Design method of large-diameter high-temperature molten salt storage tank foundation in shallow bedrock area

Abstract

This invention discloses a design method for the foundation of a large-diameter high-temperature molten salt storage tank in areas with shallow bedrock. The foundation, from bottom to top, mainly consists of: a graded sand and gravel cushion layer, a top layer of sand and gravel with a buried ventilation pipe, a steel ring wall strip foundation, installation of the steel ring wall, filling the steel ring wall with artificial expanded clay, embedding a temperature sensor within the expanded clay, and sloping the top surface of the expanded clay with a sand layer. The steel ring wall design comprehensively considers two scenarios. Scenario one derives the circumferential stress calculation formula for the steel ring wall based on the stress analysis of the steel ring wall under the load of the upper storage tank. Scenario two establishes a calculation model based on the heat conduction analysis of the steel ring wall under soil constraints, thereby obtaining the stress calculation results for the steel ring wall. By comprehensively considering these two scenarios, a safe and reliable high-temperature molten salt storage tank foundation is designed, with a short construction period and easier quality control.

Description

Technical Field

[0001] This invention belongs to the field of design and manufacturing technology of storage tank foundations, and specifically relates to a design method for large-diameter high-temperature molten salt storage tank foundations in areas with shallow bedrock. Background Technology

[0002] High-temperature molten salt storage tanks are the core equipment of molten salt thermal energy storage technology, mainly used in scenarios such as concentrated solar power (CSP) and clean heating. Molten salt thermal energy storage technology can help store curtailed wind and solar power, releasing it when needed, reducing energy costs for users, improving the energy utilization rate of the entire power generation system, and achieving peak shaving and valley filling. It also smooths the output power of solar and wind power, enhancing the absorption capacity of new energy power generation.

[0003] Currently, there are no national standards or industry regulations for the design of foundations for high-temperature molten salt storage tanks. Most current tank foundations use concrete base slabs or concrete ring walls. However, for large-diameter high-temperature storage tanks, which are characterized by high tank bottom temperatures, large foundation diameters (exceeding 40m), and long ring wall lengths, using concrete base slabs or concrete ring walls presents challenges such as long construction periods due to the large volume of concrete pouring and difficulties in quality control.

[0004] Therefore, it is necessary to invent a design method for the foundation of large-diameter high-temperature molten salt storage tanks in areas with shallow bedrock to solve the above problems. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a design method for foundations of large-diameter high-temperature molten salt storage tanks in areas with shallow bedrock, thereby resolving the issues raised in the background section.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a design method for the foundation of a large-diameter high-temperature molten salt storage tank in areas with shallow bedrock, comprising the following steps:

[0007] Step 1: Excavate the soft soil layer on top of the bedrock, and compact the graded sand and gravel in layers, with each layer not exceeding 200mm in thickness and a compaction coefficient not less than 0.96.

[0008] Step 2: Set a ring of high-temperature resistant plain concrete on top of the graded sand and gravel. Level the top of the ring beam with high-temperature resistant grout to provide a foundation for the positioning of the steel ring wall.

[0009] Step 3: Determine the thickness of the tank bottom insulation material based on heat conduction analysis. The tank bottom insulation material is generally made of ceramsite, which is then constrained by a steel ring wall.

[0010] Step 4: Implement real-time temperature monitoring at different depths at the bottom of the tank;

[0011] Step 5: Install a heat-resistant concrete annular foundation for the tank wall on the inner side of the top of the steel ring wall. The annular foundation consists of precast concrete beam segments no more than two meters long, with Z-shaped expansion joints between each segment.

[0012] Furthermore, in step one, the thickness of the graded sand and gravel backfill on the top surface of the bedrock = bedrock burial depth - tank bottom insulation thickness - insulation layer bottom graded sand and gravel thickness.

[0013] Furthermore, in step two, graded sand and gravel are laid inside the ring beam, and steel pipes are embedded in the graded sand and gravel to reduce the thermal conductivity of the graded sand and gravel layer.

