A system and method for high-temperature molten salt series heat exchange

Abstract

The present invention relates to a system and method for high-temperature molten salt series heat exchange, including a molten salt tank; also including a first reactor, a first heat exchanger, a last reactor and a last heat exchanger connected in sequence; the molten salt inlet of the first reactor is also connected to the molten salt tank through a molten salt pump; the molten salt inlet of the first heat exchanger is connected to the molten salt outlet of the first reactor, and the molten salt outlet of the first heat exchanger is connected to the molten salt inlet of the last reactor; the molten salt inlet of the last heat exchanger is connected to the molten salt outlet of the last reactor; the molten salt outlet of the first heat exchanger and the molten salt outlet of the last heat exchanger are also connected to the molten salt tank; also including a molten salt bypass, the molten salt inlet of the first reactor is also connected to the molten salt inlet of the last reactor through the first molten salt bypass, and the molten salt inlet of the last reactor is also connected to the molten salt tank through the last molten salt bypass. The present invention reduces the number of molten salt pumps, reduces investment costs, reduces failure rates, and improves stable operation cycles, while making the temperature regulation of multiple reactors more flexible and accurate.

Description

Technical Field

[0001] The invention belongs to the field of molten salt heat exchange, and relates to a system and method for high-temperature series heat exchange of molten salt. Background Art

[0002] Molten salt is a common heat exchange medium. Compared with water or heat transfer oil, the use temperature of molten salt is higher, basically above 300℃, so it is particularly suitable for high-temperature heat exchange. However, due to the high heat exchange temperature of molten salt, the cost of molten salt heat exchange system is relatively high, especially molten salt pump.

[0003] For the catalytic reaction process involved in some chemical processes, the inlet and outlet temperatures of the heat exchange medium molten salt should not be too high. This is mainly because when the inlet and outlet temperature difference is large, the catalyst in the catalyst reaction tube may have a large temperature gradient near the wall and the center of the tube, thereby affecting the catalytic reaction performance and reaction stability. Under the condition of a certain heat exchange rate, the temperature difference cannot be too large, which means that a large amount of molten salt is required. For some molten salt pumps with large flow rates and long continuous operation cycles, the cost is higher. For this reason, if the number of molten salt pumps is reduced during use, it is the key to reducing the investment in the molten salt system.

[0004] Secondly, for some catalytic reaction processes, multiple reactors are usually connected in parallel. If each reactor has a separate molten salt heat exchange system, the number of molten salt pumps will increase significantly. If the molten salt at the outlet of a molten salt pump is divided into multiple reactors, multiple molten salt flow regulating valves are required, and the cost of high-temperature flow regulating valves is also high.

[0005] Therefore, it becomes critical to reduce the number of molten salt pumps and molten salt flow regulating valves under the conditions of multiple reactors. Summary of the invention

[0006] The present invention aims to solve the above problems and proposes a system and method for high-temperature molten salt series heat exchange.

[0007] The technical solution of the present invention is:

[0008] The present invention provides a high-temperature molten salt series heat exchange system.

[0009] A high-temperature molten salt series heat exchange system comprises a molten salt tank; also comprises a first reactor, a first heat exchanger, a last reactor and a last heat exchanger connected in sequence; the molten salt inlet of the first reactor is also connected to the molten salt tank through a molten salt pump; the molten salt inlet of the first heat exchanger is connected to the molten salt outlet of the first reactor, and the molten salt outlet of the first heat exchanger is connected to the molten salt inlet of the last reactor; the molten salt inlet of the last heat exchanger is connected to the molten salt outlet of the last reactor; the molten salt outlet of the first heat exchanger and the molten salt outlet of the last heat exchanger are also connected to the molten salt tank; also comprises a molten salt bypass, the molten salt inlet of the first reactor is also connected to the molten salt inlet of the last reactor through the first molten salt bypass, and the molten salt inlet of the last reactor is also connected to the molten salt tank through the last molten salt bypass.

[0010] The molten salt tank also includes a balancing molten salt tank; a liquid level balancing valve and a balancing molten salt pump are provided between the molten salt tank and the balancing molten salt tank; when the molten salt tank is a high-temperature molten salt tank, the balancing molten salt tank is a low-temperature molten salt tank; when the molten salt tank is a low-temperature molten salt tank, the balancing molten salt tank is a high-temperature molten salt tank.

