalent to middle plate of traditional distillation column. Thus two
units of rotating bed are required for continuous distillation; one as rectifying and the other stripping.
HiGee technology can both be used in the contactor part of the process as well as the TEG regener-
ation. By using rotating bed reactors the size and weight of the contactor and still column and therefor
the total unit can decrease significantly.
Figure 3.6: HiGee distillation: (a) RPB integrated with reboiler and condenser; (b) RPB with off center
feed and integrated with reboiler [34]
3.2. Selection of alternatives
In this case, from stated above it is decided to gather the information in a way such that it can be
compiled and presented in a consistent, high visualization chart, showing the strengths and weaknesses
of each application for each criteria, accompanied by focused comments from the team, resulting in
the selection table 3.1.
There is no such thing as one solution which fits all requirements when it comes to chemical solvent
recycling or dehydration. Solutions are therefore necessarily hybrid in nature where a combination
of traditional and improved technologies is used. Each technology provides a part of the separation
required within a customized sequence and overall methodology and further research must be carried
out in terms of OPEX, CAPEX and weight to determine the improvement of the alternative.
However, there are already five possible technologies that will be rejected directly. The first one will
be Super-X packing, because it is not being commercialized anymore, avoiding any possibility of its real
implementation. Secondly, the hybrid molecular sieve plus TEG unit is not going to be implemented
due to its weight and scale makes it not suitable for platform location, which is one of the requisites.

3.2. Selection of alternatives 25
Table 3.1: List of alternatives with strengths and weaknesses
Technology Strengths Weaknesses
Improved TEG injection Less lean TEG inventory More complex design
No reduction of size
Microwave heating Direct energy coupling Design into conventional equipment
Volumetric heating
Rapid and selective heating
Super-X Packing High transfer rates Clogging
Less lean TEG inventory Fouling
P drop column ↓ 3 times No commercialization
Height column ↓ 5 times No experience
Liquid Turbochargers Large energy saving Less system flexibility
Smaller OPEX Availability of companies
Pervaporation membranes 100% efficiency TEG-wat sep. Expensive
Selectivity No solids allowed
30-50% energy saving Availability of companies
Molecular sieves + TEG unit High efficiency Expensive
Low dew points Higher CAPEX
Large flow variations Heavy & big
High inlet gas T
Addition of entrainer High separation efficiency More equipment
Low heat energy More components
Heavy & big
Vacuum operation Less lean TEG inventory Complexity
High TEG purity More equipment
Possible TEG degradation
HiGee distillation High Efficiency Moving parts
Smaller equipment (5-10 fold) Very unknown technology
More maintenance
Also, the addition of the entrainer is rejected as it will increase the size of the unit as well as it is not an
innovative solution, which is in conflict with the objectives of the project. Also earlier proposed toluene
will dissolve into TEG as well, working against all benefits as proposed earlier. Finally, the vacuum
operation in a conventional equipment setup in the regeneration part is not investigated anymore as
an alternative, because to gain energy savings, the vacuum was meant to be created by ejectors that
work with existing flash gases going out. However, this will result in a pressure drop avoiding these
gases to reach the flare header which takes them into the incineration flame. The HiGee distillation
is discarded as the introduction of moving parts and such an unknown technology is hard to achieve
offshore. Several onshore application should be achieved first to look at the effects it will have on the
structure of the platform. If it will change the integrity of the drilling platform and question like that
need to be answered first.
For the other four technologies, a full study and design was done, resulting in three combined new
process schemes shown below, stating the several assumptions used in each.
3.2.1. Turbochargers and split-flow injection
Turbocharger and semi-lean split fraction techniques will be implemented together in each different
scheme, as they do not interfere with the other alternatives. A detailed scheme is provided below in
figure 3.7.

