Heat exchanger and method for heating molten salt using steam

Abstract

The present invention relates to a heat exchanger for heating molten salt by steam, comprising a heat exchange inner tube, an outer tube connecting groove, a heat exchange outer tube, an outer tube connecting pipe and a molten salt discharge pipeline; the hollow heat exchange inner tube is formed by connecting a plurality of vertically arranged U-shaped tubes in series; the outer tube connecting groove is respectively arranged below each U-shaped tube, corresponding to the U-shaped tube; each U-shaped tube comprises two straight tube sections and an arc-shaped curved tube section connecting the lower ports of the two straight tube sections; the arc-shaped curved tube section is arranged in the corresponding outer tube connecting groove, and the outer side of the straight tube section is sleeved with a heat exchange outer tube; the lower part of the heat exchange outer tube corresponding to the same U-shaped tube is connected to the upper part of the outer tube connecting groove; between adjacent U-shaped tubes, the adjacent heat exchange outer tubes are connected through the outer tube connecting pipe. The beneficial effects of the present invention are as follows: the present invention is composed of a vertically arranged heat exchange inner tube and a heat exchange outer tube, the heat exchange inner tube passes steam, and the heat exchange outer tube passes molten salt, and the heat exchange efficiency is high.

Description

Technical Field

[0001] The invention relates to the technical field of heat exchangers, and in particular to a molten salt heat exchanger for steam heating. Background Art

[0002] Thermal storage technology uses thermal storage materials as a medium to store thermal energy such as solar thermal energy, geothermal energy, industrial waste heat, and low-grade waste heat, and releases it when needed. It strives to solve the problems caused by the mismatch between thermal energy supply and demand in time, space or intensity, and to maximize the energy utilization rate of the entire system. Common energy storage and thermal storage technologies mainly include steam thermal storage technology, molten salt thermal storage technology, phase change material thermal storage technology, and solid material thermal storage technology. At present, molten salt thermal storage technology has been successfully applied in the fields of solar thermal power generation and heating. In the field of solar thermal power generation, solar energy is mainly used to heat molten salt thermal storage; in the field of heating, valley electricity is mainly used to heat molten salt thermal storage. When releasing heat, the molten salt heats the feed water through a shell and tube heat exchanger to produce high-temperature water or steam for heating or power generation.

[0003] The utility model patent with application number CN201721190502.0 discloses a steam molten salt heat exchanger, which adopts the shell and tube heat exchanger commonly used for molten salt heat exchange. Under small working conditions, the molten salt flow rate is slow and the heat exchange efficiency is low, which makes it difficult to meet the heat exchange requirements. A baffle is provided inside the shell, and part of the molten salt will be blocked when it is shut down, and it cannot be discharged, resulting in blockage. The invention patent with application number 201810232294.9 discloses a supercritical water and molten salt heat exchanger device, in which the molten salt cannot be completely discharged by gravity, and there will be molten salt retained in the pipeline. After the equipment is shut down, the molten salt will solidify and cause pipeline blockage. The invention patent with application number CN201811652797.8 discloses a shell and tube heat exchanger used in a small molten salt heat storage system, in which the molten salt is self-drained at a small inclination angle. Since the molten salt has a certain viscosity, it takes a long time to empty the entire device, which increases the operating cost. The molten salt flows through the inner tube. If the molten salt solidifies, it is difficult to heat and melt, which makes maintenance and inspection very inconvenient. The two ends of the outer tube of the heat exchanger are fixed to the inner tube through flanges, but due to the different temperatures of the inner and outer tubes, the expansion of the two tubes is inconsistent, which will generate stress and cause equipment damage. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a heat exchanger and method for heating molten salt using steam, which can timely drain the molten salt when the heat exchanger is shut down to prevent solidification and avoid damage caused by inconsistent expansion of inner and outer tubes.

