Practical recommendations for operating the deaerator. Deaeration of water in boiler rooms without steam supply
Foreign terminology
In a significant part of foreign systems of technical terms, there is no single term “deaerator” to describe an element of the thermal circuit of a station in the form of a tank with a column; for example, in German the column is called Entragaserdom, and the concept of “deaerator” (Entgaser) refers only to it, and the feedwater storage tank is Speisewasserbehälter. IN lately and in some Russian-language publications (about non-traditional or translated designs for our enterprises) the tank is separated from the deaerator.
Purpose
- Protection of pipelines and equipment from corrosion.
- Preventing air bubbles that interfere with the permeability of hydraulic systems, the normal operation of nozzles, etc.
- Protection of pumps from cavitation.
Operating principle
In a liquid, gas can be present in the form of:
- actual dissolved molecules;
- microbubbles (about 10−7) formed around particles of hydrophobic impurities;
- as part of compounds that are destroyed at subsequent stages of the technological cycle with the release of gas (for example, NaHCO 3).
In the deaerator, a process of mass transfer occurs between two phases: liquid and vapor-gas 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 phase interface; k- speed coefficient, depending, in particular, on the characteristic diffusion path that the gas must overcome to exit the liquid. Obviously, for complete removal of gases from a liquid, it is required (the partial pressure of the gas above the liquid must tend to zero, that is, the released gases must be effectively removed and replaced by steam) and an infinite process time. In practice, they are set by a technologically permissible and economically feasible degassing depth.
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 steam (evaporation) carries away gases (decreases), and the diffusion coefficient is high (increases) k).
IN vortex deaerators do not actually heat the liquid (this is done in heat exchangers in front of them), but use hydrodynamic effects that cause forced desorption: the liquid bursts at the very weak points- along gas microbubbles, and then in a vortex the phases are separated by inertial forces under the influence of density differences.
In addition, it is 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/cm2, a decrease of 30-50% occurs, k increases approximately 1000 times, which leads to coagulation of the bubbles with subsequent release from the water under the influence of Archimedean force.
Vapor
Vapor is a mixture of gases released from water and small quantity steam to be evacuated from the deaerator. For normal operation deaerators of common designs, its consumption (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. To avoid losses of the working fluid from the cycle, the evaporation in large installations is condensed. If the vapor cooler used for this purpose is installed on the deaerator source water (as in the figure), it must be sufficiently subcooled to the saturation temperature in the deaerator. When using vapor on ejectors, it condenses on their refrigerators, and a special heat exchanger is not needed.
Thermal deaerators
Thermal deaerators are classified by pressure.
Atmospheric deaerators (see figure) require the smallest wall thickness; the vapor is removed from them by gravity under the influence of a slight excess of pressure above atmospheric pressure. Vacuum deaerators can work in conditions where there is no steam in the boiler room; however, they require a special device for suction of vapor (vacuum ejector) and greater wall thickness, in addition, bicarbonates with low temperatures do not decompose completely and there is a danger of repeated air leaks along the path 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 HPHs and use vapor as a cheap working medium for steam-jet condenser ejectors; The deaeration attachment of the condenser, in turn, is a vacuum deaerator.
How heat exchangers thermal deaerators can be mixing (usually, heating steam and/or water is supplied to the volume of the deaerator) 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 networks.
According to the method of creating the phase contact surface, mixing deaerators are divided into inkjet, 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 onto the vapor, simultaneously condensing on the water. In small deaerators, the column can be integrated into one housing with the tank; usually it looks like a vertical cylinder docked on top horizontal tank(cylindrical container with elliptical or conical bottoms). There is a water distributor at the top, a steam distributor at the bottom (for example, an annular perforated pipe), and between them is the active zone. The thickness of a column of a given productivity is determined by the permissible irrigation density active zone (water flow per unit area).
In deaerators jet type water passes through the active zone in the form of jets, into which it can be divided by 5-10 perforated plates (ring plates with a central passage of steam alternate with circular ones of smaller diameter, flowing around the edge). Jet deaeration devices have simple design and low vapor 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 high metal consumption and is inconvenient for repair work. Such columns are used as the first stage of water treatment in two-stage jet-bubble deaerators.