Figure 3.7: Process scheme with turbocharger and semi-lean TEG split flow injection, shown in yellow
boxes
Turbochargers
The size, and therefore weight, of the injection pump system can be lowered by using a turbocharger,
because as mentioned, this device interchanges the energy of a high pressure stream with a low
pressure one. This can also decrease the total energy needed for the pumps as well as the number of
them.
The total operational costs for pumping, assuming a total cost of 10 ct €per kWh[36], is 1.34 €per
hour [37]. Assuming 24/7 operation the total costs per year of this pump will be € 11.738. Using
calculation tools provided by Energy Recovery©a recovery of 70 % of energy can be achieved. This
will result in a evenly large reduction of operational costs. So a reduction of € 8.216 on a yearly basis
can be achieved. Not only that, also a reduction of 9.38 kW is achieved at the pumping section. This
leads to a reduction of approximately 79.866 kg CO which is released on a yearly basis[38]. The
total energy requirement for the plant is 205 kW. By adding a liquid turbocharger into the conventional
process a reduction of 4,6 % can be achieved without increasing the capital expenses which will be a
real benefit.
Split Flow injection
This alternative is studied with an intention of reducing the TEG inventory in the recirculation system.
Following is the discussion of the study.
The incoming lean TEG is fed to the top-most stage of the contactor. As per the design of the
conventional process in section 2.2, the contactor has 6 theoretical stages, therefore, it is possible to
study injection of TEG ranging from 2 to 6 splits, simultaneously varying the percentage of flow flowing
through each split branch. However, it should be noted that while injections with 2 and 3 splits can
be studied extensively for symmetric arrangements between theoretical plates, for higher number of
splits(eg:4-6) there would be too many combinations possible.

Hence, to restrict ourselves, we study only injections with 2 and 3 split flows with varying percentage
of flow through each split branch. Since the intention is to reduce TEG inventory, simulation was started
with lower conservative estimate for the lean TEG flow in order to check whether it is possible to still
achieve the desired specifications in the outlet dry gas. As it was found that it is indeed possible to
meet the outlet water requirements, all the simulations for split flow were started with lower estimate
of TEG flow, that of 1580 kg/h. The maximum outlet water content as per specification turns out to
be 8.5 kg/h. If the specification was found to be well within limits, TEG flow was reduced even further
for the split flow to an extent that the outlet water concentration never rises above maximum 7.7 kg/h.
On the other hand, if the specification was barely met, no further adjustments were done in that case.
Figure 3.8 summarizes the observations of the simulation modelled in Aspen Hysys G.1 which form
the basis of this study. Different types of splits were tested to see if adding more TEG in the beginning
or end has an advantage. Entries in bold represent lowest possible flow of TEG that can be achieved
for that particular split combination to achieve the water specification as mentioned above.
Figure 3.8: Results of calculations on split flow injection made in Aspen Hysys.
It can be seen that the lowest achievable flow of lean TEG in both 2-split and 3-split schemes is
1225 kg/h. There is no significant reduction of TEG on increasing the number of splits form 2 to 3. To
check whether this really adds value to the conventional process with no splits, the flow of lean TEG
was reduced to as low as possible in Hysys still ensuring that the above specs were met. This flow was

found to be 1150 kg/h. This is a result contradictory to our expectation that split flow reduces TEG
inventory.
From the above study, it can also be seen that with Hysys simulations, it is possible to reduce
the lean TEG flow even below the theoretical minimum of 12 times the amount of water removed.
However,it must be understood that such reduction may not be practically feasible. Moreover, we
cannot completely trust the thermodynamic models in Aspen Hysys to be totally accurate in their
prediction. Hence, we limit ourselves to the theoretical minimum flow of 12 times the water removed
of lean TEG as mentioned above.
3.2.2. Alternative 1: Process scheme with microwave heating
The improvements and changes suggested were then included into the conventional process of fig-
ure 2.1, getting figure 3.9. This figure shows a still column heated by microwaves. The rest of the
equipment basically remains the same.
Figure 3.9: Process scheme with microwave heating (yellow box)
Microwave heating
Microwave heating has several benefits as mentioned before, including that it can be more efficient
and requires a smaller device than conventional heating with a reboiler. In some cases it can even be
replaced in total. It can also decrease the amount of stages needed for the regeneration.
The technology for continuous operation is now in the pilot plant stage. The company Sairem
(France) is working on this. Their reactor design has a flow capacity up to 1 L/min and has a microwave
generator that generates waves of 2450 MHz. 6 kW of power is generated and there is a significant

