Fluorine-containing gas purification and high-efficiency waste heat utilization system

Abstract

The utility model relates to a waste heat utilization system, in particular to a fluorine-containing gas purification efficient waste heat utilization system, which comprises a stripping tower, a 2 # purification tower, a 3 # purification tower and a 4 # purification tower which are sequentially connected, and a liquid phase inlet of the 2 # purification tower is connected with a liquid phase outlet of the 1 # purification tower. Air heat exchange pipelines are arranged in the 2 # purification tower and the 4 # purification tower, an inlet of the air heat exchange pipeline is formed in the bottom of the 2 # purification tower, an outlet of the air heat exchange pipeline at the top is connected with the stripping tower through a connecting pipeline, an inlet of the air heat exchange pipeline is formed in the bottom of the 4 # purification tower, and an outlet of the air heat exchange pipeline at the top is connected with the stripping tower through a connecting pipeline. The system disclosed by the utility model is simple and easy to transform, can realize effective waste heat recovery and step-by-step air heating, is high in heat utilization rate, improves the concentration of byproduct sulfuric acid after steam stripping, and reduces the fluorine content of sulfuric acid.

Description

Technical Field

[0001] The utility model relates to a waste heat utilization system, in particular to a high-efficiency waste heat utilization system for purifying fluorine-containing gas. Background Technique

[0002] Anhydrous hydrogen fluoride is an important chemical raw material and one of the main raw materials for preparing fluorine-containing chemicals. In recent years, with the rapid development of emerging industries such as lithium batteries, new energy vehicles, semiconductors, and photovoltaics, the demand for fluorine chemical products has increased sharply, driving the rapid development of the anhydrous hydrogen fluoride industry.

[0003] At present, there are mainly two process routes for preparing anhydrous hydrogen fluoride. One is the traditional fluorite route, which has a mature process. However, with the increasing price of raw material fluorite year by year, the production cost of anhydrous hydrogen fluoride increases, and the industry profit is squeezed. The other is the fluosilicic acid method (by-product of wet-process phosphoric acid). Among them, the relatively mature technology is the sulfuric acid decomposition of fluosilicic acid method. The main process is to add concentrated sulfuric acid to the concentrated fluosilicic acid solution, decompose fluosilicic acid into silicon tetrafluoride gas and hydrogen fluoride. Most of the hydrogen fluoride is absorbed by sulfuric acid. The sulfuric acid absorbed with hydrogen fluoride releases hydrogen fluoride through desorption, and anhydrous hydrogen fluoride can be obtained through refining. The raw material of this route can be fluosilicic acid, a by-product of wet-process phosphoric acid, with low production cost and broad application prospects in the future.

[0004] For the anhydrous hydrogen fluoride system prepared by the fluosilicic acid method, its purification process is as follows: Concentrated sulfuric acid with a mass fraction of 98% enters the purification system through two pipelines. One pipeline enters the 1# purification tower to purify SiF4 coming from the main reactor. The gas enters the fluosilicic acid concentration process through the upper pipeline, and the liquid enters the 2# purification tower through the lower pipeline to dehydrate the HF obtained by stripping. The high-temperature mixed acid is discharged from the lower pipeline to the reaction process. The gas enters the 3# purification tower through the pipeline, makes full contact with the other concentrated sulfuric acid pipeline to absorb HF. A small amount of SiF4 enters the fluosilicic acid concentration process through the upper pipeline, and the liquid is sent to the 4# purification tower through the pipeline to fully mix with the material evaporated from the reaction liquid by heating. The high-temperature mixed acid is discharged from the lower pipeline to the reaction process, and HF enters the rectification process through the upper pipeline.

