CN113091338B

CN113091338B - Reaction heat recycling system in formaldehyde production

Info

Publication number: CN113091338B
Application number: CN202110342576.6A
Authority: CN
Inventors: 严燕平; 严炉奇; 陈勇
Original assignee: Zhangzhou Longwenhanyuan Chemical Co ltd
Current assignee: Zhangzhou Longwenhanyuan Chemical Co ltd
Priority date: 2021-03-30
Filing date: 2021-03-30
Publication date: 2023-03-31
Anticipated expiration: 2041-03-30
Also published as: CN113091338A

Abstract

The application relates to a reaction heat recycling system in formaldehyde production, which belongs to the technical field of chemical production equipment and comprises a cooling section and a methanol preheating section which are arranged between a quenching section and an absorption tower, wherein reaction gas cooled by the quenching section sequentially passes through the cooling section and the methanol preheating section and then enters the absorption tower; the methanol sequentially passes through a methanol preheating section and a cooling section and then enters a methanol evaporator. This application has the effect that improves the utilization ratio of the reaction heat in the formaldehyde production.

Description

Reaction heat recycling system in formaldehyde production

Technical Field

The application relates to the field of chemical production equipment, in particular to a reaction heat recycling system in formaldehyde production.

Background

The process principle of formaldehyde production is that methanol and air react under the action of a catalyst to generate formaldehyde, and the process can be divided into two generation processes of a silver method and an iron-molybdenum method due to different types of selected catalysts. At present, the production process of formaldehyde by a silver method is the most common in China.

At present, the existing chinese patent with reference to publication No. CN105218334a discloses a methanol production method, which includes the steps of introducing methanol into a methanol reboiler, heating the methanol reboiler to gasify methanol therein, introducing the gasified methanol into a quaternary gas mixer, and simultaneously introducing hot steam, heated air and heated tail gas into the quaternary gas mixer; filtering the mixed quaternary gas, introducing the filtered quaternary gas into an oxidizer filled with a catalyst for oxidation reaction, cooling the oxidized mixed gas through a quenching section in the oxidizer, and sequentially introducing the cooled mixed gas into a first absorption tower for absorption.

However, the reaction temperature of methanol and air in the catalyst bed of the oxidizer is 630-650 ℃, the reaction gas leaves the catalyst bed, is cooled by a quenching section, the temperature of the reaction gas is reduced to below 200 ℃, and then the reaction gas is introduced into an absorption tower for absorption. Thus, the heat generated by the oxidation reaction is taken away by the cold water, which not only causes a large amount of heat to be wasted, but also consumes a large amount of cooling water.

Disclosure of Invention

In order to improve the utilization ratio of the reaction heat in the formaldehyde production, the application provides a reaction heat recycling system in the formaldehyde production.

The application provides a reaction heat recovery utilizes system in formaldehyde production adopts following technical scheme:

a reaction heat recycling system in formaldehyde production comprises a cooling section and a methanol preheating section which are arranged between a quenching section and an absorption tower, wherein reaction gas cooled by the quenching section sequentially passes through the cooling section and the methanol preheating section and then enters the absorption tower; the methanol sequentially passes through a methanol preheating section and a cooling section and then enters a methanol evaporator.

By adopting the technical scheme, when in actual use, the methanol at room temperature firstly passes through the methanol preheating section to exchange heat with the reaction gas entering the methanol preheating section, so as to preheat the methanol; and then, the methanol output from the methanol preheating section enters a cooling section, and exchanges heat with the reaction gas of the cooling section to further heat the methanol, so that part of the methanol output from the cooling section is gasified to form a methanol gas-liquid mixture, and the gasified methanol is input into a methanol evaporator to provide methanol gas for preparing formaldehyde in a formaldehyde reactor. Therefore, the heat of the reaction gas is utilized to heat the methanol, the reaction heat generated in the formaldehyde synthesis is fully utilized, the utilization rate of the reaction heat in the formaldehyde production is improved, the energy consumption is reduced, and the heat load of the methanol evaporator can be reduced.

