Water and its application. Water use in industry

Industry cannot exist without water. It is based on "wet" technologies. Water is needed to produce steam, as well as for many processes: for cooling, washing, maintaining the concentration of chemicals in solutions, etc. Water is used as an industrial raw material, since the entire periodic table is contained in salty underground, lake and sea waters.

To meet all the needs of industry, 1000 km3 of water is annually taken from lakes and seas. Approximately half of this water is used in thermal power plants for steam and cooling, and the rest in other industries.

In fact, industry uses much more water than it takes from water sources, since since the second half of the 20th century. the use of the so-called circulating water supply began, which means the repeated use of the same water, once taken from a water source after its next purification. Of course, part of the water is lost to evaporation and filtration, and these losses have to be replenished, but they are quantitatively significantly inferior to the volumes of water that would have to be taken from the rivers. So, in Russia, the circulating water supply is 170 km3 per year, and only 70 km3 is used for industrial needs. Thus, about 4,400 km3 is withdrawn annually from natural waters for domestic, agricultural and industrial needs. This is only 1/10 of the annual rivers, 1/20 of the volume of fresh water in lakes and a completely negligible part of the fresh water supply in. It would seem that this cannot significantly affect water bodies. But in some parts of the world, water withdrawal seriously affects the environment. So, in the rivers of the Amu Darya and almost completely give their water for water supply, and therefore the sea disappears. In for the same reason, the Colorado River almost completely dried up in the lower reaches.

To use water, you need. The most common of them are dams, with the help of which artificial flowing lakes - reservoirs are created. Another well-known structure is canals that divert water from a river or reservoir. The 20th century can be called the century of dam construction, creation and canals, including the largest ones, which were built mainly in the second half of the 20th century. They are essential for energy, irrigation, water supply, flood protection and fisheries.

Large multi-purpose reservoirs, and especially cascades of reservoirs on a river or in the same basin, significantly change the state of the environment, disrupting the stability of aquatic ecosystems. But even the cascade of large reservoirs did not cause as many changes as economic activity throughout the entire basin of this river.

Water is quite widely used in industry, along with all other minerals and elements that are on Earth, water is consumed the most. Most often this applies to various industrial complexes that are engaged in metallurgy, chemicals, oil refineries and many others, they use water in 70% of cases, the remaining 30% is used by industry that directly manufactures food and so on. If we take the use of water as an example, the simplest will be metallurgical shops, in which water is used to wash parts and other things, most often the water used is clean, which is suitable for drinking. This is as important as preventing the cost of drinking water, and especially the return of water back to the source. We are talking about the fact that after the use of water for washing and other purposes, the water is returned to rivers, lakes, etc. However, the main problem is that enterprises may not be equipped with high quality and fully in order to return purified water to the source. This leads to water pollution and the continued use of drinking water in the same quantity. If the systems of purification and water supply are taken care of in a timely manner, it will be possible to avoid many causes of pollution, as well as save the water that is used, since after cleaning the water can be reused, which will provide a kind of water cycle in the enterprise with lower costs for obtaining a new one.
There are extremely many varieties of water purification, it all depends on the amount of water that needs to be purified, the substance from which it needs to be purified, and so on. Of course, purification systems are not cheap and many save on this, but in the end, someone earns money, and someone loses health after drinking poor-quality water. All this can be avoided and remain in your interests if you take care of the water supply, sewerage and water purification system.

The most common cleaning methods are mechanical, biological, physico-chemical and others. All methods speak essentially for themselves. During mechanical cleaning, water is purified from various large particles that may be in the water after use, for example, grains of any metal or sand, and so on. Biological is more aimed at purifying water from various microorganisms that may be in water after use in industry. Physico-chemical treatment is designed to purify various impurities and biological organic substances. Also quite often they can use a kind of clarifier to purify water.
The correct and most importantly humane attitude to water is very important, since in any case this water will be used for drinking and cooking. So if you see a violation of sanitation standards or how some enterprise dumps wastewater into rivers and lakes, make sure the government knows about it, because it is you who can end up drinking this water and ruining your health. Apart from industry, water plays a very important role in everything. For example,

Water and its role in industrial production

Water is of key importance in the processes of the emergence of life on Earth and its constant maintenance, since it is water that forms the climate, and it is also necessary for the chemical processes that occur in the bodies of people and animals. The role of water in people's lives cannot be overestimated. The main consumers of fresh water are: agriculture, industry, including energy and utilities. In industrial production, the most water-intensive are the chemical, pulp and paper and metallurgical industries. So, for the manufacture of 1 ton of synthetic fiber, 2500 ... 5000 m3 of water is spent, plastics - 500 ... 1000, paper - 400 ... 800, steel and cast iron - 160 ... 200 m3 of water. For industrial purposes, from 8 to 20% of all water used in the world is consumed from various sources, of which over 85% of water is consumed in cooling processes. The rest is consumed in the processes of washing, washing gases, for hydrotransport and as a solvent. Approximately half a million liters of water is used to produce each passenger car; this quantity includes both consumable water and reused water.

