Continuous acid-expelling washing method for nitrocotton

Abstract

The invention discloses a continuous acid-expelling washing method for nitrocotton, which comprises the following steps: in the acid-expelling washing process of the nitrocotton, carrying out an acid-expelling step and a replacement washing step separately, carrying out the acid-expelling step in a centrifugal machine, carrying out the replacement washing step in a vertical washing device, and carrying out countercurrent replacement washing on a material in a liquid phase from bottom to top by using washing water. The staying time of dried materials in the centrifugal machine can be shortened, on one hand, the detonation risk can be reduced, the safety of the acid expelling step is improved, on the other hand, the screen frame length of the centrifugal machine can be reduced, the structure of the centrifugal machine is simplified, and the expelling function can be achieved only through a single-stage centrifugal machine; the replacement washing step is carried out in a countercurrent washing mode in the vertical washing device, the materials can be always in a liquid phase in the replacement washing process, the stability of the materials in the replacement washing process is ensured, and the safety of the nitrocotton acid-driving washing process is further effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of nitrocellulose production, in particular to a continuous acid-dripping and washing method for nitrocellulose. Background Art

[0002] Nitrocellulose is made from refined cellulose and mixed acid as raw materials, and is produced through a series of processes including esterification reaction, acid-dripping washing, boiling and washing, fine cutting, and fine washing. Among them, the process technology of acid-dripping washing determines the consumption of nitric acid and sulfuric acid in nitrocellulose production and the cost of wastewater treatment.

[0003] In the prior art, the acid washing of nitrocellulose mainly adopts the continuous centrifugal acid washing technology. During the acid washing, the acid-cotton mixture is sent to the centrifuge to separate the acid and cotton under the action of centrifugal force; during the washing, the adsorbed acid in the acidic nitrocellulose is replaced and recovered.

[0004] For example, the Chinese invention patent document with authorization announcement number CN109056402B discloses a continuous multi-stage acid displacement washing process method, in which the acid-cotton mixture after nitration reaction is introduced into a horizontal pusher centrifuge for acid-cotton separation. The sieve plate of the horizontal pusher centrifuge includes a high-concentration waste acid separation section and a displacement washing section, and five-stage countercurrent displacement washing is performed in the displacement washing section.

[0005] For example, a Chinese invention patent document with authorization announcement number CN102807623B discloses a nitrocellulose acid-removing process, and its technical solution process includes the following steps: continuously feeding the acidic nitrocellulose into an acid-removing machine for solid-liquid separation and washing; the nitrocellulose continuously enters washing tank No. 1, and the washing liquid returned subsequently continuously enters washing tank No. 1, and water or dilute acid solution is continuously added and stirred to mix; the nitrocellulose and liquid are continuously fed into a buffer tank by a cotton feeding pump, and part of the liquid in the buffer tank is continuously returned to the acid-removing machine to wash the nitrocellulose; the nitrocellulose and the remaining liquid in the buffer tank are fed into a centrifugal washing machine for washing, and water or dilute acid solution is sprayed during washing, and the washing water obtained after washing continuously enters washing tank No. 1; the nitrocellulose enters washing tank No. 2 and is fed into the boiling and washing process by the cotton feeding pump.

[0006] In order to ensure a certain separation and washing efficiency, the technical solution of the above patent document adopts a long net pusher centrifuge to increase the residence time of the material in the centrifuge. Since the acid-containing nitrocellulose that has not been stabilized is unstable, during the acid-discharging washing process of the nitrocellulose, the material gradually becomes relatively dry under the action of centrifugal force, and in order to ensure a certain displacement washing efficiency and recovered acid concentration, there is a concentration difference between the displacement washing water and the nitrocellulose adsorbed acid, and at the same time, the displacement washing flow cannot be too large. Dilution heat will be generated during the displacement washing process, causing the material to be extremely unstable in the centrifuge, especially in the displacement washing section, and there is a risk of decomposition and deflagration. Increasing the time the material stays in the centrifuge will also increase the risk. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a nitrocellulose continuous acid-discharging washing method which can effectively improve the safety of the displacement washing process.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a continuous acid-dripping and washing method for nitrocellulose. In the acid-dripping and washing process of nitrocellulose, the acid-dripping step and the displacement washing step are carried out separately, the acid-dripping step is carried out in a centrifuge, and the displacement washing step is carried out in a vertical washing device, and the washing water is used to perform countercurrent displacement washing on the material in the liquid phase from bottom to top.