In addition, reaction gas output by the quenching section sequentially passes through the cooling section and the methanol preheating section and then enters the absorption tower, and because the reaction gas exchanges heat with methanol in the cooling section and the methanol preheating section, the temperature of the reaction gas entering the absorption tower is greatly reduced, so that the heat load of the absorption tower is reduced.

Preferably, the temperature of the methanol after being output from the methanol preheating section is 65-70 ℃, and the temperature of the methanol after being output from the cooling section is 76-79 ℃.

By adopting the technical scheme, the gas methanol evaporated by the methanol evaporator needs to enter the formaldehyde reactor, so that the methanol gasification pressure is set to be 70-75Kpa, and the gas-liquid equilibrium temperature of the methanol is 75 ℃ under the gasification pressure, and the temperature of the methanol evaporator needs to be higher than 75 ℃. Therefore, the temperature of the methanol output from the cooling section is 76-79 ℃, and the methanol can directly enter a methanol evaporator for use.

Preferably, the methanol is partially gasified and then enters a methanol evaporator after being output from the cooling section, and the methanol liquid which is not gasified enters a reboiler.

Through adopting above-mentioned technical scheme, carry out gas-liquid separation from the methyl alcohol of cooling section output, directly separate liquid methyl alcohol to the reboiler in, can avoid liquid methyl alcohol to get into the methyl alcohol steam ware.

Preferably, the temperature of the reaction gas after being output from the methanol preheating section is 90-100 ℃.

By adopting the technical scheme, before the cooling section and the methanol preheating section are arranged, the temperature of the reaction gas entering the absorption tower is about 130 ℃, while the temperature of the reaction gas output from the methanol preheating section in the application is 90-100 ℃, namely the temperature of the reaction gas entering the absorption tower is 90-100 ℃, so that the temperature of the reaction gas entering the absorption tower is greatly reduced, the heat utilization rate of the reaction gas is improved on one hand, and the heat load of the absorption tower is greatly reduced on the other hand.

Preferably, the methanol preheating section adopts a horizontal tube-and-tube heat exchanger.

Preferably, the horizontal tubular heat exchanger comprises a shell, tube plates are fixed at two ends of the shell, a plurality of heat exchange tubes are arranged in the shell and fixedly connected with the tube plates, end sockets are arranged at two ends of the shell and positioned at the outer sides of the tube plates and fixedly connected with the shell, and tube boxes are formed between the end sockets and the tube plates; the heat exchange tube comprises an inner tube and an outer tube, the end part of the inner tube penetrates through the tube plate and is positioned in the tube box, and the outer tube is arranged around the outer circumference of the inner tube; the shell is internally provided with a partition plate, the partition plate is close to one of the tube plates and forms a liquid discharge cavity with the tube plate, two ends of the outer tube are opened, one end of the outer tube is positioned outside the liquid discharge cavity, the other end of the outer tube is positioned inside the liquid discharge cavity, and the liquid discharge cavity is communicated with a liquid discharge tube.

By adopting the technical scheme, the heat exchange tube in the horizontal tube type heat exchanger adopts an inner tube and outer tube structure, and when heat exchange is carried out, reaction gas enters from one end of the inner tube and is output from the other end; methanol firstly enters the shell, then part of the methanol enters the outer pipe from one end of the outer pipe, the heat exchange efficiency of reaction gas and the methanol is improved, and then the methanol heated in the outer pipe is output from the other end of the outer pipe, enters the liquid discharge cavity and is discharged through the liquid discharge pipe.

This application is through setting up inner tube, outer tube and flowing back chamber for the methyl alcohol that gets into in the casing only can discharge through the outer tube, and methyl alcohol gets into the heat exchange efficiency of reaction gas in can greatly increased and the inner tube behind the outer tube, improves the thermal utilization ratio of reaction gas on the one hand, and on the other hand can improve the temperature reduction methyl alcohol evaporator's of methyl alcohol heat load.

Preferably, a plurality of baffles are arranged in the shell along the length direction of the shell, and adjacent baffles are arranged in a staggered mode.