At the moment, the quality of water in different regions of the country can vary greatly (it all depends on the population, rivers, runoff, the presence of large enterprises), but in general, water cannot boast of high quality. To improve the quality of water purification, it is necessary to use the most modern technologies, and to make the purification process truly complex and to carry out water treatment. In the production and release of products, the quality of water determines the characteristics of the final product. This is achieved either by removing substances harmful to the equipment used or the finished product from the water, or by cooling. Prepared water, after undergoing chemical treatment and (or) cooling in industrial equipment, enters directly into the production cycle.

Industrial water treatment.

Water treatment is a cycle of measures for water purification, which is carried out with the help of softening, iron removal plants, as well as with the help of sorption, sedimentation plants and UV disinfectors. Using such automated equipment for industrial water treatment, it is possible to make water treatment an almost continuous process that does not slow down production and provides all stages of work with water of the required quality.

Experts identify the following main problems facing industrial water treatment: water hardness, a large number of impurities, color, swing, the presence of bacteria and viruses, and other contaminants. Industrial water treatment can include a range of purification measures. One of the main negative characteristics of water is the high iron content, which affects both the operation of water-using equipment and human health (if it is, for example, the food industry), since precipitation lingers in the body for a long time and affects its daily functioning.

Industrial water treatment is not only a significant improvement in the quality of manufactured products and an extension of the service life of equipment, but also a reduction in the impact of harmful substances on the environment by reducing harmful drains. The main purpose of industrial water treatment is water purification for enterprises and facilities with high water consumption per day. Water treatment, depending on the requirements of the consumer, both general and post-treatment are used. General cleaning includes cleaning of iron and hardness salts. Post-treatment is the desalination of water and its complete softening.

To provide water to enterprises that place high demands on water quality, such as medical institutions, pharmaceutical and food facilities, sports complexes and children's institutions, a multi-stage purification system is used. Now almost all food and meat and dairy enterprises of the Russian Federation are reconstructing with the replacement of worn out or obsolete equipment with new samples of imported and Russian production. In this regard, the approach to source water coming through citywide or other general-purpose water supply networks, or water coming from artesian wells, is changing significantly. The systems use reagent water treatment - to destroy dangerous microorganisms contained in water, desalination using reverse osmosis and ion exchange, as well as selective ion exchange technologies.

At especially large enterprises of heavy industry, equipment is used in technological cycles, during the operation of which it is required to cool it. For this purpose, such enterprises often use recycling water supply systems, but during the operation of these systems, problems arise with the composition of the make-up water and pollution of the wastewater from the recycling water.

iron removal- the process of rapid water purification using an iron remover, which is produced in two main variations. Special substances are poured into the reagent iron remover used in everyday life and in industrial water treatment to improve and accelerate iron removal. Reagent-free iron remover for industrial water treatment performs water treatment by the catalytic method.

In addition to iron removal, industrial water treatment is often carried out water softening which is carried out using specialized equipment. Hard water is not only contraindicated for drinking, without water treatment it also affects the operation of the equipment, as the heating elements quickly overgrow and eventually break. Water softening during industrial water treatment is carried out using the method of ion exchange, reagent softening or nanofiltration, which, even with continuous water treatment, cope with calcium and magnesium ions, which are detrimental to subsequent water treatment equipment.

Sometimes there is a need water treatment through water treatment from large residual elements, impurities or visible particles. For such water treatment, special sedimentation plants are used to remove sand, rust or other materials from tap water or water extracted from wells. That is, sedimentation technology is engaged in mechanical water treatment, which is important, for example, for utilities and various enterprises.

For a number of industries, water purification from metals and various salts is insufficient, since there is a need for full-fledged industrial water treatment with the removal of any, even the smallest impurities. For this, they are used sorption water treatment plants, specializing in the active treatment of waste and other waters from settled small particles with a size of 5 microns. This stage of industrial water treatment follows, as a rule, a coarser water purification from colloidal impurities. Sorption water treatment plants operate through the use of synthetic fibrous materials such as polyester petals and polypropylene threads.