[0005] The heat exchanger utilizing steam to heat molten salt comprises a heat exchange inner tube, an outer tube connecting groove, a heat exchange outer tube, an outer tube connecting pipe and a molten salt discharge pipeline; the hollow heat exchange inner tube is formed by connecting a plurality of vertically arranged U-shaped tubes in series; the outer tube connecting groove is respectively arranged below each U-shaped tube, corresponding to the U-shaped tube; each U-shaped tube comprises two straight tube sections and an arc-shaped curved tube section connecting the lower ports of the two straight tube sections; the arc-shaped curved tube section is arranged in the corresponding outer tube connecting groove, and the outer side of the straight tube section is sleeved with a heat exchange outer tube; the lower part of the heat exchange outer tube corresponding to the same U-shaped tube is connected to the upper part of the outer tube connecting groove; between adjacent U-shaped tubes, adjacent heat exchange outer tubes are connected through the outer tube connecting pipe; the lower part of each outer tube connecting groove is respectively connected to the molten salt discharge pipeline, and a molten salt discharge valve is arranged on the molten salt discharge pipeline.

[0006] Preferably, between two adjacent U-shaped pipes, the upper ports of two adjacent straight pipe segments are connected via an inner pipe elbow, and the upper ports of the straight pipe segments are connected to the inner pipe elbow by welding.

[0007] Preferably, the heat exchange outer tube, the outer tube connecting groove, the outer tube connecting pipe, the molten salt discharge pipeline and the molten salt discharge valve are all provided with electric heating components; and a molten salt flow channel is formed between the heat exchange outer tube, the outer tube connecting groove and the heat exchange inner tube.

[0008] As a preference, the outer tube connecting pipe is arranged obliquely, and the inflow port of the outer tube connecting pipe is higher than the outflow port of the outer tube connecting pipe.

[0009] Preferably, the straight pipe section at one end of the heat exchange inner tube is used as the inlet pipe section, and the upper port of the inlet pipe section is used as the hot steam inlet; the straight pipe section at the other end of the heat exchange inner tube is used as the outlet pipe section, and the upper port of the outlet pipe section is used as the cold steam outlet.

[0010] Preferably, a molten salt outlet is provided at the upper portion of the heat exchange outer tube sheathed outside the inlet pipe section; and a molten salt inlet is provided at the upper portion of the heat exchange outer tube sheathed outside the outlet pipe section.

[0011] Preferably, several end covers are also included, and the upper port of each straight pipe segment and the upper port of each heat exchange outer tube are welded to a corresponding end cover; the upper end of the straight pipe segment of the heat exchange inner tube and the upper end of the heat exchange outer tube are fixed to each other by end cover welding.

[0012] Preferably, an opening is provided in the middle of each end cover, the diameter of the opening is the same as the diameter of the straight pipe segment, and the position of the opening overlaps with the corresponding straight pipe segment in the vertical direction.

[0013] As a preference, the heat exchange outer tube is connected to the outer tube connecting groove by welding, and the heat exchange outer tube is connected to the outer tube connecting pipe by welding.

[0014] The method for operating a heat exchanger for heating molten salt using steam comprises the following steps:

[0015] S1. When starting: keep the molten salt discharge valve in the closed state; turn on the electric heating component to heat the heat exchange outer tube, the outer tube connecting tube and the outer tube connecting groove to above the melting point of the molten salt; then pass steam from the hot steam inlet for a period of time to heat the heat exchange inner tube and the inner tube elbow to above the melting point of the molten salt; finally, turn off the electric heating component, pass molten salt from the molten salt inlet, and start normal heat exchange;

[0016] S2. When shutting down: first open the electric heating components to heat the molten salt discharge pipeline and the molten salt discharge valve to above the melting point of the molten salt; then stop the molten salt transportation, maintain the steam transportation, open the molten salt discharge valve, and the molten salt will rely on its own gravity to be discharged through the molten salt discharge pipeline; after the molten salt is discharged, stop the steam transportation, and close the electric heating components and the molten salt discharge valve.

[0017] The beneficial effects of the present invention are:

[0018] (1) The present invention is composed of a vertically arranged inner heat exchange tube and an outer heat exchange tube, wherein steam flows through the inner heat exchange tube and molten salt flows through the outer heat exchange tube, and the heat exchange efficiency is high.

