A method for cleaning carbon scale in a nitrotoluene waste sulfuric acid treatment device

Abstract

The invention discloses a method for cleaning carbon scale of a nitrotoluene waste sulfuric acid treatment device, and specifically relates to the technical field of chemical industry. The invention adopts the nitrotoluene waste sulfuric acid vacuum concentration treatment device itself and materials for combination, firstly uses hot water to clean out nitro compounds in the device, eliminates the safety risks that may occur when using nitric acid and sulfuric acid mixed acid for cleaning, and utilizes the oxidation side reaction of nitric acid and sulfuric acid mixed acid in nitration technology, so that concentrated sulfuric acid continuously removes hydrogen in carbon scale, and nitric acid continuously oxidizes carbon into gas, so as to achieve the purpose of removing solid carbon scale. The cleaning process adopts material circulation, cooling water cooling ingredients and steam heating, so as to achieve stable and controllable temperature change, eliminate the risk of damage to device equipment during the cleaning process, and thus achieve the cleaning of carbon scale. In addition, the invention also adopts the self-owned device equipment, DCS control system and self-owned materials of the cleaning device for formulating, so as to make the operation simple and the control precise.

Description

Technical Field

[0001] The present invention relates to the field of chemical technology, and more specifically, to a method for cleaning carbon scale in a nitrotoluene waste sulfuric acid treatment device. Background Art

[0002] During the production process of the nitrotoluene waste sulfuric acid vacuum concentration treatment device, in the equipment parts with a concentration range above 75%, under certain conditions, carbon scaling will occur in the production equipment. The conditions for this will generally be the following two:

[0003] 1. Nitrotoluene waste sulfuric acid workers dissolve more high-boiling nitro compounds, which will easily generate and accumulate carbon scale on the packing of the nitrotoluene stripping tower;

[0004] 2. The nitrotoluene waste sulfuric acid entering the device contains a large amount of free nitrotoluene, which will easily cause carbon scaling in the evaporator with a concentration of more than 75%.

[0005] At present, the existing methods for treating carbon scaling in the vacuum concentration treatment device for p-nitrotoluene waste sulfuric acid generally include the following three methods:

[0006] 1. Without cleaning, the stripping tower packing is directly replaced to discard the carbon-fouled packing. Although this method can completely deal with the carbon fouling by directly updating the packing, the treatment period is long. Under the condition of spare parts, it usually takes about a week, and the treatment cost is huge.

[0007] 2. Instead of cleaning, the carbon scale in the evaporator is cleaned manually and mechanically. However, this method has the problems of high labor intensity, troublesome cleaning and long cleaning cycle, which usually takes about 1 week, and secondary damage to the glass-lined equipment is likely to occur during the cleaning process.

[0008] 3. Use a cleaning liquid preparation method outside the device for cleaning. Specifically, a cleaning liquid preparation device is used to prepare a certain concentration of nitric acid and sulfuric acid mixed acid. This can solve the problem of carbon scaling on the stripping tower packing to a certain extent and basically restore the use function of the stripping tower. Although this method can partially remove the carbon scaling on the stripping tower packing, the temperature of the cleaning liquid is not controlled during actual operation, the effect of cleaning the stripping tower packing is unstable, and the carbon scaling in the evaporator is mixed with unreacted nitrotoluene. Due to safety reasons, this method cannot be used for cleaning evaporator carbon scaling. In addition, the preparation and transportation process of this method is more troublesome, and the cleaning time is longer, generally requiring 1-2 days.

[0009] In summary, it is of great significance to study a new carbon scaling cleaning method for nitrotoluene waste sulfuric acid treatment equipment to solve the above problems. Summary of the invention

[0010] In order to overcome the above-mentioned defects of the prior art, the present invention provides a method for cleaning carbon scale in a nitrotoluene waste sulfuric acid treatment device. The technical problem to be solved by the present invention is: At present, the treatment method of carbon scale in a nitrotoluene waste sulfuric acid vacuum concentration treatment device in the prior art has the problems of high treatment cost, long cleaning cycle and complicated operation.

[0011] To achieve the above-mentioned purpose, the present invention provides the following technical scheme: a method for cleaning carbon scale in a nitrotoluene waste sulfuric acid treatment device, comprising a carbon scale production cleaning device, wherein the carbon scale production cleaning device comprises a mixed acid tank, the lower left side of the mixed acid tank is connected to the right side of the dilute nitric acid tank through a second material pipe and a dilute nitric acid pump, the right side of the mixed acid tank is connected to a denitrification tower, the lower side of the denitrification tower is connected to a denitrification tower evaporator, the lower right side of the denitrification tower evaporator is connected to a dilute sulfuric acid tank, and the right side of the dilute sulfuric acid tank is connected to a dilute sulfuric acid pump.

[0012] The upper right side of the one-stage dilute sulfuric acid pump is connected to a stripping tower, the lower side of the stripping tower is connected to a stripping tower evaporator, the upper side of the stripping tower is connected to a three-stage scrubber, the lower right side of the stripping tower evaporator is connected to a three-stage evaporator, the lower right side of the three-stage evaporator is connected to a three-stage concentrated sulfuric acid tank, the upper side of the three-stage evaporator is connected to a three-stage scrubber, and the right side of the three-stage concentrated sulfuric acid tank is connected to a three-stage concentrated sulfuric acid pump.