An important step in industrial water treatment is additional purification from bacteria, viruses and other harmful elements, affecting water performance and its ability to be consumed and used in production. One of the most modern solutions to this issue has become ultraviolet lamps for industrial water treatment. This allows the use of UV disinfectors in water treatment at food processing plants, where the removal of harmful elements and water treatment are essential for simple safety and safety of the final product.

Industrial water treatment includes the importance of monitoring the acid-base indicators of water. For example, a liquid with a high pH level has a negative effect on equipment that breaks down when using untreated water for a long time. Moreover, unbalanced water is harmful to health, and many chemical processes in water that has not undergone water treatment and balancing of acid-base indicators are either impossible or do not occur at full strength. Thus, pretreatment of water from acids and normalization of the pH level will ensure the safety of equipment (including other water treatment devices) and a significant improvement in the quality of the water itself.

Nowadays, the problem of water purification is becoming more and more relevant. This applies to both drinking water purification and industrial water treatment. Of course, different industries require one or another degree of water purification. But in any case, if you need to get the best quality water, without impurities of salts and other components, ordinary filtration alone is not enough.

Modern technologies based on the principle of reverse osmosis make it possible to purify water at the molecular level. And free it not only from salts, but also from all sorts of organic compounds, including viruses and bacteria. desalination of water, or demineralization, is a very important physical process of removing salts when using water in technological processes of boilers, steam generators, food, medical and other installations, to prevent scale and rapid wear of equipment. Due to desalination, water treatment reduces the concentration of salts and minerals to a predetermined value, and makes the source water suitable as a drinking, cooling, or technological liquid.

Direct osmosis is used on the use of membranes capable of passing only water molecules, while retaining all other molecules. By dividing by such a membrane, for example, two communicating vessels with more or less pure water, one can see that the water level in the vessel with less pure water will rise over time. This will happen due to the fact that only water molecules will flow through the membrane, trying to balance the concentration in both vessels. This is the phenomenon of direct osmosis. It logically follows that if pressure is created in a more "dirty" vessel, then water molecules will flow, on the contrary, into a "cleaner" vessel, making the water even purer. And this is the principle of reverse osmosis.

Thus, using such membranes together with pre-filters, it is possible to create a highly efficient water treatment system for enterprises based on the principle of reverse osmosis. In other words, the reverse osmosis process is based on the passage of water through a membrane from a more saturated salt solution to a less saturated solution under the action of a pressure that exceeds the difference in osmotic pressure values in both solutions.

Use of recycled water.

The intensive development of industry and agricultural production, the improvement in the level of improvement of cities and towns, and a significant increase in the population in recent decades have led to a shortage and a sharp deterioration in the quality of water resources in almost all regions of Russia.

One of the main ways to meet the needs of society in water is the engineering reproduction of water resources, i.e. their restoration and enhancement not only quantitatively but also qualitatively.

Prospects for the rational reproduction of technological water consumption are associated with the creation of repetitive-sequential, circulating and closed water supply systems at enterprises. They are based on the amazing property of water, which allows it not to change its physical essence after participating in production processes.

The industry of Russia is characterized by a high level of development of circulating water supply systems, due to which the saving of fresh water used for production needs is on average 78%. The best indicators of the use of circulating systems are enterprises of the gas (97%), oil refining (95%) industries, ferrous metallurgy (94%), chemical and petrochemical (91%) industries, mechanical engineering (85%).

The maximum water consumption in the systems of circulating and re-sequential water supply is typical for the Ural, Central, Volga and West Siberian economic regions. In general, in Russia, the ratio of the volumes of fresh and recycled water use is 35.5 and 64.5%, respectively.

The widespread introduction of perfect water circulation systems (up to closed ones) can not only solve the problem of water supply to consumers, but also keep natural water sources in an environmentally friendly state.

Water is a substance that is in a liquid state, it is colorless, transparent, odorless, it can change shape (for example: if you tilt the test tube, then the water will change shape), it enlarges objects (example: my fingers, with which I hold the test tube, appear larger when viewed through a test tube of water) and can dissolve various substances.

The property of transparency of water can be proved by placing different pictures or even a page with text behind a test tube with water - you can see what is behind the test tube. This experiment proves that glass is also transparent. It can be proved in another way. Put the picture on a plate and pour water into it. You can also see what is in the plate filled with water. This experience also proves the property of water - transparency. The property of water transparency is used by a person very widely: aquariums with outlandish fish and algae, pools and fountains with a beautiful design of the bottom and walls, and more.

