Self-supporting falling film heat exchange tube bundle

Abstract

The utility model discloses a self-supporting falling film heat exchange tube bundle which comprises a plurality of falling film tubes which are parallel to one another and are distributed in a regular triangle shape, each falling film tube is a spiral falling film tube with a long circular section, two ends of a long shaft of each cross section are opposite semicircles, two ends of a short shaft of each cross section are parallel to one another, and the falling film tubes are continuously twisted into a spiral shape by taking the center lines of the falling film tubes as axes; the center distance between every two adjacent long-circular-section spiral falling film pipes is equal to the length of the long shaft, so that the adjacent long-circular-section spiral falling film pipes are in tangent contact with each other through two end points of the long shaft to achieve self-supporting. In the same cross section, the long axes and the short axes of all the long-circular-section spiral falling film pipes are parallel to each other, and gaps among all rows of the long-circular-section spiral falling film pipes in the short axis direction form a shell pass medium channel. The self-supporting falling film heat exchange tube bundle is high in heat transfer coefficient, low in shell pass resistance, uniform in falling film and low in manufacturing cost.

Description

Technical Field

[0001] This utility model relates to a falling film concentrator and separator, and more particularly to a self-supporting falling film heat exchanger tube bundle, belonging to the technical field of concentration equipment. Background Technology

[0002] The current mainstream technology for the concentration, purification, and separation of chemical wastewater uses four independent devices: a falling film evaporator, a vapor-liquid separator, a steam scrubbing tower, and a thickener, which respectively complete the concentration, vapor-liquid separation, small droplet collection, and clear-turbidity separation. However, the falling film evaporator uses ordinary bare tubes, which presents the following problems:

[0003] 1. Existing conventional falling film evaporators require a considerable number of arc-shaped baffles in the shell side. These baffles serve two purposes: first, they provide longitudinal support to the falling film tubes to prevent vibration caused by the Karman vortex street as the shell-side fluid flows through them; second, they allow the shell-side fluid to glide longitudinally across the tube bundle as much as possible. However, when the shell-side fluid meanders through the tops of each baffle in a wavy pattern, dead zones are formed in the triangular areas on both sides of the junction between the base of each baffle and the inner wall of the shell cylinder. This reduces the effective heat transfer length and area of ​​each falling film tube, and the existence of these dead zones significantly impacts heat transfer efficiency. Furthermore, the traditional arc-shaped baffles are limited in their ability to deflect shell-side steam within a relatively large range due to factors such as material cost and shell-side drag drop, and the number of deflections is also quite limited.

[0004] 2. Traditional vertical falling film evaporators use bare tubes. When the shell side is heated by steam condensation, a condensate film will form on the outer wall of the falling film tube after the steam condenses. Due to gravity, the condensate film will gradually thicken in the height direction of the falling film tube, resulting in poor heat transfer in the middle and lower parts of the falling film tube.

[0005] 3. In existing conventional falling film evaporators, the resistance increases when the shell-side fluid flows through the baffle plate notch area due to the reduced flow area.

[0006] 4. Existing conventional falling film evaporators require a large center distance between falling film tubes to reduce the resistance of the shell-side fluid and ensure that the resistance drop of the shell side meets the process requirements. This limits the heat exchanger shell to a larger diameter, resulting in higher material costs.

[0007] 5. Existing conventional falling film evaporators have poor uniformity of liquid film thickness in the circumferential direction within the falling film tubes. To ensure uniform liquid film thickness in the circumferential direction of the falling film tubes, the film distribution effect of the distributor must be good, and the manufacturing and installation of the falling film tube bundles must have high vertical precision. Otherwise, after the tube-side fluid passes through a specially structured distributor, it falls relatively evenly onto the tube bridge of the upper tube sheet. During the downward flow along the falling film tubes, due to deviations in the manufacturing and installation process of the heat exchanger, the non-uniformity of the liquid film in the circumferential direction within the falling film tubes may be amplified, affecting the heat transfer effect. Furthermore, when the deviation of the liquid film in the falling film tubes reaches a certain level, the liquid film thickness may decrease to zero on one side, leading to dry tubes in some areas within the falling film tubes, scaling, and further blockage of the falling film tubes. Utility Model Content

[0008] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, and such simplifications or omissions should not be construed as limiting the scope of the present invention.