[0013] The carbon scale cleaning method of the nitrotoluene waste sulfuric acid treatment device comprises the following steps:

[0014] S1. Return materials.

[0015] S2. Wash with hot water.

[0016] S3. Feed and circulation control.

[0017] S4. Cooling water is introduced.

[0018] S5, add materials and mix.

[0019] S6, heating, heat preservation and cleaning.

[0020] S7. Exhaust gas cooling treatment.

[0021] As a further solution of the present invention: the left side of the mixed acid tank is connected to the fifth material pipe and the first material pipe, a dilute nitric acid flowmeter is provided on one side of the second material pipe, the lower side of the mixed acid tank is connected to the waste acid discharge pipe, and a temperature transmitter is connected to the pipeline connecting the mixed acid tank to the denitrification tower.

[0022] The left side of the denitrification tower evaporator is connected to the first steam pipe, the lower left side of the denitrification tower evaporator is connected to the first water pipe, and the lower side of the denitrification tower evaporator is respectively connected to the first discharge pipe and the first drain pipe.

[0023] The pipeline on the upper right side of the stripping tower is connected to the gas pipeline outside the device, and a pressure transmitter is installed on the gas pipeline outside the device.

[0024] The left side of the stripping tower evaporator is connected to the second steam pipe, the lower left side of the stripping tower evaporator is connected to the second water pipe, the lower side of the stripping tower evaporator is respectively connected to the second discharge pipe and the second drain pipe, the lower side of the connecting pipe between the stripping tower evaporator and the three-stage evaporator is connected to the fourth drain pipe, the left side of the three-stage evaporator is connected to the third steam pipe, the lower left side of the three-stage evaporator is connected to the third water pipe, and the lower side of the three-stage evaporator is respectively connected to the third discharge pipe and the third drain pipe.

[0025] The upper side of the three-stage gas scrubber is connected to the gas pipeline outside the device, the left side of the three-stage concentrated sulfuric acid tank is connected to the fourth material pipe, and the lower side of the three-stage concentrated sulfuric acid tank is connected to the first drain pipe and the second drain pipe.

[0026] The lower side of the three-stage concentrated sulfuric acid tank and the three-stage concentrated sulfuric acid pump connecting pipeline is connected to the fifth drain pipe, the upper right side of the three-stage concentrated sulfuric acid pump is connected to the third material pipe, the upper side of the three-stage concentrated sulfuric acid pump is connected to the concentrated sulfuric acid flowmeter, and the upper left side of the concentrated sulfuric acid flowmeter is connected to the first material pipe.

[0027] As a further solution of the present invention: the specific method of the material withdrawal is:

[0028] The residual acid in the denitrification tower evaporator, the stripping tower evaporator and the three-stage evaporator is put into the three-stage concentrated sulfuric acid tank through the first drain pipe, the second drain pipe and the third drain pipe. The concentrated sulfuric acid in the three-stage concentrated sulfuric acid tank is controlled to be sent into the concentrated sulfuric acid tank outside the device through the three-stage concentrated sulfuric acid pump. The residual acid in the pipeline is put into the residual acid tank outside the device through the fourth drain pipe and the fifth drain pipe, and the waste acid in the mixed acid tank is put into the waste acid tank through the waste acid drain pipe.

[0029] As a further solution of the present invention: the specific method of hot water cleaning is:

[0030] S21. Ionized water enters the mixed acid tank, denitrification tower, denitrification tower evaporator, a dilute sulfuric acid tank, a dilute sulfuric acid pump, a stripping tower, a stripping tower evaporator, three-stage scrubbing tower, three-stage evaporator and three-stage concentrated sulfuric acid tank from the fifth material pipe. When the liquid level in the three-stage concentrated sulfuric acid tank reaches 60%-80%, close the valve of the fifth material pipe.

[0031] S22. Start the three-stage concentrated sulfuric acid pump, circulate water through the first material pipe, open the valves of the first steam pipe, the second steam pipe and the third steam pipe, and heat the water with steam until the temperature of the temperature transmitter reaches 70°C-80°C, and keep it warm for 1-2 hours.

[0032] S23, shut down the three-stage concentrated sulfuric acid pump, open the fifth drain pipe, the fourth drain pipe, the third drain pipe, the second drain pipe and the first drain pipe, and use hot water to discharge the liquid nitro compound to the outside of the device for treatment.

[0033] As a further solution of the present invention: the specific method of the feeding and circulation control is:

[0034] The sulfuric acid with a concentration of 91%-96% outside the device is sent to the three-stage concentrated sulfuric acid tank through the fourth material pipe. The concentrated sulfuric acid in the three-stage concentrated sulfuric acid tank enters the mixed acid tank, the denitrification tower, the denitrification tower evaporator, the first dilute sulfuric acid tank, the first dilute sulfuric acid pump, the stripping tower, the stripping tower evaporator, the three-stage scrubber, the three-stage evaporator and the three-stage concentrated sulfuric acid tank through the three-stage concentrated sulfuric acid pump and the first material pipe. When the liquid level in the three-stage concentrated sulfuric acid tank reaches 60%-80%, it is circulated, and the concentrated sulfuric acid flowmeter is controlled to display 3-4m³ / h, and the feeding of the fourth material pipe is stopped at the same time.

