Oxygen is removed from water not only by desorption (physical), but also by chemical methods. The chemical binding of oxygen into corrosive-inert substances is carried out in several ways, each of which is based on redox processes. Since these processes are also characteristic of a number of typical water treatment methods, for example, for purification from biological contaminants, and are important in assessing the corrosion of structural materials of main and auxiliary equipment, we will analyze their main provisions.

Redox reactions consist of the processes of oxidation (donating electrons to substances) and reduction (gaining electrons to substances). A substance that donates its electrons during a reaction is called a reducing agent, and a substance that accepts electrons is an oxidizing agent. Some substances can exist in oxidizing and reducing forms and are able to change from one form to another by gaining or losing electrons. With the exception of oxygen and hydrogen, which are oxidizing and reducing agents, respectively, the remaining substances, depending on the conditions, can be either oxidizing agents or reducing agents, which is characterized by the redox potential of the reaction system or redox potential. The redox potential depends on the activity of the redox form in accordance with the Nornst equation:

where n is the number of electrons participating in the redox reaction; k – parameter depending on temperature; E 0 is the standard potential that determines the equality of the activities of the oxidizing and reducing forms.

The redox potential serves as a measure of the oxidizing and reducing abilities of a system. The most powerful oxidizing agents are the and ions, used to determine permanganate or dichromate oxidation, as well as fluorine, ozone and chlorine.

Chemical methods for removing dissolved gases from water involve binding them into new chemical compounds. Strict regulation of oxygen content when using reducing water regimes in the circuits of thermal power plants with drum boilers and in heating networks determines the need to use not only physical methods of degassing, but also chemical methods of additional deoxygenation based on redox reactions.

Reducing agents used include reagents such as sodium sulfite, hydrazine, and redox groups created on high molecular weight, water-insoluble polymers.

Treatment of water with sodium sulfite is based on the oxidation reaction of sulfite with oxygen dissolved in water:

2Na 2 SO 3 + O 2 2Na 2 SO 4 .

The reaction proceeds quite quickly at a water temperature of at least 80 0 C and pH ≤ 8. This deoxygenation method is used only for medium pressure boilers (3 - 6 MPa) and for make-up water of the heating network, since at temperatures above 275 0 C and pressure more 6 MPa sulfite undergoes hydrolysis and the process of self-oxidation - self-healing:

Na 2 SO 3 + H 2 O 2NaOH + SO 2; 4Na 2 SO 3 Na 2 S + 3Na 2 SO 4.

For direct-flow boilers and drum boilers with high and ultra-high parameters, water is deoxygenated with hydrazine in the form of hydrazine hydrate (N 2 H 4 ∙ H 2 O), which does not increase the salt content of water.

N 2 H 4 ∙ H 2 O O 2 3H 2 O + N 2 .

The main factors determining the rate of this reaction are temperature, pH, excess hydrazine, and the presence of catalysts. Thus, at a temperature of 105 0 C, pH = 9 ÷ 9.5 and an excess of hydrazine of 0.02 mg/kg, the time for complete oxygen binding is 2 – 3 seconds. At pH< 7 гидразин практически не связывает кислород. При рН = 9 ÷ 11 достигается максимум скорости реакции. Органические катализаторы интенсифицируют реакцию, повышая скорость взаимодействия в 25 – 100 раз. Каталитически влияют на скорость реакции также соединения меди и некоторых других металлов.

In boiler water and superheaters, excess hydrazine decomposes to form ammonia:

3N 2 H 4 4NH 3 + N 2.

In the presence of metal oxides, the decomposition of hydrazine with the release of H 2 is also possible:

3N 2 H 4 2NH 3 + 3H 2 + 2N 2.

Redox reactions can be carried out by filtering water through water-insoluble high-molecular substances containing redox groups capable of reversible oxidation and reduction. An example of such substances are electric ion exchangers (EI), used in schemes for deoxygenation of additional water in heating networks that has undergone a preliminary stage of thermal deaeration. EI is obtained by introducing it into the structure of an ion exchanger during the synthesis of the material. On such resins, simultaneous and independent occurrence of ion exchange and redox processes is possible. EI can be obtained on the basis of copper and bismuth.

The determining factor when choosing the type of ion exchanger for packing redox substances on it is the ability of the matrix to firmly hold the deposited compounds. This ability depends on the sign of the surface charge of the ion exchanger.

Lecture No. 10

Organization of chemical deoxygenation.

A sodium sulfite solution for treating feedwater of medium-pressure boilers is prepared in a tank protected from contact with the atmosphere. A solution with a concentration of 3 - 6% is introduced into the supply pipeline in front of the pumps using washer and plunger dispensers. The dose of sodium sulfite for treating 1 m3 of feed water after thermal deaeration is calculated using the formula:

where g is the consumption of technical sulfite, g/m3;

Oxygen concentration in the treated water, g/m 3 ;

k – excess reagent (2 – 3 g/m3);

When organizing hydrazine treatment, it is necessary to take into account the properties of hydrazine hydrate. Hydrazine hydrate N 2 H 4 · H 2 O is a colorless liquid that easily absorbs oxygen, carbon dioxide and water vapor from the air, and is highly soluble in water. Hydrazine is toxic at concentrations greater than 40%, flammable, and is supplied and stored as a 64% solution in a sealed stainless steel container. Hydrazine vapors cause irritation to the respiratory tract and organs of vision; hydrazine solutions act on the skin, therefore, when handling hydrazine, the relevant safety regulations must be strictly observed.

