Fused salt heat absorber heating surface partition design method

Abstract

The invention discloses a partition design method for a heating surface of a fused salt heat absorber, which comprises the following steps of: adopting a design for increasing the flow rate of fused salt on a tube panel in an inlet area of the fused salt heat absorber so as to improve the heat exchange capacity in a heat absorber tube; the tube panel at the outlet area of the fused salt heat absorber adopts the design of reducing the flow speed of fused salt so as to reduce the flow resistance of the fused salt heat absorber; and different materials are selected in an inlet area and an outlet area of the fused salt heat absorber. According to the method disclosed by the invention, the problems of insufficient temperature resistance and overlarge fatigue resistance margin of a high-temperature section material caused by unreasonable design of a current fused salt heat absorber are solved by sufficiently demonstrating and analyzing the heat flux density, the thermal stress, the start-stop times and the like on the surface of the heat absorber; secondly, the problem that the economical efficiency of the fused salt heat absorber is poor is solved; and thirdly, the problem of insufficient design flexibility of the fused salt heat absorber is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar thermal utilization, and in particular relates to a method for designing a zoning zone of a heating surface of a molten salt heat absorber. Background Art

[0002] Molten salt absorber is the key core equipment in tower solar thermal power station that converts solar radiation energy into molten salt working fluid heat energy. Molten salt absorber has the following characteristics: first, cold start at least 30,000 times in the service life requires high fatigue resistance; second, because the outlet temperature of molten salt is about 560℃, the equipment must be able to withstand high temperature operation of 650℃; third, the corrosiveness of molten salt requires the absorber to be corrosion-resistant; fourth, the heat flux density distribution on the surface of molten salt absorber in commercial power station is extremely uneven, which makes its thermal stress extremely large; fifth, molten salt absorber in engineering projects usually requires interchangeable tube screen design.

[0003] The above technical characteristics and engineering application requirements result in the molten salt heat absorber being prone to overheating of the heating tubes during actual operation; secondly, in order to meet the above technical requirements, N06625 or Hastelloy 230 nickel-based materials are usually used as heating surface tubes, resulting in limited temperature resistance and high cost. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems of the prior art and disclose a method for zoning the heating surface of a molten salt heat absorber. The method of the present invention solves the problem of insufficient temperature resistance but excessive fatigue resistance margin of the high-temperature section material of the current molten salt heat absorber due to unreasonable design through sufficient demonstration and analysis of the heat flux density, thermal stress, start-stop times, etc. of the heat absorber surface; secondly, it solves the problem of poor economy of the molten salt heat absorber; thirdly, it solves the problem of insufficient design flexibility of the molten salt heat absorber.

[0005] The object of the present invention is achieved through the following technical solutions:

[0006] A method for designing a zoning zone of a heating surface of a molten salt heat absorber, the method comprising:

[0007] The tube screen at the inlet area of ​​the molten salt heat absorber is designed to increase the molten salt flow rate to improve the heat exchange capacity in the heat absorber tube;

[0008] The tube screen at the outlet area of ​​the molten salt heat absorber adopts a design that reduces the molten salt flow rate to reduce the flow resistance of the molten salt heat absorber;

[0009] Different materials are selected in the inlet and outlet areas of the molten salt absorber.

[0010] According to a preferred embodiment, the flow direction of the molten salt in the molten salt heat absorber is: the imported molten salt flows in through the north side of the molten salt heat absorber, passes through the east side and the west side of the molten salt heat absorber in sequence, and then flows out through the south side of the molten salt heat absorber.

[0011] According to a preferred embodiment, the tube panel at the inlet area of ​​the molten salt heat absorber includes the tube panels from the north to the east of the molten salt heat absorber, including tube panel E1, tube panel E2, tube panel E3, and tube panel E4.

[0012] According to a preferred embodiment, the tube panel in the outlet area of ​​the molten salt heat absorber includes the tube panels from the west to the south of the molten salt heat absorber, including tube panel W5, tube panel W6, tube panel W7, and tube panel W8.

[0013] According to a preferred embodiment, the tube panel in the inlet area of ​​the molten salt heat absorber is made of nickel-based material.

[0014] According to a preferred embodiment, the tube panel in the outlet area of ​​the molten salt heat absorber is made of stainless steel.

