Heat exchange device for heating fused salt through high-temperature steam

Abstract

The invention discloses a heat exchange device for heating fused salt through high-temperature steam, which comprises a first heat exchanger and a second heat exchanger, and a first pipe side steam outlet of the first heat exchanger is communicated with a second pipe side steam inlet of the second heat exchanger. A first shell side fused salt outlet of the first heat exchanger is communicated with a second shell side fused salt inlet of the second heat exchanger, the flow directions of steam and fused salt in the first heat exchanger are the same, and the flow directions of steam and fused salt in the second heat exchanger are opposite. According to the method, it can be guaranteed that the molten salt does not have the overtemperature risk, and the heat exchange requirement can be met.

Description

Technical Field

[0001] The invention belongs to the technical field of heat exchangers, and in particular relates to a heat exchange device for heating molten salt with high-temperature steam. Background Art

[0002] High-temperature molten salt heat storage technology is one of the main technologies for the transformation of existing coal-fired power units. Thermal power units transformed with high-temperature molten salt heat storage technology have high flexibility and fast adjustment speed, and can adapt to auxiliary services such as deep peak regulation, start-stop peak regulation, and rotating reserve trading. Participating in electricity spot market transactions, thermal power units with molten salt energy storage can store heat on a large scale, store valley electricity, and release heat to obtain high returns when electricity prices are high. Through heat and electricity decoupling, the heating scenarios of thermal power flexible units are expanded to create additional heating and steam supply benefits.

[0003] In the existing transformation plan, steam is directly extracted from the boiler and used to heat the molten salt. The molten salt directly absorbs the heat of the steam, eliminating the process of driving the steam turbine to generate electricity, and greatly increasing energy utilization efficiency.

[0004] HITEC ternary salt (KNO3-NaNO2-NaNO3 (53%-40%-7%)) is a low-melting-point molten salt widely used in the industrial field. Due to its excellent energy storage potential, it is often used as a heat storage and heat transfer working fluid in power stations. It can significantly improve the thermal efficiency, system reliability and economy of the power generation system, and enable the power station to achieve continuous and stable operation. Since low-melting-point molten salts often have a low decomposition temperature, there are strict restrictions on their use temperature. The crystallization temperature of HITEC ternary salt is 142°C, the decomposition temperature is 454°C, and the usual use temperature is 190°C to 450°C. Once it exceeds 450°C, there is a risk of chemical decomposition.

[0005] In the steam extraction and molten salt heating transformation plan, the temperature of the steam extracted from the boiler is above 500°C. Therefore, it is necessary to design a unique heat exchanger system to ensure that the temperature of the heat exchange tubes and tube sheet metal walls in contact with the molten salt is lower than 450°C to ensure that the molten salt does not chemically decompose. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a heat exchange device for heating molten salt with high-temperature steam, which can not only ensure that the molten salt does not have the risk of overheating, but also meet the heat exchange requirements.

[0007] The embodiments of the present invention are implemented by the following technical solutions:

[0008] A heat exchange device for high-temperature steam heating molten salt comprises a first heat exchanger and a second heat exchanger, wherein a first tube-side steam outlet of the first heat exchanger is connected to a second tube-side steam inlet of the second heat exchanger, and a first shell-side molten salt outlet of the first heat exchanger is connected to a second shell-side molten salt inlet of the second heat exchanger, wherein the flow directions of steam and molten salt in the first heat exchanger are the same, and the flow directions of steam and molten salt in the second heat exchanger are opposite.

[0009] In one embodiment of the present invention, both the first heat exchanger and the second heat exchanger are hairpin heat exchangers.

[0010] In one embodiment of the present invention, the first heat exchanger is a baffle rod hairpin heat exchanger.

[0011] In one embodiment of the present invention, the second heat exchanger is a single-bow baffle hairpin heat exchanger.

[0012] In one embodiment of the present invention, a molten salt guide tube is provided in the first heat exchanger.

