RU2399973C1 - Processing method of water containing surface-active substances - Google Patents

Abstract

FIELD: power industry.

SUBSTANCE: invention refers to processing of liquid nuclear waste (LNW), can be used during processing of water containing surface-active substances (SAS), namely special laundry water. Water containing surface-active substances is supplied to evaporator plant of additional evaporation of floor drain after salt content in it is 60 ÷ 150 g/dm³ and there performed is combined evaporation of water containing surface-active substances and floor drain by keeping them in the ratio of 1 : (3÷10); after salt content is 150 ÷ 350 g/dm³, still bottom is pumped from time to time to storage tank at the working evaporator plant till salt content value is 60 ÷ 150 g/dm³.

EFFECT: improving reliability and simplifying the treatment process of special laundry water evaporation and reducing periodicity of acid washings of evaporator plant of floor drain treatment.

Description

The invention relates to the field of nuclear technology, namely to the processing of liquid radioactive waste (LRW), can be used in the processing of water containing surface-active substances (surfactants), in particular special laundry.

During the operation of nuclear power plants and other nuclear power facilities, the main overalls of personnel, safety shoes and additional personal protective equipment are contaminated with radionuclides and sent to decontamination and washing in special laundries. A feature of special laundry water is that it contains significant amounts of surface-active substances (surfactants) from 50 mg / dm ³ to 1000 mg / dm ³ . The waste water of the special laundry can have a specific radionuclide content of up to 3.7 · 10 ^-3 Bq / dm, therefore it is necessary to treat it as liquid radioactive waste (LRW). The most common and widely used industrial application for LRW processing is the method of concentrating them by evaporation in evaporators to a salinity of 50 ÷ 500 g / dm ³ . Surfactants reduce the surface tension in aqueous solutions, especially when their concentration increases during evaporation, which contributes to foaming of the solution and intensive drip removal of LRW with secondary vapor (“Purification of radiation-contaminated waters of laboratories and research nuclear reactors”, A. A. Khonikevich ., 3rd ed., Rev. And add., M., Atomizdat, 1974, p. 83). In this case, substandard condensate forms, which requires re-processing. In addition, substandard condensate with a high surfactant content, entering the condensate purification unit, consisting of carbon filters, alluvial filters, ion-exchange filters (H ⁺ , OH ^- and FSD), poison activated carbon, and, together with oil products desorbed from the carbon filter, poison expensive ion-exchange resins in ion exchange condensate filters. In addition, after foaming, washing of the evaporator separator, secondary steam pipelines, secondary steam condenser, condensate pipelines, deaerator and washing water treatment is required. The evaporation unit is taken out of operation and is not used for its intended purpose. It is known that in order to suppress foaming during evaporation of surfactant-containing solutions, defoamers (defoaming agents) are introduced into the evaporator (“Purification of Radiation-Contaminated Waters of Laboratories and Research Nuclear Reactors”, A. Khonikevich, 3rd edition, revised and add., M., Atomizdat, 1974, p. 169) mainly based on organosilicon compounds. Known defoamers are expensive and ineffective. At the slightest change in pressure in the evaporator, foaming of the evaporated solution also occurs. Or, in order to suppress foaming during evaporation of solutions containing ionic surfactants, the solutions are liming, that is, calcium (the cheapest reagent lime) is introduced into the solution to convert ionic surfactants and soap into a poorly soluble calcium form. At the same time, foaming is reduced, since ionic surfactants and soaps are removed from the surface-active dissolved state in the form of calcium salts. On nonionic surfactants, this method does not work. The introduction of lime into the solution contributes to the deposition of hardness salts on the walls of the evaporators, the tube of the heating chambers, which quickly reduces the performance of the evaporators and requires acid washing. The introduction of lime for liming and acid for acid leaching into the solution significantly increases the amount of salts in the bottom residue, and consequently, the costs of conditioning LRW and storing the final product increase. The liming procedure is accompanied by the formation in LRW of sludges that must be removed from the solutions before evaporation, and this requires the use of additional apparatuses and devices, which complicates and increases the cost of the technological scheme.