Water has no smell. You can sniff and be sure. A person uses this property of water, for example, when escaping from pursuing predatory animals: once you enter the water, the trace of a person will be lost, the animal will not be able to determine the direction of movement of a person who has entered the water.

Water takes the form of the container into which it is poured (for example: pour water from a glass into laboratory flasks of various shapes). This property of water is also widely used by man. For example: by pouring water into a container, you can thereby emphasize the originality of this container, its design and beauty.

Water is flowing. For example: if you pour it on a flat tray, it spreads into a puddle. This property of water is widely used by man in housing and communal services: water, flowing through pipes, enters our houses and apartments.

Objects in the water appear larger than they really are. This can be seen by looking at how the part of the image that is visible through the water has increased. Or maybe this glass magnifies? No, because the fish in the aquarium also seem larger if you look only through the water.

Water can dissolve various substances. If crushed chalk is poured into a test tube, the water will become cloudy because part of the chalk has dissolved in the water.

Water is an excellent solvent and therefore it is impossible to find liquid "pure" water in nature, that is, water in which no substances are dissolved. Water is a wonderful habitat for living organisms, and therefore it is impossible to find "clean" water in nature, i.e. water in which microbes, bacteria, mollusks, fish, etc. would not live.

Water does not dissolve all substances. If you pour vaseline oil into a test tube with water, it will not mix with water, but will float on top of the water.

Water can be purified with a filter. If you put a paper napkin or cotton wool in the funnel and pass water in which chalk is dissolved through it, you can see that the water has become cleaner. If you do this a few more times, the water will become completely transparent.

It is well known that life on planet Earth arose due to the presence of water. Life originated in the water, emerged from it, gradually populating the land and air. Water forms the water shell of our planet - the hydrosphere (from the Greek words "gidor" - water, "sphere" - a ball). Water covers three quarters of the Earth's surface. In nature, it fills the bowls of the oceans, seas, lakes, rivers, swamps. There are also artificial reservoirs for storing and transferring water - ponds, reservoirs and canals. Water is also present in the depths of the Earth and in its atmosphere.

All plants and animals need water to survive. Our bodies are approximately 75% water. Without water, our body simply cannot function.

Without water, life on planet Earth is unthinkable, human life is unthinkable. Water is the most common, accessible and cheap substance. It is the availability and indispensability of water that has led to its widespread use in everyday life, industry and agriculture, medicine - in all spheres of human activity. It is difficult to remember where water is not applied.

Water is the biggest and most convenient road. Vessels sail on it day and night, carrying various cargoes and passengers. Water also feeds - thousands of fishing boats sail the seas and oceans.

In thermal power engineering, water is a heat carrier and a working fluid. Water "produces ” electric current, working in power plants. Thermal power plants use a lot of water to generate electricity. In particular, for cooling the turbine condenser of the power unit. A constant uncontrolled increase in electricity production only at thermal power plants can lead to an environmental disaster.

In metallurgy, water is used to cool equipment. Just for cooling one blast furnace, a huge amount of water is used every hour.

In chemistry, water is a solvent; one of the components of some chemical reactions; "vehicle", that is, a medium that allows you to move the constituent products of the reaction from one technological apparatus to another. Ultimately, the release of liquid production waste into the environment is also carried out in the form of aqueous solutions.

In medicine, water is a solvent, a medicine, a means of sanitation and hygiene, a "vehicle". An increase in the level of medical care and an increase in the population of the planet Earth naturally leads to an increase in water consumption for medical purposes.

In agriculture, water is a "vehicle" of nutrients to the cells of plants and animals, a participant in the process of photosynthesis, and a regulator of the temperature of living organisms. The volumes of water that are spent for irrigation of agricultural plants, when feeding animals, birds, are not inferior to the volumes used by the industry.

In everyday life, water is a means of sanitation and hygiene, a participant in chemical reactions that occur during cooking, a heat carrier, a "vehicle" that removes human waste products into the sewer. Water washes all people, cars, roads. The rate of water consumption per person is significantly different in individual cities. Think of the approximately 6 billion people who inhabit planet Earth and it will become clear to us why from time to time there is talk of ever-increasing problems with drinking water, even in regions of the planet where there is a lot of water.

Without water, you cannot knead dough for bread, you cannot prepare concrete for construction, you cannot make paper, fabric for clothes, rubber, metal, sweets, plastic, medicines - nothing can be done without water!

