Comparison of methods for pretreatment of water at thermal power plants. ultrafiltration and processing in clarifiers and mechanical filters. Water treatment in the energy sector: enemies of thermal power plants, water treatment systems

Thermal power engineering in modern conditions will not be able to survive without water treatment. Lack of water purification and softening can lead to equipment failure, poor quality steam or water, and as a result, paralysis of the entire system. Constant descaling cannot insure you against such troubles as increased fuel consumption, the formation and development of corrosion. Only water treatment at CHP can solve the whole complex of problems in one fell swoop.

In order to better understand the problems of using one or another at thermal power plants, let's start with a review of the basic concepts. What is a combined heat and power plant, and how can increased water hardness interfere with the normal operation of the system?

So, CHP or combined heat and power plant is one of the types of thermal power plant. Its task is not only to generate electricity. It is also a source of thermal energy for the heating system. These stations supply hot water and steam to provide heat to homes and businesses.

Now a few words about how a thermal power plant works. It works like a condensing power plant. The fundamental difference in water treatment at a CHP is that it is possible to take some of the heat generated from a CHP for other needs. Methods of taking heat energy depends on the type of steam turbine that is installed at the enterprise. Also at the CHP you can regulate the amount of steam that you need to select.

Everything that is separated is then concentrated in a network heater or heaters. They are already transferring energy to the water, which goes further along the system to transfer its energy to peak hot water boilers and district heating stations. If such steam extraction is not performed at the CHPP, then such CHPP has the right to qualify as a CPP.

Any water treatment at a CHP works according to one of two load schedules. One of them is thermal, the other is electric. If the load is thermal, then the electrical one is completely subordinate to it. The thermal load has parity over the electrical one.

If the load is electrical, then it does not depend on the thermal load, perhaps there is no thermal load at all in the system.

There is also the option of combining water treatment at the CHPP for electrical and thermal loads. This helps the residual heat to be used for heating. As a result, the efficiency of a CHPP is much higher than that of a IES. 80 versus 30 percent. And yet - when building a thermal power plant, you need to remember that it will not work to transfer heat over long distances. Therefore, the CHP plant must be located within the city it feeds.

The main drawback is the insoluble precipitate that forms as a result of heating such water. Removing it is not easy. At the CHP, you will have to stop the entire system, sometimes disassemble it, in order to clean the scale in all turns and narrow holes with high quality.

As we already know, the main disadvantage of scale is its poor thermal conductivity. Because of this feature, the main costs and problems arise. Even light deposits of scale on the surfaces of heating surfaces or heating elements cause a sharp increase in fuel consumption.

Eliminating scale will not work all the time, it can be done at least once a month. At the same time, fuel costs will constantly grow, and the operation of the CHP leaves much to be desired, all heating and heating equipment is slowly but surely covered with scale. To clean it later, you have to stop the entire system. To suffer losses from downtime, but to clean the scale.

The equipment itself will let you know that it's time for cleaning. Overheating protection systems will suddenly start to work. If after that the scale is not removed, then it completely blocks the operation of heat exchangers and boilers, explosions and the formation of fistulas are possible. You can lose expensive industrial equipment in just a few minutes. And it's impossible to restore it. Just buy new.

And then, any descaling is always damaged surfaces. You can use water treatment at a thermal power plant, but it will not remove scale for you, then you still have to clean it off using mechanical equipment. Having such crooked surfaces, we run the risk of a sharp development of not only the formation of scale, but also corrosion. For the equipment of a combined heat and power plant, this is a big minus. Therefore, we thought about creating water treatment plants at CHP.

Water treatment at a mini CHP

Generally speaking, such a composition will depend primarily on the chemical analysis of water. It will show the amount of water that needs to be cleaned every day. It will show the impurities that need to be eliminated first. It is impossible to do without such an analysis when compiling water treatment at a mini-CHP. Even the degree of water hardness, he will show. You never know, all of a sudden, the water is not as hard as you think, and the problem is in silicon or iron deposits, and not at all in hardness salts.

For the most part, for CHP equipment, impurities that are in make-up water are a big problem. These are the same salts of calcium and magnesium, as well as iron compounds. And this means that it will be at least difficult to do without an iron remover and an AquaShield electromagnetic water softener.

CHP, as you know, provides warm water and heating to houses in the city. Therefore, water treatment at a mini-CHP will always include not only standard ones. Here you can’t do without auxiliary water filters. Approximately, the entire water treatment scheme can be represented in the form of such stages, and the filters contained in them.

For CHPs, water from primary sources is used, which is very polluted, so the first stage of water treatment at a mini CHP will be clarification. Here, in most cases, mechanical filters are used, as well as sedimentation tanks. The latter, I think, are understandable to everyone, they defend water there so that solid impurities settle.

Mechanical filters include several stainless steel grates. They trap all solid impurities in the water. First, these are large impurities, then medium ones, and at the end very small ones, the size of a grain of sand. Mechanical filters can be used with coagulants and flocculants to purify water from harmful bacteriological impurities.

Restore mechanical filters by normal backwashing with plain water.

Next stage water treatment at a mini thermal power plant- elimination of harmful bacteria and viruses or disinfection. To do this, they can use both cheap, but harmful bleach, and expensive, but harmless when completely evaporated. ozone.

Another option for water disinfection is the use of an ultraviolet filter. Here the basis is an ultraviolet lamp, which irradiates all the water passing through a special cuvette. Passing through such a filter, the water is irradiated, and all bacteria and viruses die in it.

After disinfection comes the stage. A variety of water filters can be used here. These can be ion-exchange units, the Aquashield electromagnetic water softener or its magnetic variation. We will talk about the advantages and disadvantages of each installation a little later.

In addition to standard filters, reagent sedimentation can also be used. But the addition of various impurities can then result in the formation of insoluble deposits that are very difficult to remove.

After the softening stage, it is time to demineralise the water. For this, anion filters are used, it is possible to use a calciner, an electrodiadizer, and, as a standard, reverse osmosis or nanofiltration.