[0009] In view of the problems existing in the above and / or prior art, this utility model is proposed.

[0010] The purpose of this invention is to overcome the problems existing in the prior art and provide a self-supporting falling film heat exchanger tube bundle with high heat transfer coefficient, low shell-side resistance, uniform falling film, and low manufacturing cost.

[0011] To solve the above technical problems, this utility model provides a self-supporting falling film heat exchanger tube bundle, which includes multiple parallel falling film tubes distributed in an equilateral triangle. Each falling film tube is an oblong cross-section spiral falling film tube. The two ends of the major axis of each cross-section are opposing semicircles, and the two ends of the minor axis are parallel to each other. The tubes are continuously twisted into a spiral shape around the center line of the falling film tube. The center distance between adjacent oblong cross-section spiral falling film tubes is equal to the length of the major axis, so that adjacent oblong cross-section spiral falling film tubes are tangentially contacted to each other through the two ends of the major axis to achieve self-support.

[0012] As an improvement of this utility model, within the same cross-section, the major axis and minor axis of each oblong cross-section spiral falling film tube are parallel to each other, and the gap between each row of oblong cross-section spiral falling film tubes in the minor axis direction constitutes the shell-side medium channel.

[0013] As a further improvement of this utility model, the center line of each oblong cross-section spiral falling film tube remains unchanged during the spiral process. Within 360° of each pitch, it makes tangential contact with the adjacent oblong cross-section spiral falling film tube six times, and the position of the tangential contact point with the adjacent oblong cross-section spiral falling film tube changes every 60°.

[0014] As a further improvement of this utility model, the outer periphery of the oblong cross-section spiral falling film tube bundle is dodecagonal, and multiple straps are bound around the outer periphery.

[0015] As a further improvement of this utility model, the cross-sectional dimensions of each oblong cross-section spiral falling film tube are 45x25.5mm, and the spiral pitch is 250mm; the upper and lower ends of each oblong cross-section spiral falling film tube are circular base tubes with an outer diameter of 38mm.

[0016] Compared with the prior art, the advantages or beneficial effects of the embodiments of this application include at least the following: 1. The shell-side baffle is eliminated, which saves the material cost and machining cost of the baffle; at the same time, there is no need to set up tie rods and spacer tubes, saving material costs;

[0017] 2. By using a smaller center distance between falling film tubes, the diameter of the tube bundle can be smaller under the same heat exchange area. This means that a thinner tower body and upper and lower tube sheets can be used. The diameter and thickness of the tube sheets and tower body can be reduced, saving material costs.

[0018] 3. Using a long oval cross-section spiral falling film tube as the falling film tube, the unique structure of the long oval cross-section spiral falling film tube prevents the liquid film formed when the heating steam condenses in the shell side from continuously thickening as in traditional falling film evaporators. This reduces the thickness of the outer thermal boundary layer of the falling film tube, resulting in a smaller thermal resistance between the steam and the outer wall of the falling film tube. At the same time, the spiral structure on the inner wall of the falling film tube makes the liquid film thickness on the inner wall of the tube more uniform through secondary distribution. The secondary flow in the circumferential direction also makes the thermal boundary layer thickness of the liquid film inside the falling film tube more uniform, which also improves the heat transfer coefficient on the tube side. With the combined improvement in heat transfer efficiency inside and outside the tube, the overall heat transfer coefficient of the self-supporting falling film heat exchanger tube bundle is increased from 1600W / (㎡·K) of traditional falling film evaporators to over 2100W / (㎡·K), an increase of over 31%.

