Tail gas absorption device for rake dryer

Abstract

The utility model discloses a kind of rake dryers tail gas cascade absorption devices, including first absorption tower, second absorption tower, first water washing box, second water washing box, heat exchanger, vacuum pump, first gas duct and second gas duct;Wherein, the air inlet of the first absorption tower is used to be connected with rake dryer and is used to access the tail gas discharged by rake dryer, the gas phase outlet of the top of the first absorption tower is connected with the feed inlet of the heat exchanger, the discharge outlet of the heat exchanger is connected with the air inlet of the second absorption tower, liquid is loaded in first water washing box, first water washing box has first gas phase space above liquid, liquid is loaded in second water washing box, second water washing box has second gas phase space above liquid.The utility model can carry out secondary absorption to formaldehyde in tail gas, can improve absorption efficiency, reduce the residual amount of formaldehyde in tail gas, can reduce the loss waste of formaldehyde material, and tail gas emission can be qualified to avoid environmental pollution.

Description

Technical Field

[0001] This utility model relates to a cascade absorption device for exhaust gas from a rake dryer. Background Technology

[0002] Currently, in the production of paraformaldehyde (PFO), a rake dryer is used to dry the material. During the operation of the rake dryer, a large amount of high-temperature exhaust gas containing formaldehyde vapor, dust, and small amounts of other organic matter is generated. The pollutants such as formaldehyde in the exhaust gas need to be absorbed and treated by an exhaust gas treatment device. For example, Chinese patent CN212383487U discloses a PFO exhaust gas emission treatment device. However, some existing exhaust gas treatment devices use a single-tower absorption method. Single-tower absorption can only absorb the exhaust gas once, and the concentration and temperature of the absorbent in the absorption tower are prone to increase during single-tower absorption. Absorbents with high concentrations and temperatures have low solubility for formaldehyde, resulting in low absorption efficiency and high residual formaldehyde levels in the exhaust gas. This not only causes the loss of formaldehyde material but also results in substandard exhaust gas emissions, leading to environmental pollution. Utility Model Content

[0003] The technical problem to be solved by this utility model is to overcome the defects of the prior art and provide a cascade absorption device for the exhaust gas of a rake dryer. It can perform secondary absorption of formaldehyde in the exhaust gas, improve absorption efficiency, reduce the residual amount of formaldehyde in the exhaust gas, reduce the loss and waste of formaldehyde materials, and ensure that the exhaust gas emissions meet the standards, thereby avoiding environmental pollution.

[0004] To solve the above-mentioned technical problems, the technical solution of this utility model is: a cascade absorption device for exhaust gas from a rake dryer, comprising a first absorption tower, a second absorption tower, a first water washing tank, a second water washing tank, a heat exchanger, a vacuum pump, a first gas guide pipeline, and a second gas guide pipeline.

[0005] The air inlet of the first absorption tower is used to connect to the rake dryer and to receive the exhaust gas discharged from the rake dryer;

[0006] The gas phase outlet at the top of the first absorption tower is connected to the feed inlet of the heat exchanger;

[0007] The outlet of the heat exchanger is connected to the inlet of the second absorption tower;

[0008] The first water washing tank contains liquid, and the first water washing tank has a first gas phase space located above the liquid;

[0009] The second washing tank contains liquid, and the second washing tank has a second gas phase space located above the liquid;

[0010] The gas phase outlet at the top of the second absorption tower is connected to the first gas guide pipeline, and the first gas guide pipeline is connected to the first water washing tank and is used to pass the gas discharged from the gas phase outlet at the top of the second absorption tower into the liquid in the first water washing tank.

[0011] The inlet of the vacuum pump is connected to the first gas phase space in the first water washing tank and is used to draw gas from the first gas phase space. The outlet of the vacuum pump is connected to the second gas guide pipe, which is connected to the second water washing tank and is used to pass the gas drawn by the vacuum pump into the liquid in the second water washing tank.

[0012] Furthermore, the cascade absorption device for the exhaust gas of the rake dryer also includes an intake pipe and an exhaust pipe;

[0013] The air inlet of the first absorption tower is used to connect to the rake dryer through the air inlet pipeline;

[0014] The exhaust pipe is connected to the second gas phase space in the second water washing tank.

[0015] Furthermore, one end of the first gas guide pipe is connected to the gas phase outlet at the top of the second absorption tower, and the other end of the first gas guide pipe is connected to the first water washing tank and extends into the liquid in the first water washing tank.