[0035] As a further solution of the present invention: the specific method of introducing cooling water is:

[0036] Cooling water is introduced into the heat exchange pipes of the denitration tower evaporator, the stripping tower evaporator and the three-stage evaporator through the first water pipe, the second water pipe and the third water pipe.

[0037] As a further solution of the present invention: the specific method of adding and mixing is:

[0038] 40%-50% of the dilute nitric acid in the dilute nitric acid tank is sent to the mixed acid tank through the dilute nitric acid pump and the dilute nitric acid flowmeter to mix with concentrated sulfuric acid. The dilute nitric acid flow rate is controlled to be 0.6-1m³ / h. The mass ratio of the total amount of dilute nitric acid input is 12%-15% of the total amount of concentrated sulfuric acid in the device. 3 hours after the dilute nitric acid is added, the valves of the first water pipe, the second water pipe and the third water pipe are closed to drain the water in the denitration tower evaporator, the stripping tower evaporator and the heat exchanger in the three-stage evaporator.

[0039] As a further solution of the present invention: the specific method of heating, heat preservation and cleaning is:

[0040] Open the valves of the first steam pipe, the second steam pipe and the third steam pipe to allow steam to pass into the denitrification tower evaporator, the stripping tower evaporator and the three-stage evaporator for heating. The temperature of the temperature transmitter is controlled at 80℃-90℃. Keep warm for 3-4 hours to clean the carbon scale in the stripping tower, the stripping tower evaporator and the three-stage evaporator.

[0041] As a further solution of the present invention: the specific method of the exhaust gas cooling treatment is:

[0042] The gas generated by the device is discharged from the device through the pipeline of the pressure transmitter, and the gauge pressure of the pressure transmitter is controlled to be 0. Then the temperature of the nitric acid and sulfuric acid mixed acid in the device is reduced to room temperature and discharged into the waste sulfuric acid raw material tank outside the device through the waste acid discharge pipe, and the mixed acid cleaning process is completed.

[0043] The beneficial effects of the present invention are:

[0044] 1. The present invention combines the device and materials of the nitrotoluene waste sulfuric acid vacuum concentration treatment device, first uses hot water to clean out the nitro compounds in the device, eliminates the safety risks that may occur when using nitric acid and sulfuric acid mixed acid for cleaning, and utilizes the oxidation side reaction of nitric acid and sulfuric acid mixed acid in the nitration technology, and the concentrated sulfuric acid continuously removes hydrogen in the carbon scale, and the nitric acid continuously oxidizes carbon into gas, so as to achieve the purpose of removing solid carbon scale. The cleaning process adopts material circulation, cooling water cooling ingredients and steam heating to achieve stable and controllable temperature changes, eliminate the risk of damage to the device and equipment during the cleaning process, thereby achieving the cleaning of carbon scale in the entire device of the nitrotoluene waste sulfuric acid treatment vacuum concentration device. In addition, the present invention also adopts the self-owned device and equipment of the cleaning device, the DCS control system and the self-owned materials for formulating, so that the operation is simple and the control is precise;

[0045] 2. Compared with the carbon fouling cleaning technology in the prior art, the present invention can not only clean the carbon fouling of the stripping tower packing, but also can simultaneously clean the whole process of carbon fouling cleaning of the stripping tower evaporator and the three-stage evaporator.

[0046] 3. The present invention recycles the cleaning liquid after cleaning, so that the nitrogen oxide gas generated in the cleaning process can be recovered by the nitrogen oxide recovery system outside the device, the nitrotoluene generated in the cleaning process is recovered in the system outside the device, and the acidic water enters the wastewater biochemical treatment device outside the device for treatment and is discharged after meeting the standards, thereby reducing the pollution caused to the environment. The whole process can be completed within 24 hours, the cleaning time is short, and the annual economic value is more than 1 million yuan. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A schematic diagram of the structure of a production cleaning device used in the production method of the carbon scale cleaning technology for the nitrotoluene waste sulfuric acid vacuum concentration treatment device of the present invention;

