A method for treating radioactive waste organic phase using molecular distillation technology

Abstract

The present invention belongs to the technical field of radioactive waste liquid treatment, and specifically relates to a method for treating radioactive waste organic phase by molecular distillation technology, including waste organic phase pretreatment, primary molecular distillation, secondary molecular distillation, tertiary molecular distillation, quaternary molecular distillation, and the tributyl phosphate produced by the secondary molecular distillation tower and the sulfonated kerosene produced by the quaternary molecular distillation tower are reused and continuously circulated as extractants and diluents in the nuclear industry solvent extraction section. The molecular distillation technology for treating waste organic phase can regenerate the currently temporarily stored waste organic phase, so that the usable components such as TBP and kerosene therein can be recycled, which is of great significance to minimizing radioactive waste and reducing production and operation costs.

Description

Technical Field

[0001] The invention belongs to the technical field of radioactive waste liquid treatment, and specifically relates to a method for treating radioactive waste organic phase by molecular distillation technology, treating the waste organic phase generated in the extraction and purification process, and recovering TBP and kerosene therein. Background Art

[0002] Waste organic phases are generated during the extraction and purification process of the front and back end of the nuclear fuel cycle. Currently, these waste organic phases are temporarily stored as radioactive waste liquid. Although research on the treatment of waste organic phases has been ongoing, there are no reports on the application of other technologies except pyrolysis and incineration technology.

[0003] The pyrolysis incineration technology adopts a two-stage combustion method, that is, the waste organic phase is first mixed with slaked lime powder, dispersant, etc. to form an emulsified suspension, and then the emulsified suspension is added to the pyrolysis furnace. The emulsified suspension is thermally decomposed in the low-oxygen environment of the pyrolysis furnace to produce combustible pyrolysis gas; the pyrolysis gas is transported to the combustion furnace through a high-temperature pipeline, and is fully burned in contact with oxygen in the combustion furnace; the high-temperature flue gas generated by the combustion of the pyrolysis gas enters the exhaust gas treatment system, and is discharged after cooling and purification. When the pyrolysis incineration technology treats the waste organic phase, the organic phase is completely incinerated and cannot be recycled and reused. In addition, its system is complex and the equipment is large in size, and a large amount of secondary waste is generated, and the treatment cost is high. Summary of the invention

[0004] The purpose of the present invention is to provide a method for treating radioactive waste organic phase by molecular distillation technology, recovering tributyl phosphate (TBP), kerosene and other usable components therein, and realizing their recycling.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for treating radioactive waste organic phase using molecular distillation technology,

[0007] (1) Pretreatment of the waste organic phase: The waste organic phase is preheated and melted in a preheater, and then the molten waste organic phase is transported to a degassing tower through a delivery pump 1 for degassing. The vacuum pump 5 is turned on to control the pressure in the degassing tower to ensure that the gas dissolved in the waste organic phase can escape and the organic phase does not volatilize;

[0008] (2) Primary molecular distillation: The degassed waste organic phase is transported to the feed port of the primary molecular distillation tower by a delivery pump 2, and a molecular distillation process is performed in the primary molecular distillation tower. The pressure in the primary molecular distillation tower is controlled by a vacuum pump 1; the light components produced by the distillation are collected to obtain a fraction 1, which includes phosphoric acid and butanol; the heavy components produced by the distillation are transported to the secondary molecular distillation tower by a delivery pump 3;

[0009] (3) Secondary molecular distillation: The heavy components produced by the primary molecular distillation tower are further distilled, and the operating temperature and pressure of the secondary molecular distillation tower are adjusted. The pressure in the secondary molecular distillation tower is controlled by a vacuum pump 2; the heavy components produced by the secondary molecular distillation are collected to obtain a fraction 2, which includes tributyl phosphate. The light components produced by the distillation are transported to the tertiary molecular distillation tower by a transport pump 4;

