Orimulsion Spill Response R&D
Jump to part | 1 | 2
| 3 |
4 | 5 | of this article series
Part 1 -
What is Orimulsion?
By Paul Gunter, Bitor Europe, Ltd.
The
practical application of emulsion and emulsion
technology is considerable and includes foodstuffs,
pharmaceutical preparations, cosmetics, agricultural
sprays and bitumenous products of which Orimulsion is
one.
Orimulsion is a bitumen-in-water
emulsion comprising 70% natural bitumen (from the
Orinoco region of NE Venezuela) dispersed in fresh
water. It is manufactured in Venezuela and transported
in double-hulled vessels to customers worldwide for use
as a power station fuel or in the heavy industry sector.
The manufacture and marketing of Orimulsion is
undertaken by PDVSA Bitor and its marketing affiliates.
One commonly asked question is why make
an emulsion in the first place? The simple reason is
that the natural bitumen is solid/ semi-solid at ambient
temperatures. The addition of water acts as a carrier
that enables the bitumen to be transported and handled
as a liquid fuel at ambient temperatures.
The surfactant package that is used to
stabilise Orimulsion comprises a commercially available
alcohol ethoxylate (AE) surfactant together with a small
amount of monoethanolamine (MEA). The total amount of
surfactant is < 2000ppm. The AE is similar to those
used in baby shampoo and other down the sink
applications, and monoethanolamine is a common
ingredient and intermediary in the pharmaceutical
industry.
It is important to remember that in
Orimulsion the water is the continuous phase of the
emulsion (CF mousse which is a
water-in-oil emulsion) as this has important
implications in terms of its fate and behaviour
Fate and Behaviour
As with any spill, regardless of whether
it is oil, HFO or Orimulsion, the precise fate and
behaviour will be a function of variables including the
size of the spill and prevailing environmental
conditions. All spills have a sub-surface component and
in some cases this is not just a water-soluble fraction,
the bulk oil may also either disperse or sit below the
surface of the water.
In the case of Orimulsion the micron
sized bitumen droplets are already pre-dispersed in
water and on contact with water they naturally and
rapidly disperse. The effect is very similar to when
emulsion paint is cleaned from paint brushes. In fresh
water Orimulsion would totally disperse but in saline
water some coalescence can occur. If coalescence occurs
to a significant extent then this can lead to the
formation of some tar balls or patches of bitumen.
What causes coalescence and surface
bitumen formation? In salt water the effectiveness of
the surfactant is less than it is in the neat emulsion
(note – less effective not ineffective). In the early
stages of the spill as the droplets are diluting and
dispersing some droplet collisions can occur and some of
these collisions can lead to coalescence. If this
process is repeated enough times then some tar balls or
lumps of bitumen can be produced. Of course, as the
individual droplets disperse and dilute immediately
following the spill then they become far enough away
from other droplets so that collisions and coalescence
and hence bitumen formation will not occur.
As a rule of thumb dispersion would be
expected to be total in fresh water and this may also be
the case in saline water (small spills, continuous
releases /leaks). However it is also possible in saline
water that some coalescence and bitumen may form and in
experiments to date, in open water 90% would tend to
disperse and around 10% may coalesce and form surface
bitumen. The important thing is the equilibrium between
those droplets that disperse and those that coalesce and
this will be discussed below.
It can be appreciated from the foregoing
text that one of the difficulties in evaluating the fate
and behaviour of a dispersed product is how to best go
about this. It needs an approach that is both carefully
controlled and relates to what would happen in reality.
If Orimulsion is released in open water where it is
allowed to disperse then it can, and will predominantly
do so. However, if this natural dispersion is prevented
then coalescence is promoted.
For this reason great care has to be
taken when investigating Orimulsion behaviour in the
laboratory. If Orimulsion is just simply put in a beaker
then of course natural dispersion is prevented and the
equilibrium is shifted towards coalescence. However,
this is not a reflection of what would happen in reality
and the results become an artefact of the experiment.
Such experiments can be useful to
understand the relative importance of some
variables but gaining absolutes is often not
possible. However, there are some laboratory test
protocols that are used to measure dispersant
effectiveness on oil spills, that can also be applied to
Orimulsion. The IFP test is a particularly useful tool
as it allows a degree of dilution during the course of
the experiment. By simultaneously measuring droplet size
data/ coalescence rates and assessing the effectiveness
of dispersion as a function of several variables
(concentration, salinity) valuable information has been
gathered and added to the data base.
Larger scale tests have also been
undertaken – up to 2 tonnes has been released in the
North Sea and hundreds of litres released in experiments
in Nelson Dock in Liverpool and more recently off the
coast of Venezuela. These have all provided valuable
data but rather than providing the answer
they provide an answer to the experimental
conditions prevailing. Given that there are some
variables that are beyond our control (the weather
conditions) then it is better to work in a controlled
environment where many variables can be controlled and
investigated to give a more rounded and thorough
understanding.
In summary, the natural tendency for
Orimulsion is to disperse, although some tar balls or
patches of bitumen may form under some circumstances.
This natural dispersion is what responders try to
achieve when chemically dispersing conventional oil spills.
