Chemical water treatment is one of the the most important factors boiler service life. The higher the quality of the water, the longer the overall water supply system will last you.
The main tasks of water treatment and rational organization of the water chemistry regime of boilers, steam generators, feed water path and heating networks are:
· Prevention of the formation of scale deposits, iron oxides, etc. on the heating surfaces of boilers, heat exchangers and other parts of heating systems,
· Protection against corrosion of structural metals of the main and auxiliary equipment of heating systems in conditions of their contact with water and steam, as well as when they are in reserve, long-term downtime or conservation.
Requirements for the quality of make-up and network water are established depending on the type of heating network:
For a heating network with an open water intake, the treated water must meet:
requirements for household and drinking water, the quality of which is regulated by SanPIN 2.1.4.559-96, in particular GOST “Drinking Water”. The value of total hardness should not exceed 7 mEq/l, iron - 0.3 mg/l, pH value - 9.0.
Water quality for a closed network determined by the type of heating equipment used (boiler, boiler, etc.). Due to the lack of direct water supply for the needs of the population, less stringent requirements are imposed on the quality of water for a closed network; the main task is to ensure scale-free operation of the heating equipment used (boilers, boilers) and the regulatory permissible level of corrosion activity. Thus, it may be acceptable to increase the pH value to 10.5 with simultaneous deep softening; the determining indicator is the value of the carbonate index, which in turn determines permissible level scale formation - not higher than 0.1.
The main indicator of scale-free mode is the value of the carbonate index - the product of total alkalinity and calcium hardness, which has different values for a given temperature regime.
The main modern methods of water preparation:
· Softening by Na-cation using modern methods of ion exchange, using filter materials and corresponding filter designs;
· Decarbonization of water using modern new types of filter materials (weak acid cation exchangers) and corresponding filter designs instead of H - cationization with “hungry” regeneration;
· Water purification using membrane water treatment technologies;
· Application of chemical treatment programs for make-up water using dosing of modern, more effective reagents (corrosion inhibitors, dispersants and scale inhibitors)
· Also a combination of all the above methods;
· Alternative methods- mainly various “hardness salt converters” based on physical methods water treatment;
Let's consider the use of the first two ion exchange methods - softening by Na-cation and decarbonization of water using modern new types of filter materials (weak acid cation exchangers).
Softening
The method of single-stage parallel-precise Na-cationization is most widely used. This process implemented in filters (of various designs and sizes depending on performance, requirements for the process itself, etc.). The ion exchange process itself occurs when water is filtered through a layer of ion exchange resin (which is a strong acid cation exchanger in the Na form), loaded into the filter and periodically, when exhausted, regenerated by the solution table salt. In this case, calcium (Ca2+), magnesium (Mg2+) salts are replaced with sodium (Na+) according to the following scheme:
Thus, instead of calcium (Ca2+), magnesium (Mg2+), an equivalent amount of sodium (Na+) is introduced. The result is softened water, but the alkalinity of the source water practically does not change during processing, and if its value is increased, the water will have enhanced corrosive properties due to the decomposition of alkalinity when heated. Strongly acidic cation exchangers like KU2-8 or sulfonated carbon, regenerated with table salt, are usually used as filter media.
The disadvantages of this method are:
· Increased (usually threefold) consumption of the reagent (NaCl salt) relative to stoichiometry;
· Increased water consumption for own needs;
· Increased content in discharge waters of chlorides and sodium often exceeding the norm;
· To obtain deeply softened water, a second stage is required;
Modern methods ionization and the use of new types of cation exchangers make it possible to significantly optimize the process of Na - cationization - reduce the consumption of reagents for regeneration, reduce water consumption for own needs, and reduce the number of equipment (filters) involved. These methods include countercurrent cationization, in which the filtrate and regeneration flows have opposite directions. In particular, almost the entire volume of the filter is used for loading cation exchange resin. The percentage of own needs is reduced to 3-4%, salt consumption is reduced by 15-20%. It becomes possible to obtain a filtrate after the first stage with a water hardness quality of no higher than 10–15 µg-eq/l, that is, the second cationization stage is eliminated. But this technology requires a high degree of organization of operation and automation of technological processes is desirable.
It should be especially noted that transferring a cation exchange resin from one form to another directly at the consumer not only leads to increased labor costs and additional consumption of water and reagents, but also often leads to a decrease in performance indicators, primarily the dynamic exchange capacity. The explanation for this is the very procedure of converting from the H-form to the Na-form, in which it is first necessary to “deplete” the cation exchanger by pouring acidic water into the sewer (which leads not only to wastewater pollution, but also to corrosion of pipelines), and only then twice regenerate with sodium chloride solution and convert to Na-form. It should also be noted that a strong acid cation exchanger in the H-form, when initial water is passed through it until “depletion”, in addition to hardness salts, captures other ions from it, including metal ions (iron, aluminum, etc.), which, with subsequent regenerations with a solution of table salt are not removed. Consequently, some of the functional groups are blocked, as a result of which the exchange capacity of the cation exchanger decreases after such procedures. These negative processes do not occur if cation exchangers in Na-form are specially used for water softening processes.
