Deaeration column device. The design and principle of operation of the deaerator
A vacuum deaerator is used to deaerate water if its temperature is below 100 °C (the boiling point of water at atmospheric pressure).
The area for the design, installation and operation of a vacuum deaerator are hot water boilers (especially in a block version) and heat points. Vacuum deaerators are also actively used in Food Industry for deaeration of water necessary in the technology of preparing a wide range of beverages.
Vacuum deaeration is applied to the water flows going to make up the heating network, the boiler circuit, the hot water supply network.
Features of the vacuum deaerator.
Since the process of vacuum deaeration occurs at relatively low water temperatures (on average from 40 to 80 °C, depending on the type of deaerator), the operation of a vacuum deaerator does not require the use of a coolant with a temperature above 90 °C. The heat carrier is necessary for water heating in front of the vacuum deaerator. The coolant temperature up to 90 °C is provided at most facilities where it is potentially possible to use a vacuum deaerator.
The main difference between a vacuum deaerator and an atmospheric deaerator is in the system for removing vapor from the deaerator.
In a vacuum deaerator, vapor (vapor-gas mixture formed during the release of saturated vapors and dissolved gases from water) is removed using vacuum pump.
As a vacuum pump can be used: vacuum liquid ring pump, water jet ejector, steam jet ejector. They are different in design, but are based on the same principle - reducing static pressure(creation of rarefaction - vacuum) in the fluid flow with increasing flow rate.
The fluid flow rate increases either when moving through a converging nozzle (water jet ejector) or when the fluid swirls as the impeller rotates.
When steam is removed from the vacuum deaerator, the pressure in the deaerator drops to the saturation pressure corresponding to the temperature of the water entering the deaerator. The water in the deaerator is at the boiling point. At the water-gas interface, a difference in concentrations arises for the gases dissolved in water (oxygen, carbon dioxide) and, accordingly, appears driving force deaeration process.
The quality of the deaerated water after the vacuum deaerator depends on the efficiency of the vacuum pump.
Features of the installation of a vacuum deaerator.
Because the water temperature in the vacuum deaerator is below 100 °C and, accordingly, the pressure in the vacuum deaerator is below atmospheric - vacuum, the main question arises in the design and operation of a vacuum deaerator - how to supply the deaerated water after the vacuum deaerator further to the heat supply system. This is the main problem of using a vacuum deaerator for water deaeration at boiler houses and heating stations.
Basically, this was solved by installing a vacuum deaerator at a height of at least 16 m, which provided the necessary pressure difference between the vacuum in the deaerator and atmospheric pressure. Water flowed by gravity into the storage tank located at the zero mark. The installation height of the vacuum deaerator was chosen based on the maximum possible vacuum (-10 m.a.c.), the height of the water column in the accumulator tank, the resistance of the drain pipeline and the pressure drop necessary to ensure the movement of deaerated water. But this entailed a number significant shortcomings: an increase in the initial construction costs (a 16 m high stack with a service platform), the possibility of water freezing in the drain pipeline when the water supply to the deaerator is stopped, water hammer in the drain pipeline, difficulties in inspecting and maintaining the deaerator in winter.
For block boilers that are actively designed and installed, this solution is not applicable.
The second solution to the issue of supplying deaerated water after a vacuum deaerator is to use an intermediate deaerated water storage tank - a deaerator tank and pumps for supplying deaerated water. The deaerator tank is under the same vacuum as the vacuum deaerator itself. In fact, the vacuum deaerator and the deaerator tank are one vessel. The main load falls on the deaerated water supply pumps, which take the deaerated water from under vacuum and feed it further into the system. To prevent the occurrence of cavitation in the pump for supplying deaerated water, it is necessary to ensure that the height of the water column (the distance between the water surface in the deaerator tank and the pump suction axis) at the pump suction is not less than the value indicated in the pump passport as NPFS or NPFS. The cavitation reserve, depending on the brand and performance of the pump, ranges from 1 to 5 m.
The advantage of the second layout of the vacuum deaerator is the ability to install the vacuum deaerator at a low height, indoors. Deaerated water supply pumps will ensure that deaerated water is pumped further into storage tanks or for a drink. To ensure a stable process of pumping deaerated water from the deaerator tank, it is important to choose the right pumps for supplying deaerated water.