Water is the only substance on Earth that exists in different states at once: water can be liquid, when cooled it turns into a solid state - ice, and when heated it turns from liquid to vapor.

Let's track the "feedback" between the water consumed by a person and the set of dissolved substances, solid inclusions and microorganisms that are discharged in the form of domestic wastewater, liquid waste from industrial and agricultural production. For example, 200 years ago, only organoleptic methods were used to assess the quality of drinking water: assessment of color, taste, smell. Now the list of analyzes performed by the sanitary laboratory of a food industry enterprise is placed on two pages filled with small print. What are the methods of water treatment and water purification so that a person can use water for the right purposes?

Let's start with the concept: what is water treatment and water purification? Let's turn to reference literature. The Encyclopedic Dictionary of Medical Terms states: "Water purification is a complex of sanitary measures aimed at removing impurities that are dangerous to humans." Agricultural dictionary: "Water purification - bringing the quality of the source water in line with the requirements of the consumer. Water purification methods: clarification (removal of turbidity), decolorization (removal of organic substances), disinfection, deodorization, desalination, softening." Great Soviet Encyclopedia: "Water treatment is the treatment of water coming from a natural water source to power steam and hot water boilers or for various technological purposes. Water treatment is carried out at thermal power plants, transport, utilities, and industrial enterprises.

The chemical industry is one of the largest consumers of water. Water is used in almost all chemical industries for a variety of purposes. At individual chemical enterprises, water consumption reaches 1 million m 3 per day. The transformation of water into one of the most important elements of chemical production is explained by:

the presence of a complex of valuable properties (high heat capacity, low viscosity, low boiling point, etc.);
availability and low cost (costs solely for extraction and purification);
non-toxicity;
ease of use in production and transportation. In the chemical industry, water is used in the following areas:

For technological purposes as:
- solvent of solid, liquid and gaseous substances;
- environments for the implementation of physical and mechanical processes (flotation, transportation of solid materials in the form of pulp, etc.);
- washing liquid for gases;
- extractant and absorbent of various substances.
As a heat carrier (in the form of hot water and steam) and a refrigerant for heating and cooling equipment.
As a raw material and reagent for the production of various chemical products (for example, hydrogen, acetylene, sulfuric and nitric acids, etc.)

The waters of the seas and oceans are sources of raw materials for the extraction of many chemicals. On an industrial scale, sodium and magnesium chlorides, bromine, iodine and other products are extracted from them. At present, they are also considered as potential sources for obtaining many other elements. So, for example, the content of elements in the waters of the Ocean is (%): potassium 3.8 * 10 -2, vanadium 5 * 10 -8, gold 4 * 10 -10, silver 5 10 -9, uranium 2 * 10 -7. Taking the mass of water on the planet equal to 1.4 10 18 tons, we obtain, respectively, the content of gold in it 5.6 * 10 6 tons and uranium 2.8 * 10 9 tons. Only 0.01% of this mass of uranium is enough to provide energy for the entire planet for 100 years.

New industrial methods for obtaining useful components from the waters of the World Ocean include plants operated in Japan for the extraction of uranium using complex compounds and the domestic Hydrometal project for the extraction of iron and manganese from nodules of the Pacific Ocean, a scheme of which is shown in Fig. 3.1.

Figure 3.1- Scheme "Hydrometal":
1 - underwater reactor for the processing of nodules;
2 - floating base.
A - concretions extracted from the bottom;
B - reagents for the processing of nodules supplied to the reactor;
C - finished product;
D - waste material returned to the ocean

The scale of water consumption by the chemical industry depends on the type of production and varies widely. Thus, the consumption coefficients for water (in m 3 per ton of product) are: for nitric acid 200, viscose fiber 1200, ammonia 1500, synthetic rubber 1600, nylon fiber 2500. For example, a nylon fiber plant consumes the same amount of water as a city with with a population of 120,000 people, and a specialized plastics factory in terms of water consumption is equivalent to a city with a population of 400,000 people.

The enormous consumption of process water, along with a large volume of polluted water discharged by chemical enterprises (up to 40% of the river water flow is used only to dilute them to a safe concentration of the substances they contain), puts forward the priority task of rational use of water resources in the chemical and petrochemical industries. This task is solved by:

development of scientifically based norms of water consumption for technological operations;
maximizing the use of waste and thereby reducing the need for treatment facilities;
replacement of water cooling of equipment with air;
organization of closed without sewage production and water circulation cycles.