A further improvement of countercurrent processes was the development of ion exchangers in the form of monospheres, i.e. resins having a narrow fraction effective composition granules (the number of particles with an effective size of about 0.5-0.6 mm reaches 95%, whereas for conventional ion exchangers it is approximately 40-45%).
However, good results can be achieved if cation exchangers are used with the usual granular composition (0.3-1.2 mm), but manufactured and supplied to consumers in Na-form. For example, strong acid cation exchanger Tulsion T-42 in Na-form, with a fractional composition of 0.3-1.2 mm.
Decarbonization
When preparing make-up water for hot water supply systems, the water preparation technology N - cationization with “starvation” regeneration is also used.
The H-cationization technology with “hungry” regeneration can significantly reduce the carbonate hardness of water with a partial decrease in non-carbonate hardness. All hydrogen ions introduced into the cation exchanger with the regeneration solution are completely retained, and as a result there is practically no acid in the waste water. The consumption of the regenerating reagent - sulfuric acid - is stoichiometric, i.e. calculated.
The disadvantages of this method when using sulfonated coal in the H-form are reduced performance characteristics, in particular:
· Low speed filtering (up to 10 m 3 / h);
· Low exchange capacity (200-250 g-eq/m3), as a consequence
- high costs of reagents and water for own needs
-increased number of filters
- difficulty in controlling the process and, as a result, unstable water quality
There are weak acid cation exchangers, often called carboxylic cation exchangers, which are specifically designed to remove carbonate hardness i.e. decarbonization. These include, in particular, the weakly acidic cation exchanger Tulsion SKhO-12.
With the ion exchange method of decarbonization of water on a weakly acidic carboxyl cation exchanger to the hydrogen form (as the most economical), calcium salts (Ca2+), magnesium (Mg2+) are replaced with hydrogen (H+) according to the following scheme:
Thus, instead of calcium (Ca2+), magnesium (Mg2+), an equivalent amount of hydrogen (H+) is introduced. Next, the HCO3- anions interact with the resulting H+ cations.
As a result, the concentration of bicarbonates decreases through their “destruction” and the resulting formation of carbon dioxide. At the same time, the pH of the water decreases. Further, to stabilize the pH of the water, it must be blown off using a degasser.
For example, let’s consider a technological scheme that involves the use of a decarbonization process on a weakly acidic cation exchanger instead of H-cationization with “hungry regeneration” and softening on a strong acid cation exchanger supplied immediately in Na - form. Considering that the source of source water is drinking chlorinated water from the city water supply, to increase the service life of the cation exchangers, preliminary cleaning is provided in the form of a filter filled with activated carbon. After this, the water goes to three decarbonization filters filled with weakly acidic cation exchanger, one/two in operation, one in reserve. The resulting carbon dioxide after the ion exchanger is blown off in the degasser (decarbonizer) and enters through the deaerator for heating. Part of the decarbonized water is supplied to a two-stage softening unit to produce make-up water for steam boilers. Schematic diagram is presented in Figure 10, in the form of direct-flow filters with the organization of an upper distribution system and an inert layer to increase the efficiency of filtering and washing the cation exchanger.
Figure 10 - Fundamental technological scheme HVO boiler room
Figure 11 - Photo of the chemical treatment plant
The total amount of water added from chemical water treatment consists of the following losses:
1) Condensate losses from process consumers:
In the absence of condensate from process consumers kg/s.
2) Loss of purge water kg/s.
The effectiveness of a water purification method depends on how correctly the type of pollution is determined. In order to learn more about the type and concentration of foreign substances in water, chemical and bacteriological analysis is carried out.
Almost always, several contaminants are present in water at once, so a complex is used various methods cleaning, several filters mounted in series.
Chemical methods
Chemical methods of water purification are based on the use of chemical interactions between various elements and compounds. Reagents are selected strictly based on the results chemical analysis water. The reagents enter chemical reactions with contaminants, completely decomposing them, transforming them into a form that is safe for humans, or into a solid sediment retained by the filter.
You can set up a chemical filter (select reagents) very precisely - so that only harmful impurities are removed from the water. At the same time, the purified water will not be “dead” or sterile - it will still contain the salts necessary to maintain the water-salt balance in the human body.
Chemical methods of water purification in combination with mechanical filtration are the main ones for autonomous system water supply for a country house.