After fine purification of water, it is imperative to remove residual dissolved gases from the water. To do this, deaerate the water. Thermal, vacuum, atmospheric deaerators can be used here. That is, we have done everything that is needed for make-up water. Now there are already general steps to prepare the system itself.

Then the stage of blowing down the boiler comes into force, for this purpose washing filters for water are used and the last stage of water treatment at a mini-CHP is steam washing. For this, a whole set of chemical reagents for demineralization is used.

In Europe, the use of high-quality water treatment in CHP plants helps to achieve a loss efficiency of only a quarter of a percent per day. Just the combination of traditional methods of water softening and purification with the latest technologies helps to achieve such high results of the water treatment system at a mini CHP. And at the same time, the system itself can uninterruptedly last up to 30-50 years, without cardinal replacements of stages.

And now let's return to the water treatment system for CHP and to the water treatment plant for CHP. Here they use the whole range of filters, the main thing is to choose the right device. Most often, the system requires the use of not one, but several filters at once, connected in series, so that the water goes through both the softening stage and the demineralization stage.

The most commonly used is the ion exchange plant. In industry, such a filter looks like a tall tank in the form of a cylinder. It is necessarily equipped with a smaller tank, this is a filter regeneration tank. Since the CHP works with water around the clock, the ion exchange plant will be multi-stage and will include not one, but sometimes three or four filters. There is one control unit or controller for this entire system. Each filter is equipped with its own regeneration tank.

The controller carefully monitors how much water has passed through the unit. How much this or that filter cleaned, clearly fixes the cleaning time, cleaning speed, after a certain cleaning period or a certain volume, it gives a signal to the installation. Hard water is redistributed to other filters, and the contaminated cartridge is sent for recovery. To do this, it is removed from the installation and transferred to a tank for regeneration.

The process itself water treatment systems for CHP proceeds according to the following scheme. The heart of such an ion exchange cartridge is a resin enriched with weak sodium. When hard water comes into contact with it, metamorphoses occur. Strong hardness salts replace weak sodium. Gradually, the entire cartridge becomes clogged with hardness salts. This is the time for recovery.

When the cartridge is transferred to the recovery tank, highly purified salt tablets are already dissolved there. The saline solution that results is very saturated. The percentage of salt content is not less than 8-10 percent. But only with such a large amount of salts can strong hardness salts be removed from the cartridge. As a result of washing, highly salted waste is formed, and a cartridge refilled with sodium. He is sent to work, but there is a problem with waste. To dispose of them, they must be re-cleaned, that is, the degree of salinity must be reduced and permission for disposal must be obtained.

This is a big minus of the installation, and the cost of salt is considerable, which also gives expensive maintenance to the installation. But the water purification rate of this softener is the highest.

The next popular version of the water treatment system for thermal power plants is the AquaSHIELD electromagnetic water softener. Here, the main work is performed by an electric processor, a board and powerful permanent magnets. All this together creates a powerful electromagnetic field. These waves enter the water through a wire wound on both sides of the device. Moreover, you need to remember that you need to wind the wires in different directions from each other. Each wire must be wrapped around the pipe at least seven times. When operating this device, it is imperative to ensure that water does not get on the wiring.

The ends of the wires themselves must be closed with insulating rings or ordinary electrical tape. So, water passes through the pipe, it is irradiated by electromagnetic waves. It seems to many that the influence of this is mythical. However, hardness salts under its influence begin to transform, lose their former shape and turn into thin and sharp needles.

Having received a new form, it becomes inconvenient to stick to the surfaces of the equipment. The thin narrow body of the needle does not adhere to surfaces. But on the other hand, it perfectly tears off the old scale from the walls of the equipment. And he does it subtly and efficiently, without using any auxiliary means. Such work is the main trump card of the AquaShield electromagnetic water softener. He will do his job, that is, he will soften the water and remove the old scale very efficiently. And for this you do not have to buy anti-scale products. All will provide powerful permanent magnets made of rare earth metals and electric current.

This device has a large number of advantages over other installations. He does not need to be looked after, he does everything himself. It will completely remove from your everyday life such a thing as descaling. It is able to work with any surfaces, the main thing is to mount it on a clean piece of pipe.

Then the electromagnetic device can work without replacements for a quarter of a century. Such a long use is guaranteed just by rare earth metals, which over time practically do not lose their magnetic properties. Here, even the water does not get used to the magnetic effect. True, such a device does not work with standing water. Also, if the water flows in more than two directions at the same time, the magnetic field does not work either.

And finally, a few words about reverse osmosis as a water treatment system for thermal power plants. It is impossible to manage in the production of make-up water without this installation. Only it guarantees almost one hundred percent water purification. There are replaceable membranes that allow you to get water with the desired characteristics. But at the same time, the device cannot be used independently. Only bundled with other softeners, which makes installation more expensive. But one hundred percent compensates for all the disadvantages of high cost.

We have considered in detail all water treatment systems for CHP. Familiarized with all possible softeners that can be used in this system. Now you can easily navigate the world of softening.

One of the most important issues in the energy sector has been and remains water treatment at thermal power plants. For energy companies, water is the main source of their work, and therefore very high requirements are imposed on its content. Since Russia is a country with a cold climate, constant severe frosts, the operation of a thermal power plant is something on which people's lives depend. The quality of the water supplied to the heat and power plant greatly affects its operation. Hard water results in a very serious problem for steam and gas boilers, as well as steam turbines of thermal power plants, which provide the city with heat and hot water.

