Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF T~E INYENTION
This invention relates to an apparatus and a process for
recovering bitumen floating on the surface of a body of water, such as
a tailings pond. More parti:cularly, it has reference to the field of
oil skimmers and to the processes practised by them.
BACKGROUND OF THE I`N~ENTION
Tar sands (also known as oi`l or bitumi`nous sands) are an
extensive source of hydrocar60ns whi`ch i`n recent years have become
economically viable. There are two commercial plants presently operating
i.n the Alberta tar sands; the fi.rst produces approxi:mately 5Q,aQQ
barrels of synthetic crude/day, the second about 130,00Q 6.arrels/day. This
second plant, owned by the assignees of thi:s inventi:on, is hereafter
referred to as 'the aforementioned plant'.
Both th.ese plants use an extracti:on process known as the
'hot water processl. This process i.5 ~ell descri:6ed i:n the literature
(for example, see Canadian patent 1,055,868).
The hot water process produces a ~as:te stream, called
"tailings", which is a mixture of solids, water and some bitumen. The
solids comprise a coarse sand fraction and a fines fraction usually
described as being -44~ clay and silt particles.
The volume of this waste stream is very large. In the
aforementioned plant, dry tar sand feed enters the process at a rate of
about 13,000 tons/hour and tailings leave at a rate of about 20,000 tons/hour.
The plant design analysis of the aforementioned plant specifies
that the bitumen content of the tailings should be about 0.49~ by
weight. However the actual content varies widely depending on whether the
tar sand feed is high or low grade. Bitumen losses by way of the tailings
increase as the fines content of the tar sand feed increases. Bitumen
losses with the taili.ngs at the aforementioned plant have been known to
run as high as 11,000 barrels/day when it w-as processing high fines feed.
The tailings are dis.carded from the extraction plant into a
tai.lings pond. In the case of the 130,000 harrel/day plant, this pond
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will eventually cover about 10 square miles. The bitumen, while
constituting an undesirable process loss, also is a serious environmental
problem - because it floats on the surface of this large body of water, it
can coat wild fowl landing in it.
Clearly it would be desi:rable to contai:n the bitumen within
booms and recover it usi`ng an oil skimmer. However, several types~ of
commercially available skimmers have been tried ~ith poor results. This
failure is attributable to the peculiar nature of the 6i`tumen.
More particularly, bitumen i5 a particularly viscous material.
At 10C, its viscosity is i`n the order of 2,QOQ,QOO centistokes; at 20C
it is in the order of 2QO,OOO centistokes. B~ way of compari:son, crude
oil and bunker oil at 20C have viscosities in the order of 300 and lQOO
centistokes respectively.
When the hot bitumen discharged hy the extraction plant
contacts the cold water of the tailings pond, its lower most portion
forms into a cohesive stiff layer whi`ch supports an uppermost portion
having a butter-like consistency. This mass i`s hereinafter referred to
as a bitumen blanket.
When existing commercially available oi:l skimmers were
applied to the bitumen blanket, it was found that, instead of picking the
bitumen up, the rotating discs, drums and conveyor 6elts of these units
would tend to ride up onto the blanket and pass it beneath them. The
machines also tended to break the blanket up without picki:ng up the bitumen.
Finally, some of them would tend to clog up with the bitumen.
With the foregoing in mind, it was therefore the object of
this invention to devise a machine which would s;uccessfully recover a
bitumen blanket floating on the surface of a body of water.
SUMMARY OF THE I`NVENTION
_
In accordance with the invention, a skimming apparatus is
3n provided which operates on the principle of gripping and moving the
blanket as an integral unit onto the drum. The apparatus includes a drum
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assembly comprising a slowly rotating drum having outwardly extending
teeth protruding from its curved surface. These teeth (which preferably
are prongs) function to penetrate and grip the nearest part of the blanket
and then, as they are moved by rotation of the drum to whi:ch they are
anchored, they draw the blanket i:nto adhesive contact with the drum
surface. Preferably, the drum is partly submerged and rotates in a
direction 50 as to force the engaged part of the hlanket beneath i:t. Thus
the engaged part of the blanket is drawn down beneath the surface of the
water. The combinati:on of hydrauli`c head, acting to press the bitumen
against the lowermost curved surface of the drum, and penetrati:on into the
blanket by the teeth causes the bitumen to become affixed to the drum
assembly. Further rotati.on of the drum results i;n thi.s bi.tumen being
lifted rearwardly and upwardly clear of the water. Means, such as. a
flexi.ble comb-like doctor blade, scrape the bitumen from the drum assemhly.
A receptacle collects the bi:tumen as i:t is s.craped off~ Means, such as
an auger,may then be used to trans.fer collected bi.tumen from the receptacle
to a container, such as a barge, which conveys the viscous materi.al to
shore. Here it may be rendered pumpahle by dilution with light hydro-
carbon and returned to the extraction plant or may be otherwise treated.