[0048] The following are marked in the figure: 1. dilute nitric acid tank; 2. dilute nitric acid pump; 3. mixed acid tank; 4. denitrification tower; 5. denitrification tower evaporator; 6. one-stage dilute sulfuric acid tank; 7. one-stage dilute sulfuric acid pump; 8. stripping tower; 9. stripping tower evaporator; 10. three-stage scrubber; 11. three-stage evaporator; 12. three-stage concentrated sulfuric acid tank; 13. three-stage concentrated sulfuric acid pump; 14. dilute nitric acid flowmeter; 15. temperature transmitter; 16. concentrated sulfuric acid flowmeter; 17. first steam pipe; 18. second steam pipe; 19. Three steam pipes; 20, first water pipe; 21, second water pipe; 22, third water pipe; 23, first discharge pipe; 24, second discharge pipe; 25, third water pipe; 26, first drain pipe; 27, second drain pipe; 28, third drain pipe; 29, fourth drain pipe; 30, fifth drain pipe; 31, first material pipe; 32, second material pipe; 33, third material pipe; 34, fourth material pipe; 35, fifth material pipe; 36, waste acid drain pipe; 37, pressure transmitter. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] A method for cleaning carbon scale of a nitrotoluene waste sulfuric acid treatment device comprises a carbon scale production cleaning device, wherein the carbon scale production cleaning device comprises a mixed acid tank 3, wherein the lower left side of the mixed acid tank 3 is connected to the right side of a dilute nitric acid tank 1 through a second material pipe 32 and a dilute nitric acid pump 2, the right side of the mixed acid tank 3 is connected to a denitration tower 4, the lower side of the denitration tower 4 is connected to a denitration tower evaporator 5, the lower right side of the denitration tower evaporator 5 is connected to a dilute sulfuric acid tank 6, and the right side of the dilute sulfuric acid tank 6 is connected to a dilute sulfuric acid pump 7.

[0051] The upper right side of a first-stage dilute sulfuric acid pump 7 is connected to a stripping tower 8, the lower side of the stripping tower 8 is connected to a stripping tower evaporator 9, the upper side of the stripping tower 8 is connected to a three-stage scrubber 10, the lower right side of the stripping tower evaporator 9 is connected to a three-stage evaporator 11, the lower right side of the three-stage evaporator 11 is connected to a three-stage concentrated sulfuric acid tank 12, the upper side of the three-stage evaporator 11 is connected to the three-stage scrubber 10, and the right side of the three-stage concentrated sulfuric acid tank 12 is connected to a three-stage concentrated sulfuric acid pump 13.

[0052] The carbon scale cleaning method of the nitrotoluene waste sulfuric acid treatment device comprises the following steps:

[0053] S1. Return materials.

[0054] S2. Wash with hot water.

[0055] S3. Feed and circulation control.

[0056] S4. Cooling water is introduced.

[0057] S5, add materials and mix.

[0058] S6, heating, heat preservation and cleaning.

[0059] S7. Exhaust gas cooling treatment.

[0060] The left side of the mixed acid tank 3 is connected to the fifth material pipe 35 and the first material pipe 31, a dilute nitric acid flowmeter 14 is provided on one side of the second material pipe 32, the lower side of the mixed acid tank 3 is connected to the waste acid discharge pipe 36, and a temperature transmitter 15 is connected to the pipeline connecting the mixed acid tank 3 to the denitrification tower 4.

[0061] The left side of the denitrification tower evaporator 5 is connected to the first steam pipe 17, the lower left side of the denitrification tower evaporator 5 is connected to the first water pipe 20, and the lower side of the denitrification tower evaporator 5 is connected to the first discharge pipe 23 and the first drain pipe 26 respectively.

[0062] The pipeline on the upper right side of the stripping tower 8 is connected to the gas pipeline outside the device, and a pressure transmitter 37 is installed on the gas pipeline outside the device.

[0063] The left side of the stripping tower evaporator 9 is connected to the second steam pipe 18, the lower left side of the stripping tower evaporator 9 is connected to the second water pipe 21, the lower side of the stripping tower evaporator 9 is respectively connected to the second discharge pipe 24 and the second drain pipe 27, the lower side of the connecting pipe between the stripping tower evaporator 9 and the three-stage evaporator 11 is connected to the fourth drain pipe 29, the left side of the three-stage evaporator 11 is connected to the third steam pipe 19, the lower left side of the three-stage evaporator 11 is connected to the third water pipe 22, and the lower side of the three-stage evaporator 11 is respectively connected to the third drainage pipe 25 and the third drain pipe 28.

[0064] The upper side of the three-stage scrubber 10 is connected to the gas pipeline outside the device, the left side of the three-stage concentrated sulfuric acid tank 12 is connected to the fourth material pipe 34, and the lower side of the three-stage concentrated sulfuric acid tank 12 is connected to the first drain pipe 26 and the second drain pipe 27.

[0065] The lower side of the pipeline connecting the three-stage concentrated sulfuric acid tank 12 and the three-stage concentrated sulfuric acid pump 13 is connected to the fifth drain pipe 30, the upper right side of the three-stage concentrated sulfuric acid pump 13 is connected to the third material pipe 33, the upper side of the three-stage concentrated sulfuric acid pump 13 is connected to the concentrated sulfuric acid flowmeter 16, and the upper left side of the concentrated sulfuric acid flowmeter 16 is connected to the first material pipe 31.

[0066] The specific method of returning materials is:

[0067] The residual acid in the denitrification tower evaporator 5, the stripping tower evaporator 9 and the three-stage evaporator 11 is put into the three-stage concentrated sulfuric acid tank 12 through the first drain pipe 26, the second drain pipe 27 and the third drain pipe 28, the concentrated sulfuric acid in the three-stage concentrated sulfuric acid tank 12 is controlled to be sent to the concentrated sulfuric acid tank outside the device through the three-stage concentrated sulfuric acid pump 13, the residual acid in the pipeline is put into the residual acid tank outside the device through the fourth drain pipe 29 and the fifth drain pipe 30, and the waste acid in the mixed acid tank 3 is put into the waste acid tank through the waste acid drain pipe 36. The material withdrawal operation is to remove the acid in the nitrotoluene waste sulfuric acid treatment vacuum concentration device, especially the denitrification tower evaporator 5, the stripping tower evaporator 9 and the three-stage evaporator 11, to avoid the concentrated sulfuric acid from further reacting with nitrotoluene and create conditions for subsequent water cleaning.

