Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02813338 2013-04-15
TITLE
[0001] Method of operation for cogeneration and tii-generation systems.
FIELD
[0002] The present invention relates to methods for operation of
cogeneration and tri-
generation systems that generate and deliver electrical and thermal energy at
point of use. The
present invention provides methods for the continuous operation and balance of
electrical and
thermal loads produced in cogeneration and tii-generation systems.
BACKGROUND
[0003] Traditionally electricity is generated in large central stations
and delivered
through an electrical grid network to consumers. More recently, due to
environmental
awareness, grid capacity and reliability, the concept of smart grids, net
metering and local
distribution networks is gaining momentum. The concept of net metering is in
its infancy,
there are still obstacles set by utility regulators to promote its wide use
and
implementation. An option that overcomes the utility regulation is the
generation of
electricity at point of use. The economics for this mode of generation favors
consumers
that have balanced electrical and thermal energy loads through the use of
cogeneration and
tri-generation systems. Most applications do not have balanced electrical and
thermal
energy load requirements. To meet these conditions users of these cogeneration
and tri-
generation systems typically select the thermal energy load as the master
control source,
these units operate on a on-off system, very much like a boiler responding to
a pressure
and or temperature demand. The result is that electricity is produced as a
byproduct of the
thermal energy load. This is the normal mode of operation since thermal energy
can be
stored whereas electricity is not.
[0004] A typical cogeneration unit achieves a cogeneration efficiency of
80% from the
energy supplied by its fuel source, generally 30% is converted into
electricity and 50% is
recovered as thermal energy from the heat generated by the combustion engine
and the waste
heat in the exhaust gases (products of combustion). When the thermal energy
load demand is
greater than the thermal energy generated by the cogeneration unit a makeup
boiler is
typically employed to meet the additional thermal energy load requirement.
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[0005] The current practice and use of these cogeneration systems lack a
mode of
operation that efficiently maximizes its use and generation of electrical and
thermal energy
loads for all seasons.
[0006] A need exists
for an efficient mode of operation for cogeneration and tii-generation
systems when compared to prior art.
SUMMARY
[0007] The
present invention provides a method for an efficient mode of operation in
cogeneration and tri-generation systems that balances and delivers electrical
and thermal
energy. The proposed invention employs several unique features in cogeneration
systems.
The first is the use of variable flow pumps to recover the thermal energy
efficiently at preset
temperatures in the engine lubrication oil and flue gas exhaust streams, this
feature allows for
the efficient extraction of the thermal energy at all combustion engine
operating conditions.
The second is the use of electrical heating elements immersed in the thermal
energy delivery
streams to meet pre-set temperature thermal energy load demand, this feature
allows for the
efficient cogeneration of electrical and thermal energy, eliminating the need
for a makeup
boiler. The third is the control of heat recovery in the engine exhaust stream
able to meet all
electrical load demands even at low thermal energy demand, this feature allows
the cooling
needs for the combustion engine to be met independent of low thermal energy
requirements.
The fourth is the method of in-series liquid/liquid heat transfer, this
feature reduces
maintenance typically associated with hot water systems, such as scaling by
providing heat
transfer to the water circuit at lower temperatures.
[0008] As will
hereinafter be further described, the methods of operation are employed in
both cogeneration and tri-generation allowing for an electrical and thermal
energy balance at
all operating conditions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] These and
other features will become more apparent from the following
description in which reference is made to the appended drawings, the drawings
are for the
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purpose of illustration only and are not intended to be in any way limiting,
wherein:
FIG. 1 is a schematic diagram for the operation of a cogeneration unit
FIG. 2 is a schematic diagram for the operation of a tri-generation unit.
FIG. 3 is a schematic diagram for the operation of a in-generation unit with
an Organic Rankine Cycle unit (ORC).
DETAILED DESCRIPTION
[0010] The cogeneration method will now be described with reference to FIG.
1.
[0011] Retelling to FIG. 1, a pressurized supply water stream 1 from a
utility distribution
or internal network enters the plant. A slipstream 2 of the cold water supply
line is routed to
cold water users. The water supply to the cogeneration system is routed
through line 3 to
pressure tank 4, where it is pre-heated by circulating thermal oil stream coil
34, exiting
pressure tank 4 through line 5 into a second pressure tank 6 where it is
further heated by
circulating thermal oil stream coil 32. A temperature sensor transmitter 10
measures the
temperature of the heated pressurized water atop of pressure tank 6, and sends
a signal to
temperature controller 9, where it is compared to a pre-set hot water
operation temperature. If
the temperature transmitted by sensor 10 is less than pre-set temperature of
controller 9, the
electric operated heating element 8 is modulated to heat the water in tank 6
to its pre-set
temperature. When the water temperature in pressure tank 6 is greater than the
pre-set
temperature of controller 9, the electric heating element 8 turns off. The hot
water stream 7
exits pressure tank 6 to users.