[0014] Furthermore, in step three, the strength of the steel ring wall is verified. The internal forces of the steel ring wall mainly consider the following two states:

[0015] State 1: Circumferential tensile stress generated in the steel ring wall under the action of active ceramsite soil pressure inside the ring wall and passive crushed stone soil pressure outside the ring wall;

[0016] Scenario 2: Heat is transferred from the bottom of the high-temperature molten salt storage tank to the top and bottom of the steel ring wall. The temperature field formed inside the steel ring wall is the highest at the top and the lowest at the bottom. Under the action of this temperature gradient, stresses in different directions will be generated in the steel plate.

[0017] Furthermore, in state one, the theoretical value of the circumferential tensile stress under the action of the tank bottom pressure is derived as follows:

[0018] The net internal pressure p of the steel ring wall at any height h is (q + γh) K. a -γ s hK p (1);

[0019] The equilibrium equation inside the steel ring wall is:

[0020]

[0021] From equation (2), we can derive the following:

[0022] Substituting equation (1) into equation (3),

[0023] Arrange equation (4) to get,

[0024] Due to γK a -γ s K p <0, the maximum circumferential tensile stress of the annular steel plate is at the top of the steel ring wall:

[0025] That is, when h = 0,

[0026] Where h is the distance from the calculated section to the top surface of the steel ring wall (m); D is the diameter of the steel ring wall (m); q is the compressive stress at the bottom of the tank (kPa); Ka is the active earth pressure coefficient of the bottom insulation material; and γ is the unit weight of the bottom insulation material (kN / m³). 3 );γ s Unit weight of backfill soil outside the steel ring wall (kN / m) 3 Kp is the passive earth pressure coefficient outside the steel ring wall; Ft is the circumferential tension of the steel ring wall.

[0027] Furthermore, in state two, the distributed soil reaction force outside the steel ring wall under the action of the temperature gradient is set as p. s p s =k s ·v+P s0 , and k s =mh;

[0028] Where, p s The distributed soil reaction force (kPa) outside the steel ring wall under temperature action; k s The horizontal reaction coefficient of the soil outside the steel ring wall (kN / m) 3 v is the horizontal displacement (m) of the soil at the calculation point of the distributed soil reaction force caused by the steel ring wall under temperature action; m is the proportionality coefficient of the soil horizontal reaction force (kN / m). 4 The value can be determined based on pile horizontal load tests and local experience; p s0 The initial distributed soil reaction force outside the steel ring wall can be represented by the active earth pressure distribution (kPa), and h is the depth of the calculation point from the ground.

[0029] Furthermore, in step four, during the process of layering and filling the bottom insulation ceramsite of the tank, sleeves are buried at different depths of the ceramsite, and holes are left at specific positions on the steel ring wall. Temperature detection signals are transmitted to the sleeves and then led out from the round holes on the steel ring wall.

[0030] Furthermore, in step five, after the upper tank wall is installed in place, high-temperature resistant grout is injected between the tank bottom plate and the annular foundation, and glass fiber is used to fill the space between the steel ring wall and the annular foundation.

[0031] Furthermore, the annular foundation is used to reduce differential settlement between the tank bottom plate below the tank wall and the tank bottom plate in the middle of the tank, thereby reducing the resulting tank deformation and internal stress.

[0032] The technical effects and advantages of this invention are as follows:

[0033] 1. This invention provides a foundation for positioning the steel ring wall by setting a high-temperature resistant plain concrete ring beam on top of the graded sand and gravel, and leveling the top of the ring beam with high-temperature resistant grout. The interior of the ring beam is filled with graded sand and gravel, and steel pipes are embedded in the graded sand and gravel to reduce the thermal conductivity of the graded sand and gravel layer. The circumferential stress and shear stress of the steel ring wall can be easily calculated through two different states, namely, state one and state two. Based on the calculated circumferential stress and shear stress, a safe and reliable high-temperature molten salt storage tank foundation can be designed. Moreover, the designed high-temperature molten salt storage tank foundation has a short construction cycle and is easier to control in terms of quality.

[0034] 2. This invention provides a heat-resistant concrete annular foundation for the tank wall by setting a heat-resistant concrete ring foundation on the inner side of the top of the steel ring wall. The annular foundation is composed of precast concrete beam segments not exceeding two meters in length, with Z-shaped expansion joints between each segment. The annular foundation is used to reduce the differential settlement between the tank bottom plate below the tank wall and the tank bottom plate in the middle of the tank, thereby reducing the resulting tank deformation and internal stress. Therefore, the width of the annular foundation is determined based on the fact that the compressive stress at the bottom of the annular foundation under the pressure of the tank wall is the same as that at the bottom of the tank.