Water circulation cycles of technological installations, workshops and chemical enterprises as a whole are the most important factor in the rational use of water resources. In these cycles, water is reused without the release of polluted wastewater into water bodies, and the consumption of fresh water to replenish it is limited only by technological transformations (as a component of raw materials) and natural losses.

Figure 3.2– Cycle with circulating water cooling:

Figure 3.3– Cycle with circulating water treatment:

Pumping station;
Cooling tower (pool);
Treatment facilities;

In chemical industries, three water circulation schemes are used, depending on the changes that water undergoes during the production process:

water is only heated and must be cooled in cooling towers or pools before returning (Fig. 3.2);
water is only polluted and must be purified before return in special treatment facilities (Fig. 3.3);
water is heated and contaminated. This type of water cycle is a combination of water cycles of the first and second types (Fig. 3.4).

Figure 3.4– Cycle with purification and cooling of circulating water:

Technological installation (workshop);
Pumping station;
Cooling tower (pool);
Treatment facilities;
Chamber for replenishing water losses

The criterion for the efficiency of the water cycle is the coefficient of water use:

Kv \u003d \ frac (Vz-Vb) (Vz)
(3.1)
where: V s and V sb - the amount of fresh water taken from the source and waste water discharged into the reservoir, respectively. In the chemical industry, the share of circulating water supply reaches 85 - 90%.

2. Sources of water supply for chemical industries

The total amount of water on Earth is 1.386 * 10 9 km 3 (1.386 * 10 18 m 3) or 1.4 * 10 18 tons. Most of this water is in constant circulation under the influence of the thermal energy of the sun and the warmth of the earth's interior. Natural water is divided into atmospheric, surface water, groundwater and sea (ocean) water.

Atmospheric water falling in the form of rain and snow contains a minimum amount of impurities, mainly in the form of dissolved gases (oxygen, carbon monoxide (II), nitrogen, hydrogen sulfide), bacteria, and in industrial areas also nitrogen and sulfur oxides and various organic substances.

Surface waters represent the waters of open reservoirs: rivers, lakes, canals, reservoirs. The composition of surface waters includes various mineral and organic substances, the nature and concentration of which depend on climatic, geomorphological, soil and geological conditions, as well as on agro- and hydrotechnical methods, industrial development in the region and other factors.

Groundwater includes artesian wells, wells, springs and geysers. They are characterized by a high content of mineral salts leached from the soil and sedimentary rocks, and a low content of organic matter.

Sea water is a multicomponent solution of electrolytes and contains almost all the elements that make up the lithosphere. Various gases are also dissolved in it.

Depending on the salt content, natural waters are divided into fresh (salt content less than 1 g/kg), brackish (salt content 1-10 g/kg) and saline (salt content more than 10 g/kg). Of the total volume of the planet's hydrosphere, fresh water reserves account for only 0.03%, while only river waters become sources of industrial water supply, which is associated with a significant length of their coastline. Currently, up to 9% of the total fresh water flow is spent for industrial purposes in the Russian Federation, which is 700 cubic meters. km per year.

Water used in the chemical industry (process water) must meet the quality requirements of a particular production. The quality of water is determined by a combination of its physical and chemical characteristics, which include: color, transparency, smell, total salt content, hardness, oxidizability, reaction (pH), which depend on the content of various impurities in the water. For industrial waters, the most important of these characteristics are hardness, oxidizability, reaction, and the content of impurities of various sizes.

Hardness is a property of water due to the presence of calcium and magnesium salts in it. Depending on the nature of the anions, there are temporary (removable, carbonate) hardness, depending on the presence of bicarbonate ions HCO -, Lw in the water, and permanent (non-carbonate) hardness caused by the presence of chloride ions Cl -, nitrate ions NO 3 -, and sulfate -ions SO 4 2-, and constant hardness is called the total hardness of water:

Jo \u003d Zhp + Zhv. (3.2)

Water hardness is expressed as the sum of the concentrations of calcium and magnesium ions contained in 1 liter of water, that is, in mmol / dm 3. According to the value of the total hardness of water, they are divided into soft (W o less than 2), medium hardness (W 0 \u003d 2-10 mmol / l) and hard (W o more than 10).

Oxidability is a property of water due to the presence in it of organic substances, easily oxidized compounds of iron and hydrogen sulfide, capable of being oxidized by various oxidizing agents. Since the composition of these impurities is uncertain, the oxidizability of water is expressed in the amount of potassium permanganate or its equivalent amount of oxygen spent on the oxidation of 1 liter of water, that is, mg / l.

