Reducing absorption tower of heat pipe enhanced heat exchange for nitric acid preparation

Abstract

The invention provides a heat pipe enhanced heat exchange reducing absorption tower for nitric acid preparation, which comprises a tower body and a heat pipe exchanger, nitric oxide gas enters from the tower bottom, absorption liquid enters from the tower top, and the nitric oxide gas and the absorption liquid contact and react in the tower body to generate nitric acid, and is characterized in that the tower body is divided into a plurality of sections from top to bottom, the diameters of the sections are different, and the diameters of the sections are different in the direction from top to bottom; the diameter of the tower body is gradually increased; a plurality of heat pipe heat exchangers are arranged, an inclined angle is formed between the heat pipe heat exchangers and the tower body, an evaporation section of each heat pipe is arranged in the tower body, and a condensation end of each heat pipe extends out of the tower body. The design of the reducing absorption tower is matched with the concentration of nitrogen oxide, so that the absorption efficiency can be remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of heat pipe heat exchange and absorption tower technology, specifically to a variable diameter absorption tower for heat pipe enhanced heat exchange in nitric acid preparation. Background Technology

[0002] Absorption towers are devices used for absorption operations. Based on the gas-liquid phase contact pattern, they are classified into three categories: The first category includes plate towers, bubbling absorption towers, and stirred bubbling absorption towers where the gas is dispersed in the liquid phase as bubbles; the second category includes ejectors, venturi tubes, and spray towers where the liquid is dispersed in the gas phase as droplets; and the third category includes packed absorption towers and falling film absorption towers where the liquid moves in a film-like motion and contacts the gas phase. The flow patterns of the gas and liquid phases within the tower can be either countercurrent or cocurrent. Countercurrent operation is commonly used, with the absorbent added from the top of the tower and flowing downwards, contacting the upward-flowing gas. The liquid that has absorbed the absorbent is discharged from the bottom of the tower, and the purified gas is discharged from the top.

[0003] A heat pipe is a heat transfer component with high thermal conductivity. The technology was first discovered in 1944 by American R.S. Gaugler, who patented it as a "heat transfer device." At the time, it didn't show practical application and therefore didn't receive the attention it deserved. It wasn't until the early 1960s, with the development of the space industry and the need for efficient heat transfer components for spacecraft, that G.M. Grover of the Los Alamos National Laboratory rediscovered the principle of this heat transfer device in 1964 and named it a heat pipe. It was first successfully applied to space technology, subsequently attracting great interest and attention from scholars worldwide. Heat pipe technology entered China in the 1970s and 80s.

[0004] Heat pipes transfer heat through the evaporation and condensation of the working fluid within a fully enclosed vacuum shell. They offer a range of advantages, including extremely high thermal conductivity, good isothermal properties, adjustable heat transfer areas on both hot and cold sides, long-distance heat transfer, and temperature control. However, they have relatively poor oxidation resistance and high-temperature resistance. This can be mitigated by installing a ceramic heat exchanger at the front, which effectively addresses the challenges of high-temperature resistance and corrosion resistance. In existing dual-pressure dilute nitric acid production processes, the absorption tower is the core equipment for nitric acid generation. Its main function is to ensure sufficient contact and reaction between nitrogen oxide gases (containing NO2, N2O4, etc.) and the absorbent liquid (demineralized water) to generate nitric acid, and to promptly remove the heat released during the reaction to maintain absorption efficiency.

[0005] The heat pipe and the absorption tower are combined to exchange the heat generated in the absorption tower through the heat pipe.

[0006] Current absorption towers suffer from two major pain points: First, the fixed tower diameter leads to uneven gas-liquid contact. The concentration of nitrogen oxide gas gradually decreases from the bottom to the top of the tower. With a fixed tower diameter, the gas velocity in the upper low-concentration region is too fast, resulting in insufficient gas-liquid contact time, low NO2 absorption rate, and easy entrainment of acid mist. Conversely, the flow velocity in the lower high-concentration region is too slow, causing heat accumulation and requiring a large amount of additional chilled water for cooling. Second, cooling efficiency is low and energy consumption is high. Existing absorption towers use a coil-type cooling structure, directly exchanging heat through circulating water / chilled water. This results in limited heat exchange area and low heat exchange efficiency. Furthermore, the cooling medium requires additional power for transportation, accounting for over 35% of the total energy consumption of the absorption process.