There are also nozzle (drip) deaerators, where water is sprayed from the nozzles in a droplet form; efficiency due to phase refinement is high, however, the operation of the nozzles deteriorates when clogged and at reduced costs, and a lot of electricity is required to overcome the resistance of the nozzles.
In deaerators with columns film type the water flow is divided into films that envelop the filler nozzle, along the surface of which the water flows down. Two types of nozzle are used: ordered and disordered. 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 are 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 water flow throughout the nozzle. A disordered packing is made of small elements of a certain shape, randomly poured into a selected part of the column (rings, balls, saddles, omega-shaped elements). It provides a higher mass transfer coefficient than an ordered packing. Film deaerators are insensitive to contamination by scale, sludge and iron oxides, but are more sensitive to overload.
In deaerators bubbler type the stream of steam that is introduced into the water layer is split into bubbles. The advantage of these deaerators is their compactness with high quality deaeration. In them, some overheating of water occurs relative to the saturation temperature corresponding to the pressure in the vapor space above the surface. The amount of superheating is determined by the height of the liquid column above the bubbling device. When the water vapor entrained by the bubbles moves upward, it boils, facilitating better separation 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 the decomposition of bicarbonates NaHCO 3, turbulization of the liquid. The efficiency of bubbling devices decreases when the specific consumption pair. To ensure deep deaeration, the water in the deaerator must be heated by at least 10 °C, if it is not possible to increase the evaporation flow. Bubbler devices can be submerged in a tank in the form of perforated sheets (it is difficult to ensure failure-free operation) or installed in a column in the form of plates.
Indicators and designations
Deaerator performance- flow rate of deaerated water at the outlet of the deaerator. In deaerators of the DV type, when using superheated deaerated water as a heating medium (coolant), the consumption of the latter is not included in the performance.
Useful capacity of deaerator tank- calculated useful volume of the tank, determined at 85% of its total volume.
GOST establishes rows for selecting tank capacity (for DA 1-75 m³, DP 65-185 m³) and productivity (1-2800 /). The deaerator is designated according to the principle DA(DP,DV) - (productivity, t/h)/(useful tank capacity, m³); columns separately KDA (KDP) - (performance), tanks BDA (BDP) - (capacity).
Vortex deaerators
Literature
- Richter L. A., Elizarov D. P., Lavygin V. M. Chapter three. Deaerators // Auxiliary equipment for thermal power plants. - M.: Energoatomizdat, 1987. - 216 p.
- Kuvshinov O. M. Rust? Down with oxygen! . kwark.ru. “Science and Life” No. 12 (2006). Archived from the original on April 8, 2012. Retrieved September 3, 2011.
- Kuvshinov O. M. KVARK slot deaerators are an effective device for liquid deaeration. kwark.ru. “Industrial Energy” No. 7 (2007).
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 design, installation and operation of a vacuum deaerator is hot water boiler houses (especially in the block version) and heating points. Vacuum deaerators are also actively used in food industry for deaeration of water necessary in the technology of preparing a wide range of drinks.
Water flows used to feed the heating network, boiler circuit, and hot water supply network are subjected to vacuum deaeration.
Features of the operation of a vacuum deaerator.
Since the process 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 coolant is necessary to heat the water in front of the vacuum deaerator. Coolant temperatures of up to 90 °C are provided at most facilities where it is potentially possible to use a vacuum deaerator.
The main difference between a vacuum deaerator and atmospheric deaerator in the system for removing vapor from the deaerator.
In a vacuum deaerator, vapor (a vapor-gas mixture formed when saturated vapors and dissolved gases are released from water) is removed using a vacuum pump.
As a vacuum pump you can use: vacuum liquid ring pump, water jet ejector, steam jet ejector. They are different in design, but are based on the same principle - reduction static pressure(creation of rarefaction - vacuum) in a liquid flow with increasing flow speed.
The speed of fluid flow increases either by moving through a tapering nozzle (water jet ejector) or by swirling the fluid as the impeller rotates.
