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7/30/2019 Andresen, Arntzen, Sjblom - 2000 - Stability of model emulsions and determination of droplet size distributions in
1/12
Colloids and Surfaces
A: Physicochemical and Engineering Aspects 170 (2000) 3344
Stability of model emulsions and determination of dropletsize distributions in a gravity separator with different inlet
characteristics
Per Arild Kjlseth Andresen a,* , Richard Arntzen b, Johan Sjblom c
a Department of Chemistry, Uni6ersity of Bergen, Allegt. 41, N-5007 Bergen, Norwayb K6rner Process Systems a.s, R&D Group, S.P. Andersens 6ei 7, N-7465 Trondheim, Norway
c Statoil A/S, R&D Centre, Rot6oll, N-7005 Trondheim, Norway
Received 4 June 1999; accepted 23 November 1999
Abstract
A model system consisting of an aliphatic oil (Exxsol D60), a commercial surfactant (nonyl-phenol-ethoxylat
Berol 26) and water was examined in a gravity separator loop system. By using a surfactant, we tried to control th
stability of the dispersion and to extract the influence of some of the separator characteristics. The parameters varie
were water cut, pressure drop, volumetric flow rate and inlet device. Initial droplet size distributions (DSDs) wer
obtained and examined for both water- and oil-continuous systems. It was observed that under these experiment
conditions and for these surfactant concentrations (5330 ppm) the oil-continuous dispersion was very unstable an
consequently the DSD measurements were not representative for the whole population of droplets. For thwater-continuous emulsions, variations were found to be dependent on pressure drop, water cut and flow rate. In th
case all the DSD data seemed reliable and accurate. 2000 Elsevier Science B.V. All rights reserved.
Keywords: Gravity separator; Initial droplet size distribution; Model oil; Surfactant and separator characteristics
Nomenclature
dP pressure drop over choke (bar)
NIL normal interface level, as measured by pressure transmitters (m)
total liquid flow rate (m3 h1)Qt
WC water cutp separator efficiency
www.elsevier.nl/locate/colsur
* Corresponding author. Tel.: +47-55-583382; fax: +47-55-589490.
E-mail address: [email protected] (P.A.K. Andresen)
0927-7757/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved.
P I I : S 0 9 2 7 - 7 7 5 7 ( 9 9 ) 0 0 5 1 8 - X
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1. Introduction
New trends will emerge during the next 3 5
years in the petroleum production on the Norwe-
gian Continental Shelf. First of all the amount of
water produced from topside platform separators
will increase mainly due to ageing fields with
water-break-through and a concomitant co-pro-duction of injection water together with the oil.
This high production rate of water will place high
demands on separator efficiency and treatment of
wastewater. In addition to this, many new fields
to be explored in the future will be complicated to
develop since the crude oil produced will contain
large amounts of heavy components like asphalte-
nes and resins. These components will strongly
increase the capability of the crude oil to bind
water, which will increase the retention time in the
separator. These new types of crude oils will also
most likely necessitate an increase in the use of
production chemicals in the separator and in the
transport process.
The effects of these two trends have to be
implemented into the design tools used to opti-
mize topside gravity separators. Tools in use at
present do not have a coalescence model for the
dispersion entering the separator and use only
modified versions of Stokes law [1] of settling
when describing the settling/creaming of droplets
and the subsequent separation of phases. The
influence of higher water cuts and more stabilizingsurface active components enhance the need for a
coalescence model.
There are literature reports on break-up and
coalescence of droplets in oil/water systems, but
to our knowledge these reports are mainly based
on low dispersed fractions and are specific for the
instrumentation used. The apparatus is usually a
vessel with a stirrer implemented as an energy
dissipating device [26] and for obvious reasons,
it is difficult to convert these relations to a large-
scale continuously flowing separator system.The overall coalescence rate of the dispersion
band in a separator is the most important design
criteria. Unfortunately, this rate is a product of
several complex mechanisms like binary coales-
cence, interfacial coalescence and settling/cream-
ing. Each of these mechanisms is further related
to other even more complex processes/factors lik
hydrodynamic micro and macro motions, dropl
size distribution and interfacial components. I
order to understand the overall coalescence ra
one must also understand the interactions b
tween these mechanisms. This makes it difficult t
separate the overall rate into a sum of distin
rates, and is probably the reason why there is ngeneralized coalescence model for concentrate
dispersion with a sound theoretical foundation.