By adopting the technical scheme, the arrangement of the baffle plate can prolong the flow of methanol in the shell, increase the flow of the methanol and reaction gas, and increase the heat exchange time, thereby increasing the heat exchange efficiency. In addition, the baffle plate increases the turbulence degree of the flowing of the methanol, breaks a laminar boundary layer and increases the heat exchange efficiency of the methanol and the reaction gas.

Preferably, the baffles are arranged obliquely, and the included angle between the planes of the adjacent baffles is 60-90 degrees.

By adopting the technical scheme, the baffle plates are obliquely arranged, so that the turbulence degree of the methanol is further increased, and the heat exchange efficiency is greatly improved.

Preferably, the shell is communicated with a shell-side fluid inlet pipe, and the shell-side fluid inlet pipe is positioned at one end close to the liquid discharge cavity.

Through adopting above-mentioned technical scheme, because the outer tube must be passed through during the methanol output in the casing, and after entering the casing from shell side fluid, need flow to the open end of outer tube along the axis direction of casing and just can get into the outer tube, increase the flow of methanol in the casing, help improving heat exchange efficiency.

Preferably, a baffle is arranged in the liquid discharge cavity, a first cavity is formed between the baffle and the partition plate, a second cavity is formed between the baffle and the tube plate, the liquid discharge tube is communicated with the second cavity, and one end, far away from the liquid discharge tube, of the second cavity is communicated with the first cavity.

Through adopting above-mentioned technical scheme, all inner tubes all pass from the flowing back intracavity, separate into first cavity and second cavity with the flowing back chamber through setting up and separate the baffle, increase the flow of flowing back intracavity methyl alcohol to increase the heat exchange time of methyl alcohol and reaction gas, improve heat exchange efficiency.

In summary, the present application includes at least one of the following beneficial technical effects:

1. the cooling section and the methanol preheating section are arranged between the cooling section and the absorption tower, so that the reaction gas has heat exchange with methanol in the cooling section and the methanol preheating section, on one hand, the heat of the reaction gas is utilized to heat the methanol, the reaction heat generated in the formaldehyde synthesis is fully utilized, and the utilization rate of the reaction heat is improved; on the other hand, the temperature of the reaction gas entering the absorption tower is greatly reduced, so that the heat load of the absorption tower is reduced;

2. through the arrangement of the inner pipe, the outer pipe and the liquid discharge cavity, methanol entering the shell can be discharged only through the outer pipe, and the heat exchange efficiency of the methanol with reaction gas in the inner pipe can be greatly increased after the methanol enters the outer pipe, so that the utilization rate of heat of the reaction gas is improved, the temperature of the methanol can be improved, and the heat load of a methanol evaporator can be reduced;

3. the baffle plate prolongs the flow process of the methanol in the shell, and increases the heat exchange time of the methanol and the reaction gas, thereby increasing the heat exchange efficiency.

Drawings

FIG. 1 is a flow chart of reaction heat recovery according to an embodiment of the present application.

FIG. 2 is a schematic structural diagram of a horizontal tubular heat exchanger in the embodiment of the present application.

Fig. 3 is a sectional view of a horizontal tubular heat exchanger in the embodiment of the present application.

Fig. 4 is a partial structural schematic view intended to show a heat exchange tube.

Description of the reference numerals: 1. a formaldehyde reactor; 2. a quenching section; 3. a cooling section; 4. a methanol preheating section; 6. an absorption tower; 7. a methanol evaporator; 71. a reboiler; 81. a housing; 811. a baffle plate; 812. a shell-side fluid inlet pipe; 82. a tube sheet; 83. a heat exchange pipe; 831. an inner tube; 832. an outer tube; 84. sealing the end; 841. a pipe box; 85. a partition plate; 851. a liquid discharge cavity; 8511. a baffle plate; 8512. a first chamber; 8513. a second chamber; 852. a liquid discharge pipe; 9. a methanol storage tank.

Detailed Description

This is described in further detail below in conjunction with figures 1-4.