[0009] As an improvement of the above scheme: the following steps are included:

[0010] Step 1: continuously flooding the acid-cotton mixture after the nitration reaction is completed, and recycling the separated waste acid to prepare the nitration mixed acid;

[0011] Step 2: sending the acidic nitrocellulose after acid removal into a vertical washing device, so that the acidic nitrocellulose material naturally settles from the top of the vertical washing device to the bottom of the vertical washing device under the action of its own gravity;

[0012] Step 3: squeeze the material settled at the bottom of the vertical washing device, so that part of the liquid phase material is transported to the receiving trough connected to the bottom of the vertical washing device, and the remaining material forms a material plug at the bottom of the vertical washing device;

[0013] Step 4: passing washing water into the vertical washing device from the bottom side of the vertical washing device, contacting the material at the bottom of the vertical washing device, and performing countercurrent displacement washing on the material from bottom to top;

[0014] Step 5: After the washing water fills the vertical washing device, it overflows from the upper side of the vertical washing device after being filtered to obtain dilute acid, which is then transported to the waste acid treatment device for recovery and treatment.

[0015] As an improvement of the above scheme: in step 2, the natural sedimentation time of the material is 60s, and the concentration of the material during the natural sedimentation process is 5%; the height of the vertical washing device is 3m.

[0016] As an improvement of the above scheme: in step 2, the solid content of the acidic nitrocellulose after acid removal is 50%; in step 3, the solid content of the material is extruded to 30%, and 20% of the liquid phase material is transported to the receiving tank.

[0017] As an improvement of the above scheme: in step 4, the relationship between the flow rate of washing water delivered to the vertical washing device and the absolute dry volume of acidic nitrocellulose delivered to the vertical washing device is 1.2L / Kg.NC.

[0018] The beneficial effects of the present invention are as follows: the present invention improves the acid-dripping and washing process of nitrocellulose, performs the acid-dripping step and the displacement washing step of nitrocellulose in sections, and performs the displacement washing step in a vertical washing device, thereby reducing the residence time of the dry material in the centrifuge. On the one hand, the risk of deflagration can be reduced and the safety of the acid-dripping step can be improved. On the other hand, the length of the screen frame of the centrifuge can be reduced, thereby simplifying the structure of the centrifuge. Only a single-stage centrifuge is used to meet the acid-dripping function. The present invention adopts a countercurrent washing method in the vertical washing device to perform the displacement washing step, so that the material can always be in the liquid phase during the displacement washing process, thereby ensuring the stability of the material during the displacement washing process, and further effectively improving the safety of the nitrocellulose acid-dripping and washing process. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the vertical washing device used in the present invention.

[0020] Markings in the figure are: 100-vertical washing device, 200-feed port, 300-discharge port, 400-washing water inlet, 500-waste acid outlet, 600-receiving trough, 700-recovery acid trough. DETAILED DESCRIPTION

[0021] In order to facilitate the understanding of the present invention, the present invention is further described below in conjunction with the accompanying drawings.

[0022] In the description of the present invention, it should be noted that the directions or positional relationships indicated by terms such as “front”, “rear”, “left”, “right”, “up”, “down”, and “inside” are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of description. They do not indicate or imply that the device or component referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they cannot be understood as limitations on the present invention.

[0023] The continuous acid-removal and washing method for nitrocellulose disclosed in the present invention includes dividing the acid-removal and displacement washing steps that are continuously performed in a pusher centrifuge in the prior art into sections and stages, using a centrifuge to perform the acid-removal step alone, and using a vertical washing device to perform the displacement washing step alone in the subsequent process. Since the present invention uses a centrifuge and a vertical washing device to perform acid-removal and displacement washing respectively, the demand for equipment in each process is reduced, and the residence time of the material in the centrifuge is shortened; when a multi-stage centrifuge is used for acid-removal and washing in the prior art, the material needs to stay in the centrifuge for a long time because two processes need to be performed, and since the acid-containing nitrocellulose that has not been stabilized is unstable, the material will gradually separate the waste acid during the centrifugation process in the centrifuge, and the separated material will gradually become relatively dry. In the subsequent displacement washing process, due to the dilution heat generated, the relatively dry material is unstable and there is a risk of decomposition and deflagration. Staying in the centrifuge for a long time will easily increase the risk of decomposition and deflagration. The present invention performs the displacement washing step in a vertical washing device, which can effectively shorten the residence time of relatively dry materials in the centrifuge. Compared with the prior art, the residence time can be shortened by half, thereby reducing the risk of material decomposition and deflagration; at the same time, since there is no need to perform displacement washing in the centrifuge, the space and structural requirements of the centrifuge are reduced, the length of the screen frame of the centrifuge can be reduced, thereby simplifying the structure of the centrifuge, and only a single-stage centrifuge is required to meet the acid driving function, which is beneficial to reducing production costs and is also convenient for maintenance of the centrifuge.