part of the design devoted to cooling. The unit is a metallic vessel which assures pressure containment
and allows for fast thermal transfer.[39]
However, heating volatile, often flammable organic solvents, under well-controlled conditions is
not trivial on the large scale, but it can be done. Lastly, another Sairem 915 MHz batch reactor
was changed in the strategy to microwave scale-up through the use of a different wavelength, since
penetration depths, dielectric constants and loss factors vary with wave length as well as solvent nature
and temperature. In this case, the energy savings were due to a decrease in heating time and not in
energy efficiency, because normal household microwaves (central component of any microwave device)
has an efficiency of 50-65% transforming electricity into electromagnetic irradiation[40]. However dr.
Guido Sturm of TU Delft, a expert in microwave heating, mentioned an efficiency off up to 80 %.
Overall, there are reasons to think that together with the use of the stripping technique for glycol
regeneration, with a gas normally flowing upward counter currently to the descending liquid TEG, the
unit can achieve the requirements and reductions proposed. Depending on the stripping agent used,
i.e. outlet gas from the flash (V201), water, hydrocarbons, or both are absorbed from the glycol into
the stripping gas, thus regenerating the glycol for reuse in dehydrating the natural gas. But the reality
is that these processes produce an additional gaseous or aqueous waste stream that requires off-site
attention such as incineration, disposal, or further treatment.
An attempt has been made to model microwave in Aspen Hysys, but a working model is has not yet
been achieved. The column is split into three stages, modeled as flashes and a condenser and reboiler
part. At each stage a specific temperature is set, as is used with microwave distillation. These are all
separately heated. The feed enters the column at the middle stage, this because it gave the lowest
energy use. This model however leads to very high and fluctuating energy demands per stage. Three
different settings were used. Firstly the natural gradient occurring in the still column has been taken.
Secondly a linear decrease between the top and bottom stage has been tested and lastly the inverse
of the natural gradient is tested. This is displayed in table 3.2 and the model used is added in appendix
F.1.
Table 3.2: Energy demands from the different setting of the model described in appendix F.1
Setting 1 Setting 2
Stage
Set
Temperature (C)
Energy
Demand (kW)
Set
Temperature (C)
Energy
Demand (kW)
Condenser 97 -17.05 97 -6004
3 99.26 -162.6 125 5999
2 101.9 -16230 150 -30.85
1 150.7 16370 175 92.66
Reboiler 204 192.8 204 87.83
Setting 3 Conventional
Stage
Set
Temperature (C)
Energy
Demand (kW)
Set
Temperature (C)
Energy
Demand (kW)
Condenser 97 -7139 97 -49.85
3 145 7136 - -
2 165 32.69 - -
1 185 63.91 - -
Reboiler 204 55.17 204 191.5
As this model did not achieve realistic values different professionals in the field of modeling mi-
crowave heated column were contacted. From these conversations, it became apparent that, as this
is a very young field of research no real simulation models are achieved as for now.
The main fields in which microwave heated columns are used are pharmaceutical and food process-
ing technologies. Outside of these fields the benefits have not been sufficient enough to take the risk
of entering a new technology. To estimate the costs, the energy needed by a conventional still column
is used.
When designing the new column a few constraints should be kept in mind however. No magnetic

