Working medium heat exchange system and regulation and control method thereof

Abstract

The invention provides a working medium heat exchange system and a regulation and control method thereof. The system comprises a gas storage tank, a liquid storage tank and a heat exchanger, the heat exchanger is provided with a cold fluid area and a hot fluid area, the hot fluid area comprises a main flow path heat exchange area and a bypass heat exchange area which are independently arranged, the gas storage tank, the main flow path heat exchange area and the liquid storage tank are connected to form a main flow path, and the gas storage tank, the bypass heat exchange area and the liquid storage tank are connected to form a bypass flow path. The hot fluid flows through the main flow path heat exchange area and the bypass heat exchange area and exchanges heat with the cold fluid flowing through the cold fluid area together, and the total flow of the hot fluid can be adjusted by adjusting the flow of the main flow path or the bypass flow path, so that heat balance of the cold fluid and the hot fluid in the heat exchanger is maintained, and supercooling or superheating is avoided. Besides, by means of the regulation and control method, the flow of the hot fluid can be correspondingly regulated and controlled through the electric valve or the variable-frequency booster pump according to rapid fluctuation or slow fluctuation of the flow of the cold fluid, and therefore heat balance in the heat exchanger can be achieved under all working conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of low-temperature cold energy power generation systems, and in particular to a working fluid heat exchange system and a control method thereof. Background Art

[0002] LNG (liquefied natural gas) cold energy power generation system is an efficient way of energy utilization. Its technical principle is mainly based on the large amount of cold energy released by LNG during the gasification process, cooling the working fluid to a temperature far below normal temperature, and constructing a power cycle with a lower cold end temperature. In traditional power generation cycles, such as the water vapor Rankine cycle, the highest temperature is the gaseous temperature of water vapor, and the lowest temperature is about the ambient temperature after the water vapor condenses in the condenser. The two temperature limits limit the working range of the working medium. The calculation of cycle efficiency follows Carnot's theorem, and the improvement of efficiency is subject to the maximum temperature and condensation temperature of the cycle. Therefore, the introduction of LNG cold energy can significantly increase the temperature difference between the hot end and the cold end of the working fluid, improve the power generation and operating efficiency. In this process, LNG itself absorbs heat and evaporates, and also obtains energy, the temperature rises to above 0 degrees Celsius, and then enters the natural gas pipeline network.

[0003] However, due to the low temperature of LNG, usually around -162 degrees Celsius, organic working fluids, carbon dioxide, ammonia water, etc. are currently used as circulating working fluids for LNG cold energy power generation. The triple point temperature of some working fluids is above -100 degrees Celsius. When condensed by LNG in the heat exchanger, it is easy to cause overcooling when the LNG flow rate suddenly fluctuates, causing the working fluid temperature to drop below the triple point temperature and directly condense. The condensed circulating working fluid will block the heat exchanger channel, causing pressure to be out of control, which will bring serious safety problems. Therefore, how to quickly and real-time regulate the operating conditions of the heat exchanger and eliminate this safety hazard is a major challenge faced in the construction of low-temperature cold energy power generation systems. Summary of the invention

[0004] In view of the above problems, the present invention provides a working fluid heat exchange system and a control method thereof.

[0005] The present invention provides a working fluid heat exchange system, comprising: a gas storage tank, a liquid storage tank and a heat exchanger, the heat exchanger having a cold fluid zone and a hot fluid zone, a cold fluid circulates inside the cold fluid zone, a hot fluid circulates inside the hot fluid zone, the cold fluid and the hot fluid exchange heat with each other, the cold fluid is heated up and vaporized after flowing through the cold fluid zone, the hot fluid flows out through the gas storage tank in gaseous form, is cooled into liquid after passing through the hot fluid zone and flows into the liquid storage tank in liquid form, the hot fluid zone comprises a main flow heat exchange zone and a bypass heat exchange zone which are independently arranged, the gas storage tank, the main flow heat exchange zone and the liquid storage tank are connected in sequence to form a main flow, the gas storage tank, the bypass heat exchange zone and the liquid storage tank are connected in sequence to form a bypass flow path.

