Experimental study of oil-waterseparation techniques

Espen Olaf Hestdahl

Subsea Technology

Supervisor: Milan Stanko, IGP

Department of Geoscience and Petroleum

Submission date: June 2017

Norwegian University of Science and Technology

III

ABSTRACT

As hydrocarbon reservoirs mature they will increase their production of water, also operators

are moving to deeper waters and marginal fields. As a result, the costs of processing and

handling increases. Compact subsea separation offers a solution to the challenges associated

with this. If produced water is removed at the sea-floor and re-injected into the reservoir,

production rates and recovery can be increased, also flow assurance is improved and top-side

production capacity maintained. One method for compact separation is the use pipe-module

separators. The planning of an experimental rig for testing the efficiency of a pipe-module

separator has been conducted.

An emerging separation method is the use acoustic fields. Standing wave patterns are used to

manipulate the migration of dispersed droplets. The use of ultrasonic transducers with a

frequency 100 kHz and 1 MHz for separation has been researched, also an ultrasonic bath with

a frequency of 35 kHz has been tested. Oil-water mixtures has been irradiated for different time

intervals and frequencies. The results showed no increase in separation performance compared

to what could be expected from gravity based separation. For the ultrasonic bath the separation

performance worsened due to cavitation. Compared to other studies the power output of the

ultrasonic transducers used in the experiments was much smaller. The experiments showed that

the available ultrasonic equipment cannot be used for separation, for further investigations new

equipment must be obtained.

IV

V

SAMMENDRAG

Når hydrokarbon-reservoarer går i mot slutten av livsløpet økes vannproduksjonen, i tillegg

flytter operatørselskapene blikket mot dypere vann og marginale felter. Et resultat av dette er

økte kostnader for prosessering og håndtering. Kompakt seperasjon på sjøbunnen kan være en

løsning på alle disse utfordringene. Hvis produsert vann kan fjernes på havbunnen og re-injisert

i reservoaret kan produksjonsraten og utvinningsgraden øke. I tillegg kan strømningssikring

forbedres og produksjonskapasitet over vann opprettholdes. En metode for kompakt separering

er bruken av rørmoduler. Planleggingen av en eksperimentell rigg som skal brukes til å teste

effektiviteten til en slik separator har blitt utført.

En voksende metode for seperasjon er bruken av akustiske felt. Stående bølger blir brukt til å

manipulere forflytningen til dråper i et medium. Ultralyd-transdusere med en frekvens på 100

kHz og 1 MHz ar blitt brukt i separeringsforsøkene. I tillegg har et ultralydbad med en frekvens

på 35 kHz blitt brukt. Olje og vann har blitt mikset og utsatt for stråling i forskjellige

tidsintervaller og med forskjellige frekvenser. Resultatene viser ingen forbedring i seperasjon i

sammenlignet med hva som er forventet av gravitasjonssedimentering. For ultralydbadet ble

separasjonen verre enn kontrollprøven, dette er på grunn av kavitasjon. Sammenlignet med

liknende forsøk er effekten fra ultralyd-transduserne liten. Eksperimentet viser at utstyret som

er tilgjengelig ikke er egnet for separering, for videre forsøk må nytt utstyr skaffes.

VI

VII

ACKNOWLEDGEMENTS

First and foremost, I would like to thank Phd. candidate Håvard Slettahjell Skjefstad for letting

me contribute in the planning of the experimental rig and I hope that the future studies of the

compact separator will be successful. I would also thank to Professor Milan Stanko for help

during the project and master thesis. Thanks to senior engineers Noralf Vedvik and Steffen

Wærnes Moen for help in planning and ordering parts for the rig. I must also mention staff

engineers Håkon Myhren and Terje Bjerkan for help in construction and assembling of

equipment. At last I would like to thank Hanne Gjerstad Folde for support and laughs during

the last year.

VIII

IX

Table of Contents

Abstract .................................................................................................................................... III

Sammendrag .............................................................................................................................. V

ACKNOWLEDGEMENTS ................................................................................................... VII

List of figures .......................................................................................................................... XI

List of tables .......................................................................................................................... XIII

NOMENCLATURE ............................................................................................................ XIV

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

2 Theoretical Framework ..................................................................................................... 3

2.1 Subsea separation ......................................................................................................... 3

2.2 Multiphase Flow .......................................................................................................... 8

2.3 Separation principles .................................................................................................. 14

2.4 flow metering ............................................................................................................. 24

2.5 Pressure Measurement ............................................................................................... 25

2.6 Ultrasonic Transducers............................................................................................... 25

2.7 Experiences From the Previous Test Loop ................................................................ 26

2.8 LabView ..................................................................................................................... 28

3 Presentation of the test loop ............................................................................................ 29

3.1 P&ID .......................................................................................................................... 30

3.2 Description of Equipment and Instrumentation ......................................................... 32

3.3 National Instruments USB 6009 DAQ ....................................................................... 42

3.4 Experimental fluids .................................................................................................... 42

4 Ultrasonic separation experiments .................................................................................. 45

4.1 Experimental Equipment ............................................................................................ 45

X

4.2 Experimental .............................................................................................................. 46

5 Results ............................................................................................................................. 51

5.1 Characteristics of fluids.............................................................................................. 51

5.2 Horizontal Separator Performance ............................................................................. 52

5.3 Ultrasound .................................................................................................................. 54

6 Discussion ....................................................................................................................... 65

6.1 Flow Loop Project ...................................................................................................... 65

6.2 Ultrasonic Transducers............................................................................................... 65

6.3 Sources of Error ......................................................................................................... 66

7 Conclusions and Recommendations ............................................................................... 69

References ................................................................................................................................ 70

APPENDIX A: Risk Assessment ............................................................................................. 73

XI

LIST OF FIGURES

Figure 2-1 Increased recovery from water separation[1] ........................................................... 4

Figure 2-2 Inline gas-liquid cyclonic separator[8] .................................................................... 6

Figure 2-3 SpoolSep separation principle[10] ........................................................................... 7

Figure 2-4- Horizontal oil/water flow patterns[15] .................................................................... 9

Figure 2-5 Flow patterns – superficial velocities[15] .............................................................. 10

Figure 2-6 Flow patterns - mixture velocity and water cut)[15] .............................................. 10

Figure 2-7 Force balance on droplet[19] .................................................................................. 14

Figure 2-8 Area of the circular segment in green[20] .............................................................. 16

Figure 2-9- Trajectory of oil and water droplets[21] ............................................................... 17

Figure 2-10-Standing wave pattern[22] ................................................................................... 18

Figure 2-11- Direction of Secondary force[23] ........................................................................ 20

Figure 2-12- Eckhart streaming [24] ........................................................................................ 21

Figure 2-13 Rayleigh streaming [24] ....................................................................................... 22

Figure 2-14 The three primary electrostatic forces[11] ........................................................... 23

Figure 2-15 Coriolis effect measurement principle[26] ........................................................... 25

Figure 2-16 Current holding tank spring 2017[29] .................................................................. 27

Figure 2-17 Pump performance curve at different frequencies ................................................ 28

Figure 3-1 3D-model of loop .................................................................................................. 29

Figure 3-2 P&ID of loop .......................................................................................................... 31

Figure 3-3 Manifold with pumps ............................................................................................. 34

Figure 3-4 Manifold P&ID ....................................................................................................... 36

Figure 3-5 Mixing point ........................................................................................................... 37

Figure 3-6 The new Horizontal separator ................................................................................ 38

XII

Figure 3-7 Section view of the weir plate between the water outlet to the right and the oil outlet

to the right ................................................................................................................................ 39

Figure 3-8 3-D model of Micro Motion F200[30] ................................................................... 40

Figure 4-1 Test beaker .............................................................................................................. 46

Figure 4-2 Experimental setup, the ultrasonic transducer is attached to the side of the beaker

with a clamp (excluded from sketch) ....................................................................................... 47

Figure 4-3- Samples for ultrasonic bath after mixing .............................................................. 48

Figure 4-4- Samples mounted in ultrasonic bath ..................................................................... 48

Figure 5-1 Oil from separator mixed with distilled water ........................................................ 52

Figure 5-2 Oil from separator mixed with 3.5 WT% NaCl ..................................................... 52

Figure 5-3 Exxsol-D60+ oil red and 3.5 WT% NaCl ............................................................. 52

Figure 5-4 Exxsol-D60+3.5WT% NaCl=+IKM-C33 .............................................................. 52

Figure 5-5 Exxsol D-60+3.5WT NaCl+ Bioprotect-2 ............................................................ 52

Figure 5-6 Separator performance for 3.5 WT% NaCl water droplets in Exxsol-D60 ............ 53

Figure 5-7 Separator efficiency for Exxsol D-60 droplets in 3.5 WT% NaCl water ............... 54

Figure 5-8 Separation performance of the Panametrics transducers ........................................ 55

Figure 5-9- Control sample after 50 minutes settling time ...................................................... 57

Figure 5-10- 15 minutes of ultrasonic irradiation, total time 50 minutes ................................ 57

Figure 5-11- 30 minutes of ultrasonic irradiation, total time 50 minutes ................................ 57

Figure 5-12- 45 minutes of ultrasonic irradiation, total time 50 minutes ................................ 57

Figure 5-13- Control sample, 15, 30 and 45 minutes of irradiation ......................................... 58

Figure 5-14- Samples side by side after 126 minutes. From the left: control sample, 5, 10, 15

and 45 minutes irradiation samples .......................................................................................... 58

Figure 5-15- Samples (From left to right: Control, 3, 5, and 10 -minutes) after 307 minutes,

note that the control sample is completely separated while there is still an emulsion layer in the

irradiated samples ..................................................................................................................... 60

Figure 5-16- Control sample and irradiated sample, the oil layer of the irradiated sample is less

transparent than the oil layer of the control sample ................................................................. 62

XIII

Figure 5-17- Control sample and irradiated sample after 45 minutes. ..................................... 64

LIST OF TABLES

Table 3-1 F40-200A Characteristics at 50Hz 32

Table 3-2 F50-200B Characteristics at 50 Hz 32

Table 3-3 F65-200AR Characteristics at 50 Hz 32

Table 3-4 Manifold main configurations 35

Table 3-5 Volume flow rate for the Micromotion F200, at nominal flow rate the pressure loss

is 1 bar across the meter[31] 40

Table 3-6 Performance specifications for the Micromotion F200[31] 41

Table 3-7 PTX pressure sensor characteristics[32] 41

Table 3-8 Fluid properties at 17 °𝐶 43

Table 5-1 Fluid properties 51

Table 5-2 Interfacial tension 51

Table 5-3 Case 1, Irradiation time 15, 30 and 45 minutes 56

Table 5-4- Layer thickness of the 5, 10, 15 and 45 minute samples at different time intervals