[0010] (4) Tertiary molecular distillation: The light components produced by the secondary molecular distillation tower are further distilled, and the operating temperature and pressure of the tertiary molecular distillation tower are adjusted. The pressure in the tertiary molecular distillation tower is controlled by a vacuum pump 3; the heavy components produced by the tertiary molecular distillation are collected to obtain a fraction 3, which includes dibutyl phosphate. The light components produced by the distillation are transported to the quaternary molecular distillation tower by a transport pump 5;

[0011] (5) Four-stage molecular distillation: The light components produced by the three-stage molecular distillation tower are further distilled, and the operating temperature and pressure of the four-stage molecular distillation tower are adjusted. The pressure in the four-stage molecular distillation tower is controlled by a vacuum pump 4; the light components produced by the four-stage molecular distillation are collected to obtain a fraction 4, whose components include monobutyl phosphate; the heavy components produced by the distillation are collected to obtain a fraction 5, whose components include sulfonated kerosene.

[0012] (1) Pretreatment of waste organic phase: preheating temperature is 70-80°C.

[0013] (1) Pretreatment of waste organic phase: Turn on the vacuum pump 5 and control the pressure in the degassing tower to 10-30 kPa.

[0014] (2) Primary molecular distillation: Adjust the molecular distillation temperature at 80-100°C and the operating pressure at 1-10Pa.

[0015] (3) Secondary molecular distillation: adjust the molecular distillation temperature at 110-120°C and the operating pressure at 0.4-0.6 Pa.

[0016] (4) Three-stage molecular distillation: adjust the molecular distillation temperature at 130-140°C and the operating pressure at 0.1-0.3Pa.

[0017] (5) Four-stage molecular distillation: adjust the molecular distillation temperature at 170-180°C and the operating pressure at 0.1-0.3Pa.

[0018] The tributyl phosphate produced by the secondary molecular distillation tower and the sulfonated kerosene produced by the quaternary molecular distillation tower are reused and continuously circulated as extractants and diluents in the solvent extraction section of the nuclear industry.

[0019] The exhaust gases of vacuum pump 1, vacuum pump 2, vacuum pump 3, vacuum pump 4 and vacuum pump 5 are collected and filtered through a filter and then discharged after meeting the filtering standards.

[0020] The first-stage molecular distillation tower, the second-stage molecular distillation tower, the third-stage molecular distillation tower and the fourth-stage molecular distillation tower are all rotary scraping film type, and the rotary scraping film device has a rotation speed of 100-150rpm.

[0021] The beneficial effects achieved by the present invention are:

[0022] This molecular distillation technology for treating waste organic phase can regenerate the currently stored waste organic phase, so that the usable components such as TBP and kerosene can be recycled, which is of great significance to minimizing radioactive waste and reducing production and operation costs.

[0023] TBP is a heat-sensitive substance, which starts to decompose when the temperature is greater than 150°C, and the higher the temperature, the faster the decomposition speed. Therefore, in order to avoid the thermal decomposition of TBP, the separation process of it and the degradation products is preferably carried out at low temperature. The molecular distillation technology has the characteristics of low operating temperature and short heating time, which is suitable for the separation and purification process of TBP. The present invention separates TBP, sulfonated kerosene and its degradation products through molecular distillation technology, and uses a four-stage molecular distillation tower to separate the components according to the main components of the waste organic phase. The obtained TBP and kerosene can be recycled, and the process greatly reduces the storage of radioactive waste organic phase and reduces the production and operation cost.

[0024] The investigation found that the waste organic phase currently stored is in a paste-like state with poor fluidity. Therefore, it is necessary to first preheat the waste organic phase to melt the paste and enhance the fluidity of the waste organic phase.