CHP - combined heat and power plant - is a kind of thermal power plant, which not only provides heat to the city, but also supplies hot water to our homes and businesses. Such a power plant is designed as a condensing power plant, but differs from it in that it can take part of the thermal steam after it has given up its energy.

are different. Depending on the type of turbine, steam with different indicators is selected. Turbines in the power plant allow you to adjust the amount of steam taken.
The steam that has been extracted is condensed in the network heater or heaters. All energy from it is transferred to network water. Water, in turn, goes to peak water heating boiler houses and heat points. If the steam extraction paths are blocked at the CHPP, it becomes a conventional IES. Thus, the heat and power plant can operate according to two different load curves:

• thermal graph - directly proportional dependence of the electrical load on the thermal;
• electrical graph - there is either no heat load at all, or the electrical load does not depend on it.

The advantage of CHP is that it combines the production of both heat and electricity. Unlike IES, the remaining heat does not disappear, but is used for heating. As a result, the efficiency of the power plant increases. For water treatment at CHPPs, it is 80 percent versus 30 percent for IES. True, this does not speak of the efficiency of the heat and power plant. Here, the price includes other indicators - the specific generation of electricity and the efficiency of the cycle.
The peculiarities of the location of the CHP should include the fact that it should be built within the city. The fact is that the transfer of heat over distances is impractical and impossible. Therefore, water treatment at CHPPs is always built near consumers of electricity and heat.

Correction water treatment for steam boilers in the energy sector

Corrective water treatment inside the boiler aims to prevent unwanted processes in the steam production equipment: - corrosion in the feed water system, when the content of dissolved oxygen in the feed water tank is significantly higher than the norm. Hot water containing dissolved oxygen is highly corrosive. As a consequence, if corrosive gases are not sufficiently removed, significant corrosion of the pipelines in the feed water system can occur. - corrosion inside the steam boiler occurs if dissolved oxygen is not sufficiently removed, the pH of the boiler water does not correspond to normal levels, the boiler water contains a significant amount of free alkali. - deposits inside the steam boiler may have a different origin: deposits of corrosion products; deposits of poorly soluble hardness salts; deposits of organic matter, which occur if a significant amount of organic matter, such as humic acids, is present in the boiler water. - corrosion of steam and condensate pipelines and equipment that consumes steam is primarily due to the presence of carbon dioxide in the hot condensate. Also, the presence of dissolved oxygen is possible in the condensate.

1. Complex inhibitors of corrosion and deposits. Such chemical reagents include several components: substances for adjusting the pH of water and steam, in order to bind carbon dioxide; polymers that prevent the formation of deposits inside the boiler; volatile and non-volatile substances for oxygen binding. The use of such reagents makes it possible to comprehensively solve the problem of corrective water treatment for steam boilers, with the ability to prevent corrosion and deposit formation throughout the steam production and supply systems, as well as condensate collection and return systems.

2. Combinations and corrosion and deposit inhibitors. Often, from a technical and economic point of view, it is advisable to use not complex reagents, but reagents for the intended purpose, separately: a reagent for binding dissolved oxygen, a reagent - a pH corrector, a reagent - a sediment inhibitor. This combination of chemical reagents allows more precise control of the water chemistry regime. First of all, such solutions are relevant for medium and high pressure steam production systems.

3. Chemical reagents, including special polymers, prevent the formation of various deposits inside the boiler. The use of such reagents is consistent with the modes of continuous and periodic blowdown of boilers.

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What is the equipment for CHP? These are turbines and boilers. Boilers produce steam for turbines, turbines produce electricity from steam energy. The turbogenerator includes a steam turbine and a synchronous generator. Steam in turbines is obtained by using fuel oil and gas. These substances heat the water in the boiler. The pressurized steam turns the turbine and the output is electricity. Waste steam is supplied to homes in the form of domestic hot water. Therefore, the exhaust steam must have certain properties. Hard water with a lot of impurities will not allow you to get high-quality steam, which, moreover, can then be supplied to people for use in everyday life.
If the steam is not sent to supply hot water, then it is immediately cooled in the thermal power plant in cooling towers. If you have ever seen huge pipes at thermal stations and how smoke pours from them, then these are cooling towers, and smoke is not smoke at all, but the steam that rises from them when condensation and cooling occurs.
How does it work water treatment at CHP we figured out that the turbine and, of course, boilers that convert water into steam are most affected by hard water. The main task of any thermal power plant is to get clean water in the boiler.

Hard water differs from ordinary water by its high content of calcium and magnesium salts. It is these salts that, under the influence of temperature, settle on the heating element and the walls of household appliances. The same applies to steam boilers. Scale forms at the heating point and the boiling point along the edges of the boiler itself. Descaling the heat exchanger in this case, it is difficult, because scale builds up on huge equipment, inside pipes, all kinds of sensors, automation systems. Flushing the boiler from scale on such equipment - this is a whole multi-stage system, which can even be carried out when disassembling the equipment. But this is in the case of a high density of scale and its large deposits. The usual remedy for scale in such conditions, of course, will not help.
If we talk about the consequences of hard water for everyday life, then this is the impact on human health and the rise in the cost of using household appliances. In addition, hard water is very bad in contact with detergents. You will use 60 percent more powder, soap. Costs will grow by leaps and bounds. Water softening was therefore invented to neutralize hard water, you put one water softener in your apartment and forget that there is a descaling agent, a descaling agent.

