Technical field

[0001] The present invention relates generally to a system and a method for recovery of thermal energy from a heat source.

Background art

[0002] Utilizing a single source of heat to generate both power in the form of electricity and useful heat is known as Combined Heat and Power (CHP), or cogeneration. If the same system is furthermore used for cooling, this is known as combined cooling, heat and power (CCHP), or trigeneration.

[0003] Co- or trigeneration systems are commonly used in power plants such as coal-fired power plants. In such cases, the power plant generates electricity from a fuel source, such as coal or biowaste, and the waste heat generated in the process is utilized for heating.

[0004] In conventional systems, a high temperature circulation fluid, which comprises heat extracted from a heat source, passes through an energy recovery system in order to use the thermal energy to produce electricity. The circulation fluid is then passed through a cooler, to remove even more heat in order to be able to use the circulation fluid as a cooling media in the energy recovery system on its way back to the heat source. In the cooler, where the temperature of the circulation fluid is significantly decreased, up to 90% of the heat input from the heat source may be lost to the surroundings. Therefore, there is still a need for improving efficiency of CHP and CCHP systems in order to decrease the amount of energy going to waste.

[0005] A CHP-system is disclosed in US2017248039, where there is provided a method for operating a CHP plant comprising a heating boiler, a vaporizer, an expansion machine, and a condenser. One problem with such systems is that they cannot be easily integrated into an existing infrastructure. Systems where electricity is the main source of energy acquired form the waste heat are less flexible and cannot easily be applied in another, existing infrastructures where the waste heat is primarily used for an alternative purpose, such as district heating or heating of green houses and the like. Therefore, there is a need for solutions wherein excess waste heat may be accessed for electricity production, such as waste heat from existing heating infrastructure.

[0006] Waste heat from industrial sites may be used in district heating networks. This is especially common in countries such as Sweden having a highly developed district heating infrastructure. However, even when an industrial facility is connected to a district heating network, or another facility in need of heating, a lot of heat still goes to waste. However, accessing such waste heat can be complicated due to the rigidity and complexity of district heating infrastructure. Therefore, there is still a need for solutions where waste heat is utilized in several ways, in order to use as much as possible of the waste heat. Furthermore, there is still a need for solutions which may be easily and efficiently integrated into large scale systems, such as district heating and systems for utilization of industrial waste heat. Furthermore, there is a need for such solutions to provide versatility and flexibility.

Summary of invention

[0007] In a first aspect of the present disclosure, there is provided a system for recovery of thermal energy from a heat source comprising a heat source circuit with a first circulation fluid which receives thermal energy from the heat source, wherein the heat source is connected to a heat receiver comprising a heat receiver circuit with a second circulation fluid such that thermal energy may be transferred from the first circulation fluid to the second circulation fluid by means of a heat exchanger, the system comprising: an energy conversion module configured to work in a closed loop thermodynamic cycle and convert thermal energy into electricity, wherein the energy conversion module comprises a hot side arranged to be connected to the heat source circuit to extract thermal energy from the first circulation fluid, and a cold side arranged to be connected to the heat receiver circuit to deliver thermal energy to the second circulation fluid; and a flow control system arranged to control input and output of thermal energy into and out of the energy conversion module, wherein the flow control system comprises conduits for connecting the energy conversion module to the heat source circuit and the heat receiver circuit, and valves for selectively closing and opening the conduits to direct flow of the first and second circulation fluids therein, wherein the flow control system further comprises conduits for connecting the cold side of the energy conversion module to an additional cooling source via the heat receiver circuit, and valves for selectively closing and opening the conduits to direct flow of the second circulation fluid therein.

[0008] The system enables electricity to be produced from thermal energy in an already existing system for recovery of thermal energy. The heat source circuit to which the system may be connected is already connected to another user of heat, such as a district heating network or an agricultural facility. Thus, by connecting the system of the present invention to the heat source circuit, electricity may be produced from the heat which the heat receiver does not use, and less thermal energy goes to waste. Furthermore, since the cold side of the energy conversion module may be connected to the heat receiver circuit, when the second circulation fluid has delivered thermal energy to the heat receiver and thus has a lowered temperature, the system may deliver thermal energy back to the heat receiver circuit.

[0009] In one embodiment, system furthermore provides that an additional cooling source may be connected to the system. A cooling source, such as sea water, may even further decrease the temperature of the second circulation fluid and thereby increase the temperature difference between the hot side and the cold side of the energy conversion module. This increases the efficiency of the electricity production.