59

Table 5-5- Layer thickness of the 3, 5 and 10 minutes irradiated samples at different time

intervals. 61

Table 5-6 Effect of Irradiation in Cycles 63

XIV

NOMENCLATURE

Roman Symbols Units

𝐸𝑎𝑐 Specific energy density 𝑘𝑔 𝑚−1 𝑠−2

𝐹𝑎𝑐 Primary acoustic radiation force 𝑘𝑔 𝑚 𝑠−2

𝐹𝑑 Droplet drag force 𝑘𝑔 𝑚 𝑠−2

𝐺𝑑 Gravitational force on droplet 𝑘𝑔 𝑚 𝑠−2

𝐼𝑢 Inertia of Coriolis tube 𝑘𝑔 𝑚 𝑠−2

𝐾𝑢 Stiffness of Coriolis tube 𝑁 𝑚 𝑟𝑎𝑑−1

𝑐𝑚 Sound velocity in medium 𝑚 𝑠−1

�̇� Mass flowrate 𝑘𝑔 𝑠−1

𝑥𝑑 Distance between droplet centers 𝑚

G Gravitational acceleration 𝑚 𝑠−2

ℎ Height of continuous layer 𝑚

𝐾 Shape factor 𝑁 𝑚 𝑟𝑎𝑑−1

𝑎 Acoustic attenuation effect 𝑑𝐵 𝑐𝑚−2

𝑐𝑃 Dynamic viscosity, centi Poise 𝑚𝑃𝑎 𝑠

𝑑 Droplet diameter M

𝑓 Frequency 𝑠−1

𝑝 Pressure 𝑘𝑔 𝑚−1 𝑠−2

𝑟 Radius 𝑚

𝑢 Settling rate 𝑚 𝑠−1

XV

𝑣 Velocity in a one dimensional acoustic plane 𝑚 𝑠−1

Greek symbols Units

𝛽𝑑 Compressibility of droplet 𝑃𝑎−1

𝛽𝑚 Compressibility of medium 𝑃𝑎−1

𝜃𝑟 Angle between two droplets −

𝜇𝑚 Dynamic viscosity of medium 𝑘𝑔 𝑠−1 𝑚−1

𝜌𝑑 Droplet density 𝑘𝑔 𝑚−3

𝜌𝑚 Continuous phase density 𝑘𝑔 𝑚−3

𝜃 Angle −

𝜆 Wave length 𝑚

𝜏 Time lag 𝑠

𝜔 Angular frequency 𝑠−1

𝜙 Acoustic contrast factor −

Abbreviations

CRA Corrosion Resistant Alloy

NaCl Natrium Chloride

NDT Non-Destructive Testing

P&ID Process & Instrumentation Diagram

XVI

PWM Pulse Width Modulation

Re Reynold’s number

FPSO Floating Production, Storage and Offloading

1

1 INTRODUCTION

This master thesis is written as a part of the research activities of SUBPRO, specifically under

the PhD project "compact separation concepts" (P2.9) that belongs to the research area

"Separation Process Concepts". The PhD project aims to study experimentally and numerically

compact techniques for bulk oil water separation. The SUBPRO (Subsea Production and

Processing) research center is a collaboration between NTNU and key industry partners which

was started in the third quarter of 2015. The aim of SUBPRO is to find new and innovative

solutions to enable increasing recovery from existing fields and facilitate field development at

more demanding conditions.

Most of the easy resources has been recovered at the Norwegian continental shelf and the oil

industry must be innovative to meet future demands. To keep the production from declining,

the industry is moving into deeper waters, harsher conditions and to marginal fields at remote

locations. Also, the low oil prices in recent years and probably in the foreseeable future means

that the need for cost reduction is increasing. Subsea processing is a key enabler to development

of remote locations and marginal fields. At shallow waters the cost of conventional topside

equipment is lower than subsea installations, but as the water depth increases, subsea

installations are preferred as total cost is lowered. Also, subsea installations increase operational

safety and production potential.

The objectives of this project are listed below:

1. Design, planning and construction of an experimental setup to test compact separation

techniques for bulk oil water separation

2. Analyze/study separation due to ultrasound effect

This thesis focuses on the development of the testing facilities and the overall system. The

separation technique to study has been defined and decided upon during the spring semester

2017. To protect intellectual property on the concept, limited information is provided about the

separation concept to test. The modifications on the rig has been planned. A 3D-model of the

test rig has been constructed in Solidworks and P&ID has been made. Support in selecting

instrumentation, ordering parts, gathering and checking specifications and prices of the

equipment has been done. Also, participation in the predesign of the horizontal

2

separator/holding tank has been accomplished. A manifold has been assembled. Parts and flow

meters has been ordered and are supposed to arrive in early June,

The ultrasonic experiments have been performed in early May in cooperation with the exchange

student Chenxi Hong.

The report is structured as follows:

• Chapter 2: Background information about subsea separation; previous, current and

future developments of subsea separation. Literature review of multiphase flow,

separation principles and metrological equipment for experiments, flow meters,

pressure transducers, temperature transducers and.... Basic concepts of centrifugal pump

working principle and valves; ball valves and butterfly valves.

• Chapter 3: Presentation of the loop. All the selected equipment is presented

• Chapter 4: Results from the ultrasonic experiments and efficiency calculations of the

new horizontal separator

• Chapter 5: Discussion

• Chapter 6: Conclusion and recommendations

3

2 THEORETICAL FRAMEWORK

2.1 SUBSEA SEPARATION

2.1.1 Background

In the last 10 to 15 years subsea separation has established itself as an important marked

segment within subsea field development. The currently installed subsea has shown a high level

of reliability of the separators and their subsystems with a reported availability of 99% over the

last 10 years[1].

Due to characteristics like deep water reservoirs, long distance tiebacks, extreme operating

conditions and low reservoir pressure, many new subsea fields are currently uneconomical to

develop. Also, ageing fields are experiencing higher water cuts and lower reservoir pressures.

At higher water cuts the top-side separation capacity can become a bottleneck and due to limited

platform space, there is no way to increase the separation capacity. By installing subsea

separators, water can be removed and production can be maintained.

Deep water reservoirs require high pressures to produce back to a topside processing facility,

which leads to poor recovery rates and economics. A common way to improve recovery at deep

water reservoirs is by using subsea multiphase pumps. But this can be inefficient when the gas

content of the well stream becomes significant. The free gas content will inhibit the centrifugal

pump to deliver head since the hydraulic efficiency of the pump decreases with higher gas

content. [1]. This problem has been solved at the Perdido field in the Gulf of Mexico which at

2800 meters water depth is the deepest development to date. Here the gas is being separated

from the oil using a Caisson separator and an ESP pumps the oil to the Perdido spar located at

the surface.

4

Figure 2-1 Increased recovery from water separation[1]

By removing water subsea, the flowing backpressure (Figure 2-1) in the pipe lines decreases,

leading to a higher production rate and an increase in oil recovery. The dimension of the

production pipeline can also be reduced by removing water at the seafloor decreasing the initial

capital expenditure of the project.

The need for CRA (corrosion resistant alloy) in the pipeline can also be eliminated by removing

water from the fluid stream. Replacing the CRA with carbon steel can have a huge impact on

capital investment since CRA can be six to eight times as expensive as carbon steel. Also,

hydrate formation can be eliminated or reduced when water is removed leading to better flow

assurance and a reduction in operational expenditures since the need for hydrate inhibitors are

reduced.

By using subsea processing instead of manned platforms or FPSOs. uptime can be increased in

extreme weather conditions like storms and hurricanes. I these conditions, manned platforms

may need to be evacuated and FPSOs disconnected and relocated, leading to a shutdown of

production.

5

2.1.2 Subsea Separation Systems in Operation

In 2001 The Troll C pilot subsea separation and water injection system was installed at a water

depth of 300 m. The system contains a horizontal gravity separator a and a water injection pump

for handling the produced water. The Tordis field separator system was installed in 2007 as the

first full scale subsea separation system. The horizontal separator is installed at 200 meters

water depth. The system was developed to handle high sand production and it also has

multiphase boosting and water re-injection capabilities[2]. The Pazflor separation system was

installed in 2011 and it consists of three gas liquid vertical separators and hybrid pump

systems[3]. Caisson separators has been installed at deep waters at the Perdido and BC-10 fields

[4] The Marlim-oil water separator is installed at 870 meters. Bulk separation happens is a

special pipe separator and the water is further polishes to meet the requirements for re-injection

using cyclonic equipment.[5]

2.1.3 Compact Subsea Separation Technologies

New separator technologies are being developed to be more efficient and compact than the the

separator technologies currently in operation. By using compact separator systems, the cost of

the subsea processing station can be reduced. Also, the existing horizontal separator vessels

cannot withstand the high pressures experienced at deep and ultradeep waters. The new

technologies under development includes inline separation, separation in pipe segments and use

of electrostatic coalescence techniques[6].

2.1.3.1 Inline Cyclonic Separation

Inline separators can be used to separate liquid-liquid, liquid-gas, and to remove sand. The basic

separation principle is the same, but the design is different for each application area. Inline

technology achieves separation by high g-forces. The mixture enters a swirl element and the

fluid mixture is set in rotation. Because of the difference in densities, the heavier phase will

cling to the wall while the lighter will stay in pipe center. Figure 2-2 shows a gas-liquid inline

separator[7]

6

Figure 2-2 Inline gas-liquid cyclonic separator[8]

2.1.3.2 Linear Pipe Separators

The fundamental separation principle of the linear pipe separators is the same as for

conventional gravitation separators. The diameter of the the pipe segments is smaller than that

of a conventional pressure vessel. This leads to a reduction in Hoop stresses as can be seen from

Equation (2-1). [9] This means that pipe separators can be used at deeper waters and at higher

wellhead pressures than conventional separators.

𝜎ℎ = (𝑝𝑖 − 𝑝𝑒)

𝐷

2𝑡 (2-1)

Where

𝜎ℎ = Hoop Stresses

𝑝𝑖= Internal pressure

𝑝𝑒 = External pressure

𝐷 = Outside diameter

𝑡 = Wall thickness

Also, using several pipe segments with a smaller diameter means that the separation conditions

is easier compared to a standard separator. This is because the layer thickness of the continuous

phases is smaller. As a result, the rising distance of oil droplets is decreased and the residence

time is reduced. The new pipe separators are designed to be flexible. By changing the number

7

and length of the pipe sections, the separators can be adapted to the challenges that can arise

during the lifetime of a field.

In Figure 2-3 the separation principle for the main pipes of the Saipan SpoolSep subsea

separator can be seen. The fluid mixture enters the pipes at the spool inlet and the velocity of

the fluids is retarded. As the fluids migrates along the pipes, they become separated due to

gravity. At the end of the pipe section, oil and gas is flowing through the light outlet and water

is flowing through the heavy outlet.

Figure 2-3 SpoolSep separation principle[10]

2.1.3.3 Electrostatic Coalescence Techniques

Electrostatic Coalescence techniques enhances separation by increasing the droplet size

(chapter 2.3.3 for further description). Electrostatic treaters has successfully been tested top-

side to improve throughput and decrease the use of de-emulsifiers[11]. Water in oil separation

has not had as high priority as bulk water separation, therefore the electrostatic coalescence has

not been adapted for subsea use. In the future, it is expected that operators will want to develop

fields were sales quality oil is required after separation[6]. When that time arrives, electrostatic

coalescence is an interesting alternative to improve separation quality.

8

2.2 MULTIPHASE FLOW

The different flow patterns have a great impact on parameters such as phase separation, droplet

sizes and pressure drop. When the new compact separator is operational, it will be studied how

these parameters will influence its efficiency.