The calculated dose of hydrazine should take into account not only its consumption for oxygen binding, but also for interaction with metal oxides. Its dosage is calculated using the formula:

g g = 3C 1 + 0.3 C 2 – 0.15 C 3,

where g g is the calculated dose of hydrazine hydrate, mg/kg;

C 1 – C 3 – concentration in feed water, respectively, of oxygen, iron and copper compounds, mg/kg.

Hydrazine is dosed at one of two points: at the suction of feed pumps or into the turbine condensate in front of the low-pressure heater (LPH). The estimated amount of 100% hydrazine φ, mg/kg, required for loading into the pre-dilution tank is determined from the ratio:

where D is feed water consumption, m 3 / h;

τ – time between tank recharges, hours.

A tank capacity of 10 m 3 for hydrazine of 20% concentration provides approximately two months of reagent supply for a hydroelectric power station (GRES) with a capacity of 3600 MW.

At a given feedwater flow rate, the hourly reagent flow rate d, kg/h, is calculated using the formula:

Typically, the excess concentration of hydrazine in the feed water during normal operation is 0.03 – 0.06 mg/kg.

Let's consider the technology of using chemical deoxygenation using the example of using an iron oxide electron exchanger (EI). EI of this type is capable of deoxygenation and at the same time softening water in circuits with preliminary vacuum deaeration. Preliminary deaeration of water ensures its heating to 60 - 80 0 C and partial removal of dissolved oxygen, which has a positive effect on the efficiency of the method under consideration. Under the noted temperature conditions, the process can be based on standard designs of ion exchange filters. When the initial oxygen content of the treated water is up to 1 mg/kg, the electric ion exchanger ensures a reduction in the oxygen content to 5 – 20 μg/kg.

The presence of iron hydroxide on the surface of the electroion exchanger also promotes iron removal.

The given technological characteristics ensure high efficiency of using this material for deoxygenation of make-up water in a closed-type heating network.

Water purification using distillation methods.

Distillation method.

Purification (desalination) of waters with high salt content, including sea water, as well as processing of highly mineralized waste solutions in order to protect the environment is the most important scientific and technical task.

Treatment of highly mineralized waters and solutions can be carried out, firstly, by removing dissolved impurities from the water, which is realized, as a rule, without phase transitions of the solvent (water) into a vapor or solid state; secondly, by the method of extracting hydrogen molecules from a solution, based on a change in their state of aggregation (distillation method).

The first way of extracting salts from solution theoretically seems more expedient, since the mole fraction of dissolved even highly mineralized impurities is approximately 100 or more times less than the number of water molecules themselves. However, technical difficulties in implementing this method do not allow this advantage to be realized economically in all cases.

When aqueous solutions are heated, water molecules acquire energy exceeding the forces of molecular attraction and are carried into the vapor space. When the saturated vapor pressure in water becomes equal to external pressure, the water begins to boil. Ions and molecules of dissolved substances contained in water and in a hydrated state do not have such a reserve of energy and turn into vapor at low pressures in very small quantities. Thus, by organizing the process of boiling aqueous solutions, it is possible to separate the solvent (water) and the impurities contained in it. Distillation (thermal desalting) is carried out in evaporation units (Figure 1), in which water, by receiving heat from the primary steam supplied to the heating system, is converted into secondary steam, which is then condensed.

Figure 1 – Scheme of the evaporation plant:

1 – primary steam supply line; 2 – heating section; 3 – evaporator body; 4 – discharge line of the generated (secondary) steam; 5 – capacitor; 6 – primary steam condensate discharge line; 7 – feed water supply line; 8 – purge line; 9 – emptying line; 10 – distillate withdrawal line.

Primary steam is usually taken from a steam turbine. Substances that pollute the water remain in the volume of evaporated water and are removed from the evaporator with the discharge (blowdown) water. The distillate - condensate of secondary steam - contains only a small amount of non-volatile impurities that enter it due to the dropwise entrainment of evaporated water (concentrate).

Assuming as a first approximation that the transition of impurities to secondary steam is zero, we will estimate, based on the material balance in the evaporator, the concentration of impurities in the evaporator water C.v. and depending on the concentration of impurities in the feed water C.p.v. and the blowdown flow rate R.a. The material balance equation has the form:

R p.v · S p.v = R p · S p + R pr · S v.i,

where R p.w – feed water consumption (P p.w = P p + P pr);

R p – steam production.

Considering that C p = 0, (P p + P pr)C p.v = P pr C v.i, whence .