[0010] In one embodiment, the hot side of the energy conversion module is arranged to be connected to the heat source circuit downstream of the heat source.

[0011 ] In this way, the hot side of the energy conversion module may extract thermal energy deriving from the heat source. [0012] In one embodiment, the hot side of the energy conversion module is arranged to be connected to the heat source circuit upstream of the heat exchanger.

[0013] In this way, the temperature of the first circulation fluid is higher when passing through the hot side of the energy conversion module, than when passing through the heat exchanger.

[0014] In one embodiment, the cold side of the energy conversion module is arranged to be connected to the heat receiver circuit downstream of the heat receiver.

[0015] Connecting the cold side of the energy conversion module to the already existing structure of the heat receiver circuit, enables the heat receiver to extract thermal energy from the second circulation fluid and decrease its temperature. Because of this, the second circulation fluid may be used to cool the cold side of the energy conversion module.

[0016] In one embodiment, the cold side of the energy conversion module is arranged to be connected to the heat receiver circuit upstream of the heat exchanger.

[0017] When the cold side of the energy conversion module delivers thermal energy to the second circulation fluid, the temperature of the fluid is increased. Thus, the system returns at least some of the energy which it extracted at the hot side of the energy conversion module.

[0018] In a second aspect of the present disclosure, there is provided a method for recovery of thermal energy from a heat source in a system according to the first aspect, the method comprising: connecting a hot side of an energy conversion module, by means of conduits of a flow control system, with a heat source circuit having a first circulation fluid such that the hot side of the energy conversion module may extract thermal energy from the first circulation fluid, connecting a cold side of the energy conversion module, by means of conduits of the flow control system, with a heat receiver circuit having a second circulation fluid such that the cold side of the energy conversion module may deliver thermal energy to the second circulation fluid.

[0019] Having a flow control system by which the energy conversion module may be connected to an existing heat source circuit and an existing heat receiver circuit, has the effect that electric energy may be generated when it is most beneficial from a heat recovery perspective. This is because, by means of the flow control system, the flow may be partly or fully directed to pass or bypass the energy conversion module. Furthermore, the flow control system provides that the energy conversion module may be connected to an existing infrastructure.

[0020] In one embodiment, the method further comprises: connecting the cold side of the energy conversion module, by means of conduits of the flow control system, with an additional cooling source such that the additional cooling source may extract thermal energy from the second circulation fluid.

[0021] The flow control system furthermore provides that an additional cooling source may be connected, when it is most beneficial from a heat recovery perspective. This gives high flexibility to the system. For example because different industrial sites generating waste heat may have access to different kinds of additional cooling sources such as sea water or other, and the flow control systema allows the available cooling source to be connected. The effect of connecting an additional cooling source is that additional cooling may be provided to the cold side of the energy conversion module. This means that the energy conversion module may continue to be operative, even when the second circulation fluid has a too high temperature to cool the energy conversion module.

Brief description of drawings

[0022] The present disclosure is now described, by way of example, with refer ence to the accompanying drawings, in which: [0023] Fig. 1 shows a system according to a first embodiment of the present disclosure.

[0024] Fig. 2 shows a system according to a second embodiment present disclosure.

[0025] Fig. 3 shows a conventional system for converting thermal energy with separate circuits for heating and cooling.

Description of embodiments

[0026] In the following, a detailed description of a system, a method and an energy conversion module for recovery of thermal energy will be described.

[0027] The system 1 generally comprises an energy conversion module 3 and a flow control system, comprising conduits and valves for connecting the system 1 to an already existing structure.

[0028] By means of the flow control system, the system 1 is arranged to be connected to a heat source circuit 7a connected to a heat source 2, and to a heat receiver circuit 7b connected to a heat receiver 5. The system 1 is also arranged to be connected to a cooling source 6. The heat source circuit 7a and the heat receiver circuit 7b comprise a respective first and second circulation fluid transported therein to deliver thermal energy.

[0029] The heat source circuit and the heat receiver circuit are connected by a heat exchanger 4. The heat exchanger 4 transfers thermal energy from the first circulation fluid to the second circulation fluid, i.e. from the heat source 2 to the heat receiver 5.

[0030] The first circulation fluid transports thermal energy between the system 1 , the heat source 2 and the heat exchanger 4. The second circulation fluid transports thermal energy between the system 1 , the heat receiver 5, the heat exchanger 4 and the cooling source 6. [0031] In one embodiment the heat source 2 is a waste heat source from an industrial facility, such as a steel plant. In another embodiment the heat source 2 is a geothermal heat source. The heat source 2 may also be another source of heat.

