CN103214047B - Method for recycling NH3-N from ammoninted waste liquid - Google Patents

Abstract

The invention provides a method for recycling NH3-N from ammoninted waste liquid, and further provides a method for recycling NH3-N from ammoninted waste liquid with low radioactivity and high concentration. The method comprises the following steps of: based on an intermittent feeding mode, evaporating and condensing waste liquid; and repeatedly absorbing NH3-N to recycle NH3-N from the waste liquid, wherein the final mass concentration of ammonia water can reach about 15%. The method is low in energy consumption, capable of reducing emission of radioactive substances, high in safety, high in concentration of recycled ammonia water and broad in application prospect.

Description

A method for recovering ammonia nitrogen in low-radioactive high-ammonia nitrogen waste liquid

technical field

The invention relates to a method for treating waste liquid, in particular to a method for recovering ammonia nitrogen in low-radioactive high-ammonia nitrogen waste liquid.

Background technique

The sol-gel method is used to produce ceramic UO ₂ core particles for high-temperature gas-cooled reactor nuclear fuel elements. The gelling medium used is mainly ammonia water. The process includes two parts: wet method and dry method. , aging, washing, drying and other steps. Firstly, an aqueous solution of uranyl nitrate is prepared by heating and dissolving U ₃ O ₈ solid powder with analytically pure nitric acid, and a colloid containing a certain uranium concentration is formulated with various additives according to a certain formula and process, including complexing agent and buffering agent. organic matter such as urea, adhesive polyvinyl alcohol, and cross-linking agent tetrahydrofurfuryl alcohol; then, the glue liquid is dispersed into uniform glue droplets through a pressure-type vibrating nozzle, and the droplets enter the ammonia water column after passing through the ammonia gas zone and gradually solidify into a gel ball; the obtained gel ball is aged in ammonia water, and the gel ball is washed with dilute ammonia water to remove the ammonium nitrate; finally, the moisture is removed by vacuum drying to obtain the dried gel ball. Therefore, a large amount of low-level radioactive wastewater containing ammonia, uranium, organic matter, nitrate and other substances will be produced in the production process. Due to the complex composition of wastewater, the wastewater treatment process is relatively long. The first step is to remove and recover the volatile ammonia in it, creating conditions for the further treatment of the waste liquid, and the recovered ammonia can be reused as a raw material in the sol-gel process.

The radioactivity of wastewater is lower than 2.6×10 ² Bq/L, and the ammonia concentration is greater than 5g/L, which exists in two forms: free ammonia gas (NH 3 ) dissolved in water and ammonium ion (NH ₃ ) produced after hydrolysis reaction. ₄₊ ⁾ . At present, the vast majority of ammonia treatment and recycling objects are non-radioactive wastewater. The process method is generally to promote the release of ammonia from the water by increasing the pH value of the wastewater, aeration and other physical effects under high temperature conditions. Usually, high pressure conditions are also used to promote the dissolution of ammonia gas. In the absorption liquid, increase the concentration of recovered ammonia water. NH ₃ -N is an indicator of ammonia nitrogen content in water (wastewater), with standard control values. For wastewater containing a relatively high concentration of NH ₃ -N (concentration greater than 5g/L), the main treatment methods currently include stripping and distillation. The ammonia-containing process waste liquid produced during the production of nuclear fuel element ceramic UO ₂ particles is a low-level radioactive waste liquid, which must be effectively removed while avoiding radioactive substances. At the same time, the safety of process equipment must be fully considered, and high temperature, high pressure, etc. should be avoided as much as possible. extreme conditions. The stripping method is easy to produce a large amount of radioactive waste gas when dealing with low-radioactive ammonia-containing waste liquid, which will increase the energy consumption and form new pollution in the application; if the conventional distillation method can not control the heating conditions well, it will occur during the heating process. The rapid release of ammonia gas produces a large amount of mist entrainment, resulting in the escape of radioactive materials. Therefore, currently there is still a lack of a process for effectively treating low-level radioactive waste liquid containing high-concentration NH ₃ -N.