The greater the blowdown, the lower the concentration of impurities in the evaporator water (in the blowdown). The negative temperature coefficient of solubility of hardness salts during the evaporation of water, the concentration of Ca 2+, Mg 2+, , OH - ions to limits exceeding the product of the solubility of CaCO 3, CaSO 4 and Mg(OH) 2, is the cause of scale formation on heat transfer surfaces in evaporators . Scale formation reduces the performance of evaporators and worsens their technical and economic performance.

Evaporation plants can be single- or multi-stage. If the secondary steam is condensed directly in the evaporator condenser, then such an evaporator installation is single-stage. In multi-stage installations (Figure 2), the secondary steam of each stage, except the last, is used as heating steam for the next stage and condenses there.

Figure 2 – Diagram of a multi-stage evaporation plant:

1 – heating steam supply line; 2 – 4 – evaporator, respectively 1 – 3 stages; 5 – secondary steam exhaust line; 6 – capacitor; 7 – condensate drain line; 8 – feed water supply line; 9 – feed water heater; 10 – purge line.

As the number of stages increases, the amount of condensate (distillate) obtained in the evaporation plant from one ton of primary steam also increases. However, with an increase in the number of stages, the temperature difference between the heating and secondary steam decreases, which necessitates an increase in the specific heat exchange surfaces, which ultimately leads to an increase in overall dimensions, specific metal costs and higher installation costs.

A multi-stage installation can be powered in a parallel circuit with power supplied to each evaporator from a common collector, but more often - in a series circuit, as shown in Figure 2. In this case, all the feed water is supplied to the first stage of the installation, and then, after its partial evaporation, the water flows into the next stage, and from the latter it is discharged into the drainage. Multi-stage evaporation plants are used in combined heat and power plants with large total and external losses of steam and condensate. Single-stage evaporation units are used at condensing power plants (CPPs) with small losses (1 - 3%) and are included in wastewater treatment schemes from water treatment plants when discharges are prohibited.

Currently, distillate is mainly produced from water that has been previously softened using ion exchange filters, but in some cases water that has undergone simplified processing is used. The steam supplied to the evaporator is called primary, and the steam generated from the water entering the evaporator is called secondary.

In flash evaporators, steam is formed not by boiling, but by boiling water, preheated to a temperature several degrees higher than the saturation temperature of water, in the chamber in which steam formation occurs. They do not require high quality feed water, since the process of evaporation of water during boiling occurs without heat transfer through the surface. Flash boilers are also called adiabatic or flash units. Since the saturation temperature depends on the saturation pressure, when boiling is carried out at a pressure below atmospheric, it is possible to organize the operation of evaporators of the type in question at temperatures below 100 0 C, which reduces the likelihood of scale formation.

A single-stage flash evaporator with forced circulation operates as follows (Figure 3).

Figure 3 – Single-stage flash evaporator with forced circulation.

The source water enters the condenser 1, after which part of it is sent to the evaporation chamber 3. The circulation pump 5 takes water from the evaporation chamber and pumps it through the heater 6, returning the water through the nozzle 2 to the evaporator housing. When non-condensable gases are sucked out by the steam ejector 8, the pressure in the chamber decreases below the steam saturation pressure, resulting in evaporation from the surface of the droplets and the mirror. Separation of moisture droplets is carried out in device 7. The distillate is pumped out of the evaporator by pump 4; its quantity in single-stage installations is approximately equal to the amount of condensing steam.

Flash evaporators can be constructed using a multi-stage design, which ensures lower specific heat consumption. In seawater desalination plants, the number of stages can reach up to 30 - 40. When such a plant is included in the regenerative heating scheme of boiler feedwater, it is carried out according to the conditions of a single-stage heat balance or has three or four stages.

Prevention of scale formation in evaporation units.

Experience in operating evaporators fed with salt water indicates serious difficulties arising from the rapid formation of scale on heat transfer surfaces, a decrease in the heat transfer coefficient α and a decrease in the efficiency of evaporators.

The growth of a dense layer of crystalline deposits occurs from a supersaturated solution as a result of the growth of crystals existing on the surface (primary scale formation), as well as due to the adhesion and adsorption of fine particles already formed in the evaporated water (secondary scale formation).

As a rule, scale formation of both types occurs simultaneously. The formation of scale on the surface can be represented as follows: the formation of nucleated crystals in the recesses of metal microroughnesses; the appearance of formations such as coral bushes; filling the spaces between the branches of the “bush” with small particles of the solid phase formed in the solution and transported to the heat transfer surface.

Methods for carrying out calculations related to assessing the intensity of scale formation have not yet been developed, since all the factors influencing this process are far from being studied; in particular, it is necessary to know the exact values ​​of the activity coefficient of scale-forming ions for the real operating parameters of the evaporator.

Methods for combating scale formation in evaporators can be divided into physical, chemical and physico-chemical; In addition, it is possible to use special designs and materials for evaporators to reduce scale formation.

Reagent-free methods.