[0025] At room temperature and pressure, a certain amount of gas will be dissolved in the waste organic phase. However, in the high vacuum environment of the molecular distillation tower, the gas dissolved in the waste organic phase will escape rapidly from the liquid, producing droplets that contaminate the condensation surface and destroy the vacuum degree of the system. Therefore, the waste organic phase needs to be degassed before the molecular distillation operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0027] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] Process scheme for treating radioactive waste organic phase using molecular distillation technology:

[0029] (1) Molecular distillation technology for treating waste organic phase

[0030] The waste organic phase is mainly composed of extractant TBP and diluent sulfonated kerosene and their degradation products dibutyl phosphate (DBP), monobutyl phosphate (MBP), butanol and phosphoric acid, and the mean free paths of the components are quite different. TBP is a heat-sensitive substance, and the higher the temperature, the faster the decomposition speed. Therefore, the molecular distillation technology with low distillation temperature and short heating time is used to treat the waste organic phase, and the useful components such as TBP and sulfonated kerosene are recovered. The present invention controls the pressure of molecular distillation to be 0.01-10Pa and the distillation temperature to be 80-250°C.

[0031] (2) Functions of each system of molecular distillation

[0032] The device for treating radioactive waste organic phase with molecular distillation technology mainly includes pretreatment system, molecular distillation system, heating and cooling system, vacuum system and control system. The pretreatment system is used for the pretreatment process of radioactive waste organic phase, including preheating and degassing of waste organic phase. The molecular distillation system is used to molecularly distill radioactive waste organic phase and separate the components therein. The heating and cooling system is used to heat and cool the cold and hot media in the molecular distillation system. The vacuum system is used to vacuum the molecular distillation system to achieve the pressure required for molecular distillation. The control system is used to adjust and control the process parameters such as temperature, pressure, flow rate, speed, etc. in the entire device. The molecular distillation tower is the key to realizing this technology. According to the form and operating characteristics of the equipment, a rotary scraped film molecular distiller is selected.

[0033] (3) Molecular distillation process

[0034] When the molecular distillation technology is used to treat the radioactive waste organic phase, the waste organic phase needs to be preheated and degassed. First, the waste organic phase containing the paste is preheated and melted, and then the molten waste organic phase is transported to the degassing tower for degassing. The upper end of the degassing tower is connected to the vacuum pump 5 to control the low-pressure environment in the degassing tower. The degassing tower is heated and the vacuum pump 5 is turned on at the same time. After a certain period of time, the degassing of the waste organic phase is completed.

[0035] The primary molecular distillation tower is heated and vacuumed. When the temperature and pressure in the primary molecular distillation tower reach the specified parameters, the feeding operation is started. When feeding, the feeding rate should be adjusted according to the processing capacity, and the waste organic phase pretreated by the degassing tower is transported to the primary molecular distillation tower. The primary molecular distillation tower controls the pressure by vacuum pump 1, and the waste organic phase is molecularly distilled in the primary molecular distillation tower. The light components are collected to obtain fraction 1 (main components of phosphoric acid and butanol), and the heavy components are transported to the secondary molecular distillation tower. The secondary molecular distillation tower controls the pressure by vacuum pump 2, and the waste organic phase is molecularly distilled twice in the secondary molecular distillation tower. The heavy components are collected to obtain fraction 2 (main component TBP), and the light components are transported to the tertiary molecular distillation tower. The tertiary molecular distillation tower controls the pressure by vacuum pump 3, and the waste organic phase is molecularly distilled for the third time in the tertiary molecular distillation tower. The heavy components are collected to obtain fraction 3 (main component DBP), and the light components are transported to the quaternary molecular distillation tower. The pressure of the four-stage molecular distillation tower is controlled by a vacuum pump 4. The waste organic phase is distilled for the fourth time in the four-stage molecular distillation tower. The light components produced are collected to obtain fraction 4 (main component MBP), and the heavy components produced are collected to obtain fraction 5 (main component sulfonated kerosene OK).

[0036] Fraction 2 is mainly composed of recovered tributyl phosphate TBP, and fraction 5 is mainly composed of recovered sulfonated kerosene OK, which can be returned to the solvent extraction section for continued use as an extractant and diluent. The tail gas of each vacuum pump is collected and filtered for discharge.

[0037] A method for treating radioactive waste organic phase by molecular distillation technology, using a four-stage molecular distillation tower to separate the waste organic phase, the first, second, third and fourth molecular distillation tower structures are all rotary scraping film type, the scraping effect of the rotary scraper on the wall of the molecular distillation tower can effectively control the liquid film thickness, avoid the generation of channel flow, and improve the heat transfer and mass transfer efficiency.