[0011] An intermediate reaction system is also provided between the first heat exchanger and the last reactor, and the number of the intermediate reaction systems is ≥1; each group of intermediate reaction systems comprises an intermediate reactor, an intermediate heat exchanger and an intermediate molten salt bypass connected in sequence; the molten salt inlet of the intermediate reactor is connected to the molten salt outlet of the first heat exchanger or the molten salt outlet of the previous group of intermediate heat exchangers, one end of the molten salt outlet of the intermediate heat exchanger is connected to the molten salt inlet of the last reactor or the molten salt inlet of the next group of intermediate reactors, and the other end is connected to the molten salt tank; the molten salt inlet of the intermediate reactor is also connected to the molten salt inlet of the next group of intermediate reactors or the molten salt inlet of the last reactor through the intermediate molten salt bypass.

[0012] The molten salt bypasses are all provided with valves, which are regulating valves; the first molten salt bypass is provided with a first regulating valve, the middle molten salt bypass is provided with a middle regulating valve, and the last molten salt bypass is provided with a last regulating valve.

[0013] The molten salt tank, the balancing molten salt tank, the first heat exchanger molten salt inlet, the first heat exchanger molten salt outlet, the intermediate heat exchanger molten salt inlet, the intermediate heat exchanger molten salt outlet, the last heat exchanger molten salt inlet and the last heat exchanger molten salt outlet are all provided with temperature detectors; when the heat exchanger is a heater, the molten salt inlet temperature of the next reactor is higher than the molten salt outlet temperature of the previous reactor; when the heat exchanger is a cooler, the molten salt inlet temperature of the next reactor is lower than the molten salt outlet temperature of the previous reactor.

[0014] The molten salt tank and the balance molten salt tank are both provided with electric heaters.

[0015] The invention provides a high-temperature molten salt series heat exchange method.

[0016] A method for high-temperature molten salt series heat exchange, using any of the above high-temperature molten salt series heat exchange systems, the molten salt in the molten salt tank is transported to the first reactor through a molten salt pump, in the first reactor, the molten salt absorbs or provides heat to ensure that the experiment is carried out at the required temperature of the first reactor, and the molten salt leaving the first reactor enters the first heat exchanger for heat exchange to reach the experimental temperature requirement required to enter the next reactor.

[0017] It also includes: the amount of molten salt entering each reactor is fine-tuned through a molten salt bypass, and the temperature of the molten salt entering the first reactor and the entire high-temperature molten salt series heat exchange system is adjusted through a balanced molten salt tank.

[0018] The technical effects of the present invention are:

[0019] (1) The molten salt in the molten salt tank of the present invention enters the first reactor through the molten salt pump, and heat exchange is carried out in the first reactor, thereby achieving the purpose of controlling the temperature of the first reactor; the molten salt out of the first reactor enters the first heat exchanger for heat exchange, so that the temperature of the molten salt is restored to the outlet temperature of the molten salt tank, thereby ensuring that the temperature and flow rate of the molten salt entering each reactor are consistent;

[0020] (2) Preferably, each reactor is also provided with a molten salt bypass, so that the molten salt can flow through the molten salt bypass when the reactor is under maintenance and no molten salt is needed to enter; at the same time, the molten salt bypass can also play a certain role in regulating the temperature of the molten salt;

[0021] (3) Preferably, a balancing molten salt tank is also provided to supplement and adjust the molten salt temperature. This design can significantly reduce the number of molten salt pumps. Since the molten salt pump is a high-temperature dynamic device and a backup pump is required, the investment cost is relatively high; in addition, as a dynamic device, the failure rate of the molten salt pump is also relatively high. Therefore, reducing the number of molten salt pumps can significantly reduce the investment cost and operating cost of the entire device, and can also reduce the failure rate and increase the stable operation cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of specific experimental example 1 of the present invention.

[0023] Figure 2 It is a structural schematic diagram of comparative example 1 of the present invention.

[0024] Figure 3 It is a schematic structural diagram of comparative example 2 of the present invention.