Capable of removing from water: hardness salts, dissolved iron, dissolved manganese, increased acidity, organic compounds, microbiological contamination, chlorides, sulfates, nitrates, nitrites, free carbon dioxide, free chlorine, silicon, dissolved gases.
Physical methods
Physical methods of water purification use one or another physical effect on water or pollution.
Capable of removing from water: coarse particles, microparticles, suspensions, colloids, dissolved gases, hardness salts, salts heavy metals, free chlorine, microbiological contamination.
Ultraviolet
Ultraviolet radiation can kill all microorganisms in water. The physical effect is that the wavelength of UV radiation effectively destroys cells pathogenic bacteria. Passing through the filter, the water flows around from all sides ultraviolet lamp, protected by quartz glass. This effect makes the UV emitter one of the most effective water sterilizers.
Capable of removing from water: microbiological contamination of any type and level.
Thermal method
The process is based on the phenomenon of the transition of heated water into the vapor phase and the subsequent condensation of steam into liquid. At the same time, the level of salt concentration in the water changes. Boiling is the simplest way to partially soften water. At high temperatures, calcium bicarbonate (hardness salt) breaks down into carbon dioxide and calcium carbonate, the same white coating in the kettle. Heating water to 100C also reduces hardness caused by the presence of calcium sulfate.
Capable of removing from water: hardness, organic compounds, microbiological contamination.
Reverse osmosis
Under the influence of osmotic pressure, water containing contaminants penetrates through a special polymer membrane. The polymer membrane allows only water and oxygen molecules to pass through, retaining molecules of all foreign solutes, as well as bacteria and viruses. The reverse osmosis filter will not work if the pressure in the water supply is less than 2.5-3 atm.
Capable of removing from water: microparticles, suspensions, colloids, bacteria, viruses, molecules, ions, hardness salts, iron, manganese, total alkalinity, dissolved gases, chlorides, sulfates, nitrates, nitrites, silicon.
Very often, cleaning methods combine several principles at once. Thanks to this, physicochemical methods of water purification are more versatile and highly effective.
Physico-chemical water purification
Based on the flotation effect, it effectively removes fine and colloidal particles from water. The gas is passed through the liquid mass of waste. In this case, each gas bubble, under the influence of molecular forces, “sticks” with a particle of pollution. Bubbles accumulate on the surface in the form of foam, which can be easily removed mechanically.
Another example of a physical-chemical purification method: the electrochemical method of water purification or coagulation. The phenomenon of sedimentation of colloidal particles when exposed to direct current is used. The method is widely used in industry - mining, processing, etc.
Capable of removing from water: organic matter, fine particles, suspensions, colloids, hardness salts.
Biological methods
Biological water treatment systems use the ability of certain microorganisms to partially or completely absorb various (most often biological) types of contaminants. This happens when the pollution provides a breeding ground for bacteria. Aerobic and anaerobic methods of wastewater treatment are well known. Two types of bacteria process the organic component of household wastewater from a country house.
The anaerobic method is more effective, since microorganisms develop more intensively in an oxygen environment. In addition, oxygen serves additional source reactions of oxidation and decomposition of organic matter.
Various types of bacteria are capable of processing different types pollution, including those that are not at all “edible” in our opinion: bacteria that eat plastic have recently been discovered.
Taking into account the accelerated development genetic engineering biological methods water purification will constantly develop, expanding the scope of application. Perhaps soon, thanks to omnivorous bacteria, humanity will finally get rid of giant landfills.
Capable of removing from water: organic matter, dissolved ferrous iron.
Physico-chemical methods of water purification
As the name suggests, water purification methods in this group combine chemical and physical effects on water pollutants. They are quite diverse and are used to remove a wide variety of substances. These include dissolved gases, fine liquid or solid particles, heavy metal ions, as well as various substances in a dissolved state. Physico-chemical methods can be used both at the pre-cleaning stage and at later stages for deep cleaning.
The variety of methods in this group is great, so the most common of them are given below:
- flotation;
- sorption;
- extraction;
- ion exchange;
- electrodialysis;
- reverse osmosis;
- thermal methods.
Flotation, as applied to water treatment, is the process of separating hydrophobic particles by passing a large number of gas bubbles (usually air) through water. The wettability of the separated pollutant is such that the particles are fixed on the interface between the phases of the bubbles and, together with them, rise to the surface, where they form a layer of foam that can be easily removed. If the separated particle turns out to be larger in size than the bubbles, then together they (particle + bubbles) form a so-called flotation complex. Flotation is often combined with the use of chemical reagents, for example, those that are sorbed on pollutant particles, thereby reducing its wettability, or that are coagulants and lead to the enlargement of removed particles. Flotation is primarily used to purify water from various petroleum products and oils, but it can also remove solid impurities, the separation of which is ineffective by other methods.