The method of contact stabilization was proposed by Langelier and was named so due to the absence of solid phase separation on the heat transfer surface when it is used. It is based on the fact that the energy of crystal formation on undissolved impurity particles is less than the energy of spontaneous formation of crystallization centers. Crystallization on the stabilizer substance occurs at less supersaturation of the solution. Due to the many crystallization centers, precipitation of an excess amount of scale formers above the solubility occurs. Crushed materials are used as a stabilizer: limestone, marble, sand, through the filter layer of which evaporated water circulates.

The height of the filter should be 1.8 - 2 meters. The brine rise speed in order to avoid carryover of the stabilizing material should not be more than 35 m/h. The use of contact stabilization makes it possible to reduce the amount of scale in the evaporator by 80–90%, but it is structurally complex.

Magnetic treatment of water involves pumping it through a device in which a magnetic field is created. It is known that installations equipped with magnetic devices work effectively when the water is not stable, that is, supersaturated with CaCO 3 . The theory of magnetic processing has not yet been formed, but research has established the following. Contained in water transported through steel pipes, ferromagnetic corrosion products and colloidal particles with an electrical charge and magnetic moment accumulate in the magnetic field created by the magnetic apparatus. An increase in the concentration of the solid microphase in the gap of the magnetic apparatus promotes the crystallization of calcium carbonate from unstable water in its volume, as a result of which the rate of scale formation decreases, but the concentration of sludge increases with further heating and evaporation of the water subjected to magnetic treatment. Since the chemical and dispersed composition of impurities in natural water varies by season and region, and the degree of supersaturation of water with CaCO 3 also depends on temperature, the efficiency of magnetic treatment can vary over a wide range, down to zero values.

Ultrasonic treatment during water evaporation can create, due to elastic mechanical vibrations of the medium of significant energy, conditions leading to disruption of the kinetics of crystallization in the wall layer. The action of ultrasonic waves on the heating surface can excite alternating bending forces at the interface of crystalline bonds with the surface, ultimately causing scale peeling. The mechanism of the effect of ultrasound on scale formation has not been fully studied.

E.F. Tebenikhin, Reagent-free methods of water treatment in power plants. M.: Energoatomizdat, 1985.

Lecture No. 11

Preventing scale formation in evaporation systems

installations using chemical and other methods.

Chemical methods. Acidification stabilization is used to prevent the formation of calcium carbonate and magnesium hydroxide scale on heat transfer surfaces.

Natural water containing Ca 2+ , , , CO 2 , depending on the state of carbon dioxide equilibrium of the system, can be aggressive, stable or unstable. The main criterion for the stability of such a system, used in practice, is the “stability index” proposed by Langelier.

For natural waters, the following relationships are fulfilled: pH = ≥ pH fact. The difference between the actual and equilibrium values ​​is denoted by Y and is called the stability index or Langelier index:

pH fact – pH equal = Y.

At Y = 0 water is stable, at Y< 0 она агрессивна, при Y >0 water is unstable and capable of forming sediments. With stabilized water treatment by acidification, the stability index is ensured to be close to zero. Knowing the nature of the change in pH fact = f 1 (Sh) and pH equal = f 2 (Sh) with a decrease in water alkalinity as a result of acidification, we can solve these equations in relation to ΔSh (reduction of alkalinity to a stable state).

The required dose, mg/kg, of technical sulfuric or hydrochloric acid can be determined by the formula:

where e is the equivalent mass of acid, mEq/kg;

The dose of acid depends on the alkalinity of the feed water, the temperature of the distillation process and the frequency of evaporation and is usually 70–90% of the alkalinity of the feed water. An overdose of acid can cause corrosion of the structural materials of the evaporation plant, and therefore careful monitoring of the dosing process is necessary. The use of sodium bisulfate is similar to acidification, since hydrogen ions are formed as a result of the dissociation of NaHSO 4.

Ferric chloride can be used for acidification; in this case, along with the hydrogen ion, during hydrolysis a suspension of iron hydroxide is formed, the particles of which serve as centers for the crystallization of scale formers.

Physico-chemical methods. They are based on the use of chemical reagents, additives, and surfactants introduced into the evaporated water in such small quantities (1–20 mg/kg) that their reaction with water impurities does not play a significant role. The effectiveness of such additives is due to the fact that, due to their high surface activity, the crystallization of scale formers on the heating surface is sharply reduced. Surfactants are adsorbed in the form of a monomolecular film on the surface of the seed crystals, or impede their adhesion to the surface.

Some antiscale substances, usually present in water in the form of micelles and micromolecules, are characterized by strong stabilizing-peptizing properties that can prevent the coagulation of particles in a wide range of solid phase contents.

In addition to the listed reagents, some complexing agents are also used, for example, sodium hexametaphosphate Na(NaPO 3) 6 and some other polyphosphates.

At high temperatures (up to 120 0 C) and high water hardness, a good effect was achieved by the use of anti-scale reagents containing polyacrylic acid, EDTA salts (Trilon B), sulfonol and others.

In addition to the above, scale is removed (cleaned) from the surfaces of devices using a chemical method using reagents - sulfuric acid, hydrochloric acid, lemon, vinegar and others.