[0019] 4. Due to the secondary flow in the circumferential direction generated on the inner wall of the oblong cross-section spiral falling film tube, the flow boundary layer velocity of the liquid film inside the tube is faster, and the scaling cycle on the inner wall of the oblong cross-section spiral falling film tube is longer. This means that a lower tube-side fouling thermal resistance can be selected in the thermal calculation. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. The drawings are provided for reference and illustration only and are not intended to limit this utility model. Wherein:

[0021] Figure 1 This is a top view of the self-supporting falling film heat exchanger tube bundle of this utility model embedded in the upper tube sheet;

[0022] Figure 2 This is a perspective view of the outer circumferential self-supporting falling film heat exchanger tube bundle in this utility model;

[0023] Figure 3 This is a perspective view of a spiral falling film tube with an oblong cross-section in this utility model;

[0024] Figure 4 This is a schematic diagram of the self-support point transformation of the long oval cross-section spiral falling film tube bundle in this utility model;

[0025] In the figure: 1. Upper tube sheet; 2. Elongated cross-section spiral falling film tube; 3. Bundle. Detailed Implementation

[0026] In the following description of this utility model, the terms "upper", "lower", "front", "rear", "left", "right", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this utility model and simplifying the description, and do not mean that the device must have a specific orientation.

[0027] To make the technical means, creative features, achieved objectives and effects of this utility model easier to understand, the present utility model will be further described below with reference to specific illustrations. Obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0029] like Figures 1 to 4 As shown, the self-supporting falling film heat exchanger tube bundle of this utility model includes multiple oblong cross-section spiral falling film tubes 2. The two sides of each oblong cross-section spiral falling film tube 2 are parallel to each other, and the two ends are opposite semi-circular cross-sections. The straight line where the center of the two semi-circular cross-sections is located is the major axis of the falling film tube, and the short axis between the parallel two sides is the minor axis of the falling film tube. The tubes are continuously twisted into a spiral shape along the height direction with the center line of the falling film tube as the axis.

[0030] The major and minor axes of each oblong cross-section spiral falling film tube 2 are parallel to each other, that is, the phase of each oblong cross-section spiral falling film tube 2 on the cross-section of the tower body is consistent; the gap between each row of oblong cross-section spiral falling film tubes 2 in the minor axis direction constitutes the shell side medium channel.

[0031] The center-to-center distance between adjacent oblong cross-section spiral falling film tubes 2 is equal to the length of their major axis, allowing them to achieve self-support through tangential contact at the two ends of their major axes. This avoids a series of problems associated with using bow-shaped baffles; simultaneously, the self-support between the two ends of the falling film tube's major axis better prevents vibrations caused by the Karman vortex street. Furthermore, without the obstruction of bow-shaped baffles, shell-side steam can rapidly flow through the entire length of the tube bundle, and then, due to pressure, overcome flow resistance to flow towards the central region and the other side of the bundle. The entire shell-side flow process has no dead zones, resulting in a significantly improved heat transfer efficiency compared to traditional tube bundles. Moreover, compared to bow-shaped baffles, the flow of shell-side gas in falling film tube bundles is disturbed circumferentially by the spiral space formed between the tubes, with the number of disturbances increasing... Figure 2 Taking the tube bundle in this embodiment as an example, the turbulence can reach 38 rotations, or 38 spiral turns. Compared to the approximately 5-8 rotations required by traditional bow-shaped baffles, the shell-side turbulence effect is much better, and the turbulence intensity and shell-side Reynolds number are also correspondingly increased. Because no bow-shaped baffles are used, the flow cross-sectional area remains unchanged, and the shell-side resistance is much lower than that of the bow-shaped baffle tube bundle. In this embodiment, there are no dead zones on both sides of the root of each bow-shaped baffle during the steam flow process, and the outer periphery of the entire elongated oval cross-section spiral falling film tube is an effective heat exchange area.

