How does a deaerator work in a boiler room. Deaerators
Heating boilers most often made of steel. The water passing through them contains oxygen and carbon dioxide. Both of these elements have metal constructions the boiler is extremely Negative influence. Constant contact of steel with these gases inevitably leads to its rusting. In order to correct the situation and extend the life of the equipment, a special installation is switched on in boiler rooms - a deaerator. What it is? We will talk about this later in the article.
Definition
The deaerator is called special equipment, designed to remove oxygen from the coolant of heating systems by heating the latter with steam. Thus, in addition to the cleaning function, devices of this type also perform thermal. The same deaeration unit can be used to heat and treat both feed and make-up water.
Design features
The relative simplicity of design is what distinguishes the deaerator. What is it, we found out. Now let's see how this equipment works. It is a boiler tank deaerator (BDA) with a vertical column (KDA) mounted on it, mounted on supports. Optional element equipment of this type is a hydraulic system that protects it from overpressure. The column is welded to the tank without a flange - directly.
On the horizontal tank deaerator, inlet and outlet pipes were installed to connect the medium supply and discharge lines. Plums are installed below. Another design element is a collection tank designed to collect degassed water. It is located under the bottom of the BDA.
Equipment such as a deaerator, the diagram of which is presented below, usually consists of two water seals. One of them protects the device from any excess allowable pressure, and the second - from the dangerous. Also in the design hydraulic system deaerator included expansion tank. The vapors from the deaerator enter a special cooler, which has the form of a horizontal cylinder.
Column design
The column is a cylindrical shell with an elliptical bottom. As on the tank, it has branch pipes for supplying and discharging the medium. Inside the column there are special plates with holes through which water passes. This design allows you to significantly increase the area of contact between the medium and steam, and therefore, to produce heating at maximum speed.
Equipment types
In modern boiler rooms, a water deaerator can be installed:
vacuum;
atmospheric.
In the first type of deaerators, the removal of gases from water is carried out in a vacuum. The design of such installations additionally includes a steam or water jet ejector. The latter type of nodes is most often used in systems with medium or low power. Instead of ejectors, special pumps can be used to create a vacuum. Some disadvantage of equipment such as a vacuum deaerator is that steam must be removed from it forcibly, while it comes out of the atmosphere naturally - under pressure.
In addition to the two types of deaerators considered, high-pressure devices can be installed in boiler rooms. They work at 0.6-0.8 MPa. Sometimes in thermal scheme boiler rooms also include reduced pressure equipment.
Scope of use
Where can a deaerator be used? What is it, you now know. Since such a device is designed to degas the working environment, it is mainly used where there is heating equipment made of steel.
Most often, deaerators are used in heating and hot water systems. Boiler rooms with hot water boilers usually equipped with vacuum type. Also in such schemes atmospheric deaerators can be used. Reduced and increased pressure installations are mainly used in systems that function due to the operation of a steam boiler. The first variety (at 0.025-0.2 MPa) is mounted in not too powerful systems designed for a small number of consumers. are used in thermal circuits with boilers supplying a large number of pair.
Disc deaerator: principle of operation
The gas purification scheme in deaerators is implemented in two stages: jet (in the column) and bubbling (in the tank). In addition, a flooded bubbling device is included in the system. Water is fed into the column, where it is treated with steam. Then it flows into the tank, is kept in it and is discharged back into the system. Steam is initially supplied to the BDA. After ventilation of the internal volume, it enters the column. Passing through the holes of the bubbling tray, the steam heats the water to saturation temperature.
The jet method removes all gases from the water. At the same time, steam condenses. Its residues are mixed with the gas released from the medium and discharged into the cooler. The steam condensate drains into drainage tank. During the settling of water in the tank, residual small gas bubbles come out of it. Water is drained into a collection tank. Sometimes a horizontal tank is used only for settling. In such installations, both stages of degassing are placed in a column.
