Note: Descriptions are shown in the official language in which they were submitted.
CA 02691389 2010-01-28
METHOD AND APPARATUS FOR HEATING BITUMEN SLURRY STORED IN A
TANK
Field of the Invention
This invention relates to the field of heating devices used to separate heavy
oil
from a bitumen slurry consisting of heavy oil, sand and water, and in
particular to a method
and apparatus for heating the bitumen slurry which uses recaptured. heat from
a well head
pump power plant.
Background of the Invention
Many oil well sites in western Canada use an extraction method referred to as
Cold Heavy Oil Production with Sand ("CHOPS"). These wells are typically
small, remote
sites that use a progressive cavity pump to draw a slurry or mixture of heavy
oil, sand and
water from the ground and pump it into a large on-site storage tank. It is
estimated that over
3500 CHOPS wells currently exist in western Canada.
At each of these wells an internal combustion engine power plant is provided
to
generate the hydraulic power required to run the oil well pump. A large
storage tank, for
example of 750 or 1000 barrel capacity, is also provided at the site. It is
used to contain the
mixture of oil, sand and water which is extracted from the earth by the oil
well pump. To be
useful, for example so that the oil in the mixture may be processed for
pumping through a
pipeline, the mixture being pumped from the well must be separated during a
primary
separation process at the well site. The primary separation is achieved by
maintaining the
temperature of the mixture in the storage tank at approximately 80 degrees
Celsius. At this
temperature, the sand, water and oil in the mixture separates into distinct
layers within the
storage tank. Since the oil component of the mixture is typically too viscous
to effectively
flow in a pipeline, the oil once separated is regularly drained from the
storage tank into tanker
trucks and delivered to local "upgrader" facilities where the oil is processed
and thinned in
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order to make it suitable for introduction into a pipeline network. The water
that accumulates
in the tank is drained as necessary and sand is also removed on a regular
basis.
Unlike most light oil wells, CHOPS sites often do not produce adequate
amounts of well gas to provide fuel either for the power plant engine that
generates hydraulic
power for the well head pump or for the prior art large burner-style tank
heaters that are placed
inside the storage tanks and used to heat the oil once it is in the storage
tank. Consequently
propane to be consumed by the engine and storage tank heater has to be brought
to the well
sites at great expense due to the remote location of the well site and lack of
usable onsite gas.
Next to the actual trucking of the oil, propane consumption accounts for the
most significant
cost in the production of CHOPS oil.
Summary of the Invention
An internal combustion engine is provided which powers a prime mover for a
bitumen slurry well head pump used at a CHOPS site to pump bitumen slurry from
a well
borehole. A storage tank is also provided in a location adjacent to the CHOPS
site. Bitumen
slurry is pumped from the CHOPS site and stored in the storage tank. When
running at its
operating temperature the engine provides heated exhaust along an exhaust
conduit and into an
exhaust inlet of a first heat exchanger an exhaust-to-heat transfer fluid heat
exchanger. Heat
transfer fluid, for example glycol from the exhaust-to-heat transfer fluid
heat exchanger is
pumped into and through a second heat exchanger, namely, a heat transfer fluid-
to-bitumen
slurry heat exchanger mounted in the storage tank to thereby heat the bitumen
slurry in the
storage tank.
The exhaust-to-beat transfer fluid heat exchanger includes:
i) an engine exhaust duct having the exhaust inlet and an engine
exhaust outlet in gas-flow communication along said exhaust duct
with said exhaust inlet; and,
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ii) a beat transfer fluid duct having said exhaust duct adjacent to and
isolated from said fluid duct so as to transfer heat but not said
gas-flow or said fluid between said exhaust duct and said fluid
duct.
The engine exhaust is directed along an exhaust conduit from the engine into
the engine exhaust inlet of the exhaust-to-heat transfer fluid heat exchanger.
The heat transfer
fluid is pumped by heat transfer fluid pump from the heat transfer fluid inlet
to the heat
transfer fluid outlet of the exhaust-to-heat transfer fluid heat exchanger.