Active water reaction characterizes its acidity and alkalinity. It depends on the presence in the water of certain gases that react with water (chlorine, carbon monoxide, etc.), soluble humic acids and substances introduced into the reservoir by industrial effluents. For most natural waters, the active medium is characterized by pH=6.5-8.5.

3. Industrial water treatment

The harmful effect of impurities contained in industrial water depends on their chemical nature, concentration, dispersed state, as well as the technology of a particular production using water. All substances present in water can be in the form of a true solution (salts, gases, some organic compounds, in a colloidal state (aluminum and iron silicates, some hydroxides, silicic acid, organic compounds such as lignin, etc.) and in a suspended state ( clay, sand and lime particles).

When heated, substances dissolved in water form scale on the walls of the equipment and cause its corrosive destruction. Colloidal impurities cause pollution of the diaphragms of electrolyzers, foaming of water. Coarse suspensions clog pipelines, reducing their performance, and can cause blockage. All this causes the need for preliminary treatment of water supplied to the production of water treatment.

Water treatment is a complex of operations to remove from natural water impurities harmful to the production contained in it in the form of suspensions, colloidal particles, dissolved salts and gases. Water treatment includes the operations of clarification, softening, degassing, and in some cases, desalination and disinfection for drinking water. The scheme of industrial water treatment is shown in fig. 3.5.

Figure 3.5 - Scheme of industrial water treatment

Clarification of water is achieved by settling it, followed by filtration through a granular material of various dispersion. For coagulation of colloidal impurities and absorption of colored substances contained in water, electrolytes are added to it - aluminum and iron sulfates.

Disinfection water is provided by its chlorination (Ca (ClO) 2 bleach) or ozonation.

Degassing - the removal of dissolved gases from water is achieved by a chemical method in which gases are absorbed by chemical reagents, for example, in the case of carbon dioxide:

CO2 + Ca(OH)2 = CaCO3 + H2O

or physical methods of thermal deaeration in air or in vacuum.

Desalting is used in those industries where particularly stringent purity requirements are imposed on water, for example, in the production of semiconductor materials, chemically pure reagents, and pharmaceuticals. Water desalination is achieved by ion exchange, distillation and electrodialysis.

The ion exchange method is based on the property of some solids (ion exchangers) to absorb ions from a solution in exchange for an equivalent amount of other ions of the same sign. Ion exchangers are divided into cation exchangers and anion exchangers.

Cation exchangers are water-insoluble substances that are salts or acids with an anion that causes insolubility in water; cation (sodium or hydrogen) is able to enter into an exchange reaction with the cations of the solution. Cation exchangers are respectively called Na - cation exchangers and H - cation exchangers.

Anion exchangers are bases or salts with a solid, insoluble cation. They contain a mobile hydroxyl group (OH - anion exchangers).

Accordingly, the processes of ion exchange are divided into H (Na) - cationization, for example:

Na2[Cat] + Ca(HCO3)2 = Ca[Cat] +2NaHCO3

and anionization, for example:

An + HCl → An + H 2 O

where: [Cat] and [An] - ion exchanger matrix not participating in the exchange.

Since the ion exchange process is reversible, the establishment of equilibrium in the system means the termination of the desalination process. The absorbing capacity of the ion exchanger is characterized by its exchange capacity equal to the amount of calcium and magnesium ions that a unit of volume or mass of the ion exchanger can absorb, expressed in gram equivalents: g-eq / m 3 and g-eq / kg. The operating cycle time of ion exchanger filters depends on the value of the exchange capacity for a given volume of ion exchanger. When the ion exchanger is saturated, it can be regenerated by washing with solutions for H-acid cation exchangers, and sodium chloride cation exchangers and for anion exchangers with an alkali solution. In the above examples of the operation of anion exchangers, the reactions proceed:

Ca[Cat] +2NaCl = Na2[Cat] + CaCl2
And

An + KOH = An + KCl

Complete desalination of water is ensured by its distillation (thermal desalination), usually after the water has been previously purified using ion exchange filters.

On fig. 3.6 shows a diagram of water desalination by ion exchange.

Figure 3.6 - Scheme of installation for water desalination:

1 - cationite filter; 2 - anion-exchange filter;

3 - degasser; 4 - collection of purified water

Water sequentially passes through the cation and anion filters and enters the degasser by spraying, where dissolved carbon dioxide, oxygen and other gases are removed from it. For regeneration of the cation exchanger, acid or sodium chloride solution is periodically supplied to the filter, for regeneration of the anion exchanger - an alkali solution.