[0032] In one embodiment the energy conversion module 3 is a thermodynamic Organic Rankine Cycle module, ORC-module, which converts thermal energy into electricity. The energy conversion module 3 comprises a hot side and a cold side. Each of the hot side and the cold side comprises a heat exchanger to deliver and collect thermal energy to and from the energy conversion module 3.

[0033] The hot side heat exchanger extracts thermal energy from a circulation fluid for heating in order to vaporize a working medium inside the ORC-module. Therefore, the circulation fluid for heating passing the hot side heat exchanger must have a temperature higher than the temperature of the hot side of the ORC- module. The cold side heat exchanger on the other hand, outputs thermal energy to a circulation fluid for cooling in order to condense the working medium. Therefore, the circulation fluid for cooling passing through the cold side heat exchanger must have a temperature below the temperature of the cold side of the ORC-module.

[0034] Usually this is solved by guiding the circulation fluid for cooling through a cooler which extracts thermal energy from the circulation fluid for cooling. After passing through the cooler, the circulation fluid for cooling is cold enough to be guided back to the cold side heat exchanger to cool the ORC-module. Such a conventional system is illustrated in Fig. 3.

[0035] The present disclosure is based on the insight that, instead of a using a cooler to cool the circulation fluid for cooling, a heat receiver 5 may be used to extract the thermal energy from the circulation fluid. Then, after the heat receiver 5 has extracted thermal energy, the circulation fluid is cold enough to be guided to the cold side of the energy conversion module 3 and be used to cool the ORC- module. [0036] In one embodiment, the heat receiver 5 is a district heating network. In another embodiment the heat receiver 5 is an agricultural facility such as a green house, a fish plant or waste treatment facility.

[0037] In one embodiment, the heat source 2 and the hot side of the energy conversion module 3 are in fluid communication with each other and form part of the heat source circuit 7a. In this embodiment the first circulation fluid transported in the heat source circuit 7a extracts thermal energy from the heat source 2, wherein the temperature of the first circulation fluid is increased to approximately 100-140 °C. The first circulation fluid is then transported to the hot side of the energy conversion module 3 where thermal energy is extracted in order to vaporize the working medium therein, thus decreasing the temperature of the first circulation fluid to approximately 80-100 °C. The remaining thermal energy in the first circulation fluid is transported to a heat exchanger 4 which is also connected to the heat source circuit 7a, in fluid communication with the heat source 2 and the hot side of the energy conversion module 3. The heat exchanger 4 transfers at least some of the remaining thermal energy to the second circulation fluid in the heat receiver circuit 7b, to be transported to the heat receiver 5. For example, the second circulation fluid can be heated to 60-80 °C in the heat exchanger 4 before being transported to the heat receiver 5, which lowers the temperature of the second circulation fluid to about 50 °C.

[0038] In one embodiment, the flow control system guides the first circulation fluid, after passing the heat source 2, to bypass the hot side of the energy conversion module 3 to flow directly to the heat exchanger 4 to deliver thermal energy to the heat receiver circuit 7b. In one embodiment, the flow control system guides the first circulation fluid, after passing the heat source 2, to be divided, such that a first part of the first circulation fluid is guided pass the hot side of the energy conversion module 3, and second part of the first circulation fluid bypasses the hot side and flows directly to the heat exchanger 4 to deliver thermal energy to the heat receiver 5. Controlling the flow of the first circulation fluid to completely or partly bypass the hot side of the energy conversion module 3 may be upon meeting a predetermined criterion. Such a criterion may for example be a temperature of the first circulation fluid, or a temperature of the second circulation fluid, or another criterion. In this way, a user may, by means of the flow control system, direct thermal energy to the place where it may be of most use, in order not to waste thermal energy. For example, when the heat receiver 5 is a district heating network, the heating receiver energy need may display large fluctuations between summertime and winter. Thus, during summer when the energy need is lower, more energy may be used for electricity production. During winter when the need is higher, more energy may be used for heating. Similarly, if the heat receiver 5 is a green house, the heating need may for example decrease during summer.