When a mixture of two immiscible phases flow together in a horizontal pipe the large-scale

distribution of these phases are called flow patterns. The different flow patterns are a result on

how the phases are distributed in the pipe. The key parameters that decides what kind of flow

pattern that will develop are: Input phase ratio, mixture flow rate, density ratio, viscosity ratio,

wetting properties, surface tension, and pipe geometry[12]. The flow patterns are identified

using different methods. These methods can both be subjective or objective. A common method

is to use equipment like cameras and video recorders to capture pictures of the flow regime and

analyze the pictures later. The drawback of this method is that it is subjective leading to

different conclusions for different observers. In the last decades, more objective methods like

conductive probes, impedance probes and gamma ray densitometry.

2.2.1 Classification of oil-water Flow Patterns

Oil-water flow patterns can be divided into four main flow regimes that can further be divided

into sub-regimes[13]. Since the flow regimes are determined subjectively and the experimental

setups used in the various studies differ from each other, the names on the different flow

patterns may change from author to author. Below are some descriptions given by[14].

• Stratified flow- Two continuous phases of immiscible liquids on top and below each

other based on the difference in their densities. Stratified flow usually occurs at lower

flowrates.

• Dispersed flow- Only one continuous phase exists. The continuous phase can be oil or

water. The other phase is dispersed in it as droplets. At high velocities or in stable

emulsions, there is a homogenic distribution of droplets over the cross section. At lower

velocities, there is a vertical concentration gradient of droplets over the pipe cross

section[14]. If the continuous phase is water the droplet will be concentrated in the top

of the pipe section and the opposite if the continuous phase is oil.

• Dual continuous flow- A combination of stratified and dispersed flow. Both phases are

continuous at the top and bottom of the pipe with dispersion of one phase into the other.

Dual continuous flow often appears at medium velocities.

9

• Annular flow- Is when one of the liquids flow on the pipe wall while the other liquid

flows in the center of the pipe. This flow regime can occur when when two immiscible

liquids have a small difference in density or one of the phases have large viscosities

• Bubble/Plug flow- plugs or bubbles flow on top of the pipe.

Figure 2-4- Horizontal oil/water flow patterns[15]

2.2.2 Flow pattern maps

The flow regimes are usually plotted in flow pattern maps, this can help to see at which flow

rates and water cuts the transition from one flow regime to another takes place. There are two

types of flow pattern maps commonly in use, the difference being which parameters plotted on

the x and y axis. In one version, the superficial velocities are of oil and water are plotted against

each other, whereas in the other version the mixture velocity is plotted versus the water cut. In

Figure 2-5 and Figure 2-6, the flow patterns seen in Figure 2-4 are plotted in two different flow

pattern maps. Figure 2-5 shows the superficial velocity of water versus the superficial velocity

of oil while Figure 2-6 shows the mixing velocity versus the water cut.

10

Figure 2-5 Flow patterns – superficial velocities[15]

Figure 2-6 Flow patterns - mixture velocity and water cut)[15]

11

2.2.3 Factors influencing flow pattern development

2.2.3.1 Mixture velocity and Superficial velocity

The most important parameter influencing the flow regimes is the mixture velocity. The flow

regime is stratified at low mixture velocities and it gets dispersed at higher mixture velocities.

The mixing velocity is given by:

𝑈𝑚 =

𝑄𝑜 + 𝑄𝑤

𝐴 (2-2)

Another way of expressing the mixture velocity is using the superficial velocities:

𝑈𝑠𝑜 =

𝑄𝑜

𝐴 𝑈𝑠𝑤 =

𝑄𝑤

𝐴 (2-3)

When calculating the superficial velocities, it is assumed that each phase covers the whole cross

section of the pipe, when in reality the individual phases only cover a fraction of the pipe

section. Therefore, the superficial velocity will always be lower than the actual velocity.

2.2.3.2 Water Cut

At low mixture velocities and when the pipe is horizontal, a stratified flow regime is usually

expected. But when the water cut is very high or very low, the dispersed flow pattern may

appear[12]. This means that when the water cut is low the oil phase will be continuous and the

water phase will be dispersed as droplets. And at high water cuts the opposite is true.

2.2.3.3 Density

As the difference in density gets larger the higher the probability for a separated flow pattern

becomes. When the density is equal, no stratified flow has been observed, only dispersed and

annular.[13]

2.2.3.4 Viscosity

A low viscosity oil will have a larger degree of mixing and water penetration than a high

viscosity oil. Still the effect of viscosity seems to have a small effect on the development of

flow patterns[13].

2.2.3.5 Inlet Geometry

The mixing unit is where the oil and water is mixed and it is situated at the beginning of the

flow development section. The mixing unit can be designed so that the initial flow pattern is

12

stratified or it can be shaped to disperse the flow. This can have a severe effect on the flow

pattern development. According to [16],when using a mixer unit were the initial flow is

stratified, a stratified appearance can be seen over a wider range of flow velocities.

2.2.3.6 Length of Flow Development Section

After the mixing unit, the multiphase flow starts to develop, after a certain point the flow is

fully developed. Therefore, the pipes length-diameter ratio (𝐿𝑒/𝐷) of the flow development

section is important as it may have a great impact of the observed flow patterns. In the numerous

horizontal flow studies this value has varied from around 80 to 480. Still, there is a problem to

validate if the flow is fully developed at the observation point and researchers cannot be sure if

the flow patterns observed are true. Attempts have been tried to verify if the flow is truly fully

developed including visual observation over the pipe length, pressure drop measurements over

pipe sections and hold-up measurement. Also, the researchers compare their experimental data

with previous data[17].

2.2.3.7 Pipe Diameter

The pipe diameter used during experiments usually ranges from 1/2" to 2” which is

considerable smaller than diameters expected to be seen in real life. This means that the Re

number and shear rates seen during experiments will not match real ones when the mixture

velocity is equal. To match the Re number seen under real conditions the mixture velocity will

have to be larger during experiments leading to a higher shear rate. Still the pipe diameter does

not seem to have any significant impact on the flow pattern[13].

2.2.3.8 Interfacial Tension

There are not many studies concerning the effect of interfacial tension. [18] observed dispersed

flow patterns at all water cuts and mixture velocities between 0.8 and 1.5 m/s when the

interfacial tension was 12.9 mN/m. At an interfacial tension of more than 30 mN/m and

comparable mixing velocities and water cuts [15] observed dual continuous flow patterns at oil

volume fractions from 0.25 to 0.7. Therefore, it can be stated that the flow pattern map will be

dominated by dispersed flows and stratified flows will be almost nonexistent when the

interfacial tension is low.

13

2.2.3.9 Emulsions

Oil in water and water in oil dispersions are by many authors referred to as emulsions.

Homogenous emulsions can only be seen at high mixing velocities. When the emulsion goes

from oil to water continuous the flow goes through a phase inversion process

14

2.3 SEPARATION PRINCIPLES

2.3.1 Gravity based separation

The principle behind gravity based separation was formulated in 1851 by George Stokes.

Stokes’ law describes the physical relationship that governs the settling of solid particles in a

liquid. The same principle can also describe the rising or settling of a droplet in a liquid medium

of a different density.

Stokes’ law is derived by looking at the force balance on a droplet settling at a constant rate[19]:

(Figure 2-7)

Figure 2-7 Force balance on droplet[19]

Here 𝐹𝑑 is the droplet drag force:

𝐹𝑑 = 3𝜋𝑑𝜇𝑢 (2-4)

and 𝐺𝑑 is the gravitational force on the droplet:

𝐺𝑑 =𝜋

6𝑑3𝑔(𝜌𝑑 − 𝜌𝑚) (2-5)

and when setting 𝐹𝑑 = 𝐺𝑑 and solving for 𝑢, the mathematical relationship can be described as:

𝑢 =

𝑔𝑑2(𝜌𝑑 − 𝜌𝑚)

18𝜇𝑚 (2-6)

15

Where

𝑢 = Settling rate

𝑑 = Droplet diameter

𝜌 = density, subscripts d is for droplet and m is for the continuous phase.

𝜇𝑚 = Dynamic viscosity of medium

And the assumptions that Stoke made are:

1. Particles are spherical

2. Particles are the same size

3. Flow is laminar, both vertical and horizontally

From equation (2-6) it can be seen that the settling speed is determined by the droplet size,

difference in densities between the droplet and continuous liquid and the viscosity of the

continuous liquid.

The retention time is the time it takes for an oil droplet to rise from the bottom of the water

column to the top when the continuous phase is oil, the time it takes for a water droplet to sink

from the surface of the oil layer to the bottom. To find the retention time the column height of

the continuous phase is divided by the rise rate. The height of the continuous phase is dependent

on the geometry of the separator and the volume of each phase. For a circular separator, the

height of the continuous phases can be found using trigonometry.

ℎ = 𝑅 (1 − cos

𝜃

2) (2-7)

Where ℎ is the height of the continous phase and 𝑅 is the radius of the separator and the angle

𝜃 is:

𝜃 = 2 arccos (1 −

ℎ

𝑅) (2-8)

To find the volume of the area of the circular segment must also be known:

𝐴 =

𝑅2

2 (𝜃 − sin 𝜃) (2-9)

16

Figure 2-8 Area of the circular segment in

green[20]

The retention time can be defined as the time a liquid is contained inside a vessel and it is

determined by the vessel size (diameter and length) and the flow rate. When the retention time

for a given flow rate is known, the size of the separator can be found by dividing the droplet

settling rate with the retention time. I we assume that a droplet starts in the bottom end of the

separator and rises as the continuous phase travels along the separator. The length of the

separator must be so that the droplet has time to reach its destination at the opposite end of the

separator. Figure 2-9 shows the ideal trajectory of oil and water droplets in a horizontal

separator. In most cases crude oil has a viscosity that is higher than water. Since the droplet

settling rate is inverse with the viscosity (2-6), water in oil dispersions will always get a smaller

settling rate. Therefore, under normal conditions, the separator should always be sized using oil

as the continuous phase.

17

Figure 2-9- Trajectory of oil and water droplets[21]

When using this method to calculate the vessel size of a horizontal separator it is assumed that

the droplets are all of the same size. If the selected droplet size is 150 microns, it can be expected

that the remaining oil in water is 1000 ppm[21]. In real life situations droplets sizes will vary

and are will be difficult to quantify. This together with inevitable turbulence in the separator

can make the use of Stokes’s law inaccurate when the droplets are very small.

2.3.2 Acoustic separation

In recent years, the use ultrasonic waves for the separation of particulates from a carrier medium

has shown to be a promising alternative to more conventional separation methods such as

centrifugation, gravitational or membrane filtering techniques. However, these technologies

have some inherent limitations since they rely on a specific range of flowrates and water cuts

to maintain an acceptable level of performance. If these flow conditions are not met, the only

solution is to replace the separators, which is costly since the well must be shut down so that

the workover can be performed. While still in the early concept phase, [22] proposes a solution

were the frequency can be tuned to match changes in flowrates and water cuts. Also, the

conventional separation methods require a multiple of components to be inserted into the

producing well. These components may cause a significant drop in pressure when the fluid

passes through them. Using acoustic separation, the transducers can be mounted on the outside

of the tube keeping flow restrictions to a minimum.