materials can be used around microwave heated volumes. These magnetic properties cause extensive
heating effects on the magnetic walls and equipment. A still column made of carbon steel as proposed
earlier in this report is not feasible anymore as the microwaves will heat the carbon steel. A still column
of stainless steel or a copper coating on the carbon steel are needed to evade this effect. To power the
microwave a cable of 8000 Volts needs to be added to the plant. These high voltages impose a new
risk to the plant as well, as there were no high voltage operations present before. Microwave units
themselves are also an additional risk as, when they are displaced, can cause severe burning into the
skin. That way not only the skin is burnt but it will penetrate the skin and burn internally as well.
Moreover, an economic evaluation has been done. By adding microwave heating in the column the
total CAPEX will increase. A rough cost estimation is provided by Dr Guido Sturm. A 6 kW microwave
unit costs around € 20,000, which scales more or less linearly. From Aspen Hysys the energy require-
ment is calculated for a conventional unit. The figure found there is 141 kW for heating. Therefore an
investment of around € 470,000 is needed for the energy requirement leading from the conventional
process. Contact with the French company Sairem was also made. They are currently investigating
the use of microwave heated still columns. Their cost estimation is around € 550,000 for the internals
of such a column. The column itself will cost € 147,850 if it is made from stainless steel (SS316). This
is a significant rise in capital expenses, as the initial capital expenses, as will be calculated in chapter 5
are almost 10 times less. The weight of one 6 kW microwave unit is around 15 kg, so the total weight
of a column with this duty will be 352.5 kg which is in the same ballpark as a gas fire heater.
Using microwave heating an efficiency of 80% can be expected. If the system stays unaltered and
the energy demands are more or less and a cost of € 0.1 per kWh is used the total yearly cost of
reboiling with microwave technology is € 264,278. This is almost € 100,000 more then a gas fired
heater.
Dr. Guido Sturm also mentioned that microwave heating is only beneficial when a stream needs to
a lot of heating. Regarding this system, due to good heat integration, the inlet stream in the column
already is 170 °C. The additional 30 °C needed for distillation are presumably not enough to favor
microwave heating.
Considering all these additional costs and no guarantee that the reboiler can be taken out of the
system it is decided not to pursue this technology any further. The investment is 10 times higher then
a conventional still column and in OPEX no savings can be expected either. The presence of natural
gas at the platform makes a gas fired reboiler a better substitute for heating in the still column.
3.2.3. Alternative 2: Process scheme with pervaporation membranes and
semi lean injection
In this case, figure 3.10 shows a unit where the regeneration will be carried out with pervaporation
membranes.
Pervaporation membranes
With the use of only pervaporation membranes, the whole reboiler and still column may be replaced,
with the consequent reduction of size and weight. Also the benefit of only having one piece of equip-
ment to maintain is to be considered. However, it needs vacuum operation to improve the performance
of this technology for reaching the purity required (99.2% wt TEG). It will be created by condensation
in the heat exchangers E201 as shown in figure 3.10 plus a vacuum pump. Moreover, an extra heater
is needed to achieve the proper temperature of operation. However, to reach the purity described by
the water specifications a large amount of membranes modules are needed which can lead to large
and heavy equipment. That is the reason to consider a combination with a stripper column, too.
Furthermore, it should be mentioned that increasing the temperature till the required 150°C before
the flash unit will lead to a reduction of water content in the liquid that will be sent to the membrane
unit. However, this could not be done due to the high losses over the limits (around 0.08 kg/h TEG in
the vapour flash stream) in TEG encountered in the flash unit. Thus, the heating of the liquid stream
is done after flash without creating vapour in that stream (0.004 vapour fraction) which will lower the
effectivness of the pervaporation membrane unit. It has been decided to follow with the design shown
in 3.10.

Figure 3.10: Process scheme with pervaporation membranes (yellow box)
For a specific organic mixture (in this case TEG with water) one has to test to determine selectivity
and fluxes during the process of dehydration, because the binding force of TEG to water is high, so
fluxes will be lower compared to some other organics e.g. ethanol or IPA. In addition, it is more
difficult to dehydrate to such low water concentrations. Then a preliminary study of different types of
membranes was carried out to find out these fluxes on basis of the conventional process outlet vapour
stream from the flash.
First of all, apart from company claims, a paper was found which states that with commercial silica
membrane modules of the company Pervatech, if a feed of 0.054 wt water, 0.936 wt TEG and 0.005
wt Toluene and 0.005 wt Hexane at 150 °C, a 99.99+% wt of water purity in the permeate can be
achieved, at an average flux of 0.255 kg/m ·h [41].
In addition, an experiment performed to determine the water flux of a zeolite membrane module
from Mitsui USA was tested at 100 °C with a TEG mixture containing 5% wt water resulting in 0.13
kg/m ·h as permeate.
Other sources say that 95% wt water purity can be achieved with NaA zeolite membranes exhibiting
high separation performance and fluxes of 0.5 kg/m ·h for 5% wt feed water content at 120 °C. [42]
Also, a realistic research with improved membranes such as Sulfonated Poly-ether-ether Ketone
(SPEEK) was carried, resulting in only 98% of water purity the permeate side with 5% wt water content
in the feed at 32 °C and flux of 0.2 kg/m ·h as depicted in Huang et al (2002) [43].
In other words, in order to estimate the area required for a complete separation we carried this
analysis. It means roughly, avoiding pressure drops, no TEG losses in permeate, constant flux, 100%
water permeation and no membrane size limitation, that if our stream of 1657 kg/h (0.0033 wt others,