[0068] The specific method of hot water cleaning is:

[0069] S21, ionized water enters the mixed acid tank 3, the denitrification tower 4, the denitrification tower evaporator 5, the first stage dilute sulfuric acid tank 6, the first stage dilute sulfuric acid pump 7, the stripping tower 8, the stripping tower evaporator 9, the three-stage scrubbing tower 10, the three-stage evaporator 11 and the three-stage concentrated sulfuric acid tank 12 from the fifth material pipe 35. When the liquid level in the three-stage concentrated sulfuric acid tank 12 reaches 60%-80%, the valve of the fifth material pipe 35 is closed.

[0070] S22, start the three-stage concentrated sulfuric acid pump 13, circulate water through the first material pipe 31, open the valves of the first steam pipe 17, the second steam pipe 18 and the third steam pipe 19, heat the water with steam until the temperature of the temperature transmitter 15 reaches 70°C-80°C, keep warm for 1-2 hours, and the hot water cleaning temperature is 70°C-80°C, which is used to melt the dinitrotoluene entrained in the carbon scale of the stripping tower 8, the stripping tower evaporator 9 and the three-stage evaporator 11.

[0071] S23, shut down the three-stage concentrated sulfuric acid pump 13, open the fifth purge pipe 30, the fourth purge pipe 29, the third purge pipe 28, the second purge pipe 27 and the first purge pipe 26, and use hot water to discharge the liquid nitro compound to the outside of the device for treatment.

[0072] The specific methods of feeding and circulation control are:

[0073] Sulfuric acid with a concentration of 91%-96% outside the device is sent to the three-stage concentrated sulfuric acid tank 12 through the fourth material pipe 34. The formula of sulfuric acid with a concentration of 91%-96% is to ensure that nitric acid is not evaporated and consumed under the temperature condition of 80°C-90°C. The concentrated sulfuric acid in the three-stage concentrated sulfuric acid tank 12 enters the mixed acid tank 3, the denitration tower 4, the denitration tower evaporator 5, the first dilute sulfuric acid tank 6, the first dilute sulfuric acid pump 7, the stripping tower 8, the stripping tower evaporator 9, the three-stage scrubber 10, the three-stage evaporator 11 and the three-stage concentrated sulfuric acid tank 12 through the three-stage concentrated sulfuric acid pump 13 and the first material pipe 31. When the liquid level in the three-stage concentrated sulfuric acid tank 12 reaches 60%-80%, it is circulated. The circulation rate of %-96% concentrated sulfuric acid is 3-4m³ / h, the flow rate of dilute nitric acid is controlled to be 0.6-1m³ / h, the total amount of dilute nitric acid input is 12%-15% of the total mass ratio of concentrated sulfuric acid in the device, the process formula ensures the total amount of effective nitric acid for cleaning carbon scale, the concentrated sulfuric acid flowmeter 16 is controlled to display 3-4m³ / h, and the feeding of the fourth material pipe 34 is stopped at the same time. 91%-96% concentrated sulfuric acid outside the device is sent into the three-stage concentrated sulfuric acid tank 12 through the fourth material pipe 34, and circulated in the nitrotoluene waste sulfuric acid treatment vacuum concentration device, so that the concentrated sulfuric acid of the cleaning liquid formula one contacts with the carbon scale in the stripping tower 8, the stripping tower evaporator 9 and the three-stage evaporator 11.

[0074] The specific method of cooling water introduction is:

[0075] Cooling water is introduced into the heat exchange pipes of the denitrification tower evaporator 5, the stripping tower evaporator 9 and the three-stage evaporator 11 through the first water pipe 20, the second water pipe 21 and the third water pipe 22. Cooling water is introduced into the heat exchange pipes of the denitrification tower evaporator 5, the stripping tower evaporator 9 and the three-stage evaporator 11 through the first water pipe 20, the second water pipe 21 and the third water pipe 22 to prevent local overheating of the dilute nitric acid to dilute the concentrated sulfuric acid and damage the equipment when the dilute nitric acid is added.

[0076] The specific method of adding and mixing is:

[0077] 40%-50% of the dilute nitric acid in the dilute nitric acid tank 1 is sent to the mixed acid tank 3 through the dilute nitric acid pump 2 and the dilute nitric acid flowmeter 14 to mix with concentrated sulfuric acid, and the dilute nitric acid flow rate is controlled to be 0.6-1m³ / h. The mass ratio of the total amount of dilute nitric acid input is 12%-15% of the total amount of concentrated sulfuric acid in the device. 3 hours after the dilute nitric acid is added, the valves of the first water pipe 20, the second water pipe 21 and the third water pipe 22 are closed, and the water in the heat exchanger of the denitrification tower evaporator 5, the stripping tower evaporator 9 and the three-stage evaporator 11 is drained. 40%-50% of the dilute nitric acid in the dilute nitric acid tank 1 is sent to the mixed acid tank 3 through the dilute nitric acid pump 2 and the dilute nitric acid flowmeter 14 to mix with concentrated sulfuric acid so that the nitric acid of formula 2 contacts with the carbon scale in the stripping tower 8, the stripping tower evaporator 9 and the three-stage evaporator 11.