When vapor 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 its boiling point. At the water-gas phase boundary, a difference in concentrations of gases dissolved in water (oxygen, carbon dioxide) arises and, accordingly, a driving force deaeration process.
The quality of deaerated water after the vacuum deaerator depends on the efficiency of the vacuum pump.
Features of installing a vacuum deaerator.
Because the temperature of the water in the vacuum deaerator is below 100 °C and, accordingly, the pressure in the vacuum deaerator is lower than atmospheric - vacuum, the main question arises when designing and operating a vacuum deaerator - how to supply deaerated water after the vacuum deaerator further into the heat supply system. This is the main problem of using a vacuum deaerator for deaerating water in boiler houses and heating points.
This was mainly 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. The water flowed by gravity into battery tank located at the zero mark. The installation height of the vacuum deaerator was selected based on the maximum possible vacuum (-10 m.water column), the height of the water column in the battery tank, the resistance of the drain pipeline and the pressure drop necessary to ensure the movement of deaerated water. But this entailed a number of significant shortcomings: increase in initial construction costs (16 m high shelving 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 boiler houses that are actively being designed and installed, this solution is not applicable.
The second option for solving the issue of supplying deaerated water after a vacuum deaerator is to use an intermediate tank for storing deaerated water - a deaerator tank and deaerated water supply pumps. 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 deaerated water from the vacuum and supply it further into the system. To prevent the occurrence of cavitation in the deaerated water supply pump, 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 specified in the pump passport as cavitation reserve 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 design option for the vacuum deaerator is the ability to install the vacuum deaerator at a low height, indoors. Deaerated water supply pumps will ensure pumping of deaerated water further into storage tanks or for make-up. To ensure a stable process of pumping deaerated water from a deaerator tank, it is important to select the correct deaerated water supply pumps.
Increasing the efficiency of the vacuum deaerator.
Since vacuum deaeration of water is carried out at water temperatures below 100 °C, the requirements for the technology of the deaeration process increase. The lower the water temperature, the higher the solubility coefficient of gases in water, the more complicated process deaeration. It is necessary to increase the intensity of the deaeration process; apply accordingly constructive solutions 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 the saturation pressure and obtain a superheated state of water can significantly increase the efficiency of the deaeration process and reduce overall dimensions and the weight of the vacuum deaerator.
For comprehensive solution On the issue of installing a vacuum deaerator in a boiler room at zero level with a minimum overall height, a block vacuum deaerator BVD was developed, tested, and successfully put into serial production. With a deaerator height of just under 4 m, the block vacuum deaerator BVD allows for effective deaeration of water in a capacity range from 2 to 40 m3/h for deaerated water. A block vacuum deaerator occupies a space in the boiler room of no more than 3x3 m (at the base) in its most productive design.
To understand the principle of operation of a deaerator, it is necessary to understand why water is deaerated at all.
Why do you need a deaerator at a thermal power plant?
Metal corrosion occurs on the surface of the metal, where it comes into contact with water, then destruction occurs inside the metal. Corrosion mainly depends on the content of dissolved oxygen in water and carbon dioxide (it makes it difficult to form a protective layer of metal oxides).
The corrosion rate of steel has a linear dependence on the oxygen concentration in water. Moreover, this dependence is directly proportional (if you increase the oxygen concentration by 2 times, then the corrosion rate will also increase by 2 times).
Pipelines with cold water (less than 25 C) are little susceptible to corrosion. When the temperature rises, if you do not want to pay for repairs and downtime of insanely expensive equipment (for example, pipes in a steam boiler may burn out, heaters break down, or pipeline fittings etc.) it is necessary to use chemical or thermal methods to remove dissolved gases from water.
For domestic and foreign boilers, there are feedwater quality standards, which, depending on the temperature and pressure of the boiler, specify the requirements for the oxygen content in the feedwater.
A simple but very interesting example
The example is taken from the book; we will omit the calculations given there so as not to fill our heads with unnecessary information.
- Consumption network water V DHW networks— 400 t/h
- Pipeline diameter – DN300
- Oxygen content in starting point pipes 9.3 mg/kg
- Oxygen content at the end point of the pipe is 4.15 mg/kg (50% of the oxygen went to corrosion)
- The heating network operates 5000 hours per year
The bottom line is that such a pipe loses 0.55 mm of its wall thickness per year due to corrosion. Now imagine what will happen in a few years with our 325x8 pipe? That is why it is necessary to consider how the dearator of steam boilers of thermal power plants works.