[0019] (2) The present invention is provided with an outer pipe connecting groove, which can not only mix the molten salt to make the molten salt temperature uniform, but also when the heat exchanger is shut down, the molten salt is emptied quickly with less residue, thereby preventing the molten salt from solidifying and causing blockage in the molten salt flow channel.

[0020] (3) The inner heat exchange tube and one end of the outer heat exchange tube of the present invention can expand freely and are not prone to stress damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the heat exchanger structure for heating molten salt using steam.

[0022] Explanation of the reference numerals: 1-molten salt inlet; 2-cold steam outlet; 3-molten salt outlet; 4-hot steam inlet; 5-heat exchange outer tube; 6-heat exchange inner tube; 7-end cover; 8-inner tube elbow; 9-outer tube connecting tube; 10-outer tube connecting groove; 11-molten salt discharge valve; 12-molten salt discharge pipeline; 13-electric heating component. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with embodiments. The description of the following embodiments is only used to help understand the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principles of the present invention, several improvements and modifications may be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0024] Embodiment 1

[0025] like Figure 1 As shown, the present invention provides a heat exchanger for heating molten salt by steam, comprising a heat exchange inner tube 6, an outer tube connecting groove 10, a heat exchange outer tube 5, an outer tube connecting pipe 9, and a molten salt discharge pipeline 12; the hollow heat exchange inner tube 6 is formed by connecting two vertically arranged U-shaped tubes in series, and the heat exchange inner tube 6 serves as a water medium flow channel; the outer tube connecting groove 10 is respectively arranged under each U-shaped tube, corresponding to the U-shaped tube; each U-shaped tube includes two straight tube sections and an arc-shaped curved tube section connecting the lower ports of the two straight tube sections; the arc-shaped curved tube section is arranged in the corresponding outer tube connecting groove 10, and the outer side of the straight tube section is sleeved with a heat exchange outer tube 5; the heat exchange outer tube 5 corresponding to the same U-shaped tube is connected to the upper part of the outer tube connecting groove 10; between adjacent U-shaped tubes, the adjacent heat exchange outer tubes 5 are connected through an outer tube connecting pipe 9; the lower part of each outer tube connecting groove 10 is respectively connected to a corresponding molten salt discharge pipeline 12, and a molten salt discharge valve 11 is arranged on the molten salt discharge pipeline 12.

[0026] The working principle of the present invention is: when the heat exchanger operates normally, the molten salt discharge valve 11 is in a closed state; when the heat exchanger stops, the molten salt discharge valve 11 is opened, and the molten salt in the molten salt flow channel can be quickly emptied through the molten salt discharge pipe 12 by its own gravity.

[0027] In the present invention, the heat exchange inner tube 6 and the heat exchange outer tube 5 are arranged vertically, so that the molten salt can be quickly discharged by its own gravity, preventing the molten salt that is not discharged from solidifying during shutdown and causing the molten salt flow channel to be blocked.

[0028] The outer pipe connecting groove 10 can mix the molten salt to make the temperature of the molten salt more uniform.

[0029] Furthermore, between two adjacent U-shaped pipes, an inner pipe elbow 8 is used to connect the upper ports of two adjacent straight pipe sections.

[0030] Furthermore, the heat exchange outer tube 5, the outer tube connection groove 10, the outer tube connection pipe 9, the molten salt discharge pipeline 12 and the molten salt discharge valve 11 are all provided with an electric heating component 13. Before starting the heat exchanger, the electric heating component 13 is turned on to heat the heat exchanger to a temperature above the melting point of the molten salt to prevent the molten salt from solidifying after the heat exchanger is started. A molten salt flow channel is formed between the heat exchange outer tube 5, the outer tube connection groove 10 and the heat exchange inner tube 6. Even if the molten salt solidifies in the molten salt flow channel, the molten salt can be heated and melted by turning on the electric heating component 13, which is convenient for maintenance and inspection.

[0031] Further, the outer tube connecting pipe 9 has a predetermined inclination angle, and the inflow port of the outer tube connecting pipe 9 is higher than the outflow port of the outer tube connecting pipe 9 .