Heat transfer fluid
from the heat transfer fluid outlet of the exhaust-to-heat transfer fluid heat
exchanger is
directed along a heat transfer fluid conduit into the heat transfer fluid-to-
bitumen slurry heat
exchanger so as to transfer heat from the heat transfer fluid to bitumen
slurry in the storage
tank. The heat transfer fluid is re-circulated from the heat transfer fluid-to-
bitumen slurry heat
exchanger back to the heat transfer fluid inlet of the exhaust-to-heat
transfer fluid heat-
exchanger. The re-circulating circuit between the exhaust-to-heat transfer
fluid heat exchanger
and the heat transfer fluid-to-bitumen slurry heat exchanger re-circulates of
the heat transfer
fluid continuously therealong.
The following are also advantageously provided:
a) an inlet temperature sensor for monitoring temperature of the heat transfer
fluid entering the heat transfer fluid inlet,
b) an outlet temperature sensor for monitoring temperature of the heat
transfer
fluid exiting the exhaust-to-heat transfer fluid heat exchanger from the heat
transfer fluid outlet.
c) a selectively actuable flow diverter for diverting exhaust into an exhaust
bypass to inhibit the exhaust from entering the exhaust inlet.
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d) a controller and/or processor for comparing at least one of the monitored
temperatures with a threshold temperature of the heat transfer fluid, wherein
the threshold temperature is substantially an upper maximum desired
temperature range of the heat transfer fluid, for example to avoid at least
vapourization of the fluid, and if the monitored temperature substantially
equals or exceeds the threshold temperature then the diverter is actuated to
bypass the exhaust from the exhaust inlet and into the exhaust bypass.
The controller and/or processor also monitors at least one of the temperature
sensors for a drop in temperature of the heat transfer fluid. When said
temperature of the heat
transfer fluid drops below the threshold temperature, the exhaust is directed
back into said
exhaust inlet.
Where the engine is liquid cooled and includes a radiator, so that liquid
coolant
circulates through the radiator and cools the engine, the method of this
present invention may
further include the step of capturing heat from the engine by directing the
liquid coolant into
the heat transfer fluid-to-bitumen slurry heat exchanger. Advantageously the
liquid coolant is
of the same composition as the heat transfer fluid. The liquid coolant thus is
mingled with the
heat transfer fluid, for example inter-mingled downstream of the radiator and
downstream of
the heat transfer fluid downstream of the heat transfer fluid outlet of said
exhaust-to-heat
transfer fluid heat exchanger, and upstream of the heat transfer fluid-to-
bitumen slurry heat
exchanger, so that a mixture of the heat transfer fluid and the liquid coolant
enters the beat
transfer fluid-to-bitumen slurry heat exchanger.
Further advantageously an engine coolant temperature sensor is provided to
monitor the liquid coolant temperature. The liquid coolant is directed as
between the radiator
and the heat transfer fluid-to-bitumen slurry heat exchanger so as to maintain
an operational
engine temperature in the engine while optimizing heat transfer from the
liquid coolant to the
heat transfer fluid-to-bitumen slurry heat exchanger.
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A bitumen slurry temperature sensor may be provided for monitoring the
temperature of the bitumen slurry. The controller compares the bitumen slurry
temperature
and determines or estimates (herein collectively referred to as determines)
when bitumen
slurry separation has substantially occurred, whereupon the controller
performs at least one
further step chosen from the group: continue heating the bitumen slurry,
reduce heating of the
bitumen slurry, send out a signal indicating status of separation. of the
bitumen slurry.
The heat transfer fluid-to-bitumen slurry heat exchanger may include a helical
or other coil heat exchanger, and the exhaust-to-beat transfer fluid heat
exchanger may include
a counter-flow heat exchanger.
Brief Description of the Drawings
Figure 1 is a top perspective view of a portion of the apparatus according to
the
present invention including an internal combustion engine, an exhaust-to-heat
transfer fluid
heat exchanger and an exhaust bypass.