[0032] like Figure 4 As shown, the oblong cross-section spiral falling film tubes are arranged in an equilateral triangle, and their centerline remains unchanged during the spiral process. Within 360° of each pitch, they make tangential contact with adjacent oblong cross-section spiral falling film tubes six times, and the position of the tangential contact point with adjacent oblong cross-section spiral falling film tubes changes every 60°. Self-support is achieved through the contact points. In addition, multiple straps 3 are tied around the outer periphery of the falling film tube bundle to fix the tube bundle as a whole. The tube bundle is arranged in a specially designed dodecagon, which maximizes the use of the circular area of ​​the upper tube sheet 1 and can be perfectly matched with the liquid distribution unit above. The straps 3 contact the outermost layer of falling film tubes of the tube bundle, so that all falling film tubes support each other through contact points. There is no need to use the traditional bow-shaped baffle to fix the tube bundle. The oblong cross-section spiral falling film tubes can also be precisely positioned with each other, and the shell-side fluid can automatically change direction along the flow channel between the oblong cross-section spiral falling film tubes. When the shell-side fluid flows through the gap between the falling film tubes, it transfers heat to the condensate film on the wall of the falling film tube. Due to the greatly shortened flow length, the shell-side resistance is much lower than that of the traditional structure, and the resistance distribution along the tube bundle height is also more uniform.

[0033] Taking 0° as an example, the shell-side steam first flows along the vertical channel. When it reaches 60°, the shell-side steam flows along the inclined channel, and so on. This causes the flow channel of the shell-side steam to switch constantly, creating a continuous disturbance to the shell-side fluid, keeping the steam in a turbulent state and improving heat exchange efficiency.

[0034] When the steam in the shell side condenses into a liquid film on the outer wall of the falling film tube, it falls down the outer wall of the falling film tube due to gravity. After hitting the contact point with the surrounding falling film tubes, it undergoes periodic disturbance. Therefore, the thickness of the condensate film is always kept within a small range, and the heat transfer coefficient of the shell side film is significantly improved compared to the bare tube. Furthermore, the steam inlet method adopted in this invention is to introduce steam from the upper middle part and discharge condensate from the bottom. As the steam flows downward along the spiral flow channel formed between the falling film tubes, it can push the condensate film to flow downward at an accelerated speed.

[0035] Because the elongated oval cross-section spiral falling film tubes achieve self-support through their contact points with surrounding falling film tubes, the center-to-center distance between adjacent falling film tubes can be directly set as the major axis of the cross-section. This significantly reduces the center-to-center distance compared to traditional falling film evaporators. Furthermore, due to the absence of baffles, the shell-side fluid resistance drop is also lower than in traditional falling film evaporators, resulting in a substantial increase in heat transfer per unit shell-side resistance drop. Simultaneously, the reduced shell diameter compared to traditional falling film evaporators allows for reductions in parameters such as tube sheet diameter, tube sheet thickness, and tube box flange thickness, thereby significantly lowering material costs.

[0036] When the fluid in the tubes falls at the center of each tube bridge in the upper tube sheet 1, even if the manufacturing and installation of the heat exchanger causes some deviation in the verticality of the falling film tubes, it will not affect the uniformity of the liquid film thickness in the circumferential direction. When the liquid film falls along the inner wall of the falling film tube, due to the spiral action, the liquid film will autonomously form a secondary distribution in the circumferential direction. This offsets the negative impact of the verticality deviation of the falling film tube, which greatly improves the heat transfer coefficient in the tubes and also better prevents scaling problems caused by dry tubes in the falling film tubes.