[0016] One end of the second air guide pipe is connected to the outlet of the vacuum pump, and the other end of the second air guide pipe is connected to the second water washing tank and extends into the liquid in the second water washing tank.

[0017] Furthermore, the cascade absorption device for the exhaust gas of the rake dryer also includes a first circulating pump;

[0018] The first absorption tower has a first tower bottom located at the bottom, a first heat exchange device located above the first tower bottom, a first packing layer located above the first heat exchange device, and a first spray assembly located above the first packing layer;

[0019] The air inlet of the first absorption tower is located at the upper end of the first tower vessel;

[0020] The inlet of the first circulating pump is connected to the outlet of the first tower, and the outlet of the first circulating pump is connected to the first spray assembly.

[0021] Furthermore, the cascade absorption device for the exhaust gas of the rake dryer also includes an extraction pipeline and an extraction valve. The outlet of the first circulating pump is also connected to the extraction pipeline, and the extraction valve is connected in the extraction pipeline.

[0022] Furthermore, the cascade absorption device for the exhaust gas of the rake dryer also includes a second circulation pump, a circulation pipeline, a material transfer pipeline, and a material transfer valve;

[0023] The second absorption tower has a second tower bottom located at the bottom, a second heat exchange device located above the second tower bottom, a second packing layer located above the second heat exchange device, and a second spray assembly located above the second packing layer;

[0024] The air inlet of the second absorption tower is located at the upper end of the second tower vessel;

[0025] The inlet of the second circulating pump is connected to the liquid outlet of the second tower, and the outlet of the second circulating pump is connected to one end of the circulating pipeline and one end of the transfer pipeline, respectively.

[0026] The other end of the circulation pipeline is connected to the second spray assembly;

[0027] The other end of the transfer pipeline is connected to the liquid inlet of the first tower.

[0028] The transfer valve is connected in the transfer pipeline.

[0029] Furthermore, the cascade absorption device for the exhaust gas of the rake dryer also includes a controller, a first level gauge, and a second level gauge;

[0030] The first level gauge is connected to the first column reboiler and is used to detect the liquid level in the first column reboiler;

[0031] The second level gauge is connected to the second column reboiler and is used to detect the liquid level in the second column reboiler;

[0032] The first level gauge and the second level gauge are respectively connected to the controller;

[0033] The controller is connected to the extraction valve and is used to control the opening and closing of the extraction valve based on the liquid level information measured by the first liquid level gauge.

[0034] The controller is connected to the transfer valve and is used to control the opening and closing of the transfer valve based on the liquid level information measured by the second liquid level gauge.

[0035] Furthermore, the exhaust gas cascade absorption device of the rake dryer also includes a cooler;

[0036] The inlet of the cooler is connected to the second water washing tank and is used to receive the liquid in the second water washing tank;

[0037] The outlet of the cooler is connected to the working fluid inlet of the vacuum pump;

[0038] The feed inlet of the cooler is connected to a first valve;

[0039] The working fluid inlet of the vacuum pump is connected to a second valve;

[0040] The vacuum pump is a water ring vacuum pump.

[0041] Furthermore, at least two water ring vacuum pumps and at least two heat exchangers are connected in parallel.

[0042] Furthermore, the cascade absorption device for the exhaust gas of the rake dryer also includes a third level gauge connected to the first water washing tank and a fourth level gauge connected to the second water washing tank.

[0043] Employing the aforementioned technical solution, the rake dryer, also known as a rake-type dryer, can dry materials during the production of paraformaldehyde. In the rake dryer, heating is achieved by introducing steam into the jacket, and the rotation of the rake teeth continuously stirs the material, ensuring uniform and thorough heating so that moisture and free formaldehyde in the material evaporate rapidly, forming exhaust gas. The exhaust gas generated in the rake dryer enters the first absorption tower through the inlet. The absorbent in the first absorption tower absorbs the dust formaldehyde and gaseous formaldehyde in the exhaust gas for the first time. Then, the exhaust gas flows from the gas phase outlet at the top of the first absorption tower into a heat exchanger, where it is cooled. The cooled exhaust gas then flows into the second absorption tower, where the absorbent absorbs the formaldehyde and other substances in the exhaust gas for the second time. Subsequently, the exhaust gas in the second absorption tower... The gas flows into the first gas guide pipe and is then fed into the liquid in the first water washing tank for washing. The washed exhaust gas then enters the first gas phase space. The vacuum pump can draw the exhaust gas from the first gas phase space. Under the pumping of the vacuum pump, the exhaust gas flows into the second gas guide pipe and is fed into the liquid in the second water washing tank for washing again. The washed exhaust gas then enters the second gas phase space. The exhaust gas that cannot be absorbed will be discharged from the second water washing tank. The process involves two absorption towers, one for formaldehyde and the other for exhaust gas, significantly improving absorption efficiency. All dry dust and other contaminants remain in the first tower. After exiting the first tower, the exhaust gas is cooled by a heat exchanger before entering the second tower. The temperature and formaldehyde concentration of the exhaust gas are already lower in the second tower, resulting in less heat and formaldehyde absorbed by the absorbent liquid. This lower temperature and concentration of the absorbent liquid in the second tower enhances its solubility in formaldehyde, further improving absorption efficiency and reducing residual formaldehyde levels. This ensures that exhaust gas emissions meet standards and prevent environmental pollution. Furthermore, the recovered formaldehyde can be reused, minimizing waste. Attached Figure Description