[0035] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description and the drawings. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 A structural diagram of the high-temperature molten salt storage tank foundation according to an embodiment of the present invention is shown;

[0038] Figure 2 An embodiment of the present invention is shown. Figure 1 ① Schematic diagram;

[0039] Figure 3 An embodiment of the present invention is shown. Figure 1 Schematic diagram of part ② in the diagram;

[0040] Figure 4 An embodiment of the present invention is shown. Figure 2 A schematic diagram of the cross-sectional structure;

[0041] Figure 5 The diagram shows the stress analysis of the steel ring wall under the action of tank bottom pressure according to an embodiment of the present invention;

[0042] Figure 6 This diagram illustrates the circumferential tensile force analysis of the steel ring wall under the action of tank bottom pressure according to an embodiment of the present invention.

[0043] Figure 7 The diagram shows a calculation model of the steel ring wall under the action of a temperature gradient according to an embodiment of the present invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] This invention provides a design method for the foundation of a large-diameter high-temperature molten salt storage tank in areas with shallow bedrock, such as... Figure 1-7 As shown, it includes the following steps:

[0046] Step 1: Excavate the soft soil layer on top of the bedrock, and compact the graded sand and gravel in layers. Each layer should be no more than 200mm thick and the compaction coefficient should be no less than 0.96. The thickness of the graded sand and gravel backfill on the top of the bedrock is equal to the bedrock burial depth, the insulation thickness at the bottom of the tank, and the thickness of the graded sand and gravel at the bottom of the insulation layer.

[0047] Step Two: A high-temperature resistant plain concrete ring beam is installed on top of the graded sand and gravel. The top of the ring beam is leveled with high-temperature resistant grout to provide a foundation for the positioning of the steel ring wall; Figure 3 In the middle, the inside of the ring beam is paved with graded sand and gravel, and steel pipes are embedded in the graded sand and gravel to reduce the thermal conductivity of the graded sand and gravel layer.

[0048] Step 3: Determine the thickness of the tank bottom insulation material based on heat conduction analysis. The tank bottom insulation material is generally made of ceramsite, which is then constrained by a steel ring wall.

[0049] Strength calculations for the steel ring wall are performed, and the internal forces of the steel ring wall mainly consider the following two states:

[0050] Status 1: In Figure 5 and Figure 6 In the process, the steel ring wall generates circumferential tensile stress under the action of active ceramsite soil pressure inside the ring wall and passive crushed stone soil pressure outside the ring wall.

[0051] The theoretical value of the circumferential tensile stress under the action of the tank bottom pressure is derived as follows:

[0052] The net internal pressure p of the steel ring wall at any height h is (q + γh) K. a -γ s hKp (1);

[0053] The equilibrium equation inside the steel ring wall is:

[0054]

[0055] From equation (2), we can derive the following:

[0056] Substituting equation (1) into equation (3),

[0057] Arrange equation (4) to get,

[0058] Due to γK a -γ s K p <0, the maximum circumferential tensile stress of the annular steel plate is at the top of the steel ring wall:

[0059] That is, when h = 0,

[0060] Where h is the distance from the calculated section to the top surface of the steel ring wall (m); D is the diameter of the steel ring wall (m); q is the compressive stress at the bottom of the tank (kPa); K a γ is the active earth pressure coefficient of the tank bottom insulation material; γ is the unit weight of the tank bottom insulation material (kN / m³). 3 );γ s Unit weight of backfill soil outside the steel ring wall (kN / m) 3 ); K p F is the passive earth pressure coefficient outside the steel ring wall. t This refers to the circumferential tension of the steel ring wall.

[0061] State 2: In Figure 7 In the process, heat is transferred from the bottom of the high-temperature molten salt storage tank to the top and bottom of the steel ring wall. The temperature field formed inside the steel ring wall is the highest at the top and the lowest at the bottom. Under the action of this temperature gradient, stresses in different directions will be generated in the steel plate.