Make-up water deaeration
The coolant in the heating system circulates continuously. But its volume over time, as a result of leaks, still gradually decreases. Therefore, make-up water is supplied to the heating system. Like the main one, it must undergo a deaeration process. Initially, water enters the heater, and then passes through the filters chemical cleaning. Further, as well as nutrient, it enters the deaerator column. Released from flows to the latter directs it to the suction manifold or storage tank.
Chemical deaeration
Thus, the answer to the question of what a boiler room deaerator is is simple. This is equipment designed to boil water with hot steam in order to remove oxygen. However, sometimes gases from the coolant in such installations are not completely removed. In this case, for additional purification, boiler water can be added different kind reagents designed to bind oxygen. It can be, for example, In this case, for high-quality deaeration of water, its heating is required. Otherwise chemical reactions will be too slow. Also, various kinds of catalysts can be used to accelerate the process of oxygen binding. Sometimes water is also deaerated by passing through a layer of ordinary metal shavings. The latter in this case are rapidly oxidized.
Mounting Features
The deaerator device is not too complicated. However, its installation must be carried out with strict observance of all required technologies. When installing such equipment, they are primarily guided by the drawings attached to it by the manufacturer and the design of the boiler room. Before installation, the installation is inspected and depreserved. Found defects are eliminated. The actual installation procedure itself includes the following steps:
the tank is mounted on the foundation;
a spillway neck is welded to it;
the lower part of the column is cut to the outer diameter;
the column is installed on the tank (at the same time, the plates fixed inside it must be located strictly horizontally);
the column is welded to the tank;
a vapor cooler and a water seal are installed;
in accordance with the drawings, the lines are connected;
shut-off and control valves are installed;
are held hydraulic tests equipment.
Spray installations
The designs discussed above are called dish-shaped. There are also spray deaerators. Devices of this type are used less often and also represent a horizontal storage tank large capacity. The absence of a column is what distinguishes such a deaerator. Its working principle is also slightly different. Steam in such installations comes from below - from a comb located horizontally in the tank. The container itself is divided into a heating and deaeration zone. The feed water of the boiler enters the first compartment from the atomizer located on top. Here it is heated to the boiling point and enters the deaeration zone, where oxygen is removed from it by steam.
So, that's all that can be said about such a device as a deaerator. What is it, we hope you understand, since we have given a fairly detailed answer to this question. This is the name of the installation that provides long work hot water and steam boilers. The choice of the type and methods of installation of this equipment is carried out in accordance with technical specifications heating equipment and boiler room project.
Deaeration plants
AND CONDENSATE PUMPS
§ Types, designs, deaerator switching schemes.
§ Material and heat balances of the deaerator.
§ Switching schemes feed pumps, type of drive.
§ Schemes for switching on condensate pumps.
Air dissolved in condensate, feed and make-up water contains corrosive gases (oxygen, carbon dioxide) that cause corrosion of power plant equipment and pipelines. Corrosion increases with increasing water temperature and pressure.
Oxygen and free carbon dioxide enter the feed water with air suction into the condenser and equipment of the regenerative system, which is under vacuum, and with additional water.
For protection against gas corrosion water deaeration is used, i.e. removal of air dissolved in it, or degassing of water, i.e. removal of the corrosive gas dissolved in it.
Used to remove dissolved air thermal deaeration water, which is the main method for removing dissolved gases from water. The oxygen remaining in the water after thermal deaeration is additionally neutralized by binding it chemical reagent(ammonia compounds).
Thermal deaeration of water is based on the following. According to the Henry-Dalton law, the equilibrium concentration of a gas dissolved in water, µg/kg, is proportional to the partial pressure of this gas above its surface and does not depend on the presence of other gases
where is the coefficient of proportionality, depending on the type of gas, its pressure and temperature, mg/(kgּPa). The relative composition of gases when air is dissolved in water, in accordance with this law, differs from their composition in air. For example, at 0°C and normal pressure water contains 34.9% oxygen by volume (21% in air), 2.5% carbon dioxide (0.04% in air), 62.6% nitrogen and other inactive gases (78.96% in air).