[0007] Therefore, there is an urgent need for an absorption tower structure that can adapt to gas concentration gradients, enhance gas-liquid contact, improve heat exchange efficiency, and reduce energy consumption, in order to overcome the shortcomings of existing technologies. Summary of the Invention

[0008] The purpose of this invention is to overcome the problems of uneven gas-liquid contact, low heat exchange efficiency, and high energy consumption in existing nitric acid absorption towers, and to provide a heat pipe-enhanced heat exchange variable-diameter absorption tower for nitric acid preparation. To achieve the above objective, the technical solution of this invention is as follows: A variable-diameter absorption tower for nitric acid preparation with enhanced heat exchange via heat pipes includes a tower body and heat pipe heat exchangers. Nitrogen oxide gas enters from the bottom of the tower, and the absorbent enters from the top of the tower. The two react in the tower body to generate nitric acid. The tower body is divided into multiple sections from top to bottom, each with a different diameter, and the diameter of the tower body gradually increases from top to bottom. Multiple heat pipe heat exchangers are provided and are set at an inclined angle to the tower body. The evaporation section of the heat pipe is located inside the tower body, and the condensation end of the heat pipe extends outside the tower body.

[0009] As an improvement, the diameter of the tower gradually increases from top to bottom.

[0010] As an improvement, the tower body is divided into three sections: the upper section, the middle section, and the lower section. Screen plates with different spacings are set in the corresponding three sections of the tower body.

[0011] As an improvement, d1 is the diameter of the upper section of the tower, d2 is the diameter of the middle section of the tower, and d3 is the diameter of the lower section of the tower. The range of d2 / d1 is 1.1-2.1, and the range of d3 / d2 is 1.3-2.3.

[0012] As an improvement, the spacing between the upper sieve plates is greater than that between the middle sieve plates, and the spacing between the middle sieve plates is greater than that between the lower sieve plates.

[0013] As an improvement, the spacing between the upper sieve plates is 1500-2500mm, the spacing between the middle sieve plates is 1000-2000mm, and the spacing between the lower sieve plates is 800-1200mm.

[0014] As an improvement, annular liquid distributors are installed in the upper, middle, and lower sections of the tower.

[0015] As an improvement, the circumferential angle between adjacent heat pipe heat exchangers in the upper section is 40°-60°, the circumferential angle between adjacent heat pipe heat exchangers in the middle section is 30°-40°, and the circumferential angle between adjacent heat pipe heat exchangers in the lower section is 20°-30°. From top to bottom, the density of heat pipe heat exchangers gradually increases.

[0016] As an improvement, guide fins are added to the surface of the evaporation section of the middle and lower heat pipe heat exchangers.

[0017] As an improvement, the heat pipe heat exchanger uses gravity heat pipes, and the working medium is ethanol or acetone; from top to bottom, the angle between the heat pipe heat exchanger and the tower body becomes smaller and smaller.

[0018] Compared with the prior art, the present invention has the following advantages: Significantly improved absorption efficiency: The design of the variable diameter absorption tower is adapted to the concentration of nitrogen oxides, resulting in a significant improvement in NO2 absorption rate. The concentration of the finished nitric acid is more stable and the color is lower, reducing the load on subsequent bleaching processes.

[0019] Significantly reduced energy consumption: The density of heat pipe distribution is adapted to the generation of reaction heat, the heat exchange efficiency of heat pipe is greatly improved compared with traditional coils, the consumption of chilled water is significantly reduced, and the heat pipe non-powered circulation design saves cooling medium and transportation.

[0020] Highly adaptable: It can directly replace the absorption tower in the existing double-pressure nitric acid production process without requiring major modifications to the existing process pipelines, making industrialization easier. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the overall structure of the absorption tower; Figure 2 A schematic diagram of a heat pipe heat exchanger; Figure 3 This is a schematic diagram of the heat pipe heat exchanger distribution in the absorption tower.