[0044] Figure 1 This is a process flow diagram showing the connection between the exhaust gas cascade absorption device of the rake dryer and the rake dryer according to this utility model.

[0045] Figure 2 This is a process flow diagram of the tail gas cascade absorption device for the rake dryer of this utility model;

[0046] In the diagram: 1. First absorption tower; 2. Second absorption tower; 3. First washing tank; 4. Second washing tank; 5. Heat exchanger; 6. Vacuum pump; 7. First gas guide pipeline; 8. Second gas guide pipeline; 9. Rake dryer; 10. First gas phase space; 11. Second gas phase space; 12. Inlet pipeline; 13. Exhaust pipeline; 14. First circulating pump; 15. First tower bottom; 16. First heat exchanger; 17. First packing layer; 18. First... 19. Spray assembly; 20. Outlet pipeline; 21. Outlet valve; 22. Second circulation pump; 23. Circulation pipeline; 24. Transfer pipeline; 25. Transfer valve; 26. Second reboiler; 27. Second heat exchanger; 28. Second packing layer; 29. ​​Second spray assembly; 30. First level gauge; 31. Second level gauge; 32. Cooler; 33. First valve; 34. Second valve; 35. Third level gauge; 36. Fourth level gauge. Detailed Implementation

[0047] To make the contents of this utility model easier to understand, the present utility model will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0048] like Figure 1 , 2 As shown, a cascade absorption device for exhaust gas from a rake dryer includes a first absorption tower 1, a second absorption tower 2, a first water washing tank 3, a second water washing tank 4, a heat exchanger 5, a vacuum pump 6, a first gas guide line 7, and a second gas guide line 8.

[0049] The air inlet of the first absorption tower 1 is used to connect to the rake dryer 9 and to receive the exhaust gas discharged from the rake dryer 9;

[0050] The gas phase outlet at the top of the first absorption tower 1 is connected to the feed inlet of the heat exchanger 5;

[0051] The outlet of the heat exchanger 5 is connected to the inlet of the second absorption tower 2;

[0052] The first water washing tank 3 contains liquid, and the first water washing tank 3 has a first gas phase space 10 located above the liquid;

[0053] The second water washing tank 4 contains liquid, and the second water washing tank 4 has a second gas phase space 11 located above the liquid;

[0054] The gas phase outlet at the top of the second absorption tower 2 is connected to the first gas guide pipe 7, and the first gas guide pipe 7 is connected to the first water washing tank 3 and is used to pass the gas discharged from the gas phase outlet at the top of the second absorption tower 2 into the liquid in the first water washing tank 3.

[0055] The inlet of the vacuum pump 6 is connected to the first gas phase space 10 in the first water washing tank 3 and is used to draw gas from the first gas phase space 10. The outlet of the vacuum pump 6 is connected to the second gas guide pipe 8. The second gas guide pipe 8 is connected to the second water washing tank 4 and is used to pass the gas drawn by the vacuum pump 6 into the liquid in the second water washing tank 4.