[0024] like Figure 1 As shown, the present invention adopts a vertical washing device 100 to perform replacement washing of the material after acid removal. The vertical washing device 100 is a cylindrical structure with an inner cavity, and is also provided with a screw extruder coaxial with the vertical washing device 100, and the spiral blade segment of the screw extruder is located in the inner cavity of the vertical washing device 100; the top of the vertical washing device 100 is provided with a feed port 200 connected to the inner cavity of the vertical washing device 100, and the bottom of the vertical washing device 100 is provided with a discharge port 300 connected to the inner cavity of the vertical washing device 100. At the same time, a washing water inlet 400 connected to the inner cavity of the vertical washing device 100 is provided on the bottom side of the vertical washing device 100, and a waste acid outlet 500 connected to the inner cavity of the vertical washing device 100 is provided on the top side of the vertical washing device 100, and a filtering component is provided at the waste acid outlet 500; a receiving trough 600 connected to the discharge port 300 and an acid recovery trough 700 connected to the waste acid outlet 500 are also provided.

[0025] like Figure 1As shown, the material that has completed the acid removal work in the centrifuge is fed into the vertical washing device 100 through the feed port 200. The material entering the inner cavity of the vertical washing device 100 falls from top to bottom under the action of its own gravity, and finally settles at the bottom of the vertical washing device 100. The material fills the discharge port 300 at the bottom of the vertical washing device 100. After the material settles, the screw extruder is started to extrude the material settled at the bottom of the vertical washing device 100, squeeze out part of the liquid phase in the material, and transport it to the receiving trough 600 through the discharge port 300, and then transport it to the subsequent boiling and washing process; the remaining material after extrusion is pressed against the bottom of the vertical washing device 100, and there is still part of the liquid phase in the material after extrusion, so that the material is always in the liquid phase. The extruded material forms a material plug at the bottom of the vertical washing device 100 and blocks the discharge port 300, thereby preventing the remaining liquid phase in the material from being lost from the discharge port 300. After the extrusion is completed, the washing water is transported to the inner cavity of the vertical washing device 100 through the washing water inlet 400, and the washing water directly contacts the material and replaces the adsorbed acid in the material. With the continuous transportation of the washing water, the adsorbed acid in the material is completely replaced, and with the increase of the washing water in the vertical washing device 100, the liquid level in the vertical washing device 100 continues to rise until it rises to the waste acid outlet 500 located at the top of the vertical washing device 100, and after filtering, it overflows into the recovery acid tank 700 connected to the waste acid outlet 500, and is finally transported to the waste acid treatment device for recovery treatment. In the present invention, washing water is transported from the bottom of the vertical washing device 100 to the inside of the vertical washing device 100. After the washing water enters the inner cavity of the vertical washing device 100, it directly performs displacement washing with the material squeezed at the bottom of the vertical washing device 100. The washing water spreads from bottom to top in the inner cavity of the vertical washing device 100 to perform countercurrent displacement washing on the material. The material is completely placed in the liquid phase during the displacement washing process, thereby avoiding the decomposition and deflagration problem caused by the dilution heat generated by the dry material during the displacement washing process, and effectively improving the safety of the displacement washing work. The displacement washing work in the present invention has greater process flexibility, and the flow rate of the washing water transported to the vertical washing device 100 can be flexibly adjusted according to demand, thereby adjusting the concentration and flow rate of the recovered acid finally produced, so that the nitrocellulose can reach a lower residual acidity.

[0026] Example

[0027] The nitrocellulose continuous acid-washing method of the present invention is carried out according to the following steps:

[0028] Step 1: Use a single-stage horizontal pusher centrifuge to continuously drive the acid-cotton mixture after the nitration reaction is completed, separate the acid-cotton under the action of centrifugal force, and obtain acidic nitrocellulose with a solid content of 50%. The separated waste acid is recycled and used to prepare the nitration mixed acid.