[0015] According to a preferred embodiment, at the inlet area of ​​the molten salt absorber, the molten salt flow rate in the absorber tube of the inlet tube panel is increased from 3.0 m / s to 3.5 m / s.

[0016] According to a preferred embodiment, at the outlet area of ​​the molten salt absorber, the molten salt flow rate in the absorber tube of the outlet tube panel is reduced from 3.32 m / s to 2.5 m / s.

[0017] The aforementioned main scheme of the present invention and its further options can be freely combined to form multiple schemes, all of which are schemes that can be adopted and claimed for protection by the present invention. After understanding the scheme of the present invention, those skilled in the art can understand that there are multiple combinations based on the prior art and common knowledge, all of which are technical schemes to be protected by the present invention, and they are not exhaustively listed here.

[0018] Beneficial effects of the present invention:

[0019] The method of the present invention solves the risk of fatigue failure caused by excessive thermal stress in the inlet area of ​​the current molten salt heat absorber; solves the risk of short-term over-temperature failure caused by insufficient temperature resistance of the material in the outlet section of the heat absorber; solves the problem of unreasonable material selection; solves the problem of low economy of the molten salt heat absorber. According to the method of this patent, the cost of the heat absorber pipe can be reduced by about 40%. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the heat flux density in the molten salt flow direction of each tube panel of the molten salt absorber;

[0021] Figure 2 It is a schematic diagram of heat flux density and temperature of the heating pipe of the molten salt absorber;

[0022] Figure 3 It is the molten salt absorber circuit and heat flux density diagram;

[0023] Figure 4 It is a schematic diagram of the molten salt heat absorber circuit;

[0024] Figure 5 Different tube panels use different tube specifications and material drawings;

[0025] Among them, 1: axial heat flux density of 1# tube screen, 2: axial heat flux density of 2# tube screen, 3: axial heat flux density of 3# tube screen, 4: axial heat flux density of 4# tube screen, 5: axial heat flux density of 5# tube screen, 6: axial heat flux density of 6# tube screen, 7: axial heat flux density of 7# tube screen, 8: axial heat flux density of 8# tube screen, 9: absorber inlet tube screen, 10: absorber inlet tube screen heat flux density; 11: absorber inlet molten salt; 12: absorber outlet molten salt; 13: absorber outlet tube screen heat flux density; 14: absorber outlet tube screen; 15: absorber front end tube screen, 16: φ33.4×1.3 nickel-based tube, 17: absorber rear end tube screen, 18: φ40.0×1.5 stainless steel tube. DETAILED DESCRIPTION

[0026] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0027] It should be noted that similar numbers and letters represent similar items in the following figures, so once an item is defined in one figure, it does not need to be further defined and explained in the subsequent figures. In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate the orientation or position relationship based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the invented product is usually placed when used. It 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, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0028] In addition, the present invention should be pointed out that, in the present invention, unless the specific structure, connection relationship, positional relationship, power source relationship, etc. are specifically written out, the structure, connection relationship, positional relationship, power source relationship, etc. involved in the present invention are all known by those skilled in the art on the basis of the prior art without creative work.

[0029] The molten salt heat absorber is usually installed at an altitude of about 200 meters. The cold salt pump for conveying the medium is a centrifugal pump with an outlet head of about 800 meters of water column, a flow rate of about 1000t / h, a liquid depth of about 18 meters, and a conveying temperature of about 300℃. High head, large flow, long liquid depth, high temperature medium, etc. put forward extremely high technical requirements for the design and manufacture of the pump. In order to control the energy consumption of the pump operation and avoid excessive outlet head, the working fluid of the heat absorber is usually limited to a design flow rate of no more than 4m / s in the project. When designing the heat absorber, a high heat flux density method is usually used to reduce heat dissipation losses. Figure 1 The low-temperature molten salt enters the absorber from the north and is gradually heated to high-temperature molten salt flowing from the south. The absorber is composed of 1# to 8# tube panels in series. The axial distribution of heat flux density of each tube panel from north to south is as follows: Figure 3 and Figure 4 As shown. The tube screens in the 1#~4# section at the front end of the absorber process are high heat flux density areas, all greater than 600kW / ㎡, especially the 1# tube screen with the highest heat flux density of nearly 1000kW / ㎡; while the tube screens in the 5#~8# section at the rear end of the absorber process are low heat flux density areas, except for the 5# tube screen with a heat flux density exceeding 600kW / ㎡, the maximum heat flux densities of the other tube screens are less than 600kW / ㎡.