The concentration of gas dissolved in water can be expressed in terms of the equilibrium partial pressure:
When the partial pressure of the gas above the water surface is below the equilibrium< происходит десорбция (выделение) газа из раствора; если >, the gas is adsorbed (absorbed) by water, and if = is equal, a state of dynamic equilibrium occurs. Thus, in order to ensure the removal of the gas dissolved in it from water, it is necessary to lower its partial pressure in the surrounding space. This can be achieved by filling the space with water vapor. The process of gas desorption from the solution will in this case be accompanied by water heating to saturation temperature. driving force process of gas desorption is the difference between the equilibrium partial pressure of gas in deaerated water and its partial pressure in a vapor medium.
The absolute pressure above the liquid phase is the sum of the partial pressures of gases and water vapor:
.
Therefore, it is necessary to increase the partial pressure of water vapor above the water surface, achieving , and as a result, obtain .
Feed water for steam boilers of TPPs in accordance with the Rules technical operation power plants (PTE) should contain oxygen less than 10 mcg/kg.
Compared with the removal of O, the release of CO from water is a more difficult task, since in the process of heating water, the amount of carbon dioxide increases due to the decomposition of bicarbonates and the hydrolysis of the formed carbonates.
In addition to removing dissolved aggressive gases from water, deaerators also serve for regenerative heating of the main condensate and are a place for collecting and storing stock feed water.
Thermal deaerators of steam turbine power plants are divided into:
Assigned to:
1) deaerators for feed water of steam boilers;
2) deaerators for additional water and return condensate of external
consumers;
3) make-up water deaerators for heating networks.
Heating steam pressure on the:
1) high pressure deaerators (type DP, working pressure 0.6–0.7 MPa, less often 0.8–1.2 MPa, saturation temperature 158–167 C and 170–188 C, respectively);
2) atmospheric deaerators(type DA, working pressure 0.12 MPa, saturation temperature 104 C;
3) vacuum deaerators (type DV, operating pressure 0.0075–0.05 MPa, saturation temperature 40–80 C).
According to the method of heating deaerated water on the:
1) deaerators of mixing type with mixing of heating steam and heated deaerated water. This type of deaerators is used at all TPPs and NPPs without exception;
2) superheated water deaerators with external preheating of water with selective steam.
By design (according to the principle of formation of an interfacial surface) on the:
1) deaerators with a contact surface formed during the movement of steam and water:
a) jet-sparging;
b) film type with random packing;
c) jet (dish) type;
2) deaerators with a fixed phase contact surface (film type with an ordered packing).
AT vacuum deaerators, the pressure is below atmospheric and an ejector is required to suck the gases released from the water. There is a danger of re-contamination of water with oxygen due to suction atmospheric air in the path before the pump. Vacuum deaerators are used when it is required to deaerate water at a temperature below 100 (make-up water of heating networks, water in the chemical treatment path). These also include condenser deaeration attachments.. Water deaeration is carried out not only in deaerators, but also in condensers steam turbines. However, on the way from the condenser to the condensate pump, the oxygen content may increase due to air leakage through the pump seals and other leaks.
atmospheric deaerators operate with a slight excess of internal pressure above atmospheric pressure (approximately 0.02 MPa), which is necessary for gravity evacuation of released gases into the atmosphere. The advantage of atmospheric deaerators is minimum thickness body walls (metal savings).
Currently, atmospheric deaerators are mainly used for make-up water of evaporators and make-up water of heating networks.