The closest analogue of the claimed invention is a method for processing LRW of nuclear power plants, including separate evaporation of water from the special laundry and technological LRW of nuclear power plants (floor drain, regeneration of ion-exchange filters, decontamination solutions) in the evaporator before saturation with salts, or until salinity of 200 ÷ 250 g / dm ³ , at which ensures the quality of the condensate of the secondary steam, acceptable for supply to the condensate purification on carbon and ion-exchange filters. ("The water regime and the treatment of radioactive waters of nuclear power plants". M: Energoatomizdat, 1983, p. 179-185). VAT residue is poured into the storage tank.

The disadvantage of this method is the low reliability and complexity of the process, due to the fact that when water is evaporated by the special laundry in a separate stream, it is impossible to achieve a high salt content in the bottom residue of the evaporator due to foaming of the solution and its entrainment with secondary steam. During the evaporation of technological LRW, as a rule, it is possible to achieve a sufficiently high salt content in the still bottom, until saturated with salts, the value of which is determined by the presence and content of oxalates, the solubility of which decreases with increasing total salt content. But at the same time, hardness salts, hydroxides of corrosion products and oxalates are overgrown with the surfaces of the heating chambers, especially of the second case of double-shell evaporator units for processing drain water, which reduces the performance of the entire evaporator unit and must be stopped periodically for acid washing. The experience of special laundry water treatment shows that in case of their evaporation, it is necessary to carry out acid washing of heating chambers 2-3 times less often. If the acid washing of the heating chambers is carried out 1-2 times a month during the evaporation of floor drain water, then during the processing of additional special laundry water this interval of work between washing increases to two months. This is due to the presence of organic complexones, polymetaphosphates and other emollients in the composition of washing powders that bind hardness salts to water-soluble compounds.

The problem solved by the invention is to increase the reliability and simplify the process of evaporation of water from the special laundry and reduce the frequency of acid washes of the evaporation plant processing waste water.

The essence of the invention lies in the fact that in the method of processing water containing surfactants by evaporating them in an evaporation apparatus to the desired salt content and periodically pumping the bottom residue into storage tanks, it is proposed that water containing surfactants be supplied to the evaporator with an additional evaporation of drain water therein after the TDS 60 ÷ 150 g / dm ³ and hold a joint evaporation of water containing surfactants and drain water, keeping them in ootnoshenii 1 ÷ (3 ÷ 10), when the salt content of 150 ÷ 350 g / ^dm3, bottoms are periodically pumped to a storage tank in operating evaporator until a salinity values of 60 ÷ 150 g / ^dm3.

A novelty in comparison with the closest analogue is the joint processing of separate streams of water of special laundry and floor drain in one evaporator of drain water. Drain water is fed for evaporation to the first building of the double-shell evaporator for the treatment of drain water and, when the salt content in the second evaporation apparatus is reached (before evaporation), 60 ÷ 150 g / dm ³ are supplied with special laundry water containing surfactants, and the ratio between the amount of supplied laundry water is maintained, containing surfactant, and floor drain 1: (3 ÷ 10). When this occurs, evaporation of water without foaming the solution to a salinity of 150 ÷ 350 g / DM ³ . When evaporating high salt solutions with a high ionic strength of the solution, the surface tension increases, which compensates for the decrease in surface tension due to the presence of surfactants. The upper salt content of 350 g / dm ³ is determined by the evaporation of surfactants and soap, in which their content in the condensate of the secondary steam reaches 0.1 mg / dm ³ . Then the bottom residue is pumped into storage tanks without stopping the evaporation unit and stopping the supply of floor drain and special laundry water until the salt content in the second building is 60 ÷ 150 g / dm ³ , that is, to the initial value.

