Method for treating spent acid using low pressure steam

Abstract

The application discloses a method for treating waste acid by using low-pressure steam, wherein the low-pressure steam is introduced into a denitration tower, a nitric acid concentration kettle and a sulfuric acid concentration kettle in a waste acid treatment device; the waste acid and concentrated sulfuric acid are introduced into the denitration tower, and under the action of the concentrated sulfuric acid and the low-pressure steam in the denitration tower, nitric acid is distilled from the top of the denitration tower and enters a bleaching tower, and the nitric acid vapor is condensed by a nitric acid condenser and a finished nitric acid cooler to obtain the finished nitric acid; the sulfuric acid and water flow out from the bottom of the denitration tower and then enter the nitric acid concentration kettle and a flash evaporator in sequence to be concentrated, and the concentrated dilute sulfuric acid from the bottom of the flash evaporator enters the sulfuric acid concentration kettle, and the concentrated sulfuric acid from the sulfuric acid concentration kettle is cooled by a sulfuric acid cooler to obtain the finished sulfuric acid. The method does not need to replace or transform the equipment, only needs to optimize the waste acid treatment process, and can realize the treatment of waste cellulose nitrate acid by using the low-pressure steam, and the quality of the generated finished sulfuric acid and nitric acid completely meets the requirements.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of waste acid treatment method of nitrocellulose, and relates to a method for treating waste acid by using low-pressure steam. BACKGROUND

[0002] In the production process of nitrocellulose, mixed acid prepared by sulfuric acid and nitric acid is used to react with refined cotton, and a corresponding waste acid treatment device is used to separate sulfuric acid and nitric acid by using medium-pressure steam, and the waste acid treatment device is matched with a medium-pressure steam gas-fired boiler, but sometimes, due to boiler failure or gas supply shortage, the waste acid treatment device cannot be started and operated, and thus the waste acid of the nitrocellulose production line expands and cannot be normally operated.

[0003] In order to solve the problem, a method for treating waste acid by using low-pressure steam is established, and the problem that the waste acid treatment system cannot be started due to medium-pressure steam boiler failure or gas supply shortage can be solved. SUMMARY

[0004] The application aims to provide a method for treating waste acid by using low-pressure steam, which can treat waste acid of nitrocellulose by using low-pressure steam and produce qualified finished sulfuric acid and nitric acid.

[0005] The technical scheme adopted by the application is that low-pressure steam is introduced into a denitration tower, a nitric acid concentration kettle and a sulfuric acid concentration kettle in a waste acid treatment device; waste acid and concentrated sulfuric acid are introduced into the denitration tower, and under the action of concentrated sulfuric acid and low-pressure steam in the denitration tower, nitric acid is distilled out from the top of the denitration tower and enters a bleaching tower, and then the nitric acid vapor passes through a nitric smoke condenser and a finished nitric acid cooler to obtain finished nitric acid; sulfuric acid and water flow out from the bottom of the denitration tower and then enter the nitric acid concentration kettle and a flash evaporator in sequence to be concentrated, and then the concentrated dilute sulfuric acid from the bottom of the flash evaporator enters the sulfuric acid concentration kettle, and then the concentrated sulfuric acid from the sulfuric acid concentration kettle passes through a sulfuric acid cooler to obtain finished sulfuric acid.

[0006] The application has the following characteristics:

[0007] The flash evaporator flashes out part of water and the water vapor from the top of the flash evaporator enters a steam washing tower; water vapor distilled from the sulfuric acid concentration kettle also enters the steam washing tower, and the water vapor from the flash evaporator and the water vapor from the sulfuric acid concentration kettle are discharged into waste water through a cooler.

[0008] A small amount of non-condensable nitric smoke gas in the nitric smoke condenser and a small amount of non-condensable gas in the cooler enter a nitric smoke absorption system.

[0009] The pressure of the low-pressure steam used is 0.55MPa-0.6MPa, the temperature of the steam pipeline is 151℃-161℃, and the steam flow is greater than or equal to 4000kg / h.

[0010] The temperature in the denitration tower is required to be:

[0011] Denitration tower top temperature: 12℃~82℃; denitration tower middle temperature: 125℃~121℃; denitration tower bottom temperature: 140℃~148℃.

[0012] The sulfuric acid return flow into the denitration tower is 1400kg / h~2150kg / h; the nitric acid return flow at the top of the denitration tower is 105kg / h~320kg / h.

[0013] The outlet temperature of the nitric acid concentration kettle is 131℃~144℃; the system pressure of the nitric acid concentration kettle is -3.6kPa~-4.0kPa.

[0014] The outlet temperature of the sulfuric acid concentration kettle is 140℃~150℃; the system pressure of the sulfuric acid concentration kettle is 10kPa~12kPa.