[0039] In one embodiment the heat receiver 5 and the cold side of the energy conversion module 3 are in fluid communication with each other and form part of the heat receiver circuit 7b. In this embodiment the second circulation fluid transported in the heat receiver circuit 7b extracts thermal energy from the heat exchanger 4 derived from the heat source 2, and transports it to the heat receiver 5. When the heat receiver 5 utilizes the thermal energy, the temperature of the second circulation fluid is decreased, e.g. to about 50 °C. It is then guided to the cold side of the energy conversion module 3 to cool the module. After cooling of the energy conversion module 3, the second circulation fluid in the heat receiver circuit 7b, now having an increased temperature, e.g. of about 65 °C, is guided back to extract thermal energy from the heat exchanger 4. The disclosure is based on the insight that, during large parts of a year, the cold side of the energy conversion module 3 does not require more cooling than what may be provided by the second circulation fluid downstream of the heat receiver. As such, energy efficiency may be increased by utilizing the cooling provided form the second circulation fluid.

[0040] The present disclosure also relates to an additional cooling source 6, as shown in Fig. 2. In one embodiment, the additional cooling source 6 is a natural cooling source 6, such as seawater cooling system. The system 1 is arranged to be connected to the additional cooling source 6 and it may be utilized for example when the heat receiver 5 does not extract enough thermal energy from the second circulation fluid, such that the temperature of the second circulation fluid is not low enough to cool the energy conversion module 3. In one embodiment, connecting the additional cooling source 6 means that the additional cooling source 6 helps the heat receiver 5 to cool down the second circulation fluid before the circulation fluid enters the cold side heat exchanger of the energy conversion module 3, one such case is displayed in Fig. 2. For example, the additional cooling source 6 may provide a cooling temperature of about 15-25 °C.

[0041] Since the thermal input to the cold side of the energy conversion module 3 may be controlled by adding cooling from the additional cooling source 6, the electricity production may be increased. This is highly beneficial during periods, such as during summer, when the heat receiver 5 extracts less energy from the system 1 , and thus does not contribute with sufficient cooling to the energy conversion module 3. This ensures that the electricity production may be maintained, even during these periods. It furthermore provides flexibility to the system, wherein additional cooling may be provided only when needed, and may be connected to the existing structure by means of the flow control system.

[0042] The present disclosure also relates to a method for increasing the recovery of thermal energy from a heat source 2. The method generally comprises controlling how much of the thermal energy from the heat source 2 is delivered to the heat receiver 5, and how much is delivered to the energy conversion module 3. The method further comprises determining what cooling source 6 is most efficient to use to cool the energy conversion module 3, in order to recover as much thermal energy as possible from the heat source 2.

[0043] The method comprises guiding circulation fluid to extract thermal energy from a heat source 2, and deliver it to both the energy conversion module 3 which converts thermal energy to electricity, and to a heat receiver 5 which may use the thermal energy to heat facilities such as housings or agricultural facilities. Using the energy for heating, means that more energy can be utilized compared to using a conventional cooler. The method also related to determining how much of the flow of the circulation fluid is guided to the hot side of the energy conversion module 3 and the heat receiver 5 respectively. In order to increase the efficiency of the energy use, it may be more beneficial to guide a higher flow to the energy conversion module 3, to produce more electricity. At other times, it may be more beneficial to do the opposite, namely to guide a greater flow to the heat receiver 5. One of the heat receiver 5 and the hot side of the energy conversion module 3 may even be completely cut off. The method also relates to allowing the energy conversion module 3 and the heat receiver 5 to decrease the temperature of the circulation fluid enough to use it as a cooling medium in the energy conversion module 3. To do so, the circulation fluid is guided back to the energy conversion module 3, after the heat receiver 5 has extracted thermal energy. The method also relates to providing an additional cooling source 6, for those periods during a year when the heat receiver 5 is not sufficiently able to cool the circulation fluid in order to use it as a cooling medium in the energy conversion module 3. This additional cooling source 6 may for example be connected when it is determined that the production of electricity in the energy conversion module 3 is insufficient. This decision may for example be based on a threshold criterion, such as a temperature criterion of the circulation fluid. Or, it may be determined by a user.

[0044] It will be understood that when reference is made to an energy conversion module 3, this could be one single energy conversion module or a plurality of energy conversion modules.

[0045] Embodiments of a system and a method according to the present disclosure have been presented above. However, a person skilled in the art realises that this can be varied within the scope of the appended claims without departing from the inventive idea.

[0046] All the described alternative embodiments above or parts of an embodiment can be freely combined or employed separately from each other without departing from the inventive idea as long as the combination is not contradictory.