[0013] The technical solution of the present invention has at least the following advantages and beneficial effects:

[0014] The present invention adopts two co-current and counter-current heat exchangers. The steam goes through the tube side and the molten salt goes through the shell side. The first heat exchanger adopts co-current heat exchange. The high-temperature steam inlet and the low-temperature molten salt inlet are on the same side to solve the problem of molten salt overheating. The second heat exchanger adopts counter-current heat exchange to ensure that the molten salt reaches the required temperature, which can not only ensure that the molten salt does not have the risk of overheating, but also meet the heat exchange requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0016] Figure 1 is a schematic diagram of a heat exchange device in the present invention;

[0017] Figure 2 is a schematic diagram of a first hairpin heat exchanger in the present invention;

[0018] Figure 3 Schematic diagram of the second hairpin heat exchanger in the present invention.

[0019] Icons: 1-first hairpin heat exchanger, 11-first tube side steam inlet, 12-first tube side steam outlet, 13-first shell side molten salt inlet, 14-first shell side molten salt outlet, 2-second hairpin heat exchanger, 21-second tube side steam inlet, 22-second tube side steam outlet, 23-second shell side molten salt inlet, 24-second shell side molten salt outlet, 31-molten salt guide tube. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0021] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. 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.

[0022] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0023] In the description of the present invention, it should be noted that if the terms "inside" or "outside" appear to indicate an orientation or position relationship, it is based on the orientation or position relationship shown in the accompanying drawings, or is the orientation or position relationship in which the product of the invention is usually placed when in use. This is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0024] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "configure", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0025] Example

[0026] Please refer to Figure 1-3This embodiment provides a heat exchange device for high-temperature steam heating molten salt, which includes a first hairpin heat exchanger 1 and a second hairpin heat exchanger 2. The first hairpin heat exchanger 1 adopts a baffle rod hairpin heat exchanger, and the second hairpin heat exchanger 2 adopts a single-bow baffle hairpin heat exchanger. The first tube-side steam outlet 12 of the first hairpin heat exchanger 1 is connected to the second tube-side steam inlet 21 of the second hairpin heat exchanger 2 through a pipeline. The high-temperature steam enters the first hairpin heat exchanger 1 from the first tube-side steam inlet 11, then flows out of the first hairpin heat exchanger 1 from the first tube-side steam outlet 12, enters the second hairpin heat exchanger 2 through the second tube-side steam inlet 21, and finally flows out of the second hairpin heat exchanger 2 from the second tube-side steam outlet 22.

[0027] The first shell-side molten salt outlet 14 of the first hairpin heat exchanger 1 is connected to the second shell-side molten salt inlet 23 of the second hairpin heat exchanger 2 through a pipeline, and the low-temperature molten salt enters the shell of the first hairpin heat exchanger 1 from the first shell-side molten salt inlet 13, flows out of the first hairpin heat exchanger 1 from the first shell-side molten salt outlet 14, flows into the second hairpin heat exchanger 2 through the second shell-side molten salt inlet 23, and finally flows out of the second hairpin heat exchanger 2 from the second shell-side molten salt outlet 24.

[0028] It should be noted that in the first hairpin heat exchanger 1 and the second hairpin heat exchanger 2, the steam flows along the tube side and the molten salt flows along the shell side. In the first hairpin heat exchanger 1, the high-temperature steam and the low-temperature molten salt flow in the same direction, i.e., downstream, and in the second hairpin heat exchanger 2, the high-temperature steam and the low-temperature molten salt flow in opposite directions, i.e., countercurrent. The first hairpin heat exchanger 1 adopts downstream heat exchange to solve the problem of molten salt overheating, and the first hairpin heat exchanger 1 adopts countercurrent heat exchange to ensure that the molten salt reaches the required temperature, which can not only ensure that the molten salt does not have the risk of overheating, but also meet the heat exchange requirements.

[0029] It should be noted that the heat exchange device is not limited to the hairpin heat exchanger, and any heat exchanger that can adopt the co-current + counter-current mode can be used.

[0030] In this embodiment, a molten salt guide tube 31 is provided in the first hairpin heat exchanger 1 to ensure uniform flow of the molten salt and avoid the occurrence of a molten salt heat exchange dead zone, which is conducive to uniform flow and heat exchange of the molten salt.