There are various options for implementing the flotation process, which is why the following types are distinguished:
- foam;
- pressure;
- mechanical:
- pneumatic;
- electric;
- chemical, etc.
Let us give an example of the operating principle of some of them. A widely used method is pneumatic flotation, in which the formation of an upward flow of bubbles is created by installing aerators, usually in the form of perforated pipes or plates, at the bottom of the tank. The air supplied under pressure passes through the perforations, due to which it is split into separate bubbles, which carry out the flotation process itself. In pressure flotation, the stream of purified water is mixed with a stream of water supersaturated with gas and under pressure, and fed into the flotation chamber. At sharp drop pressure, gas dissolved in water begins to release in the form of small bubbles. In the case of electroflotation, the process of bubble formation occurs on the surface of electrodes located in the water being purified when an electric current flows through them.
Sorption methods are based on the selective absorption of pollutants in the surface layer of the sorbent (adsorption) or in its volume (absorption). In particular, for water purification, the adsorption process is used, which can be physical and chemical character. The difference lies in the way the adsorbed pollutant is retained: through molecular interaction forces (physical adsorption) or through the formation of chemical bonds (chemical adsorption or chemisorption). Methods of this group are capable of achieving great efficiency and removing even low concentrations of pollutants from water at high flow rates, which makes them preferable as post-treatment methods at the final stages of the water purification and water treatment process. By sorption methods can remove various herbicides and pesticides, phenols, superficial active substances etc.
Substances such as activated carbons, silica gels, aluminum gels and zeolites are used as adsorbents. Their structure is made porous, which significantly increases the specific area of the adsorbent per unit volume, which is why the process is more efficient. The adsorption purification process itself can be carried out by mixing the water to be purified and an adsorbent, or by filtering water through a layer of adsorbent. Depending on the sorbent material and the pollutant being extracted, the process can be regenerative (the adsorbent is used again after regeneration) or destructive, when the adsorbent must be disposed of due to the impossibility of its regeneration.
Water purification using the liquid method extraction consists in the use of extractants. In relation to water purification, an extractant is an immiscible or slightly miscible liquid with water that dissolves pollutants extracted from water much better. The process is carried out as follows: the purified water and the extractant are mixed to develop a large phase contact surface, after which a redistribution of dissolved pollutants occurs in them, most of which passes into the extractant, then the two phases are separated. The extractant saturated with extracted pollutants is called extract, and purified water is called raffinate. The extractant can then be utilized or regenerated depending on the process conditions. This method mainly removes organic compounds such as phenols and organic acids from water. If the extracted substance is of a certain value, then after regeneration of the extractant, instead of disposal, it can be usefully used for other purposes. This fact promotes the application of the extraction method of purification to wastewater from enterprises for the extraction and subsequent use or return to production of a number of substances lost with wastewater.
Ion exchange It is mainly used in water treatment for the purpose of softening water, that is, removing hardness salts. The essence of the process is the exchange of ions between water and a special material called an ion exchanger. Ion exchangers are divided into cation exchangers and anion exchangers depending on the type of exchanged ions. From a chemical point of view, an ion exchanger is a high-molecular substance consisting of a framework (matrix) with a large number of functional groups capable of ion exchange. There are natural ion exchangers, such as zeolites and sulfonated carbons, which have been used in early stages development of ion exchange purification, but currently artificial ion exchange resins, significantly superior to their natural analogues in ion exchange capacity. The ion exchange cleaning method has become widespread, both in industry and in everyday life. Household ion exchange filters, as a rule, are not used to work with heavily contaminated water, so the resource of one filter is enough for cleaning large quantity water, after which the filter must be disposed of. At the same time, during water treatment, the ion-exchange material is most often subject to regeneration using solutions with high content H + or OH - ions.
Electrodialysis is a complex method combining membrane and electrical processes. It can be used to remove various ions from water and carry out desalting. Unlike conventional membrane processes, electrodialysis uses special ion-selective membranes that allow ions of a certain sign to pass through. The apparatus for carrying out electrodialysis is called an electrodialyzer and is a series of chambers separated by alternating cation-exchange and anion-exchange membranes into which purified water flows. In the outer chambers there are electrodes to which direct current is supplied. Under the influence of the resulting electric field, the ions begin to move towards the electrodes according to their charge until they encounter an ion-selective membrane with the same charge. This leads to the fact that in some chambers there is a constant outflow of ions (desalting chambers), while in others, on the contrary, their accumulation is observed (concentration chamber). By dividing the flows from different chambers, it is possible to obtain concentrated and desalted solutions. The undeniable advantages of this method lie not only in purifying water from ions, but also in obtaining concentrated solutions of the separated substance, which allows it to be returned back to production. This makes electrodialysis especially popular at various chemical plants, where some of the valuable components are lost along with the wastewater, and the use of this method is made cheaper by obtaining a concentrate.