0.912 wt TEG and 0.0847 wt water, see figure 3.11) from the flash is fed to a membrane unit we will
obtain the results shown in table 3.3 and explained with two examples below.
Figure 3.11: Schematic representation of pervaporation membrane unit with inflow of 1657 kg/h
coming from liquid stream of flash unit.
• Example calculation for silica membranes:
All water in feed goes into permeate
1657 · 0.0847 = 140.35 kg/h, representing the 0.9999+ wt water in that stream, because this is
the maximum for this membrane.
Therefore, 1657 - 140.35 = 1516.65 kg/h of TEG plus other compounds in retentate. All TEG in
feed goes to retentate,
1657 · 0.912 = 1511.18 kg/h, representing the 1511.18 / 1516.65 = 0.996 wt TEG and 0.004 wt
of others in that stream.
Hence, if the average flux of permeate is 0.255 kg/m ·h, we need 140.35 / 0.255 = 550 m of
membrane.
• Example calculation for SPEEK membranes:
All water in feed goes into permeate
1657 · 0.084 = 140.35 kg/h, representing the 0.98 wt water in that stream, because that is the
maximum for this membrane. It means that the total permeate flow is 140.35/0.98=143.21 kg/h,
where 143.21 - 140.35 = 2.86 kg/h are other compounds except from TEG.
Therefore, if in the feed there were 1657 · 0.0033 = 5.47 kg/h of others, 5.47 - 2.86 = 2.61 kg/h
go to retentate. Hence, if all TEG in feed goes to retentate,
1657 · 0.912 = 1511.18 kg/h plus 2.61 kg/h results into 1513.79 kg/h of TEG plus other com-
pounds in permeate, representing the 1511.18/1513.79= 0.998 wt TEG and 0.002 wt of others
in that stream.
Finally, if the average flux of permeate is 0.2 kg/m ·h, we need 143.21 / 0.2 = 716 m of mem-
brane.
Following the same reasoning, the results shown in table 3.3 were calculated, which in all cases is

more than the minimum required in the design case.
Table 3.3: Results of membrane area estimation
Membrane Temperature TEG in retentate water in permeate Area
type °C wt wt m
Silica 130-150 0.996 0.999 562
Zeolite 92-100 0.996 0.999 1080
NaA Zeolite 120 1.00 0.950 295
SPEEK 30-70 0.998 0.980 716
It is observed that nowadays there is a lot of research on new membranes and that most of them
fulfill the requirements for our dehydration purpose. However, there are not many supplier companies.
Examples are Sulzer Chemtech Membrane Systems, based in Heinitz, Germany; and Pervatech BV of
Enter, The Netherlands, allowing a wide range of different temperatures, modules and flows.
Furthermore, although the major component in the over head vent is water stream, as shown, this
stream may contain organic compounds, including aromatic and non-aromatic organic vapours, such
as BTEX. The emissions of them are now classified as Hazardous Air Pollutants (HAPs), and are subject
to regulations which can be better handled by these membranes.
This is, therefore, a simple and reliable method to reduce or eliminate the release of these compo-
nents, basically caused by the hydrophilic membranes which in one step both regenerate the solvent
and capture any hazardous components. Despite efforts, a cost-effective regeneration technology that
truly minimizes or eliminates HAP emissions has not yet been developed.
To finish, also a comparison of the energy consumption based on the heat requirement for evap-
oration for the removal of 1 kg water from feed mixtures can be seen in the following figure 3.12,
extracted from Huang et al (2002) [43].
It is clear in figure 3.12 that the advantage of applying pervaporation for dehydration of Glycol
becomes significant when the water content in the feed is significantly low. It should also be pointed
out that this simple comparison was based only on the theoretical energy consumption at a constant
pressure. Many other factors such as cooling of distillation, thermodynamic heat effectiveness, and
capital cost are not considered, all of which are important for the economic evaluation of these two
separation technologies.
To maintain more realism in the design, Pervatech membranes were selected for further consider-
ations. In the following study, a commercial Pervatech module PVM-080 SS 316 37×4-tube (120cm)
with 3,7 m² membrane surface was used with these assumptions and characteristics[44] [45] [46].
In the following images 3.13 and 3.14, a commercial Pervatech module is presented to get an overall
impression of the module we are using. In our case, instead of 7 elements of 4 channels each, we will
used 37 elements of 4 channels each.
• Membrane element characteristics:
– Size: 1200 x 25 mm (LxD), effective area 0,10 m² (standard). Each element has 4 channels
with 7 mm inside diameter.
– Membrane type: Hybrid silica hydrophilic membrane.
– Substrate material: α-Al2O3.
– Intermediate layer: Gamma alumina.
– Top layer: Hybrid Silica coated on inside of the support tube.
– Pore Size: 0.3–0.5 nm.
• Limits of membrane:
– Temperature: limit max. 150 °C.
– Pressure: limit max. 50 bar.