[0062] The distributed soil reaction force outside the steel ring wall under the action of temperature gradient is set as p. s p s =k s ·v+P s0 , and k s =mh;

[0063] Where, p s The distributed soil reaction force (kPa) outside the steel ring wall under temperature action; k s The horizontal reaction coefficient of the soil outside the steel ring wall (kN / m) 3v is the horizontal displacement (m) of the soil at the calculation point of the distributed soil reaction force caused by the steel ring wall under temperature action; m is the proportionality coefficient of the soil horizontal reaction force (kN / m). 4 The value can be determined based on pile horizontal load tests and local experience; p s0 The initial distributed soil reaction force outside the steel ring wall can be represented by the active earth pressure distribution (kPa), and h is the depth of the calculation point from the ground.

[0064] By determining the above parameters and substituting them into the finite element software for modeling and calculation, the circumferential stress and shear stress of the steel ring wall are obtained.

[0065] Step 4: Implement real-time temperature monitoring at different depths at the bottom of the tank; among other things... Figure 7 As shown, during the layered filling of the tank bottom insulation ceramsite, sleeves are buried at different depths of the ceramsite, and holes are left at specific positions on the steel ring wall. Temperature detection signals are transmitted to the sleeves and then led out from the round holes on the steel ring wall.

[0066] Step 5: Construct a heat-resistant concrete annular foundation for the tank wall on the inner side of the top of the steel ring wall. The annular foundation consists of precast concrete beam segments no more than two meters long, with Z-shaped expansion joints between each segment. Figures 2-4 In the process, after the upper tank wall is installed in place, high-temperature resistant grout is poured between the tank bottom plate and the annular foundation, and glass fiber is used to fill the space between the steel ring wall and the annular foundation.

[0067] The ring foundation is used to reduce differential settlement between the tank bottom plate below the tank wall and the tank bottom plate in the middle of the tank, thereby reducing the resulting tank deformation and internal stress. Therefore, the width of the ring foundation is determined based on the fact that the compressive stress at the bottom of the ring foundation under tank wall pressure is the same as that at the tank bottom. Using segmented precast concrete ring beams avoids the risk of concrete slurry contaminating the tank insulation material during concrete pouring, thus ensuring the insulation performance of the tank bottom insulation material.

[0068] This invention provides a foundation for positioning a steel ring wall by setting a high-temperature resistant plain concrete ring beam on top of graded sand and gravel, and leveling the top of the ring beam with high-temperature resistant grout. Graded sand and gravel are laid inside the ring beam, and steel pipes are embedded in the graded sand and gravel to reduce the thermal conductivity of the graded sand and gravel layer. The circumferential stress and shear stress of the steel ring wall can be easily calculated through two different states, namely, state one and state two. Based on the calculated circumferential stress and shear stress, a safe and reliable high-temperature molten salt storage tank can be designed. Moreover, the designed high-temperature molten salt storage tank has a short construction cycle and is easier to control in terms of quality.

[0069] A heat-resistant concrete annular foundation for the tank wall is set on the inner side of the top of the steel ring wall. The annular foundation consists of precast concrete beam segments of no more than two meters in length, with Z-shaped expansion joints between each segment. The annular foundation is used to reduce the differential settlement between the tank bottom plate below the tank wall and the tank bottom plate in the middle of the tank, thereby reducing the resulting tank deformation and internal stress. Therefore, the width of the annular foundation is determined based on the fact that the compressive stress at the bottom of the annular foundation under the pressure of the tank wall is the same as that at the bottom of the tank.

[0070] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A design method for the foundation of a large-diameter high-temperature molten salt storage tank in a shallow bedrock area, characterized in that: Includes the following steps: Step 1: Excavate the soft soil layer on top of the bedrock, and compact the graded sand and gravel in layers. The thickness of each layer should not exceed 200mm, and the compaction coefficient should not be less than 0.