Scale is also characterized by poor thermal conductivity. This lack of it is the main cause of breakdowns of expensive household appliances. A thermal element covered with scale simply burns out, trying to give off heat to the water. Plus, due to the poor solubility of detergents, the washing machine must be additionally turned on for rinsing. These are the costs of water and electricity. In any case, water softening is the surest and most cost-effective way to prevent scale formation.
Now imagine what is water treatment at a thermal power plant on an industrial scale? There, the descaler is used by the gallon. Flushing the boiler from scale carried out periodically. It happens regularly and repair. To make descaling more painless, water treatment is needed. It will help prevent the formation of scale, protect both pipes and equipment. With it, hard water will not exert its destructive effect on such an alarming scale.
If we talk about industry and energy, then most of all hard water brings trouble to thermal power plants and boiler houses. That is, in those areas where there is direct water treatment and heating of water and the movement of this warm water through water supply pipes. Water softening is as necessary here as air.
But since water treatment at a thermal power plant is work with huge volumes of water, water treatment must be carefully calculated and thought out, taking into account all sorts of nuances. From the analysis of the chemical composition of water and the location of a particular water softener. In CHP, water treatment is not only a water softener, it is also equipment maintenance after. After all, descaling will still have to be done in this production process, with a certain frequency. More than one descaler is used here. It can be formic acid, and citric, and sulfuric. In various concentrations, always in the form of a solution. And they use one or another solution of acids, depending on what components the boiler, pipes, controller and sensors are made of.
So, which energy facilities need water treatment? These are boiler stations, boilers, this is also part of the CHPP, water heating installations, pipelines. Pipelines remain the weakest points, including CHPs. Scale accumulating here can also lead to depletion of pipes and their rupture. When the scale is not removed in time, it simply does not allow water to pass through the pipes normally and overheats them. Along with scale, the second problem of equipment in CHP is corrosion. It also cannot be left to chance.
What can lead to a thick layer of scale in the pipes that supply water to the CHP? This is a difficult question, but we will now answer it knowing what water treatment at CHP. Since scale is an excellent heat insulator, the heat consumption increases sharply, while the heat transfer, on the contrary, decreases. The efficiency of boiler equipment drops significantly, and as a result, all this can lead to rupture of pipes and explosion of the boiler.

Water treatment at CHP, this is something that cannot be saved on. If in everyday life, you still think whether to buy a water softener or choose a descaler, then such bargaining is unacceptable for thermal equipment. At thermal power plants, every penny is counted, so descaling in the absence of a softening system will cost much more. And the safety of devices, their durability and reliable operation also play a role. Descaled equipment, pipes, boilers work 20-40 percent more efficiently than equipment that has not been cleaned or works without a softening system.
The main feature of water treatment at thermal power plants is that it requires deeply demineralized water. To do this, you need to use precise automated equipment. In such production, reverse osmosis and nanofiltration, as well as electrodeionization, are most often used.
What stages does water treatment in the energy sector include, including at a heat and power plant?
The first stage includes mechanical cleaning from all kinds of impurities. At this stage, all suspended impurities are removed from the water, up to sand and microscopic rust particles, etc. This is the so-called coarse cleaning. After it, the water comes out clean for the human eye. Only dissolved hardness salts, ferrous compounds, bacteria and viruses, and liquid gases remain in it.

Developing water treatment system it is necessary to take into account such a nuance as the source of water supply. Is it tap water from public water systems or is it water from a primary source?
The difference in water treatment is that the water from the water supply systems has already passed the primary treatment. Only hardness salts should be removed from it, and deferrized if necessary.
Water from primary sources is absolutely untreated water. That is, we are dealing with a whole bouquet. Here it is imperative to carry out a chemical analysis of water in order to understand what impurities we are dealing with and what filters to install to soften the water and in what sequence.
After rough cleaning, the next stage in the system is called ion-exchange demineralization. An ion exchange filter is installed here. Works on the basis of ion-exchange processes. The main element is an ion exchange resin, which includes sodium. It forms weak bonds with resin. As soon as hard water at a thermal power plant enters such a softener, the hardness salts instantly knock sodium out of the structure and firmly take its place. Restoring such a filter is very simple. The resin cartridge is moved to the recovery tank, where the saturated brine is located. Sodium takes its place again, and hardness salts are washed into the drain.

The next step is to obtain water with desired characteristics. Here, a water treatment plant is used at a thermal power plant. Its main advantage is the receipt of 100% pure water, with the specified indicators of alkalinity, acidity, mineralization level. If the company needs industrial water, then the reverse osmosis plant was created just for such cases.
The main component of this installation is a semi-permeable membrane. The selectivity of the membrane varies, depending on its cross section, water with different characteristics can be obtained. This membrane divides the tank into two parts. One part contains a liquid with a high content of impurities, the other part contains a liquid with a low content of impurities. Water is launched into a highly concentrated solution, it slowly seeps through the membrane. Pressure is applied to the installation, under the influence of it, the water stops. Then the pressure is sharply increased, and the water begins to flow back. The difference between these pressures is called osmotic pressure. The output is perfectly pure water, and all deposits remain in a less concentrated solution and are discharged into the drain. The disadvantages of this method drinking water treatment include high water consumption, hazardous waste and the need for water pretreatment.
Nanofiltration is essentially the same reverse osmosis, only low-pressure. Therefore, the principle of operation is the same, only the water pressure is less.
The next stage is the elimination of gases dissolved in it from the water. Since CHP plants need clean steam without impurities, it is very important to remove oxygen, hydrogen and carbon dioxide dissolved in it from the water. The elimination of impurities of liquid gases in water is called decarbonation and deaeration.
After this stage, the water is ready for supply to the boilers. Steam is obtained at exactly the concentration and temperature that is needed. No additional cleaning is required.

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E.N. Bushuev, N.A. Eremina, A.V. Zhadan

Background: A large number of new water treatment equipment with high environmental performance has appeared on the domestic energy market. Their widespread introduction into production is hampered by the lack of a regulatory framework for their use and the contradictory experience of operating head units at domestic thermal power plants, especially for waters with a high content of organic substances, which is typical for surface waters in the center and north of Russia. In this regard, there is a need to improve traditional technologies and create new desalination systems.

Materials and methods: The results of operation of new water treatment plants at a number of domestic and foreign TPPs were used.

Results: An analysis was made of two main directions for improving the technology for obtaining demineralized water at thermal power plants: countercurrent ionization and based on membrane methods. A schematic solution for ensuring the operation of a reverse osmosis unit at reduced productivity is considered.

Conclusions: The results of the analysis of water treatment technologies must be taken into account both in the design and reconstruction of the chemical shops of TPPs.

Key words: thermal power plants, water treatment, membrane methods, reverse osmosis, electrodeionization.