Types of deaerators
Thermal deaerators of steam turbine installations of power plants are divided into:
By purpose to:
- steam boiler feedwater deaerators;
- deaerators of additional water and return condensate of external consumers;
- deaerators of make-up water of heating networks.
By heating steam pressure to:
- high-pressure deaerators (DP), operating at a pressure of 0.6-0.8 MPa, and at nuclear power plants - up to 1.25 MPa and used as deaerators of feedwater at thermal power plants and nuclear power plants;
- atmospheric deaerators (DA), operating at a pressure of 0.12 MPa;
- vacuum (DV), in which deaeration occurs at a pressure below atmospheric: 7.5-50 kPa.
According to the method of heating deaerated water to:
- deaerators of mixing type with mixing of heating steam and heated deaerated water. This type of deaerators is used at all thermal power plants and nuclear power plants without exception;
- deaerators of superheated water with external preheating of water with selected steam.
According to the design (according to the principle of formation of the interphase surface) to:
Deaerators with a contact surface formed during the movement of steam and water:
- a) jet-bubbling;
- b) film type with a random packing;
- c) jet (disc) type;
Deaerators with a fixed phase contact surface (film type with an ordered nozzle).
According to the method of increasing the contact surface of water with heating steam, deaerators are divided into
- drip
- inkjet
- film
- with nozzles
- bubbling
- combined.
In drip deaerators, water is supplied to the deaerator in the form of drops using nozzles or nozzles. Spraying water into droplets ensures high efficiency of water deaeration; however, due to clogged nozzles, drip deaerators are not reliable enough in operation. In addition, the use of nozzles and nozzles requires significant energy consumption for spraying.
In jet deaerators, the water supplied to top part deaerator column, enters the water distribution device, under which several perforated plates (sieves or baking trays) are installed. Merging in streams from the distributor and plates, the water forms a rain drift, which is intersected by the flow of heating steam supplied to the bottom part columns.
In film deaerators, water is supplied through a nozzle and, hitting the rosette, is sprayed onto the vertical (concentric or rectangular) sheets located underneath it. Thin films of deaerated water flow down the sheets, and heating steam passes between the sheets from bottom to top.
In deaerators with nozzles, the water supplied to the upper part of the deaerator column is divided into separate jets, which flow onto the nozzle that fills the deaeration column. The purpose of the nozzle is to crush the flow into the finest streams and films. Heating steam is supplied between the elements of the nozzle from the bottom up towards the water. Wooden gratings, Raschig rings, metal ceramic rings, and specially shaped elements are used as attachments. Ring elements are placed in a certain order or randomly on a grid supporting them. As a result, effective interaction of water with heating steam occurs.
In bubble deaerators, contact between steam and water is achieved by passing steam through a layer of liquid. Bubbling provides several times (from 3 to 10) large surface contact of water and steam than when splitting water into jets. However, the use of bubbling deaerators is complicated by the fact that the heat of the steam supplied to the bubbling deaerator is usually not enough to heat the water to the saturation temperature.
As a rule, bubbling is used as a second stage of deaeration in combination with a jet or nozzle method of water distribution. Such deaerators are called two-stage. In jet-bubbling deaerators, heating of water to saturation temperature and initial gas removal occur in small-sized jet columns, and final deaeration is carried out by treating the water with steam in a bubbling device located in the storage tank.
Combined deaerators combine several methods of dividing water into jets and drops.
Based on the pressure in the deaerator at which the deaeration process occurs, thermal deaerators are divided into vacuum, atmospheric, medium and high pressure. In vacuum deaerators, gas removal occurs at a pressure below atmospheric (
Types of deaerators
Species thermal deaerators for turbines exist for installation in boiler houses, power plants, thermal power plants, nuclear power plants for water deaeration: by purpose, by heating steam pressure, by the method of heating deaerated water, by design. The whole list is on helpinginer.ru
Deaeration of feed and make-up water in the boiler room
Deaeration of feed and make-up water in a steam boiler house is the release of feed water from air dissolved in it, which includes oxygen and carbon dioxide. When dissolved in water, oxygen and carbon dioxide cause corrosion of the supply pipes and heating surfaces of the boiler, as a result of which the boiler equipment fails.