High pressure deaerators are used for the treatment of feed water of power boilers with an initial steam pressure of 10 MPa and above. The use of deaerators of the DP type at thermal power plants allows, at more than high temperature regenerative water heating is limited in the thermal scheme to a small number of series-connected HPH (no more than three), which contributes to an increase in reliability and reduction in the cost of the installation and has a positive effect on operation due to a smaller drop in the temperature of the feed water when the HPH is turned off.
In deaerators superheated water water first enters the upstream surface heater, where the water to be subsequently deaerated is heated to a temperature that is 5–10 °C higher than the saturation temperature at the pressure in the deaerator. To prevent the water from boiling in the heater, the water pressure must be 0.2–0.3 MPa higher than in the deaerator. When entering the deaerator, the water pressure decreases and the water boils, releasing steam, which fills the column.
The principle of preheating followed by boiling water improves the quality of deaeration. However, superheated water deaerators are complex in design, not reliable enough, difficult to regulate, and therefore are not currently used in our power industry.
Useful for thermal deaeration, the principle of preheating water with subsequent boiling is implemented in deaerators bubbling type. In them, steam is introduced under the water level in the accumulator or in an intermediate tank located in the column. Due to the hydrostatic backwater, the steam introduced into the water layer has a slightly increased pressure compared to the pressure in the vapor space of the column. Upon contact with water in the depth of the layer, the steam heats it to a temperature exceeding the saturation temperature at the surface. When the water moves, entrained by steam bubbles up the bubbling compartment, the water boils and intensively releases dissolved gases.
In deaerators mixing type heating steam is introduced into lower part columns, filling it, and water in it upper part. The water flow is broken up into drops, jets or films to increase the surface of contact with steam and moves towards it from top to bottom. The gases escaping from the water are removed through the flash line located at the top of the column.
Together with the gases, a certain amount of steam, called evaporation, is removed from the deaerator column. Usually, evaporation is 1–2 kg, and if there is a significant amount of free or bound carbon dioxide in the source water, it is 2–3 kg per ton of deaerated water. Evaporation causes an additional loss of heat and coolant and, for these reasons, should be minimal.
Table 10.1
Free carbon dioxide in the water after the deaerator should be absent, and the pH value (at 25) of the feed water should be maintained within 9.1 0.1.
Dokotlovaya water treatment for steam boilers necessarily includes a deaeration stage. Water treatment for hot water boilers and heating networks also sometimes require the removal of oxygen and carbon dioxide. It is obvious that dissolved oxygen when heating water has a very negative effect on the equipment of the boiler room. Deaeration can be done by various methods. It should be noted that even in the presence of deaeration equipment, it may be necessary to additionally reduce the concentration of dissolved oxygen and carbon dioxide using special reagents .
If deaeration does not work well, apply corrective water treatment technologies (see here) .
Methods for deaeration of feed water in boiler rooms
Use of reagents
To bind oxygen in the feed and network water, you can use complex reagents for water treatment, allowing not only to reduce the concentration of oxygen and carbon dioxide to standard values, but to stabilize the pH of the water and prevent the formation of deposits. Thus, the required quality can be achieved. network water without the use of special deaerating equipment.
Chemical deaeration
The essence of chemical deaeration is the addition of reagents to the feed water, which make it possible to bind the dissolved corrosive gases contained in the water. For hot water boilers, we recommend the use of a complex reagent - an inhibitor of corrosion and deposits Advantage K350B. To remove dissolved oxygen from water during water treatment for steam boilers - Amersite 10L, which allows you to work without deaeration. If the existing deaerator does not work correctly, we recommend using a reagent to correct the water chemistry regime Boilex E460B.
Atmospheric deaerators with steam supply
For water deaeration in boiler rooms with steam boilers, mainly thermal two-stage atmospheric deaerators (DSA) are used, operating at a pressure of 0.12 MPa and a temperature of 104 ° C. Such a deaerator consists of a deaeration head with two or more perforated plates, or other special devices, due to which the source water, breaking into drops and jets, falls into the storage tank, encountering countercurrent steam on its way. In the column, water is heated and the first stage of its deaeration takes place. Such deaerators require the installation of steam boilers, which complicate the thermal scheme of a hot water boiler and the scheme of chemical water treatment.