NPK "Median-Filter" presents modern systems for water purification and water treatment:

A.V. Zhadan, First Deputy gene. dir. (ZAO NPKMedian-Filter),

B.A. Smirnov, senior researcher (JSC VTI), O.V. Smirnoe, early chem. departments (CHPP-EVS JSC "Severstal"), V.N. Vinogradov, Ph.D., chief engineer (ZAO Ivenergoservis),

VC. Avan, E.A. Karpychev, Asp. (ISUE)

For the majority of thermal and nuclear power plants in Russia, open reservoirs serve as a source of water supply: rivers, lakes, reservoirs. Their water contains coarse (suspended substances), colloidal impurities and truly dissolved substances. Optimal water treatment schemes contain specialized functional units. And the first of these nodes in the treatment of surface water is preliminary purification (pre-treatment), which ensures the removal of suspended and colloidal substances from water, its discoloration and partial disinfection, as well as, in particular cases, iron removal, reduction of hardness, alkalinity and salinity of water. The report presents the results of comparative surveys of pre-treatment of various types of water treatment plants (WTP). By analyzing the results of surveys of the TLU TPP, the advantages and disadvantages of the main schemes for preliminary water treatment were established.

1. Pre-treatment of water using ultrafiltration technology

The source water, heated to a temperature of 10 to 25 ° C, enters the self-cleaning filters of the VPU, where it occurs. After self-cleaning filters, a coagulant is dosed into the pipeline, and water enters the coagulation tanks and then to the coagulation formed as a result of coagulation, then to the clarified water tanks. Clarified water can be directed to osmotic or ion exchange desalination.

Benefits of the scheme (item 1):

• compactness of the equipment;
• full automation;
• high degree of purification from suspended solids, .

The disadvantages of the scheme (clause 1):

• large in the absence of systems for their reuse;
• high cost of replacing membrane elements;
• ultrafiltration systems often require pre-treatment plants;
• if the controller of the automatic control system fails, manual control is almost impossible;
• The use of ultrafiltration in an efficient water treatment system is recommended when the mass concentration of suspended solids in the water in front of it is not more than 50 mg/dm 3 . At the same time, and at a concentration of suspended solids up to 200 mg/dm 3 . This unit was equipped with an internal recirculation circuit with a pump. With an increase in the concentration of suspended solids in the source water up to 200 mg/dm3, a decrease in its productivity by about 20% was observed;
• the high cost of water treatment equipment, which, however, can be compensated by reducing the cost of the WLU building during new construction;
• high sensitivity of membrane systems to the presence of anthropogenic pollution in water, such as oil products.

Water washings of the ultrafiltration system are carried out with clarified water obtained by treating the source water with a coagulant. The more often water washes are carried out, the greater the consumption of coagulant for the own needs of the WTP. Wastewater from chemically enhanced washes needs to be neutralized and.

The use of sorption effects in combination with the use of ultrafiltration technology is possible when implementing the so-called pressure coagulation technology, when water treated with a coagulant is first fed into pressure contact tanks. Such a scheme was successful, and the exclusion of contact containers from the coagulation scheme instantly led not only to an increase in the color and turbidity of the filtrate, but also to a decrease in the filter cycles of ultrafiltration modules.

Water consumption for own needs for this technological scheme directly depends on the mass concentration of suspended solids. An increase in this concentration in the source water increases the number of washes of self-cleaning filters and ultrafiltration modules.

Thus, the dependence of the operation of the installation on the quality of the source water narrows the area of ​​effective application of this technological scheme of water treatment. Such a scheme can be used in Russia to treat the water of such rivers as the Yenisei, Angara (upper reaches), lakes Imandra, Baikal. The low mineralization of the waters of these sources reduces the economic efficiency of the osmotic stage of the scheme (item 1), and therefore, at the CHPP-11 in Usolye-Sibirskoye, the ultrafiltration unit precedes the one operating according to the Schwebebett technology. As is known, this countercurrent technology imposes the most stringent requirements on the quality of the water supplied to it.

2. Pre-treatment of water using the technology of liming and coagulation in clarifiers

The source water, heated to a temperature of 35 ± 1 ° C, enters the clarifier, which works according to the technology of water treatment by liming and coagulation, then - into the tank of lime-coagulated water and from it to mechanical filters. Clarified water can be directed to ion exchanger or. It should be noted that modern clarification technologies developed by foreign experts, such as Veolia's Multiflo or Degremont's Densadeg, provide stable good performance at much lower temperatures.

Benefits of the scheme (item 2):

• softening and decarbonization of water at the stage of preliminary purification, reduction of the ion load on Na - cation exchange filters;
• minimum consumption of waste water and the possibility of their disposal;
• no dependence of the fundamental technological solution on the degree of contamination of the source water with suspended solids;
• good moisture-releasing properties of the sludge, which make it possible, when using filter presses, to practically eliminate the formation of liquid waste at the pre-treatment stage;
• effective removal of iron compounds and colloidal silicic acid from water.

The disadvantages of the scheme (clause 2):

• the presence of a lime economy, poorly amenable to automation;
• The efficiency of the equipment depends on the quality of the source water. Waters with high hardness and alkalinity are considered as initial ones, for which the technology of liming and coagulation is most applicable. At least this pretreatment technology is recommended for use when the total alkalinity of the source water is more than 2 meq/dm3;
• a large amount of sludge;
• unstable quality of clarified water. For example, they ended outside the clarifier, which led to the formation of calcium carbonate deposits in the filter media of mechanical filters;
• the need for a mechanical filtration stage for the post-treatment of lime-coagulated water;
• large dimensions of the plant and, as a result, a large volume of the TLU building and the cost of construction. Large metal consumption and cost of domestic clarifiers.

Thus, the dependence of the operation of the plant on the quality of the source water narrows the scope of applicability of this technological scheme (p. 2). In Russia, it is applicable for the treatment of waters that have increased hardness and alkalinity.