Contents of the invention

The purpose of the present invention is to provide a wastewater treatment method, especially a method for recovering NH ₃ -N in high-concentration ammonia-containing waste liquid, which can be applied to the treatment of low-radioactive high-concentration ammonia-containing waste liquid.

In order to realize the object of the present invention, the present invention provides a kind of NH in ammonia-containing waste liquid The recovery method of _-N , this method comprises:

(a) Put ammonia-containing waste liquid into a heating container and heat to form ammonia vapor;

(b) Pass the ammonia vapor into the falling film condensation absorption tower to condense, and the condensed ammonia vapor flows into the bottom of the tower to form ammonia water;

(c) The ammonia water at the bottom of the tower is cooled and returned to the top of the tower, and sprayed to contact with the uncondensed ammonia vapor entering the tower;

(d) After cyclic absorption, ammonia water with a concentration greater than 5% is obtained.

The original ammonia-containing waste liquid can be passed into a heating container after pretreatment such as precipitation and heat exchange, and the heating container can be an evaporation kettle.

After cyclic absorption, the remaining tail gas can be passed into the tail gas absorption tank to contact with water and react to form ammonia solution; after that, the waste gas can be passed into the tail gas degradation tank to contact with acid and react to form ammonium salt solution.

More preferably, during step (a), intermittently add ammonia-containing waste liquid to the heating container to ensure that the total volume of ammonia-containing waste liquid accounts for more than one-fifth and less than four-fifths of the volume of the heating container.

When the waste liquid is evaporated to no less than one-fifth of the volume of the heating vessel, feeding can prevent the macromolecules in the system from scaling due to the thickening of the solution due to concentration.

More preferably, the total volume of ammonia-containing waste liquid accounts for more than one-third and less than two-thirds of the volume of the heating container.

More preferably, the recovery method also includes detecting the pH value of the ammonia-containing waste liquid in the heating container, and when the pH value is lower than 8, stop heating, cooling, and discharging; detecting the pH value of the ammonia water at the bottom of the tower, when the pH value is higher than 11 , discharge the ammonia water at the bottom of the tower.

More preferably, the heating container is heated by a closed-circuit controlled heat transfer oil circulation heating method.

More preferably, in the above steps, the temperature inside the heating container is 65-85° C., and the pressure is 1.0-1.3 MPa.

More preferably, the temperature inside the heating container in the above steps is 67-75°C.

The above recovery method also includes: the ammonia vapor formed in the step (a) is first cooled to condense most of the water below 90°C and a small part of the ammonia vapor, and then enters the condensation absorption tower.

The liquid of water and ammonia vapor that has been condensed by cooling down flows to the bottom of the condensation absorption tower to form ammonia water with a relatively dilute concentration.

The condensation absorption tower adopts the structure of falling film packing. The upper and lower parts of the tower adopt Raschig ring packing layer, and the middle part is a tubular structure; the Raschig ring packing layer can increase the contact area and evenly distribute the water flow. In step (c), the ammonia water sprayed on the top of the absorption tower passes through the tube wall in the intermediate falling film device, and flows to the packing layer to contact with the uncondensed ammonia vapor.

In the above recovery method, the temperature at the top of the condensation absorption tower is 20-40°C, and the temperature of ammonia water at the bottom of the tower is 20-35°C.

More preferably, the temperature at the top of the condensation absorption tower is 25-30°C, and the temperature of the ammonia water at the bottom of the tower is 20-30°C.