Vacuum deaeration
In boiler rooms with hot water boilers, as a rule, vacuum deaerators are used, which operate at water temperatures from 40 to 90 ° C.
Vacuum deaerators have many significant drawbacks: high metal consumption, a large number of additional auxiliary equipment (vacuum pumps or ejectors, tanks, pumps), the need to be located at a considerable height to ensure the operation of make-up pumps. The main disadvantage is the presence of a significant amount of equipment and pipelines under vacuum. As a result, air enters the water through the seals of pump shafts and fittings, leaks in flanged joints and welded joints. In this case, the effect of deaeration completely disappears, and even an increase in the oxygen concentration in the make-up water is possible compared to the initial one.
Lab #4
STUDYING THE PRINCIPLE OF OPERATION AND SCHEMES OF DEAERATORS
Objectives of the work: to study the principle of operation and schemes of deaerators, laboratory equipment that allows deaeration, to study the operation of a deaerator, to perform working water purification.
1. General information
Deaeration of feed water of steam boilers and make-up water of heating networks is mandatory for all boiler houses. Deaerators are designed to remove non-condensable gases dissolved in water from water. The presence of oxygen and carbon dioxide in feed and make-up water leads to corrosion of feed pipes, boiler pipes, boiler drums and network pipelines, which can lead to a severe accident. The presence of even such inert gases as nitrogen is also extremely undesirable, it interferes with heat transfer and reduces the heat output of heaters.
The amount of residual content of O 2 and CO 2 in the feed water of steam boilers is strictly regulated by the rules of Gosgortekhnadzor. So for boilers with a steel economizer at a pressure of up to 1.4 MPa, the content of O 2 should be no more than 30 μg / kg. Free carbon dioxide (CO 2 ) in the feed water after the deaerators should be absent.
For deaeration of feed water in boiler houses, jet mixing thermal deaerators are used. Depending on the pressure maintained in the deaerator, there are high pressure deaerators, atmospheric and vacuum deaerators. In boiler plants with steam boilers for pressures up to 4.0 MPa, atmospheric deaerators are used.
2. Thermal deaeration of water
Thermal deaeration of water. Corrosive (O2, CO2, NH3) and other gases are dissolved in the water of thermal power plants and require removal. The removal of gases from water is carried out mainly with the help of thermal deaerators, calciners and chemically.
Thermal deaeration (degassing) of water is based on the Henry-Dalton law, which is expressed in relation to this case by the following equation, valid for equilibrium conditions:
m = kppg = kp (p - pp),
where m is the solubility of gases in water;
p is the total pressure of gas and water vapor in the space above water;
pp, pg - partial pressures of steam and gas, respectively, in the same space;
kp is the solubility coefficient of a gas in water, depending on the temperature (the higher the temperature, the lower the solubility coefficient).
If water is heated to the boiling point, then, on the one hand, the solubility coefficients of gases in water become equal to zero, and on the other hand, the partial vapor pressure above the water surface becomes equal to the total pressure of the mixture. As a result of equilibrium, the solubility of gases in water becomes equal to zero. Hence the conclusion: to remove the gases dissolved in it from water, it is enough to heat it to the boiling point. This is the essence of thermal degassing.
Equation (18.2.1) characterizes the limit state of equilibrium, to which the system will come if certain conditions are created and enough
time. Let's briefly consider these conditions.
From the above it follows that the water must be heated. Usually, deaerated water flowing down in streams, drops and a film is heated by steam flowing towards it. Then the required amount of heat Q to heat water per unit time in the amount W from the initial temperature t1 to the boiling point tb (and the corresponding values of enthalpy i1, i")
where F- heat exchange surface area;
tWed- average water temperature for heat exchange conditions;
t- temperature head;
- heat transfer coefficient.