The aim of this work was to carry out exper
mental work in a pilot-scale separator and obta
empirical correlations between separator chara
teristics, initial droplet size distribution (DSD
and upstream conditions (choke pressure drop
By using some of the typical geometric features o
a full-scale separator, the experimental data w
be much more suitable for performing scale-u
and implementation into design tools.
Another weakness with most design tools
that they assume an initial DSD. Based on liter
ture the reason for this is the lack of experiment
data connecting initial DSD and upstream cond
tions. Since the droplet size entering the separato
determines the settling velocity and hence rete
tion time, correct DSD is crucial.
Most authors have examined water/oil system
that coalesce completely within seconds after th
energy-dissipating device is stopped. Alternative
they have examined extraction columns [7,
which have different design and dispersing deviccompared to gravity separators. The experimen
conducted are usually small-scale with regard t
mass flow.
With the objective to carry out tests in a contin
uously flowing separator and to examine the di
persion band along the separator length, it w
desirable to create a dispersion that did not coa
lesce completely within the retention time of th
separator (24 min). It was, however, imperativ
for the system to separate during the model loop
total retention time (
15 min). Outside theboundaries, the result would be no dispersio
band at all or circulation of a stable dispersion
emulsion. Using a pure, classical model oil in
large-scale apparatus will fail to create a dispe
sion band that can be examined without usin
flow rates that are too large with regard to th
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rate region of interest. The reasons why one can-
not use crude oil directly are obvious. First, it is
very cost effective and easy to use an open system
since environmental issues can be maintained.
This is not the case when a crude oil is used.
Secondly, many crude oils may generate stable
dispersions within the model loops retention time
and hence are of no use in a continuous modelloop. A third factor is that one will lose the
advantages of a transparent dispersion. Finally
one should keep in mind that crude oil batches
are not reproducible due to ageing effects.
When using an aliphatic oil containing a surfac-
tant (ppm range) one should get dispersions with
characteristics between stable and unstable. The
final level of stability is also determined by the
flow conditions. By controlling the amount of
surfactant, it is reasonable that one also would
control the separation characteristics, particularly
the dispersion band. Additions of a suitable com-
mercial surfactant will not remove the advantages
of a transparent system or make the system envi-
ronmentally hostile. The surfactant used in this
study is a non-ionic ethoxylated nonyl phenol,
with approximately six EO groups. The commer-
cial name is Berol 26. The reason for choosing
this surfactant is that the group in Bergen has
collected a lot of data on emulsions (w/o) stabi-
lized by this chemical.
2. Experimental
This section is divided into four parts. The first
two describe the chemical system and some pre-
liminary tests performed to establish a concentra-
tion range with regard to the surfactant. The third
part is related to the separator system and how
separation characteristics are extracted. The last
part describes the method used for sampling the
DSD.
2.1. Chemical system
The dispersions were prepared by using Exxsol
D-60 model oil (mixture of aliphatic hydrocar-
bons with chain lengths from C10H22 to C13H28,
transparent) and water with a salinity of 2.2 wt.%.
The inversion point between water- and oil-co
tinuous systems is in the range of WC=0.38
0.40 for flow conditions in our tests. Hence a
tests at [WC=0.16, 0.25 and 0.35] are oil-contin
uous, while tests at [WC=0.5 and 0.84] are w
ter-continuous. Berol 26 (Berol Nobel Industrie
Sweden) was used as w/o surfactant in order t
control the stability. Berol 26 is a commercinonyl-phenol-ethoxylate with approximately s
EO groups (in reality a distribution of EOs).
