157
Recovery of Heavy Oil and Tar Sand Bitumen
purge in order to control the fines concentration in the middlings. The amounts of water that can
enter with the feed and leave with the separation-cell tailings and froth are relatively fixed. Thus, the
size of the drag stream determines the makeup water requirement for the separation cell. The separation cell is an open vessel with straight sides and a cone bottom. Mechanical rakes on the bottom
move the sand toward the center for discharge. Wiper arms rotating on the surface push the froth
to the outside of the separation cell where it overflows into launders for collection.
The combined froth from the separation cell and scavenging operation contains an average of
about 10% by weight mineral material and up to 40% by weight water. Dewatering and demineralizing are accomplished in two stages of centrifuging: In the first stage the coarser mineral material is removed but much of the water remains, the feed then passes through a filter to remove any
additional large-size mineral matter that would plug up the nozzles of the second stage centrifuges.
The third step in the hot-water process is scavenging. Depending on the dragstream size and
composition, enough bitumen may leave the process in the drag stream to make another recovery
step economical. Froth flotation with air is usually employed. The scavenger froth is combined with
the separation-cell froth to be further treated and upgraded to synthetic crude oil. Tailings from the
scavenger cell join the separation-cell tailings stream and go to waste. Conventional froth-flotation
cells are suitable for this step.
Froth from the hot-water process may be mixed with a hydrocarbon diluent, for example, coker
naphtha, and centrifuged. The Suncor process employs a two-stage centrifuging operation and each
stage consists of multiple centrifuges of conventional design installed in parallel. The bitumen product contains 1% by weight to 2% by weight mineral (dry bitumen basis) and 5% by weight to 15%
by weight water (wet diluted basis). Syncrude also utilizes a centrifuge system with naphtha diluent.
One of the major problems that comes from the hot-water process is the disposal and control of
the tailings. The fact is that each ton of oil sand in place has a volume of about 16 ft 3 , which will generate about 22 ft 3 of tailings giving a volume gain on the order of 40%. If the mine produces about
200,000 tons of oil sand per day, the volume expansion represents a considerable solids disposal
problem. Tailings from the process consist of about 49%–50% by weight of sand, 1% by weight of
bitumen, and about 50% by weight of water. The average particle size of the sand is about 200 am
and it is a suitable material for dike building. Accordingly, Suncor used this material to build the
sand dike, but for fine sand, the sand must be well compacted.
Environmental regulations in Canada or the United States will not allow the discharge of tailings streams into (1) the river, (2) on to the surface, or (3) on to any area where contamination of
groundwater domains or the river may be contaminated. The tailings streams is essentially high in
clays and contains some bitumen, hence the current need for tailings ponds, where some settling of
the clay occurs. In addition, an approach to acceptable reclamation of the tailings ponds will have
to be accommodated at the time of site abandonment.
The structure of the dike may be stabilized on the upstream side by beaching. This gives a shallow slope but consumes sand during the season when it is impossible to build the dike. In remote
areas such as the Fort McMurray (Alberta) site, the dike can only be built in above-freezing weather
because (1) frozen water in the pores of the dike will create an unstable layer and (2) the vapor
emanating from the water creates a fog, which can create a work hazard. The slope of the tailings
dike is about 2.5:1 depending on the amount of fines in the material. It may be possible to build with
2:1 slopes with coarser material, but steeper slopes must be stabilized quickly by bleaching. After
discharge from the hot-water separation system, it is preferable that attempts be made to separate
the sand, sludge, and water; hence, the tailings pond. The sand is used to build dikes and the runoff
that contains the silt, clay, and water collects in the pond. Silt and some clay settle out to form sludge
and some of the water is recycled to the plant.