There are a number various devices for deaeration of feed water. Thermal deaerators are the most widely used atmospheric type low pressure (0.02-0.025 MPa) and high pressure (0.6 MPa), as well as vacuum with pressure below atmospheric. The latter are used in boiler houses with hot water boilers, since in these boiler houses there is no steam and degassing of the feed water is carried out due to the vacuum created by water-jet ejectors.
The thermal deaerator is used to remove dissolved oxygen and carbon dioxide from feed and make-up water by heating it to boiling temperature. In Fig. Figure 5 shows a diagram of the operation of a mixing-type atmospheric deaerator. The deaerator consists of a tank 1 and speakers 13, inside which a number of distribution plates 5, 6 and 12. Feed water (condensate) from the pumps enters the upper part of the deaerator at
Rice. 5. Mixing type atmospheric deaerator with vapor cooler
1 - tank (battery), 2 - release of feed water from the tank, 5 - water indicator glass, 4 - pressure gauge, 5, 6 And 12 - plates, 7 - draining water into drainage, 8 - automatic regulator supply of chemically purified water, 9 - steam cooler, 10 - release of steam into the atmosphere, 11 i 15 - pipes, 13 - deaerator column, 14 - steam distributor, 16 - water inlet into the hydraulic seal, 17 - hydraulic valve, 18 - release of excess water from the hydraulic seal
distribution plate 12; via another pipeline through the regulator 8 on a plate 12 chemically purified water is supplied as an additive; From the plate, feed water is distributed in separate and uniform streams over the entire circumference of the deaerator column and flows down sequentially through a series of intermediate plates 5 and 6 located one below the other with small holes.
Steam for heating water is introduced into the deaerator through a pipe 15 k steam distributor 14 underneath water curtain, formed when water flows from plate to plate, and, diverging in all directions, rises upward, towards the feed water, heating it to 104 - 106 ° C, which corresponds to excess pressure in the deaerator 0.02 - 0.025 MPa (0.20 - 0.25 kgf/cm2).
At this temperature, air is released from the water and, together with the remainder of the uncondensed steam, leaves through the pilot pipe 11, located in the upper part of the deaeration head, directly into the atmosphere or steam cooler 9.
Oxygen-free and heated water is poured into a collection tank 1, located under the deaerator column, from where it is used to power the boilers.
To avoid a significant increase in pressure in the deaerator, two hydraulic valves are installed on it, as well as a hydraulic valve 17 in case of vacuum formation in it. If the pressure is exceeded, the deaerator may explode, and if there is a vacuum, atmospheric pressure can crush it.
The deaerator is equipped with a water-indicating glass 3 s three taps - steam, water and purge, a water level regulator in the tank, a pressure regulator and the necessary measuring equipment. For reliable operation feed pumps the deaerator is installed at a height of at least 7 m above the pump.
Water is also deoxygenated by filtering it through a layer of ordinary steel filings, which oxidize due to oxygen dissolved in the water.
Technological scheme for deaeration of source water in an industrial boiler room.
The construction of the circuit presented below allowed us to solve two problems:
1. The water treatment scheme uses Russian fast filter housings with imported filling and controls, which made it possible to significantly reduce the hardness of the source water due to the larger ion-exchange capacity of the resin.
2. The use of an additional heat exchanger led to significant fuel savings.
According to the existing technological scheme In the production boiler room, chemically purified water is supplied to a steam-water heater and at a temperature of t = 50 - 60 degrees Celsius enters the deaerator, where it is heated by bubbling heating steam to a temperature of t = 102 - 104 degrees Celsius. After the deaerator, the feed water enters the feed pump and through the economizer into the upper drum of the steam boiler. The temperature of the flue gases is 140 - 160 degrees Celsius.