[0012] The heat to pressure tanks 6 and 4 is provided by a low pressure
circulating closed
loop thermal oil system. Thermal oil from receiver 11, is supplied through
stream 12 to a
variable speed pump 13, a temperature sensor transmitter 18 ensures the
temperature of
stream 22 is constant by transmitting the temperature to controller 20 which
in turn controls
the speed of pump 13, thus controlling the thermal oil flowrate 14 into heat
exchanger 15,
through coil 16 and exiting the heat exchanger through line17. Its purpose is
to cool and
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control the combustion engine 23 closed loop oil system and maintain the
lubrication oil at a
constant pre-set temperature into the engine. The lubrication oil stream exits
engine 23
through stream 21 into heat exchanger 15, where it is cooled by thermal oil
coil 16 and returns
back to the engine through line 22, a temperature sensor in line 22 ensures
the flowrate of
thermal oil to heat exchanger 15 is sufficient to keep stream 22 temperature
constant at all
combustion engine operating conditions. The heated thermal oil stream 17 goes
through
check valve 19 into stream 28 and enters exhaust heat exchanger 29. The
thermal oil stream
flows through coil 30 in heat exchanger 29 where it is further heated from
engine exhaust
stream 40. The cooling of engine exhaust stream 41 is controlled by a
temperature sensor
transmitter 36. The temperature of the exhaust stream 36 is transmitted to
temperature
controller 37 which controls through a pre-set temperature, variable speed
pump 26. A make-
up thermal oil stream is supplied through line 25 into pump 26 and pumped
through line 27
into line 28. The thermal oil stream 27 provides the extra flowrate of thermal
oil as required
to cool the exhaust stream 40 in heat exchanger 29, this flowrate is
controlled by a pre-set
temperature of exhaust stream 41 through temperature controller 37.
Temperature controller
37 can also shut off variable pump speed 26 when heating element 8 is off in
pressure tank 6
and the temperature of sensor transmitter 10 is greater than the pe-set
temperature of
controller 9. This results in stream 41 leaving heat exchanger 29 at an higher
temperature and
less thermal heat recovered while maintaining the combustion engine
lubrication oil circuit
within its pre-set temperature. This mode of operation may occur at conditions
when there is
an high electrical load demand but a low thermal heat demand.
The heated thermal oil stream 31 enters pressure tank 6 and through immersed
thermal oil coil
32 gives up its heat content to the water filled tank 6, the cooled thermal
oil stream exits coil
32 in pressure tank 6 through stream 33 and enters pressure tank 4 and through
immersed
thermal oil coil 34 is further cooled by the water in tank 4, the cooled
thermal oil exits thermal
oil coil 34 in pressure tank 4 through stream 35 back into thermal oil
receiver 11.
[0013] Heat to the facilities is provided by closed loop glycol heating
system through a
glycol distribution header 53. The return cooler glycol header stream 42
enters continuous
circulating pump 43, the pumped glycol stream 44 is routed through pressure
tank 4 through
glycol coil 45 were it is pre-heated, exits pressure tank 4 through stream 46
into pressure tank
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6 where it is further heated through glycol coil 47. The heated glycol exits
pressure tank 6
into glycol expansion tank 49. Expansion tank 49 has an electric heating
element 50 which
further heats the glycol to a pre-set temperature in glycol distribution
header 53. The
temperature sensor transmitter 52 measures the temperature of glycol
distribution header 53
5 and transmits it to temperature controller 51, which modulates electric
heating element 50 to
its pre-set temperature.