Improving the efficiency of the vacuum deaerator.
Because vacuum deaeration water is carried out at a water temperature below 100 ° C, the requirements for the technology of the deaeration process increase. The lower the water temperature, the higher the coefficient of solubility of gases in water, the harder process deaeration. It is necessary to increase the intensity of the deaeration process, respectively apply Constructive decisions based on new scientific developments and experiments in the field of hydrodynamics and mass transfer.
The use of high-speed flows with turbulent mass transfer when creating conditions in the liquid flow to further reduce the static pressure relative to saturation pressure and obtain a superheated state of water can significantly increase the efficiency of the deaeration process and reduce dimensions and the weight of the vacuum deaerator.
For complete solution the issue of installing a vacuum deaerator in the boiler room at zero with a minimum overall height, a block vacuum deaerator BVD was developed, tested, and successfully put into mass production. With a deaerator height slightly less than 4 m, the block vacuum deaerator BVD allows efficient deaeration of water in the performance range from 2 to 40 m3/h for deaerated water. The block vacuum deaerator occupies no more than 3x3 m space in the boiler room (at the base) in its most productive design.
In order to achieve durability and quality of the hydraulic system, it is necessary to use a deaerator. It is used in all boiler houses, as it establishes a stable and correct work systems. In our article, we will consider in more detail what a deaerator is in a boiler room.
What is a deaerator and why is it used in a boiler room
Deaeration is the process of purifying a liquid from various impurities. For example, from carbon dioxide and oxygen. To organize a water treatment system in a boiler room, a deaerator must be used. It helps improve the quality of your work.
The first method is chemical deaeration. In this case, reagents are added to the water, as a result of which excess gases are removed from the water. The second method is called thermal deaeration. Water is heated to a boil until it is clear of gaseous substances that are dissolved in it.
Deaerators are divided into atmospheric and vacuum. The former are used with water or steam. And vacuum only with steam.
Deaerators have a common two-stage device. Thus, water enters the tank, where it flows through the membranes, and then it is cleaned of impurities. Chemical water, which is in the tank, prevents the formation of various natural impurities in the coolant.
Deaerators are of low and high pressure. Since oxygen and carbon dioxide are corrosive gases, they contribute to the formation of corrosion in pipelines, and also wear them out. In order to prevent this from happening, it is necessary to prepare it before supplying water through pipelines. This is what air filters are used for.
Due to the gas content of water, various malfunctions occur in the system. Some of them can lead to a water or gas leak or completely disable the system. The presence of gas bubbles in the water leads to poor performance of pumps, nozzles and impairs the function of the hydraulic system. Installing a deaerator in a boiler room will be cheaper than frequently repairing the system.
Deaeration of water in a steam boiler
Water deaeration in a steam boiler is necessary to protect the entire steam generator system and pipelines. In the presence of harmful impurities, the system will wear out and begin to corrode.
Gaseous and natural impurities can cause pump cavitation. And it, in turn, can lead to hydraulic shocks and disrupt the operation of the pumping mode. IN worst case the hydraulic system may break or the pumps will stop working altogether.
The deaerator, which is used for a steam boiler, has the form of a tank with special membranes and plates. They are arranged vertically on the water tank. Under low pressure, water enters the tank from the supply line, then flows through the membranes and plates, and thus impurities are removed.
Spray deaerators are sometimes used in steam boilers. In them, water is sprayed in such a way that impurities immediately go into the evaporation.
High pressure system
The high pressure system is used for boilers with high power. They supply a lot of steam and also provide the necessary temperature regime for centralized heating system under high pressure. The operation of the system requires a pressure of more than 0.6 MPa.
Such an installation is thermal as well as a reduced pressure deaerator. This means that with an increase in the temperature regime of water and steam supply, the system is released from gaseous impurities.
Water seals are installed in the system. They lower the pressure when it rises.
Reduced pressure system
For a reduced pressure system, atmospheric and vertical type, which are equipped with a bubbling additional tank. Evaporation occurs through it.
In the main tank of the system, the chemically prepared mixture is mixed with water, then it flows through membranes and plates, and then all impurities are separated.
Boilers that provide hot water need a vacuum thermal system. Since vacuum degassing is best suited for such a boiler room. Such a system is used to purify water in water-heating boilers.