According to the literature (D.M. Khzmamen. “Combustion Theory and Combustion Devices,” Moscow, Energy, 1976), to reduce low-temperature sulfur corrosion, the metal temperature in the boiler economizer should be about 75 degrees Celsius, but not lower than 70.
When installing plate heat exchanger produced by OJSC Alfa Laval Potok brand M15-M with a capacity of 1000 μcal/hour and deaerator vapor cooler brand M10-M, we provide: firstly, cooling of the feed water from the deaerator to a temperature of 74 degrees Celsius; secondly, heating water from cold water treatment, first at M10-M and then at M15-M. Estimated thermal difference t = 28 degrees Celsius.
The economic effect is achieved by saving heating steam for heating the source water in the deaerator. For example, the power of M15-M is 1000 μcal/hour and, accordingly, per year will be:
Q year. = 1000 μcal/hour * 24 hours * 360 days = 8,640,000 μcal/year.
Lower calorific value in terms of dry fuel heating oil according to GOST 10585-63
Deaeration of feed and make-up water in the boiler room
Deaeration of feed and make-up water in a boiler room Deaeration of feed and make-up water in a steam boiler room is the release of feed water from the air dissolved in it, which contains
DEAERATION = PROTECTION AGAINST CORROSION
Catalog All
Deaerator operation.
The operation of the deaerator depends on the efficiency of the device that removes the vapor-gas mixture released from the water. A vacuum liquid ring pump serves as a device that removes the vapor-gas mixture.
Deaerator operating principle.
The principle of operation of the deaerator is based on the creation above the phase contact surface (water-gas) of zero partial pressure of corrosive gases dissolved in water (oxygen and carbon dioxide).
This is achieved by reducing the pressure in the deaerator to saturation pressure according to the temperature of the water entering the deaerator and by removing the formed vapor-gas mixture from the internal volume of the deaerator. When the saturation pressure is reached, the partial pressure above the water surface is equal to the partial pressure of water vapor, and the partial pressure of dissolved gases tends to zero. There is a difference in the concentrations of dissolved gases in water and the vapor-gas mixture above the water.
Installation of a deaerator.
The deaerator is installed taking into account the vacuum level in the deaerator. The installation height of the deaerator and deaerator tank is determined by the vacuum value, water temperature and the water column at the suction of the feed pump.
Types of deaerators.
The productivity of deaerators ranges from 100 l/h to 100 m3/h.
Purpose of the deaerator.
Deaeration of make-up water of heating networks.
Deaeration of water from the network circuit of the boiler room.
Deaeration of water from the boiler circuit of the boiler room.
Deaeration of water from the hot water supply system.
Deaeration of steam boiler feedwater.
Water deaeration technology.
Deaerator design.
The design of the deaerator allows for deep deaeration of water at a water temperature of 65 °C.
The deaerator design includes two stages of deaeration. The first stage is cavitation, the second stage is film.
At the first stage, the flow of source water passes through the working nozzles, where intense boiling of water occurs with the formation of a large number of vapor-gas bubbles inside the water flow. When water moves through a nozzle with changing geometry, the flow speed increases and the static pressure in the water decreases. When the static pressure in the water flow decreases to a pressure below the saturation pressure, explosive boiling occurs inside the water flow. The high speed of water flow creates conditions for intensive mixing and crushing of vapor-gas bubbles with the formation of a phase contact surface that significantly exceeds the contact surface in jet-drip deaerators.
At the second stage, the flow of water with vapor-gas bubbles enters the overflow plate, where the vapor-gas bubbles are separated from the water. Then the water in the form of a film flows down the vertical surface into the lower part of the deaerator.
Increasing the intensity of the deaeration process makes it possible to reduce the overall dimensions and weight of the deaerator.
Deaerator diagram.
The flow of initial chemically purified water passes through a water-to-water heat exchanger, where it is heated to a temperature of 65 °. Direct boiler water is used as the heating medium.
The heated water enters the inlet of the deaerator, where the water is deaerated under vacuum, the depth of which depends on the water temperature. As the temperature increases, the vacuum depth decreases.