[0006] According to the above technical solution, the hot fluid flows through the main flow heat exchange area and the bypass heat exchange area which are independently arranged, and exchanges heat with the cold fluid flowing through the cold fluid area. The total flow rate of the hot fluid can be adjusted by adjusting the flow rate of the main flow or the bypass flow, thereby maintaining the heat balance between the cold fluid and the hot fluid in the heat exchanger and avoiding overcooling or overheating.

[0007] Optionally, the cold fluid zone is connected to an external cold source and an underground pipe network. The external cold source provides cold fluid, which enters the cold fluid zone in liquid form, absorbs heat and vaporizes, flows out of the cold fluid zone in gaseous form and flows into the underground pipe network.

[0008] Optionally, a flow sensor is provided between the external cold source and the cold fluid zone, and the flow rate of the cold fluid is monitored in real time by the flow sensor.

[0009] According to the above technical solution, the flow rate of the cold fluid flowing into the cold fluid zone is monitored by a flow sensor, so that the flow rate of the hot fluid can be adjusted accordingly according to the flow rate of the cold fluid to maintain the heat balance between the cold fluid and the hot fluid in the heat exchanger.

[0010] Optionally, an electrically controlled valve is provided between the bypass heat exchange area and the liquid storage tank. The electrically controlled valve is communicatively connected to a flow sensor. The electrically controlled valve adjusts its opening according to monitoring data of the flow sensor to regulate the flow of the hot fluid in the bypass flow path.

[0011] According to the above technical scheme, the opening of the electric valve is adjusted accordingly according to the cold fluid flow data monitored by the flow sensor, so that the hot fluid flow in the bypass flow path can be quickly adjusted, thereby quickly adjusting the total hot fluid flow passing through the hot fluid area and maintaining the heat balance between the cold fluid and the hot fluid in the heat exchanger.

[0012] Optionally, a variable frequency booster pump is provided between the main flow heat exchange area and the liquid storage tank. The variable frequency booster pump is communicatively connected to the flow sensor. The variable frequency booster pump adjusts the pump frequency according to the monitoring data of the flow sensor to regulate the flow of the hot fluid in the main flow.

[0013] According to the above technical scheme, the pump frequency of the variable frequency booster pump is adjusted accordingly according to the cold fluid flow data monitored by the flow sensor, so that the hot fluid flow in the main flow path can be adjusted, thereby adjusting the total flow of the hot fluid flowing through the hot fluid area and maintaining the heat balance between the cold fluid and the hot fluid in the heat exchanger.

[0014] Optionally, the temperature of the cold fluid circulating in the cold fluid zone is lower than the triple point temperature of the hot fluid circulating in the hot fluid zone.

[0015] Optionally, the thermal fluid is an organic working fluid, carbon dioxide or ammonia water.

[0016] The present invention also provides a control method, which is applied to the above-mentioned working fluid heat exchange system, and includes the following steps: a cold fluid flow monitoring step, in which the flow rate of the cold fluid entering the cold fluid zone is monitored in real time by a flow sensor;

[0017] The hot fluid flow control step is to control the flow of the hot fluid by controlling the electric control valve or the variable frequency booster pump according to the flow change of the cold fluid.

[0018] According to the above technical solution, by monitoring the flow rate of the cold fluid entering the cold fluid zone and adjusting the flow rate of the hot fluid passing through the hot fluid zone in real time according to the flow rate of the cold fluid, the heat balance between the cold fluid and the hot fluid in the heat exchanger can be maintained to avoid overcooling or overheating.

[0019] In the control method provided by the present invention, optionally, in the hot fluid flow control step, when the flow of the cold fluid fluctuates rapidly, the hot fluid flow in the bypass flow path is adjusted by controlling the electronically controlled valve, comprising the following sub-steps:

[0020] When the flow of the cold fluid is stable, the electronically controlled valve maintains a preset opening, maintains the bypass flow area unchanged, and maintains the flow of the hot fluid in the bypass flow path unchanged;

[0021] When the flow rate of the cold fluid decreases rapidly, the opening of the electric control valve decreases, the bypass flow area decreases, and the flow rate of the hot fluid in the bypass flow path decreases;

[0022] When the flow rate of the cold fluid increases rapidly, the opening of the electronically controlled valve increases, the bypass flow area increases, and the flow rate of the hot fluid in the bypass flow path increases.