[0032] Furthermore, the straight pipe section at one end of the heat exchange inner tube 6 is used as the inlet pipe section, and the upper port of the inlet pipe section is used as the hot steam inlet 4; the straight pipe section at the other end of the heat exchange inner tube 6 is used as the outlet pipe section, and the upper port of the outlet pipe section is used as the cold steam outlet 2.

[0033] Furthermore, a molten salt outlet 3 is provided on the upper portion of the heat exchange outer tube 5 sheathed outside the inlet pipe section; and a molten salt inlet 1 is provided on the upper portion of the heat exchange outer tube 5 sheathed outside the outlet pipe section.

[0034] Furthermore, it also includes a plurality of end caps 7; the upper end of each straight pipe segment and the upper end of each heat exchange outer tube 5 are welded to a corresponding end cap 7. The upper end of the straight pipe segment of the heat exchange inner tube 6 and the upper end of the heat exchange outer tube 5 are welded and fixed to each other through the end caps 7. The lower end of the straight pipe segment or the arc-shaped curved pipe segment is not fixed to the lower end of the heat exchange outer tube 5, and the lower end can expand freely, so as to avoid the heat exchanger damage caused by the stress generated by the inconsistent expansion degree of the heat exchange inner tube 6 and the heat exchange outer tube 5 due to the inconsistent temperature.

[0035] Furthermore, an opening is provided in the middle of each end cover 7, the diameter of the opening is the same as the diameter of the straight pipe segment, and the position of the opening overlaps with the corresponding straight pipe segment in the vertical direction.

[0036] Furthermore, the heat exchange outer tube 5 is connected to the outer tube connection groove 10 by welding, and the heat exchange outer tube 5 is connected to the outer tube connection pipe 9 by welding to ensure the circulation of the molten salt.

[0037] Furthermore, the upper port of the straight pipe section is connected to the inner pipe elbow 8 by welding.

[0038] Embodiment 2

[0039] The method for operating a heat exchanger for heating molten salt using steam comprises the following steps:

[0040] S1. At startup: ensure that the molten salt discharge valve 11 is closed; open the electric heating component 13, heat the heat exchange outer tube 5, the outer tube connecting tube 9 and the outer tube connecting groove 10 to above the melting point of the molten salt to prevent the molten salt from solidifying inside these components; then pass steam from the hot steam inlet 4 for a period of time to heat the heat exchange inner tube 6 and the inner tube elbow 8 to above the melting point of the molten salt to prevent the molten salt from solidifying outside these components; finally, close the electric heating component 13, pass molten salt from the molten salt inlet 1, and start normal heat exchange.

[0041] S2. When shutting down: first open the electric heating component 13 to heat the molten salt discharge pipe 12 and the molten salt discharge valve 11 to above the melting point of the molten salt; then stop the molten salt transportation, keep the steam transportation, open the molten salt discharge valve 11, and the molten salt in the heat exchanger will rely on its own gravity to be quickly discharged through the molten salt discharge pipe 12; after the molten salt is discharged, stop the steam transportation, and close the electric heating component 13 and the molten salt discharge valve 11.

[0042] This operation method can ensure that during the operation of the heat exchanger, especially in the start-up and shutdown stages, all surfaces contacted by the molten salt are at a temperature higher than the melting point of the molten salt, thereby fundamentally avoiding the solidification of the molten salt on the inside of the heat exchange outer tube, the outside of the heat exchange inner tube and the various joints, thereby ensuring the high heat exchange efficiency and service life of the heat exchanger; and during shutdown, the molten salt is quickly emptied, which can save time and operating costs.