[0031] It should be noted that the first hairpin heat exchanger 1 and the second hairpin heat exchanger 2 in the present application adopt the hairpin heat exchanger in the prior art, and the molten salt guide tube 31 is also the prior art. Refer to the invention patent application "A three-stage flow-equalizing heat exchanger" applied by the applicant, publication number CN117928280A, in which the guide tube is consistent with the molten salt guide tube 31 in the present application.

[0032] The first hairpin heat exchanger 1 of the present invention adopts a baffle rod structure, and the molten salt flows along the shell side to ensure the longitudinal flow of the molten salt and avoid the formation of a flow dead zone. The first hairpin heat exchanger 1 does not consider the heat exchange area margin to avoid excessive arrangement of the heating surface, which leads to over-temperature decomposition of the molten salt after absorbing heat. The second hairpin heat exchanger 2 considers a certain area margin to ensure the heat exchange requirements.

[0033] The present invention adopts two hairpin heat exchangers of co-current + counter-current, with steam going through the tube side and molten salt going through the shell side. The first hairpin heat exchanger 1 adopts co-current heat exchange to solve the problem of molten salt overheating, and the second hairpin heat exchanger 1 adopts counter-current heat exchange to ensure that the molten salt reaches the required temperature, which can not only ensure that the molten salt does not have the risk of over-temperature, but also meet the heat exchange requirements.

[0034] Taking a certain project as an example, high-temperature steam is used to heat HI TEC ternary salt, and the steam inlet and outlet temperatures are 563℃ and 305℃ respectively. The molten salt inlet and outlet temperatures are 190℃ and 390℃ respectively.

[0035] The first hairpin heat exchanger 1 adopts downstream heat exchange, with an inlet steam temperature of 563°C and an inlet molten salt temperature of 190°C. The first hairpin heat exchanger 1 has a diameter of 1000mm and adopts a Φ25×2 heat exchange tube. After calculation, the metal temperature of the outer wall of the heat exchange tube is 371°C. A molten salt guide tube 31 is provided at the first shell-side molten salt inlet 13 of the first hairpin heat exchanger 1, which effectively avoids the formation of a flow dead zone near the inlet and outlet of the molten salt side of the tube sheet of the heat exchanger, thereby avoiding molten salt overheating. The first hairpin heat exchanger 1 adopts a baffle rod structure, and the molten salt flows more evenly on the shell side. At the same time, a hairpin structure heat exchanger is used to avoid temperature difference stress problems.

[0036] The outlet steam of the first hairpin heat exchanger 1 is 440°C, and the outlet molten salt is 286°C, that is, the inlet steam temperature of the second hairpin heat exchanger 2 is 440°C, and the inlet molten salt temperature is 286°C.

[0037] The second hairpin heat exchanger 2 has a diameter of 1200mm and uses Φ25×2 heat exchange tubes. The final steam outlet temperature is 305℃ and the molten salt outlet temperature is 390℃. The hairpin structure heat exchanger is used to solve the problem of temperature difference stress on the tube sheet. The heat exchanger adopts a baffle structure with a high heat transfer coefficient, reduces the heat exchange area, and the heat exchanger design is more economical.

[0038] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A heat exchange device for high-temperature steam heating molten salt, characterized in that: The invention comprises a first heat exchanger and a second heat exchanger, wherein a first tube-side steam outlet of the first heat exchanger is connected to a second tube-side steam inlet of the second heat exchanger, and a first shell-side molten salt outlet of the first heat exchanger is connected to a second shell-side molten salt inlet of the second heat exchanger, wherein the flow directions of the steam and the molten salt in the first heat exchanger are the same, and the flow directions of the steam and the molten salt in the second heat exchanger are opposite.

2. A heat exchange device for high-temperature steam heating molten salt according to claim 1, characterized in that: The first heat exchanger and the second heat exchanger are both hairpin heat exchangers.

3. A heat exchange device for high-temperature steam heating molten salt according to claim 2, characterized in that: The first heat exchanger is a baffle rod hairpin heat exchanger.

4. A heat exchange device for high-temperature steam heating molten salt according to claim 2, characterized in that: The second heat exchanger is a single-bow baffle hairpin heat exchanger.

5. A heat exchange device for high-temperature steam heating molten salt according to claim 2, characterized in that: A molten salt guide tube is provided in the first heat exchanger.

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