[0005] A large amount of high-temperature (greater than 140 °C) mixed acid generated in the above process is directly returned to the reaction section, and the heat is not fully utilized. In the context of energy conservation and emission reduction today, it is urgent to optimize and update the system and equipment. At the same time, the concentration of the by-product dilute sulfuric acid generated after stripping is generally about 70%, and the fluorine content is between 1500 ppm and 3000 ppm. The low concentration of dilute sulfuric acid affects downstream applications, and the high fluorine content causes waste of fluorine, which also needs to be further optimized. Summary of the Invention

[0006] The invention object of the present utility model is to solve the above technical problems, and provide a highly efficient waste heat utilization system for fluorine-containing gas purification, which has a simple system, is easy to transform, can realize effective waste heat recovery, gradually heats air, has a high heat utilization rate, improves the sulfuric acid concentration of by-products after stripping, and reduces the fluorine content in sulfuric acid.

[0007] The system of the present utility model includes a stripping tower, a 2# purification tower, a 3# purification tower and a 4# purification tower connected in sequence. The liquid phase inlet of the 2# purification tower is connected to the liquid phase outlet of the 1# purification tower. Air heat exchange pipes are provided in both the 2# purification tower and the 4# purification tower. The inlet of the air heat exchange pipe is provided at the bottom of the 2# purification tower, and the outlet of the air heat exchange pipe at the top is connected to the stripping tower through a connecting pipe. The inlet of the air heat exchange pipe is provided at the bottom of the 4# purification tower, and the outlet of the air heat exchange pipe at the top is connected to the stripping tower through a connecting pipe.

[0008] An air heat exchange pipe is provided in the 3# purification tower. The inlet of the air heat exchange pipe is provided at the bottom of the 3# purification tower, and the outlet of the air heat exchange pipe at the top is connected to the inlet of the air heat exchange pipe at the bottom of the 4# purification tower through a connecting pipe.

[0009] An air heat exchange pipe is provided in the 1# purification tower. The inlet of the air heat exchange pipe is provided at the bottom of the 1# purification tower, and the outlet of the air heat exchange pipe at the top is connected to the inlet of the air heat exchange pipe at the bottom of the 2# purification tower through a connecting pipe.

[0010] An air heat exchange pipe is provided in the 1# purification tower. The inlet of the air heat exchange pipe is provided at the bottom of the 1# purification tower, and the outlet of the air heat exchange pipe at the top is connected to the inlet of the air heat exchange pipe at the bottom of the 2# purification tower through a connecting pipe.

[0011] The air heat exchange pipe is at least one of a shell-and-tube type, a sleeve type, a plate type, a spray type, and a spiral wound tube type.

[0012] Existing stripping towers usually use cold air and steam to strip the residual liquid after reaction heating and evaporation, which has the problem of high energy consumption. Based on the internal heat exchange structure of the purification tower, the present utility model fully utilizes the waste heat generated in the purification process by adjusting the inlet and outlet paths of the air used for stripping, reduces the overall energy consumption of the process, improves the concentration of by-product sulfuric acid, and reduces its fluorine content, having good application prospects.

[0013] Beneficial effects:

[0014] 1) The present utility model fully utilizes the waste heat of high-temperature mixed acid, reasonably designs the route according to the characteristics of each purification tower in the purification system and the inlet and outlet temperatures of materials, gradually heats the heat exchange air, and has a high energy utilization efficiency; by heat exchanging with air, the temperature of the purification tower can be effectively controlled, preventing the tower from overheating and improving the process safety;

[0015] 2) The air after heat exchange is used to replace the low-pressure steam and sent to the stripping column for stripping. On the one hand, the production cost is reduced. On the other hand, since no steam is introduced into the stripping process, the water content introduced into the system can be effectively reduced, and the sulfuric acid concentration can be increased to 73% - 78%. At the same time, the fluorine content in the sulfuric acid can be effectively reduced to 500 ppm - 1000 ppm. All these are helpful for the effective utilization of sulfuric acid and the full utilization of fluorine in the downstream, and avoid the loss and waste of fluorine.

[0016] 3) The two air heat exchange routes run in parallel without interference, and the corresponding routes can be adaptively set according to needs, with good flexibility and adaptability.