[0078] The specific method of heating and heat preservation cleaning is:

[0079] Open the valves of the first steam pipe 17, the second steam pipe 18 and the third steam pipe 19 to allow steam to pass into the denitrification tower evaporator 5, the stripping tower evaporator 9 and the three-stage evaporator 11 for heating. The temperature of the temperature transmitter 15 is controlled at 80°C-90°C and kept warm for 3-4 hours to clean the carbon scale in the stripping tower 8, the stripping tower evaporator 9 and the three-stage evaporator 11. Under the conditions of 80°C-90°C, keeping warm for 3-4 hours and the presence of sulfuric acid, nitric acid oxidizes carbon into carbon dioxide to achieve the purpose of cleaning carbon scale.

[0080] The specific methods of exhaust gas cooling treatment are:

[0081] The gas generated by the device is discharged from the device through the pipeline of the pressure transmitter 37, and the gauge pressure of the pressure transmitter 37 is controlled to be 0. Then, the temperature of the nitric acid and sulfuric acid mixed acid in the device is reduced to room temperature and then discharged into the waste sulfuric acid raw material tank outside the device through the waste acid discharge pipe 36. The mixed acid cleaning process is completed. The gas generated by the device is discharged from the device through the pipeline of the pressure transmitter 37, and the gauge pressure of the pressure transmitter 37 is controlled to be approximately 0. When the temperature of the nitric acid and sulfuric acid mixed acid in the device is reduced to room temperature, it is discharged into the waste sulfuric acid raw material tank outside the device through the waste acid discharge pipe 36 to recover the nitrogen oxides and cleaning liquid generated in the cleaning process, thereby realizing resource recycling and avoiding environmental pollution.

[0082] Different from other cleaning technologies, the present invention can not only clean the carbon scale of the stripping tower 8 filler, but also clean the stripping tower evaporator 9 and the three-stage evaporator 11 at the same time.

[0083] In conclusion, compared with the prior art, the present invention has the following advantages:

[0084] The nitrotoluene waste sulfuric acid vacuum concentration treatment device is combined with its own devices and materials to achieve the cleaning of carbon scale. The oxidation side reaction of nitric acid and sulfuric acid mixed acid in the nitration technology is used. Concentrated sulfuric acid continuously removes hydrogen from carbon scale, and nitric acid continuously oxidizes carbon into gas to achieve the purpose of removing solid carbon scale. A three-step cleaning method is used to first clean out the nitro compounds in the device to eliminate the safety risks that may occur when using nitric acid and sulfuric acid mixed acid for cleaning. In addition, the cleaning process uses material circulation, cooling water to cool the ingredients, and steam heating to achieve stable and controllable temperature changes, eliminating the risk of damage to the device and equipment during the cleaning process;

[0085] In addition, due to the simplicity and economy of this technology, it has a strong promotion value and can be used in similar nitrotoluene waste sulfuric acid vacuum concentration devices and other devices that can withstand carbon scaling caused by nitric acid and sulfuric acid mixed acid corrosion above 100°C. This production method is simple and easy to install.

[0086] The cleaning principle of the present invention for carbon fouling is:

[0087] 1. As concentrated sulfuric acid has dehydrating properties, sulfuric acid with a concentration of more than 75% has gradually shown dehydrating properties. Concentrated sulfuric acid removes hydrogen from nitrotoluene and forms carbon scale;

[0088] 2. Concentrated sulfuric acid is oxidizing, and nitric acid is oxidizing. The higher the temperature, the stronger the oxidizing property.

[0089] 3. Concentrated sulfuric acid dilution releases heat;

[0090] 4. High concentration of nitric and sulfuric acid mixture can nitrate nitrotoluene and release heat;

[0091] 5. In a certain concentration of nitric and sulfuric acid mixture, nitric acid and carbon scaling can react chemically. Nitric acid reacts with carbon, and the chemical equation is C+4HNO3=4NO2+CO2+2H2O;

[0092] 6. Nitric acid in low-concentration nitric-sulfur mixed acid is removed at above 95°C;

[0093] 7. The freezing point of dinitrotoluene containing impurities is about 53℃-55℃; the specific gravity is about 1.3-1.35;

[0094] 8. Carbon scale is insoluble in water, commonly used organic solvents and fresheners. It does not react chemically with concentrated sulfuric acid below 300°C, nor with dilute nitric acid or concentrated nitric acid at higher temperatures. It is slightly soluble in concentrated sulfuric acid, dilute nitric acid and concentrated nitric acid.