[0038] The distillation process mainly includes the following steps:

[0039] (1) Pretreatment of waste organic phase: Preheat the waste organic phase containing paste to melt in a preheater at a temperature of 70-80° C. Then, the molten waste organic phase is transported to a degassing tower through a delivery pump 1 for degassing. The vacuum pump 5 is turned on to control the pressure in the degassing tower at 10-30 kPa to ensure that the gas dissolved in the waste organic phase can escape and the organic phase will not volatilize.

[0040] (2) Primary molecular distillation: The degassed waste organic phase is transported to the feed port of the primary molecular distillation tower through the delivery pump 2, and the molecular distillation process is carried out in the primary molecular distillation tower. The pressure in the primary molecular distillation tower is controlled by the vacuum pump 1. The molecular distillation temperature is adjusted to 80-100°C, the operating pressure is 1-10Pa, and the speed of the scraper is 100-150rpm. The light components produced by distillation are collected to obtain fraction 1, which contains phosphoric acid, butanol, etc. The heavy components produced by distillation are transported to the secondary molecular distillation tower through the delivery pump 3.

[0041] (3) Secondary molecular distillation: The heavy components produced by the primary molecular distillation tower are further distilled, and the operating temperature and pressure of the secondary molecular distillation tower are adjusted. The pressure in the secondary molecular distillation tower is controlled by vacuum pump 2. The molecular distillation temperature is adjusted to 110-120°C, the operating pressure is 0.4-0.6Pa, and the speed of the scraper is 100-150rpm. The heavy components produced by the secondary molecular distillation are collected to obtain fraction 2, the main component of which is tributyl phosphate TBP. The light components produced by the distillation are transported to the tertiary molecular distillation tower by the delivery pump 4.

[0042] (4) Tertiary molecular distillation: The light components produced by the secondary molecular distillation tower are further distilled, and the operating temperature and pressure of the tertiary molecular distillation tower are adjusted. The pressure in the tertiary molecular distillation tower is controlled by a vacuum pump 3. The molecular distillation temperature is adjusted to 130-140°C, the operating pressure is adjusted to 0.1-0.3Pa, and the speed of the scraper is 100-150rpm. The heavy components produced by the tertiary molecular distillation are collected to obtain fraction 3, the main component of which is dibutyl phosphate DBP. The light components produced by the distillation are transported to the quaternary molecular distillation tower by a delivery pump 5.

[0043] (5) Quaternary molecular distillation: The light components produced by the tertiary molecular distillation tower are further distilled, and the operating temperature and pressure of the quaternary molecular distillation tower are adjusted. The pressure in the quaternary molecular distillation tower is controlled by a vacuum pump 4. The molecular distillation temperature is adjusted to 170-180°C, the operating pressure is adjusted to 0.1-0.3Pa, and the speed of the scraper is 100-150rpm. The light components produced by the quaternary molecular distillation are collected to obtain fraction 4, the main component of which is monobutyl phosphate MBP; the heavy components produced by the distillation are collected to obtain fraction 5, the main component of which is sulfonated kerosene OK.

[0044] The TBP produced by the secondary molecular distillation tower and the kerosene produced by the quaternary molecular distillation tower can be reused and continued to be used as an extractant and diluent in the solvent extraction section of the nuclear industry.

[0045] The exhaust gases of vacuum pump 1, vacuum pump 2, vacuum pump 3, vacuum pump 4 and vacuum pump 5 are collected and filtered through a filter and then discharged after meeting the filtering standards.

[0046] The present invention adopts molecular distillation technology to treat radioactive waste organic phase, and the process includes pretreatment of waste organic phase, primary molecular distillation, secondary molecular distillation, tertiary molecular distillation, and quaternary molecular distillation. The process device mainly includes a waste organic phase pretreatment system, a molecular distillation system, a heating and cooling system, a vacuum system, and a control system. Through the molecular distillation technology, the temporarily stored radioactive waste organic phase can be regenerated, and the usable components such as tributyl phosphate TBP and kerosene can be recovered to achieve recycling, which is of great significance to minimizing radioactive waste and reducing production and operation costs.