[0056] Specifically, the rake dryer 9, also known as a rake dryer, dries materials during the production of paraformaldehyde. In the rake dryer 9, heating is achieved by introducing steam into the jacket, and the rotation of the rake teeth continuously stirs the material, ensuring uniform and thorough heating so that moisture and free formaldehyde in the material evaporate rapidly, forming exhaust gas. More specifically, the exhaust gas generated in the rake dryer 9 enters the first absorption tower 1 through its inlet. The absorbent in the first absorption tower 1 absorbs formaldehyde and other substances in the exhaust gas for the first time. Then, the exhaust gas flows from the gas phase outlet at the top of the first absorption tower 1 into the heat exchanger 5, where it is cooled. The cooled exhaust gas then flows into the second absorption tower 2, where the absorbent absorbs formaldehyde and other substances for the second time. Subsequently, the exhaust gas from the second absorption tower 2 flows into the first absorption tower 1. The exhaust gas is washed in the liquid in the first water washing tank 3 through the first gas guide pipe 7. Then, the exhaust gas washed in the first water washing tank 3 will enter the first gas phase space 10. The vacuum pump 6 can draw the exhaust gas in the first gas phase space 10. The exhaust gas will flow into the second gas guide pipe 8 through the vacuum pump 6 and be washed again in the liquid in the second water washing tank 4. The exhaust gas washed in the second water washing tank 4 will enter the second gas phase space 11. Then, the exhaust gas that cannot be absorbed will be discharged from the second water washing tank 4. The first absorption tower 1 and the second absorption tower 2 can absorb formaldehyde and other substances in the exhaust gas twice, which greatly improves the absorption efficiency. After the exhaust gas exits from the first absorption tower 1, it is cooled down by the heat exchanger 5 before entering the second absorption tower 2. The temperature of the exhaust gas entering the second absorption tower 2 has been reduced, and the concentration of formaldehyde in the exhaust gas has also been reduced. Therefore, the amount of heat and formaldehyde absorbed by the absorbent in the second absorption tower 2 is relatively small, which keeps the temperature and concentration of the absorbent in the second absorption tower 2 at a low level. The absorbent with a low concentration and temperature has a higher solubility for formaldehyde, which greatly improves the absorption efficiency of the second absorption tower 2 for formaldehyde in the exhaust gas. This reduces the residual amount of pollutants such as formaldehyde in the exhaust gas, and ensures that the exhaust gas emissions meet the standards to avoid environmental pollution. In addition, the recovered formaldehyde can be reused, thereby reducing the loss and waste of formaldehyde materials.

[0057] like Figure 1 , 2 As shown, the cascade absorption device for the exhaust gas of the rake dryer may further include an intake pipe 12 and an exhaust pipe 13.

[0058] The air inlet of the first absorption tower 1 is used to connect to the rake dryer 9 through the air inlet pipe 12, and the exhaust gas generated in the rake dryer 9 will enter the first absorption tower 1 through the air inlet pipe 12.

[0059] The exhaust pipe 13 is connected to the second gas phase space 11 in the second water washing tank 4. The exhaust pipe 13 is connected to the exhaust gas network. The exhaust gas in the second gas phase space 11 will be discharged from the exhaust pipe 13 to the exhaust gas network.

[0060] like Figure 1 , 2 As shown, one end of the first gas guide pipe 7 is connected to the gas phase outlet at the top of the second absorption tower 2, and the other end of the first gas guide pipe 7 is connected to the first water washing tank 3 and extends into the liquid in the first water washing tank 3, so that gas can be introduced into the liquid in the first water washing tank 3 through the first gas guide pipe 7.

[0061] One end of the second gas guide pipe 8 is connected to the outlet of the vacuum pump 6, and the other end of the second gas guide pipe 8 is connected to the second water washing tank 4 and extends into the liquid in the second water washing tank 4, so that gas can be introduced into the liquid in the second water washing tank 4 through the second gas guide pipe 8.

[0062] like Figure 1 , 2 As shown, the cascade absorption device for the exhaust gas of the rake dryer may further include a first circulating pump 14;

[0063] The first absorption tower 1 has a first tower bottom 15 at the bottom, a first heat exchange device 16 above the first tower bottom 15, a first packing layer 17 above the first heat exchange device 16, and a first spray assembly 18 above the first packing layer 17.

[0064] The air inlet of the first absorption tower 1 is located at the upper end of the first tower bottom 15;

[0065] The inlet of the first circulating pump 14 is connected to the liquid outlet of the first reboiler 15, and the outlet of the first circulating pump 14 is connected to the first spray assembly 18. Specifically, the exhaust gas from the rake dryer 9 enters the first reboiler 15 through the air inlet and flows upward through the first heat exchanger 16, the first packing layer 17, and the first spray assembly 18 before exiting from the gas phase outlet at the top of the first absorption tower 1. The first circulating pump 14 pumps the absorbent liquid from the first reboiler 15 to the first spray assembly 18, where it is sprayed down and flows through the first packing layer 17. In the first packing layer 17, the downward-flowing absorbent liquid flows counter-currently to the upward-flowing exhaust gas, ensuring sufficient contact and allowing the absorbent liquid to absorb formaldehyde and other substances from the exhaust gas. After passing through the first packing layer 17, the absorbent liquid flows downward through the first heat exchanger 16, is cooled, and then flows back to the first reboiler 15. The first heat exchanger 16 lowers the temperature of the absorbent liquid to improve the formaldehyde absorption efficiency.