[0017] 4) The system of the present utility model is simple, easy to transform, can achieve effective waste heat recovery, and save energy and reduce consumption. According to calculations, when using the system of the present utility model, the consumption of fluorosilicic acid (in terms of pure) raw materials per ton of anhydrous hydrogen fluoride can be reduced by 2% - 10%, the fluorine recovery rate of the whole system can be increased by 2% - 8%, and the energy consumption can be reduced by 5% to 10%. Brief Description of the Drawings

[0018] Figure 1 It is a system diagram of an efficient waste heat utilization for fluorine-containing gas purification shown in Embodiment 1 of the method of the present utility model.

[0019] Figure 2 It is a system diagram of an efficient waste heat utilization for fluorine-containing gas purification shown in Embodiment 2 of the method of the present utility model.

[0020] Figure 3 It is a system diagram of an efficient waste heat utilization for fluorine-containing gas purification shown in Embodiment 3 of the method of the present utility model.

[0021] Figure 4 It is a system diagram of an efficient waste heat utilization for fluorine-containing gas purification shown in Embodiment 4 of the method of the present utility model.

[0022] Among them, 1 - 1# purification tower, 2 - 2# purification tower, 3 - 3# purification tower, 4 - 4# purification tower, 5 - stripping tower. Detailed Embodiments

[0023] See Figures 1-4 , the connections of the four purification towers and the stripping tower in the four embodiments are the same, and the difference lies in the different air heat exchange lines. Heat exchange internal structures, namely air heat exchange pipes, are correspondingly arranged in the purification towers where air is introduced. The specific structure is prior art and will not be elaborated, nor is it shown in the drawings. Preferably, it is at least one of shell-and-tube type, double-pipe type, plate type, spray type, and spiral-wound tube type. The material is preferably at least one of high-silicon stainless steel, high-nickel-based alloy, super duplex stainless steel, and Hastelloy.

[0024] Among them, the connection relationship between multiple purification towers and strippers in Examples 1-4 is as follows: stripper 5, 2# purification tower 2, 3# purification tower 3, and 4# purification tower 4. The liquid-phase inlet of the 2# purification tower 2 is connected to the 1# purification tower 1;

[0025] The technological process of fluorine-containing gas purification is as follows:

[0026] Concentrated sulfuric acid with a mass fraction of 98% enters the purification system through two pipelines. One pipeline enters the 1# purification tower 1 to refine SiF4 coming from the main reactor. The gas enters the fluorosilicic acid concentration process through the upper pipeline, and the liquid enters the 2# purification tower 2 through the lower pipeline and dehydrates the HF stripped from the stripper 5. The high-temperature mixed acid is discharged to the reaction process through the lower pipeline. The gas enters the 3# purification tower 3 through the pipeline, makes full contact with the other pipeline of concentrated sulfuric acid, and absorbs HF. A small amount of SiF4 enters the fluorosilicic acid concentration process through the upper pipeline, and the liquid is sent to the 4# purification tower 4 through the pipeline and is fully mixed with the material evaporated by heating the reaction liquid. The high-temperature mixed acid is discharged to the reaction process through the lower pipeline, and HF enters the rectification process through the upper pipeline.

[0027] The difference between Examples 1-4 lies in the heat exchange route of air, which is specifically as follows:

[0028] Example 1:

[0029] The inlet of the air heat exchange pipeline is provided at the bottom of the 1# purification tower 1, and the outlet of the air heat exchange pipeline at the top is connected to the stripper 5 through the air heat exchange pipeline of the 2# purification tower 2 via a connecting pipeline; the inlet of the air heat exchange pipeline is provided at the bottom of the 3# purification tower 3, and the outlet of the air heat exchange pipeline at the top is connected to the stripper 5 through the 4# purification tower 4 via a connecting pipeline.