Technological methods for limiting scale formation. They are used primarily in evaporation plants with vertical tube heating sections. Examples of technological methods for limiting scale formation can be the use of organized gas removal (gas blowing) of evaporators to saturate feedwater with carbon dioxide. During the thermal decomposition of bicarbonates, carbon dioxide is released into the gas phase. By mixing it with water in an amount that exceeds the equilibrium value, the water is given aggressive properties towards calcium carbonate, which prevents its release in feedwater heaters. It should be taken into account that when there is an excess content of carbon dioxide in water, which reduces the pH, the corrosion processes of structural materials intensify.

Methods for obtaining pure steam in evaporation plants.

Contamination of saturated steam with inorganic compounds is associated, firstly, with the entrainment of moisture (mechanical entrainment) and, secondly, with the solubility of certain substances in water vapor. The main contribution to steam pollution is made by mechanical (drip) entrainment. Typically, evaporated water is carried out in the form of droplets ranging in size from 0.5 to 3 microns, formed by the destruction of steam bubbles that extend beyond the water volume.

The removal of salts with steam intensifies when the evaporator water foams, and the structure of the foam depends on the load and pressure in the evaporator. It should be emphasized that the patterns of entrainment of moisture droplets by steam operate in the same way both for evaporation installations and for other units producing steam. To ensure high purity of steam in evaporators, the following is used: volumetric separation in the steam space, for which the height of the steam space is chosen to be at least 1.5 meters, and for highly foaming solutions - 2.5 - 3 meters; perforated sheets in front of steam receiving pipes to equalize steam velocities in this area; louvered separators to catch moisture droplets.

An effective means of ensuring steam purity is to flush the steam with feed water. Washing is usually carried out by bubbling small steam bubbles through a layer of wash water, the salt content of which is significantly less than the salt content of the evaporated water, which ensures a wash efficiency of at least 90%. If there are high requirements for the quality of the distillate, steam washing is carried out with external or internal condensate; in some cases, two-stage steam washing is organized. The measures considered make it possible to obtain a distillate by feeding evaporators with softened water that meets the requirements of the PTE of power plants and networks, used for feeding without additional purification as additional water (feed) of drum boilers. At power units with once-through boilers, additional purification of the distillate is required at the BOU.

| | | | | | | | | | | 12 | | | sometimes the binding of oxygen and carbon dioxide is required. Deaeration can be carried out using various methods. Even with deaeration equipment (deaerator), it may be necessary to further reduce the concentration of dissolved oxygen and carbon dioxide using special .

Methods for deaerating feedwater in boiler rooms

. Use of reagents

To bind oxygen in feed and supply water, complex systems can be used, which not only reduce the concentration of oxygen and carbon dioxide to standard values, but also stabilize the pH of the water and prevent the formation of deposits. Thus, the required quality of network water can be achieved without the use of special deaeration equipment.

. Chemical deaeration

The essence of chemical deaeration is the addition of reagents to the feed water, which make it possible to bind dissolved corrosive gases contained in the water. For hot water boilers We recommend using a complex corrosion and deposit inhibitor reagent. To remove dissolved oxygen from water during water treatment for steam boilers - , which often allows operation without deaeration. If the existing deaerator does not work correctly, we recommend using a reagent to correct the water chemistry. For food production it is also recommended to use Advantage 456 reagent

. Atmospheric deaerators with steam supply

To deaerate water in boiler houses with steam boilers, thermal two-stage atmospheric deaerators (DSA) are mainly used, operating at a pressure of 0.12 MPa and a temperature of 104 °C. Such a deaerator consists of a deaeration head having two or more perforated plates, or other special devices, thanks to which the source water, breaking into drops and jets, falls into the accumulator tank, encountering steam moving countercurrently on its way. In the column, water is heated and the first stage of its deaeration occurs. Such deaerators require the installation of steam boilers, which complicate the thermal circuit of the hot water boiler house and the chemical water treatment circuit.

. Vacuum deaeration

In boiler houses with hot water boilers, as a rule, vacuum deaerators are used, which operate at water temperatures from 40 to 90 °C.
Vacuum deaerators have many significant disadvantages: large metal consumption, a large number of additional auxiliary equipment (vacuum pumps or ejectors, tanks, pumps), the need to be located at a significant height to ensure the operation of make-up pumps. The main disadvantage is the presence of a significant amount of equipment and pipelines that are under vacuum. As a result, air enters the water through the shaft seals of pumps and fittings, leaks in flange connections and welded joints. In this case, the deaeration effect completely disappears and it is even possible to increase the oxygen concentration in the make-up water compared to the initial one.

. Thermal deaeration

Water always contains dissolved aggressive gases, primarily oxygen and carbon dioxide, which cause corrosion of equipment and pipelines. Corrosive gases enter the source water as a result of contact with the atmosphere and other processes, for example, ion exchange. Oxygen has the main corrosive effect on metal. Carbon dioxide accelerates the action of oxygen and also has independent corrosive properties.