The embodiment of the application discloses reaction heat recycling system in formaldehyde production. Referring to fig. 1, the reaction heat recycling system in formaldehyde production comprises a formaldehyde reactor 1, a cooling section 3, a methanol preheating section 4, an absorption tower 6, a methanol evaporator 7 and a reboiler 71, wherein the quenching section 2 adopts a vertical tubular heat exchanger, the height of the vertical tubular heat exchanger is 0.9m, the diameter of a tube plate 82 is 1.9m, and the heat exchange area is 64m ² (ii) a The methanol preheating section 4 adopts a horizontal tubular heat exchanger, the length of the horizontal tubular heat exchanger is 1.9m, and the heat exchange area is 7m ² 。

Referring to fig. 1, a quenching section 2 is arranged at the bottom of a formaldehyde reactor 1, an outlet of the quenching section 2 is connected and communicated with a tube side inlet of a vertical tube side heat exchanger, a tube side outlet of the vertical tube side heat exchanger is connected and communicated with a tube side inlet of a horizontal heat exchanger, and a tube side outlet of the horizontal tube side heat exchanger is communicated with an absorption tower 6.

Referring to fig. 1, a shell pass inlet of the horizontal tubular heat exchanger is connected with a methanol storage tank 9, a shell pass outlet of the horizontal tubular heat exchanger is connected with a shell pass inlet of the vertical tubular heat exchanger, a shell pass outlet of the vertical tubular heat exchanger is connected with a tee joint, and two outlets of the tee joint are respectively communicated with a methanol evaporator 7 and a reboiler 71.

When formaldehyde is prepared, the path of the reaction gas output after the reaction in the formaldehyde reactor 1 is as follows: firstly, reaction gas enters a quenching section 2 to be cooled and then enters a tube side of a vertical tube type heat exchanger, reaction gas output from the vertical tube type heat exchanger enters a tube side of a horizontal tube type heat exchanger, and then the reaction gas is output from the horizontal tube type heat exchanger and enters an absorption tower 6 to be absorbed.

The flow path of methanol supplied to the formaldehyde reactor 1 is: firstly, outputting methanol from a methanol storage tank 9, and entering a shell pass of a horizontal tubular heat exchanger from a shell pass inlet of the horizontal tubular heat exchanger; then carrying out heat exchange with reaction gas in the tube pass of the horizontal tubular heat exchanger, and outputting methanol from a shell pass outlet of the horizontal tubular heat exchanger, wherein the temperature of the output methanol is 65-70 ℃; then, methanol output from the horizontal tubular heat exchanger enters the shell side of the vertical tubular heat exchanger from the shell side inlet of the vertical tubular heat exchanger, then exchanges heat with reaction gas in the tube side of the vertical tubular heat exchanger, and is output from the shell side outlet of the vertical tubular heat exchanger, wherein the temperature of the output methanol is 76-79 ℃, and at the moment, part of the methanol is gasified to form a methanol gas-liquid mixture; the methanol gas-liquid mixture passes through two outlet branches of the tee joint, namely, gasified methanol rises to enter the methanol evaporator 7, and liquid methanol flows into the reboiler 71. In addition, after the reaction gas sequentially passes through the vertical tubular heat exchanger and the horizontal tubular heat exchanger, the temperature of the reaction gas before entering the absorption tower 6 is 90-100 ℃, and is reduced by 30-35 ℃ compared with the temperature when the vertical tubular heat exchanger and the horizontal tubular heat exchanger are not arranged.

Referring to fig. 2, the horizontal tube and tube heat exchanger includes a cylindrical housing 81, and hemispherical shell-shaped headers 84 are fixedly connected to both ends of the housing 81 to form a sealing structure inside the housing 81. Referring to fig. 3, two tube plates 82 are fixedly connected to the inside of the shell 81 along the axial direction thereof, the two tube plates 82 are respectively located at two ends of the shell 81, tube boxes 841 are formed between the tube plates 82 and the end sockets 84, one tube box 841 is connected to the tube side inlet, and the other tube box 841 is connected to the tube side outlet. A plurality of heat exchange tubes 83 are provided between the two tube plates 82, and ends of the heat exchange tubes 83 are positioned inside the tube tank 841 through the tube plates 82.