Figure 2 is in perspective view, a representation of a storage tank and one
embodiment of a heat transfer fluid-to-bitumen slurry heat exchanger mounted
therein.
Figure 3 is, in partially cut-away perspective view, the exhaust conduits of
Figure 1 directing engine exhaust from the internal combustion engine of
Figure 1 to an
exhaust bypass and an exhaust-to-heat transfer fluid beat exchanger.
Figure 4 is, in schematic view, the exhaust, heat transfer fluid and engine
coolant heat recapture circuits according to one aspect of the present
invention.
Figure 5 is, an enlarged partially cut-away view of the heat exchanger Figure
2.
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Figure 6 is, in partially cut-away perspective view, a further embodiment of a
heat transfer fluid-to-bitumen slurry heat exchanger mounted in a storage
tank.
Figure 6a is an enlarged partially cut-away view of the heat exchanger of
Figure
6.
Detailed Description of Embodiments of the Invention
The present invention reclaims heat that is currently wasted from the exhaust
system and in a preferred embodiment also the cooling jacket of an internal
combustion engine
10 used to power a hydraulic well pump. Engine 10 may run on propane, but this
is not
intended to be limiting as other fuel services would also work. The reclaimed
heat from
engine 10 is used to heat, and thereby to separate, a mixture of heavy oil
(bitumen), sand and
water (referred to herein as bitumen slurry) pumped by the well pump into an
elevated storage
tank 12. The exhaust gases from engine 10 are routed through an exhaust gas-to-
heat transfer
liquid heat exchanger 14. The heat transfer fluid (e.g. glycol) may in a
preferred embodiment
be combined with the liquid coolant from the heated water jacket and radiator
circuit 16 of
engine 10. The heat transfer fluid heated in heat exchanger 14, in the
preferred embodiment
combined with the liquid coolant from circuit 16, is pumped in direction A by
pump(s) 18 for
the heat transfer fluid flowing through check valve 20a in direction A' into
the inlet port 36a of
heat exchanger 4, and for the engine coolant circuit through, for example,
diverter valve 20b
into the inlet 22a of a heat transfer fluid-to-bitumen slurry heat exchanger
22 mounted in
storage tank 12.
The extreme temperature of the engine exhaust gas from engine 10 (which may
typically be 800 degrees Celsius) necessitates that controls be used to ensure
that the glycol, or
other heat transfer fluid, does not vapourize during the heat transfer
process. A system of
sensors and control software in a controller monitors the heat reclamation
system according to
the present invention and makes the necessary control decisions to prevent the
vapourization
of the heat transfer fluid (glycol) in heat exchanger 14. A pressure relieving
system for
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example pressure relief valve 50, may be incorporated into heat exchanger 14
to allow the safe
release of pressurized glycol gas in the event that vapourization occurs.
Figures 1 depicts one embodiment of exhaust heat exchanger 14 mounted on
exhaust manifolds I Oa of engine 10, and Figure 3 a. further embodiment not
intended to
limiting. The various exhaust and fluid circuits are illustrated schematically
in Figure 4.
Examples of storage tank 12 containing examples of heat exchanger 22 are
illustrated in
Figures 5 and 6.
In operation, during initial system startup the engine air drawn in through
air
intakes 10b and exiting the engine as exhaust bypasses the exhaust-to-glycol
heat exchanger
14 by the operation of diverter valves 24a and 24b and is routed in direction
B through conduit
26 to the engine exhaust silencer or muffler 28. During this time the engine
liquid coolant is
pumped by pump 30 through the water jacket of engine 10 and the engine
radiator 32 in order
to maintain adequate cooling of engine 10. Once it is determined by a
controller (not shown)
that by comparing measured glycol temperature with a known vapourization
threshold
temperature; and if the temperature of the circulating glycol is low enough to
accept additional
heat input without vapourizing the glycol, then the two exhaust diverter
valves 24a and 24b are
biased to divert the exhaust gas flow in direction C through heat exchanger
14. If the
measured circulating glycol temperature is also below the maximum allowable
engine cooling
jacket temperature then the engine liquid coolant is diverted in direction D
away from radiator
32 through check valve 34 so as to be mixed with the glycol outlet flow in
direction A from
heat exchanger 14. This glycol outlet flow from heat exchanger 14 exits from
outlet port 36a
into outflow conduit 38 (shown in dotted outline in Figure 2, partially cut-
away, and in Figure
4) which carries the heated glycol through check valve 38a to inlet 22a of
heat exchanger 22.