[0023] According to the above technical solution, when the flow of the cold fluid entering the cold fluid zone fluctuates rapidly, the flow of the hot fluid in the bypass flow path can be quickly adjusted by adjusting the opening of the electric valve, thereby quickly adjusting the total flow of the hot fluid flowing through the hot fluid zone, thereby maintaining the heat balance between the cold fluid and the hot fluid in the heat exchanger.

[0024] In the control method provided by the present invention, optionally, in the hot fluid flow control step, when the flow of the cold fluid fluctuates slowly, the hot fluid flow in the main flow path is adjusted by controlling the variable frequency booster pump, comprising the following sub-steps:

[0025] When the flow of the cold fluid is stable, the variable frequency booster pump maintains the preset pump frequency to keep the main flow unchanged;

[0026] When the flow of the cold fluid decreases slowly, the pump frequency of the variable frequency booster pump decreases, and the flow of the hot fluid in the main flow path decreases;

[0027] When the flow rate of the cold fluid increases slowly, the pump frequency of the variable frequency booster pump increases, and the flow rate of the hot fluid in the main flow path increases.

[0028] According to the above technical solution, when the flow of the cold fluid entering the cold fluid zone fluctuates slowly, the flow of the hot fluid in the main path can be adjusted by adjusting the pump frequency of the variable frequency booster pump, so that the flow of the hot fluid flowing through the main path is slowly adjusted following the flow of the cold fluid, thereby adjusting the total flow of the hot fluid flowing through the hot fluid zone and maintaining the heat balance between the cold fluid and the hot fluid in the heat exchanger. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of a working medium heat exchange system according to a first embodiment of the present invention;

[0030] Figure 2 It is a schematic structural diagram of a working medium heat exchange system according to a second embodiment of the present invention.

[0031] Figure numerals: liquid storage tank 1, heat exchanger 2, main flow heat exchange area 21, cold fluid area 22, bypass heat exchange area 23, gas storage tank 3, flow sensor 4, electric control valve 5, variable frequency booster pump 6. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] <First Embodiment>

[0034] Figure 1 It is a schematic structural diagram of a working medium heat exchange system according to a first embodiment of the present invention.

[0035] like Figure 1 As shown, the working medium heat exchange system of this embodiment includes a liquid storage tank 1, a heat exchanger 2 and a gas storage tank 3.

[0036] The heat exchanger 2 has a cold fluid zone 22 and a hot fluid zone, and the hot fluid zone includes a main flow heat exchange zone 21 and a bypass heat exchange zone 23 which are independently arranged.

[0037] Cold fluid circulates inside the cold fluid zone 22 , and hot fluid circulates inside the main heat exchange zone 21 and the bypass heat exchange zone 23 . The hot fluid in the main heat exchange zone 21 and the bypass heat exchange zone 23 can simultaneously exchange heat with the cold fluid in the cold fluid zone 22 .

[0038] Specifically, the main heat exchange area 21 and the bypass heat exchange area 23 are not connected to each other and have independent inlets and outlets. The gas storage tank 3, the main heat exchange area 21 and the liquid storage tank 1 are connected in sequence to form a main flow path, and the gas storage tank 3, the bypass heat exchange area 23 and the liquid storage tank 1 are connected in sequence to form a bypass flow path.

[0039] The thermal fluid is an organic working fluid (organic compound), carbon dioxide or ammonia. The gaseous thermal fluid is stored in the gas storage tank 3, and the liquid thermal fluid is stored in the liquid storage tank 1. The thermal fluid flows out of the gas storage tank 3 in the form of gas, and is cooled into liquid after heat exchange in the thermal fluid area and flows into the liquid storage tank in the form of liquid.

[0040] The cold fluid area 22 is connected to an external cold source (not shown in the figure) and an underground pipe network (not shown in the figure). The external cold source provides cold fluid, such as LNG (liquefied natural gas). The cold fluid enters the cold fluid area 22 in liquid form, absorbs heat and heats up to gasify, flows out of the cold fluid area 22 in gaseous form and flows into the underground pipe network.