In typical cogeneration systems the main challenge is balancing the electrical
and thermal
load demands, where external sources are employed such as auxiliary fired
boilers. In this
process, the electrical and thermal loads are always in balance at all modes
of operation. A
main feature of the process is the ability to control cogeneration efficiency
by controlling the
engine exhaust temperature (41) to the atmosphere. A second feature of the
process is the
ability to make up thermal heat demand by using electrical heating elements
for thermal heat
make up, where the electrical load for the heating elements is provided by the
combustion
engine. This feature demanding an increase in electrical output from the
engine (23) and
generator (24) simultaneously increases the output in waste heat generated
which is recovered
in heat exchangers 15 and 29. This combination of electrical and thermal
supply maximizes
the efficiency and use of the cogeneration unit. A third feature of this
cogeneration process is
the employment of variable speed pumps to meet and deliver the thermal load
requirements at
constant pre-set temperatures, traditionally these operate at a constant flow
thus creating
temperature swings. A fourth feature of the process is the mode of thermal
energy recovery in
this cogeneration process. Typically in cogeneration systems the main concern
in the thermal
energy recovery units is the corrosion and scaling caused by the dissolved
gases and dissolved
solids in the water circuit. This is due to the large temperature difference
between the engine
exhaust stream (can be as high as 750 F) and the heated water. In this
cogeneration process,
thermal oil is employed to recover the heat from the engine block (stream 21)
and from the
engine exhaust gas (stream 40) in a closed circulating loop. The heat is
captured by the
circulating thermal oil and is transferred in liquid/liquid heat exchangers to
the heated water at
much lower temperatures (200 ¨ 220 F) thus preventing and minimizing scale and
corrosion.
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[0014] The tri-generation method will now be described with reference to
FIG. 2.
[0015] Referring to FIG. 2, a pressurized supply water stream 1 from a
utility distribution
or internal network enters the plant. A slipstream 2 of the cold water supply
line is routed to
.. cold water users. The water supply to the cogeneration system is routed
through line 3 to
pressure tank 4, where it is pre-heated by circulating thermal oil stream coil
34, exiting
pressure tank 4 through line 5 into a second pressure tank 6 where it is
further heated by
circulating thermal oil stream coil 32. A temperature sensor transmitter 10
measures the
temperature of the heated pressurized water atop of pressure tank 6, and sends
a signal to
.. temperature controller 9, where it is compared to a pre-set hot water
operation temperature. If
the temperature transmitted by sensor 10 is less than pre-set temperature of
controller 9, the
electric operated heating element 8 is modulated to heat the water in tank 6
to its pre-set
temperature. When the water temperature in pressure tank 6 is greater than the
pre-set
temperature of controller 9, the electric heating element 8 turns off. The hot
water stream 7
.. exits pressure tank 6 to users.
[0016] The heat to pressure tanks 6 and 4 is provided by a low pressure
circulating closed
loop thermal oil system. Thermal oil from receiver 11, is supplied through
stream 12 to a
variable speed pump 13, a temperature sensor transmitter 18 ensures the
temperature of
.. stream 22 is constant by transmitting the temperature to controller 20
which in turn controls
the speed of pump 13, thus controlling the thermal oil flowrate 14 into heat
exchanger 15,
through coil 16 and exiting the heat exchanger through line17. Its purpose is
to cool and
control the combustion engine 23 closed loop oil system and maintain the
lubrication oil at a
constant pre-set temperature into the engine. The lubrication oil stream exits
engine 23
.. through stream 21 into heat exchanger 15, where it is cooled by thermal oil
coil 16 and returns
back to the engine through line 22, a temperature sensor in line 22 ensures
the flowrate of
thermal oil to heat exchanger 15 is sufficient to keep stream 22 temperature
constant at all
combustion engine operating conditions. The heated thermal oil stream 17 goes
through
check valve 19 into stream 28 and enters exhaust heat exchanger 29. The
thermal oil stream
.. flows through coil 30 in heat exchanger 29 where it is further heated from
engine exhaust
stream 40. The cooling of engine exhaust stream 41 is controlled by a
temperature sensor
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transmitter 36. The temperature of the exhaust stream 36 is transmitted to
temperature
controller 37 which controls through a pre-set temperature, variable speed
pump 26. A make-
up thermal oil stream is supplied through line 25 into pump 26 and pumped
through line 27
into line 28. The thermal oil stream 27 provides the extra flowrate of thermal
oil as required
to cool the exhaust stream 40 in heat exchanger 29, this flowrate is
controlled by a pre-set
temperature of exhaust stream 41 through temperature controller 37.