2.2. Preliminary bottle tests
The objective of the bottle tests was to establis
an emulsion stability range with regard to th
concentration of commercial surfactant. The tes
were very simple and were performed by shakin
bottles with different Berol 26 concentrations an
visually observing the evolution of the wat
phase. With concentrations lower than 100 ppm
no visual differences were observed, and for in
stance with a concentration of 1% a very stab
emulsion was formed.
2.3. Separator system
2.3.1. Separator efficiency
The separator tests were carried out under th
prerequisite that the normal interface level (NIL
should be at fixed values, contrary to standar
operation conditions (for example, keeping a
ceptable water quality for downstream proces
ing). As the model separator has limite
dimensions, the water quality will normally e
ceed standard downstream specifications. It w
also desirable to do both water- and oil-continu
ous runs within the same parameter ranges, whe
one would expect different separator behavio
The system will generally behave more robustly
this prerequisite is disregarded. This howev
made it necessary to define an efficiency based o
combined outlet qualities (Eq. (1)) as the phaqualities are generally interdependent. In norm
separator operation the first term (1WCwa
outlet) is close to 1, and the efficiency is hen
based on the oil quality only.
p= (1WCwater outlet)WCoil outlet (
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Fig. 1. P&ID of the multiphase separator loop.
2.3.2. SystemThe separator system consists of a multiphase
flow loop with a bulk feed gravity separator, two
positive displacement pumps, and a model separa-
tor made in acrylic plastic. Total liquid volume in
the flow loop is approx. 2.4 m3. Fig. 1 shows the
Process and Instrument Diagram (P&ID) for the
loop. Geometry data and explanation of the
figure indices for the model separator are given in
Tables 1 and 2.
The bulk gravity separator is several times
larger than the model, and has consequently alarger operational window with respect to load-
ing. This will give stable feed conditions to the
model. The positive displacement pumps deliver a
stable pressure to the choke valve within their
capacity, and facilitate the experimental work.
The model separator is a pilot-scale first-stage
separator, with a flow distributor (perforated
plate) to remove unwanted channelling and un-
even flow distribution. The levels are controlled
by differential pressure (DP) measurements up-
and downstream of the weir, connected to but-
terfly control valves at the outlets.
In order to investigate the effect of shear within
a cyclone inlet on separation and also the effect of
the liquid outlet height, four inlets were tested as
shown in Fig. 2. Inlet B is a simple 2 bend and
tube, designed for low shear. Inlets C (and D) are
Table 1
Geometry data for model separator in Fig. 1
Symbol/unitParameter Value
Length tan-tan LTT [m] 2.80
ID [m]Inner diameter 0.63
LTW [m] 2.53Length tan-weir
0.55LTP [m]Length tan-perforated plate
HW [m]Height weir 0.25
Table 2
Explanation of indices in Fig. 1
Symbol in Fig. Explanation
1
LCVO NOL [oil] level control valve
LCVW NIL [water] level control valve
Qw Electromagnetic water flow meter
Qo Oil turbine flow meter
P Pressure gauge
CV Choke valve (manual ball valve)1 Weir, height 250 mm from vessel bottom
Perforated distribution plate, 500 mm2
from vessel bottom
3 Inlet device
4 Feed separator, tan-tan length 3 m, inner
diameter 1 m
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Fig. 2. Inlet device geometries used in the tests.