Additional information on electrodialysis
Reverse osmosis refers to membrane processes and is carried out under pressure greater than osmotic. Osmotic pressure- excess hydrostatic pressure applied to a solution separated by a semi-permeable partition (membrane) from a pure solvent, at which diffusion of the pure solvent through the membrane into the solution stops. Accordingly, at an operating pressure above the osmotic pressure, a reverse transition of the solvent from the solution will be observed, due to which the concentration of the dissolved substance will increase. In this way, dissolved gases, salts (including hardness salts), colloidal particles, as well as bacteria and viruses can be separated. Also, reverse osmosis installations are distinguished by the fact that they are used to obtain fresh water from the sea. This type of cleaning has been successfully used both in living conditions, and in wastewater treatment and water treatment.
Additional information on reverse osmosis and reverse osmosis systems
Thermal methods are based on the effect of elevated or low temperatures. Evaporation is one of the most energy-intensive processes, but it produces highly pure water and a highly concentrated solution containing non-volatile contaminants. Also, concentration of impurities can be carried out using freezing, since it begins to crystallize first clean water, and only then the remaining part with dissolved pollutants. By evaporation, as well as by freezing, it is possible to carry out crystallization - the separation of impurities in the form of precipitated crystals from saturated solution. As an extreme method, thermal oxidation is used, when the purified water is atomized and exposed to high-temperature combustion products. This method is used to neutralize highly toxic or difficult to degrade pollutants.
Chemically purified water for feeding the heating network enters a vacuum deaerator (р - 0 02 - 0 05 MPa), in which hot network water serves as the heating working fluid.
Chemically purified water for feeding the heating network enters a vacuum deaerator (p 0 02 - 0 05 MPa), in which hot network water serves as the heating working fluid.
Chemically purified water is supplied to the deaerator to replenish condensate losses in the lines. To satisfy the boiler house's own needs, continuous blowdown water is also used. Water from the continuous blowdown line enters the RNP continuous flow expander, where it boils due to a drop in pressure. The resulting steam enters the auxiliary steam line, and water with increased salt content gives off heat raw water in PSV1 and removed to the sewer.
Chemically purified water from the chemical water treatment plant is supplied to the main building of the thermal power plant through two pipelines; each pipeline is designed for 100% supply of chemically purified water. Pipelines between the main building and the chemical water treatment plant are laid either in a channel or along a ground overpass. In addition to water, a compressed air pipeline is laid from the main building to the chemical water treatment room, which is required in all modern water treatment plants. Fittings on pipelines connecting containers and devices installed on outdoors, is located inside the chemical water treatment room. Water treatment equipment for industrial boiler houses is usually located in the boiler house building at level 0 0 (see chapter. The possibility of expanding chemical water treatment must be provided.
Steam supply diagram for coke plant.| Steam supply diagram for a coke plant with a control system in the absence of external sources parotep-losnabzhepiya. Chemically purified water for the water treatment plant is supplied from the water treatment plant of the thermal power plants of the metallurgical plant.
Chemically purified water (distillate) with an output hardness of 0 4 mEq/l, which meets the requirements for water supplied to humidification nozzles, can be obtained by two-stage filtration in sodium cation filters. C) the air humidification device is turned off, and the units are cooled using air coolers, the number of which depends on the air conditioner.
Additional chemically purified water is supplied through a separate line to the deaerators through water level regulators in the deaerated water tanks.
The mixture of chemically purified water and condensate entering the boiler is commonly called feed water.
The mixture of chemically purified water and condensate behind the feed pump is usually called feed water. About 65% of the heat of fresh steam supplied to the turbine and about 90% of the heat of steam exhausted in the turbine are carried away with the cooling water, which is uselessly lost.
Chemically purified water pipelines are laid in the soil below the freezing depth. In addition, pipelines can be laid above ground (on racks, astacades) - insulated, and with periodic flow, with steam traces.
The salt content of chemically purified water depends on the salt content of the source water and the adopted water treatment scheme. Proper organization The water regime of medium-pressure boilers in the presence of three-stage evaporation allows, in most cases, to ensure the required quality of chemically purified water without the use of a desalting stage.
The alkalinity of chemically purified water is a controlled indicator. When using chemically purified water to feed boilers high pressure reducing its alkalinity to a minimum significantly facilitates the organization of the water regime of boilers with phosphate alkalinity.
The supply of chemically purified water in the tank is sufficient for one and a half hour operation of the installation.