[0025] Figure numerals: 1, molten salt tank; 2, molten salt pump; 6-1, first reactor; 6-2, intermediate reactor; 6-3, final reactor; 7-1, first heat exchanger; 7-2, intermediate heat exchanger; 7-3, final heat exchanger; 8, balance molten salt tank; 9, balance molten salt pump; 10, electric heater; 1-1, first valve; 1-2, second valve; 1-3, third valve; 1-4, fourth valve; 1-5, fifth valve, T, temperature detector. DETAILED DESCRIPTION

[0026] Example 1

[0027] A high-temperature molten salt series heat exchange system comprises a molten salt tank 1; and also comprises a first reactor 6-1, a first heat exchanger 7-1, a last reactor 6-3 and a last heat exchanger 7-3 which are connected in sequence; the molten salt inlet of the first reactor 6-1 is also connected to the molten salt tank 1 through a molten salt pump 2; the molten salt inlet of the first heat exchanger 7-1 is connected to the molten salt outlet of the first reactor 6-1, and the molten salt outlet of the first heat exchanger 7-1 is connected to the molten salt inlet of the last reactor 6-3; the molten salt inlet of the last heat exchanger 7-3 is connected to the molten salt outlet of the last reactor 6-3; the molten salt outlet of the first heat exchanger 7-1 and the molten salt outlet of the last heat exchanger 7-3 are also connected to the molten salt tank 1; and also comprises a molten salt bypass, the molten salt inlet of the first reactor 6-1 is also connected to the molten salt inlet of the last reactor 6-3 through the first molten salt bypass, and the molten salt inlet of the last reactor 6-3 is also connected to the molten salt tank 1 through the last molten salt bypass.

[0028] The specific implementation process of this embodiment is as follows:

[0029] The molten salt in the molten salt tank 1 is transported to the first reactor 6-1 through a molten salt pump 2. In the first reactor 6-1, the molten salt absorbs or provides heat to ensure that the experiment is carried out at the required experimental temperature of the first reactor 6-1. The molten salt leaving the first reactor 6-1 enters the first heat exchanger 7-1 for heat exchange to reach the experimental temperature requirement required for entering the next reactor.

[0030] Example 2

[0031] On the basis of Example 1, it also includes:

[0032] The molten salt tank 1 also includes a balancing molten salt tank 8; a liquid level balancing valve and a balancing molten salt pump 9 are provided between the molten salt tank 1 and the balancing molten salt tank 8; when the molten salt tank 1 is a high-temperature molten salt tank 1, the balancing molten salt tank 8 is a low-temperature molten salt tank 1; in order to prevent the high temperature of the high-temperature molten salt tank 1 from causing the reaction temperature to be too high, a large amount of low-temperature molten salt in the low-temperature molten salt tank 1 is fed into the high-temperature molten salt tank 1, thereby reducing the temperature of the high-temperature molten salt tank 1. When the molten salt tank 1 is a low-temperature molten salt tank 1, the balancing molten salt tank 8 is a high-temperature molten salt tank 1.

[0033] Example 3

[0034] On the basis of Example 2, the invention further includes:

[0035] An intermediate reaction system is also provided between the first heat exchanger 7-1 and the last reactor 6-3, and the number of the intermediate reaction systems is ≥1; each group of intermediate reaction systems includes an intermediate reactor 6-2, an intermediate heat exchanger 7-2 and an intermediate molten salt bypass connected in sequence; the molten salt inlet of the intermediate reactor 6-2 is connected to the molten salt outlet of the first heat exchanger 7-1 or the molten salt outlet of the previous group of intermediate heat exchangers 7-2, one end of the molten salt outlet of the intermediate heat exchanger 7-2 is connected to the molten salt inlet of the last reactor 6-3 or the molten salt inlet of the next group of intermediate reactors 6-2, and the other end is connected to the molten salt tank 1; the molten salt inlet of the intermediate reactor 6-2 is also connected to the molten salt inlet of the next group of intermediate reactors 6-2 or the molten salt inlet of the last reactor 6-3 through the intermediate molten salt bypass.