[0066] like Figure 1 , 2 As shown, the cascade absorption device for the exhaust gas of the rake dryer may further include an outlet pipeline 19 and an outlet valve 20. The outlet of the first circulating pump 14 is also connected to the outlet pipeline 19, and the outlet valve 20 is connected in the outlet pipeline 19. Specifically, the outlet pipeline 19 may be connected to a storage tank. When the outlet valve 20 is opened, the absorbent liquid in the first tower bottom 15 will be pumped by the first circulating pump 14, and part of it will flow to the first spray assembly 18, while the other part will flow from the outlet pipeline 19 to the storage tank, thereby controlling the liquid level in the first tower bottom 15.

[0067] like Figure 1 , 2 As shown, the cascade absorption device for exhaust gas from the rake dryer may further include a second circulation pump 21, a circulation pipeline 22, a material transfer pipeline 23, and a material transfer valve 24.

[0068] The second absorption tower 2 has a second tower bottom 25 at the bottom, a second heat exchange device 26 above the second tower bottom 25, a second packing layer 27 above the second heat exchange device 26, and a second spray assembly 28 above the second packing layer 27.

[0069] The air inlet of the second absorption tower 2 is located at the upper end of the second tower vessel 25;

[0070] The inlet of the second circulating pump 21 is connected to the liquid outlet of the second tower 25, and the outlet of the second circulating pump 21 is connected to one end of the circulating pipeline 22 and one end of the transfer pipeline 23, respectively.

[0071] The other end of the circulation pipe 22 is connected to the second spray assembly 28;

[0072] The other end of the transfer pipeline 23 is connected to the liquid inlet of the first tower 15;

[0073] The transfer valve 24 is connected to the transfer pipeline 23. Specifically, the exhaust gas cooled in the heat exchanger 5 enters the second tower 25 through the inlet and flows upward through the second heat exchange device 26, the second packing layer 27, and the second spray assembly 28 before exiting from the gas phase outlet at the top of the second absorption tower 2. Under normal operating conditions, the transfer valve 24 is closed. At this time, the absorbent liquid in the second tower 25 is pumped by the second circulation pump 21 to the second spray assembly 28. The absorbent liquid is then sprayed down from the second spray assembly 28 and flows through the second packing layer 27. In the second packing layer 27, the downward-flowing absorbent liquid flows counter-currently to the upward-flowing exhaust gas and makes full contact so that the absorbent liquid absorbs formaldehyde and other substances in the exhaust gas. After flowing through the second packing layer 27, the absorbent liquid flows through the second heat exchange device 26 and is cooled before flowing back to the second tower 25. The second heat exchange device 26 can reduce the temperature of the absorbent liquid to improve the absorption efficiency of formaldehyde. When new absorbent is added to the second reboiler 25, the liquid level in the second reboiler 25 will rise. At this time, the transfer valve 24 needs to be opened so that the absorbent in the second reboiler 25 is pumped by the second circulation pump 21, and part of it flows from the circulation pipeline 22 to the second spray assembly 28, and the other part flows from the transfer pipeline 23 to the first reboiler 15. This not only controls the liquid level in the second reboiler 25, but also replenishes the lower concentration absorbent in the second reboiler 25 to the first reboiler 15, so that the absorbent in both the first reboiler 15 and the second reboiler 25 can be kept at a low concentration level. In this embodiment, two of the first circulating pump 14 and the second circulating pump 21 are respectively connected in parallel. The first spray assembly 18 and the second spray assembly 28 may each include a spray pipe and a plurality of spray heads. The specific structures of the first spray assembly 18 and the second spray assembly 28 are existing technologies well known to those skilled in the art, and will not be described in detail in this embodiment. The first heat exchange device 16 and the second heat exchange device 26 may each be a shell-and-tube heat exchange device. The shell-and-tube heat exchange device has an inlet for receiving the cooling medium and an outlet for discharging the cooling medium.

[0074] like Figure 1 , 2 As shown, the cascade absorption device for the exhaust gas of the rake dryer may further include a controller, a first level gauge 29, and a second level gauge 30.

