CA2813338C

CA2813338C - Method of operation for cogeneration and tri-generation systems.

Info

Publication number: CA2813338C
Application number: CA2813338A
Authority: CA
Inventors: Claudine CORBETT-LOURENCO; Luigi Zaccardelli; Jose Lourenco
Original assignee: LOURENCO TECHNOLOGY Corp
Current assignee: LOURENCO TECHNOLOGY Corp
Priority date: 2013-04-15
Filing date: 2013-04-15
Publication date: 2020-01-14
Anticipated expiration: 2033-04-15
Also published as: WO2014169387A1; CA2813338A1

Abstract

A method to continuously operate and balance electrical and thermal energy in cogeneration and tri-generation processes. The methods employ the use of variable speed pumps, electrical heating elements, liquid/liquid exchangers to efficiently operate and balance electrical and thermal energy loads in cogeneration and tri-generation processes.

Description

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.

[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 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 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 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.

[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 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 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 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.

Claims

What is Claimed is:

1. A method to balance the electrical and thermal loads in a cogeneration or tri-generation system comprising the steps of:
using variable speed pumps to:
control and maintain at pre-set temperature a constant temperature of a lubrication oil stream to a combustion engine using thermal oil as an engine heat removing stream; and control and maintain at a pre-set temperature a constant temperature of an engine exhaust stream of the combustion engine using a make-up thermal oil stream as an exhaust heat removing stream;
using temperature controlled electrical heating elements to make-up thermal energy requirements of the cogeneration or tri-generation system; and using thermal oil coils in series to transfer the thermal heat to a water storage tank

2. The method as defined in Claim 1, where the variable speed pump for the make-up thermal oil stream is turned off at a predetermined high water temperature in the water storage tank.

3. The method as defined in Claim 1, where the temperature controlled electrical heating elements that make-up the thermal energy requirements are powered by electrical energy supplied by a combustion engine generator that further increases the thermal energy delivered by the combustion engine.

4. The method as defined in Claim 1, where the cogeneration unit is a fuel cell.

5. The method as defined in claim 1, where excess thermal energy is employed in an Organic Rankine Cycle (ORC) unit to produce electricity.

6. The method as defined in Claim 5, wherein the use of an ORC as an external electrical generation unit also generates low thermal energy from its condensation unit.