156
The Chemistry and Technology of Petroleum
7.2.2 Hot-WAter ProCess
Tar sand, as mined commercially in Canada, contains an average of 10%–12% bitumen, 83%–85%
mineral matter, and 4%–6% water. A film of water coats most of the mineral matter, and this property permits extraction by the hot-water process.
The hot-water process is, to date, the only successful commercial process to be applied to bitumen recovery from mined tar sands in North America (Clark, 1944; Fear and Innes, 1967; Speight,
2009). Many process options have been tested with varying degrees of success and one of these
options may even supersede the hot-water process.
The process utilizes the linear and the nonlinear variation of bitumen density and water density,
respectively, with temperature so that the bitumen that is heavier than water at room temperature
becomes lighter than water at 80°C (180°F). Surface-active materials in the tar sand also contribute to the process. The essentials of the hot-water process involve a conditioning, separation, and
scavenging.
Thus, in the hot-water extraction process, the tar sand feed is introduced into a conditioning
drum. In this step, the oil sand is heated, mixed with water, and agglomeration of the oil particles
begins. The conditioning is carried out in a slowly rotating drum that contains a steam-sparging
system for temperature control as well as mixing devices to assist in lump size reduction and a size
ejector at the outlet end. The oil sand lumps are reduced in size by ablation and mixing action. The
conditioned pulp has the following characteristics: (1) solids 60%–85% and (2) pH 7.5–8.5.
In the conditioning step, also referred to as mixing or pulping, tar sand feed is heated and mixed
with water to form a pulp of 60% by weight to 85% by weight solids at 80°C–90°C (175°F–196°F).
First, the lumps of tar sand as mined are reduced in size by ablation, that is, successive layers
of lump are warmed and sloughed off revealing cooler layers. The conditioned pulp is screened
through a double-layer vibrating screen. Water is then added to the screened material (to achieve
more beneficial pumping conditions) and the pulp enters the separation cell through a central feed
well and distributor. The bulk of the sand settles in the cell and is removed from the bottom as tailing, but the majority of the bitumen floats to the surface and is removed as froth. A middlings stream
(mostly of water with suspended fines and some bitumen) is withdrawn from approximately midway
up the side of the cell wall. Part of the middlings is recycled to dilute the conditioning drum effluent for pumping. Clays do not settle readily and generally accumulate in the middlings layer. High
concentrations of clays increase the viscosity and can prevent normal operation in the separation
cell. Thus, it is necessary to withdraw a drag stream to act as a purge; this is usually done at high
clay concentrations but may not be as essential with a low-clay oil sand charge.
Under certain operating conditions, it may be necessary to withdraw a middling stream to the
scavenger cells (air flotation cells to recover bitumen from the drag stream). The froth from the
scavenger unit(s) usually has a high mineral and water content that can be removed by gravity settling in froth settlers after which the froth is combined with the froth from the main separation cell
from centrifuge plant for dewatering and demineralizing. Before the centrifuging operation, the
froth is deaerated and naphtha added to lower the viscosity for a more efficient water and mineral
removal operation.
The separation cell acts like two settlers, one on top of the other. In the lower settler the sand
settles down, whereas in the upper settler the bitumen floats. The bulk of the sand in the feed is
removed from the bottom of the separation cell as tailings. A large portion of the feed bitumen floats
to the surface of the separation cell and is removed as froth. A middlings stream consists mostly of
water with some suspended fine minerals and bitumen particles. A portion of the middlings may be
returned for mixing with the conditioning-drum effluent in order to dilute the separation-cell feed
for pumping. The remainder of the middlings is called the drag stream, which is withdrawn from the
separation cell to be rejected after processing in the scavenger cells. Tar sand feed contains a certain
portion of fine minerals that, if allowed to build up in concentration in the middlings, increases the
viscosity and eventually disrupts settling in the separation cell. The drag stream is required as a
The Chemistry and Technology of Petroleum
7.2.2 Hot-WAter ProCess
Tar sand, as mined commercially in Canada, contains an average of 10%–12% bitumen, 83%–85%
mineral matter, and 4%–6% water. A film of water coats most of the mineral matter, and this property permits extraction by the hot-water process.
The hot-water process is, to date, the only successful commercial process to be applied to bitumen recovery from mined tar sands in North America (Clark, 1944; Fear and Innes, 1967; Speight,
2009). Many process options have been tested with varying degrees of success and one of these
options may even supersede the hot-water process.
The process utilizes the linear and the nonlinear variation of bitumen density and water density,
respectively, with temperature so that the bitumen that is heavier than water at room temperature
becomes lighter than water at 80°C (180°F). Surface-active materials in the tar sand also contribute to the process. The essentials of the hot-water process involve a conditioning, separation, and
scavenging.
Thus, in the hot-water extraction process, the tar sand feed is introduced into a conditioning
drum. In this step, the oil sand is heated, mixed with water, and agglomeration of the oil particles
begins. The conditioning is carried out in a slowly rotating drum that contains a steam-sparging
system for temperature control as well as mixing devices to assist in lump size reduction and a size
ejector at the outlet end. The oil sand lumps are reduced in size by ablation and mixing action. The
conditioned pulp has the following characteristics: (1) solids 60%–85% and (2) pH 7.5–8.5.
In the conditioning step, also referred to as mixing or pulping, tar sand feed is heated and mixed
with water to form a pulp of 60% by weight to 85% by weight solids at 80°C–90°C (175°F–196°F).
First, the lumps of tar sand as mined are reduced in size by ablation, that is, successive layers
of lump are warmed and sloughed off revealing cooler layers. The conditioned pulp is screened
through a double-layer vibrating screen. Water is then added to the screened material (to achieve
more beneficial pumping conditions) and the pulp enters the separation cell through a central feed
well and distributor. The bulk of the sand settles in the cell and is removed from the bottom as tailing, but the majority of the bitumen floats to the surface and is removed as froth. A middlings stream
(mostly of water with suspended fines and some bitumen) is withdrawn from approximately midway
up the side of the cell wall. Part of the middlings is recycled to dilute the conditioning drum effluent for pumping. Clays do not settle readily and generally accumulate in the middlings layer. High
concentrations of clays increase the viscosity and can prevent normal operation in the separation
cell. Thus, it is necessary to withdraw a drag stream to act as a purge; this is usually done at high
clay concentrations but may not be as essential with a low-clay oil sand charge.
Under certain operating conditions, it may be necessary to withdraw a middling stream to the
scavenger cells (air flotation cells to recover bitumen from the drag stream). The froth from the
scavenger unit(s) usually has a high mineral and water content that can be removed by gravity settling in froth settlers after which the froth is combined with the froth from the main separation cell
from centrifuge plant for dewatering and demineralizing. Before the centrifuging operation, the
froth is deaerated and naphtha added to lower the viscosity for a more efficient water and mineral
removal operation.
The separation cell acts like two settlers, one on top of the other. In the lower settler the sand
settles down, whereas in the upper settler the bitumen floats. The bulk of the sand in the feed is
removed from the bottom of the separation cell as tailings. A large portion of the feed bitumen floats
to the surface of the separation cell and is removed as froth. A middlings stream consists mostly of
water with some suspended fine minerals and bitumen particles. A portion of the middlings may be
returned for mixing with the conditioning-drum effluent in order to dilute the separation-cell feed
for pumping. The remainder of the middlings is called the drag stream, which is withdrawn from the
separation cell to be rejected after processing in the scavenger cells. Tar sand feed contains a certain
portion of fine minerals that, if allowed to build up in concentration in the middlings, increases the
viscosity and eventually disrupts settling in the separation cell. The drag stream is required as a