[0095] Finally, a few points should be explained: Although the present invention has been described in detail above with general descriptions and specific embodiments, on the basis of the present invention, the above embodiments are only used to illustrate the technical solution of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the aforementioned embodiments, ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for cleaning carbon scale in a nitrotoluene waste sulfuric acid treatment device, comprising a carbon scale production cleaning device, characterized in that: The carbon scale production cleaning device comprises a mixed acid tank (3), the lower left side of the mixed acid tank (3) is connected to the right side of the dilute nitric acid tank (1) through a second material pipe (32) and a dilute nitric acid pump (2), the right side of the mixed acid tank (3) is connected to a denitration tower (4), the lower side of the denitration tower (4) is connected to a denitration tower evaporator (5), the lower right side of the denitration tower evaporator (5) is connected to a dilute sulfuric acid tank (6), and the right side of the dilute sulfuric acid tank (6) is connected to a dilute sulfuric acid pump (7); The upper right side of the first dilute sulfuric acid pump (7) is connected to a stripping tower (8), the lower side of the stripping tower (8) is connected to a stripping tower evaporator (9), the upper side of the stripping tower (8) is connected to a three-stage scrubber (10), the lower right side of the stripping tower evaporator (9) is connected to a three-stage evaporator (11), the lower right side of the three-stage evaporator (11) is connected to a three-stage concentrated sulfuric acid tank (12), the upper side of the three-stage evaporator (11) is connected to the three-stage scrubber (10), and the right side of the three-stage concentrated sulfuric acid tank (12) is connected to a three-stage concentrated sulfuric acid pump (13); The carbon scale cleaning method of the nitrotoluene waste sulfuric acid treatment device comprises the following steps: S1, material return; S2, hot water cleaning, after cleaning is completed, the hot water is drained; S3, feeding and circulation control, feeding 91%-96% sulfuric acid into the three-stage concentrated sulfuric acid tank (12), and circulating in the nitrotoluene waste sulfuric acid treatment vacuum concentration device; S4, cooling water is introduced; S5, adding and mixing, sending 40%-50% of the dilute nitric acid in the dilute nitric acid tank (1) into the mixed acid tank (3) to mix with the concentrated sulfuric acid, and contacting with the carbon scale in the stripping tower (8), the stripping tower evaporator (9) and the three-stage evaporator (11); S6, heating, heat preservation and cleaning; S7. Exhaust gas cooling treatment.

2. The method for cleaning carbon scale in a nitrotoluene waste sulfuric acid treatment device according to claim 1, characterized in that: The left side of the mixed acid tank (3) is connected to the fifth material pipe (35) and the first material pipe (31); a dilute nitric acid flow meter (14) is provided on one side of the second material pipe (32); the lower side of the mixed acid tank (3) is connected to the waste acid drain pipe (36); and a temperature transmitter (15) is connected to the pipeline connecting the mixed acid tank (3) to the denitration tower (4); The left side of the denitrification tower evaporator (5) is connected to a first steam pipe (17), the lower left side of the denitrification tower evaporator (5) is connected to a first water pipe (20), and the lower side of the denitrification tower evaporator (5) is respectively connected to a first discharge pipe (23) and a first drain pipe (26); The upper right pipeline of the stripping tower (8) is connected to the gas pipeline outside the device, and a pressure transmitter (37) is installed on the gas pipeline outside the device; The left side of the stripping tower evaporator (9) is connected to the second steam pipe (18), the lower left side of the stripping tower evaporator (9) is connected to the second water pipe (21), the lower side of the stripping tower evaporator (9) is respectively connected to the second discharge pipe (24) and the second drain pipe (27), the lower side of the connecting pipe between the stripping tower evaporator (9) and the three-stage evaporator (11) is connected to the fourth drain pipe (29), the left side of the three-stage evaporator (11) is connected to the third steam pipe (19), the lower left side of the three-stage evaporator (11) is connected to the third water pipe (22), and the lower side of the three-stage evaporator (11) is respectively connected to the third discharge pipe (25) and the third drain pipe (28); The upper side of the three-stage gas scrubber (10) is connected to a gas pipeline outside the device, the left side of the three-stage concentrated sulfuric acid tank (12) is connected to a fourth material pipe (34), and the lower side of the three-stage concentrated sulfuric acid tank (12) is connected to a first drain pipe (26) and a second drain pipe (27); The lower side of the connecting pipeline between the three-stage concentrated sulfuric acid tank (12) and the three-stage concentrated sulfuric acid pump (13) is connected to the fifth drain pipe (30), the upper right side of the three-stage concentrated sulfuric acid pump (13) is connected to the third material pipe (33), the upper side of the three-stage concentrated sulfuric acid pump (13) is connected to the concentrated sulfuric acid flow meter (16), and the upper left side of the concentrated sulfuric acid flow meter (16) is connected to the first material pipe (31).

3. The method for cleaning carbon scale in a nitrotoluene waste sulfuric acid treatment device according to claim 2, characterized in that: The specific method of the material return is: The residual acid in the denitration tower evaporator (5), the stripping tower evaporator (9) and the three-stage evaporator (11) is discharged into the three-stage concentrated sulfuric acid tank (12) through the first discharge pipe (26), the second discharge pipe (27) and the third discharge pipe (28). The concentrated sulfuric acid in the three-stage concentrated sulfuric acid tank (12) is controlled to be sent to the concentrated sulfuric acid tank outside the device through the three-stage concentrated sulfuric acid pump (13). The residual acid in the pipeline is discharged into the residual acid tank outside the device through the fourth discharge pipe (29) and the fifth discharge pipe (30). The waste acid in the mixed acid tank (3) is discharged into the waste acid tank through the waste acid discharge pipe (36).