[0036] Example 4

[0037] On the basis of Example 3, the invention further includes:

[0038] The molten salt tank 1, the balancing molten salt tank 8, the molten salt inlet of the first heat exchanger 7-1, the molten salt outlet of the first heat exchanger 7-1, the molten salt inlet of the intermediate heat exchanger 7-2, the molten salt outlet of the intermediate heat exchanger 7-2, the molten salt inlet of the last heat exchanger 7-3 and the molten salt outlet of the last heat exchanger 7-3 are all provided with a temperature detector T; when the heat exchanger is a heater, the molten salt inlet temperature of the reactor at the next sequence is higher than the molten salt outlet temperature of the reactor at the previous sequence; when the heat exchanger is a cooler, the molten salt inlet temperature of the reactor at the next sequence is lower than the molten salt outlet temperature of the reactor at the previous sequence.

[0039] Example 5

[0040] On the basis of Example 4, the invention further comprises:

[0041] The molten salt bypass is provided with a valve, which is a regulating valve; the first molten salt bypass is provided with a first regulating valve, the middle molten salt bypass is provided with an intermediate regulating valve, and the last molten salt bypass is provided with a last regulating valve. The molten salt tank 1 and the balance molten salt tank 8 are both provided with an electric heater 10.

[0042] Specific experimental example - taking the exothermic reaction as an example, there are three reactors including the first reactor 6-1, the middle reactor 6-2 and the last reactor 6-3, the molten salt pump 2 is a high-temperature molten salt pump 2, and the balance molten salt pump 9 is a low-temperature molten salt pump 2;

[0043] When the experimental temperatures required by the three reactors are the same,

[0044] The molten salt in the high-temperature molten salt tank 1 is sent to the first reactor 6-1 through the molten salt pump 2; the heat generated by the exothermic reaction is absorbed, the temperature of the molten salt rises, and the reaction temperature is controlled within a certain range. For the stability of the reaction, the temperature difference between the molten salt inlet of the first reactor 6-1 and the molten salt outlet of the first reactor 6-1 should not exceed 50°C. If the temperature difference is too high, it may mean that the temperature gradient of the first reactor 6-1 is too high, affecting the reaction performance and reaction stability. Since the temperature difference is not large, and there is no phase change process in the heat exchange of the molten salt (compared with the change of water into water vapor), the heat capacity is relatively small, which requires a large molten salt flow rate, that is, a molten salt pump 2 with a large flow rate is required. After the molten salt at the molten salt outlet of the first reactor 6-1 is heat exchanged by the first heat exchanger 7-1, the temperature is reduced, and a certain amount of superheated steam is generated (water can be used for cooling and heat exchange to generate a certain amount of high-temperature steam). The temperature of the molten salt after heat exchange is restored to the temperature before entering the first reactor 6-1, that is, the same as the temperature of the high-temperature molten salt tank 1. After heat exchange, the molten salt enters the intermediate reactor 6-2 and the final reactor 6-3 in sequence;

[0045] The first reactor 6-1, the intermediate reactor 6-2 and the final reactor 6-3 are all equipped with five valves; taking the first reactor 6-1 as an example, there are five valves, namely the first valve 1-1, the second valve 1-2, the third valve 1-3, the fourth valve 1-4 and the fifth valve. During normal operation, the first valve 1-1 and the second valve 1-2 are opened, and the other valves are closed. When the first reactor 6-1 needs to be repaired or shut down, the molten salt shall not enter the first reactor 6-1, but the molten salt still needs to enter the intermediate reactor 6-2. At this time, the third valve 1-3 and the fourth valve 1-4 are opened, and the first valve 1-1 and the second valve 1-2 are closed. At the same time, the fifth valve is opened to discharge all the molten salt in the first reactor 6-1 to prevent the temperature of the first reactor 6-1 from lowering and solidifying the molten salt.

[0046] When the experimental temperatures required by the three reactors are different,

[0047] It is regulated together by each heat exchanger and molten salt bypass. For example, when only the temperature requirement of the first reactor 6-1 is lower than the set value, the third valve 1-3 and the fourth valve 1-4 can be used to prevent a part of the molten salt from entering the first reactor 6-1; when only the temperature requirement of the first reactor 6-1 is higher than the set value, it is necessary to increase the temperature of the molten salt tank 1 or the flow rate of the molten salt pump 2. For another example, when only the temperature requirement of the intermediate reactor 6-2 is lower than the set value, the third valve 1-3 and the fourth valve 1-4 can be used to prevent a part of the molten salt from entering the intermediate reactor 6-2, and the heat exchange of the first heat exchanger 7-1 can also be increased, thereby reducing the temperature of the molten salt entering the intermediate reactor 6-2; when only the temperature requirement of the intermediate reactor 6-2 is higher than the set value, it is necessary to reduce the heat exchange through the first heat exchanger 7-1 to increase the temperature of the molten salt entering the intermediate reactor 6-2.