18

2.3.2.1 Acoustic separation principles

To separate particulates, either droplets or particles dispersed in a medium, a standing wave

pattern is exited within the dispersion. The standing wave pattern is created by reflecting a

pressure wave on a wall surface or using a second transducer on the opposite site of the primary

one to create a second wave. When these two waves have an identical frequency and amplitude,

and are 180° out of phase, they are called an ideal standing wave pattern. The standing wave

pattern within the vessel consists of 𝑛 number of loops with an alternating pattern of 𝑛 − 1

pressure nodes (displacement antinodes) and 𝑛 pressure antinodes (displacement nodes). From

Figure 2-10 it can be seen that the maximum pressure variations are at the pressure antinodes

while minimum pressure variations are at the pressure node. The number of loops in the

standing wave pattern is determined by the frequency of the acoustic wave and it must be tuned

so that the half-wavelength is an integer of the vessel it traverses. For a pipe with an inner

diameter, 𝐷, the frequency therefore must be tuned to satisfy:

𝐷 = 𝑛

𝜆

2 (𝑛 = 1,2,3 … ) (2-10)

Figure 2-10-Standing wave pattern[22]

2.3.2.2 Primary Acoustic Radiation Force

The primary radiation force in the direction of the propagating wave is a result of the spatial

gradient of the acoustic wave pressure and can be expressed as[22]:

𝐹𝑎𝑐 = −

4𝜋

3𝑟3𝑘𝐸𝑎𝑐𝜙 sin(2𝑘𝑥) (2-11)

19

Where, 𝑟 is the radius of the particulate, 𝑘 = 2𝜋/𝜆 is the wave number, 𝐸𝑎𝑐 is the specific

energy density, 𝑥 is the distance between the droplet and the nodal point and 𝜙 is the acoustic

contrast factor:

𝜙 =

5𝜌𝑑 − 2𝜌𝑚

2𝜌𝑑 + 𝜌𝑚−

𝛽𝑑

𝛽𝑚 (2-12)

𝛽 = 1/𝜌𝑐𝑚2 is the is the compressibility and the subscripts 𝑑 and 𝑚 are for droplets and the

medium, 𝑐 is the sound velocity in the medium. The acoustic contrast factor is determined by

the density and compressibility ratios between the particulates and the fluid. The acoustic

contrast factor gives an indication of the separability of the particulate suspended in the

medium. Also, it determines the direction the particulate will migrate, towards a pressure node

or an anti-pressure node. If the contrast factor is positive, the direction of the radiation force is

negative and the particulate will be displaced towards the pressure nodes. and if the contrast

factor is opposite, the particulate will be driven to the pressure anti-node. For example, oil

droplets dispersed in water will have a negative contrast factor and will migrate towards the

pressure anti-node while sand particles will have a positive contrast factor and migrate to the

pressure node. This means that acoustic separation can be used to separate both oil and sand

from water.

2.3.2.3 Secondary Acoustic Radiation Force

When the particulates move closer the pressure nodes or pressure anti nodes, the secondary

radiation known as the secondary Bjerknes force takes effect. The secondary radiation force

arises because the sound field scatters between particulates in proximity to each other. The

secondary force is given by (2-13)[23]

𝐹𝑠𝑒𝑐 = 4𝜋𝑟𝑑1

3 𝑟𝑑23 (

(3 cos2(𝜃𝑟) − 1)) (𝜌𝑑 − 𝜌𝑚)2𝑣2

6𝜌𝑚𝑥𝑑4 −

(𝛽𝑑 − 𝛽𝑚)2𝜌𝑚𝜔2𝑝2

9𝑥𝑑2 ) (2-13)

Where

𝜃𝑟= angle between two droplets and the direction of the propagating sound wave

𝑟= Radius of droplet 𝑑1 and 𝑑2

𝑥𝑑= Distance between the centers of two particulates

𝜔= angular frequency of the oscillation

20

𝑣= Velocity in a one dimensional acoustic plane wave

𝑝= Pressure

The direction of the secondary acoustic force between two droplets depends on their relative

position to the direction of the sound propagation. From Figure 2-11 it can be seen that the force

is repulsive when the angle is 0° and and attractive when the angle is 90°.

Figure 2-11- Direction of Secondary force[23]

2.3.2.4 Acoustic Streaming

By increasing the acoustic input power and frequency it can have an adverse effect on

separation, this is because of an effect called acoustic streaming. Acoustic streaming is a result

of viscous attenuation of an acoustic wave[24] which is given by equation (2-14). The

consequence of this is that the whole fluid is set into motion. This motion will make the

particulates migrate around in the fluid preventing the them to be manipulated by the acoustic

radiation forces.

𝛼 =

2𝜇𝑚(2𝜋𝑓)2

3𝜌𝑚𝑐𝑚3 (2-14)

Where:

𝛼 = Acoustic attenuation coefficient

21

𝜇𝑚 = Viscosity of medium

𝜌𝑚 = Density of medium

𝑐 = Sound velocity in medium

The effect of acoustic streaming increases with with the acoustic energy input and the streaming

velocity will vary with the sine wave squared.[23]

The three main acoustic streaming effects are Eckhart streaming, Rayleigh streaming and

Schlichting streaming.

Eckhart streaming arises when the amplitude of the sound wave becomes attenuated with

distance from the ultrasonic source which makes the acoustic pressure decrease over said

distance. The result of this is that a jet of fluid forms on the inside of the acoustic beam in the

direction of acoustic propagation (Figure 2-12).

Figure 2-12- Eckhart streaming [24]

Schlichting streaming, also known as inner boundary layer streaming, occurs because the

acoustic dissipation is larger at the boundary layer than in the bulk of the fluid. The acoustic

velocity has a gradient over the boundary layer that varies from zero at the solid surface to the

free stream value at about 1 𝜇m from the solid surface. When a standing wave form is present

and parallel to the surface, and because of the acoustic dissipation, steady boundary layer

vortices are formed between the nodes and anti-nodes. Because of these vortices, counter

rotating vortices are formed in the bulk of the fluid (Figure 2-13), also known as Rayleigh

streaming or outer boundary layer acoustic streaming.

22

Figure 2-13 Rayleigh streaming [24]

2.3.3 Electrostatic Coalescence

Coalescence is the process when droplets collide with each other with enough force to break

coalescence barriers. These barriers include interfacial tension, electrical double layer effects,

and surface films adsorbed to the droplets surface.

Electrostatic field are used to improve coalescence of water-in-oil dispersions. There are three

primary electrostatic forces: dipolar attraction, electrophoresis and dielectrophoresis.

23

Figure 2-14 The three primary electrostatic forces[11]

- Dipolar attraction: Because water molecules are dipolar they have a tendency to align

themselves in an electrostatic field. The polarized droplets experience attraction forces

between each other which improve the chance for coalescence. Dipolar attraction forces

are proportional to the square of the electric field strength, the sixth power of the drop

radius and inversely proportional to the fourth power of the drop center to center

distance. This means that the dipolar attraction forces are most effective in high water

content dispersions (large droplets) and less effective in low water content dispersions

(small droplets)[11]

- Electrophoresis: The movement of charged droplets within a uniform electrostatic field.

When the movement of droplets is increasing, the probability of droplet collisions

resulting in coalescence gets higher.[11]

- Dielectrophoresis: The movement of polarized droplets in a non-uniform field with the

movement toward the convergence of the field.[11]

The electrostatic fields can be induced in several different ways. These include AC-fields,

DC-fields, a combination of AC and DC.

24

AC fields only rely on the dipolar attraction force and are therefore only effective in bulk

water removal when the water content is water content is high. Compared to AC-fields, DC-

fields offer a superior coalescence performance since the effect of electrophoresis can be

utilized. The drawback is that the use of DC-fields will induce galvanic corrosion currents

if the medium is conductive. When the two field types are combined, the streaming fluid is

first subjected to an AC-field for bulk water removal and the to the DC-field for removal of

the remaining water droplets.

2.4 FLOW METERING

2.4.1 Coriolis Flow meters

The Coriolis effect is named after the French mathematician and engineer Gaspard Coriolis.

Coriolis wrote a paper in 1835 where he described the behavior of objects moving in a rotating

frame of reference. In a mass flow meter the Coriolis effect is used to measure the mass flow

rate and density of a liquid or a gas. This is done by measuring the phase shift between two

oscillating tubes. An electromagnetic drive system makes the tubes oscillate in opposition to

each other. They vibrate at their resonance frequency which is determined by the mass and

stiffness of the tubes. Two sensors, one upstream and one downstream of the tubes picks up the

oscillations. When the tubes are empty the oscillations are in phase, but when fluid is flowing

through the inertia of the fluid makes the tubes twist. The Coriolis effect makes the downstream

end of the tube twist ahead of the upstream one leaving the oscillations out of phase (Figure

2-15). The time difference of the phase shift varies linearly with the mass flow rate and the

correct flow rate can be determined by measuring this time shift. The density is determined by

measuring the natural frequency of the tubes. Since the natural frequency of the tubes changes

with mass and the volume of the tubes is constant, a change in density will change the natural

frequency of the tubes. In a Coriolis flow meter the temperature must also be monitored. This

is because the modulus of elasticity changes with temperature which changes the stiffness of

the tubes. When the stiffness changes the natural frequency also changes, but since the

temperature is measured the changes in stiffness can be corrected for. The mass flow rate can

be calculated by Equation ((2-15))[25]

25

�̇� =

𝐾𝑢 − 𝐼𝑢𝜔2

2𝐾𝑑2 𝜏 (2-15)

Where:

𝐾𝑢= Stiffness of the tube

𝐼𝑢= Inertia of the tube

𝐾= Shape factor

𝑑= Diameter of the tube

𝜔= Vibration frequency of the tube

𝜏 = Time lag

Figure 2-15 Coriolis effect measurement principle[26]

2.5 PRESSURE MEASUREMENT

There are several reasons why pressure measurement is a crucial part of experimental setups.

Safety from accidents like pipe burst and ruptured tanks, performance of pumps and degradation

of filters can be evaluated by measuring pressure. Also, pressure is an important parameter to

measure during experiments.

2.6 ULTRASONIC TRANSDUCERS

The ultrasonic transducer converts electric energy to mechanical energy in the form of sound.

The active element of the transducers used during experiments is a piezoelectric transducer. A

26

piezoelectric element will accumulate an electric charge in response to applied mechanical

stress. For the piezoelectric element in the ultrasonic transducer the opposite is true, this is

called the reverse piezoelectric effect[27].

The ultrasonic transducer is excited by a negative spike excitation pulser. The pulser sends a

short electrical pulse, the pulse width is in the range of 0.1 to 4 microseconds. One drawback

of using spike excitation compared to a square wave is a loss in signal amplitude[28].

2.7 EXPERIENCES FROM THE PREVIOUS TEST LOOP

In the fall of 2016 there were conducted some experiments to determine the efficiency of the

current holding tank in the test hall (Figure 2-16). In summary, the efficiency was too poor to

conduct experiments for any length of time. At high water cuts and flowrates, oil droplets

dispersed in water would contaminate the flow of water. But the biggest problem was the

formation of stable emulsions in the test loop. These emulsions would build up in the holding

tank and contaminate both water and oil outlets. The emulsion layer could also be seen as a

lighter layer between the oil and water layers. At high flow rates, the emulsions would build up

to critical level in less than one minute and the maximum time an experiment could be

conducted was below one minute. The time it took for the emulsions to break down would limit

the number of experiments that could be conducted in a day. To be confident that the holding

tank was free of emulsions only two experiments could be conducted each day.