Referring to fig. 3, a plurality of baffles 811 are disposed in the housing 81 along the length direction thereof, adjacent baffles 811 are staggered up and down, the baffles 811 are disposed obliquely, and the included angle between the planes of the adjacent baffles 811 is 60 to 90 °.

Referring to fig. 3 and 4, the heat exchange tube 83 includes an inner tube 831 and an outer tube 832, the axial direction of the inner tube 831 being the same as the axial direction of the shell 81, and the end of the inner tube 831 passing through the tube sheet 82 and being located in the tube tank 841; a partition plate 85 is arranged between the two tube plates 82, the partition plate 85 is fixedly connected with the inner wall of the shell 81, and the partition plate 85 is close to one tube plate 82 and forms a liquid discharge cavity 851 together with the tube plate 82; the outer tube 832 is surrounded on the outer periphery of the inner tube 831 and is spaced from the outer periphery of the inner tube 831, and the outer tube 832 is open at both ends, one end of which passes through the partition plate 85 and is located inside the liquid discharge chamber 851, and the other end of which is located outside the liquid discharge chamber 851.

Referring to fig. 4, a baffle 8511 is disposed in the liquid discharge chamber 851, a first chamber 8512 is formed between the baffle 8511 and the partition plate 85, a second chamber 8513 is formed between the baffle 8511 and the tube plate 82, a liquid discharge pipe 852 is communicated with the top of the second chamber 8513, and one end of the second chamber 8513, which is far from the liquid discharge pipe 852, is communicated with the first chamber 8512. A shell-side fluid inlet pipe 812 is communicated with the housing 81, and the shell-side fluid inlet pipe 812 is located at one end close to the liquid discharge chamber 851.

When the reaction gas and the methanol exchange heat in the horizontal type tube-in-tube heat exchanger, the reaction gas enters the inner tube 831 from the tube side inlet, flows along the inner tube 831 and is output from the tube side outlet; methanol enters the housing 81 from the shell-side fluid inlet pipe 812, part of the methanol enters the outer pipe 832 from one end of the outer pipe 832, flows along the outer pipe 832 to the first chamber 8512, and the methanol in the first chamber 8512 flows into the second chamber 8513 and is discharged through the liquid discharge pipe 852. Because this application inner tube 831, the setting of outer tube 832 for the methyl alcohol that gets into in the casing 81 only can discharge through outer tube 832, and methyl alcohol gets into behind the outer tube 832 can greatly increased with the inner tube 831 in the heat exchange efficiency of reaction gas, thereby improve the thermal utilization ratio of reaction gas, and the temperature when can improving the methanol output, reduce the heat load of methyl alcohol evaporimeter 7.

The implementation principle of the reaction heat recycling system in the formaldehyde production in the embodiment of the application is as follows: firstly, inputting the methanol at room temperature into a shell 81 of a horizontal tubular heat exchanger, and carrying out heat exchange with reaction gas in a tube pass of the horizontal tubular heat exchanger to preheat the methanol; then, the methanol output from the horizontal tubular heat exchanger enters the shell 81 of the vertical tubular heat exchanger, and exchanges heat with the reaction gas in the tube pass of the vertical tubular heat exchanger, so that the methanol is further heated, so that part of the methanol is gasified when the methanol is output from the vertical tubular heat exchanger, a methanol gas-liquid mixture is formed, the gasified methanol is input into the methanol evaporator 7 to provide methanol gas for preparing formaldehyde in the formaldehyde reactor 1, and the methanol in the liquid flows into the reboiler 71. In this application, utilize the heat of reaction gas to heat methyl alcohol for methyl alcohol obtains the partial condensation heat of reaction gas, and the reaction heat that produces in the make full use of formaldehyde is synthetic, improves the utilization ratio of reaction heat in the formaldehyde production, thereby reduces the energy consumption, can also alleviate the heat load of methyl alcohol evaporimeter 7 simultaneously.