The method provided by the present invention has the following advantages:

(1) The method of the present invention can gradually increase the concentration of ammonia in the recovered ammonia water, the concentration can reach more than 5%, and the final mass concentration can reach about 15%, corresponding to a pH value of about 11. In the production of spherical fuel elements, the raw material concentration of ammonia water is required to be higher than 5%, and the recovered ammonia water fully meets the requirements for reuse;

(2) The entire invention has compact technological process, high efficiency, no pollution, greatly improved economy and safety;

(3) The method of the present invention can not only be used for the treatment of nuclear core preparation process wastewater in the production of high-temperature gas-cooled reactor fuel elements, but also can be used for the treatment of general high-concentration ammonia-containing industrial waste liquid, and has a wide range of applications;

(4) The intermittent feeding step can ensure the dynamic balance between the release of NH ₃ -N from the waste liquid system and the dissolution in the absorption liquid, and can also prevent the system in the heating container from viscous polymer substances due to excessive evaporation and make the heating container Internal fouling;

(5) Using this method in the treatment of low-radioactive and high-concentration ammonia waste liquid overcomes the problems of violent boiling and radioactive mist entrainment caused by continuous heating, and at the same time improves the safety of the equipment and avoids extreme conditions such as high temperature and high pressure. Reduce energy consumption and avoid the escape of radioactive materials;

(6) The cooling step before entering the condensation absorption tower can reduce the amount of water replenishment and increase the recovery rate of ammonia. The condensation absorption tower can increase the concentration of absorbed ammonia water under normal pressure conditions.

Description of drawings

Fig. 1 is a process flow chart of the method for recovering NH ₃ -N in ammonia-containing waste liquid according to the present invention.

Detailed ways

The "high-concentration ammonia waste liquid" mentioned in the present invention refers to the waste liquid whose NH ₃ -N concentration is greater than 5 g/L. The method of the present invention is not only applicable to waste liquid containing uranium 235, but also waste liquid containing radioactive substances such as uranium 238 and thorium 232, and is not limited to these types. ⁵ Bq/L. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

Example 1

During the production of a batch of fuel elements, about 250 liters of ammonia-containing process waste liquid needs to be treated. The mass concentration of NH ₃ -N in the raw water is 8.9%, and the main radioactive substance is uranium 235, with a concentration of about 10ppm. In order to realize the removal and recovery of ammonia in wastewater and avoid the secondary pollution of radioactive uranium-235, the mode of intermittent heating and intermittent feeding is used to recover ammonia by distillation. The whole process is shown in Figure 1, and the specific process is as follows:

(1) The ammonia-containing process waste liquid is left standing in the waste liquid tank. After the solid matter in the waste liquid is precipitated, the supernatant liquid is sent to the heat exchanger by a pump. After heat exchange to increase the temperature, it is pumped into the evaporator for heating.

(2) First pump two-thirds of the volume of feed liquid into the evaporating kettle, and use the closed-circuit controlled heat conduction oil circulation heating method to control the temperature of the evaporating kettle to about 70°C; the internal pressure of the evaporating kettle is 1.3MPa, when the pH in the kettle When the meter reading drops to about 8, and the waste liquid accounts for more than one-fifth of the volume of the evaporating kettle, then pump one-third of the volume of feed liquid into the kettle and heat it to 85°C. Circulate back and forth until the feed liquid reaches four-fifths of the maximum volume of the evaporator (about 23 liters). When the pH drops to 8 the discharge is for further processing.

(3) In the ammonia gas absorption part, the ammonia water at the bottom of the absorption tower is drawn by the circulating pump, and then flows back to the top of the absorption tower for spraying through the flow meter and cooler. The sprayed ammonia water passes through the pipe wall in the intermediate falling film device and flows to the packing layer Exchange heat with the high-temperature ammonia water in the lower part of the absorption tower, and control the temperature at the top of the tower at about 40°C; the ammonia water after heat exchange enters the tower from the upper part of the tower and sprays, and exchanges heat and mass with the rising ammonia-containing vapor, and the concentration of ammonia in the ammonia water Gradually increase the temperature at the bottom of the control tower to about 35°C.

(4) After a cycle period of about two hours, the pH meter at the bottom of the tower shows a reading of 11.2. At this time, the mass concentration of ammonia water in the absorption tower reaches 13.7%, and the radioactivity is less than 0.1Bq/L, which can be directly reused in the process. Table 1 is a comparison table of changes in the concentration of ammonia nitrogen in the influent and effluent water.