[0048] In addition, since the reaction is an exothermic reaction, the most worrying situation is overheating. At this time, the molten salt temperature needs to be quickly lowered. For this reason, a balancing molten salt tank 8 is also provided, and at this time, the balancing molten salt tank 8 is a low-temperature molten salt tank 1. When the temperature is too high, the low-temperature molten salt can be quickly added to the high-temperature molten salt tank 1, or it can be more directly added to the outlet of the molten salt pump 2. A liquid level balancing valve is provided between the high-temperature molten salt tank 1 and the low-temperature molten salt tank 1. When the liquid level of the high-temperature molten salt tank 1 is high, the liquid level balancing valve can be opened to introduce the high-temperature molten salt into the low-temperature molten salt tank 1.

[0049] It can be seen that when three reactors are used as an example, a total of one molten salt pump 2 with a flow rate of Q and 15 valves (3 flow regulating valves and 12 shut-off valves) are required. Comparative Example 1 - There are three reactors with a first reactor 6-1, an intermediate reactor 6-2 and a final reactor 6-3, each reactor is equipped with a molten salt pump 2;

[0050] A total of three molten salt pumps 2 with a flow rate of Q are required, and the five valves configured for each reactor are eliminated;

[0051] Refer to the following price system:

[0052] equipment Shut-off valve Flow Control Valve Molten salt pump with flow rate Q Molten salt pump with flow rate of 3Q price 1M 2-5M 20-50M 50-100M

[0053] By comparison, it can be seen that for three reactors, Comparative Example 1 adds two high-temperature molten salt pumps 2, but reduces 15 valves. Since the price of the molten salt pump 2 is much higher than the flow regulating valve. When the price of the cut-off valve is 1M, the price of the flow regulating valve is 2M, and the flow of the molten salt pump 2 is 20M, without considering other factors, the investment of the specific experimental example is 38M, while the investment of Comparative Example 1 is 60M, and the investment has increased by 58%. In addition, in Comparative Example 1, the operating power consumption of the three molten salt pumps 2 will also increase, while the specific experimental example has only one first molten salt pump 2.

[0054] Comparative Example 2: There are three reactors, namely, the first reactor 6-1, the middle reactor 6-2 and the last reactor 6-3. Only one large-flow molten salt pump 2 is needed, and one flow regulating valve is configured at the inlet of each reactor.

[0055] A total of 1 molten salt pump with a flow rate of 3Q and 3 flow regulating valves are required, and 12 cut-off valves are cancelled;

[0056] When the price of the cut-off valve is 1M, the price of the flow regulating valve is 2M, the flow of the molten salt pump 2 with a flow rate of Q is 20M, and the flow of the molten salt pump 2 with a flow rate of 3Q is 50M, without considering other factors, the investment of the specific experimental example is 38M, and the investment of the comparative example 2 is 56M, which increases by 47%. In addition, due to the increase in the flow rate of the molten salt pump 2, its operating power consumption will also increase.

[0057] By comparing the specific experimental examples with comparative examples 1 and 2, the method provided by the present invention can effectively reduce the number of molten salt pumps 2, while reducing the flow requirements of the molten salt pumps 2, and can effectively reduce the system investment cost.

[0058] In addition, in Comparative Examples 1 and 2, since the molten salt of each reactor comes directly from the molten salt tank 1, the temperature of the molten salt entering each reactor is the same, and the temperature of the reactor can only be adjusted by the amount of molten salt. In the present invention, the amount and temperature of the molten salt entering the reactor can be adjusted by the dual adjustment of the flow control valve and the heat exchanger, thereby achieving precise control of the reactor temperature.