[0022] Reference numerals: 1-Upper head, 2-Annular liquid distributor, 3-Upper section, 4-Heat pipe heat exchanger, 5-Middle section, 6-Circulating water, 7-Lower section, 8-Gas distributor, 9-Lower head. Detailed Implementation

[0023] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0024] A variable-diameter absorption tower for nitric acid preparation with enhanced heat transfer via heat pipes, such as... Figure 1As shown, the absorption tower, from top to bottom, includes an upper head 1, a tower body, and a lower head 9. Nitrogen oxide gas enters from the bottom of the tower, and the absorbent enters from the top of the tower. The two react in the tower body to generate nitric acid. The tower body is divided into multiple sections from top to bottom, each with a different diameter, and the diameter of the tower body gradually increases from top to bottom. The absorption tower also includes heat pipe heat exchangers 4, of which multiple heat pipe heat exchangers 4 are installed at an inclined angle to the tower body. The evaporation section of the heat pipe is located inside the tower body, and the condensation end of the heat pipe extends outside the tower body.

[0025] This invention features a variable-diameter absorption tower that is adapted to the concentration of nitrogen oxides, significantly improving the NO2 absorption rate, resulting in a more stable concentration of nitric acid in the finished product and lower color, thus reducing the load on subsequent bleaching processes.

[0026] As an improvement, the diameter of the tower gradually increases in a wider range from top to bottom. This invention, by varying the diameter of the absorption tower, further enhances absorption efficiency and increases the formation rate of nitric acid.

[0027] As an improvement, the tower body is divided into three sections: the upper section, the middle section, and the lower section. Screen plates with different spacings are set in the corresponding three sections of the tower body.

[0028] As an improvement, d1 is the diameter of the upper column, d2 is the diameter of the middle column, and d3 is the diameter of the lower column. The ratio of d2 / d1 ranges from 1.1 to 2.1, and the ratio of d3 / d2 ranges from 1.3 to 2.3. This invention further improves the nitric acid production rate by increasing the range of variation in the ratio of the upper, middle, and lower column diameters.

[0029] As an improvement, the spacing between the upper sieve plates is greater than that between the middle sieve plates, and the spacing between the middle sieve plates is greater than that between the lower sieve plates. This design allows the gas to maintain a constant flow rate within the optimal contact range in each section, adapting to the reaction requirements of different concentrations of nitrogen oxide gas.

[0030] As an improvement, the spacing between the upper sieve plates is 1500-2500 mm, the middle sieve plates are 1000-2000 mm, and the lower sieve plates are 800-1200 mm. This design allows the gas to maintain an optimal contact range of 0.5-1.2 m / s in each section, adapting to the reaction requirements of different concentrations of nitrogen oxide gas. The optimized dimensions significantly improve the gas-liquid contact efficiency at different locations, thereby enhancing reaction efficiency.

[0031] As an improvement, annular liquid distributors are installed in the upper, middle, and lower sections of the tower.

[0032] As an improvement, the circumferential angle between adjacent heat pipe heat exchangers in the upper section is 50°-70°, the circumferential angle between adjacent heat pipe heat exchangers in the middle section is 25°-40°, and the circumferential angle between adjacent heat pipe heat exchangers in the lower section is 15°-25°. From top to bottom, the distribution density of the heat pipe heat exchangers gradually increases. The distribution density of the heat pipes is adapted to the generation of reaction heat. The heat transfer efficiency of the heat pipes is greatly improved compared with that of the traditional coil pipes, the consumption of chilled water is significantly reduced, and the heat pipes have a non-powered circulation design, saving cooling medium and transportation.

[0033] As an improvement, flow guiding fins are added to the evaporation section surfaces of the heat pipe heat exchangers in the middle and lower sections. By arranging fins in the middle and lower parts, the reaction speed in the middle and lower parts is increased, making the reaction efficiency in the middle and lower parts correspond to that in the upper part.

[0034] As an improvement, the heat pipe heat exchanger uses a gravity heat pipe, and the working medium is ethanol or acetone; from top to bottom, the included angle between the heat pipe heat exchanger and the tower body becomes smaller. Through the change of the inclination angle, the heat absorption efficiency of the heat pipes becomes faster from the upper part to the lower part, avoiding different thermal stresses caused by different temperatures in different sections, making the overall temperature constant, and improving the service life of the absorption tower.

