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The Chemistry and Technology of Petroleum
cations must be excluded because they tend to flocculate the clays and thus raise the viscosity of
the middlings in the separation cell.
7.2.3 otHer ProCesses
It is conceivable that the problems related to bitumen mining and bitumen recovery for the tar sand
may be alleviated somewhat by the development of process options that require considerably less
water in the sand/bitumen separation step. Such an option would allow a more gradual removal of
the tailings ponds.
The proposed cold-water process for bitumen separation from mined tar sand has also been
recommended (Misra et al., 1981; Miller and Misra, 1982). The process uses a combination of
cold water and solvent and the first step usually involves disintegration of the tar sand charge that
is mixed with water, diluent, and reagents. The diluent may be a petroleum distillate fraction such
as kerosene and is added in approximately a 1:1 weight ratio to the bitumen in the feed. The pH
is maintained at 9–9.5 by the addition of wetting agents and approximately 0.77 kg of soda ash
per ton of tar sand. The effluent is mixed with more water, and in a raked classifier the sand is
settled from the bulk of the remaining mixture. The water and oil overflow the classifier and are
passed to thickeners where the oil is concentrated. Clay in the tar sand feed has a distinct effect
on the process; it forms emulsions that are hard to break and are wasted with the underflow from
the thickeners.
The sand-reduction process is a cold-water process without solvent. In the first step, the tar
sand feedstock is mixed with water at approximately 20°C (68°F) in a screw conveyor in a ratio
of 0.75–3 ton per ton of tar sand (the lower range is preferred). The mixed pulp from the screw
conveyor is discharged into a rotary-drum screen, which is submerged in a water-filled settling
vessel. The bitumen forms agglomerates that are retained by an 840 μm (20 mesh) screen. These
agglomerates settle and are withdrawn as oil product. The sand readily passes through the 840 μm
(20 mesh) screen and is withdrawn as waste stream. The process is called sand reduction because
its objective is the removal of sand from the tar sand to provide a feed suitable for a fluid coking
process; ca. 80% of sand is removed. Nominal composition of the oil product is 58% by weight
(bitumen), 27% by weight mineral matter, and 15% by weight water.
The spherical agglomeration process resembles the sand-reduction process. Water is added to
tar sands and the mixture is ball-milled. The bitumen forms dense agglomerates of 75% by weight
to 87% by weight bitumen, 12% by weight to 25% by weight sand, and 1% by weight to 5% by
weight water.
An oleophilic sieve process (Kruyer, 1982, 1983) offers the potential for reducing tailings pond
size because of a reduction in the water requirements. The process is based on the concept that when
a mixture of an oil phase and an aqueous phase is passed through a sieve made from oleophilic
materials, the aqueous phase and any hydrophilic solids pass through the sieve but the oil adheres
to the sieve surface on contact. The sieve is in the form of a moving conveyor, the oil is captured in
a recovery zone, and recovery efficiency is high.
An anhydrous solvent extraction process for bitumen recovery has been attempted and usually
involves the use of a low-boiling hydrocarbon. The process generally involves up to four steps. In
the mixer step, fresh tar sand is mixed with recycle solvent that contains some bitumen and small
amounts of water and mineral. Solvent-to-bitumen weight ratio is adjusted to approximately 0.5.
The drain step consists of a three-stage countercurrent wash. Settling and draining time is approximately 30 min for each stage. After each extraction step, a bed of sand is formed and the extract is
drained through the bed until the interstitial pore volume of the bed is emptied. From time to time,
the bed is plugged with fine mineral or emulsion. In these cases, the drainage rate is essentially zero
and the particular extraction stage is ineffective. The last two steps of the process are devoted to
solvent recovery. Stripping of the solvent from the bitumen is straightforward. The solvent recovery
from the solids holds the key to the economic success of an anhydrous process.
The Chemistry and Technology of Petroleum
cations must be excluded because they tend to flocculate the clays and thus raise the viscosity of
the middlings in the separation cell.
7.2.3 otHer ProCesses
It is conceivable that the problems related to bitumen mining and bitumen recovery for the tar sand
may be alleviated somewhat by the development of process options that require considerably less
water in the sand/bitumen separation step. Such an option would allow a more gradual removal of
the tailings ponds.
The proposed cold-water process for bitumen separation from mined tar sand has also been
recommended (Misra et al., 1981; Miller and Misra, 1982). The process uses a combination of
cold water and solvent and the first step usually involves disintegration of the tar sand charge that
is mixed with water, diluent, and reagents. The diluent may be a petroleum distillate fraction such
as kerosene and is added in approximately a 1:1 weight ratio to the bitumen in the feed. The pH
is maintained at 9–9.5 by the addition of wetting agents and approximately 0.77 kg of soda ash
per ton of tar sand. The effluent is mixed with more water, and in a raked classifier the sand is
settled from the bulk of the remaining mixture. The water and oil overflow the classifier and are
passed to thickeners where the oil is concentrated. Clay in the tar sand feed has a distinct effect
on the process; it forms emulsions that are hard to break and are wasted with the underflow from
the thickeners.
The sand-reduction process is a cold-water process without solvent. In the first step, the tar
sand feedstock is mixed with water at approximately 20°C (68°F) in a screw conveyor in a ratio
of 0.75–3 ton per ton of tar sand (the lower range is preferred). The mixed pulp from the screw
conveyor is discharged into a rotary-drum screen, which is submerged in a water-filled settling
vessel. The bitumen forms agglomerates that are retained by an 840 μm (20 mesh) screen. These
agglomerates settle and are withdrawn as oil product. The sand readily passes through the 840 μm
(20 mesh) screen and is withdrawn as waste stream. The process is called sand reduction because
its objective is the removal of sand from the tar sand to provide a feed suitable for a fluid coking
process; ca. 80% of sand is removed. Nominal composition of the oil product is 58% by weight
(bitumen), 27% by weight mineral matter, and 15% by weight water.
The spherical agglomeration process resembles the sand-reduction process. Water is added to
tar sands and the mixture is ball-milled. The bitumen forms dense agglomerates of 75% by weight
to 87% by weight bitumen, 12% by weight to 25% by weight sand, and 1% by weight to 5% by
weight water.
An oleophilic sieve process (Kruyer, 1982, 1983) offers the potential for reducing tailings pond
size because of a reduction in the water requirements. The process is based on the concept that when
a mixture of an oil phase and an aqueous phase is passed through a sieve made from oleophilic
materials, the aqueous phase and any hydrophilic solids pass through the sieve but the oil adheres
to the sieve surface on contact. The sieve is in the form of a moving conveyor, the oil is captured in
a recovery zone, and recovery efficiency is high.
An anhydrous solvent extraction process for bitumen recovery has been attempted and usually
involves the use of a low-boiling hydrocarbon. The process generally involves up to four steps. In
the mixer step, fresh tar sand is mixed with recycle solvent that contains some bitumen and small
amounts of water and mineral. Solvent-to-bitumen weight ratio is adjusted to approximately 0.5.
The drain step consists of a three-stage countercurrent wash. Settling and draining time is approximately 30 min for each stage. After each extraction step, a bed of sand is formed and the extract is
drained through the bed until the interstitial pore volume of the bed is emptied. From time to time,
the bed is plugged with fine mineral or emulsion. In these cases, the drainage rate is essentially zero
and the particular extraction stage is ineffective. The last two steps of the process are devoted to
solvent recovery. Stripping of the solvent from the bitumen is straightforward. The solvent recovery
from the solids holds the key to the economic success of an anhydrous process.