Electrodialysis is the process of dialysis under the influence of an electric field. In this case, the release of salts from the dialyzable solution occurs as a result of the movement of ions through porous membranes containing cation exchange resin (at the cathode) and anion exchange resin (at the anode), followed by their discharge at the electrodes. On fig. 3.7 shows a diagram of an electrodialyzer for water desalination.

Figure 3.7 - Scheme of the electrodialyzer: 1 - electrodes; 2 - cationite membrane; 3 - anion exchange membrane; 4 - inner chamber; 5 - external cameras

One of the main and mandatory operations of process water treatment is its softening.

Softening is the treatment of water to reduce its hardness, that is, to reduce the concentration of Ca +2 ions by various physical, chemical and physico-chemical methods.

With the physical method, water is heated to a boil, as a result of which soluble calcium and magnesium bicarbonates are converted into their carbonates, which precipitate:

Ca(HCO3)2 = CaCO3 + CO2 +H2O

This method removes only temporary stiffness.

Chemical softening methods include phosphate and lime-soda, which consist in treating water with trisodium phosphate or a mixture of calcium hydroxide and sodium carbonate. In the first case, the reaction of the formation of insoluble tricalcium phosphate, which precipitates, proceeds:

2Na 3 PO4 + 3CaSO 4 \u003d Ca 3 (PO 4) 2 + 3Na 2 SO 4

In the second case, two reactions take place. Calcium and magnesium bicarbonates react with calcium hydroxide, which eliminates temporary hardness:

Ca(HCO3)2 + Ca(OH)2 = 2CaCO3 + 2H2O
,

and sulfates, nitrates and chlorides - with sodium carbonate, which eliminates constant hardness:

CaSO4 + Na2CO3 = CaCO3 + Na2SO4

The physico-chemical method of ion-exchange water softening has been described above.

Water treatment in chemical production is a very laborious process and requires large capital and operating costs. At modern chemical enterprises, the share of capital costs for water treatment is 10-15% of the total costs for the production of chemical products.

Modern industrial water treatment schemes include all the main operations: clarification in coarse and coagulation sedimentation tanks, filtration through granular material, softening by ion exchange, and degassing. On fig. 3.8 shows a similar scheme for industrial water treatment.

Figure 3.8 - Scheme of industrial water treatment: 1 - coarse sedimentation tank; 2 - coagulant mixer; 3 - coagulation sump; 4 - filter; 5 - cationite filter; 6 - anion-exchange filter; 7 - heat exchanger; 9 - deaerator

Problem solution example

To 25 cm 3 of tap water was added 5 cm 3 of an ammonia buffer mixture and the indicator eriochrome black T. The resulting solution was titrated with 0.02 N EDTA solution until the color of the indicator changed from wine red to bright blue. The titration was repeated 3 times. The average volume of EDTA used for titration was V 1 sr (EDTA) cm 3 . A similar experiment was repeated with tap water boiled for 30 minutes. The average volume of EDTA used for titration was V 2sr (EDTA) cm 3 . Calculate the total and permanent hardness of tap water.

V 1 cf (EDTA) \u003d 3.00 cm 3, V 2 cf (EDTA) \u003d 2.50 cm 3.

1) The calculation of the total hardness of water is carried out according to the formula

Zhtot = \frac(Seq(EDTA)\cdot V1av(EDTA)\cdot 1000)(Va.h.(H2O))

AND( common) - total water hardness, mmol / dm 3;

C eq (EDTA) - molar concentration of EDTA solution equivalents, mol/dm 3 ;

V 1 cf (EDTA) - the average volume of EDTA used for titration of water before boiling, cm 3;

V a.h. (H 2 O) - an aliquot of the analyzed water, cm 3.

W (total) \u003d 0.02 * 3.00 * 1000 / 25.00 \u003d 2.4 mmol / dm 3

2) The calculation of the temporary hardness of water is carried out according to the formula

where V 2 cf (EDTA) is the average volume of water used to titrate water after boiling, cm 3.

F (vr)= 0.02 * 2.50 * 1000 / 25.00 \u003d 2.0 mmol / dm 3

3) Permanent stiffness is calculated from the difference between the total and temporary

F p \u003d Zhtot - Zhvr \u003d 2.4 - 2.0 \u003d 0.4 mmol / dm 3