An example implementation of the method is illustrated in the flowchart shown in the drawing. The technological scheme of supplying special laundry to the second evaporator for additional evaporation was mounted and the technology of processing special washing water at evaporation plants during the processing of drain water from the Leningrad NPP was tested. In accordance with the scheme, from the receiving and temporary storage of floor drain 1, the pump 2 through the flow meter 3, the flow regulator 4, the drain water is fed for evaporation into the first building of the double-shell evaporator unit 5 for processing the drain water. Secondary steam formed during evaporation enters the second housing of the double-shell evaporator installation for additional evaporation of special laundry 7, and the condensed water in the first housing flows through the automatic flow regulator 6 to the second apparatus of the double-boiler evaporator 7. The automatic flow controller operates according to the readings of the solution level sensors on second housing doublecase evaporator 7. Upon reaching the salt content in the bottoms in the second housing 60 ÷ 150 g / dm ³ of it The reception and temporary storage of water by the special laundry 8 by the pump 9 through the flow meter 10 and the flow regulator 11 feed the special laundry from the tank 8 into the circulation pipe of the second building 7. The flow of water from the special laundry from the tank 8 is maintained in relation to the drain of water to the first building from 1:10 to 1: 3. The limiting value for the surfactant content was obtained with a ratio of water containing surfactant and floor drain equal to 1: 3, and salinity in the bottom residue of 350 g / dm ³ . The lower salt content in the bottom residue of 150 g / dm ³ is explained by the fact that, with a high content of oxalates, precipitation can occur here and clog the waste pipeline. When water containing surfactant is supplied to the second building, the entry of the floor drain solution from the first building into the second is automatically reduced, and therefore, the concentration of salts in this solution increases. And the more the flow rate of water containing surfactants is established in the second building, the higher the salt concentration, the solutions of floor drain come from the first building into the second. That is, this system has automatic feedback. Periodically, when the salinity in the evaporation apparatus reaches an additional evaporation of 7 - 150 ÷ 350 g / dm ³ , without stopping the evaporation unit by pump 12, the bottoms are pumped into the storage tanks of bottoms 13. The bottoms are removed until the salinity in the solution in the second building is reduced to 60 ÷ 150 g / dm ³ . At the same time, the operation of evaporator units 1, 8 and the supply of floor drain and special laundry water is not interrupted. During the process of water treatment by the special laundry in this way, foaming is completely prevented and it is possible to collect conditioned condensate in the condensate receiver 14 with a rather low surfactant content, which allows it to be further treated from salts and oils on condensate filters.

Table 1 shows the experimental results when working out the boundary process parameters.

Control Points:

KOV2 - bottom residue in the second building of the evaporator;

VPV2 - condensate of the secondary steam of the second body of the evaporator;

OKVA - combined condensate from the first and second body of the evaporator.

* - bottoms discharge started, carried out according to the testimony of A.Kh. -automatic chemical control (conductometer).

** - the discharge of the bottom residue according to the indications of the amount of oxalates has begun.

*** - the discharge of the bottom residue according to the testimony of the surfactant content in VPV2 and OKVA has begun.

From the results shown in table 1, it is seen that foaming did not occur in all experiments (controlled by foam sensors in the separator). In all cases, in the condensate of the secondary steam, the surfactant content at the OKVA and VPV2 points was lower than the standard values.

Claims (1)

A method of processing water containing surfactants by evaporating them in the evaporator to the desired salinity and periodically pumping the bottom residue into storage tanks, characterized in that the water containing surfactants is fed to the evaporator for additional evaporation of floor drains when reaching it has a salt content of 60 ÷ 150 g / dm ³ and conduct joint evaporation of water containing surfactants and floor drain water, maintaining them in a ratio of 1: (3 ÷ 10), when salt is reached contents of 150 ÷ 350 g / dm ^{3 the} cubic residue is periodically pumped into the storage tank on a working evaporator until the salinity is set to 60 ÷ 150 g / dm ³ .

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