27

Figure 2-16 Current holding tank spring 2017[29]

When running experiments at high water cuts another problem occurred regarding the control

of flow rate from the pumps. This can best be seen in Figure 2-17. Here we can see that for a

water cut of 90% the rate of change of system curve is much higher than the rate of change at

50% water cut. This means that the oil pump would have to operate at a broader range of

frequencies than the water pump at high water cuts. The response time of the control system

and the pump was to slow to respond to changes in flow rate which led to backflow and

oscillations around the desired flow rate.

28

Figure 2-17 Pump performance curve at different frequencies

2.8 LABVIEW

LabView is a graphical programming language developed by National Instruments. LabView

consists of two main parts, the front panel and the block diagram. The front panel is a graphical

user interface where the user can monitor different processes like flow measurements,

temperature and pressure. The front panel is also used to control different aspect of the process

using switches and icons. The block diagram is used for programming. Since LabView uses a

graphical programming environment, no prior experience with more common programming

languages are necessary. Programming in LabView is done by dragging and dropping different

icons on the block diagram and the data flows from icon to icon according to how they are

programmed. In this setup LabView is used both for data acquisition and control. Parameters

that are currently monitored are flow, pressure and temperature.

29

3 PRESENTATION OF THE TEST LOOP

In early 2017 a second floor was built in the test hall at PTS to allow for room to build the

compact separation test loop. The test loop will be on the second floor while the pump manifold

and horizontal holding tank will be on the ground floor. The plan is that construction of the test

loop will take place summer 2017 and completion is estimated to be in August 2017.

Figure 3-1 3D-model of loop

30

3.1 P&ID

- The valves V-3 to V-6 will act as gates and can be opened and closed according to which

pumps are going to be used

- The valves in the manifold are described in section 3.2.4

- The flow meters F-1 and F-2 will measure the flow rate of oil and water respectively

- Valve V-15 is a remotely actuated butterfly valve and will be used to create dispersions

in the multiphase flow, this is to see how dispersions will affect separation performance

- DP-1 is a differential pressure transmitter and will measure the pressure drop over the

butterfly valve, V-15

- At the flow visualization section the different flow patterns will be observed and

recorded

- DP-2 and DP-3 are differential pressure transmitters and they will measure the pressure

drop between the inlet of the separator and the water and oil outlets respectively

- At the sampler, samples of separated water will be taken to measure the oil content

- The flow meter F-3 will measure the flow rate of water coming out of the compact

separator

- The valves V-16 and V-17 are remotely actuated and are used to adjust the back pressure

of the system

31

Figure 3-2 P&ID of loop

32

3.2 DESCRIPTION OF EQUIPMENT AND INSTRUMENTATION

Below is a brief description of the equipment that is going to be used in the experimental rig.

3.2.1 Centrifugal Pumps

The pumps in the experimental rig are manufactured by Pedrollo. There are a total of four

pumps in the experimental loop, two high capacity and two low capacity. The reason for this is

to deliver flow rates from about 100 – 1500 l/min efficiently. In the past, there were only two

high capacity pumps and they proved difficult to control when the flow rates were low and the

water cut was either very high or very low. At low flowrates one F40-200A is used for oil and

water while the other is used for water. At high flow rates the F65-200AR is used for water and

the F50-200B is used for oil.

Model Power

[kW]

Q

[l/min] 100 150 200 250 300 400 500 600 700

F40-200A 7.5 H

[m] 55 55 55 54.5 54 52.5 49.5 46 41

Table 3-1 F40-200A Characteristics at 50Hz

Model Power Q

[l/min] 400 600 800 1000 12500 1400 1600 1700

F50-200B 15 H

[m] 52 52 52 50 47 44 40 38

Table 3-2 F50-200B Characteristics at 50 Hz

Model Power Q

[l/min] 400 100 1200 1400 1600 1800 2000 2100

F65-200AR 22 H

[m] 57 56 55 54 53 50.5 47.5 46

Table 3-3 F65-200AR Characteristics at 50 Hz

33

3.2.2 Frequency converters

To achieve the desired flow rates from the pumps the rotational speed of the impeller will be

controlled. This is done by varying the input frequency of the pumps AC-motor. The Vacon

100 HVAC frequency converters receives electrical energy at a fixed frequency and voltage.

The output frequency is converted using pulse width modulation (PWM). The frequency

converters are the Vacon 100 HVAC: 22kW for the F65-200AR, 15 kW for the F50-200B and

7.5 kW converter for each of the F40-200As.

3.2.3 Pump flushing system

As mentioned in section 2.7, stable emulsions would form when running experiments. Bottle

tests with different combinations of water, salt and biocide were conducted to see if there were

some problems with the fluids. It was discovered that when replacing tap water with 3.5 WT%

NaCl distilled water the emulsion problem would go away. The pump houses and impellers of

all the pumps are made of cast iron which is prone to a high level of corrosion if they are not

flushed after use. The flushing system will be comprising of hoses running from the taps on the

bottom of the pumps. The hoses will empty the experimental fluids into a sump were a small

pump can pump them back into the holding tank. When the experimental fluids have been

drained, the pumps can be flushed with fresh water until the operator is confident that there is

no remaining salt in the pumps.

3.2.4 Manifold

The test loop shares common facilities with another flow loop “the Leaky Boy” Therefore a

manifold was constructed to utilize all the pumps for both the new flow loop and the Leaky

Boy. Also, the oil and water can be diverted so that both high and low flow rates can be achieved

for the flow loop without driving the large pumps below their rated minimum flow rates.

The manifold is constructed of PVC pipes, PVC ball valves and PVC fittings. From the small

oil and water pumps the dimensions of the PVC-pipes, fittings and ball valves are DN40/PN10.

For the two larger pumps the dimensions are DN65/PN10 for pipes, fittings and the four ball

valves. The Leaky boy is connected to the manifold via a T-joint and the dimensions for the

PVC-pipes are DN50/PN10. For safety when running experiments on the Leaky Boy, a pressure

gauge indicator has been mounted between valves V-5 and V-6.

34

Figure 3-3 Manifold with pumps

The manifold has four main operation modes:

1. High capacity to the flow loop, The F65-200AR and the F50-200B pumps water and oil

respectively.

2. Low capacity to the flow loop: The F40-200As pump oil and water

3. Water to the leaky boy: One of the F40-200As pumps water

4. Oil to the Leaky Boy: One of the F40-200As pump oil.

To achieve the operation modes the valves must be opened and closed according to Table 3-4.

The valve positions are shown in the P&ID for the manifold (Figure 3-4).

35

Valve 1 2 3 4 5 6 7 8

High Capacity O C C O C C O O

Low Capacity C C O C C C O O

Water Leaky Boy C C O C C O C C

Oil Leaky Boy C O C C O C C C

Table 3-4 Manifold main configurations

36

Figure 3-4 Manifold P&ID

3.2.5 Pipes

All piping is made from transparent PVC to visualize flow patterns. The dimension of the pipes

from the manifold until the compact separator will be DN65 with a pressure rating, outer

dimension 75 mm, inner diameter 67.8 mm. Since the flow meter dimensions are 2” or DN50,

pipes of corresponding dimensions must therefore be used at the inlets and outlets of the

flowmeters.

3.2.6 Mixing Point

The mixing point is a Y-type mixing point. This type of mixing point has been used in many

experiments regarding horizontal flow. The mixing point was built autumn 2016 to try to

combat the formation of emulsions in the previous flow loop.

37

Figure 3-5 Mixing point

3.2.7 Valves

3.2.7.1 Ball Valves

The ball valves are used to divert the flow in the desired direction. The ball valves are the

VKDIV PVC ball valves in various sizes ranging from DN40 to DN65.

The two remotely actuated ball valves are the VKDIV/CE electrically actuated ball valves, the

size is DN65.

3.2.7.2 Butterfly Valves

The remotely controlled butterfly valve will be mounted directly ahead of the flow visualization

section. When this valve is regulated, droplets of various sizes will be produced and these will

affect the efficiency of the compact separator. This valve will be the FKOV/CE actuated ball

valve, size DN65

All valves are delivered by GPA.

38

3.2.8 Horizontal separator

Figure 3-6 The new Horizontal separator

The efficiency of the old gravity separator was not good enough conduct experiments for the

desired amount of time. Both phases would contaminate each other after a short amount of time.

Therefore, it was decided to purchase a new horizontal separator.

The new horizontal separator uses gravity to drive separation. The size of the vessel was

determined the same procedure described in Chapter 2.3.1. In the calculations, Exxsol-D60 and

3.5 WT% salt water was used as model fluid. The maximum flowrate to allow for separation of

a 150 𝜇m droplet when using these fluids is around 700 l/min and the operating time can be

around three minutes.

The separator is made of fiberglass reinforced polyester with an inside liner of vinyl ester due

to its chemical resistance and low permeability. The separator has a total length of 5.5 meters

and an inner diameter of 1.2 meters. The effective separation length of the separator is from the

closest 75 mm inlet to the 90 mm water outlet of the separator. This length is about 4.4 meters

and is an important factor when determining the efficiency of the separator. The water and oil

outlets are separated by a 740 mm high weir plate.

39

Figure 3-7 Section view of the weir plate

between the water outlet to the right and the oil

outlet to the right

To dispose of flammable fumes from the oil there is a 110 mm PVC outlet on the top of the

tank. When the tank is filled with oil, the suction hose must be connected at all time and the

suction pump must be running 24/7. On the side of the tank there are two manholes with

Plexiglas covers. Here the separator can be entered for cleaning and, during experiments, the

separation between oil and water can be observed.

40

3.2.9 Flow Meters

In the future, the plan is to use an oil with a higher viscosity than the present one. Since the old

turbine flow meters can only measure flow rates accurately at low viscosities it was decided to

buy new flow meters that can handle higher viscosities. The new flow meters are the

Micromotion F200 Coriolis mass flow meters. In addition to measure flow, the flow meters

can also measure density and temperature. The advantage of density measurement is that it can

be monitored when one continuous phase has been contaminated by the other one due to poor

separation in the horizontal separator.

Figure 3-8 3-D model of Micro Motion F200[30]

The flow rates will be measured by two flow meters. Two of the flow meters are up stream of

the compact separator, one will measure the flow rate of oil and the second will measure the

flow rate of water. The third flow meter will be downstream of the compact separator and it

will measure the flow rate at the water outlet of the compact separator

Model Line Size Nominal flow rate Maximum Flowrate

[mm] [l/min] [l/min]

F200 DN50 869.33 1451.67

Table 3-5 Volume flow rate for the Micromotion F200, at nominal flow rate the pressure loss is 1 bar across the

meter[31]

41

Performance Specifications

Mass flow accuracy ± 0.20% of rate

Volume flow accuracy ± 0.20% of rate

Mass flow repeatability ± 0.10% of rate

Volume flow repeatability ± 0.10% of rate

Density accuracy ± 0.002 g/cm3

Density repeatability ± 0.001 g/cm3

Temperature accuracy ± 1°C 0.5% of reading

Temperature repeatability ± 0.2 °C

Table 3-6 Performance specifications for the Micromotion F200[31]

3.2.10 Pressure Transducers

3.2.10.1 General Electric PTX Pressure sensor

. The General electric supplied pressure sensors are the PTX 5072-tc-a1-ca-h1-pa from

the UNIK 5000 pressure sensing platform. The transducer is a piezo electric type that

converts pressure into an electric charge. The sensor has an operating range of 0-16 bar

and its 4-20 mA output is according to the manufacturer proportional with applied

pressure[32].