96. The thickness of the graded sand and gravel backfill on the top of the bedrock = the bedrock burial depth - the insulation thickness at the bottom of the tank - the thickness of the graded sand and gravel at the bottom of the insulation layer. Step 2: A high-temperature resistant plain concrete ring beam is installed on top of the graded sand and gravel. The top of the ring beam is leveled with high-temperature resistant grout to provide a foundation for the positioning of the steel ring wall. Graded sand and gravel is laid inside the ring beam, and steel pipes are embedded in the graded sand and gravel to reduce the thermal conductivity of the graded sand and gravel layer. Step 3: Determine the thickness of the tank bottom insulation material based on the heat conduction analysis. The tank bottom insulation material is ceramsite, which is then constrained by a steel ring wall. Step 4: Implement real-time temperature monitoring at different depths at the bottom of the tank; Step 5: Install a heat-resistant concrete annular foundation for the tank wall on the inner side of the top of the steel ring wall. The annular foundation consists of precast concrete beam segments not exceeding two meters in length, with Z-shaped expansion joints between each segment. The width of the annular foundation is determined based on the compressive stress at the bottom of the annular foundation under the pressure of the tank wall being the same as that at the bottom of the tank. In step three, the strength of the steel ring wall is verified. The internal forces of the steel ring wall mainly consider the following two states: State 1: Circumferential tensile stress generated in the steel ring wall under the action of active ceramsite soil pressure inside the ring wall and passive crushed stone soil pressure outside the ring wall; Scenario 2: Heat is transferred from the bottom of the high-temperature molten salt storage tank to the top and bottom of the steel ring wall. The temperature field formed inside the steel ring wall is the highest at the top and the lowest at the bottom. Under the action of the temperature field, stresses in different directions will be generated in the steel plate. In state one, the theoretical value of the circumferential tensile stress under the action of the tank bottom pressure is derived as follows: at any height Net internal pressure of the steel ring wall ; The equilibrium equation inside the steel ring wall is: ； From equation (2), we can derive the following: ; Substituting equation (1) into equation (3), ; Arrange equation (4) to get, ; because The maximum circumferential tensile stress of the annular steel plate is at the top of the steel ring wall: Right now hour, ; Where h is the distance from the calculated section to the top surface of the steel ring wall (m); D is the diameter of the steel ring wall (m); q is the compressive stress at the bottom of the tank (kPa); K a γ is the active earth pressure coefficient of the tank bottom insulation material; γ is the unit weight of the tank bottom insulation material (kN / m³). 3 ); γ s Unit weight of backfill soil outside the steel ring wall (kN / m) 3 ); K p F is the passive earth pressure coefficient outside the steel ring wall. t This refers to the circumferential tensile force on the steel ring wall; In state two, the distributed soil reaction force outside the steel ring wall under the action of the temperature gradient is set as p. s p s =k s ·v+P s0 , and k s =mh; Where, p s The distributed soil reaction force (kPa) outside the steel ring wall under temperature action; k s The horizontal reaction coefficient of the soil outside the steel ring wall (kN / m) 3 v is the horizontal displacement (m) caused by the steel ring wall compressing the soil at the calculation point of the distributed soil reaction force under the action of temperature; m is the proportionality coefficient of the soil horizontal reaction force (kN / m). 4 ), based on pile horizontal load tests and regional experience; p s0 The initial distributed soil reaction force outside the steel ring wall is taken according to the active earth pressure distribution (kPa), and h is the depth of the calculation point from the ground.

2. The design method for foundations of large-diameter high-temperature molten salt storage tanks in shallow bedrock areas according to claim 1, characterized in that: In step four, during the process of layering and filling the bottom insulation ceramsite of the tank, sleeves are buried at different depths of the ceramsite, and holes are left at specific positions on the steel ring wall. Temperature detection signals are transmitted to the sleeves and then led out from the round holes on the steel ring wall.

3. The design method for foundations of large-diameter high-temperature molten salt storage tanks in shallow bedrock areas according to claim 1, characterized in that: In step five, after the upper tank wall is installed in place, high-temperature resistant grout is injected between the tank bottom plate and the annular foundation, and glass fiber is used to fill the space between the steel ring wall and the annular foundation.

4. The design method for foundations of large-diameter high-temperature molten salt storage tanks in shallow bedrock areas according to claim 3, characterized in that: The annular foundation is used to reduce differential settlement between the tank bottom plate below the tank wall and the tank bottom plate in the middle of the tank, thereby reducing the resulting tank deformation and internal stress.

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