The right side of equation (18.2.2) allows us to conclude that it is desirable to make the heat exchange surface area as large as possible. This makes it possible to speed up the process of heat transfer and reduce the dimensions of the apparatus. Solving these problems, the water flow is crushed into jets, drops or thin films. To ensure maximum temperature difference, a counterflow of steam and water is created. The splitting of the flow and, especially, its runoff with thin films provide turbulence of the flow and, accordingly, an increase in the heat transfer coefficient.
By the same means, an increase in the rate of gas desorption from water is achieved, since the amount of gas removed from it per unit time is equal to the concentration of gas in water and in space above water, and therefore, is taken into account. (18.2.1), the difference in gas pressure in accordance with the equation
m = kdF p = kdF (pr .p - pr), (18.2.3)
where pr.p is the so-called equilibrium partial pressure of gas in water, it corresponds to the concentration of gas in water under equilibrium conditions in accordance with (18.2.1.);
pr is the partial pressure of gas over water;
kd is the desorption coefficient, which depends on the turbulence of the water flow, viscosity, surface tension, the rate of diffusion of gas in water, and, consequently, on temperature.
To achieve the minimum partial gas pressure in the space above the water, gases (with an admixture of vapors) are continuously removed from the working space of the deaerator through a special fitting for removing the deaerator steam. If the deaerator is vacuum (i.e., the pressure in it is less than atmospheric pressure), then air is sucked off by steam-jet or water-jet ejectors.
Examples of constructive implementation of deaerators are shown in fig. 12.2.3, 12.2.4. In the first of these cases, the film principle of crushing the water flow is implemented, in the second, the jet principle. On fig. 12.2.4 bubbling is used as the second stage of degassing, i.e., steam bubbles are passed through a layer of water. Bubbling is used for more complete degassing of water, especially for more complete removal of carbon dioxide.
At industrial CHP plants, deaerators are most often fed with steam from industrial controlled turbine extraction, and at condensing power plants - from unregulated turbine extractions (Fig. 18.2.5). When degassing the feed water at the TPP, the deaerator simultaneously performs the function of a heater for the next heating stage in the regeneration system.
Deaerators of the type shown in fig. 12.2.4 are called "superheated" water deaerators. Deaerators do not require heating steam to be supplied to them, steam is formed in them as a result of
throttling heated water to such a pressure, the saturation temperature at which is less than the temperature of the water entering the deaerator. This water turns out to be preliminarily superheated above the temperature in the deaerator, to which it is cooled as a result of throttling and partial conversion into steam.
In the condensers of steam turbines, a fairly complete removal of gases from the main condensate occurs, i.e., the condenser simultaneously acts as a deaerator.
Rice. 18.2.5. Feed water deaerator circuit diagrams.
a-as an independent stage of regenerative water heating; b - as an upstream heater in a given heating stage; c - to controlled extraction at CHPP; /-.steam generator; 2 - turbine; 3-capacitor; 4 - condensate pump; 5 - low pressure heater; 6 - deaerator; 7 - feed pump; 8 - high pressure heater; 9 - pressure regulator.
However, due to air suction through the glands of condensate pumps and other leaks in vacuum system turbine condensate is again polluted with gases. These gases are then removed in atmospheric deaerators (slightly above atmospheric pressure) or pressurized deaerators (pressures several times atmospheric).
The atmospheric deaerator consists of a cylindrical deaeration column and a feed water tank. The flows of deaerated water enter the water distributor, from which they flow evenly over the annular section of the column onto perforated baking sheets. Passing through the holes of the baking sheets, the water breaks into small streams and falls down. Steam is supplied to the lower part of the deaerator column to heat the deaerated water to the boiling point. At a water temperature equal to the boiling point, the solubility of gases in water is zero, which determines the removal of oxygen and carbon dioxide from water. The released oxygen and carbon dioxide with a small amount of steam is removed through the wind pipe at the top of the deaeration column. For the efficient operation of the deaeration column, it is necessary that the gases released from the water are quickly removed from the column, which is ensured by evaporation. The amount of vapor is taken equal to 2 kg per 1 ton of deaerated water.