Temperature controller
37 can also shut off variable pump speed 26 when heating element 8 is off in
pressure tank 6
and the temperature of sensor transmitter 10 is greater than the pe-set
temperature of
controller 9. This results in stream 41 leaving heat exchanger 29 at an higher
temperature and
less thermal heat recovered while maintaining the combustion engine
lubrication oil circuit
within its pre-set temperature. This mode of operation may occur at conditions
when there is
an high electrical load demand but a low thermal heat demand.
The heated thermal oil stream 31 enters pressure tank 6 and through immersed
thermal oil coil
32 gives up its heat content to the water filled tank 6, the cooled thermal
oil stream exits coil
32 in pressure tank 6 through stream 33 and enters pressure tank 4 and through
immersed
thermal oil coil 34 is further cooled by the water in tank 4, the cooled
thermal oil exits thermal
oil coil 34 in pressure tank 4 through stream 35 back into thermal oil
receiver 11.
[0017] Heat to the facilities is provided by closed loop glycol heating
system through a
glycol distribution header 53. The return cooler glycol header stream 42
enters continuous
circulating pump 43, the pumped glycol stream 44 is routed through pressure
tank 4 through
glycol coil 45 were it is pre-heated, exits pressure tank 4 through stream 46
into pressure tank
6 where it is further heated through glycol coil 47. The heated glycol exits
pressure tank 6
into glycol expansion tank 49. Expansion tank 49 has an electric heating
element 50 which
further heats the glycol to a pre-set temperature in glycol distribution
header 53. The
temperature sensor transmitter 52 measures the temperature of glycol
distribution header 53
and transmits it to temperature controller 51, which modulates electric
heating element 50 to
its pre-set temperature.
[0018] .
[0019] When a demand for cooling is required the chiller glycol circuit
is activated by
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thermostat 62. A slipstream 54 from the glycol heating header 53 is routed
through
modulating temperature control valve 55, providing thermal energy to thermal
chiller 56
through heated glycol coil 57, and routed to returning glycol header 42 for re-
heating.
The chiller glycol returning header 59 discharges into glycol chiller storage
tank 60. The
glycol is fed through circulating pump 61 into chiller 56 where it is cooled
in glycol chiller
coil 62 to a pre-set temperature measured and transmitted by 63. Modulating
controller 62
controls heated glycol thermal valve 55 to supply the thermal energy required
for chiller 56.
[0020] A feature of this tri-generation system is the add-on to the
cogeneration system in
Fig. 1 where the same benefit of generating a continuous electrical and
thermal load allows
the combustion engine to generate both electrical and thermal loads in balance
year around.
This is an added dimension for balancing electrical and thermal energy loads
throughout all
seasons. In cogeneration systems, the predominant energy requirement in the
winter is
thermal energy, whereas in the summer, the predominant energy load is
electricity. Since
both heating and cooling energy requirements are both driven at all seasons by
both electricity
and thermal energy, the proposed process meets the balance demand at all
times.
[0021] Referring to FIG. 3, a variation on the tri-generation process
where an ORC is
employed to utilize thermal energy available from the combustion engine
generator to
produce additional electrical energy. This feature is an alternative to
convert excess thermal
energy into electrical energy. An ORC unit works on the principle of expanding
and
condensing a low boiling point fluid. A low boiling point fluid 68, is pumped
to an high
pressure (300 ¨ 600 psi) and heated up in heat exchanger 70 through coil 71. A
temperature
transmitter 73, through controller 72, controls the temperature of the low
boiling fluid stream
74 to vaporize it. The heated vapour stream enters 74 ORC expander/generator
75 and exits
as a two phase stream 66 into a condenser and storage unit 67.
In this mode of operation electrical heating elements 8 and 50 are turned off,
ORC unit is used
for applications where thermal energy is abundant.
[0022] In this patent document, the word "comprising" is used in its non-
limiting sense to
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mean that items following the word are included, but items not specifically
mentioned are not
excluded. A reference to an element by the indefinite article "a" does not
exclude the
possibility that more than one of the element is present, unless the context
clearly requires that
there be one and only one of the elements.
[0023] The following claims are to be understood to include what is
specifically
illustrated and described above, what is conceptually equivalent, and what can
be obviously
substituted. Those skilled in the art will appreciate that various adaptations
and modifications
of the described embodiments can be configured without departing from the
scope of the
claims. The illustrated embodiments have been set forth only as examples and
should not be
taken as limiting the invention. It is to be understood that, within the scope
of the following
claims, the invention may be practiced other than as specifically illustrated
and described.