[0015] The beneficial effects of the present application are:

[0016] The method of the present application can solve the problem that the waste acid cannot be treated in time due to boiler failure or insufficient gas supply when treating waste acid with medium-pressure steam. The method of the present application does not need to replace or modify the equipment, only needs to optimize the waste acid treatment process, can realize the treatment of nitrocellulose waste acid with low-pressure steam, and the produced finished sulfuric acid and nitric acid are qualified in quality, and has the advantages of fast implementation, safety and low cost. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a flow chart of the existing gas boiler steam production;

[0018] Figure 2 is a flow chart of a method provided by the present application for introducing external steam into a waste acid treatment system;

[0019] Figure 3 is a process flow chart of the method of the present application.

[0020] In the figure, 1. denitration tower, 2. bleaching tower, 3. nitric smoke condenser, 4. finished nitric acid cooler, 5. nitric acid concentration kettle, 6. flash evaporator, 7. steam washing tower, 1. sulfuric acid concentration kettle, 8. cooler, 10. sulfuric acid cooler, 11. boiler steam cylinder, 12. boiler medium-pressure steam inlet valve. DETAILED DESCRIPTION

[0021] The present application will be described in detail below in combination with the drawings and specific embodiments.

[0022] Firstly, the present application provides a method for introducing external low-pressure steam into a waste acid treatment system, as shown in Figure 1 Fig. 1 is a flow chart of the existing boiler steam production, the steam produced by the boiler passes through the boiler steam cylinder 11, the medium-pressure steam is treated with waste acid, and the low-pressure steam is supplied to the nitrocellulose production line. As shown inFigure 2 As shown in the figure, the method for providing medium-pressure steam to the waste acid treatment system provided by the present application is to modify the steam supply pipeline of the existing boiler. When using the modified boiler, the medium-pressure steam inlet valve 12 of the boiler is closed, and the external low-pressure steam is directly introduced into the waste acid treatment system after passing through the boiler distributing cylinder 11 for waste acid treatment. The pressure of the external low-pressure steam is required to be greater than or equal to 0.55 MPa.

[0023] Secondly, the method for treating waste acid using low-pressure steam provided by the present application introduces low-pressure steam into three parts of the existing waste acid treatment device, namely the denitration tower 1, the nitric acid concentration kettle 5, and the sulfuric acid concentration kettle 1, and improves the existing part of the process and parameters. The improved process flow is shown in the figure, and specifically comprises the following steps. Figure 3 As shown in the figure, specifically:

[0024] The waste acid and concentrated sulfuric acid are introduced into the middle and upper middle of the denitration tower 1, respectively, and the low-pressure steam is introduced from the bottom of the denitration tower 1, so as to ensure that the system temperature of the denitration tower 1 meets the requirement of nitric acid vapor separation. In the denitration tower 1, the concentrated sulfuric acid absorbs water and releases heat, and the boiling point of nitric acid is lower than that of sulfuric acid and water. Nitric acid is first distilled from the top of the denitration tower 1 and introduced into the bleaching tower 2, and the nitric acid vapor is then introduced into the nitric smoke condenser 3 for condensation. A small amount of non-condensable nitric smoke gas is introduced from the nitric smoke condenser 3 into the nitric smoke absorption system. The condensed nitric acid vapor is introduced into the finished nitric acid cooler 4, reaches a concentration of 87%, and flows to the nitric acid finished product tank to obtain finished nitric acid. The sulfuric acid and water flow out from the bottom of the denitration tower 1 and are introduced into the nitric acid concentration kettle 5. Under the action of low-pressure steam, part of the water is removed to obtain dilute sulfuric acid, which is then introduced into the flash evaporator 6 for further concentration. Part of the water is introduced from the top of the flash evaporator 6 into the steam washing tower 7. The concentrated dilute sulfuric acid is introduced into the sulfuric acid concentration kettle 1. Under the action of low-pressure steam, water vapor is distilled from the sulfuric acid concentration kettle 1. The water vapor is introduced into the steam washing tower 7 and then passes through the cooler 8 and is discharged into waste water. A small amount of non-condensable gas in the cooler 8 is introduced into the nitric smoke absorption system. The concentrated sulfuric acid from the sulfuric acid concentration kettle 1 is introduced into the sulfuric acid finished product tank through the sulfuric acid cooler 10 to obtain finished sulfuric acid.

[0025] In the above treatment process, the denitration system process is improved, including adjusting the temperature of the top, middle and bottom of the denitration tower, the sulfuric acid reflux flow into the denitration tower, the nitric acid flow of the denitration tower reflux, the pressure and temperature of the nitric acid concentration kettle system, to ensure the effective separation of nitric acid and sulfuric acid in the denitration tower. The process of the sulfuric acid concentration system is improved, including adjusting the pressure in the sulfuric acid concentration kettle and the outlet temperature of the sulfuric acid concentration kettle. The main process control parameters after improvement are shown in Table 1.