After the deaerator, the deaerated water is discharged into the deaerator tank, where the deaerated water accumulates. The pressure in the deaerator and deaerator tank is same value, the vacuum is created and maintained by vacuum liquid ring pumps. The deaerator is installed directly above the deaerator tank. The deaerator is mounted on a flange.
Deaerated water from the deaerator tank is supplied by deaerated water pumps further according to the scheme to feed the heating network or to storage tanks.
The installation height of the deaerator tank with the deaerator installed above it is determined by the cavitation reserve of the deaerated water supply pumps. On average, with a make-up water flow rate of 50 m3/h, the distance between the water surface in the deaerator tank and the pump suction axis is 5 m.
Creating a vacuum and pumping out the released vapor-gas mixture is provided by a vacuum liquid ring pump. The vacuum pump requires a constant flow of cold water to operate. For example, a vacuum pump for a vacuum deaerator with a capacity of 50 m3/h consumes up to 500 l/h of water.
After the vacuum pump, the waste water is discharged into the gas separator tank, from where it can be returned to the water treatment cycle by adding it to the main flow of water entering the deaerator.
We recommend using chemically purified water upstream of the heat exchanger as working water for the vacuum pump.
There are several types of water deaeration in boiler rooms
Deaeration of water in boiler rooms is pre-boiler water treatment, during which dissolved oxygen and carbon dioxide are removed from the water. The fact is that when heating water in boiler rooms, it is dissolved oxygen that has a negative effect on the equipment. But it must be said that even after deaeration, the use of special chemical reagents to reduce the concentration of dissolved gases.
To bind oxygen in the network and nutrient medium, complex reagents can be used, with the help of which you can not only reduce the concentration of carbon dioxide and oxygen to an acceptable level, but also normalize the pH level of boiler water, and also prevent the formation lime deposits. Thus, in some cases, acceptable water quality in boiler rooms can be achieved even without the use of deaeration equipment.
Chemical deaeration consists of adding reagents to the boiler water, with the help of which it is possible to bind the dissolved substances present there. gaseous substances, causing corrosion. For water heating boilers, it is recommended to use complex reagents - inhibitors of deposits and corrosion. To remove dissolved oxygen, you can use reagents specifically designed for water treatment of steam boilers, and you can even do without deaeration. In some cases, if the deaeration equipment does not work correctly, then special reagents can be used to normalize the water chemistry of the boilers.
In any water large quantities There are aggressive dissolved gases, mainly carbon dioxide and oxygen, which contribute to corrosion of pipelines and equipment. Thermal deaeration of water in boiler rooms can significantly reduce the amount of gases. Corrosive gases penetrate into the feed water from the surrounding atmosphere or through the process of ion exchange. But the biggest thing negative impact provides oxygen, causing corrosion. As for carbon dioxide, it acts as a kind of catalyst, enhancing the effect of oxygen. But she herself is able to have a negative impact.
Thermal deaeration is most often used. When water is heated in a boiler room at constant pressure, dissolved gases are released. As the temperature increases, when it reaches a boil, the concentration of gases gradually decreases to a minimum, as a result of which the water is completely freed from them. If the water in the boiler room is not heated to boiling temperature, the residual gas content in it will increase. Moreover, the influence of this parameter is quite significant. There are certain standards regulating the condition of water in boiler rooms, and if the water is underheated by even one degree, it will not be possible to achieve compliance with these standards.
Since the concentration of dissolved gases in boiler water is very small, it is not enough to simply remove them from the water - it is very important to completely free the deaeration installation from them. In order to achieve this, it is necessary to supply excess steam to the installation, in an amount much greater than that required to bring the water to a boil. If we take the steam consumption in the amount of treated water within the range of 15-20 kg/t, then the evaporation will be 2-3 kg/t, and its reduction can lead to a significant deterioration of the water in the boiler room. In addition, the capacity of the deaeration installation must be large enough so that the water can remain in it for at least 20-30 minutes. Such a long period of time is required not only for the removal of gases, but also for the complete decomposition of carbonates.
Vacuum deaeration of water in boiler rooms is used when hot water boilers are installed in boiler rooms. In this case, deaerators can operate at temperatures ranging from 40-90 degrees.