[0047] It should be emphasized that the above are only preferred embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any simple modification or equivalent transformation made by any technician familiar with the technical field within the essential scope of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for treating radioactive waste organic phase using molecular distillation technology, characterized in that: (1) Pretreatment of the waste organic phase: preheating and melting the waste organic phase in a preheater at a temperature of 70 to 80° C.; then, the molten waste organic phase is transported to a degassing tower through a transport pump 1 for degassing, and a vacuum pump 5 is turned on to control the pressure in the degassing tower at 10 to 30 kPa to ensure that the gas dissolved in the waste organic phase can escape and the organic phase does not volatilize; (2) Primary molecular distillation: The degassed waste organic phase is transported to the feed port of the primary molecular distillation tower through a delivery pump 2, and a molecular distillation process is carried out in the primary molecular distillation tower. The pressure in the primary molecular distillation tower is controlled by a vacuum pump 1; the molecular distillation temperature is adjusted to 80-100° C., and the operating pressure is 1-10 Pa; the light components produced by the distillation are collected to obtain a fraction 1, which includes phosphoric acid and butanol, and the heavy components produced by the distillation are transported to the secondary molecular distillation tower through a delivery pump 3; (3) Secondary molecular distillation: further distill the heavy components produced by the primary molecular distillation tower, adjust the operating temperature and pressure of the secondary molecular distillation tower, and control the pressure in the secondary molecular distillation tower by vacuum pump 2; adjust the molecular distillation temperature at 110-120° C. and the operating pressure at 0.4-0.6 Pa; collect the heavy components produced by the secondary molecular distillation to obtain fraction 2, which includes tributyl phosphate, and transport the light components produced by the distillation to the tertiary molecular distillation tower by transport pump 4; (4) Tertiary molecular distillation: The light components produced by the secondary molecular distillation tower are further distilled, and the operating temperature and pressure of the tertiary molecular distillation tower are adjusted. The pressure in the tertiary molecular distillation tower is controlled by a vacuum pump 3; the molecular distillation temperature is adjusted to 130-140° C., and the operating pressure is 0.1-0.3 Pa; the heavy components produced by the tertiary molecular distillation are collected to obtain a fraction 3, which includes dibutyl phosphate. The light components produced by the distillation are transported to the quaternary molecular distillation tower by a transport pump 5; (5) Four-stage molecular distillation: The light components produced by the three-stage molecular distillation tower are further distilled, and the operating temperature and pressure of the four-stage molecular distillation tower are adjusted. The pressure in the four-stage molecular distillation tower is controlled by a vacuum pump four; the molecular distillation temperature is adjusted at 170-180°C, and the operating pressure is adjusted at 0.1-0.3Pa. The light components produced by the four-stage molecular distillation are collected to obtain a fraction four, whose components include monobutyl phosphate; the heavy components produced by the distillation are collected to obtain a fraction five, whose components include sulfonated kerosene.

2. The method for treating radioactive waste organic phase by molecular distillation technology according to claim 1, characterized in that: The tributyl phosphate produced by the secondary molecular distillation tower and the sulfonated kerosene produced by the quaternary molecular distillation tower are reused and continuously circulated as extractants and diluents in the solvent extraction section of the nuclear industry.

3. The method for treating radioactive waste organic phase by molecular distillation technology according to claim 1, characterized in that: Vacuum pump 1, vacuum pump 2, vacuum pump 3, vacuum pump 4 、 The exhaust gas from vacuum pump 5 is collected and filtered through a filter and then discharged after meeting the filtering standards.

4. The method for treating radioactive waste organic phase by molecular distillation technology according to claim 1, characterized in that: The first-stage molecular distillation tower, the second-stage molecular distillation tower, the third-stage molecular distillation tower and the fourth-stage molecular distillation tower are all rotary scraping film type, and the rotary scraping film device has a rotation speed of 100-150rpm.

Images