To protect against gas corrosion, deaeration (degassing) of water is used. The most widespread is thermal deaeration. When water is heated at constant pressure, the gases dissolved in it are gradually released. When the temperature rises to the saturation (boiling) temperature, the concentration of gases decreases to zero. Water is freed from gases.

Underheating of water to the saturation temperature corresponding to a given pressure increases the residual content of gases in it. The influence of this parameter is very significant. Underheating of water even by 1 °C will not allow achieving the requirements of “PUBE” for feed water of steam and hot water boilers.

The concentration of gases dissolved in water is very low (on the order of mg/kg), so it is not enough to separate them from the water, but it is also important to remove them from the deaerator. To do this, it is necessary to supply excess steam or vapor to the deaerator, in excess of the amount required to heat the water to a boil. With a total steam consumption of 15-20 kg/t of treated water, evaporation is 2-3 kg/t. Reduced evaporation can significantly degrade the quality of deaerated water. In addition, the deaerator tank must have a significant volume, ensuring that water remains in it for at least 20 ... 30 minutes. A long time is necessary not only to remove gases, but also to decompose carbonates.

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The invention can be used in chemical water treatment of industrial boiler houses and other enterprises that receive hot network water, in the production of sodium cationized water for feeding steam boilers. To implement the method, water is filtered through a highly basic anion exchanger AM with a gel structure in SO 3 form. The contact time of water with the ion exchanger is at least 7.5 minutes. Regeneration of the spent anion resin is carried out with a solution of sodium sulfite with a concentration of no higher than 8%. The method improves the efficiency of removing oxygen from water. 1 z. items f-ly, 2 tables.

The invention is intended for removing oxygen from water at chemical water treatment plants (CWT) of industrial boiler houses and other enterprises receiving hot network water. Particularly promising is the use of the invention in the production of Na-cationized water for feeding (or make-up) steam boilers. The most universal method for removing dissolved oxygen from water for treating most tap water is vacuum deaeration / Losev V. L. Electrochemical deoxygenation of water in hot water supply systems. Water supply and sanitary technology, 1965, N3, p. 18-23/. The disadvantages of the method include the significant dimensions of the devices, which forces the heating unit to be increased in area and height, and the high cost of constructing the installation. There is a known method for removing oxygen dissolved in water by using special electron exchange resins with iron or copper cations introduced into them. The industrially produced electron exchange resin EI-12 has an oxygen absorption capacity of 45 kg O 2 /m 3 /Designer's Handbook. Water supply to populated areas and industrial enterprises. -M.: Stroyizdat, 1977, p.230/. The disadvantage of this method is the low absorption capacity of the material, leading to frequent regeneration of EI-12, and the low chemical stability of the electron-exchange ion exchanger relative to reducing agents. Thus, the regeneration of spent EI-12 is carried out with solutions of sodium sulfite or thiosulfate with a concentration of no higher than 1-2%. The use of such diluted solutions for regeneration leads to an increase in the duration of the regeneration operation and the volume of discharged wash water. The objective of this invention is to increase the efficiency of removing oxygen from water by passing the source water through a highly basic anion exchanger AM of a gel structure, obtained sequentially by the reactions of chloromethylation and amination with trimethylamine of a granular copolymer of styrene with 4-8% DVB (Laskorin B.N., Ioanisiani P.G., Nikulskaya G.N. Synthesis of new ion exchangers. - In the book: Ion-exchange sorbents in industry. Publishing House of the USSR Academy of Sciences, 1963, pp. 21-31), which is in the working sulfite form. Moreover, the contact time of water with the anion exchanger is at least 7.5 minutes, since with a shorter contact time there is a sharp increase in the oxygen content in the filtrate even with a relatively small amount of water passed through, probably due to a decrease in the efficiency of oxygen diffusion to the surface of the anion exchanger due to the reduction time of contact of the latter with water. Regeneration of the spent anion exchanger is carried out with a solution of sodium sulfite with a concentration of no higher than 8%. When the concentration of the regenerating solution of sodium sulfite is more than 8%, there is a noticeable decrease in the capacity of the anion exchanger for sulfite ion (Table 2), a change in the color of the anion exchanger from yellow to black, due to the destruction of the latter upon contact with a highly concentrated solution of the reducing agent. Example. Tap water (CO 2 - 9.2 mg/dm 3 at 21.2 o C) was passed through a highly basic anion exchanger of the gel structure AM, which is in sulfite form, at a speed of 75 cm 3 /h. Contact time 7.5 min. The volume of the anion exchanger in a column with a diameter of 10 mm was 10 cm 3 . Regeneration of the spent anion exchanger was carried out (after the appearance of a filtrate with a dissolved oxygen content of 1.0 mg/dm 3) with a solution of 8% sodium sulfite. Tables 1 and 2 present the results of the experiments. When the source water is filtered through a layer of anion exchanger AM, which is in sulfite form, oxidation of the sulfite ion of the anion exchanger to SO 4 occurs with oxygen dissolved in the water. The efficiency of the mass transfer process ensures a low oxygen content in the treated water (no more than 1.0 mg/dm 3) over a significant duration of the filter cycle. Regeneration of the anion exchanger is carried out when it reaches an oxygen absorption capacity of no more than 180 mg O 2 /dm 3 . At high values ​​of the absorption capacity of the anion exchanger, the quality of the filtrate in terms of oxygen may deteriorate (more than 1.0 mg O 2 /dm 3). The high chemical stability of the anion exchanger in a reducing environment makes it possible to regenerate the AM anion exchanger with a sodium sulfite solution of 8% concentration, which is four to eight times higher than the concentration of the solution for the case of regeneration of the prototype material (EI-12). At high concentrations of Na 2 SO 3 solution, there is a noticeable decrease in the content of sulfite ion in the anion exchanger (capacity), and, consequently, in the oxygen absorption capacity of the anion exchanger.