[0035] As an improvement, the amplitude of the decreasing included angle between the heat pipe heat exchanger and the tower body from top to bottom continuously increases. Through the change of the amplitude of the above angle, the overall temperature can be further made constant, reducing the temperature difference between different sections and avoiding local overheating or overcooling.

[0036] As an improvement, the tower body is divided into an upper section (low-concentration reaction zone), a middle section (medium-concentration reaction zone), and a lower section (high-concentration reaction zone) from top to bottom. The three sections of the tower body adopt a variable diameter design, and the tower diameter sizes satisfy d1 < d2 < d3, where d1 is the upper section tower diameter, d2 is the middle section tower diameter, and d3 is the lower section tower diameter; sieve plates with different spacings are respectively arranged in the three corresponding regions inside the tower, and multiple heat pipe heat exchangers are built in the tower wall. The evaporation section of the heat pipe extends into the tower at an angle of 30-75° with the tower body, and the condensation section extends outside the tower.

[0037] Furthermore, d2 / d1 = 1-2, d3 / d1 = 1-2; the sieve plate spacing in the upper section is 1500-2500 mm, the sieve plate spacing in the middle section is 1000-2000 mm, and the sieve plate spacing in the lower section is 800-1200 mm. This design can keep the gas in the optimal contact interval of 0.5-1.2 m / s in each section, adapting to the reaction requirements of nitrogen oxide gas with different concentrations.

[0038] Furthermore, the heat pipe heat exchanger employs gravity-type heat pipes, with ethanol or acetone as the working medium. The circumferential angle between adjacent heat pipes in the upper section is 50°-70°, in the middle section it's 25°-40°, and in the lower section it's 15°-25°, with the density gradually increasing. Guide fins are added to the surface of the evaporation sections of the middle and lower heat pipes. Gravity-type heat pipes require no additional power, reducing energy consumption, and the fin design improves heat exchange area and efficiency. The varying density of heat pipes at different locations in the absorption tower accommodates the removal of reaction heat from different concentrations of nitrogen oxide gas.

[0039] Furthermore, annular liquid distributors are installed in the upper, middle, and lower sections of the tower, with an orifice diameter of φ2mm and a spray density controlled at 15m³ / (m²·h); the tower body is made of 316L stainless steel. The annular liquid distributors ensure uniform spraying of the absorbent liquid and enhance the gas-liquid contact effect.

[0040] Furthermore, the heat pipe outer diameter is 25-38mm, the wall thickness is 2.5mm, the evaporation section length is the tower wall thickness + 0.5-0.8m, and the condensation section length is 1.0-1.2m. The axial spacing of the lower heat pipes is 100-500mm, the middle heat pipes are 500-1000mm, and the upper heat pipes are 1000-1500mm, with adjacent axial sections arranged in a staggered pattern. This reasonable heat pipe size and spacing design can match the exothermic reaction intensity of each section, achieving precise temperature control.

[0041] Preferred embodiment: The tower has a total height of 50m, with the upper section being 20m high and having a tower diameter of d1=3m, the middle section being 15m high and having a tower diameter of d2=4m, and the lower section being 15m high and having a tower diameter of d3=5m; the tower body is made of 316L stainless steel.

[0042] The upper section is equipped with 9 sieve plates with a plate spacing of 2000mm, the middle section is equipped with 9 sieve plates with a plate spacing of 1500mm, and the lower section is equipped with 14 sieve plates with a plate spacing of 1000mm. Each of the upper, middle, and lower sections is equipped with an annular liquid distributor with an orifice diameter of φ2mm and a spray density controlled at 15m³ / (m²·h).

[0043] The heat pipes are gravity-type heat pipes with an outer diameter of 30 mm and a wall thickness of 2.5 mm. The working medium is ethanol. The circumferential angle between adjacent heat pipes in the upper section is 60°, that in the middle section is 30°, and that in the lower section is 20°. The evaporation section is the thickness of the tower wall + 0.5 m (extending into the tower), and the condensation section is 1.0 m long (exposed in the external circulating water jacket). The axial spacing between the heat pipes in the lower section is 200 mm; the axial spacing between the heat pipes in the middle section is 500 mm; and the axial spacing between the heat pipes in the upper section is 1000 mm. Adjacent axial sections are arranged in a staggered manner. Guide fins are added to the surface of the evaporation sections of the middle and lower heat pipes.