Depending on what mode of steam supply is required for steam boilers, deaerators of increased or reduced pressure are used. For less powerful boiler rooms that provide a low temperature regime, which is suitable for central heating, use the setup with reduced pressure. It can be 0.025-0.2 MPa.
Proper operation
For high-quality operation of the boiler and to prevent emergency situations, it is necessary to use the deaerator and the entire system correctly. To do this, it is necessary to maintain the water in the tank at a certain level with a decrease in pressure, check the conditions of the required mode, follow all the rules for use and check the operation of the devices more than 1 time per shift.
IN chemical water it is necessary to add substances correctly, as well as to control their level. Check the quality of chemical water.
Water seals must be easy to move. In the event of an increase in pressure, they must be used without any interference. All devices must be metrologically qualified and tested. They must comply with pre-established schedules. The water level can be monitored using a special water-indicating glass. Do not forget about the control of the manometer readings.
All automation devices must work properly for the correct operation of the deaerator. It is necessary to check the operation of machines and devices. To do this, regular inspections and checks are carried out.
The deaerator acts as protection for the entire boiler system. Therefore, each boiler room is equipped with such an installation.
Since cavitation leads to failure of the pump and hydraulic system, the deaerator is simply necessary in the boiler room. Such a device completely purifies water from all impurities. Thus, the system works without any damage.
Heading:Hello, dear customers of the MetalExportProm enterprise and who are interested in our products. Today I want to tell you in detail what are deaerators dp - high blood pressure, which are rarely, but still used and represent technically complex and responsible capacities. Everyone who works with such equipment is familiar with an atmospheric or vacuum deaerator, but not many people know about the devices that I am talking about now. And so in order.
The name itself suggests that the device, unlike conventional devices, operates at elevated pressure. In the DA series, a pressure of 0.12 MPa is used, and in the DP series, which we are talking about now, from 0.23 to 1.08 MPa DP1000/120, which is nine times more than aspirated. Accordingly, the walls of the vessels are much thicker. If it is interesting to immediately see the technical specifications, then go for nuclear power plants, or read on.
The device itself belongs to capacitive equipment, you can see more about the tanks, but since heat transfer processes also take place inside it, it can also be attributed to heat exchangers, about which everything is written in this section. Let's look at what it consists of.
And it consists of a deaeration column, symbol kdp, starting from kdp-80 to kdp-6000, is deciphered respectively KDP - a column of a high-pressure deaerator, and the numbers next to it are the nominal capacity measured in tons per hour or t / h, i.e. are from 80 to 6000 tons per hour. The performance of the deaerator is the amount of prepared water at the outlet of it, i.e. how much it can process and produce water in tons per hour. And so there can be from one to four or more such columns, in contrast to a simple atmospheric deaerator with one column, and they can be both vertical and horizontal, depending on the design of the apparatus. Now let's consider what function the column performs. To do this, let's start from the very beginning, but why do we need the dp deaerator itself and where and where it is installed.
And they are installed at thermal power plants and nuclear power plants, in which there are power boilers with an initial steam pressure of 10 MPa, in contrast to atmospheric workers, respectively, at low atmospheric pressure and with small hot water boilers at a pressure of 0.07 MPa. The difference is obvious, the steam pressure of energy boilers is more than a hundred times greater, however, like themselves. Let's take a closer look to make the process of water treatment more understandable, since the entire capacitive and heat exchanger is designed for this.
Water treatment
Since we are considering thermal and nuclear power plants, we will consider the processes occurring in them. Any power station is needed to generate electricity, which then goes to homes or businesses. And where does it come from? It is produced by a generator that drives a turbine, which requires steam to operate, and the steam is generated by a steam generator or the steam boiler itself, depending on the design of the station. But steam must be formed from somewhere, but it is obtained by evaporation feed water.
The water entering the reactor or boiler must be purified both from mechanical impurities and from gases that may be present in it. These impurities can be deposited on the walls of pipelines and the boilers themselves, thereby reducing the flow of liquids and heat transfer, and the gases present in the water cause corrosion of the pipes of the boiler walls. All this not only leads to a deterioration in work efficiency, but can also cause emergency. To prevent this, water treatment and purification are needed, in which it is directly involved and takes in our case, which removes corrosive gases from the feed water of reactors and steam boilers.