Claim

1. A method for removing oxygen from water, which consists in filtering water containing dissolved oxygen through an ion exchanger with subsequent regeneration, characterized in that filtration is carried out through a highly basic anion exchanger AM with a gel structure in SO 3 form, and the regeneration of the spent anion exchanger is carried out with a solution of sodium sulfite with concentration not higher than 8%.2. The method according to claim 1, characterized in that the contact time of the source water with the ion exchanger is at least 7.5 minutes.

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The invention relates to continuous installations for the desalination of sea, salt water and electrically conductive solutions and can be used for processing contaminated wastewater from industrial enterprises, including petroleum products, as well as for producing make-up water for boilers of thermal and power plants

The invention relates to methods for isolating heavy metal ions by sorption on cellulose-containing sorbents from solutions of various natures formed after various technological processes, and can be used to improve membrane and sorption technologies

The invention relates to the field of wastewater treatment and can be used for the purification of chromium-containing wastewater when organizing recycling water supply, for the purification of wash waters of galvanic production from heavy metals and a number of organic substances, the purification of oil-scale-containing wastewater, arsenic-containing solutions, for the purification of wastewater from mining and metallurgical enterprises , chemical and other industries

The water treatment process is often accompanied by the removal of gases such as carbon dioxide, oxygen and hydrogen sulfide. These gases are corrosive, as they have the ability to cause or enhance corrosion of metals.In addition, carbon dioxide is aggressive towards concrete, and the presence of hydrogen sulfide gives the water an unpleasant odor. Due to the above, the task of most completely removing these gases from water is urgent.

Degassing of water- this is a set of measures aimed at removing gases dissolved in it from water. There are chemical and physical methods of water degassing. Chemical methods of water degassing involve the use of certain reagents that bind gases dissolved in water. For example, deoxygenation of water is achieved by introducing sodium sulfite, hydrazine or sulfur dioxide into it. When sodium sulfite is introduced into water, it is oxidized to sodium sulfate by oxygen dissolved in water:

2Na 2 SO 3 + O 2→2Na2SO4

Sulfur dioxide introduced into water reacts with it and turns into sulfurous acid:

SO 2 + H 2 O → H 2 SO 3,

Which, in turn, is oxidized by oxygen dissolved in water to sulfuric acid:

2H 2 SO 3 + O 2 → 2H 2 SO 4

At the same time, modified solutions of sodium sulfite are currently used (reagents, etc.), which have a number of advantages in comparison with a pure solution of sodium sulfite.

Hydrazine promotes almost complete deoxygenation of water.

Hydrazine introduced into water binds oxygen and promotes the release of inert nitrogen:

N 2 H 4 + O 2 → 2H 2 O + N 2

Deoxygenation of water using the latter method is the most advanced, but at the same time, the most expensive method (due to the high cost of hydrazine). In this regard, this method is used mainly after physical methods of deoxygenation of water in order to remove residual oxygen concentrations. At the same time, hydrazine belongs to substances of the first hazard category, which also entails restrictions on the possibility of its use.

One of the variants of the chemical method is treating water with chlorine:

a) with the oxidation of hydrogen sulfide to sulfur:

H 2 S+Cl 2 → S+2HCl

b) with the oxidation of hydrogen sulfide to sulfates:

H2S+4WITHl 2 + 4N 2 ABOUT-> H 2 SO 4 + 8HCl

These reactions (as well as intermediate reactions for the formation of thiosulfates and sulfites) occur in parallel; their ratio is determined primarily by the dose of chlorine and the pH of the water.

Disadvantages of chemical gas removal methods:

a) The water treatment process becomes more complicated and expensive due to the need to use reagents. At large hourly flows through degassing with chemical reagents, despite the comparative simplicity of its implementation, it begins to lose significantly to thermal degassing in terms of operating costs.

b) Violation of the dosage of reagents leads to a deterioration in water quality.

These reasons determine the significantly less frequent use of chemical gas removal methods at large facilities than physical ones.

There are two main ways to remove dissolved gases from water by physical methods:

1) aeration - when water purified from gas is actively in contact with air (provided that the partial pressure of the gas being removed in the air is close to zero);

2) creating conditions under which the solubility of gas in water is reduced to almost zero.