Chemically purified water brings in 50% of iron oxides due to corrosion of chemical water treatment equipment. Chemical water treatment equipment operating at relatively low temperatures, is subject to corrosion under the influence of dissolved oxygen, carbon dioxide and aggressive solutions used in the process of filter regeneration.
Deaerated and chemically purified water after cooling the elements lower structure The furnace is supplied to the feed tank, from where it is sent through the economizer to the boiler drum by the feed pump. Water is supplied from the boiler drum circulation pump into the evaporation coils of the waste heat boiler and into the cooled elements superstructure ovens.
When adding chemically purified water, the same indicators of feed water quality are also monitored; samples are taken every tea.
To prepare chemically purified water used as an additive to feed steam boilers of any pressure with shielded fireboxes, two-stage cationization must be used in combination with other stages of water purification. In addition, for boilers with a pressure of 70 ata and higher, desiliconization or chemical desalination of water should be used.
To prepare chemically purified water used as an additive to feed steam boilers of any pressure with shielded fireboxes, two-stage cationization must be used in combination with other stages of water purification. In addition, for boilers with a pressure of 70 hundred and above, desiliconization or chemical desalination of water should be used.
Oil dust trap. Chemically purified water is deaerated. Deaerated water is mixed with cooled network water passing through a heater and a coil located in the tank and enters the suction pipeline to the network pumps.
Pipelines for chemically purified water are laid without channels below the freezing depth of the soil. In addition, pipelines can be laid above ground (on racks, trestles), in isolation, and during periodic operation, with steam traces.
When chemically purified water is added, the accumulation of salts in the boiler is carried out at a rate no higher than 50 - 70 mg / kg-hour in the boiler water of the clean compartment, and with stepwise evaporation in the salty compartments 200 - 300 mg / kg-hour and is brought to the appearance of surges that are recorded salt meters.
When adding chemically purified water, the same indicators of feed water quality are also monitored; samples are taken every hour.
The excessive hardness of chemically purified water, reaching 43 mcg-eq/l, and the high salt content of steam were the source of many problems with boilers, turbines and steam shut-off valves, creating additional difficulties during repairs (the need for frequent pipe grinding, etc.
The hardness of make-up chemically purified water is determined by the oleate method with a calibration curve (according to VTI) or the complexometric method.
Deaeration of additional chemically purified water and production condensate containing greatest number dissolved gases is carried out according to a two-stage scheme.
It is possible to heat chemically purified water with steam in a steam-water heater.
The economizer heats chemically purified water. Along the water path, it is installed between the cold water treatment unit and heat exchangers designed to heat softened water before the deaerator.
Fill the tank with chemically purified water.
Chemically purified water of 35 C entering the deaerator is heated to a temperature of 60 C due to the heat of condensation of the vapor mixture, at which deaeration is carried out. Non-condensed vapors and gases are sucked out of the deaerator by an auxiliary ejector and pumped into an auxiliary condenser, where water is also deaerated (cooling medium - chemically purified water). The exhaust steam is condensed, and non-condensed vapors and gases are released into the atmosphere. Deaerated water from the auxiliary condenser and deaerator flows into a container and is sent to consumers by pump. The use of such combined installations makes it possible to reduce overall steam consumption and eliminate consumption recycled water for a capacitor.
Schematic diagram of columnless three-stage deaerators (DSP-6 and DSP-13. In the mixing chamber, chemically purified water is mixed with condensate and then supplied to the bubble sheet. By an ascending flow of steam, water is picked up into the lifting shaft, from the upper part of which, through circulation channels formed by partitions, it is again directed downwards, falling onto the bubble sheet. Thus, stable circulation circuits are created in the circulation shaft 15. From the upper bubbler device, water is discharged through the lower tray 16 into the accumulating part of the deaerator. A constant circulation of water is maintained in the accumulating part of the deaerator, which is provided by the lower bubbler. device.
Chemically purified water is also supplied here to replenish water lost during the process, as well as to dissolve the soda that adheres to the walls of the drums.
In the mixing chamber, chemically purified water is mixed with condensate and then supplied to the bubble sheet. By an ascending flow of steam, water is picked up into the lifting shaft, from the upper part of which, through circulation channels formed by the partitions, it falls down, again falling onto the bubble sheet. Thus, stable circulation circuits are created in the circulation shaft 15.
The cooling medium is chemically purified water.
The quality of demineralized or chemically purified water for feeding drum boilers, as well as the quality of the on-site components of the feed water of once-through and drum boilers (condensates from regenerative, network and other heaters, water from drainage tanks, tanks of low points, condensate reserve tanks and other flows) must be such that to ensure compliance with feedwater quality standards.