Table 1 Comparison table of changes in ammonia nitrogen concentration in influent and effluent water

project Raw water (g/L) Effluent (g/L) absorb ammonia NH ₃ -N 13000 180 13700

Example 2

During the production of a certain batch of fuel elements, about 200 liters of ammonia-containing process waste liquid needs to be treated. The mass concentration of NH ₃ -N in the raw water is 5.3%, and the main radioactive substance is uranium 235 with a concentration of about 10ppm. In order to realize the removal and recovery of ammonia in wastewater and avoid the secondary pollution of radioactive uranium-235, the mode of intermittent heating and intermittent feeding is used to recover ammonia by distillation. The whole process is shown in Figure 1, and the specific process is as follows:

(1) The ammonia-containing process waste liquid is left standing in the waste liquid tank. After the solid matter in the waste liquid is precipitated, the supernatant liquid is sent to the heat exchanger by a pump. After heat exchange to increase the temperature, it is pumped into the evaporator for heating.

(2) First pump two-thirds of the volume of feed liquid into the evaporator, and use the closed-circuit controlled heat transfer oil circulation heating method to control the temperature of the evaporator to about 85°C; the internal pressure of the evaporator is 1.0MPa, when the pH in the evaporator When the meter reading drops to about 8, pump one-fifth of the volume of feed liquid into the kettle and heat it to 70°C. Cycle back and forth in turn until the feed liquid reaches four-fifths of the maximum volume of the evaporator (about 23 liters). When the pH drops to 8 the discharge is for further processing.

(3) In the ammonia gas absorption part, the ammonia water at the bottom of the absorption tower is drawn by the circulating pump, and then flows back to the top of the absorption tower for spraying through the flow meter and cooler. The sprayed ammonia water passes through the pipe wall in the intermediate falling film device and flows to the packing layer Exchange heat with the high-temperature ammonia water in the lower part of the absorption tower, and control the temperature at the top of the tower at about 40°C; the ammonia water after heat exchange enters the tower from the upper part of the tower and sprays, and exchanges heat and mass with the rising ammonia-containing vapor, and the concentration of ammonia in the ammonia water Gradually increase the temperature at the bottom of the control tower to about 35°C.

(4) After a cycle period of about two hours, the pH meter at the bottom of the tower shows a reading of 10.7. At this time, the mass concentration of ammonia water in the absorption tower reaches 13.2%, and the radioactivity is less than 0.1Bq/L, which can be directly reused in the process. Table 2 is a comparison table of changes in the concentration of ammonia nitrogen in the influent and effluent water.

Table 2 Comparison table of changes in ammonia nitrogen concentration in influent and effluent water

project Raw water (g/L) Effluent (g/L) absorb ammonia NH ₃ -N 5300 120 13200

Example 3

During the production of a certain batch of fuel elements, about 200 liters of ammonia-containing process waste liquid needs to be treated. The mass concentration of NH ₃ -N in the raw water is 7.8%, and the main radioactive substance is uranium 235 with a concentration of about 10ppm. In order to realize the removal and recovery of ammonia in wastewater and avoid the secondary pollution of radioactive uranium-235, the mode of intermittent heating and intermittent feeding is used to recover ammonia by distillation. The whole process is shown in Figure 1, and the specific process is as follows:

(1) The ammonia-containing process waste liquid is left standing in the waste liquid tank. After the solid matter in the waste liquid is precipitated, the supernatant liquid is sent to the heat exchanger by a pump. After heat exchange to increase the temperature, it is pumped into the evaporator for heating.

(2) First pump one-third of the volume of feed liquid into the evaporator, and use the closed-circuit controlled heat conduction oil circulation heating method to control the temperature of the evaporator to about 65°C; the internal pressure of the evaporator is 1.0MPa, when the pH in the When the meter reading drops to about 8, pump one-fifth of the volume of feed liquid into the kettle and heat it to 70°C. Cycle back and forth in turn until the feed liquid reaches four-fifths of the maximum volume of the evaporator (about 23 liters). When the pH drops to 8 the discharge is for further processing.