Aeration usually removes free carbon dioxide and hydrogen sulfide from water, the partial pressure of which in atmospheric air is close to zero. Degassers that carry out aeration, depending on the design, the nature of the movement of water and air and the course of the degassing process, are divided into:

1) Film degassers (decarbonizers) are columns with a nozzle (wooden, Raschig rings, etc.) through which water flows in a thin film. The purpose of the nozzle is to create an extensive contact surface between water and air. The air pumped by the fan moves towards the flow of water;

2) They blow compressed air through a layer of slowly moving water;

The second method is used when removing oxygen from water, since it is clear that the first method will not work here due to the significant partial pressure of oxygen in the atmospheric air. To remove oxygen, water is brought to a boil, and a sharp decrease in the solubility of all gases in water occurs.

Bringing water to a boil is carried out:

1) by heating it (in atmospheric deaerators);

2) reducing the boiling point of water by lowering the pressure (in vacuum deaerators).

IN In atmospheric deaerators, preliminary deaeration is carried out in special deaeration columns for due to the excess amount of steam entering the deaeration tank through the supply steam line , and the final one - in deaeration tanks due to steam blowing. In vacuum degassers (deaerators), special devices (such as vacuum pumps or water-jet ejectors) create pressure at which water boils at a given temperature.

In the water treatment process, film degassers have found their main application in carbon dioxide removal processes to remove hydrogen sulfide (together with a number of other tasks - supplying oxygen as an oxidizing agent in , ) - bubbling, and for deoxygenation of water in the presence of steam sources at the facility - thermal, in the absence - vacuum.

The design of degassers involves determining the cross-sectional area of ​​the degasser, the height of the water column in it, the required air flow, the type and surface area of ​​the nozzle required to achieve a given degassing effect.

Purifying water from carbon dioxide is called degassing; this process can be chemical or physical. All natural water always contains dissolved gases, and some of them have a corrosive effect on pipes - such as oxygen, carbon dioxide and hydrogen sulfide. In addition, the latter gives the water an unpleasant smell of rotten eggs, and carbon dioxide can even actively destroy concrete. Therefore, one of the priority tasks is to get rid of these components during production.

Chemical degassing

In the process of chemical purification of water from carbon dioxide and other gases, reagents are used that chemically bind gases dissolved in it. For example, you can remove oxygen from water by adding sulfur dioxide, sodium sulfite or hydrazine.

Sodium sulfite is oxidized by oxygen to sulfate; sulfurous acid is first obtained from sulfur dioxide, which is oxidized to sulfuric acid. It is almost completely possible to purify water using hydrazine - when reacting with it, oxygen is completely absorbed and inert nitrogen is released. The use of hydrazine is the most effective method of chemical water purification, but also the most expensive due to the high cost of the reagent. Therefore, it is most often used for the final degassing of water after using physical methods.

When removing hydrogen sulfide, chlorine is most often used, which oxidizes hydrogen sulfide to sulfur or sulfates. Both reactions occur in parallel, and the predominance of one of them depends on the pH of the medium and the concentration of chlorine.

Disadvantages of chemical methods for purifying water from carbon dioxide and other gases:

• the use of reagents increases the cost and complexity of the water purification process;
• An overdose of reagents leads to a deterioration in the quality of the treated water.

Because of this, chemical degassing is used less frequently than physical degassing.

Physical degassing

Physically dissolved gases can be removed from water in two ways:

1. bring the partial pressure of the removed gas to almost zero in the atmosphere in contact with water;
2. create conditions when the solubility of gas in water tends to zero.

The first method is called water aeration; it purifies water from carbon dioxide and hydrogen sulfide, which have a very low partial pressure in the atmosphere.

Oxygen, which makes up a significant proportion of the atmosphere, cannot be removed by aeration. Therefore, to remove it, the water is brought to a boil, at which point any gas tends to leave it. Water is either heated in thermal deaerators, or it is vacuumed until it boils in vacuum degassers.

There are several types of degassers, differing in design, the nature of air and water movement and the conditions of the degassing process:

• film degassers. These are columns filled with various nozzles through which water flows in a thin film. The nozzles repeatedly increase the surface of contact between water and air, which is supplied by a fan in the opposite direction;
• bubble degassers. In them, bubbles of compressed air pass through the thickness of slowly moving water;
• vacuum degassers. Here, a vacuum above the water is created by special devices until it begins to boil at the existing temperature.

In the field, film degassers are more often used, and thermal or vacuum ones are used to get rid of oxygen. The high cost of operating bubble degassers due to the high energy consumption for air compression limits their use.

The design of degassers should be based on the following parameters:

• cross-sectional area of ​​the apparatus, which depends on the permissible irrigation density of the nozzle;
• the surface area of ​​the nozzle required for effective degassing;
• air flow.

Purifying water from carbon dioxide, oxygen and hydrogen sulfide is an important stage in complex water treatment. This procedure allows you to get rid of harmful components that otherwise have a detrimental effect on expensive industrial equipment.