[0041] The temperature of the cold fluid circulating in the cold fluid zone 22 is lower than the triple point temperature of the hot fluid circulating in the hot fluid zone.

[0042] A flow sensor 4 is provided between the external cold source and the cold fluid zone 22 , and the flow sensor 4 is used to monitor the flow of the cold fluid in real time.

[0043] An electrically controlled valve 5 is also provided between the bypass heat exchange area 23 and the liquid storage tank 1. The electrically controlled valve 5 is in communication connection with the flow sensor 4. The electrically controlled valve 5 adjusts its opening according to the monitoring data of the flow sensor 4 to regulate the flow of the hot fluid in the bypass flow path.

[0044] Specifically, the monitoring data of the flow sensor 4 is fed back in the form of an electrical signal, and the electronically controlled valve 5 can receive the electrical signal in real time and adjust its own opening, thereby controlling the bypass flow area to regulate the flow of the thermal fluid in the bypass flow path.

[0045] At the same time, the internal pressure of the gas tank 3 is greater than the internal pressure of the liquid tank 1, and the pressure difference between the gas tank 3 and the liquid tank 1 can push the thermal fluid from the gas tank 3 to flow through the thermal fluid area into the liquid tank 1. When the opening of the electric control valve 5 increases, due to the pressure difference between the gas tank 3 and the liquid tank 1, the flow in the bypass flow path can be rapidly increased, and the flow adjustment of the thermal fluid can be rapidly realized.

[0046] In conventional heat exchangers, since there is no bypass or additional heat exchange area, when the flow of the fluid on one side fluctuates, it is impossible to adjust the flow of the fluid on the other side in real time. Therefore, when it comes to cooling conditions near the triple point, there are major safety hazards, which increases the risk of system operation and the difficulty of regulation.

[0047] In this embodiment, by setting up a bypass flow path and an additional bypass heat exchange area 23, and supplemented by a flow sensor 4 and an electrically controlled valve 5 for flow control, the hot fluid flow can be quickly regulated according to changes in the cold fluid flow, so that the hot fluid flow can be followed in real time, the heat exchange temperature can be kept stable at all times, the temperature can be controlled not to deviate, and potential safety hazards can be effectively eliminated.

[0048] Furthermore, the control method of the working medium heat exchange system in this embodiment includes the following steps:

[0049] The cold fluid flow monitoring step is to monitor the flow of the cold fluid entering the cold fluid area 22 in real time through the flow sensor 4.

[0050] The hot fluid flow control step is to control the flow of the hot fluid by controlling the electronically controlled valve 5 according to the flow change of the cold fluid.

[0051] In this embodiment, in the hot fluid flow control step, when the flow of the cold fluid fluctuates rapidly, the hot fluid flow in the bypass flow path is adjusted by controlling the electrically controlled valve 5, which includes the following sub-steps:

[0052] When the flow rate of the cold fluid provided by the external cold source input into the cold fluid zone 22 is stable (i.e., the flow rate does not fluctuate or the fluctuation is very small), the electric-controlled valve 5 is not triggered to act, and the electric-controlled valve 5 maintains the preset opening, maintains the bypass flow area unchanged, and maintains the flow rate of the hot fluid in the bypass flow path unchanged.

[0053] Furthermore, under the condition that the flow rate of the cold fluid input into the cold fluid zone 22 is stable and the flow rate of the hot fluid in the main path through the main path heat exchange zone 21 is also kept stable, the bypass heat exchange zone 23 can maintain a lower circulation heat exchange load or directly close the circulation by controlling the opening of the electric control valve 5.

[0054] When the flow rate of the cold fluid input into the cold fluid zone 22 decreases rapidly, the flow sensor 4 outputs an electrical signal to trigger the electric control valve 5 to operate, the opening of the electric control valve 5 decreases, the bypass flow area decreases, and the flow rate of the hot fluid in the bypass flow path decreases.

[0055] When the flow rate of the cold fluid input into the cold fluid zone 22 increases rapidly, the flow sensor 4 outputs an electrical signal to trigger the electric control valve 5 to operate, the opening of the electric control valve 5 increases, the bypass flow area increases, and the flow rate of the hot fluid in the bypass flow path increases.