Speaking of liming, it is appropriate to mention rapid decarbonization reactors. They carry out chemical treatment of water by adding lime, and sometimes caustic soda (as, for example, at the Kiev CHPP-5). When using soda ash, it is possible to remove not only temporary, but also part of the permanent hardness. There are known cases of using sand as an intensification of the process, while instead of flakes of sludge, grains of calcium carbonate are formed on the grains of sand. They have high hydraulic fineness and low moisture content. It is possible to use grains of calcium carbonate as an additive in the production of building structures. The disadvantage of this technology is the irretrievable loss of sand and, consequently, the need for their regular replenishment. With an unfavorable combination of calcium and magnesium hardness, the sludge resulting from liming is more amorphous, and its sedimentation sometimes requires a long time or the introduction of additional reagents, such as coagulants and (or) flocculants.

Rapid decarbonization reactors are appropriate to use when feeding circulating cycles with waters characterized by high salinity along with low color and turbidity.

3. Pre-treatment of water in clarifiers using coagulation technology and subsequent ultrafiltration or mechanical filtration in filters with granular loading

The source water, heated to a temperature of 25 ± 1 °C (as noted above, clarifiers with horizontal water movement are less sensitive to temperature changes and provide stable operation in its wider range), enters the clarifier operating on the technology of water treatment with coagulants and flocculants. In all other respects, the technological scheme repeats the scheme given in paragraph 1. The washing water of the ultrafiltration unit is returned to the clarifier. When the clarifier is operating properly, the mass concentration of suspended solids in the coagulated water is less than 2 mg/dm3. The ultrafiltration plant is under ideal conditions for a given water quality, reagents are not dosed into the water in front of it. Such schemes are often implemented at foreign waterworks, in countries where the legal framework does not allow regular water treatment with chlorine-containing reagents. In such projects, the main role of ultrafiltration is not to clarify the water, but to retain viruses and bacteria.

Benefits of the scheme (item 3)

• low consumption of waste water from pre-treatment and the possibility of their disposal;
• no dependence of the fundamental technological solution on the contamination of the source water with suspended solids;
• combination of the possibility of removing microparticles of suspended and colloidal substances from water with the possibility of sorption removal of low molecular weight organic acids, polysaccharides, colloidal compounds of silicic acid;
• coagulation is most effective in water treatment;
• the possibility of using both pressure and submersible ultrafiltration membranes;
• increasing the service life of ultrafiltration elements and, as a result, reducing operating costs.
• The disadvantage of the scheme (p. 3)
• the high cost of construction, both the building and the process equipment;
• the choice of flocculants is complicated, since not all flocculants that are optimal for the coagulation process are compatible with the ultrafiltration process (many high molecular weight anionic polymers are prone to the formation of heavy and sticky macroflakes, the sediment of which is practically not washed out of the hollow fibers of ultrafiltration. That is, when selecting flocculants and mode coagulation, it is necessary to ensure the minimum residual concentrations of the flocculant in the coagulated water).

The dosing of inhibitors (antiscalants) before the reverse osmosis installation is due to the need for stabilization water treatment to prevent deposits from fixing on the membranes. The secondary use of the concentrate in technological schemes of water treatment is difficult due to the presence of inhibitors in it. Sometimes the concentrate can be used in the technological schemes of thermal power plants. Schemes are known where acidification is used instead of inhibitors.

The technological scheme (item 3) is quite often applicable in Russia. However, almost everywhere, ultrafiltration with pre-treatment in the form of disc or mesh filters comes to the forefront in terms of frequency of use in projects. There are two main reasons for this trend: the practical absence of modern effective clarifiers of domestic production and the “convenience” of designing block-modular membrane water treatment systems. However, the applicability of the scheme (clause 3) can be justified technically and economically in comparison with the schemes presented in clauses. 1, 2 and classical schemes with pretreatment in clarifiers and ion-exchange or thermal water desalination.

4. Preliminary purification of water by direct coagulation

The source water, heated to a temperature of 28 ± 2 °C, enters the mechanical filters through the pipeline. In this pipeline before the static mixer, possibly closer to the mechanical filters, the working solution of the coagulant is dosed in proportion to the flow rate of the source water. The dose (mass concentration) of the coagulant is selected according to the condition of the contact coagulation process on the grains of the stationary filtration load of mechanical filters, which ensures maximum use of its dirt capacity. The coagulated water is sent for further processing to the subsequent elements of the technological scheme. In some cases, the best effect of coagulation treatment of water is achieved when the coagulant is introduced into the point of the source water pipeline, remote from mechanical filters. It is advisable to use the direct-flow coagulation scheme when the source water is not heated enough, when the process of coagulant hydrolysis is slowed down, and more time is required for the formation of well-retained flakes. As a filtering load, the most optimal is the use of several filter materials loaded in layers, for example, gravel, quartz sand and hydroanthracite. Filters with layered loading during clarification of water coagulated in the clarifier have not only a 3-5 times higher dirt capacity, but also provide excellent quality of the filtrate with a suspended solids content of not more than 0.2 mg/dm3 and a turbidity of not more than 0.2 NTU. Such water satisfies in its quality the requirements for water supplied to both ion exchange filters and reverse osmosis plants.

Benefits of the co-current coagulation scheme

• compactness of pretreatment;
• lower requirements for the accuracy of control of the heating of the source water;
• reduction of coagulant costs in comparison with coagulation in clarifiers.

Disadvantages of direct-flow coagulation scheme

• increased water consumption for own needs of mechanical filters;
• increased number of mechanical filters (or mechanical filter housings);
• the need to use a tank and pumps for loosening washing of mechanical filters;
• worse, compared with the combination of coagulation and mechanical filtration, the quality of clarified water, especially in terms of retention of bacteria, polysaccharides and low molecular weight organic acids;
• reuse of wash water requires additional equipment;
• direct-flow coagulation is applicable when the content of suspended solids in the source water is not more than 30 mg/dm3 (taking into account those formed during the coagulation process). At high concentrations of these substances, the water consumption for the auxiliary needs of mechanical filters increases and the time intervals between their loosening (back) flushes decrease.