[0030] Conventional design methods require that each tube panel is interchangeable, that is, the structure and material of each tube panel are exactly the same. This design method has the following problems: First, the high heat flux density of 1000kW / ㎡ at the inlet of the absorber and the low molten salt flow rate of about 3m / s cause the temperature T of the light-facing surface of the heated tube to be high. o and backlight surface temperature T i The temperature difference between them exceeds 200℃, which leads to great thermal fatigue loss of the heat receiving pipe at the inlet section, and the heat absorbing pipe is prone to long-term failure accidents; secondly, the heat flux density at the outlet of the heat absorber does not exceed 600kW / ㎡, the molten salt flow rate is about 3.3m / s, and the outer wall temperature of the heat absorbing pipe is T o =T i +T f , the molten salt temperature T in the rear section of the absorber f Above 480℃, the molten salt temperature at the outlet is T f Above 550℃, the outer wall temperature of the heat absorption tube is T oThe temperature is all above 600℃. In addition, the heat flux density on the surface of the heat absorbing tube screen in operation inevitably deviates from the design. When the deviation exceeds a certain degree, the heat absorbing tube is very likely to fail due to short-term over-temperature. Third, in order to meet the design fatigue and interchangeability requirements of the molten salt absorber, each tube screen uses nickel-based materials. The cost of nickel-based materials is more than ten times that of stainless steel, but its high temperature resistance is lower than that of stainless steel. As a result, the high-priced materials selected are not only expensive but also fail to give full play to the material's strengths. The material selection is unreasonable. The heat flux density on the surface of the heated tube, the inner wall temperature, the external temperature, and the molten salt temperature are as follows: Figure 2 shown.

[0031] The present invention discloses a method for designing a zoning zone of a heating surface of a molten salt heat absorber, and the method for designing a zoning zone of a heating surface of a molten salt heat absorber comprises:

[0032] The tube screen at the inlet area of ​​the molten salt heat absorber is designed to increase the molten salt flow rate to improve the heat exchange capacity in the heat absorber tube, effectively reduce the temperature difference between the heat absorber tube To and Ti, thereby reducing fatigue loss and improving the long-term operation safety of the heat absorber;

[0033] The tube screen at the outlet area of ​​the molten salt heat absorber adopts a design that reduces the molten salt flow rate to reduce the flow resistance of the molten salt heat absorber;

[0034] Different materials are used in the inlet and outlet areas of the molten salt heat absorber. Preferably, the inlet area of ​​the molten salt heat absorber uses a nickel-based material with a high fatigue cycle, and the outlet area uses a stainless steel material with a higher temperature resistance.

[0035] Preferably, the flow direction of the molten salt in the molten salt heat absorber is: the imported molten salt flows in through the north side of the molten salt heat absorber, passes through the east side and the west side of the molten salt heat absorber in sequence, and then flows out through the south side of the molten salt heat absorber.

[0036] Preferably, the tube panel at the inlet area of ​​the molten salt heat absorber includes the tube panels from the north to the east of the molten salt heat absorber, including tube panel E1, tube panel E2, tube panel E3, and tube panel E4.

[0037] Preferably, the tube panel in the outlet area of ​​the molten salt heat absorber includes the tube panels from the west to the south of the molten salt heat absorber, including tube panel W5, tube panel W6, tube panel W7, and tube panel W8.

[0038] The method of the present invention solves the risk of fatigue failure caused by excessive thermal stress in the inlet area of ​​the current molten salt heat absorber; solves the risk of short-term over-temperature failure caused by insufficient temperature resistance of the material in the outlet section of the heat absorber; solves the problem of unreasonable material selection; solves the problem of low economy of the molten salt heat absorber. According to the method of this patent, the cost of the heat absorber pipe can be reduced by about 40%.