[0075] The first level gauge 29 is connected to the first reboiler 15 and is used to detect the liquid level in the first reboiler 15;

[0076] The second level gauge 30 is connected to the second reboiler 25 and is used to detect the liquid level in the second reboiler 25;

[0077] The first level gauge 29 and the second level gauge 30 are respectively connected to the controller;

[0078] The controller is connected to the extraction valve 20 and is used to control the opening and closing of the extraction valve 20 according to the liquid level information measured by the first liquid level gauge 29.

[0079] The controller is connected to the transfer valve 24 and is used to control the opening and closing of the transfer valve 24 based on the liquid level information measured by the second level gauge 30. Specifically, when new absorbent is added to the second reboiler 25, the liquid level in the second reboiler 25 will rise. When the second level gauge 30 measures that the liquid level in the second reboiler 25 is higher than a threshold, the controller will control the transfer valve 24 to open so that a portion of the absorbent in the second reboiler 25 is pumped by the second circulation pump 21 and flows from the transfer pipeline 23 to the first reboiler 15. When the second level gauge 30 measures that the liquid level in the second reboiler 25 is lower than the threshold, the controller will control the transfer valve 24 to close, thereby controlling the liquid level in the second reboiler 25. When the lower concentration of absorbent in the second reboiler 25 is replenished into the first reboiler 15, the liquid level in the first reboiler 15 will rise. When the first level gauge 29 detects that the liquid level in the first reboiler 15 is higher than a threshold, the controller will control the opening of the extraction valve 20 so that a portion of the absorbent in the first reboiler 15 is pumped by the first circulation pump 14 and flows from the extraction pipeline 19 into the storage tank. When the first level gauge 29 detects that the liquid level in the first reboiler 15 is lower than the threshold, the controller will control the closing of the extraction valve 20, thereby controlling the liquid level in the first reboiler 15. The specific structures of the first level gauge 29 and the second level gauge 30 are existing technologies well-known to those skilled in the art and will not be described in detail in this embodiment.

[0080] like Figure 1 , 2 As shown, the exhaust gas cascade absorption device of the rake dryer may also include a cooler 31;

[0081] The feed inlet of the cooler 31 is connected to the second water washing tank 4 and is used to receive the liquid in the second water washing tank 4;

[0082] The outlet of the cooler 31 is connected to the working fluid inlet of the vacuum pump 6;

[0083] The feed inlet of the cooler 31 is connected to a first valve 32;

[0084] The working fluid inlet of the vacuum pump 6 is connected to a second valve 33;

[0085] The vacuum pump 6 is a water ring vacuum pump. Specifically, a certain amount of liquid needs to be injected before the water ring vacuum pump starts working. At this time, the first valve 32 and the second valve 33 can be opened so that the liquid in the second water washing tank 4 flows through the cooler 31 to be cooled down before flowing into the water ring vacuum pump from the working fluid inlet. The cooler 31 can be a plate cooler, and the cooling medium used in the cooler 31 is pure water at 5°C.

[0086] like Figure 1 , 2 As shown, at least two water ring vacuum pumps and at least two heat exchangers 5 are connected in parallel. Specifically, the inlet of each heat exchanger 5 is connected to the gas phase outlet at the top of the first absorption tower 1, the outlet of each heat exchanger 5 is connected to the gas inlet of the second absorption tower 2, and each heat exchanger 5 has an inlet for receiving cooling medium and an outlet for discharging cooling medium. The heat exchanger 5 can be a plate heat exchanger. Further specifically, the inlet of each water ring vacuum pump is connected to the first gas phase space 10 in the first water washing tank 3, the outlet of each water ring vacuum pump is connected to the second gas guide pipe 8, and the working fluid inlet of each water ring vacuum pump is connected to the outlet of the cooler 31. In this embodiment, two heat exchangers 5 and three vacuum pumps 6 are connected in parallel.

[0087] like Figure 1 , 2 As shown, the cascade absorption device for the exhaust gas of the rake dryer may further include a third level gauge 34 connected to the first washing tank 3 and a fourth level gauge 35 connected to the second washing tank 4, so as to monitor the liquid level in the first washing tank 3 through the third level gauge 34 and monitor the liquid level in the second washing tank 4 through the fourth level gauge 35. The cascade absorption device for the exhaust gas of the rake dryer in this embodiment can simultaneously treat the exhaust gas of multiple rake dryers 9, optimizes the circulation path of the absorbent liquid, creates a vacuum environment for the entire system through the vacuum pump 6, simplifies the vacuum system, reduces energy consumption, saves electricity costs, improves the vacuum degree, and reduces the consumption of absorbent liquid.