Figure 3.12: Theoretical comparison of the energy consumption of pervaporation against distillation.
Energy consumption (P) based on the heat requirement for evaporation for the removal of 1 kg water
from feed mixtures using 𝑃 = ∆𝐻 + ((1/𝑌 ) − 1) · ∆𝐻 where ∆H and ∆H represent the
evaporation heat (kcal/kg) of water and Ethylene Glycol, respectively.
– pH: 2-8.5.
• Limits of operation:
– Maximal allowable working pressure 20 bar at 175 °C.
– Minimum design material temperate -20 °C at 20 bar.
– Vacuum: Level of vacuum depends on the application.
– Feed pump capacity: Linear velocity of the feed to be high enough to guarantee turbu-
lent flow inside the tubes (Re ≥19000), this to prevent concentration polarization and limit
fouling.
• Assumptions:
– 3.7 m of membrane/module (37 elements).
– TEG composition of 0.9895 wt in retentate, because it is needed for the semi-lean TEG split
strategy.
– Water composition of 1.0000 wt in permeate (only water permeates).
– Temperature: 150°C.

Figure 3.13: Front view of PVM-094 SS 316 7×4-tube (120cm).
Figure 3.14: Side view of PVM-094 SS 316 7×4-tube (120cm).
– Pressure: 3 bar inlet feed, 20 mbar in permeate side and 1.5 bar retentate side.
– Permeate flux 0.255 kg/m ·h from the sensitivity analysis over a range between 120°C-
150°C explained below 3.15.
The reason to do is analysis is helping to decide the optimum temperature conditions of our
membrane system. Therefore, it was tested the temperature effect versus different water
compositions for different temperatures which are presented in the following figure 3.15.
Due to the fact that the flux depends on the water content along the length of the membrane
because the chemical potential changes with water concentration in the TEG, a logarithmic average of
the inlet value of water and the outlet was taken into account at 8.5% wt of water at the inlet and
0.7% wt of water at the outlet. Hence, taking into account the assumptions mentioned, it led to the
results in table 3.4. One example of calculation has been provided below.

Figure 3.15: Feed water concentration against water flux in permeate for Ethylene Glycol- water
mixtures [41]. In red is represented extrapolated data.
• Example of calculation of number of modules estimation:
At 150 °C, the inflow for the membrane module is 1657 kg/h (0.0033 wt others, 0.912 wt TEG
and 0.0847 wt water), this is take from Aspen Hysys. For achieving the purity required after
membrane module (98.95% wt TEG) we follow:
All TEG goes to the retentate 1657 · 0.912 = 1511.18 kg/h of TEG, representing 0.9895 wt of
that stream. Therefore, the total flow of retentate is 1511.18 / 0.9895 = 1527.22 kg/h.
Hence, 1527.22 - 1511.18 = 16.04 kg of water plus other compounds. All other compounds go
to the retentate too, due to high water selectivity of the membrane, 1657·0.0033 = 5.47 kg/h
of other compounds(BTEX etc.). 16.04 - 5.47 = 10.57 kg/h of water goes into the retentate,
representing 10.57/1527.22 = 0.0069 wt water purity in that stream.
If 1657·0.0847 = 140.35 kg/h of water is fed, 140.35 - 10.57 = 129.8 kg/h is in the permeate
with 1.00 wt water purity.
At the entrance of the module, the water content in TEG is 0.085 wt, which represents a flux
of 0.612 kg/m ·h, while at the exit of the module the water content is the required 0.007 wt
of water in TEG, which gives a flux of 0.075 kg/m ·h. Therefore, doing an logarithmic average