dresen et al. [9]. The technique was developed i
order to examine unstable dispersions with a hig
internal phase in flowing systems. The basic prin
ciple is a fast dilution of the dispersion with th
continuous phase, typically with a dilution rat
of 1:100. Fig. 3 shows the set-up of the measur
ment apparatus. By inserting a sampling tube int
the inlet pipeline, one can withdraw a sampiso-kinetically without subjecting the dispersion t
any dissipating force. Using two magnetic valv
(MV1, MV2) connected to a timer, a controlle
injection of a sample into the dilution tank can b
obtained. Depending on the continuous phase o
the dispersion, the droplets will settle on the bo
tom plate (oil-continuous) or cream onto the to
plate (water-continuous). To prevent the drople
from wetting the plates, the bottom plate w
made of a hydrophobic material (acrylic plasti
and the top plate was made of a hydrophilmaterial (glass). A video camera was mounte
beneath or over the dilution tank and sever
images of droplets were captured and analyzed i
order to extract the DSD. The image analysis too
Image Pro Plus was used to measure the size an
generate droplet size distributions. The smalle
droplets possible to measure are about a few m
since the Brownian force will prevent them from
settling/creaming.
In the experiments, DSDs were extracted from
points 1 and 2 described above. The samplintubes were placed in the middle of the pipelin
and inlet liquid diffuser.
The major weakness of the technique is th
large amount of time consumed in extracting th
DSD. The analysis vessel has to be draine
cleaned and filled up between each experimen
The measurement of the droplet sizes on th
images is also rather time-consuming. The dilu
tion behavior can be performed in two differen
ways, i.e. either in a pure oil phase or alternativel
in an oil phase with the same amount of surfac
tant as used in the experiments. The advantage o
using a continuous phase containing the stabiliz
is that there will be no drainage of surfactant
the interface of the droplets. Such effects migh
accelerate the coalescence of especially larg
droplets.
conventional twin CCI as manufactured by
Kvrner Process Systems. Inlet F is the same twin
cyclone, but with one cyclone blocked at the gas-
and liquid outlets. Thus inlet B represents a low
shear inlet, C and D are reference cases, and F is
a high shear inlet (double load vs. inlet C/D). The
other parameter investigated is the outlet height
of the liquid diffuser; inlets B, D, and F have aliquid exit above NIL, while inlet C has a liquid
exit below NIL.
2.3.3. Sampling
Seven sample points were chosen for character-
izing the separator performance. These were lo-
cated at: (1) 0.4 m upstream from the inlet, (2)
inside the inlet liquid diffuser, (3 5) 0.2 m up-
stream from the weir plate at heights of 0.12, 0.15
and 0.19 m (measured from the bottom of the
vessel), (6) at the water outlet, and (7) at the oil
outlet. These are indicated in Fig. 1.
2.4. Droplet size measurement technique
The technique used for extracting the DSD has
been developed and described elsewhere by An-
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3. Results and discussion
This section is divided into one part concerning
the separator performance and one related to the
droplet size distribution.
3.1. Separator performance
The results showed very high separation effi-
ciency and little variation in the oil-continuous
systems, which indicates that the separator load-
ing was far from the limit for this system, and all
variations were of the same order as the measure-
ment resolution. Fig. 5 shows results typically
found during the experiments. As can be seen, the
major influence in the tests was the effect of Berol
26 in the water-continuous regime.
No significant difference was found between the
various inlets, as shown in Fig. 4. This indicates
that the impact of shear and liquid diffuser height
is less than the resolution of the measurement
technique for the given system. Neither was the
effect of choke pressure drop found significant
within the varied interval. Higher water cuts gave
an increase in separation efficiency, as shown in
Fig. 5. This is in accordance with Refs. [1,10], a
the dispersed fraction decreases with increasin
water cut for water-continuous systems.
The separator performed well for all water-co
tinuous flow rates at Qt=12 m3 h1, but faile
for [Qt=18 m3 h1, WC=50%, 330 ppm Ber
26] and performed poorly (p=0.84) for [Qt=1
m3
h1
, WC=83%, 330 ppm Berol 26].
3.1.1. Separator efficiency
Typical results from the water-continuous sep
rator efficiency tests are shown in Fig. 5. As ca
be seen from the figure, the only significan
parameters found were water cut (amount of di
persed phase) and concentration of Berol 2
Also, the water cut was only a significant param
ter for runs with 330 ppm of Berol 26. The effec
of Berol 26 is obviously to stabilize the oil-in-wa
ter droplets. This surfactant effect is somewh
surprising and will be discussed in more deta
below. The effect of water cut is attributed to th
amount of internal phase required to be tran
ported through the coalescing interface, as su
gested by Refs. [1,10].