Deaerator columns are not designed for heating water by more than 10-40 ° C. The optimal mode of operation of the deaerator column, i.e. The best removal of gases from the feed water occurs when the average temperature of all water streams entering the column is 10-15°C below the boiling point at the pressure maintained in the deaerator. For complete deaeration of the feed water, it is absolutely necessary to heat it to the boiling point. Underheating of water even by a few degrees leads to a sharp increase in the residual oxygen content in it. Therefore, deaerators are necessarily equipped with automatic regulators that maintain a correspondence between the flow of steam and water into the column.
Deaerator schemes
a - atmospheric; b - bubbling; 1 - tank; 2 - release of feed water;
3 - water-indicating glass; 4 - safety valve; 5 - plates; 6 - input of chemically purified water; 7 - wind pipe; 8 – condensate inlet; 9 - deaerator column; 10 - steam inlet; 11 - hydraulic shutter; 12 - tray; 13 - lattice; 14 - partition with blinds.
The number and capacity of the installed feed water deaerators are selected based on the full coverage of the feed water consumption by the boilers, taking into account their blowdown and the feed water consumption for injection into the ROU in the maximum winter mode. At least two deaerators must be installed. Backup deaerators are not installed. The useful total capacity of the feed water tanks should ensure its supply for at least 15 minutes in the maximum winter mode. The useful capacity of the tanks is assumed to be 85% of their geometric capacity.
Make-up water must also be deaerated in all cases. The oxygen content in the make-up water should be no more than 50 µg/kg, and free carbon dioxide should be completely absent. In heat supply systems with direct water intake, the quality of make-up water, in addition, must comply with GOST 2874-82 "Drinking water".
Make-up water deaeration is carried out either in thermal mixing atmospheric deaerators or in vacuum deaerators.
Deaerators should be installed on sites with a mark higher than the mark for the installation of feed pumps. The value of this excess is determined by the sum of the required water pressure at the pump inlet, set by the pump manufacturer, and the required hydrostatic head to overcome the resistance of pipelines from the deaerator to the pump. For boilers at pressures of ~4.0 and 1.4 MPa (40 and 14 kgf/cm2), the elevation of the deaerator platform is 10 and 6 m, respectively.
In central boiler plants operating for large open-drawn heat supply systems that require deaeration of make-up water in quantities measured in hundreds of tons, the installation of vacuum make-up deaerators is preferable. A make-up plant with atmospheric deaerators at high make-up water consumption due to the limited unit capacity of atmospheric deaerators (maximum 300 t/h) and the need to install make-up water coolers (up to 70 ° C) behind them turns out to be very cumbersome and expensive. In addition, make-up plants with atmospheric deaerators have one more significant disadvantage: in order to preserve the heating steam condensate, the chemically treated water supplied to the deaerators must be preheated to 90 ° C.
It is heated in water-water heat exchangers-coolers of deaerated make-up water and in steam-water heaters. These heaters, as well as pipelines behind them, are subject to intensive corrosion destruction and do not provide the necessary duration of operation of the heating network feed unit.
Deaeration of make-up water under vacuum makes it possible to get rid of the disadvantages of the make-up installation listed above. The industry produces vacuum deaerators with a unit capacity of up to 2000 t/h, the temperature of the make-up water given out by the deaerator is 40 ° C, and installation of special coolers is not required. At a vacuum in the deaerator of ~0.0075 MPa (0.075 kgf/cm2) at a deaeration temperature of 40°C, no preheating of the chemically treated water supplied to the deaerator is required;
When used for deaeration of make-up water in small vacuum deaerators operating under vacuum - pressure ~ 0.03 MPa (0.3 kgf / cm2), created by water jet ejectors or water ring pumps, the deaeration process proceeds at a temperature of 70 ° C. At the same time, the chemically purified water supplied to the deaerators must be preheated only up to 50°C.