PTX Pressure Sensor Unit

Input range 0-16 bar

Output range 4-20 mA

Accuracy ±0.2 %

Table 3-7 PTX pressure sensor characteristics[32]

42

3.2.10.2 Sitrans P310

To measure the differential pressure over the butterfly valve and the water and oil outlets of the

compact separator, the Sitrans P310 pressure transmitter will be used. The transmitter is made

by Siemens and it uses four piezo-resistors fitted on a diaphragm to measure pressure[33].

3.2.11 Temperature

The temperature will be measured using the built-in temperature sensors of the Coriolis flow

meters and the specifications can be found in table Table 3-6.

3.3 NATIONAL INSTRUMENTS USB 6009 DAQ

The data acquisition device is the interface between the sensors and the computer. The NI USB-

6009 has 8 single-ended analog inputs with an input range of ± 10.4 differential inputs and 2

analog outputs. In this setup, the USB- 6009 is both used for control of the pumps and

acquisition of sensor telemetry. The device converts voltage and current signals into binary with

a resolution of 13 bits for the analog inputs. The analog outputs have an output range of 0 to 5

V and a resolution of 12 bits.[34]

3.4 EXPERIMENTAL FLUIDS

3.4.1 Exxsol-D60

The oil use during experiments is the Exxsol-D60 de-aromatized hydrocarbon fluid. Exxsol-

D60 is composed of C-10 to C-13 n-alkanes, iso-alkanes and cyclics, and its aromatic content

is below 2%.[35]

3.4.2 Salt Water

A 3.5 WT% NaCl and distilled water will be used for the water phase.

3.4.3 Biocides

The biocides are used to try to combat the buildup of microbes in the holding tank. The “IKM-

C33” was added to the tank in the spring of 2016. Originally 1.8 liters of IKM-C33 was added

to a total of 5 𝑚3 liquid. But since then the water in the tank has been replaced, the solution of

IKM-C33 is unknown at this point. The use of IKM-C33 has not been successful and the current

holding tank has been emptied and cleaned twice. Therefore “Bio-protect-2” has been tested

43

spring 2017. The active component in Bio-protect-2 is glutaraldehyde which have several

modes of action to combat bacteria [36]. 2.5 liters of Bio-protect-2 was added to 5 𝑚3 of liquid.

after two months bacteria have started to build up in the tank.

3.4.4 Fluid Properties

Density

[𝐤𝐠/𝐦𝟑]

Viscosity

[Cp]

Interfacial tension

[𝐦𝐍/𝐦]

Oil with IKM-C33 and Bio protect 2 786.39 1.60

27.46 (±1.72)

3.5 WT% NaCl and distilled water 1022.38 1.16

Table 3-8 Fluid properties at 17 °𝐶

44

45

4 ULTRASONIC SEPARATION EXPERIMENTS

The ultrasonic separation experiments have been conducted in cooperation with Chenxi Hong.

The experiments aim is to see if acoustic waves can be used to increase the separation

performance by manipulating the migration of droplets thereby increasing their coalescence

using acoustic fields.

4.1 EXPERIMENTAL EQUIPMENT

4.1.1 Transducers

The ultrasonic transducer used in these experiments are the Panametrics X1020 100 kHz and P

V103 1 MHz contact transducers. Both transducers are piezo-electric and are used for

nondestructive testing and inspection of metallic and non-metallic components[37].

4.1.2 Panametrics Model 5058PR Pulser Receiver

The pulser drives the transducer by sending an electric pulse that is converted into mechanical

energy in the transducer. The pulse type of the model 5058PR is a negative impulse with a

range from -100 V to – 900. The pulse rise time of less than 40 ns at the voltage currently

employed[38].

4.1.3 RK156BH Ultrasonic bath

The ultrasonic bath used in the experiments is the Bandelin Sonorex super. It has an output

frequency of 35 kHz. The ultrasonic peak output is 860 W and the nominal output is 215 W.[39]

4.1.4 Beaker

For the experiments with the Panametrics transducers, a test beaker was constructed in the

workshop. The is made of aluminum with acrylic sides so that the separation process can be

observed and recorded. The beaker has following dimensions: height 60 mm, width 60 mm and

and a depth of 50 mm. The capacity is 1.8 dl.

46

Figure 4-1 Test beaker

4.2 EXPERIMENTAL

4.2.1 100 kHz and 1 MHz Ultrasonic Transducer

The transducer was connected to the model 5058PR pulser/receiver and clamped to the test

beaker. The pulser/receiver was set to -400 V which corresponds to an energy output of 170

microjoules and the pulse frequency was set to its maximum setting which is 2000 Hz. This

will give an output power of 0.34 W and about 0.0022 W/cm2 intensity in front of the

transducer. The oil/water mixture was prepared in the Wering blender at 18000 rpm. for 20

seconds and then immediately poured in the test beaker (Figure 4-2). To determine if the

ultrasonic excitation would improve on separation time, pictures were taken of the test beaker

every 15 minute. These pictures were imported into Digimizer where the oil, water and

emulsion layers were measured and compared to each other.

47

Figure 4-2 Experimental setup, the ultrasonic transducer is attached to the side of the beaker with a clamp

(excluded from sketch)

4.2.2 Ultrasonic bath

Several experiments were performed using the ultrasonic bath. For all the experiments, a 400

ml 50% mixture of tap water and Exxsol-D60 was prepared for 30 seconds at 22000 rpm. 60

ml. of the resulting emulsion was then poured into beakers (Figure 4-3). One of the samples,

the control sample, was left on the counter for comparison and the rest was mounted in the

ultrasonic bath (Figure 4-4).

4.2.2.1 Case 1: Effect of irradiation time

The samples were exposed to ultrasonic irradiation for a predetermined number of minutes. At

each interval, one sample was removed from the ultrasonic bath. When the last sample had been

removed from the ultrasonic bath, they all were left on the counter to settle.

48

Figure 4-3- Samples for ultrasonic bath after mixing

Figure 4-4- Samples mounted in ultrasonic bath

4.2.2.2 Case 2: Effect of irradiation in cycles

In this experiment, the samples were exposed to irradiation for 30 seconds and left to settle for

5 minutes and then irradiated again for 30 seconds and left to settle for 5 minutes etc. This was

repeated for 10 cycles. Between each cycle the irradiated sample was compared with the control

sample and a picture was taken.

49

4.2.2.3 Case 3: Effect of heat on separation

During experiments, the temperature in the ultrasonic bath would increase as the experiment

went along. In one experiment, it was measured that the temperature increased from 30 °C to

47 °C.

Two experiments were conducted, one where the temperature was held at a constant

temperature of 30 °C and a second experiment at 50 °C. Two samples were prepared. One was

mounted in the ultrasonic bath and would experience both heat and irradiation. The second

sample was mounted in a thermal bath and would only experience heat. The experiments would

run for 45 minutes and when they were completed, the samples were removed from the baths

and compared to each other.

50

51

5 RESULTS

5.1 CHARACTERISTICS OF FLUIDS

5.1.1 Fluid Properties

The viscosity of the oil was measured using a capillary viscometer and the density was

measured using a pycnometer. The results can be seen in Table 5-1 Fluid properties

Fluid Density

[𝐤𝐠/𝐦𝟑]

Viscosity

[𝐜𝐏]

Fresh Exxsol-D60 794 1.337

Exxsol-D60 from holding tank 789 1.348

Distilled water 986 0.917

Distilled water with 3.5g NaCl/100 ml 1037 1.149

Table 5-1 Fluid properties

The interfacial tension was measured using the pendant drop test

Sample Temperature

[°𝐂]

Interfacial tension

[𝐦𝐍/𝐦]

Exxsol-D60 + distilled water 20 31.65

Exxsol-D60 + 3.5 g NaCl/ 100 ml distilled water 20 31.43

Oil from holding tank + distilled water 20 30.57

Exxsol-D60 + IKM CC-33 (0.25ml/100ml) 20 36.03

Table 5-2 Interfacial tension

5.1.2 Beaker, bottle tests

The bottle tests were conducted to investigate if the fluids had an impact on the formation of

stable emulsions. Five different combinations of fluids were investigated.

When using oil from the holding tank and tap water, a stable emulsion would form (Figure 5-1).

It would take six hours for the emulsion to break down. When adding salt to distilled water

(3.5% salinity) no stable emulsions would form. This can be seen in Figure 5-2 to Figure 5-5,

the two phases are separated in all these combinations. From these figures, it can also be seen

that there are droplets dispersed in both continuous phases. I would take several days for these

droplets to separate. The biocides did not seem to have an effect on emulsion formation.

52

Figure 5-1 Oil from separator

mixed with distilled water

Figure 5-2 Oil from separator

mixed with 3.5 WT% NaCl

Figure 5-3 Exxsol-D60+ oil

red and 3.5 WT% NaCl

Figure 5-4 Exxsol-D60+3.5WT%

NaCl=+IKM-C33

Figure 5-5 Exxsol D-60+3.5WT

NaCl+ Bioprotect-2

5.2 HORIZONTAL SEPARATOR PERFORMANCE

The performance of the new horizontal separator was calculated using the procedure described

in section 2.3.1. For the first case the properties of are Exxsol-D60 and 3.5 WT% NaCl solution

are used in the calculations.

5.2.1 Case 1 Exxsol-D60 and salt water

The maximum flow rates for the new horizontal separator to separate 150 micrometer droplets

is 681 l/min for water and 707 l/min for oil. At these flow rates the retention time for oil-in-

water is 221 seconds and 193 seconds for water-in-oil.

53

Figure 5-6 Separator performance for 3.5 WT% NaCl water droplets in Exxsol-D60

54

Figure 5-7 Separator efficiency for Exxsol D-60 droplets in 3.5 WT% NaCl water

5.3 ULTRASOUND

5.3.1 Effect on Separation Using Panametrics Transducers

The results from the ultrasonic transducer experiments can be seen in Figure 5-8.

5.3.1.1 100 kHz Transducer

The rate of separation in the first 15 minutes is the same for the 100 kHz transducer as for the

control sample. At the end of the experiment, the emulsion layer of the irradiated sample is

around 3 mm thinner than the emulsion layer of the control sample.

5.3.1.2 1 MHz Transducer

There is a big difference between the two samples irradiated with the 1 MHz transducer. In the

first 45 minutes sample 1 has a larger separation rate than the other samples. After 45 minutes

the separation rate of sample 1 is the same as the control samples. Because of the high separation

rate of sample 1 in the first 45 minutes it has the highest degree of separation at the end of the

experiments. Sample 2 has the same separation rate as the control samples in the beginning of

the experiment, but after 180 minutes the separation rate decreases. At the end of the experiment

sample 2 has the least degree of separation.