[0088] In summary, the rake dryer 9, also known as a rake dryer, is used to dry materials during the production of paraformaldehyde. In the rake dryer 9, heating is achieved by introducing steam into the jacket, and the rotation of the rake teeth continuously stirs the material, ensuring uniform and thorough heating so that moisture and free formaldehyde in the material evaporate rapidly, forming exhaust gas. The exhaust gas generated in the rake dryer 9 enters the first absorption tower 1 through the inlet. The absorbent in the first absorption tower 1 absorbs formaldehyde and other substances in the exhaust gas for the first time. Then, the exhaust gas flows from the gas phase outlet at the top of the first absorption tower 1 into the heat exchanger 5, where it is cooled. The cooled exhaust gas then flows into the second absorption tower 2, where the absorbent absorbs formaldehyde and other substances for the second time. Finally, the exhaust gas from the second absorption tower 2 flows into the first gas guide pipe. The exhaust gas is washed in the liquid in the first water washing tank 3 along the first gas guide pipe 7. Then, the exhaust gas washed in the first water washing tank 3 will enter the first gas phase space 10. The vacuum pump 6 can draw the exhaust gas in the first gas phase space 10. The exhaust gas will flow into the second gas guide pipe 8 and be washed again in the liquid in the second water washing tank 4 along the second gas guide pipe 8. The exhaust gas washed in the second water washing tank 4 will enter the second gas phase space 11. Then, the exhaust gas that cannot be absorbed will be discharged from the second water washing tank 4. The first absorption tower 1 and the second absorption tower 2 can absorb formaldehyde and other substances in the exhaust gas twice, which greatly improves the absorption efficiency. After the exhaust gas exits from the first absorption tower 1, it is cooled down by the heat exchanger 5 before entering the second absorption tower 2. The temperature of the exhaust gas entering the second absorption tower 2 has been reduced, and the concentration of formaldehyde in the exhaust gas has also been reduced. Therefore, the amount of heat and formaldehyde absorbed by the absorbent in the second absorption tower 2 is relatively small, which keeps the temperature and concentration of the absorbent in the second absorption tower 2 at a low level. The absorbent with a low concentration and temperature has a higher solubility for formaldehyde, which greatly improves the absorption efficiency of the second absorption tower 2 for formaldehyde in the exhaust gas. This reduces the residual amount of pollutants such as formaldehyde in the exhaust gas, and ensures that the exhaust gas emissions meet the standards to avoid environmental pollution. In addition, the recovered formaldehyde can be reused, thereby reducing the loss and waste of formaldehyde materials.

[0089] The specific embodiments described above further illustrate the technical problems, technical solutions, and beneficial effects of this utility model. It should be understood that the above descriptions are merely specific embodiments of this utility model and are not intended to limit this utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this utility model should be included within the protection scope of this utility model.

Claims

1. A cascade absorption device for exhaust gas from a rake dryer, characterized in that, It includes a first absorption tower (1), a second absorption tower (2), a first water washing tank (3), a second water washing tank (4), a heat exchanger (5), a vacuum pump (6), a first gas guide line (7), and a second gas guide line (8); The air inlet of the first absorption tower (1) is used to connect to the rake dryer (9) and to receive the exhaust gas discharged by the rake dryer (9); The gas phase outlet at the top of the first absorption tower (1) is connected to the feed inlet of the heat exchanger (5); The outlet of the heat exchanger (5) is connected to the inlet of the second absorption tower (2); The first water washing tank (3) contains liquid and has a first gas phase space (10) located above the liquid. The second water washing tank (4) contains liquid and has a second gas phase space (11) located above the liquid. The gas phase outlet at the top of the second absorption tower (2) is connected to the first gas guide pipe (7), and the first gas guide pipe (7) is connected to the first water washing tank (3) and is used to pass the gas discharged from the gas phase outlet at the top of the second absorption tower (2) into the liquid in the first water washing tank (3). The inlet of the vacuum pump (6) is connected to the first gas phase space (10) in the first water washing tank (3) and is used to draw gas from the first gas phase space (10). The outlet of the vacuum pump (6) is connected to the second gas guide pipe (8). The second gas guide pipe (8) is connected to the second water washing tank (4) and is used to pass the gas drawn by the vacuum pump (6) into the liquid in the second water washing tank (4).