In steam industrial heating boilers with closed heat supply systems, where the consumption of make-up water is determined only by leakages of the heating network, it is allowed to make up the heating network with water from feed water deaerators. Technical characteristics of deaerators are given in tables 10.1 and 10.2 (see appendix).
3. Deaerator vapor coolers
The removal of released oxygen and carbon dioxide from the deaerator column is carried out through a wind pipe in the cover of the deaerator column. Together with oxygen and carbon dioxide, a certain amount of steam leaves the column and takes heat with it, which is lost when the vapor is released into the atmosphere. In order to use the heat of the flash steam, the deaerators are equipped with special surface heat exchangers-coolers of the flash steam, in which the flash steam is condensed with chemically treated water supplied to the deaerator.
4. Feed pumps
Feeding devices are critical elements of the boiler plant, ensuring the safety of its operation. The Gosgortekhnadzor rules impose a number of requirements on feeding facilities.
Feeding devices must provide the necessary flow of feed water, at a pressure corresponding to the full opening of the working safety valves installed on the steam boiler. The total performance of the main pumps must be at least 110% for all working boilers at their nominal steam capacity, taking into account the costs of continuous blowdown, desuperheaters, reduction-cooling and cooling units. The total performance of the feed standby pumps should provide 50% of the normal performance of all operating boilers, taking into account the blowdown, water flow to the reduction-cooling and cooling units. When choosing a pump, it is necessary to strive to ensure that, under operating conditions, the pump load is close to the nominal one. When installing multiple centrifugal pumps for parallel operation it is necessary to install pumps with the same characteristics. The loading of pumps with different characteristics in the process of capacity control changes unevenly, and the pumps may not provide the required water supply in modes other than the nominal (for which they are selected), or they will work uneconomically.
The design head of the feed pump Рnas, Pa, is determined from the following expression:
Pnas = Pk (1 +
R) + Rack + Rp.v.d + 
,
where Rk - overpressure in the boiler drum;
р – pressure reserve for opening safety valves, taken equal to 5%;
Рк – resistance of the water economizer of the boiler;
Рp.v.d – resistance of high-pressure regenerative heaters;
Рnag tr - resistance of feed pipelines from the pump to the boiler, taking into account the resistance of automatic boiler power regulators;
Рvsos tr - resistance of suction pipelines;
Рс.в - pressure created by a column of water, equal in height to the distance between the axis of the boiler drum and the axis of the deaerator;
Pdr - pressure in the deaerator.
When calculating resistances, the density of water is taken from its average temperature in the discharge path, including the water economizer.
The calculated pressure in the discharge pipe of the feed pumps should be increased by 5-10% to provide a margin for an unforeseen increase in the resistance of the feed path. A non-return valve must be installed on the discharge pipe of the feed centrifugal pump.
The operation of feed pumps with a capacity below 10-15% of the nominal flow rate is not allowed, as this leads to pump “steaming”. To protect against a decrease in feed water consumption in excess of the allowable level, the pumps are equipped with special relief valves and recirculation lines connecting them to deaerators, where water is discharged. The recirculation lines are switched on when the pumps are started and stopped. Shut-off valves on these lines have manual control. Check valves installed downstream of the pumps have branch pipes for connecting recirculation lines.
The range of feed pumps for boilers used in boiler houses is shown in Table 10.5. Both feed centrifugal pumps and steam pumps should be installed at 0.0 below the deaerators or at a small distance from them, so that the resistance of the suction pipelines is as low as possible, according to the technological design standards - no more than 10000 Pa (1000 mm w.c.) .
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. AT 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 emergencies the deaerator and the entire system must be used 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.
AT 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.