55

Figure 5-8 Separation performance of the Panametrics transducers

5.3.2 Ultrasonic Bath

5.3.2.1 Case 1, Irradiation time 15, 30 and 45 minutes

The samples that had been radiated for 15 and 30 minutes did not show any sign of increased

separation compared to the control sample. Instead the ultrasonic irradiation seems to have

worsened the separation. The sample that had been radiated for 45 minutes is more separated

than the ones that was radiated for 15 and 30 minutes, but still not as separated as the control

sample. The samples were observed while settling on the counter in room temperature. The

control sample (Figure 5-9) had the best degree of separation, here there is a clear distinction

between the oil, emulsion and the water -layer. The irradiated samples did not show any

accelerated separation time, instead the separation rate seemed to have slowed down due to the

ultrasonic irradiation. Figure 5-10 and Figure 5-11 shows that there is no distinct water layer

after irradiation and a total settling time of 50 minutes .The sample that had stayed in the bath

for 45 minutes (Figure 5-12) had the best separation of the radiated ones, but this may be

because the water in the ultrasonic bath had heated from room temperature to 31°C.

56

Sample irradiation

time [minutes]

Settling

time [mm]

Oil layer

thickness

[mm]

Emulsion layer

thickness [mm]

Water layer

thickness [mm]

Control sample

0 0 37,5 0

56 7,4 25,1 5.0

156 12,3 13,2 11,6

288 18,4 0 20,5

15

0 0 34,9 0

56 3,9 29,6 1,3

156 9,3 23.0 1,9

288 13,3 20,6 2,7

30

0 0 37,6 0

56 4,1 32,6 1,3

156 11,1 25,7 1,5

288 14,8 22,6 1,3

45

0 0 35,8 0

56 3,6 29,5 2,7

156 11,7 21,3 2,3

288 15,5 16,2 4,3

Table 5-3 Case 1, Irradiation time 15, 30 and 45 minutes

57

Figure 5-9- Control sample after 50 minutes settling

time

Figure 5-10- 15 minutes of ultrasonic irradiation,

total time 50 minutes

Figure 5-11- 30 minutes of ultrasonic irradiation,

total time 50 minutes

Figure 5-12- 45 minutes of ultrasonic irradiation,

total time 50 minutes

After five hours, the emulsion layer of the control sample was completely separated. The

irradiated samples still have an emulsion layer present (Figure 5-13).

58

Figure 5-13- Control sample, 15, 30 and 45 minutes of irradiation

5.3.2.2 Case 1, Irradiation time 5, 10, 15 and 45 minutes

After an irradiation time of 5 minutes and a total settling time of 9 the sample has a visible oil

layer compared to the control sample. The sample that was irradiated for 10 minutes (total

settling time 14 minutes) also had a larger oil layer compared to the control sample, but it could

be observed that water droplets dispersed in the oil. At an irradiation time of 15 minutes (total

settling time 20 minutes) the oil layer is larger than the control sample, but also here there are

water droplets dispersed in the oil. For the last sample that had been irradiated for 45 minutes

(total settling time 50 minutes), the oil layer was smaller than the oil layer of the control sample.

For this sample, the water layer was also observable, but it was smaller than the water layer of

the control sample and it was more difficult to distinct were the layer between the two phases

was.

The samples were also compared after a total settling time of 126 minutes (Figure 5-14)

Figure 5-14- Samples side by side after 126 minutes. From the left: control sample, 5, 10, 15 and 45 minutes

irradiation samples

59

Sample

Irradiation time

[minutes]

Total settling

time [minutes]

Oil layer

thickness

[mm]

Emulsion layer

thickness [mm]

Water layer

thickness

[mm]

Control sample

9 - 35.0 1.6

14 1.4 33.0 2.50

20 2.4 31.7 3.1

50 3.4 28.9 3.6

56 4.1 28.1 3.3

120 9.3 19.9 8.0

5 9 2.7 32.4 1.0

56 7.1 24.3 4.0

120 10.2 16.8 8.8

10 14 1.4 32.1 1.8

56 6.0 27.9 2.6

120 9.1 23.1 3.5

15 20 3.9 28.3 3.0

56 8.0 23.3 3.0

120 10.4 20.6 3.2

45 50 2.9 30.7 3.4

56 4.7 28.5 4.2

120 9.5 22.3 5.5

Table 5-4- Layer thickness of the 5, 10, 15 and 45 minute samples at different time intervals

60

5.3.2.3 Case 1, Irradiation time 3, 5 and 10 minutes

After 40 minutes of total settling time, all the irradiated samples had a thicker oil layer than the

control sample. After 150 minutes and for the rest of the experiment the control sample has the

best degree of separation, the differences between the irradiated samples can be seen in Table

5-5. After 307 minutes the control sample has completely separated. For the irradiated samples

the emulsion layer was still present (Figure 5-15). This layer is difficult to distinguish from the

water layer.

Figure 5-15- Samples (From left to right: Control, 3, 5, and 10 -minutes) after 307 minutes, note that the

control sample is completely separated while there is still an emulsion layer in the irradiated samples

61

Sample

Irradiation time

[minutes]

Total settling

time [minutes]

Oil layer

thickness

[mm]

Emulsion layer

thickness [mm]

Water layer

thickness

[mm]

Control sample

10 - 36.9 -

13 0.3 36.0 1.1

19 0.7 35.1 1.9

40 1.7 32.3 3.1

150 10.1 18.2 9.4

203 12.5 12.4 12.9

307 17.0 2.9 18.4

353 19.2 0 20.7

3

10 0.9 32.9 0.5

40 2.5 30.0 2.3

150 7.6 22.9 3.8

203 10.7 21.6 2.9

307 14.0 18.8 2.1

353 14.7 18.7 2.0

5

13 1.8 34.9 -

40 3.5 30.6 2.4

150 7.7 25.6 3.4

203 10.8 23.2 2.9

307 14.0 21.7 1.7

353 15.4 20.6 1.4

10

19 2.3 30.4 1.3

40 5.9 28.0 2.7

150 9.9 23.6 2.6

203 10.4 22.6 2.8

307 13.8 21.6 1.4

353 14.3 19.6 2.4

Table 5-5- Layer thickness of the 3, 5 and 10 minutes irradiated samples at different time intervals.

62

5.3.2.4 Case 2: Effect of Irradiation in Cycles

The control sample had a better degree of separation than the irradiated sample. Both the oil

layer and the water layer for the control sample had a better separation than the irradiated one.

After 10 radiation cycles, when observing the oil layer, it could be seen that there were water

droplets mixed with the oil.

Figure 5-16- Control sample and irradiated sample, the oil layer of the irradiated sample is less transparent

than the oil layer of the control sample

63

Sample Cycle Oil layer

thickness [mm]

Emulsion

layer

thickness

[mm]

Water layer

thickness [mm]

Control sample

1 1,5 34,1 0,0

2 2,6 32,5 1,6

3 3,0 29,3 2,1

4 2,9 31,0 2,3

5 4,1 29,2 3,2

6 3,9 29,5 3,0

7 5,4 26,9 3,2

8 6,3 26,2 3,6

9 6,8 25,5 4,4

10 7,4 24,7 4,6

Irradiated sample

1 0,0 36,5 0,0

2 1,3 34,4 1,1

3 2,0 33,3 1,2

4 2,3 31,9 1,7

5 2,4 31,7 1,9

6 2,1 32,5 1,5

7 2,1 33,0 2,1

8 2,6 31,9 2,3

9 4,0 30,8 2,7

10 3,2 31,0 2,9

Table 5-6 Effect of Irradiation in Cycles

64

5.3.2.5 Case 3: Effect of Heat on Separation Performance

At the beginning of the experiment the emulsion layer of the sample set for irradiation was

measured to be 35.8 mm and the emulsion layer of the control sample was measured to be 35.2

mm. After 45 minutes the samples were measured again. For the irradiated sample the oil layer

was measured to be 6.2 mm. and the emulsion layer was measured to be 29.6 mm. There was

no visible water layer for the irradiated sample. The oil layer of the control sample was

measured to be 8.3 mm, the emulsion layer 20.6 mm. and the water layer 6.4 mm. The oil layer

of the irradiated sample was not as transparent as the oil layer of the control sample.

Figure 5-17- Control sample and irradiated sample after 45 minutes.

65

6 DISCUSSION

6.1 FLOW LOOP PROJECT

The design and assembly of the pump manifold was the first task that was conducted to

contribute to the flow loop project. After the manifold was completed, the planning for the rest

of the loop started. The main contributions to the planning are:

- Pre-design of the new holding tank

- Selection of instrumentation, pipes and fittings

- Contact with suppliers and vendors

- Construction of a 3D- model and P&ID of the rig

According to the time-schedule the construction of the rig should start in the beginning of May

and completion was set to the end of May. Due to long delivery times on parts, completion has

been delayed to the end of August.

The length of the separator was limited to the allotted space in the test hall and fluid properties

from section 3.4.4 was used to determine the maximum flow rates that could be achieved

without contamination.

The bottle tests show that the inclusion of salt in the water solves the problem of stable

emulsions during experiments, but there is still a problem regarding microbial formation in the

holding tank.

6.2 ULTRASONIC TRANSDUCERS

6.2.1 Panametrics Transducers

The separation efficiency of the Panametrics transducers is not better than the efficiency

expected using only gravity. These transducers are designed for NDT applications and do not

offer the output power that is needed to manipulate a droplet. In [40], the output power was 40

W and in [41] the intensity was 35 W. Both these experiments use an output power that is more

than 100 times larger than the output power of 0.34 W that was used in the experiments

described in section 4.2.1. Also, in [40], the dimensions of the sample container was different

than the one used in these experiments. In this experiment, they used a microfluidic cell (Starna

66

48-Q-0.01) with an interior width of 8 mm length of 0.1 mm and height of 38 mm. This means

that the power output of the ultrasonic transducers in our experiment was more attenuated than

the the one used in [40].

6.2.2 Ultrasonic bath

None of the experiments show that the degree of separation will increase when using the

ultrasonic bath as an acoustic separation device. Contrary, for all the samples that was irradiated

the separation time increased when compared to the control sample. The separation that had

taken place was because of heat and not due to irradiation. When the samples were left on the

counter to settle, the irradiated samples had a lower rate of separation than the control sample.

This is an indication that irradiation makes the droplets smaller.

In [42], an ultrasonic bath is used to create emulsions. This bath has a frequency of 22 kHz and

a power output of 120 W, in comparison the bath used in the experiments described in section

4.2.2 has a power output of 215 W and a frequency of 35 kHz. In [42], it is stated that droplets

are formed due to cavitation in the liquid-liquid interface. When the cavitation bubble implodes,

the shockwave tare parts of the droplets in vicinity of the collapsing cavity.

6.3 SOURCES OF ERROR

- The oil used under the experiments was taken from the holding tank in the test hall. At

the time the ultrasonic experiments were conducted, some other experiments were going

on in the test hall where the oil in the holding tank was circulated. The oil that was

collected from the holding would have different appearance if it was collected on a day

when experiments were running in the test hall than on days when no experiments were

running. This would affect the emulsion that was mixed in the blender. It could have

been tried to use oil from the laboratory, but at the time the experiments were conducted,

this oil was depleted.