At high flow rates of chemically purified water to feed heating networks, hot industrial and domestic water supplies, its heating before the vacuum deaerator can be carried out in the condensers of steam turbines operating with a low (deteriorated) vacuum. In this case, chemically purified water replaces the cooling circulating water.
The medium from the chemically purified water pipeline is pumped through the calorimetric pipes. To measure water flow, restriction devices are installed at the inlet of each pipe. Boiling of water in the pipes is not allowed, which is controlled by two thermocouples installed in the unheated zone at the outlet of each pipe. The water flow is adjusted so that the water is underheated to the saturation temperature by 5 - 10 C. The calorimetric circuit can be mounted without a pump by taking feed water up to the economizer and discharging it into the economizer outlet manifold or into the drum.
The chemically purified water system is fed via line 7 to the buffer tank. The pressure in front of the network pumps 3 in this scheme is determined by the height of the water column from its level in the buffer tank to the network pumps.
With a large addition of chemically purified water under the conditions of a thermal power plant for effective removal Two-stage deaeration is used from CO2 water. In this case, the second stage is a bubbling device located in the storage tank. In a bubbling device, steam is passed through a layer of water, resulting in a significant contact surface between steam and liquid and turbulization of the liquid.
Deaerator automatic control circuit high blood pressure with the supply of additional water to the turbine condenser.| Scheme of automatic control of high-pressure deaerators at power plants with cross connections with the installation of individual pressure and level regulators. GRES, the addition of chemically purified water will be extremely small, as a result of which it can easily flow into the turbine condenser.
Heating of this amount of chemically purified water to a temperature in the deaerator of 6 atm was taken into account when drawing up the regime diagrams and, therefore, does not need to be taken into account separately.
The boilers are fed with a mixture of chemically purified water and condensate. The water treatment scheme is two-phase: preliminary liming with coagulation and sodium cationization.
At the beginning of the process, chemically purified water or condensate from the collection / is supplied by a centrifugal pump through the refrigerator 7 into the system. Then in bottom part Ammonia is introduced into absorber 4 (stage I), the resulting ammonia water flows into collection 3, located under the absorbers and separated by a partition.
These waste heat boilers are fed with chemically purified water and steam low pressure used in a regenerative circuit to heat feedwater.
Determination of the exchange capacity of a cation exchange resin for cobalt. The pre-evaporated residue is diluted with chemically purified water in a mixer, heated to 145 - 165 C in a heat exchanger and sent to the extractor. Aromatic compounds (acids, aldehydes, high-molecular-weight products of oxidative condensation of l-xylene), when the temperature of the reaction mass in the refrigerator decreases, precipitates (up to 90%) from the solution, after which the solid phase precipitates from the resulting suspension on filter 1. The aqueous solution of the catalyst is sent to the stage of concentration and purification of cobalt or a mixture of cobalt, manganese and nickel.
The prepared solution is diluted with chemically purified water to a concentration of 70 - 90 g/l for AlgOg, then it is separated from undissolved particles of alumina hydrate, pumped out of the reactor and used to precipitate aluminum hydroxide. The undissolved part of the alumina hydrate remains in the reactor to prepare the next portion of the basic aluminum sulfate solution.
When feeding evaporators with chemically purified water with a total salt content of more than 2000 mg/l, it is recommended that the evaporated water be phosphated.
Individual cleaning of superheater coils. Then the superheater is filled with chemically purified water at a temperature of 50 - 70 C, which is supplied through a special flushing pipeline with a diameter of 38 - 50 mm. Cover the access of water to the superheater and purge.
The steam converters are powered by chemically purified water.
For problem 9 - 31.| For problem 9 - 34. The loss of condensate is covered by chemically purified water having a temperature of / IBM 90 C.
When feeding evaporators with chemically purified water with a total salt content of more than 2,000 mg/kg, phosphating is allowed.
Water from wells and natural sources has a number of dissolved components and suspended matter. To obtain a liquid that can be used in industry, for household purposes and for drinking, it must be thoroughly purified. Modern methods of water purification are very diverse. They are divided into several groups according to the nature of the processes occurring. Using methods, devices are created that provide optimal cleaning. This process requires integrated approach, therefore several suitable methods are used at once.
Rice. 1 Some water treatment methodsPhysical methods are based on appropriate physical processes affecting water and the contaminants present. Typically, such methods are used to eliminate insoluble, large inclusions. Sometimes they also affect dissolved substances and biological objects. The main physical methods of purification are boiling, settling, filtering and ultraviolet treatment.
Boiling
During the boiling process, water is affected high temperature. As a result of this effect, microorganisms are eliminated, some dissolved salts precipitate, forming scale. With prolonged boiling, more stable substances, for example, chlorine compounds, can decompose. The method is simple and optimal for use at home, but it purifies only relatively small volumes of water.