(3) In the ammonia gas absorption part, the ammonia water at the bottom of the absorption tower is drawn by the circulating pump, and then flows back to the top of the absorption tower for spraying through the flow meter and cooler. The sprayed ammonia water passes through the pipe wall in the intermediate falling film device and flows to the packing layer Exchange heat with the high-temperature ammonia water in the lower part of the absorption tower, and control the temperature at the top of the tower at about 20 ° C; the ammonia water after heat exchange enters the tower from the upper part of the tower and sprays, and exchanges heat and mass with the rising ammonia-containing vapor, and the ammonia concentration in the ammonia water Gradually increase, and control the temperature at the bottom of the tower to be about 20°C.

(4) After a cycle period of about two hours, the pH meter at the bottom of the tower shows a reading of 10.7. At this time, the mass concentration of ammonia water in the absorption tower reaches 14.8%, and the radioactivity is less than 0.1Bq/L, which can be directly reused in the process. Table 3 is a comparison table of changes in the concentration of ammonia nitrogen in the influent and effluent water.

Table 3 Comparison table of changes in ammonia nitrogen concentration in influent and effluent water

project Raw water (g/L) Effluent (g/L) absorb ammonia NH ₃ -N 7800 120 14800

Although the present invention has been described in detail with general descriptions and specific embodiments above, it is obvious to those skilled in the art that some modifications or improvements can be made on the basis of the present invention. Therefore, the modifications or improvements made on the basis of not departing from the spirit of the present invention all belong to the protection scope of the present invention.

Claims (8)

1. A method for recovering ammonia nitrogen in a low-radioactive high-ammonia nitrogen waste liquid, the method comprising: (a) Put the ammonia-containing waste liquid into the heating container to heat to form ammonia vapor; the temperature in the heating container is 65-85°C, and the pressure is 1.0-1.3Mpa; add ammonia-containing waste liquid to the heating container intermittently during the heating process , to ensure that the total volume of ammonia-containing waste liquid accounts for more than one-fifth and less than four-fifths of the volume of the heating vessel; (b) Pass the ammonia vapor into the falling film condensation absorption tower to condense, and the condensed ammonia vapor flows into the bottom of the tower to form ammonia water; (c) The ammonia water at the bottom of the tower is cooled and returned to the top of the tower, and sprayed to contact with the uncondensed ammonia vapor entering the tower; (d) After cyclic absorption, ammonia water with a concentration greater than 5% is obtained. 2. The recovery method according to claim 1, characterized in that the total volume of ammonia-containing waste liquid accounts for more than one-third and less than two-thirds of the volume of the heating vessel. 3. The recovery method according to claim 1 or 2, characterized in that, it also includes detecting the pH value of ammonia waste liquid in the heating container, and when the pH value is lower than 8, stop heating, cool down, and unload; the detection tower The pH value of the ammonia water at the bottom, when the pH is higher than 11, the ammonia water at the bottom of the tower is discharged. 4. The recovery method according to claim 1 or 2, characterized in that the heating vessel is heated by means of closed-circuit controlled heat conduction oil circulation heating. 5. The recovery method according to claim 1, characterized in that the temperature in the heating container is 67-75°C. 6. The recovery method according to claim 1 or 2, characterized in that the ammonia vapor formed in step (a) is first cooled to condense most of the water below 90°C and a small part of ammonia vapor, and then enters condensation absorption tower. 7. The recovery method according to claim 1 or 2, characterized in that the temperature at the top of the condensation absorption tower is 20-40°C, and the temperature of ammonia water at the bottom of the tower is 20-35°C. 8. The recovery method according to claim 7, characterized in that the temperature at the top of the condensation absorption tower is 25-30°C, and the temperature of the ammonia water at the bottom of the tower is 20-30°C.

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