(0.612-0.075)/ln(0.612/0.075) = 0.255 kg/m ·h.
Finally, if the permeate flow is calculated to be 129.8 kg/h, 129.8 / 0.255 = 509 m is needed. If
every module gives 3.7 m of effective membrane, around 509 / 3.7 = 138 modules are estimated.
Table 3.4: Results of number of modules estimation with PVM-080 SS 316 37×4-tube
Temp. Flux Retent. TEG Water Others Perm. Water Area Modules
°C kg/m ·h kg/h wt wt wt kg/h wt m Nr
150 0.255 1527.22 0.9895 0.0069 0.0036 129.8 1.00 509 138
140 0.206 1527.22 0.9895 0.0069 0.0036 129.8 1.00 629 170
130 0.255 1527.22 0.9895 0.0069 0.0036 129.8 1.00 828 224
120 0.255 1527.22 0.9895 0.0069 0.0036 129.8 1.00 1350 365
To conclude with the temperature selection sensitivity analysis, it was decided to follow with 150°C,
because it is the maximum allowed temperature for such a module as well as it gives the minimum
number of modules. Furthermore, this temperature will be achieve thanks to a heater before the
pervaporation module and not before the flash for the already mentioned high TEG losses in the flash
at 150°C.
It is also very instructive and valuable to follow a sensitivity analysis about the maximum purity
that can be achieved with these membranes modules at 150°C if the semi lean split technique is
neglected. Hence, taking into account the previous considerations and way of calculate the purity, the
results shown below were obtained for an inlet feed of 1657 kg/h (0.0033 wt others, 0.912 wt TEG
and 0.0847 wt water, see figure 3.11) and a flux of 0.255 kg/m ·h .
Table 3.5: Results of TEG purity estimation in retentate with PVM-080 SS 316 37×4-tube
Retentate TEG Water Others Permeate Water Area Modules
kg/h wt wt wt kg/h wt m nr
1557.9 0.9700 0.02649 0.00351 99.1 1.00 389 105
1542.0 0.9800 0.01645 0.00355 115.0 1.00 451 122
1527.2 0.9895 0.00692 0.00358 129.8 1.00 509 138
1523.4 0.9920 0.00441 0.00359 133.6 1.00 524 142
1516.7 0.9964 0.00000 0.00361 140.3 1.00 550 149
In table 3.5 it can be observed how the TEG purity increases as the membrane area increases and
therefore the number of modules, due to an increment in permeate flow. Three important values of
the study should be noticed:
The first one is 98.95% wt TEG purity, which would be the value that allows the removal of the
still column, resulting in only one unit where a stripper increases the purity further from 98.95% till
99.2%. This scheme is discarded however as TEG losses in the stripper column will be higher than the
specified limit, as shown in the proposed scheme 3.10.
Secondly, 523 m representing 142 modules would be the theoretical value needed to directly
achieve the minimum purity required for the process (99.2 %wt of TEG), with the removal of the still
column and stripper too.
Finally, with 149 modules would achieve the maximum of 99.64% wt TEG purity with only perva-
poration modules, which is above the minimum.
However, as conservative criteria are always more intelligent in design-wise thinking it is decided
not to go for the maximum purity, so the 98.95 %wt purity of TEG as the outlet stream unit is selected.
The rest of the water needs to be taken out using a still and stripping column.
To check if the process can still be improvised with the lean TEG flow at theoretical minimum,
another strategy was studied, called semi-lean TEG split flow.

Here, a part (50%) of incompletely regenerated TEG (98.95% wt TEG) exiting the Pervaporation
is fed back to the contactor in the middle (above 4 stage).The choice of this flow and the stage in
the contactor to which it is sent is completely arbitrary. To maintain the total flow to contactor at the
theoretical minimum, the lean TEG flow is also reduced accordingly. Furthermore, these flows have
not been studied by splitting them to different contactor stages. This is based on the fact that we are
restricting ourselves to the theoretical minimum flow based on the findings of study of TEG split flow
study done earlier in section 3.2.1.
It was observed that by using the above strategy, the stripping gas to the regeneration section
can be reduced by up to 20% of the conventional process without affecting the quality of lean TEG
regenerated. The remaining 80% can be sent to overhead treatment or used somewhere else. By
reducing the flow to 50% after the Pervaporation membranes, the still column and surge vessel size
can be reduced. The power requirement for the booster pump and the high pressure injection pump
would also reduce in this case. But, in order to pump the 98.95% wt TEG to the contactor, an additional
high pressure pump would then be required. So to conclude with, this suggestion is added into the
final different proposals shown below.
3.2.4. Alternative 3: Process scheme with hybrid system
The third option considered is a combination of previous schemes with some little changes such as the
incorporation of one heat exchange and a pump, resulting in figure 3.16 shown below.
Figure 3.16: Process scheme with hybrid system (turbocharge plus semi-lean split injection and
pervaporation module (yellow boxes))
A pervaporation unit can be added to the still column heated with a gas fired reboiler. Pervaporation

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