Only nuclear power plants have two circuits. In the first, water is prepared and poured. And this circuit has been working for many months, but the second circuit works a little differently, read on. There are also single-circuit ones, then the coolant water passes full cycle from the boiler through the steam generator to the turbine, then to the condenser and back to the reactor. Such stations are cheaper, but the equipment operates in radiation conditions. Therefore, double-circuit ones are safer, since radioactive water moves only in a closed primary circuit, which is located behind the casing and concrete, this is the reactor itself, the interaction takes place in the steam generator, but this is not so strong.
Processes taking place in nuclear power plants
Let's consider all the processes from start to finish using the example of a nuclear power plant, but only those related to our topic. So. There is the heart of the station - this is a reactor block, inside of which there are rods, in which flows nuclear reaction. This releases a huge amount of heat. This container is inside another container, between which there is water. Those. two tanks are a nuclear boiler, inside which a nuclear reaction takes place and heats the water in the gap between them.
The heated water enters a heat exchanger called a steam generator, passes through it, giving off heat, and leaves it and is then pumped circulation pump back into the boiler. This is the first loop. And it is closed, i.e. water is poured there and circulates for a long time, of course, sometimes replenishing.
But there is also a second loop. In the heat exchanger-steam generator, almost boiling water is pumped by the pump and it already boils turning into steam, which is part of the generator. The steam comes out and hits the turbine blades, setting it in motion, the rotor rotates, which is connected to the generator rotor. And the generator produces electrical energy. So, the steam passing through the turbine does not dissipate, why waste it, but leaves the turbine and enters the condenser, which serves to condense the steam and turn it into a liquid.
You can learn more about capacitors.
Water treatment
The condensate leaving the condenser enters the deaeration column from above. The other part of the steam at the outlet of the turbine from the second selection is also fed into the column only from below. Condensate moves down, and steam towards it. As a result of this process, corrosive gases, their mixture, called vapor, oxygen, nitrogen and others rise to the top and exit getting into the vapor cooler, which is shell and tube heat exchanger with a set of brass or stainless steel heat exchange tubes. The steam condenses and enters the tank, and the gases are discharged into the atmosphere. This is how the water treatment process, which is closely related to deaeration, looks like.
With speakers for atmospheric deaerators can be consulted. It also discusses in detail the principle of its operation and purpose.
Deaeration
Deaeration is the process of preparing feed water for boilers, associated with the removal of gases. And so in the column, the water is purified from gases and drained into the deaerator tank, accumulating in it. Next, the pump and pumps it into the heat exchanger steam generator. The water inside rises and is heated by the primary water and enters the evaporator.
Technical characteristics of deaerators for nuclear power plants
| Name | Nominal productivity, t/h | Working absolute pressure, MPa (kgf / cm 2) | Column | Number of columns | Column diameter, mm | Tank capacity, m 3 | Tank capacity useful mm 3 | Tank diameter, mm | Deaerator length, mm | Deaerator height, mm | Weight, kg | Deaerator weight with water, mm |
| dp-2000-2x1000/120-A | 2000 | 0.7(7.0) | kdp-10A vertical | 2 | 2400 | 150 | 120 | 3400 | 17000 | 8300 | 43200 | 227200 |
| dp-3200-2x1600/185-A | 3200 | 0.69(0.7) | kdp-1600-A vertical | 2 | 3400 | 210 | 185 | 3400 | 23415 | 11160 | 93000 | 361000 |
| dp-3200/220-A | 3200 | 1.35(13.8) sliding | kdp-3200-A horizontal | 1 | 3000 | 350 | 220 | 3800 | 32180 | 7900 | 230000 | 710000 |
| dp-6000/250-A | 6000 | 0.82(8.4) | kdp-6000-A horizontal | 1 | 3000 | 400 | 250 | 3800 | 32180 | 7900 | 190000 | 74000 |
| dp-6000/250-A-1 tables above. Foreign terminologyIn a significant part of foreign systems of technical terms, there is no single term "deaerator" to describe an element of the station's thermal circuit in the form of a tank with a column; for example, in German the column is called Entragaserdom, and the term "deaerator" (Entgaser) refers only to it, and the feedwater storage tank is Speisewasserbehälter. IN Lately and in some Russian-language publications (on non-traditional designs for our enterprises or translated), the tank is separated from the deaerator. Purpose
Operating principleIn a liquid, a gas can be present in the form of:
In the deaerator, there is a process of mass transfer between two phases: liquid and gas-vapor mixture. The kinetic equation for the concentration of a gas dissolved in a liquid at its equilibrium (taking into account the content in the second phase) concentration, based on Henry's law, looks like ,where is time; f- specific surface area of phases; k is the velocity coefficient, which depends, in particular, on the characteristic diffusion path , which the gas must overcome in order to exit the liquid. Obviously, for the complete removal of gases from the liquid, it is required (the partial pressure of the gas over the liquid must tend to zero, that is, the released gases must be effectively removed and replaced by steam) and an infinite time of the process. In practice, they are set by a technologically acceptable and economically feasible depth of degassing. IN thermal deaerators based on the principle diffusion desorption, the liquid is heated to a boil; in this case, the solubility of gases is close to zero, the resulting vapor (vapour) carries away gases (decreases), and the diffusion coefficient is high (increases k). IN vortex deaerators, the actual heating of the liquid does not occur (this is done in the heat exchangers in front of them), but hydrodynamic effects are used, causing forced desorption: the liquid bursts in the most weak points- along the gas microbubbles, and then in the vortex, the phases are separated by inertia forces under the action of the density difference . In addition, known small installations, where some degree of deaeration is achieved by irradiating the liquid with ultrasound. When water is irradiated with ultrasound with an intensity of about 1 W / cm 2, a decrease by 30-50% occurs, k increases by about 1000 times, which leads to coagulation of the bubbles with subsequent exit from the water under the action of the Archimedean force. VyparVypar is a mixture of gases released from water and a small amount steam to be evacuated from the deaerator. For normal operation deaerators of common designs, its consumption (for steam in relation to productivity) should be at least 1-2 kg / t, and if there is a significant amount of free or bound carbon dioxide in the source water - 2-3 kg / t. In order to avoid losses of the working fluid from the cycle, the vapor in large plants is condensed. If the vapor cooler used for this purpose is installed on the deaerator feed water (as in the figure), it must be sufficiently subcooled to the saturation temperature in the deaerator. When using flash steam on ejectors, it condenses on their refrigerators, and a special heat exchanger is not needed. Thermal deaeratorsThermal deaerators are classified by pressure. Atmospheric deaerators (see figure) require the smallest wall thickness; vapor is removed from them by gravity under the action of a small excess of pressure above atmospheric. Vacuum deaerators can work in conditions when there is no steam in the boiler room; however, they require a special device for suction of the vapor (vacuum ejector) and a greater wall thickness, besides, bicarbonates at low temperatures do not decompose completely and there is a danger of repeated suction of air along the tract to the pumps. DP deaerators have a large wall thickness, but their use in the TPP circuit makes it possible to reduce the number of metal-intensive HPH and use flash steam as a cheap working medium for steam-jet condenser ejectors; the condenser deaeration attachment, in turn, is a vacuum deaerator. How heat exchangers thermal deaerators can be mixing (usually, heating steam and/or water is supplied to the deaerator volume) or surface (the heating medium is separated from the heated heat exchange surface); the latter is often found in vacuum make-up deaerators of heating systems. According to the method of creating the phase contact surface, mixing deaerators are divided into jet, film And bubbling(there are mixed designs). In jet and film deaerators, the main element is deaerator column- a device in which water flows from top to bottom into the tank, and heating steam rises from bottom to top to evaporate, condensing on the water along the way. In small deaerators, the column can be integrated into one housing with a tank; usually it looks like a vertical cylinder, docked from above to horizontal tank(cylindrical tank with elliptical or conical bottoms). Above is a water distributor, below is a steam distributor (for example, an annular perforated pipe), between them is an active zone. The thickness of a column of a given capacity is determined by the allowable irrigation density active zone (water consumption per unit area). In deaerators jet type water passes through the core in the form of jets, into which it can be broken up by 5-10 perforated plates (annular with a central steam passage alternate with circular ones of smaller diameter, streamlined along the edge). Jet deaeration devices have simple design and low steam resistance, but the intensity of water deaeration is relatively low. Jet-type columns have a large height (3.5-4 m or more), which requires a high metal consumption and is inconvenient during repair work. Such columns are used as the first stage of water treatment in two-stage deaerators of the jet-bubbling type. There are also nozzle (drip) deaerators where water is sprayed from nozzles in