The above embodiments are preferred embodiments of the present application, and the protection scope of the present application is not limited by the above embodiments, so: all equivalent changes made according to the structure, shape and principle of the present application shall be covered by the protection scope of the present application.

Claims

1. The utility model provides a reaction heat recycle system in formaldehyde production which characterized in that: comprises a cooling section (3) and a methanol preheating section (4) which are arranged between a quenching section (2) and an absorption tower (6), wherein reaction gas cooled by the quenching section (2) sequentially passes through the cooling section (3) and the preheating section and then enters the absorption tower (6); the methanol sequentially passes through the methanol preheating section (4) and the cooling section (3) and then enters the methanol evaporator (7).

2. The system for recycling reaction heat in formaldehyde production according to claim 1, wherein: the temperature of the methanol after being output from the methanol preheating section (4) is 65-70 ℃, and the temperature of the methanol after being output from the cooling section (3) is 76-79 ℃.

3. The system for recycling reaction heat in formaldehyde production according to claim 1, wherein: the methanol is output from the cooling section (3), and then the partially gasified methanol enters a methanol evaporator (7), and the methanol liquid which is not gasified enters a reboiler (71).

4. The system for recycling reaction heat in formaldehyde production according to claim 1, wherein: the temperature of the reaction gas after being output from the methanol preheating section (4) is 90-100 ℃.

5. The system for recycling reaction heat in formaldehyde production according to claim 1, wherein: the methanol preheating section (4) adopts a horizontal tubular heat exchanger.

6. The system for recycling reaction heat in formaldehyde production according to claim 5, wherein: the horizontal type tube heat exchanger comprises a shell (81), tube plates (82) are fixed at two ends of the shell (81), a plurality of heat exchange tubes (83) are arranged in the shell (81), the heat exchange tubes (83) are fixedly connected with the tube plates (82), end sockets (84) are arranged at two ends of the shell (81), the end sockets (84) are located on the outer sides of the tube plates (82) and fixedly connected with the shell (81), and a tube box (841) is formed between the end sockets (84) and the tube plates (82); the heat exchange tube (83) comprises an inner tube (831) and an outer tube (832), the end part of the inner tube (831) passes through the tube plate (82) and is positioned in the tube box (841), and the outer tube (832) is arranged around the periphery of the inner tube (831); a partition plate (85) is arranged in the shell (81), the partition plate (85) is close to one of the tube plates (82) and forms a liquid discharge cavity (851) with the tube plate (82), two ends of the outer tube (832) are opened, one end of the outer tube is positioned outside the liquid discharge cavity (851), the other end of the outer tube is positioned inside the liquid discharge cavity (851), and the liquid discharge cavity (851) is communicated with a liquid discharge tube (852).

7. The system for recycling reaction heat in formaldehyde production according to claim 5, wherein: a plurality of baffle plates (811) are arranged in the shell (81) along the length direction of the shell, and the adjacent baffle plates (811) are arranged in a staggered mode.

8. The system for recycling reaction heat in formaldehyde production according to claim 7, wherein: the baffle plates (811) are obliquely arranged, and the included angle between the planes of the adjacent baffle plates (811) is 60-90 degrees.

9. The system for recycling reaction heat in formaldehyde production according to claim 6, wherein: and a shell-side fluid inlet pipe (812) is communicated with the shell (81), and the shell-side fluid inlet pipe (812) is positioned at one end close to the liquid discharge cavity (851).

10. The system for recycling reaction heat in formaldehyde production according to claim 6, wherein: be equipped with in flowing back chamber (851) and separate baffle (8511), separate and form first cavity (8512) between baffle (8511) and division board (85), separate and form second cavity (8513) between baffle (8511) and tube sheet (82), fluid-discharge tube (852) and second cavity (8513) intercommunication, one end and first cavity (8512) intercommunication that fluid-discharge tube (852) were kept away from in second cavity (8513).