2. The cascade absorption device for exhaust gas from a rake dryer according to claim 1, characterized in that, It also includes an intake pipe (12) and an exhaust pipe (13); The air inlet of the first absorption tower (1) is used to connect to the rake dryer (9) through the air inlet pipe (12); The exhaust pipe (13) is connected to the second gas phase space (11) in the second water washing tank (4).

3. The cascade absorption device for exhaust gas from a rake dryer according to claim 1, characterized in that, One end of the first gas guide pipe (7) is connected to the gas phase outlet at the top of the second absorption tower (2), and the other end of the first gas guide pipe (7) is connected to the first water washing tank (3) and extends into the liquid in the first water washing tank (3); One end of the second air guide pipe (8) is connected to the outlet of the vacuum pump (6), and the other end of the second air guide pipe (8) is connected to the second water washing tank (4) and extends into the liquid in the second water washing tank (4).

4. The cascade absorption device for exhaust gas from a rake dryer according to claim 1, characterized in that, It also includes the first circulation pump (14); The first absorption tower (1) has a first tower bottom (15) at the bottom, a first heat exchange device (16) above the first tower bottom (15), a first packing layer (17) above the first heat exchange device (16) and a first spray assembly (18) above the first packing layer (17). The air inlet of the first absorption tower (1) is located at the upper end of the first tower bottom (15); The inlet of the first circulating pump (14) is connected to the outlet of the first tower (15), and the outlet of the first circulating pump (14) is connected to the first spray assembly (18).

5. The cascade absorption device for exhaust gas from a rake dryer according to claim 4, characterized in that, It also includes a production pipeline (19) and a production valve (20), the outlet of the first circulating pump (14) is also connected to the production pipeline (19), and the production valve (20) is connected in the production pipeline (19).

6. The cascade absorption device for exhaust gas from a rake dryer according to claim 5, characterized in that, It also includes a second circulation pump (21), circulation pipeline (22), material transfer pipeline (23) and material transfer valve (24); The second absorption tower (2) has a second tower bottom (25) at the bottom, a second heat exchange device (26) above the second tower bottom (25), a second packing layer (27) above the second heat exchange device (26), and a second spray assembly (28) above the second packing layer (27). The air inlet of the second absorption tower (2) is located at the upper end of the second tower vessel (25); The inlet of the second circulating pump (21) is connected to the outlet of the second tower (25), and the outlet of the second circulating pump (21) is connected to one end of the circulating pipeline (22) and one end of the transfer pipeline (23); The other end of the circulation pipeline (22) is connected to the second spray assembly (28); The other end of the transfer pipeline (23) is connected to the liquid inlet of the first tower (15); The transfer valve (24) is connected in the transfer pipeline (23).

7. The cascade absorption device for exhaust gas from a rake dryer according to claim 6, characterized in that, It also includes a controller, a first level gauge (29), and a second level gauge (30); The first level gauge (29) is connected to the first reboiler (15) and is used to detect the liquid level in the first reboiler (15); The second level gauge (30) is connected to the second reboiler (25) and is used to detect the liquid level in the second reboiler (25); The first level gauge (29) and the second level gauge (30) are respectively connected to the controller; The controller is connected to the extraction valve (20) and is used to control the opening and closing of the extraction valve (20) according to the liquid level information measured by the first liquid level gauge (29); The controller is connected to the transfer valve (24) and is used to control the opening and closing of the transfer valve (24) according to the liquid level information measured by the second liquid level gauge (30).

8. The cascade absorption device for exhaust gas from a rake dryer according to claim 1, characterized in that, It also includes a cooler (31); The inlet of the cooler (31) is connected to the second washing tank (4) and is used to receive the liquid in the second washing tank (4); The outlet of the cooler (31) is connected to the working fluid inlet of the vacuum pump (6); The feed inlet of the cooler (31) is connected to a first valve (32); The working fluid inlet of the vacuum pump (6) is connected to a second valve (33). The vacuum pump (6) is a water ring vacuum pump.

9. The cascade absorption device for exhaust gas from a rake dryer according to claim 8, characterized in that, At least two water ring vacuum pumps are connected in parallel, and at least two heat exchangers (5) are connected in parallel.

10. The cascade absorption device for exhaust gas from a rake dryer according to claim 1, characterized in that, It also includes a third level gauge (34) connected to the first water washing tank (3) and a fourth level gauge (35) connected to the second water washing tank (4).

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