An appraisal of mop skimmer technology.
By Peter Ilsley, Founder of OPEC LTD
offers many alternative types such as mop, disc, drum, brush,
belt, tube or weir skimmers.
A World patent was
awarded to Shell international in 1967, for the use
of a continuous belt of material, synthetic or otherwise,
which would remove oil from the surface of water,
by means of adsorption or absorption.
From that time until the formation
of the company - Oil Pollution Environmental Control
Ltd., (in 1980), I, together with two other former
colleagues, developed a "Rope Mop" system.
|Fig 1. Example of two OPEC Mop Skimmers
in operation on an airfield interceptor in the UK
This, utilized a polypropylene material
to form a continuous loop of material, which would float
on the surface of water, at the interface of the oil and
water, to adsorb oil and not water, to remove surface oil
contamination from sea water or fresh water. Other companies
came and went during this time with variations, which failed
for one reason or another. Others have since started up
making versions of this. The technology they employ is still
circa early 1970's. We - on the other hand - have continued
to develop the systems, constantly improving the design
as a result of experience gained in the day to day continuous
operation of our Mop skimmer systems, world-wide. Also during
this time and subsequent periods, various other skimming
systems have evolved as listed above.
2.0 Comparison of OPEC mop skimmers
and other mop skimmers
Two important factors need to be noted:
2.1 The Mop
yarn used by OPEC to produce the mop material has
a very high degree of surface area, due to the network
structure of the special polypropylene base yarn.
This produces a phenomenal surface area, whether it
be for use in heavy oil (viscous) or in light oils
such as gas oil, diesel, Jet fuel, spindle oil, light
to medium lube oil, etc....Other manufacturers use
a much coarser material that does not have the surface
area that the OPEC material has. Also, the construction
of the mop itself is special and we incorporate a
centre tape within the structure (not on the outside)
which gives a much better performance and strength
support. We manufacture two basic types of mop, one
Black and one White. The white mop is deployed when
picking up light oils and the black mop is used for
picking up the heavy oils.
|Fig 2. OPEC Mop Skimmer vertical
subtle differences in the two mop types which make them
so efficient in the oil recovery duty they perform. Also,
because of the tremendous surface area we have, the adsorption
and retention of oil is so much better than any other mop.
Also note that we can produce ready looped mops at the factory,
which can be threaded into the OPEC mop drive/oil extraction
machines, as ready looped mop, so reducing the time spent
in setting up on site, by not having to cut, splice &
join mops on site. This is unique!!
2.2 The mop drive/oil extraction unit
Our range of equipment offers the unique
facility of threading ready looped mop in between the drive
rollers of the "E" Series machines - the whole
range and the same with the OM range. Again this gives two
very important main advantages over competitor’s equipment:
2.2.1 Health & Safety
The fact that OPEC MOP Skimmer Systems
can be set up and deployed on site, without the need for
the drive rollers to be rotating, offers the client a major
advantage of not presenting a potential DANGER to the operatives.
If an operator should accidentally trap his or her fingers
in between the rollers during the threading of the mop,
it can cause serious injury and we are aware of at least
one major claim in Indonesia against one of our competitors.
An operator had his hand crushed by a diesel driven unit,
before they could shut down the engine when his hand was
trapped between the drive rollers.
2.2.2 Ease and speed of equipment
By having ready looped mops ready to
thread through the rollers of the OPEC equipment, it obviates
the need to cut, splice and join - open ended mops. It makes
the job much easier and simpler for the operators, especially
on industrial sites, where mop replacement may be a regular
3.0 Comparison of OPEC mop skimmers
and other skimmer technology
3.1 Belt Skimmers
These are only available as vertical
deployment systems. This seriously limits the effectiveness
of the skimmer, since it is located down through the oil
layer at one very localized location. O.K. for boreholes,
but not lakes lagoons or rivers where oil may be spread
over a wide area, or on an industrial interceptor, which
may have a large surface area. Also the belt skimmers are
prone to limitations in performance due to the presence
of debris. This blocks up the feed of the oil into the V
shaped hopper feed when the oil is scraped off the belt.
This causes any oil removed from the belt to spill over
and fall back into the area from which it has been picked
up. The belt also has a very small surface area compared
to a mop - see notes above and there is a very poor retention
of oil because of the relatively smooth surface which allows
recovered oil to run off - especially the lighter oil range.
Because the belt has to be kept straight,
there has to be a bottom roller attached to the bottom of
the belt. This then means that the belt passes through the
oil on the surface and due to the movement of the belt,
will carry some of the surface oil down with it and displace
it into the water phase. - Not a good idea. Again note there
is a very small contact surface area with the oil.
OPEC Mop skimmers can be deployed vertically
- down bore hole or through access manholes in tanks. With
the use of floating pulleys (or as in the case of permanent
installations in industrial sites, fixed guide rollers)
the mop can be set out with different flow patterns on the
oil/water surface to create surface oil movement. It will
also make a large contact surface area with the floating
oil. As regards to floating debris, - such as dead birds,
wooden logs, tree branches, leaves, packaging materials
rubber gloves etc. If the debris comes into contact with
the mop and is small enough to adhere to it, the worst that
can happen, will be for the debris to be squeezed between
the drive rollers and will drop into the recovered oil container.
The larger items of debris will not adhere to the mop, so
will not affect the operation.
3.2 Drum Skimmers
Basically the same as 3.1 above. Surface
area is small, oil pushed below the surface by drum rotation,
problems with handling debris at the scrape off point.
3.3 Tube Skimmers
area, same problems with debris, small surface area contact.
Same as 3.1/3.2
3.4 Disc Skimmers
small surface area. Localized oil contact and pick as for
3.1-3.3 above. Due to the centrifugal force created by the
rotation of the discs, oil will be ejected from the discs
(even "T" discs), so putting the oil back into
the water phase. Again prone to debris problems, especially
being caught up between the discs, so distorting them and
causing mechanical damage. Also causes a blockage of the
recovered oil to the oil collection in the centre of the
disc skimmer, which can even cause the skimmer to sink.
3.5 Weir Skimmers
Due to the
inherent design, even auto adjusting weir skimmers, will
pick up a lot of free water. Also, very prone to debris
blocking the flow of oil to the weir - depending upon the
location of the support floats. This is particularly apparent
when "sticky" - viscous oil is present, - such
as Bunker "C" fuel oil.
3.6 Brush skimmers
Better than most of the units described
above, but again prone to problems with debris being caught
up in the bristles. Works ok in very viscous oil, but with
light oil, not so good, because the oil readily runs off
the filaments. Not constructed like the mop, with a fibrous
In all cases noted above 3.1-3.6 inclusive. All of these
systems have to be deployed using an oil transfer pump at
all times, no matter what the duty, either emergency spill
response or as industrial fixtures. In the majority of cases
the OPEC mop skimmer systems do not need transfer pumps
to be fitted and if a pump is required, this can be provided
independently by the contractor on spill clean up.
This could be the
road tanker integral pumping system. Also most of
the systems described have to be hydraulically driven,
to allow the skimmer drive - say the rotation of the
drum, or the brush elements or the discs or the belt....
As well as providing a separate drive for the pump
system. Again the OPEC mop skimmer system is supplied
with a direct drive, which can be electric, hydraulic,
air, or diesel. In the case of the diesel drive unit,
we drive both the drive rollers for the mop drive
rollers and the pump (where fitted) from the same
diesel drive motor.
The OPEC mop skimmer system provides
so many advantages over its competitors - and to top
it all we manufacture in Stainless Steel!!
|Fig. 3 OPEC Skimmer ready for shipment
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