[0039] Example

[0040] refer to Figure 5As shown, taking a molten salt heat absorber with a thermal power of 300MWt as an example, when the design method of the present invention is adopted, nickel-based pipes of φ33.4×1.3 are selected in E1, E2, E3, and E4, and the molten salt flow rate in the heat absorbing tube of the inlet tube screen is increased from 3.0m / s to 3.5m / s, and the average heat transfer coefficient of the heat absorbing tube of the inlet tube screen is increased from 5878 (W / ㎡·℃) to 6600 (W / ㎡·℃), and the corresponding maximum metal wall temperature is reduced from 560℃ to 540℃, and the maximum temperature difference is reduced from 220℃ to 200℃. The fatigue loss is effectively reduced by reducing the temperature difference and the maximum temperature of the heat absorbing tube. φ40×1.5 iron-based pipes are used on W5, W6, W7 and W8 tube screens. The molten salt flow rate in the heat absorption tube of the outlet tube screen is reduced from 3.32m / s to 2.5m / s. The average heat transfer coefficient in the tube is reduced from 11000 (W / ㎡·℃) to 8500 (W / ㎡·℃), and the corresponding maximum metal wall temperature is increased from 630℃ to 665℃.

[0041] Therefore, according to the design method of the present invention, appropriately increasing the flow rate in the tubes on the E1, E2, E3, and E4 tube screens in the front area of ​​the heat absorber to improve the cooling capacity of the molten salt can reduce the thermal stress of the heat absorber tube and effectively reduce fatigue loss. Appropriately reducing the flow rate in the tubes on the W5, W6, W7, and W8 tube screens in the rear area of ​​the heat absorber increases the metal temperature, but the use of iron-based stainless steel materials with higher temperature resistance can effectively adapt to the above temperature. At the same time, the reduction in the flow rate in the rear area also offsets the increase in flow resistance caused by the increase in the flow rate in the front area, making the design of the heat absorber more reasonable.

[0042] By adopting this patented method and selecting different specifications and materials according to the heating characteristics of the absorber, not only the reliability of the molten salt absorber can be improved, but also its economy can be effectively improved.

[0043] The above description is only a preferred embodiment of the present invention and is 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 method for designing the heating surface zoning of a molten salt heat absorber, characterized in that: The molten salt heat absorber heating surface zoning design method comprises: The tube screen at the inlet area of ​​the molten salt heat absorber is designed to increase the molten salt flow rate to improve the heat exchange capacity in the heat absorber tube; The tube screen at the outlet area of ​​the molten salt heat absorber adopts a design that reduces the molten salt flow rate to reduce the flow resistance of the molten salt heat absorber; Different materials are selected in the inlet and outlet areas of the molten salt absorber.

2. The method for designing the heating surface zoning of a molten salt heat absorber according to claim 1, characterized in that: The flow direction of the molten salt in the molten salt heat absorber is as follows: the imported molten salt flows in through the north side of the molten salt heat absorber, passes through the east side and the west side of the molten salt heat absorber in turn, and then flows out through the south side of the molten salt heat absorber.

3. The method for designing the heating surface zoning of a molten salt heat absorber according to claim 2, characterized in that: The tube panels in the inlet area of ​​the molten salt heat absorber include the tube panels from the north to the east of the molten salt heat absorber, including tube panel E1, tube panel E2, tube panel E3, and tube panel E4.

4. The method for designing the heating surface zoning of a molten salt heat absorber according to claim 2, characterized in that: The tube panel in the outlet area of ​​the molten salt heat absorber includes the tube panels from the west to the south of the molten salt heat absorber, including tube panel W5, tube panel W6, tube panel W7, and tube panel W8.

5. The method for designing the heating surface zoning of a molten salt heat absorber according to claim 1, characterized in that: The tube screen in the inlet area of ​​the molten salt heat absorber is made of nickel-based material.

6. The method for designing the heating surface zoning of a molten salt heat absorber according to claim 1, characterized in that: The tube panel in the outlet area of ​​the molten salt heat absorber is made of stainless steel.

7. The method for designing the heating surface zoning of a molten salt heat absorber according to claim 1, characterized in that: In the inlet area of ​​the molten salt absorber, the molten salt flow rate in the absorber tube of the inlet tube panel is increased from 3.0m / s to 3.5m / s.

8. The method for designing the heating surface zoning of a molten salt heat absorber according to claim 1, characterized in that: In the outlet area of ​​the molten salt absorber, the molten salt flow rate in the absorber tube of the outlet tube panel is reduced from 3.32m / s to 2.5m / s.

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