Direct-flow coagulation is applicable for treatment of surface waters with low water oxidizability that do not require liming, and for treatment of waters at WLU, which have a low utilization factor of the installed capacity. In the latter case, the WTP equipment, including clarifiers, stands idle most of the time in reserve. Frequent starts make it difficult to operate clarifiers.

Direct-flow coagulation of water is implemented, for example, at the Vologda CHPP in the scheme for preparing water for feeding the heating network. An example of the potential rationality of using direct-flow coagulation is the Norilsk CHPP-2, which uses water with low oxidizability, which increases noticeably, like its silicon content, only by a factor. Thus, the installation of a reagent unit and a small coagulant warehouse is recommended for use at this CHPP. In the absence of coagulation, it violates the PTE requirements for the quality of feed water and vapors for the content of silicon compounds.

When implementing direct-flow coagulation technology, some objects used DynaSand filters. These filters are characterized by a continuous mode of operation and, accordingly, their total number can be reduced, since a backwash shutdown is not required. Compared to traditional pressure filters, this is the only advantage, with the following disadvantages:

• leachate and effluent discharge is carried out without pressure, which creates serious inconveniences when designing a high-rise installation scheme;
• relatively large water consumption for own needs;
• more complex design and operating conditions;
• higher cost.

Conclusion

As a result of the survey of the WLU, the main technical and economic differences in the technological schemes for preliminary water treatment were identified.

At present, it is technically and economically preferable to pretreat water using clarifiers, including for water treatment systems, followed by

13.08.2012

One of the most important issues in the energy sector has been and remains water treatment at CHP. For energy companies, water is the main source of their work, and therefore very high requirements are imposed on its content. Since Russia is a country with a cold climate, constant severe frosts, the operation of a thermal power plant is something on which people's lives depend. The quality of the water supplied to the heat and power plant greatly affects its operation. Hard water results in a very serious problem for steam and gas boilers, as well as steam turbines of thermal power plants, which provide the city with heat and hot water.
In order to clearly understand how and what exactly hard water negatively affects, it would not hurt to first understand what a CHP is? And with what it "eat"?
So, a CHPP - a heat and power plant - is a kind of thermal power plant that not only provides heat to the city, but also supplies hot water to our homes and enterprises. Such a power plant is designed as a condensing power plant, but differs from it in that it can take part of the thermal steam after it has given up its energy.

Steam turbines are different. Depending on the type of turbine, steam with different indicators is selected. Turbines in the power plant allow you to adjust the amount of steam taken.
The steam that has been extracted is condensed in the network heater or heaters. All energy from it is transferred to network water. Water, in turn, goes to peak water heating boiler houses and heat points. If the steam extraction paths are blocked at the CHPP, it becomes a conventional IES. Thus, the heat and power plant can operate according to two different load curves:

• thermal graph - directly proportional dependence of the electrical load on the thermal;
• electrical graph - there is either no heat load at all, or the electrical load does not depend on it.

The advantage of CHP is that it combines both heat and electricity. Unlike IES, the remaining heat does not disappear, but is used for heating. As a result, the efficiency of the power plant increases. For water treatment at CHPPs, it is 80 percent versus 30 percent for IES. True, this does not speak of the efficiency of the heat and power plant. Here, the price includes other indicators - the specific generation of electricity and the efficiency of the cycle.
The peculiarities of the location of the CHP should include the fact that it should be built within the city. The fact is that the transfer of heat over distances is impractical and impossible. Therefore, water treatment at CHPPs is always built near consumers of electricity and heat.
What is the water treatment equipment for CHP? These are turbines and boilers. Boilers produce steam for turbines, turbines produce electricity from steam energy. The turbogenerator includes a steam turbine and a synchronous generator. Steam in turbines is obtained by using fuel oil and gas. These substances heat the water in the boiler. The pressurized steam turns the turbine and the output is electricity. Waste steam is supplied to homes in the form of domestic hot water. Therefore, the exhaust steam must have certain properties. Hard water with a lot of impurities will not allow you to get high-quality steam, which, moreover, can then be supplied to people for use in everyday life.
If the steam is not sent to supply hot water, then it is immediately cooled in the thermal power plant in cooling towers. If you have ever seen huge pipes at thermal stations and how smoke pours from them, then these are cooling towers, and smoke is not smoke at all, but the steam that rises from them when condensation and cooling occurs.
How does it work water treatment at CHP we figured out that the turbine and, of course, boilers that convert water into steam are most affected by hard water. The main task of any thermal power plant is to get clean water in the boiler.
Why is hard water so bad? What are its consequences and why do they cost us so much?
Hard water differs from ordinary water by its high content of calcium and magnesium salts. It is these salts that, under the influence of temperature, settle on the heating element and the walls of household appliances. The same applies to steam boilers. Scale forms at the heating point and the boiling point along the edges of the boiler itself. Descaling in the heat exchanger in this case is difficult, because. scale builds up on huge equipment, inside pipes, all kinds of sensors, automation systems. Flushing the boiler from scale on such equipment is a whole multi-stage system that can even be carried out when disassembling the equipment. But this is in the case of a high density of scale and its large deposits. The usual remedy for scale in such conditions, of course, will not help.
If we talk about the consequences of hard water for everyday life, then this is the impact on human health and the rise in the cost of using household appliances. In addition, hard water is very bad in contact with detergents. You will use 60 percent more powder, soap. Costs will grow by leaps and bounds. Water softening was therefore invented to neutralize hard water, you put one water softener in your apartment and forget that there is a descaling agent, a descaling agent.