4. The method for cleaning carbon scale in a nitrotoluene waste sulfuric acid treatment device according to claim 3, characterized in that: The specific method of hot water cleaning is: S21, the ionized water enters the mixed acid tank (3), the denitration tower (4), the denitration tower evaporator (5), the first dilute sulfuric acid tank (6), the first dilute sulfuric acid pump (7), the stripping tower (8), the stripping tower evaporator (9), the three-stage scrubber (10), the three-stage evaporator (11) and the three-stage concentrated sulfuric acid tank (12) from the fifth material pipe (35). When the liquid level in the three-stage concentrated sulfuric acid tank (12) reaches 60%-80%, the valve of the fifth material pipe (35) is closed; S22, starting the three-stage concentrated sulfuric acid pump (13), circulating water through the first material pipe (31), opening the valves of the first steam pipe (17), the second steam pipe (18) and the third steam pipe (19), heating the water with steam until the temperature of the temperature transmitter (15) reaches 70° C. to 80° C., and keeping the temperature for 1 to 2 hours; S23, shut down the three-stage concentrated sulfuric acid pump (13), open the fifth purge pipe (30), the fourth purge pipe (29), the third purge pipe (28), the second purge pipe (27) and the first purge pipe (26), and use hot water to discharge the liquid nitro compound to a location outside the device for treatment.

5. The method for cleaning carbon scale in a nitrotoluene waste sulfuric acid treatment device according to claim 4, characterized in that: The specific method of the feeding and circulation control is: Sulfuric acid with a concentration of 91% to 96% outside the device is fed into the three-stage concentrated sulfuric acid tank (12) through the fourth material pipe (34). The concentrated sulfuric acid in the three-stage concentrated sulfuric acid tank (12) enters the mixed acid tank (3), the denitrification tower (4), the denitrification tower evaporator (5), the first stage dilute sulfuric acid tank (6), the first stage dilute sulfuric acid pump (7), the stripping tower (8), the stripping tower evaporator (9), the three-stage scrubbing tower (10), the three-stage evaporator (11) and the three-stage concentrated sulfuric acid tank (12) through the three-stage concentrated sulfuric acid pump (13) and the first material pipe (31). When the liquid level in the three-stage concentrated sulfuric acid tank (12) reaches 60% to 80%, the circulation is carried out, and the concentrated sulfuric acid flow meter (16) is controlled to display 3 to 4 m³ / h, and the feeding through the fourth material pipe (34) is stopped at the same time.

6. The method for cleaning carbon scale in a nitrotoluene waste sulfuric acid treatment device according to claim 5, characterized in that: The specific method of introducing cooling water is: Cooling water is introduced into the heat exchange pipes of the denitration tower evaporator (5), the stripping tower evaporator (9) and the three-stage evaporator (11) through the first water pipe (20), the second water pipe (21) and the third water pipe (22).

7. The method for cleaning carbon scale in a nitrotoluene waste sulfuric acid treatment device according to claim 6, characterized in that: The specific method of adding and mixing is: 40%-50% of the dilute nitric acid in the dilute nitric acid tank (1) is fed into the mixed acid tank (3) through the dilute nitric acid pump (2) and the dilute nitric acid flowmeter (14) to be mixed with the concentrated sulfuric acid. The dilute nitric acid flow rate is controlled to be 0.6-1 m³ / h. The mass ratio of the total amount of dilute nitric acid input is 12%-15% of the total amount of concentrated sulfuric acid in the device. Three hours after the dilute nitric acid is added, the valves of the first water pipe (20), the second water pipe (21) and the third water pipe (22) are closed to drain the water in the denitration tower evaporator (5), the stripping tower evaporator (9) and the heat exchanger in the three-stage evaporator (11).

8. The method for cleaning carbon scale in a nitrotoluene waste sulfuric acid treatment device according to claim 7, characterized in that: The specific method of the heating, heat preservation and cleaning is as follows: The valves of the first steam pipe (17), the second steam pipe (18) and the third steam pipe (19) are opened to allow steam to enter the denitration tower evaporator (5), the stripping tower evaporator (9) and the three-stage evaporator (11) for heating. The temperature transmitter (15) controls the temperature at 80°C-90°C and keeps the temperature for 3-4 hours to clean the carbon scale in the stripping tower (8), the stripping tower evaporator (9) and the three-stage evaporator (11).

9. The method for cleaning carbon scale in a nitrotoluene waste sulfuric acid treatment device according to claim 8, characterized in that: The specific method of the exhaust gas cooling treatment is: The gas generated by the device is discharged from the device through the pipeline of the pressure transmitter (37), and the gauge pressure of the pressure transmitter (37) is controlled to be 0. Then, the temperature of the nitric acid and sulfuric acid mixed acid in the device is lowered to room temperature and discharged into the waste sulfuric acid raw material tank outside the device through the waste acid discharge pipe (36), and the mixed acid cleaning process is completed.

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