While the invention has been describ.ed in terms of a drum,
it will be appreciated that it can probably be extended to other curved
endless members, such as a conveyor belt.
Broadly stated, the inventi:on i.s a skimming apparatus for
collecting a cohesi.ve bi.tumen blanket floati:ng on a body of water, s.aid
blanket having a lowermost portion which.is stiffer than its uppermost
portion due to cooling by the water, sai:d apparatus comprisi.ng: buoyant
means for floati.ng on the water and carrying the other components of the
apparatus, a drum assembly comprising a horizontally disposed drum
rotatably carried by the buoyant means and arranged to be partly submerged
in the water when operative, said drum having a plurality of prongs
di.stributed over and extending outwardly from its curved surface~
said prongs being operative, when the drum is rotating, to penetrate
through the uppermost portion and grip the lowermost portion of the nearest
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part of the blanket to thereby pull th~t part into submerged adhesive
engagement with the lower surface of the drum, means positioned to the
rear of the drum assembly for scraping bitumen from it; a receptacle for
collecting the bitumen as it is scraped from the drum assembly; and means
for rotating the drum assembly.
In another aspect of the invention, a process is provided
for collecting part or all of a cohesive bitumen blanket floating on a
body of water with a rotatable curved endless member hav;ng teeth
extending out~ardly from its outer surface compri.sing: gripping the nearest
part of the blanket with the teeth of the rotating member and pulling
said nearest part into adhesi.ve contact with the member at a sufficiently
slow rate whereby the blanket does not tear; carrying adhering bitumen
upwardly out of the water on the member; recover;ng adhering bitumen from
the member; and continui:ng said steps to gradually collect part or all
of the blanket.
DESCRIPTION OF THE DRAWINGS:
Figure 1 is a partly exploded perspecti:ve view of the ,k;mming
apparatus;
Figure 2 is a s.implifi.ed diagrammatic side view showing the
apparatus in operation;
Figure 3 is a fanciful representation of a side section of
a bitumen blanket as commonly encountered on the tailings pond. A prong
is shown gripping the blanket by penetrating i:t. The hlanket is shown
adhering to the drum. The shadi.ng identifi.es the cohesive, stiff portion.
DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference now to the drawi.ng, the apparatus. comprises a
pai.r of buoyant, spaced, parallel pontoons l which float on the pond
water 2 and carry the other components.
A pair of guide memb.ers 3 may be provided to extend forwardly
and outwardly from the pontoons l. A floating boom, not shown, will
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extend laterally from each guide member 3 to contain the bitumen
blanket 4.
A drum assembly 5, comprising a drum 6 having a horizontal
drive shaft 7, i5 mounted for rotation in bearings 8 carried by the pontoons
1. A plurality of prongs 9 are anchored to the drum 6 and extend outwardly
from its curved surface 10. In the prototype unit, the drum 6 was a
common 45 gallon steel drum having 1/4" x 2" steel prongs attached
thereto.
While only a steel drum has been tested, ;t is anticipated
that other rotating curved endless members, such as a conveyor belt,
could be used. Also, while only steel prongs have been used, it is
antic;pated that other tooth-like members, capable of penetrating through
the entire bitumen blanket, could also function satisfactorily.
Means are provided for totating the drum assembly 5 As
B~5 shown, such means may compr;se a motor ~-dr;v;ng the drum shaft 7
through a gear reducer 11 and belt 12.
Means are provided to the rear of the drum assembly 5 for
scraping b;tumen from it. Such means may comprise a comb-like doctor
blade 13 made of stiff rubber. The open;ngs 14 of the blade 13 are
aligned with the rows of prongs 9 to scrape excess b;tumen from them.
A receptacle or open-topped container 15 is provided beneath
the doctor blade 13 to catch bitumen being scraped from it.
An auger 16 may be provided to transfer the bitumen from the
receptacle 15 into a barge for transfer to shore. The auger 16 is
conveniently driven by the motor 10 through a suitable gear reducer-
belt-shaft system 1~.
In use, the drum 6 is partly submerged in the water.
A key feature of the invention is that the prongs 9 must
penetrate the bitumen blanket 4 and take a grip on it. If the drum 6 is
rotated slowly, so as not to tear the blanket, the entire blanket will
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bit by bit be drawn down and onto the lowermost submerged surface of
the drum. The combination of prong penetration and adhesion of the
bitumen to the oily surface of the drum is such that the drum assembly
5 will carry the attached part of the blanket up out of the water to a
level where it may be scraped off.
Care has to be taken tn operate the drum assembly 5 slowly
enough so as not to tear the blanket. This speed w;ll of course vary
with the size of the drum, the temperature of the water and other
factors. We found that with a drum having a diameter af 560 mm
operating in a blanket having a thickness of 30 mm, an r.p.m. of 6 was
suitable - if the r.p.m. was increased to about 12, tearing would occur
200 - 500 mm forward of the drum. Even so the paddle effect of the
prongs tends to push the water to the rear thereby pulling the bitumen
blanket again to the rotating drum.