[0026] Table 1 Main process control parameters after improvement

[0027]

[0028]

[0029] The low-pressure steam with an external pressure of 0.55 MPa is introduced into the waste acid treatment system through the boiler pipeline, and the waste nitrocellulose acid is treated under the process parameters shown in Table 1, so that the concentration of the nitric acid produced from the nitric acid condenser is more than 87%, the concentration of the concentrated sulfuric acid is more than 12%, and the continuous mass production capacity can be realized, the waste acid treatment capacity is more than 4500 kg / h, and long-term production can be realized.

[0030] Example 1

[0031] The specific process parameters of the waste acid treatment using low-pressure steam in this example are shown in Table 2, and the concentrations of the obtained products are shown in Table 3, specifically: the concentration of the finished nitric acid is 81.65%, the concentration of the finished sulfuric acid is 12.64%, and the nitric acid content in the sulfuric acid is 0.43%. It can be seen that the concentrations of the obtained nitric acid and sulfuric acid completely meet the quality requirements after waste acid treatment.

[0032] Example 2

[0033] The specific process parameters of the waste acid treatment using low-pressure steam in this example are shown in Table 2, and the concentrations of the obtained products are shown in Table 3, specifically: the concentration of the finished nitric acid is 88.31%, the concentration of the finished sulfuric acid is 12.0%, and the nitric acid content in the sulfuric acid is 0.34%. It can be seen that the concentrations of the obtained nitric acid and sulfuric acid completely meet the quality requirements after waste acid treatment.

[0034] Example 3

[0035] The specific process parameters of the waste acid treatment using low-pressure steam in this example are shown in Table 2, and the concentrations of the obtained products are shown in Table 3, specifically: the concentration of the finished nitric acid is 87.5%, the concentration of the finished sulfuric acid is 12.17%, and the nitric acid content in the sulfuric acid is 0.36%. It can be seen that the concentrations of the obtained nitric acid and sulfuric acid completely meet the quality requirements after waste acid treatment.

[0036] Table 2: Specific process parameters used in Examples 1-3

[0037]

[0038] Table 3: Concentration list of products obtained in Examples 1-3

[0039]

[0040]

[0041] In summary, the method of the present application not only realizes the treatment of nitrocellulose waste acid using low-pressure steam, but also the quality of the products obtained after treatment completely meets the requirements, so that the waste acid treatment can completely get rid of the dependence on medium-pressure steam, and has a wider application range.

Claims

1. A method for treating spent acid using low-pressure steam, characterized in that: Low-pressure steam is introduced into the denitrification tower (1), the nitric acid concentration kettle (5) and the sulfuric acid concentration kettle (8) in the waste acid treatment device; waste acid and concentrated sulfuric acid are introduced into the denitrification tower (1); under the action of concentrated sulfuric acid and low-pressure steam in the denitrification tower (1), nitric acid is distilled from the top of the denitrification tower (1) and enters the bleaching tower (2); the nitric acid vapor then passes through the nitrate fume condenser (3) and the finished nitric acid cooler (4) to obtain finished nitric acid; sulfuric acid and water flow out from the bottom of the denitrification tower (1) and enter the nitric acid concentration kettle (5) and the flash evaporator (6) in sequence for concentration; the concentrated dilute sulfuric acid enters the sulfuric acid concentration kettle (8) from the bottom of the flash evaporator (6); the concentrated sulfuric acid from the sulfuric acid concentration kettle (8) passes through the sulfuric acid cooler (10) to obtain finished sulfuric acid; The low-pressure steam used has a pressure of 0.55MPa~0.6MPa, a steam pipe temperature of 158℃~168℃, and a steam flow rate of ≥4000kg / h; The temperature requirements in the denitrification tower are: denitrification tower top temperature: 82℃~92℃; denitrification tower middle temperature: 125℃~128℃; denitrification tower bottom temperature: 140℃~149℃; The sulfuric acid reflux rate into the denitrification tower is 1400kg / h~2150kg / h; the nitric acid reflux rate at the top of the denitrification tower is 105kg / h~320kg / h; The outlet temperature of the nitric acid concentration kettle is 138℃~144℃; the system pressure of the nitric acid concentration kettle is -3.6kPa~-4.0kPa; The outlet temperature of the sulfuric acid concentration kettle is 140℃~150℃; the system pressure of the sulfuric acid concentration kettle is 10kPa~12kPa.

2. The method for treating waste acid using low-pressure steam according to claim 1, wherein: The flash evaporator (6) flashes out a portion of water, which enters the steam scrubber (7) from the top of the flash evaporator (6); the water vapor distilled out of the sulfuric acid concentration kettle (8) also enters the steam scrubber (7), and together with the water vapor from the flash evaporator (6), they are discharged into the wastewater through the cooler (9).

3. The method for treating waste acid using low-pressure steam according to claim 2, wherein: A small amount of non-condensable smoke gas in the smoke condenser (3) and a small amount of non-condensable gas in the cooler (9) all enter the smoke absorption system.

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