In summary, the hot-water separation process involves extremely complicated surface chemistry with interfaces among various combinations of solids (including both silica sand and aluminosilicate clays), water, bitumen, and air. The control of pH seems to be critical with the preferred
range being 8.0–8.5, which is achievable by use of any of the monovalent bases. Polyvalent
Recovery of Heavy Oil and Tar Sand Bitumen
purge in order to control the fines concentration in the middlings. The amounts of water that can
enter with the feed and leave with the separation-cell tailings and froth are relatively fixed. Thus, the
size of the drag stream determines the makeup water requirement for the separation cell. The separation cell is an open vessel with straight sides and a cone bottom. Mechanical rakes on the bottom
move the sand toward the center for discharge. Wiper arms rotating on the surface push the froth
to the outside of the separation cell where it overflows into launders for collection.
The combined froth from the separation cell and scavenging operation contains an average of
about 10% by weight mineral material and up to 40% by weight water. Dewatering and demineralizing are accomplished in two stages of centrifuging: In the first stage the coarser mineral material is removed but much of the water remains, the feed then passes through a filter to remove any
additional large-size mineral matter that would plug up the nozzles of the second stage centrifuges.
The third step in the hot-water process is scavenging. Depending on the dragstream size and
composition, enough bitumen may leave the process in the drag stream to make another recovery
step economical. Froth flotation with air is usually employed. The scavenger froth is combined with
the separation-cell froth to be further treated and upgraded to synthetic crude oil. Tailings from the
scavenger cell join the separation-cell tailings stream and go to waste. Conventional froth-flotation
cells are suitable for this step.
Froth from the hot-water process may be mixed with a hydrocarbon diluent, for example, coker
naphtha, and centrifuged. The Suncor process employs a two-stage centrifuging operation and each
stage consists of multiple centrifuges of conventional design installed in parallel. The bitumen product contains 1% by weight to 2% by weight mineral (dry bitumen basis) and 5% by weight to 15%
by weight water (wet diluted basis). Syncrude also utilizes a centrifuge system with naphtha diluent.
One of the major problems that comes from the hot-water process is the disposal and control of
the tailings. The fact is that each ton of oil sand in place has a volume of about 16 ft 3 , which will generate about 22 ft 3 of tailings giving a volume gain on the order of 40%. If the mine produces about
200,000 tons of oil sand per day, the volume expansion represents a considerable solids disposal
problem. Tailings from the process consist of about 49%–50% by weight of sand, 1% by weight of
bitumen, and about 50% by weight of water. The average particle size of the sand is about 200 am
and it is a suitable material for dike building. Accordingly, Suncor used this material to build the
sand dike, but for fine sand, the sand must be well compacted.
Environmental regulations in Canada or the United States will not allow the discharge of tailings streams into (1) the river, (2) on to the surface, or (3) on to any area where contamination of
groundwater domains or the river may be contaminated. The tailings streams is essentially high in
clays and contains some bitumen, hence the current need for tailings ponds, where some settling of
the clay occurs. In addition, an approach to acceptable reclamation of the tailings ponds will have
to be accommodated at the time of site abandonment.
The structure of the dike may be stabilized on the upstream side by beaching. This gives a shallow slope but consumes sand during the season when it is impossible to build the dike. In remote
areas such as the Fort McMurray (Alberta) site, the dike can only be built in above-freezing weather
because (1) frozen water in the pores of the dike will create an unstable layer and (2) the vapor
emanating from the water creates a fog, which can create a work hazard. The slope of the tailings
dike is about 2.5:1 depending on the amount of fines in the material. It may be possible to build with
2:1 slopes with coarser material, but steeper slopes must be stabilized quickly by bleaching. After
discharge from the hot-water separation system, it is preferable that attempts be made to separate
the sand, sludge, and water; hence, the tailings pond. The sand is used to build dikes and the runoff
that contains the silt, clay, and water collects in the pond. Silt and some clay settle out to form sludge
and some of the water is recycled to the plant.
In summary, the hot-water separation process involves extremely complicated surface chemistry with interfaces among various combinations of solids (including both silica sand and aluminosilicate clays), water, bitumen, and air. The control of pH seems to be critical with the preferred
range being 8.0–8.5, which is achievable by use of any of the monovalent bases. Polyvalent