a drop form; the efficiency due to phase refinement is high, however, the operation of the nozzles deteriorates with clogging and at reduced costs, and a lot of electricity is consumed to overcome the resistance of the nozzles. In deaerators with columns film type the water flow is divided into films enveloping the filler nozzle, over the surface of which the water flows down. Two types of packing are used: ordered and unordered. An ordered packing is made from vertical, inclined or zigzag sheets, as well as from rings, concentric cylinders or other elements laid in regular rows. The advantages of an ordered nozzle - the ability to work with high densities irrigation with significant water heating (20-30 °C) and the possibility of deaeration of unsoftened water. The disadvantage is the uneven distribution of the water flow over the nozzle. Random nozzle is made of small elements certain form arbitrarily filled in the selected part of the column (rings, balls, saddles, omega-shaped elements). It provides a higher mass transfer coefficient than ordered packing. Film deaerators are insensitive to contamination with scale, sludge and iron oxides, but are more sensitive to overload. In deaerators bubbling type the flow of steam that is introduced into the water layer is broken up into bubbles. The advantage of these deaerators is their compactness with high quality deaeration. Some overheating of water occurs in them relative to the saturation temperature corresponding to the pressure in the vapor space above the surface. The superheat value is determined by the height of the liquid column above the bubbling device. When the water vapor entrained by bubbles moves upwards, it boils, which contributes to a better release from the solution of not only oxygen, but also carbon dioxide, which is not completely removed from the water in other types of deaerators; including bicarbonates NaHCO 3 decompose, liquid turbulence. The efficiency of bubbling devices decreases with a significant decrease in specific consumption pair. To ensure deep deaeration, the water in the deaerator must be heated by at least 10 °C, if there is no possibility to increase the steam flow. Bubbling devices can be flooded in the tank in the form of perforated sheets (it is difficult to provide a no-dip mode) or installed in a column in the form of plates. Indicators and symbolsDeaerator performance- consumption of deaerated water at the outlet of the deaerator. In deaerators of the DV type, when superheated deaerated water is used as a heating medium (heat carrier), the consumption of the latter is not included in the performance. Usable capacity of the deaerator tank- the estimated useful volume of the tank, determined in the amount of 85% of its total volume. GOST establishes rows for the selection of tank capacity (for DA 1-75 m³, DP 65-185 m³) and productivity (1-2800 /). The deaerator is designated according to the principle YES (DP, DV) - (productivity, t / h) / (useful tank capacity, m³); columns separately KDA (KDP) - (productivity) , tanks BDA (BDP) - (capacity) . Vortex deaeratorsLiterature
An indispensable condition for the efficient and economical operation of atmospheric deaerators is their competent setting. About what requirements the work of deaerators must satisfy, and how you can configure it yourself - our article. Typical violations in the operation of deaeratorsIn practice, the most common typical mistakes regulation of the operation of atmospheric deaerators: operation without bubbling 1 and operation without a deaeration column.Both of these methods can be successful in terms of removing dissolved gases, the residual content of which is prescribed by the regulations. But the efficiency of deaerators under such regimes is extremely low due to the high specific steam consumption for deaeration. Criteria and conditions for high-quality operation of deaeratorsDuring deaeration, 6-7 grams of dissolved gases are usually removed from 1 ton of water. It has been experimentally established that during the operation of atmospheric deaerators, the maximum amount of vapor should not exceed 22 kg per ton. Based on this, the section of the outlet pipeline and the vapor cooler are selected. Optimum can be considered such a method of operation of the deaerator, in which the required operating parameters are automatically provided both in the deaeration column and in the bubble tank at a minimum required quantity vapor.The main factors affecting the quality of the deaerator are well known:
The principle of operation of the automatic control system for the operation of the deaeratorLet's first look at how the system works automatic control in general (Fig. 1).With an increase in steam consumption, the consumption of feed water from the deaerator tank increases. In this case, there is a deviation of its level, measured by the sensor, from the specified value. The level controller acts on the control valve for supplying water to the deaerator column so that its flow increases and the level is restored. In this case, the valve stem takes a new position corresponding to a higher flow rate.