Fig. 3. Iso-kinetic injection system for measuring DSD.
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Fig. 4. Water-continuous tests of different inlet types, efficiency versus inlet type. Constant Qt=12 m3 h1.
3.2. Dispersion layer measurements
The sample points inside the separator (points
3, 4, and 5) showed pure phases in at least two
sample points for all oil-continuous tests. This is
caused by the low stability of the system, being
unable to produce a dispersion layer thicker than
the resolution of the sample point (0.03 m). These
results are therefore not discussed further. The
only experiments where the separator performed
satisfactorily, i.e. having all the three sample
points within the dispersion band are shown in
Fig. 6. The linear concentration gradients for the
different systems are shown in Table 3. As can be
seen from the table, the difference in dispersion
layer gradient between systems [water cut 50%,
no Berol 26] and [water cut 83%, 330 ppm Berol
26] is 1.8 versus 2.6 WC% cm1. In Fig. 5,
the difference in separator efficiency for these
cases is 0.99 and 0.84, which probably is the
result of a difference in dispersion layer thickness.
However, the dispersion concentration gradients
suggest the opposite effect; the thickness of the
dispersion layer should be larger with decreasing
slope. This implies that the concentration gradi-
ent of the dispersion layer is non-linear, at least
for the [water cut 83%, 330 ppm Berol 26]-sys-
tem.
The reason for the variance within the calcu
lated concentrations at Normal Interface Lev
(NIL) origins is difficulties with the pressu
transmitter calibrations between runs. Assuming
linear gradient and neglecting all other forces bu
gravity, these values should coincide at WC=0
which is the definition of NIL when using pre
sure transmitters as controllers. The gradient ma
indeed be non-linear and/or discontinuous (ha
ing a discontinuity at a maximum dispersed pha
Fig. 5. Tests of different Berol 26 concentrations, efficien
versus two-way interactions between WC and Berol 26 conce
tration. Constant inlet type D, flow rate Qt=18 m3 h
Pressure drop variations disregarded. This figure also includ
the oil-continuous regime, for comparison.
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Fig. 6. Dispersion layer gradients.
Table 3
Dispersion layer gradientsa
CorrelationBerol 26 (ppm)Water cut Concentration gradient Calculated interception (water fraction at
measured NIL)(WC% cm1)coefficient
0.992 1.8 0.3650% 0
0.996 12.60 0.4484%
0.96684% 2.6330 0.31
a All flow rates are Qt=18 m3 h1.
value), but this cannot explain the large variance
found. The slopes should however be unaffected
by this absolute value at calculated NIL.
3.3. Droplet size distribution
Table 4 shows the experimental set-up and val-
ues for the DSD experiments. The set-up consist
of five parts: Two 23 factorial design (w/o, o/w)
with 330 ppm Berol 26, extended data points forevaluating the pressure drop effect, effect of dif-
ferent inlet devices and the effect of no surfactant
added. The DSDs are in all cases represented as
linear average diameter, which is defined as the
sum of measured diameters divided with the num-
ber of measurements. Although many authors
prefer volumetric or maximal diameter [11], it wa
found that in these experiments a weighting of th
measured values would respond to a large erro
due to the broadness of the distribution and th
limiting number of droplets counted (1000 p
experiment). The volumetric weighting of th
largest droplet would typically represent 30% o
the total volume.
3.3.1. 23 factorial design oil-continuous
The combined effects expressed as interactioterms are relatively small and by neglecting them
one will get a model (Eq. (2)) which explain
89.9% of the total variation in the experiment
data.
d(lin=63+9WC+7Qt7.3 dP (
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The predicted values from the model versus
measured values are given in Fig. 7. The effect of
higher water cut and total flow rate in Eq. (2) is to
increase the linear average drop size while higher
pressure drops will create smaller linear drop size.