Claims

1. A high-temperature molten salt series heat exchange system, comprising a molten salt tank (1); characterized in that: It also includes a first reactor (6-1), a first heat exchanger (7-1), a last reactor (6-3) and a last heat exchanger (7-3) connected in sequence; the molten salt inlet of the first reactor (6-1) is also connected to the molten salt tank (1) through a molten salt pump (2); the molten salt inlet of the first heat exchanger (7-1) is connected to the molten salt outlet of the first reactor (6-1), and the molten salt inlet of the last heat exchanger (7-3) is connected to the molten salt outlet of the last reactor (6-3); the molten salt outlet of the first heat exchanger (7-1) and the molten salt outlet of the last heat exchanger (7-3) are also connected to the molten salt tank (1); it also includes a molten salt bypass, the molten salt inlet of the first reactor (6-1) is also connected to the molten salt inlet of the last reactor (6-3) through the first molten salt bypass, and the molten salt inlet of the last reactor (6-3) is also connected to the molten salt tank (1) through the last molten salt bypass; It also includes a balancing molten salt tank (8); a liquid level balancing valve and a balancing molten salt pump (9) are provided between the molten salt tank (1) and the balancing molten salt tank (8); when the molten salt tank (1) is a high-temperature molten salt tank, the balancing molten salt tank (8) is a low-temperature molten salt tank; when the molten salt tank (1) is a low-temperature molten salt tank, the balancing molten salt tank (8) is a high-temperature molten salt tank; The molten salt bypass is provided with a valve, which is a regulating valve; the first molten salt bypass is provided with a first regulating valve, the middle molten salt bypass is provided with an intermediate regulating valve, and the last molten salt bypass is provided with a last regulating valve; An intermediate reaction system is also provided between the first heat exchanger (7-1) and the last reactor (6-3), and the number of the intermediate reaction systems is ≥1; each group of intermediate reaction systems comprises an intermediate reactor (6-2), an intermediate heat exchanger (7-2) and an intermediate molten salt bypass which are connected in sequence; the molten salt inlet of the intermediate reactor (6-2) is connected to the molten salt outlet of the first heat exchanger (7-1) or the molten salt outlet of the previous group of intermediate heat exchangers (7-2); one end of the molten salt outlet of the intermediate heat exchanger (7-2) is connected to the molten salt inlet of the last reactor (6-3) or the molten salt inlet of the next group of intermediate reactors (6-2), and the other end is connected to the molten salt tank (1); the molten salt inlet of the intermediate reactor (6-2) is also connected to the molten salt inlet of the next group of intermediate reactors (6-2) or the molten salt inlet of the last reactor (6-3) through the intermediate molten salt bypass.

2. The high-temperature molten salt series heat exchange system according to claim 1 is characterized in that: The molten salt tank (1), the balancing molten salt tank (8), the molten salt inlet of the first heat exchanger (7-1), the molten salt outlet of the first heat exchanger (7-1), the molten salt inlet of the intermediate heat exchanger (7-2), the molten salt outlet of the intermediate heat exchanger (7-2), the molten salt inlet of the last heat exchanger (7-3) and the molten salt outlet of the last heat exchanger (7-3) are all provided with temperature detectors (T); when the heat exchanger is a heater, the molten salt inlet temperature of the reactor at the next sequence is higher than the molten salt outlet temperature of the reactor at the previous sequence; when the heat exchanger is a cooler, the molten salt inlet temperature of the reactor at the next sequence is lower than the molten salt outlet temperature of the reactor at the previous sequence.

3. The high-temperature molten salt series heat exchange system according to claim 2 is characterized in that: The molten salt tank (1) and the balance molten salt tank (8) are both provided with an electric heater (10).

4. A method for high-temperature molten salt series heat exchange, utilizing a high-temperature molten salt series heat exchange system as described in any one of claims 1 to 3 above, wherein the molten salt in the molten salt tank (1) is transported to a first reactor (6-1) through a molten salt pump (2), wherein the molten salt absorbs or provides heat in the first reactor (6-1) to ensure that the experiment is carried out at the required experimental temperature of the first reactor (6-1), and the molten salt leaving the first reactor (6-1) enters a first heat exchanger (7-1) for heat exchange to reach the experimental temperature requirement required for entering the next reactor.

5. The method for high-temperature molten salt series heat exchange according to claim 4, characterized in that: Also includes: The amount of molten salt entering each reactor is fine-tuned through a molten salt bypass, and the temperature of the molten salt entering the first reactor (6-1) and the entire high-temperature molten salt series heat exchange system is adjusted through a balanced molten salt tank (8).

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