The glycol circuit may include an expansion tank 38b and corresponding
pressure relief valve
38c.
This combination of heated glycol from heat exchanger 14 and from radiator 32
is then circulated through storage tank heat exchanger 22 by pump(s) 18 and
30. Without
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intending to be limiting, heat exchanger 22 may be helical as in Figure 6, or,
for example as
seen in Figure 5, may be non-helical so long as heat from the glycol is
transferred efficiently to
the bitumen slurry 40 in tank 12. Once the temperature of the glycol that is
leaving outlet 22b,
returning in direction E to pump(s) 18 from storage tank heat exchanger 22,
exceeds the
maximum allowable engine cooling jacket temperature as measured for example by
temperature sensor 42, the engine coolant is once again constrained by the
actuation of valve
20b to circulate through engine radiator 32 in order to maintain adequate
cooling of engine 10.
The remaining circulating glycol is allowed to continue receiving heat from
heat exchanger 14
until such time as either the desired bitumen slurry temperature is reached as
measured by
sensor 42 or the maximum safe temperature of the glycol is reached as
indicated for example
by a temperature sensor mounted in tank 12 or for example by measurements by
temperature
sensor 44. When either of these conditions occur, the engine exhaust from
manifolds 10a and
flowing through exhaust conduit 46 is diverted into bypass conduit 26 and
thereby around
exhaust heat exchanger 14 so as to flow directly into engine exhaust silencer
28. This control
method is used to continuously monitor the temperature of the circulating
glycol and add heat
to it as required from either of the two engine heat sources.
If it is determined that there is not enough engine heat available to maintain
an
adequate bitumen slurry temperature in storage tank 12, an additional inline,
gas fired glycol
heater (not shown) may be used to supplement the heat provided by engine 10.
These types of
heaters are typically much more efficient than the burner type commonly used
in the prior art
as described above and therefore the amount of propane consumed by such gas-
fired glycol
heaters is less than typically encountered in the prior art.
In order to maintain a safe and controlled system, sensors 42, 44 are used to
monitor the temperature and sensor 48 monitors flow rate of the glycol in the
recirculation
loop (A - E). The temperature is measured by sensor 42 just prior to the
glycol coming into
the recirculation glycol pump(s) 18, which may have parallel circuits as seen
in dotted outline
in Figure 4, and then again by sensor 44 just downstream of heat exchanger 14
and
downstream of where heat transfer fluid (glycol) is mixed with the cooling
jacket fluid (glycol
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also). Flow meter 48 is used to ensure that the glycol is flowing at an
acceptable rate. If at
any time the temperatures or flow rates are not within acceptable ranges, the
controller
actuates valves 24a, 24b to force the exhaust into conduit 26 to bypass heat
exchanger 14 and
ensure that the glycol does not vapourize due to excessive heat input.
The sensors located in the circuit may also be used to provide data as to how
much energy is being recovered and therefore, how much propane is not being
consumed
(such as would be consumed by the standard tank heater). To calculate the
energy being
recovered the temperature of the glycol is measured as it enters and exits the
engine
recirculation loop as well as the mass flow rate of the glycol.
Expansion joints 52 may be included on heat exchanger 14 and exhaust bypass
26.
As will be apparent to those skilled in the art in the light of the foregoing
disclosure, many alterations and modifications are possible in the practice of
this invention
without departing from the spirit or scope thereof
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