Advocacy
In this case, the effect of natural gravity on relatively large mechanical inclusions is used. Under the influence of their own gravity, they sink to the bottom of the container, forming a layer of sediment. Water is settled in special settling tanks. These containers are equipped with devices for collecting and removing the resulting sediment.
Filtration
When water passes through material with pores or other holes, some of the contaminants are retained. Particles that are larger than pores or cells remain on the surface. Based on the degree of purification, there are coarse and fine filtration. Coarse cleaning only retains large particles. The fine process retains inclusions that are only a few microns in size.
Rice. 2 Filtration levels Ultraviolet treatment
Usage ultraviolet radiation allows you to eliminate biological contaminants. Light in this spectrum affects basic molecules, which leads to the death of microorganisms. It is worth considering that water that is purified from suspended matter is treated with ultraviolet light, i.e. made preliminary . Solid inclusions create a shadow that protects bacteria from ultraviolet light.
Chemical methods of water treatment
Chemical methods of water purification are based on oxidation-reduction and neutralization reactions. As a result of the interaction of special reagents with pollutants, a reaction occurs, the result of which is an insoluble precipitate, decomposition into gaseous components, or the appearance of harmless components.
Neutralization
The use of this method ensures the elimination of acidic or alkaline environment and its indicators approaching neutral. Reagents are added to water with a certain acidity level to create an acidic or alkaline environment. To neutralize the acidic environment, use alkaline compounds: soda ash, sodium hydroxide and some others. To eliminate the alkaline environment, solutions of certain acids or oxides of carbon, sulfur and nitrogen are chosen. The latter, when dissolved in water, form weak acids. Neutralization reactions are usually . In preparation drinking water from natural sources, no change in reaction is required; it is initially close to neutral.
Oxidation and reduction processes
Oxidation is most often used in water purification. In the process of reaction with oxidizing agents, polluting compounds are converted into harmless components. They can be solid, gaseous or soluble. Chlorine compounds, ozone and some other substances act as strong oxidizing agents.
Rice. 3 Ozone oxidation unit Water purification using physical and chemical methods
Water purification methods belonging to this group include both physical and chemical methods of influence. They are very diverse and help remove a significant part of the contaminants.
Flotation
In the process of water purification by flotation, a gas, such as air, is passed through the liquid. Bubbles are created, onto the surface of which hydrophobic contaminant particles adhere. Bubbles rise to the surface and form foam. This layer of foam with dirt is easily removed. Additionally, reagents that increase hydrophobicity or adhere and enlarge contaminant particles can be used.
Rice. 4 Principle of flotation Sorption
Water purification by the sorption method is based on the selective retention of substances. Adsorption is most often used when retention occurs on the surface of the sorbent. Sorption can be physical or chemical. In the first case, the forces of intermolecular interaction are used, and in the second - chemical bonds. The sorbents are usually activated carbon, silica gel, zeolite and others. Some types of adsorbents can be recovered, while others are disposed of after contamination.
Extraction
The extraction process is performed using a solvent that does not mix well with water but is better at dissolving contaminants. Upon contact with the liquid being purified, contaminants are transferred to the solvent and concentrated in it. In this way, organic acids and phenols are removed from water.
The ion exchange method is mainly used to remove hardness salts from water. In some cases it is used to eliminate dissolved iron. The process involves the exchange of ions between water and a special material. Such materials are special synthetic ion exchange resins. This method of water purification has become widespread not only in industry, but also in everyday life. Nowadays it won’t be difficult to purchase a filter with an ion exchange cartridge.
Rice. 5 Ion exchange
Another way in which this is done is reverse osmosis. Cleaning requires a special membrane with very fine pores. Only small molecules pass through the pores. Contaminants are larger than water molecules and therefore do not pass through the membrane. This filtration is performed under pressure. The resulting solution of pollutants is disposed of.
Rice. 6 Reverse osmosis Methods used in household filters
All these methods are used to purify liquids, including wastewater. But in most cases, people are interested in how to purify water at home for food and household purposes. Purifying water at home does not involve using all of the above methods. Only some of them are implemented in modern devices. It is possible to purify tap water without a filter. This method is boiling. However, much more often water is cleaned with specialized filtering devices.
The filters use drinking water purification methods such as mechanical filtration, ion exchange, sorption, reverse osmosis. Sometimes some others are used, but much less frequently.
All these modern methods Water purification is implemented in cartridge flow filters. In such devices they clean tap water in several stages. At the first stage, mechanical filtration is carried out, then dissolved substances are eliminated by sorption and ion exchange methods, and finally the water can be passed through a reverse osmosis membrane.