[0037] Each oblong cross-section spiral falling film tube has a circular base tube with an outer diameter of 38mm at both ends, facilitating insertion into the upper and lower tube sheets. The cross-sectional dimensions of each oblong cross-section spiral falling film tube are 45x25.5mm, with a spiral pitch of 250mm. These dimensions are the result of multiple verifications: firstly, machining the 38mm outer diameter circular base tube to a cross-sectional major axis of 45mm achieves a yield rate exceeding 99% in the processing of irregularly shaped tubes; secondly, when the cross-sectional major axis is set to 45mm, the cross-sectional area formed by the gaps between the oblong cross-section spiral falling film tubes accounts for 43.4% of the total cross-sectional area of ​​the tube bundle (within the dodecagon). Taking the tube bundle application condition shown in this embodiment as an example, the cross-sectional velocity of the shell-side steam is 4.5m / s, and the shell-side resistance is approximately 52kPa. The shell-side film heat transfer coefficient can reach over 3100W / (㎡*K). This dimension represents the optimal solution for the cross-sectional shape at this pitch. Specific data comparisons are shown in the table below (assuming the heat exchange area and pitch are the same).

[0038] Spiral elliptical tube cross-sectional length (mm) Shell-side flow velocity (m / s) Shell-side resistance drop kPa <![CDATA[Shell-side film heat transfer coefficient W / (m 2 *K)]]> 44 5.88 75 2933 45 4.92 52 3135 46 4.43 42 2836

[0039] As can be seen from the table above, in the most common operating conditions of falling film evaporation of liquid materials containing solids in inorganic salt solutions or biochemical industries, the optimal solution is to set the long axis of the spiral falling film tube to 45 mm and the short axis to 25.5 mm.

[0040] The above description is merely a preferred embodiment of the present utility model, showing and describing the basic principles, main features, and advantages of the present utility model. It is not intended to limit the scope of patent protection of the present utility model. Those skilled in the art should understand that the present utility model is not limited to the above embodiments. In addition to the above embodiments, the present utility model may have other implementations without departing from the spirit and scope of the present utility model. Various changes and improvements to the present utility model are also possible. All technical solutions formed by equivalent substitutions or equivalent transformations fall within the scope of protection claimed by the present utility model. The scope of protection claimed by the present utility model is defined by the appended claims and their equivalents. Technical features not described in the present utility model can be implemented by or using existing technology, and will not be elaborated here.

Claims

1. A self-supporting falling film heat exchanger tube bundle, comprising multiple parallel falling film tubes arranged in an equilateral triangle, characterized in that: Each falling film tube is an oblong cross-section spiral falling film tube. The two ends of the major axis of each cross-section are opposing semicircles, and the two ends of the minor axis are parallel to each other. They are continuously twisted into a spiral shape with the center line of the falling film tube as the axis. The center distance between adjacent oblong cross-section spiral falling film tubes is equal to the length of the major axis, so that adjacent oblong cross-section spiral falling film tubes are tangentially contacted to each other through the two ends of the major axis to achieve self-support.

2. The self-supporting falling film heat exchanger tube bundle according to claim 1, characterized in that: Within the same cross-section, the major and minor axes of each oblong-section spiral falling film tube are parallel to each other, and the gaps between each row of oblong-section spiral falling film tubes in the minor axis direction constitute the shell-side medium channel.

3. The self-supporting falling film heat exchanger tube bundle according to claim 1, characterized in that: Each oblong cross-section spiral falling film tube maintains its centerline during the spiraling process. Within 360° of each pitch, it makes tangential contact with the adjacent oblong cross-section spiral falling film tube six times, and changes the position of the tangential contact point with the adjacent oblong cross-section spiral falling film tube every 60°.

4. The self-supporting falling film heat exchanger tube bundle according to claim 2, characterized in that: The outer periphery of the oblong cross-section spiral falling film tube bundle is dodecagonal, and multiple straps are bound around the outer periphery.

5. The self-supporting falling film heat exchanger tube bundle according to any one of claims 1 to 4, characterized in that: The cross-sectional dimensions of each oblong-section spiral falling film tube are 45x25.5mm, and the spiral pitch is 250mm; the upper and lower ends of each oblong-section spiral falling film tube are circular base tubes with an outer diameter of 38mm.

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