[0056] In this embodiment, the rapid fluctuation refers to the fluctuation of the cold fluid flow rate exceeding ±5% per second. In view of the rapid fluctuation of the cold fluid flow rate entering the cold fluid zone 22, the flow rate of the bypass flow path can be quickly adjusted by adjusting the opening of the electric control valve 5, so as to achieve a rapid increase or decrease in the bypass flow rate, thereby regulating the total flow rate of the hot fluid in real time, maintaining the heat balance between the cold fluid and the hot fluid in the heat exchanger 2, and avoiding the occurrence of overcooling or overheating.

[0057] <Second Embodiment>

[0058] Figure 2 It is a schematic structural diagram of a working medium heat exchange system according to a second embodiment of the present invention.

[0059] like Figure 2 As shown, the working medium heat exchange system in this embodiment is based on the first embodiment, and a variable frequency booster pump 6 is further provided between the main flow heat exchange area and the liquid storage tank 1.

[0060] The variable frequency booster pump 6 is connected to the flow sensor 4 in communication, and the variable frequency booster pump 6 adjusts the pump frequency according to the monitoring data of the flow sensor 4 to control the flow rate of the thermal fluid in the main flow path. The monitoring data of the flow sensor 4 is fed back in the form of an electrical signal, and the variable frequency booster pump 6 can receive the electrical signal in real time and adjust its own pump frequency, thereby controlling the flow rate of the thermal fluid in the main flow path.

[0061] Specifically, when the flow rate of the cold fluid changes slowly but the trend is obvious, it is no longer suitable to adjust the flow rate by quickly cutting in the bypass. By adjusting the pump frequency through the variable frequency booster pump 6, the flow rate can change slowly with the adjustment of the pump frequency, and the heat balance can be achieved under the state of slowly changing flow rate, thereby maintaining the stability of the overall system parameters.

[0062] Furthermore, the control method of the working medium heat exchange system in this embodiment includes the following steps:

[0063] The cold fluid flow monitoring step is to monitor the flow of the cold fluid in real time through the flow sensor 4.

[0064] The hot fluid flow control step is to control the flow of the hot fluid by controlling the variable frequency booster pump according to the flow change of the cold fluid.

[0065] In this embodiment, in the hot fluid flow control step, when the flow of the cold fluid fluctuates slowly, the hot fluid flow in the main flow path is adjusted by controlling the variable frequency booster pump 6, which includes the following sub-steps:

[0066] When the flow rate of the cold fluid provided by the external cold source input into the cold fluid zone 22 is stable (i.e., the flow rate does not fluctuate or the fluctuation is very small), the variable frequency booster pump 6 is not triggered to operate, and the variable frequency booster pump 6 maintains the preset pump frequency to keep the main flow path unchanged.

[0067] When the flow rate of the cold fluid input into the cold fluid zone 22 decreases slowly, the flow sensor 4 outputs an electrical signal to trigger the variable frequency booster pump 6 to operate, the pump frequency of the variable frequency booster pump 6 decreases, and the flow rate of the hot fluid in the main flow path decreases.

[0068] When the flow rate of the cold fluid input into the cold fluid zone 22 increases slowly, the flow sensor 4 outputs an electrical signal to trigger the variable frequency booster pump 6 to operate, the pump frequency of the variable frequency booster pump 6 increases, and the flow rate of the hot fluid in the main flow path increases.

[0069] In this embodiment, the slow fluctuation means that the fluctuation of the cold fluid flow rate per second is less than ±5%. In view of the slow fluctuation of the cold fluid flow rate entering the cold fluid zone 22, the pump frequency of the variable frequency booster pump 6 can be adjusted to slowly adjust the hot fluid flow rate in the main flow path following the change of the cold fluid flow rate, thereby adjusting the total flow rate of the hot fluid in real time, maintaining the heat balance between the cold fluid and the hot fluid in the heat exchanger 2, and avoiding the occurrence of overcooling or overheating.