[0030] The air for stripping enters the 1# purification tower 1 and the 3# purification tower 3 separately through two pipelines, enters the tower from the lower part of the tower, enters the independent air heat exchange pipeline, makes convective contact with the hot material in the tower, and is discharged from the upper part of the tower. The heated air for stripping enters the 2# purification tower from the 1# purification tower and the 4# purification tower from the 3# purification tower for re-heat exchange, and finally enters the stripper 5 as stripping gas.

[0031] The temperature of the air for stripping exiting the 2# purification tower is 180 °C, and the temperature of the air for stripping exiting the 4# purification tower is 200 °C. The temperature during stripping after mixing is 188 °C.

[0032] The concentration of by-product sulfuric acid after stripping in this example is 77.9% (mass fraction), the fluorine content is 508 ppm (mass fraction), the raw material consumption of fluorosilicic acid (in terms of pure fluorine) per ton of anhydrous hydrogen fluoride is reduced by 9.6% compared with the original process, the fluorine recovery rate of the whole system is increased by 7.8%, and the energy consumption is reduced by 9.3%.

[0033] Example 2:

[0034] At the bottom of the 1# purification tower 1, there is an inlet of the air heat exchange pipeline, and the outlet of the air heat exchange pipeline at the top is connected to the stripping tower 5 through a connecting pipeline via the air heat exchange pipeline of the 2# purification tower 2; at the bottom of the 4# purification tower 4, there is an inlet of the air heat exchange pipeline, and the outlet of the air heat exchange pipeline at the top is connected to the stripping tower 5 through a connecting pipeline.

[0035] The air for stripping enters the 1# purification tower 1 and the 4# purification tower 4 separately in two paths, enters the tower from the lower part of the tower, enters the independent air heat exchange pipeline, makes convective contact with the hot material in the tower, and is discharged from the upper part of the tower. The air for stripping heated in the 1# purification tower 1 enters the 2# purification tower 2 for heat exchange here, and the air coming out of the 2# purification tower and the 4# purification tower finally enters the stripping tower 5.

[0036] The temperature of the air for stripping coming out of the 2# purification tower 2 is 174 °C, and the temperature of the air for stripping coming out of the 4# purification tower 4 is 156 °C. The temperature during stripping after mixing is 165 °C.

[0037] After stripping in this embodiment, the concentration of by-product sulfuric acid is 75.3% (mass fraction), the fluorine content is 715 ppm (mass fraction), the raw material consumption of fluosilicic acid (in terms of pure) per ton of anhydrous hydrogen fluoride is reduced by 5.7% compared with the original process, the fluorine recovery rate of the whole system is increased by 4.6%, and the energy consumption is reduced by 7.7%.

[0038] Example 3:

[0039] At the bottom of the 2# purification tower 1, there is an inlet of the air heat exchange pipeline, and the outlet of the air heat exchange pipeline at the top is connected to the stripping tower 5 through a connecting pipeline; at the bottom of the 3# purification tower 3, there is an inlet of the air heat exchange pipeline, and the outlet of the air heat exchange pipeline at the top is connected to the stripping tower 5 through a connecting pipeline via the 4# purification tower 4.

[0040] The air for stripping enters the 2# purification tower 2 and the 3# purification tower 3 separately in two paths, enters the tower from the lower part of the tower, enters the independent air heat exchange pipeline, makes convective contact with the hot material in the tower, and is discharged from the upper part of the tower. The air heated in the 3# purification tower 3 enters the 4# purification tower for heat exchange again, and the air coming out of the 2# purification tower 2 and the 4# purification tower 4 finally enters the stripping tower 5.

[0041] The temperature of the air for stripping coming out of the 2# purification tower 2 is 136 °C, and the temperature of the air for stripping coming out of the 4# purification tower 4 is 191 °C. The temperature during stripping after mixing is 155 °C.