[0044] The working principle of this invention is as follows: Nitrogen oxide gas enters from the bottom (lower section) of the tower, and its concentration gradually decreases as the reaction proceeds. The tower diameter gradually increases from top to bottom, keeping the gas flow rate within the optimal contact range and avoiding the problem of excessively fast flow rate at the top and excessively slow flow rate at the bottom. After the absorbent enters from the top of the tower, it is evenly distributed through the annular liquid distributors in the upper, middle, and lower sections, forming a "stepped gas-liquid contact path" in conjunction with the tower plates with different spacing, thereby enhancing the reaction effect. The heat released by the reaction is transferred to the heat pipe evaporation section. After absorbing the heat, the working fluid in the heat pipe vaporizes and rises to the condensation section, where it exchanges heat with the circulating water in the outer jacket of the tower before condensing and flowing back, achieving efficient heat exchange without power.

[0045] The absorbent (demineralized water) is at a temperature of 20°C and is introduced from the top of the column; the nitrogen oxide gas is at a temperature of 45°C and a pressure of 11.0 Bar and is introduced from the bottom of the column; the operating pressure inside the column is maintained at 10 Bar, and the temperature inside the column is regulated by the flow rate of circulating water in the heat pipe condenser section.

[0046] While the present invention has been disclosed above with reference to preferred embodiments, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A variable-diameter absorption tower for nitric acid preparation with enhanced heat exchange via heat pipes, comprising a tower body and a heat pipe heat exchanger, wherein nitrogen oxide gas enters from the bottom of the tower, and absorbent enters from the top of the tower, and the two react in contact within the tower body to generate nitric acid, characterized in that, The tower body is divided into multiple sections from top to bottom, each with a different diameter. The diameter of the tower body gradually increases from top to bottom. Multiple heat pipe heat exchangers are installed at an inclined angle to the tower body. The evaporation section of the heat pipe is located inside the tower body, while the condensation end of the heat pipe extends outside the tower body.

2. The absorption tower according to claim 1, characterized in that, From top to bottom, the diameter of the tower gradually increases in a larger and larger manner.

3. The absorption tower according to claim 1, characterized in that, The tower body is divided into three sections: upper section, middle section and lower section. Screen plates with different spacings are set in the corresponding three sections of the tower body.

4. The absorption tower according to claim 3, characterized in that, d1 is the diameter of the upper section of the tower, d2 is the diameter of the middle section of the tower, and d3 is the diameter of the lower section of the tower. The range of d2 / d1 is 1.1-2.1, and the range of d3 / d2 is 1.3-2.

3.

5. The absorption tower according to claim 3, characterized in that, The spacing between the upper sieve plates is greater than that between the middle sieve plates, and the spacing between the middle sieve plates is greater than that between the lower sieve plates.

6. The absorption tower according to claim 5, characterized in that, The spacing between the upper sieve plates is 1500-2500mm, the spacing between the middle sieve plates is 1000-2000mm, and the spacing between the lower sieve plates is 800-1200mm.

7. The absorption tower according to claim 3, characterized in that, Annular liquid distributors are installed in the upper, middle and lower sections of the tower.

8. The absorption tower according to claim 3, characterized in that, The circumferential angle between adjacent heat pipe heat exchangers in the upper section is 40°-60°, the circumferential angle between adjacent heat pipe heat exchangers in the middle section is 30°-40°, and the circumferential angle between adjacent heat pipe heat exchangers in the lower section is 20°-30°. From top to bottom, the density of heat pipe heat exchangers gradually increases.

9. The absorption tower according to claim 8, characterized in that, Guide fins are added to the surface of the evaporation section of the middle and lower heat pipe heat exchangers.

10. The absorption tower according to claim 3, characterized in that, The heat pipe heat exchanger uses gravity heat pipes, and the working medium is ethanol or acetone; from top to bottom, the angle between the heat pipe heat exchanger and the tower body becomes smaller and smaller.

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