[0070] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A working fluid heat exchange system, characterized in that: include: A gas storage tank, a liquid storage tank and a heat exchanger, wherein the heat exchanger has a cold fluid area and a hot fluid area, A cold fluid circulates inside the cold fluid zone, and a hot fluid circulates inside the hot fluid zone. The cold fluid and the hot fluid exchange heat with each other. The cold fluid is heated up and vaporized after flowing through the cold fluid zone. The hot fluid flows out through the gas storage tank in gaseous form, is cooled into liquid after passing through the hot fluid zone, and flows into the liquid storage tank in liquid form. The thermal fluid zone includes a main flow heat exchange zone and a bypass heat exchange zone which are independently arranged. The gas storage tank, the main flow heat exchange zone and the liquid storage tank are connected in sequence to form a main flow, and the gas storage tank, the bypass heat exchange zone and the liquid storage tank are connected in sequence to form a bypass flow path.

2. The working medium heat exchange system according to claim 1, characterized in that: The cold fluid zone is connected to an external cold source and an underground pipe network. The external cold source provides the cold fluid, which enters the cold fluid zone in liquid form, absorbs heat and vaporizes after heating, flows out of the cold fluid zone in gaseous form and then flows into the underground pipe network.

3. The working medium heat exchange system according to claim 2, characterized in that: A flow sensor is provided between the external cold source and the cold fluid zone, and the flow rate of the cold fluid is monitored in real time by the flow sensor.

4. The working medium heat exchange system according to claim 3, characterized in that: An electrically controlled valve is also provided between the bypass heat exchange area and the liquid storage tank. The electrically controlled valve is communicatively connected to the flow sensor. The electrically controlled valve adjusts its opening according to monitoring data of the flow sensor to regulate the flow of the thermal fluid in the bypass flow path.

5. The working medium heat exchange system according to claim 3, characterized in that: A variable frequency booster pump is also provided between the main flow heat exchange area and the liquid storage tank. The variable frequency booster pump is communicatively connected to the flow sensor. The variable frequency booster pump adjusts the pump frequency according to the monitoring data of the flow sensor to regulate the flow of the hot fluid in the main flow.

6. The working medium heat exchange system according to claim 1, characterized in that: The temperature of the cold fluid circulating in the cold fluid zone is lower than the triple point temperature of the hot fluid circulating in the hot fluid zone.

7. The working medium heat exchange system according to claim 1, characterized in that: The thermal fluid is an organic working fluid, carbon dioxide or ammonia water.

8. A control method, applied to the working medium heat exchange system according to any one of claims 1 to 7, characterized in that: The following steps are involved: A cold fluid flow monitoring step, monitoring the flow of the cold fluid entering the cold fluid zone in real time by means of the flow sensor; The hot fluid flow control step is to control the flow of the hot fluid by controlling an electric control valve or a variable frequency booster pump according to the flow change of the cold fluid.

9. The control method according to claim 8, characterized in that: In the hot fluid flow control step, when the flow of the cold fluid fluctuates rapidly, the hot fluid flow in the bypass flow path is adjusted by controlling the electronically controlled valve, comprising the following sub-steps: When the flow rate of the cold fluid is stable, the electronically controlled valve maintains a preset opening, maintains the bypass flow area unchanged, and maintains the flow rate of the hot fluid in the bypass flow path unchanged; When the flow rate of the cold fluid decreases rapidly, the opening of the electric control valve decreases, the bypass flow area decreases, and the flow rate of the hot fluid in the bypass flow path decreases; When the flow rate of the cold fluid increases rapidly, the opening of the electric control valve increases, the bypass flow area increases, and the flow rate of the hot fluid in the bypass flow path increases.

10. The control method according to claim 8, characterized in that: In the hot fluid flow control step, when the flow of the cold fluid fluctuates slowly, the hot fluid flow in the main flow path is adjusted by controlling the variable frequency booster pump, including the following sub-steps: When the flow rate of the cold fluid is stable, the variable frequency booster pump maintains a preset pump frequency to keep the flow rate of the main flow path unchanged; When the flow rate of the cold fluid decreases slowly, the pump frequency of the variable frequency booster pump decreases, and the flow rate of the hot fluid in the main flow path decreases; When the flow rate of the cold fluid increases slowly, the pump frequency of the variable frequency booster pump increases, and the flow rate of the hot fluid in the main flow path increases.

Images