The water cut and the pressure drop show effects
that are consistent with theory [12], i.e. higher
internal phase fraction gives larger droplets andhigher shears give smaller droplets. A higher total
flow rate should result in smaller droplets since it
gives rise to a higher shear and the retention time
between the choke and the measuring point (inle
would be less, hence shorter time for coalescenc
to occur.
The reason for this is probably the fact that a
the oil-continuous experiments suffered to som
degree from coalescence in the dilution tank an
this would further increase the experimental erro
to the value of the data variation. This coalecence gave rise to a couple of very large, non-me
surable droplets, and numerous small satelli
droplets. Measurements of these satellite drople
Table 4
Experimental results from the DSD experiments
Qt (m3 h1) DP (bar) Measuring pointWC Berol 26 (ppm) Linear average diameter (mm)
Oil-continuous, 23 factorial design
0.25 33018 787 1
0.25 33018 863 1
5833010.25 7120.25 33012 663 1
18 70.16 1 330 46
7033010.16 318
12 70.16 1 330 41
330 590.16 12 3 1
Water-continuous, 23 factorial design
7 1 330 820.83 18
3 118 3300.83 95
12133017120.83
12 30.83 1 330 102
10133010.5 718
18 30.5 1 330 99
3300.5 12412 7 1330 1220.5 12 3 1
Pressure drop effect
10.5 68330120.16
873300.25 112 0.5
10.5 206120.5 330
1060.83 12 3300.5 1
Inlet de6ice effect
180.16 487 3302, device D
630.16 18 7 2, device B 330
2, device F18 330 4970.16
7 1 0 470.16 18
Effect of no surfactant0.25 5701718
01 2757180.5
7 1 0 212180.83
18 70.83 2, device D 0 227
22902, device D70.83 18
18 7 1 0 2070.83
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Fig. 7. Linear regression line, oil-continuous factorial design.
The combined effects and the pressure dro
effect are relatively small and by neglecting the
one will get a model (Eq. (3)) which explain
83.1% of the total variation in the experiment
data.
d(lin=105.85.8WC11.5Qt (
The predicted values from the model versumeasured values are given in Fig. 8. The effect o
higher water cut, in this case lower disperse pha
fraction, and higher total flow rate sugges
smaller droplets. Both these trends are in acco
dance with common theory [12].
3.3.3. Pressure drop effect
In order to evaluate the pressure drop effe
more precisely, four additional experiments with
pressure drop of 0.5 bar at a flow of 12 m 3 h
were carried out. Fig. 9 displays the results an
the effect of larger pressure drops and low
internal phase fraction is definitely small
droplets. Theory [12] based on the viscosity an
density of dispersed and continuous phase pr
dicts that water droplets in general should b
larger than the oil droplets and this is the opposi
of these results. The coalescence of the large wate
droplets observed for the oil-continuous system
is one possible explanation.
3.3.4. Inlet de6ice effect
Unfortunately these experiments were carrieout with the oil-continuous system and one mu
have the experimental drawbacks in mind. Th
different inlet devices tested are shown in Fig.
and their effects on the linear droplet size a
shown in Table 4. The table indicates very litt
difference in the linear droplet size due to diffe
ent inlet devices. Hence the shear arising from th
different configuration of the inlets does not seem
to be large enough to alter the average diamete
of the droplets.
3.3.5. Effect of no surfactant
Fig. 10 displays the effect of surfactant on th
linear average drop size at a total flow rate of 1
m3 h1 and at 7 bar pressure drop. For oil-con
tinuous systems and experimental condition
given above it seems that addition of surfacta
Fig. 8. Linear regression line, water-continuous factorial de-
sign.
would then give a smaller average diameter than
the actual one entering the separator. The coales-
cence of water droplets is obviously affecting the
results for the oil-continuous emulsions.