Entering the deaeration column more cold water accompanied by intense condensation of steam coming from the vapor space of the tank. As a result, the pressure in the vapor space decreases. This leads to a change in the control action in the direct acting pressure regulator. In this case, the stem of the control valve occupies a new position corresponding to a higher steam flow. But the pressure in the vapor space, however, will be somewhat lower than the original. This is how proportional control should be. How will the water temperature in the tank change in this case (Fig. 2)? It is obvious that it will quickly drop to a new value corresponding to the established pressure in the vapor space. This will happen partly due to the entry of water with a lower temperature from the column, partly due to the evaporation of a small amount of "overheated" water accumulated in the tank. A decrease in water temperature will increase the opening of the steam supply valve for bubbling. The steam consumption for bubbling will increase, part of it will condense in the water volume, and part, having passed the steam space, will fall into the deaeration column.
Now consider the reverse situation. What happens when the load is reduced? There will be no peculiarities in the operation of the level regulator and the pressure regulator. The level regulator will restore it, while reducing the water flow, and the pressure regulator will reduce the steam supply to the steam space. In this case, the established pressure will be slightly higher than the initial one, respectively, the water temperature will also be somewhat higher after a while. After all, the boiling point (condensation) is uniquely related to pressure. An example of temperature change depending on the load is shown in fig. 3.
Unlike level and pressure regulators, the result of the action of the steam flow regulator on bubbling can have an unpleasant feature. And it is directly related to how well it is configured. The fact is that with a careless setting, the set temperature may be less than or the same as that established at elevated pressure. In this case, there will be no reduction in the supply of steam for bubbling, but its complete cessation. As a result, the deaeration regime will be violated. The principle of operation of automatic regulatorsNow let's look at how each regulator works separately. Let's start with the pressure regulator, which determines the flow of steam into the deaeration column. We only note that in fact it supplies steam to the vapor space of the tank. From the tank through impulse tube pressure is transferred to the regulator actuator diaphragm. Thus carried out Feedback. Example flow characteristics direct acting valve is shown in fig. 4.
This regulator has a proportional characteristic. With such a characteristic, a larger difference between the current and set value of the parameter corresponds to a larger stroke of the rod. Change range set pressure depends on diaphragm area and spring range. The control deviation in our case is the difference between the pressure of 0.2 bar, corresponding to the operating pressure in the deaerator, and the current pressure, corresponding to the operating point on the flow characteristic of the valve. The regulator responds to pressure changes almost instantly. The delay time is mainly determined by the time the drive cavity is filled or emptied. Now let's take a closer look at how the steam flow regulator for bubbling works. We will call it a flow controller, although such a system is usually used as a temperature controller. This regulator also has a proportional characteristic. The range of change in the reference depends on the volume of liquid in the sensing element and its coefficient of volumetric expansion. With this characteristic, a larger difference between the current temperature value and its set value corresponds to a larger stem stroke. The full stroke of the pusher rod is 10 mm and corresponds to a change in the temperature of the liquid in the sensing element by 10ºС. The full stroke of the valve plunger, depending on the diameter, is from 3 to 9 mm. In this case, when the valve stem is moved from 0 to 20%, the flow increases from 0 to 75% of the total flow. This is a feature of the flow characteristic of the quick opening valve. Thus, the flow rate will change linearly only if the current movement of the valve plug does not go beyond linear section consumption characteristics. Another feature of the regulator under consideration is its inertia. The fact is that it takes some time to heat or cool the liquid in the sensing element. Its duration, among other things, depends on the method of installation of the sensor. The longest delay time will be when using a dry sleeve. The smallest - when mounting without a protective sleeve. It is important to note that in any case, the delay time of the flow controller is significantly longer than that of the pressure controller. Therefore, when joint work regulators, their mutual influence does not lead to regime fluctuations. Let us dwell briefly on the operation of the level controller. The correctness of its operation is determined by the observance of the procedure for setting up, prescribed in the instructions. As a result of tuning, PID parameters are set corresponding to the integral quality criterion. Conditions for the successful completion of work on setting up the deaeratorIt is necessary to say about the most important conditions, without which any attempt to set up the work of deaerators is like wandering in the dark.
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