- To be able to create an emulsion that could separate in a reasonable amount of time tap

water was used, the properties of tap water may change from day to day. This can also

influence separation

- The separation efficiency was determined by measuring the thickness of the liquid-

layers. There is a difference in the refractive index between the beaker materials and the

67

liquids. Also, the refractive index is different between the liquids. This can influence

how the the thickness of the liquid-layers is perceived by the camera

68

69

7 CONCLUSIONS AND RECOMMENDATIONS

The primary goal of this project was to contribute in the planning of the new experimental test

rig. Piping and fittings has been ordered. It is expected that a re-supply of PVC parts is needed

as the rig is being constructed due to uncertainties in the early stages of the planning. The flow

meters and the holding tank has also been ordered.

The results show that saline water eliminates the formation of stable emulsions during

experiments. There is still a problem with bacterial formation in the tank and it should be

investigated what can be done to solve this problem.

The ultrasonic experiments did not show any increase in separation performance. Still, the

concept has been proven in other studies and further studies would be interesting. It would be

interesting to see if separation can be enhanced inside a pipe of realistic size or if the acoustic

intensity needed would have to be so great that cavitation would occur on the pipe wall and in

the liquids close to the pipe wall. In these studies it should also be assessed at what pressure

cavitation would stop occurring.

70

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[17] B. Grassi, D. Strazza, and P. Poesio, "Experimental validation of theoretical models in two-phase high-viscosity ratio liquid–liquid flows in horizontal and slightly inclined pipes," International Journal of Multiphase Flow, vol. 34, no. 10, pp. 950-965, 2008.

[18] A. Abubakar, Y. Al-Wahaibi, T. Al-Wahaibi, A. Al-Hashmi, A. Al-Ajmi, and M. Eshrati, "Effect of low interfacial tension on flow patterns, pressure gradients and holdups of medium-viscosity oil/water flow in horizontal pipe," Experimental Thermal and Fluid Science, vol. 68, pp. 58-67, 2015.

[19] A. Faanes, "Subsea Separation," ed, 2015.

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[21] M. Bothamley. (2017, 22.05). Quantifying Oil/Water separation Performance in Three-Phase Separators.

[22] A. I. Abdel-Fattah, "Acoustic Downhole Three-Phase Separation Method in Oil Field Applications," 2016.

[23] T. Leong, L. Johansson, P. Juliano, S. McArthur, and R. Manasseh, "Ultrasonic Separation of Particulate Fluids in Small and Large Scale Systems: A Review," in Ind. Eng. Chem. Res. vol. 52, ed, 2013, pp. 16555-16576.

[24] M. Wiklund, R. Green, and M. Ohlin, "Acoustofluidics 14: Applications of acoustic streaming in microfluidic devices," Lab on a Chip, vol. 12, no. 14, pp. 2438-2451, 2012.

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73

APPENDIX A: RISK ASSESSMENT

Detaljert Risikorapport

Norges teknisk-naturvitenskapelige universitet (NTNU)

Utskriftsdato:

Utskrift foretatt av:

Side:

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10.06.2017

Espen Olaf Hestdahl

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ID

17022

Status

Dato

Risikoområde

Risikovurdering: Helse, miljø og sikkerhet (HMS)

Opprettet

10.06.2017

Opprettet av

Espen Olaf Hestdahl

Vurdering startet

10.06.2017

Espen Olaf Hestdahl

Tiltak besluttet

Ansvarlig

Avsluttet

Forsøk i laboratorium med Exxsol D-60

Gyldig i perioden:

12/4/2016 - 6/30/2017

Sted:

Laboratorium ved PTS

Mål / hensikt

Redusere risiko ved forsøk hvor Exxsol D-60 vil bli brukt

Bakgrunn

Krav fra NTNU sier at en risikovurdering skal gjennomføres ved forsøk som kan innebære en risiko for helse, miljø og sikkerhet

Beskrivelse og avgrensninger

Exxsol D-60 er et brannfarlig stoff og kan være giftig ved inntak. Exxsol D-60 kan også gi tørr og sprukket hud ved gjentatt eksponering. Før forsøk med dette stoffet begynner, er det derfor viktig å vurdere farer og planlegge sikkerhetstiltak ved bruk og ved uønskede hendelser. Denne risikovurderingen er avgrenset til risiko rundt forsøket og bruk av Exxsol D-60.

Forutsetninger, antakelser og forenklinger

Risikovurderingen er basert på tiltak og farer beskrevet i sikkerhetsdatabladet til Exxsol D-60, samt tenkte scenarioer og tiltak spesifikt for vårt forsøk.

Vedlegg

exxsol-d60-fluid-product-safety-summary-en.pdf

Referanser

[Ingen registreringer]

Detaljert Risikorapport

Norges teknisk-naturvitenskapelige universitet (NTNU)

Utskriftsdato:

Utskrift foretatt av:

Side:

Unntatt offentlighet jf. Offentlighetsloven § 14

10.06.2017

Espen Olaf Hestdahl

2/8

Oppsummering, resultat og endelig vurdering

I oppsummeringen presenteres en oversikt over farer og uønskede hendelser, samt resultat for det enkelte konsekvensområdet.

Farekilde:

Exxsol-D60

Uønsket hendelse:

Huden blir eksponert for exxsol-d60

Konsekvensområde:

Helse

Risiko før tiltak:

Risiko etter tiltak:

Ytre miljø

Risiko før tiltak:

Risiko etter tiltak:

Materielle verdier

Risiko før tiltak:

Risiko etter tiltak:

Omdømme

Risiko før tiltak:

Risiko etter tiltak:

Uønsket hendelse:

Øyne blir eksponert for exxsol-d60

Konsekvensområde:

Helse

Risiko før tiltak:

Risiko etter tiltak:

Ytre miljø

Risiko før tiltak:

Risiko etter tiltak:

Materielle verdier

Risiko før tiltak:

Risiko etter tiltak:

Omdømme

Risiko før tiltak:

Risiko etter tiltak:

Endelig vurdering

Detaljert Risikorapport

Norges teknisk-naturvitenskapelige universitet (NTNU)

Utskriftsdato:

Utskrift foretatt av:

Side:

Unntatt offentlighet jf. Offentlighetsloven § 14

10.06.2017

Espen Olaf Hestdahl

3/8

Oversikt involverte enheter og personell

En risikovurdering kan gjelde for en, eller flere enheter i organisasjonen. Denne oversikten presenterer involverte enheter og personell for gjeldende risikovurdering.

Enhet /-er risikovurderingen omfatter

- Institutt for petroleumsteknologi og anvendt geofysikk

Deltakere

[Ingen registreringer]

Lesere

[Ingen registreringer]

Andre involverte/interessenter

[Ingen registreringer]

Følgende akseptkriterier er besluttet for risikoområdet Risikovurdering: Helse, miljø og sikkerhet (HMS):

Helse

Materielle verdier

Omdømme

Ytre miljø

Detaljert Risikorapport

Norges teknisk-naturvitenskapelige universitet (NTNU)

Utskriftsdato:

Utskrift foretatt av:

Side:

Unntatt offentlighet jf. Offentlighetsloven § 14

10.06.2017

Espen Olaf Hestdahl

4/8

Oversikt over eksisterende, relevante tiltak som er hensyntatt i risikovurderingen

I tabellen under presenteres eksisterende tiltak som er hensyntatt ved vurdering av sannsynlighet og konsekvens for aktuelle uønskede hendelser.

Farekilde Uønsket hendelse Tiltak hensyntatt ved vurdering

Exxsol-D60 Huden blir eksponert for exxsol-d60 Tiltak mot eksponering av Exxsol-D60

Øyne blir eksponert for exxsol-d60 Tiltak mot eksponering av Exxsol-D60

Eksisterende og relevante tiltak med beskrivelse:

Eksisterende tiltal

[Ingen registreringer]

Tiltak mot eksponering av Exxsol-D60

Bruk vernebriller Bruk hansker Bruk tette sko, helst værnesko

Risikoanalyse med vurdering av sannsynlighet og konsekvens

I denne delen av rapporten presenteres detaljer dokumentasjon av de farer, uønskede hendelser og årsaker som er vurdert. Innledningsvis oppsummeres farer med tilhørende uønskede hendelser som er tatt med i vurderingen.

Følgende farer og uønskede hendelser er vurdert i denne risikovurderingen:

• Exxsol-D60

• Huden blir eksponert for exxsol-d60

• Øyne blir eksponert for exxsol-d60

Oversikt over besluttede risikoreduserende tiltak med beskrivelse:

Exxsol-D60 (farekilde)

Detaljert Risikorapport

Norges teknisk-naturvitenskapelige universitet (NTNU)

Utskriftsdato:

Utskrift foretatt av:

Side:

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10.06.2017

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Exxsol-D60/Huden blir eksponert for exxsol-d60 (uønsket hendelse)

Årsak:

Beger veltes eller knuses

Beskrivelse:

Samlet sannsynlighet vurdert for hendelsen:

Sannsynlig (3)

Kommentar til vurdering av sannsynlighet:

[Ingen registreringer]

Vurdering av risiko for følgende konsekvensområde: Helse

Vurdert sannsynlighet (felles for hendelsen):

Sannsynlig (3)

Vurdert konsekvens:

Liten (1)

Kommentar til vurdering av konsekvens:

[Ingen registreringer]

Exxsol-D60/Øyne blir eksponert for exxsol-d60 (uønsket hendelse)

Årsak:

Beger veltes eller knuses

Beskrivelse:

Samlet sannsynlighet vurdert for hendelsen:

Sannsynlig (3)

Kommentar til vurdering av sannsynlighet:

[Ingen registreringer]

Vurdering av risiko for følgende konsekvensområde: Helse

Vurdert sannsynlighet (felles for hendelsen):

Sannsynlig (3)

Vurdert konsekvens:

Liten (1)

Kommentar til vurdering av konsekvens:

[Ingen registreringer]

Detaljert Risikorapport

Norges teknisk-naturvitenskapelige universitet (NTNU)

Utskriftsdato:

Utskrift foretatt av:

Side:

Unntatt offentlighet jf. Offentlighetsloven § 14

10.06.2017

Espen Olaf Hestdahl

6/8

Detaljert Risikorapport

Norges teknisk-naturvitenskapelige universitet (NTNU)

Utskriftsdato:

Utskrift foretatt av:

Side:

Unntatt offentlighet jf. Offentlighetsloven § 14

10.06.2017

Espen Olaf Hestdahl

7/8

Oversikt over besluttede risikoreduserende tiltak:

Under presenteres en oversikt over risikoreduserende tiltak som skal bidra til å reduseres sannsynlighet og/eller konsekvens for uønskede hendelser.

Oversikt over besluttede risikoreduserende tiltak med beskrivelse:

Detaljert Risikorapport

Norges teknisk-naturvitenskapelige universitet (NTNU)

Utskriftsdato:

Utskrift foretatt av:

Side:

Unntatt offentlighet jf. Offentlighetsloven § 14

10.06.2017

Espen Olaf Hestdahl

8/8