[0029] Step 2: After the continuous acid removal of the acid-cotton mixture is completed, the acidic nitrocellulose material obtained after the acid removal is fed into the inner cavity of the vertical washing device 100 through the feed port 200. The acidic nitrocellulose material is discharged from the top of the vertical washing device 100 and settles to the discharge port 300 at the bottom of the vertical washing device 100 under the action of its own gravity. The concentration of the acidic nitrocellulose material during the sedimentation process is about 5%. The height of the vertical washing device 100 is 3m, and the natural sedimentation time of the acidic nitrocellulose material from top to bottom in the vertical washing device 100 is about 60s.

[0030] Step 3: Start the screw extruder to extrude the acidic nitrocellulose material deposited at the bottom of the vertical washing device 100 and in the discharge port 300, and extrude about 20% of the liquid phase in the acidic nitrocellulose material into the receiving tank 600. The solid content of the acidic nitrocellulose material after extrusion is 30%, and a material plug is formed at the bottom of the vertical washing device 100 to prevent the liquid phase from continuing to flow out.

[0031] Step 4: After the extrusion of the acidic nitrocellulose material is completed, washing water is fed into the inner cavity of the vertical washing device 100 through the washing water inlet 400. Since the washing water inlet 400 is located on the side of the bottom of the vertical washing device 100, the washing water entering the vertical washing device 100 directly contacts the acidic nitrocellulose material squeezed at the bottom of the vertical washing device 100, and as the washing water rises, the acidic nitrocellulose material is subjected to countercurrent displacement washing from bottom to top, and the adsorbed acid in the acidic nitrocellulose material is replaced by the washing water. In this step, the absolute dry weight relationship between the flow rate of the washing water fed into the vertical washing device 100 and the acidic nitrocellulose material fed into the vertical washing device 100 is 1.2L / Kg.NC. The absolute dry weight mentioned here is an indicator for measuring the weight difference of the water content of a substance in a dry state.

[0032] Step 5. As the washing water is continuously delivered, the liquid level in the vertical washing device 100 continues to rise. The displaced adsorbed acid reaches the waste acid outlet 500 located on the top side of the vertical washing device 100 as the liquid level rises, is filtered by the filter component, and then overflows into the waste acid outlet 500 and is delivered to the recovery acid tank 700 connected to the waste acid outlet 500, and finally can be delivered to the waste acid treatment device for recovery treatment.

Claims

1. A continuous acid-washing method for nitrocellulose, characterized in that: In the acid-removing and washing process of nitrocellulose, the acid-removing step and the displacement washing step are carried out separately. The acid-removing step is carried out in a centrifuge, and the displacement washing step is carried out in a vertical washing device. The washing water is used to perform countercurrent displacement washing on the material in the liquid phase from bottom to top.

2. The continuous acid-washing method for nitrocellulose according to claim 1, characterized in that: The following steps are involved: Step 1: continuously flooding the acid-cotton mixture after the nitration reaction is completed, and recycling the separated waste acid to prepare the nitration mixed acid; Step 2: sending the acidic nitrocellulose after acid removal into a vertical washing device, so that the acidic nitrocellulose material naturally settles from the top of the vertical washing device to the bottom of the vertical washing device under the action of its own gravity; Step 3: squeeze the material settled at the bottom of the vertical washing device, so that part of the liquid phase material is transported to the receiving trough connected to the bottom of the vertical washing device, and the remaining material forms a material plug at the bottom of the vertical washing device; Step 4: passing washing water into the vertical washing device from the bottom side of the vertical washing device, contacting the material at the bottom of the vertical washing device, and performing countercurrent displacement washing on the material from bottom to top; Step 5: After the washing water fills the vertical washing device, it overflows from the upper side of the vertical washing device after being filtered to obtain dilute acid, which is then transported to the waste acid treatment device for recovery and treatment.

3. The continuous acid-washing method for nitrocellulose according to claim 2, characterized in that: In step 2, the natural sedimentation time of the material is 60s, and the concentration of the material during the natural sedimentation process is 5%; The height of the vertical washing device is 3m.

4. The continuous acid-discharging and washing method of nitrocellulose according to claim 2, characterized in that: In step 2, the solid content of the acidic nitrocellulose after acid removal is 50%; in step 3, the solid content of the material is extruded to 30%, and 20% of the liquid phase material is transported to the receiving tank.

5. The continuous acid-washing method for nitrocellulose according to claim 2, characterized in that: In step 4, the relationship between the flow rate of washing water delivered to the vertical washing device and the absolute dry volume of acidic nitrocellulose delivered to the vertical washing device is 1.2L / Kg.NC.

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