Claims

1. A heat exchanger for heating molten salt using steam, Features: The invention comprises a heat exchange inner tube (6), an outer tube connection groove (10), a heat exchange outer tube (5), an outer tube connection pipe (9) and a molten salt discharge pipeline (12); the hollow heat exchange inner tube (6) is formed by connecting a plurality of vertically arranged U-shaped tubes in series; the outer tube connection groove (10) is respectively arranged below each U-shaped tube and corresponds to the U-shaped tube; each U-shaped tube comprises two straight tube sections and an arc-shaped curved tube section connecting the lower ports of the two straight tube sections; the arc-shaped curved tube section is arranged in the corresponding outer tube connection groove (10), and the outer side of the straight tube section is sleeved with a heat exchange outer tube (5); the lower part of the heat exchange outer tube (5) corresponding to the same U-shaped tube is connected to the upper part of the outer tube connection groove (10); between adjacent U-shaped tubes, adjacent heat exchange outer tubes (5) are connected through the outer tube connection pipe (9); the lower part of each outer tube connection groove (10) is respectively connected to the molten salt discharge pipeline (12), and the molten salt discharge pipeline (12) is provided with a molten salt discharge valve (11) ; The heat exchange outer tube (5), the outer tube connection groove (10), the outer tube connection pipe (9), the molten salt discharge pipeline (12) and the molten salt discharge valve (11) are all provided with an electric heating component (13); a molten salt flow channel is formed between the heat exchange outer tube (5), the outer tube connection groove (10) and the heat exchange inner tube (6); it also includes a plurality of end covers (7), the upper end of each straight tube segment and the upper end of each heat exchange outer tube (5) are welded to a corresponding end cover (7); the upper end of the straight tube segment of the heat exchange inner tube (6) and the upper end of the heat exchange outer tube (5) are fixed to each other by welding through the end covers (7); the outer tube connection pipe (9) is arranged in an inclined manner, and the inflow port of the outer tube connection pipe (9) is higher than the outflow port of the outer tube connection pipe (9); an opening is provided in the middle of each end cover (7), the diameter of the opening is the same as the diameter of the straight tube segment, and the position of the opening and the corresponding straight tube segment overlap in the vertical direction; the operation method of a heat exchanger for heating molten salt by steam comprises: S1. When starting: the molten salt discharge valve (11) is in a closed state; the electric heating component (13) is opened to heat the heat exchange outer tube (5), the outer tube connecting tube (9) and the outer tube connecting groove (10) to a temperature above the melting point of the molten salt; then steam is introduced from the hot steam inlet (4) for a period of time to heat the heat exchange inner tube (6) and the inner tube elbow (8) to a temperature above the melting point of the molten salt; finally, the electric heating component (13) is closed, and molten salt is introduced from the molten salt inlet (1) to start normal heat exchange; S2. When shutting down: first open the electric heating component (13) to heat the molten salt discharge pipe (12) and the molten salt discharge valve (11) to above the melting point of the molten salt; then stop the molten salt transportation, maintain the steam transportation, open the molten salt discharge valve (11), and the molten salt will be discharged through the molten salt discharge pipe (12) by its own gravity; after the molten salt is completely discharged, stop the steam transportation, and close the electric heating component (13) and the molten salt discharge valve (11).

2. The heat exchanger for heating molten salt using steam according to claim 1, Features: Between two adjacent U-shaped pipes, the upper ports of two adjacent straight pipe sections are connected via an inner pipe elbow (8), and the upper ports of the straight pipe sections are connected to the inner pipe elbow (8) by welding.

3. The heat exchanger for heating molten salt using steam according to claim 1, Features: The straight pipe section at one end of the heat exchange inner tube (6) is used as an inlet pipe section, and the upper end of the inlet pipe section is used as a hot steam inlet (4); the straight pipe section at the other end of the heat exchange inner tube (6) is used as an outlet pipe section, and the upper end of the outlet pipe section is used as a cold steam outlet (2).

4. The heat exchanger for heating molten salt using steam according to claim 3, Features: A molten salt outlet (3) is provided at the upper portion of the heat exchange outer tube (5) sleeved outside the inlet tube section; and a molten salt inlet (1) is provided at the upper portion of the heat exchange outer tube (5) sleeved outside the outlet tube section.

5. The heat exchanger for heating molten salt using steam according to claim 1, Features: The heat exchange outer tube (5) is connected to the outer tube connection groove (10) by welding, and the heat exchange outer tube (5) is connected to the outer tube connection tube (9) by welding.

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