[0042] After stripping in this embodiment, the concentration of by-product sulfuric acid is 74.1% (mass fraction), the fluorine content is 781 ppm (mass fraction), the raw material consumption of fluosilicic acid (in terms of pure) per ton of anhydrous hydrogen fluoride is reduced by 3.8% compared with the original process, the fluorine recovery rate of the whole system is increased by 3.3%, and the energy consumption is reduced by 6.5%.

[0043] Example 4:

[0044] The inlet of the air heat exchange pipeline is provided at the bottom of the 2# purification tower 2, and the outlet of the air heat exchange pipeline at the top is connected to the stripping tower 5 through a connecting pipeline; the inlet of the air heat exchange pipeline is provided at the bottom of the 4# purification tower 4, and the outlet of the air heat exchange pipeline at the top is connected to the stripping tower 5 through a connecting pipeline.

[0045] The air for stripping is divided into two paths and enters the 2# purification tower 2 and the 4# purification tower 4 respectively. It enters the tower from the lower part of the tower, enters the independent air heat exchange pipeline, makes convective contact with the hot material in the tower, and is discharged from the upper part of the tower. The air coming out of the 2# tower and the 4# tower finally enters the stripping tower 5.

[0046] The temperature of the air for stripping coming out of the 2# purification tower 2 is 138 °C, and the temperature of the air for stripping coming out of the 4# purification tower 4 is 158 °C. The temperature during stripping after mixing is 142 °C.

[0047] In this embodiment, the by-product sulfuric acid concentration after stripping is 73.6% (mass fraction), the fluorine content is 926 ppm (mass fraction), the raw material consumption of fluosilicic acid (in terms of pure) per ton of anhydrous hydrogen fluoride is reduced by 2.9% compared with the original process, the fluorine recovery rate of the whole system is increased by 2.4%, and the energy consumption is reduced by 5.9%.

Claims

1. A fluorine-containing gas purification and efficient waste heat utilization system, comprising a stripping tower, a 2# purification tower, a 3# purification tower and a 4# purification tower connected in sequence, wherein the liquid phase inlet of the 2# purification tower is connected to the liquid phase outlet of the 1# purification tower, characterized in that: The 2# purification tower and the 4# purification tower are both provided with air heat exchange pipes. The 2# purification tower has an inlet for the air heat exchange pipe at the bottom, and the outlet of the air heat exchange pipe at the top is connected to the stripping tower via a connecting pipe. The 4# purification tower has an inlet for the air heat exchange pipe at the bottom, and the outlet of the air heat exchange pipe at the top is connected to the stripping tower via a connecting pipe.

2. The fluorine-containing gas purification and high-efficiency waste heat utilization system according to claim 1, characterized in that: An air heat exchange pipe is arranged in the 3# purification tower, an inlet of the air heat exchange pipe is arranged at the bottom of the 3# purification tower, and an outlet of the air heat exchange pipe at the top is connected to the inlet of the air heat exchange pipe at the bottom of the 4# purification tower via a connecting pipe.

3. The fluorine-containing gas purification and high-efficiency waste heat utilization system according to claim 2, characterized in that: An air heat exchange pipe is arranged in the 1# purification tower, an inlet of the air heat exchange pipe is arranged at the bottom of the 1# purification tower, and an outlet of the air heat exchange pipe at the top is connected to the inlet of the air heat exchange pipe at the bottom of the 2# purification tower via a connecting pipe.

4. The fluorine-containing gas purification and high-efficiency waste heat utilization system according to claim 1, characterized in that: An air heat exchange pipe is arranged in the 1# purification tower, an inlet of the air heat exchange pipe is arranged at the bottom of the 1# purification tower, and an outlet of the air heat exchange pipe at the top is connected to the inlet of the air heat exchange pipe at the bottom of the 2# purification tower via a connecting pipe.

5. The fluorine-containing gas purification and efficient waste heat utilization system according to any one of claims 1 to 4, characterized in that: The air heat exchange pipe is at least one of a tube-in-tube type, a sleeve-in-tube type, a plate type, a spray type, and a winding tube type.

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