Scale is also characterized by poor thermal conductivity. This lack of it is the main cause of breakdowns of expensive household appliances. A thermal element covered with scale simply burns out, trying to give off heat to the water. Plus, due to the poor solubility of detergents, the washing machine must be additionally turned on for rinsing. These are the costs of water and electricity. In any case, water softening is the surest and most cost-effective way to prevent scale formation.
Now imagine what is water treatment at a thermal power plant on an industrial scale? There, the descaler is used by the gallon. Flushing the boiler from scale is carried out periodically. It happens regularly and repair. To make descaling more painless, water treatment is needed. It will help prevent the formation of scale, protect both pipes and equipment. With it, hard water will not exert its destructive effect on such an alarming scale.
If we talk about industry and energy, then most of all hard water brings trouble to thermal power plants and boiler houses. That is, in those areas where there is direct water treatment and heating of water and the movement of this warm water through water supply pipes. Water softening is as necessary here as air.
But since water treatment at a thermal power plant is work with huge volumes of water, water treatment must be carefully calculated and thought out, taking into account all sorts of nuances. From the analysis of the chemical composition of water and the location of a particular water softener. In CHP, water treatment is not only a water softener, it is also equipment maintenance after. After all, descaling will still have to be done in this production process, with a certain frequency. More than one descaler is used here. It can be formic acid, and citric, and sulfuric. In various concentrations, always in the form of a solution. And they use one or another solution of acids, depending on what components the boiler, pipes, controller and sensors are made of.
So, which energy facilities need water treatment? These are boiler stations, boilers, this is also part of the CHPP, water heating installations, pipelines. Pipelines remain the weakest points, including CHPs. Scale accumulating here can also lead to depletion of pipes and their rupture. When the scale is not removed in time, it simply does not allow water to pass through the pipes normally and overheats them. Along with scale, the second problem of equipment in CHP is corrosion. It also cannot be left to chance.
What can lead to a thick layer of scale in the pipes that supply water to the CHP? This is a difficult question, but we will now answer it knowing what water treatment at CHP. Since scale is an excellent heat insulator, the heat consumption increases sharply, while the heat transfer, on the contrary, decreases. The efficiency of boiler equipment drops significantly, and as a result, all this can lead to rupture of pipes and explosion of the boiler.

This is something you can't skimp on. If in everyday life, you still think whether to buy a water softener or choose a descaler, then such bargaining is unacceptable for thermal equipment. At thermal power plants, every penny is counted, so descaling in the absence of a softening system will cost much more. And the safety of devices, their durability and reliable operation also play a role. Descaled equipment, pipes, boilers work 20-40 percent more efficiently than equipment that has not been cleaned or works without a softening system.
The main feature of water treatment at thermal power plants is that it requires deeply demineralized water. To do this, you need to use precise automated equipment. In such production, reverse osmosis and nanofiltration, as well as electrodeionization, are most often used.
What stages does water treatment in the energy sector include, including at a heat and power plant?
The first stage includes mechanical cleaning from all kinds of impurities. At this stage, all suspended impurities are removed from the water, up to sand and microscopic rust particles, etc. This is the so-called coarse cleaning. After it, the water comes out clean for the human eye. Only dissolved hardness salts, ferrous compounds, bacteria and viruses, and liquid gases remain in it.

When developing a water treatment system, it is necessary to take into account such a nuance as the source of water supply. Is it tap water from public water systems or is it water from a primary source?
The difference in water treatment is that the water from the water supply systems has already passed the primary treatment. Only hardness salts should be removed from it, and deferrized if necessary.
Water from primary sources is absolutely untreated water. That is, we are dealing with a whole bouquet. Here it is imperative to carry out a chemical analysis of water in order to understand what impurities we are dealing with and what filters to install to soften the water and in what sequence.
After rough cleaning, the next stage in the system is called ion-exchange demineralization. An ion exchange filter is installed here. Works on the basis of ion-exchange processes. The main element is an ion exchange resin, which includes sodium. It forms weak bonds with resin. As soon as hard water at a thermal power plant enters such a softener, the hardness salts instantly knock sodium out of the structure and firmly take its place. Restoring such a filter is very simple. The resin cartridge is moved to the recovery tank, where the saturated brine is located. Sodium takes its place again, and hardness salts are washed into the drain.
The next step is to obtain water with desired characteristics. Here, a water treatment plant is used at a thermal power plant. Its main advantage is the receipt of 100% pure water, with the specified indicators of alkalinity, acidity, mineralization level. If the company needs industrial water, then the reverse osmosis plant was created just for such cases.

The main component of this installation is a semi-permeable membrane. The selectivity of the membrane varies, depending on its cross section, water with different characteristics can be obtained. This membrane divides the tank into two parts. One part contains a liquid with a high content of impurities, the other part contains a liquid with a low content of impurities. Water is launched into a highly concentrated solution, it slowly seeps through the membrane. Pressure is applied to the installation, under the influence of it, the water stops. Then the pressure is sharply increased, and the water begins to flow back. The difference between these pressures is called osmotic pressure. The output is perfectly pure water, and all deposits remain in a less concentrated solution and are discharged into the drain. The disadvantages of this method of drinking water treatment include high water consumption, hazardous waste and the need for water pretreatment.
Nanofiltration is essentially the same reverse osmosis, only low-pressure. Therefore, the principle of operation is the same, only the water pressure is less.
The next stage is the elimination of gases dissolved in it from the water. Since CHP plants need clean steam without impurities, it is very important to remove oxygen, hydrogen and carbon dioxide dissolved in it from the water. The elimination of impurities of liquid gases in water is called decarbonation and deaeration.
After this stage, the water is ready for supply to the boilers. Steam is obtained at exactly the concentration and temperature that is needed. No additional cleaning is required.
As can be seen from the above, water treatment in CHP- one of the most important components of the production process. Without clean water, there will be no good quality steam, which means there will be no electricity in the right amount. Therefore, water treatment in thermal power plants should be dealt with tightly, trust this service exclusively to professionals. A properly designed water treatment system is a guarantee of long-term equipment service and quality energy supply services. Now you know that LLC NPI "GENERATION Ufa" knows how to treat water at a thermal power plant.
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