3.3.2. 23 factorial design water-continuous
The water-continuous experiments did not suf-
fer from coalescence in the dilution tank and gave
much more accurate values than the correspond-ing oil-continuous experiments discussed above.
This is probably due to the fact that Berol 26
stabilized the oil droplets and this is also in
accordance with Fig. 5 which clearly shows that
the dispersions are more stable in the water-con-
tinuous regime.
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Fig. 9. Average linear diameter versus pressure drop at differ-
ent water cuts.
droplets will increase at the expense of wat
droplets. However at higher surfactant concentr
tions the w/o stability will predominate, which
also experimentally observed.
The experiments with inlet device D and repl
cates without surfactant confirm that the wate
continuous system gives reliable results (227 an
229 mm).Another important factor concerning the use o
surfactants are the ageing of the system due to th
different processes. Especially when working wit
large apparatus and flowing systems open to a
mosphere one cannot discard that the concentra
tion of the surfactant in the two phases w
change with time. The surfactant molecules ca
for instance interact with impurities, biologic
agents degrading the oil phase, forming unwante
by-products or be accumulated in the syste
thereby affecting the bulk concentration an
hence the equilibrium. In the separator system
is possible that a small layer of stable emulsion
formed and accumulated in the feed tank. I
order to create this emulsion one must have
relatively large amount of surfactant; in this ca
]330 ppm since this gave an unstable dispersion
Local regions with higher surfactant concentr
tion than in the bulk can be created when dense
packed droplets coalesce and the interfacial are
is greatly reduced. If these local regions are sub
jected to turbulence, droplets with enough su
gives rise to somewhat larger droplets. On the
other hand the water-continuous systems clearly
show that the surfactant alters the droplets tosmaller sizes. In other words Berol 26 seems to
stabilize the oil droplets. There might be a
straightforward explanation for the findings with
regard to emulsion stabilization at these surfac-
tant concentrations and flow rates. Since the com-
mercially available surfactant will have a
polydispersity in the number of EO units, one can
presume that the molecules with the highest
amount of EO groups will possess the highest
surface activity. A direct consequence of this is
that at low concentrations the stability of oil
Fig. 10. Average linear diameter versus water cut at different Berol 26 concentrations.
7/30/2019 Andresen, Arntzen, Sjblom - 2000 - Stability of model emulsions and determination of droplet size distributions in
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P.A.K. Andresen et al. /Colloids and Surfaces A: Physicochem. Eng. Aspects 170 (2000) 334444
face-active components to create a stable emul-
sion can be formed. The amount of surfactant
consumed in these processes will increase with
time given ageing of the system. Therefore it is
important when using these kinds of systems to
carry out the experiments in a rapid sequence and
hopefully without errors.
4. Conclusions
The main objectives of these experiments were
to establish a model system that performed with
some of the same characteristics as a crude oil
system. It was especially important to achieve
some stability with regard to the oil-continuous
experiments. The use of a commercial surfactant
did not come up with the anticipated results,
which is attributed to the dual and effective na-
ture of the commercial surfactant. In the concen-
tration range selected for the experiments, the
opposite effects occurred. The dispersions in the
oil-continuous experiments were unstable, but the
dispersions in the water-continuous experiments
performed well with the desired stability. The
results from the water-continuous experiments
with regard to the influence of instrument
parameters and flow showed the same trends as
found in earlier work.
In order to obtain more reliable results, a new
type of model oil system with promising resultsregarding stability of the oil-continuous disper-
sions has been established and will be published
soon.
Acknowledgements
Per Arild Kjlseth Andresen would like to ac-
knowledge the technology program Flucha
financed by the Norwegian Research Council
(NFR) and the industry for a Ph.D. gran
Kvrner Process Systems is especially acknow
edged for allowing the experimental work to b
carried out on their gravity separator and wil
ingly sharing their knowledge regarding separato
systems. Richard Arntzen would like to acknow
edge the Mobility Program financed by the No
wegian Research Council (NFR) and Kvrner foa Ph.D. grant.
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