But with all our positive qualities water purification and water treatment systems by vacuum deaeration also have significant disadvantages - high metal consumption, a lot of auxiliary equipment(vacuum ejectors and pumps, tanks, etc.), the need to mount them on a hill.
Deaerator- technical device, which implements the process of deaeration of some liquid (usually water), that is, its purification from unwanted gas impurities present in it (oxygen and carbon dioxide). When dissolved in water, these gases cause corrosion of feed pipes and boiler heating surfaces, resulting in equipment failure. At steam turbine stations, thermal deaeration of water is used.
The operating principle of thermal deaerators is based on the fact that the absolute pressure above a liquid is the sum of the partial pressures of gases and steam.
If we increase the partial pressure of steam so that while simultaneously removing vapor (this is a mixture of gases released from the water and a small amount of steam that must be evacuated from the deaerator), then as a result we obtain the total partial pressure of gases. Then, according to Henry's law (the equilibrium mass concentration of gases in a solution is proportional to the partial pressure in the gaseous medium above the solution), i.e. there are no dissolved gases. An increase in the partial pressure of steam, in turn, can be achieved by increasing the water temperature to the saturation temperature at a given pressure at .
Classification of thermal deaerators.
Intended use: steam boiler feedwater deaerators; additional water and return condensate from external consumers; make-up water of the heating network.
By heating steam pressure: high pressure (0.6-0.8 MPa)( D); atmospheric (0.12 MPa)( YES); vacuum (7.5-50 kPa)( Far East).
According to the method of heating deaerated water: mixing type (with mixing heating steam with heated water); deaerators of superheated water with external preheating of water with selected steam.
By design (according to the principle of formation of the interphase surface): with a contact surface formed in a turbulent mode (slim-bubble, film type with a disordered nozzle, jet disc type); with a fixed phase contact surface (film type with an ordered packing).
Schematic diagram deaeration installation.
Rice. Atmospheric deaerator of mixing type: 1 - tank (accumulator), 2 - outlet of feed water from the tank, 3 - water indicator glass, 4 - pressure gauge, 5, 6 and 12 - plates, 7 - draining water into the drainage tank, 8 - automatic feed regulator Chemically purified water, 9 - steam cooler, 10 - release of steam into the atmosphere, 11 and 15 - pipes, 13 - deaerator column, 14 - steam distributor, 16 - water inlet into the hydraulic valve, 17 - hydraulic valve, 18 - release of excess water from hydraulic valve
The deaerator consists of a tank 1 and a column 13, inside of which a number of distribution plates 5, 6 and 12 are installed. Feed water (condensate) from the pumps enters the upper part of the deaerator onto the distribution plate 12; through another pipeline through regulator 8, chemically purified water is supplied to plate 12 as an additive; From the plate, feed water is distributed in separate and uniform streams over the entire circumference of the deaerator column and flows down sequentially through a series of intermediate plates 5 and 6 located one below the other with small holes. Steam for heating water is introduced into the deaerator through pipe 15 and steam distributor 14 from below under the water curtain formed when water flows from plate to plate, and, diverging in all directions, rises up towards the feed water, heating it. At this temperature, air is released from the water and, together with the remainder of the uncondensed steam, leaves through the lead pipe 11, located in the upper part of the deaeration head, directly into the atmosphere or steam cooler 9. The oxygen-free and heated water is poured into the collection tank 1, located under the deaerator column , from where it is used to power boilers. To avoid a significant increase in pressure in the deaerator, two hydraulic valves are installed on it, as well as a hydraulic valve 17 in case of vacuum formation in it. If the pressure is exceeded, the deaerator may explode, and if there is a vacuum, atmospheric pressure can crush it. The deaerator is equipped with a water indicator glass 3 with three taps - steam, water and purge, a water level regulator in the tank, a pressure regulator and the necessary measuring equipment. For reliable operation of feed pumps, the deaerator is installed at a height of at least 7 m above the pump.
N.N. Gromov, chief engineer AP "Teploset" Krasnogorsk region
Last time large number steam boilers (DKVr, DE, E, etc.) are converted to hot water mode, while the boiler room deaerators remain without steam. Effective method, developed and tested for 10 years in the AP “Teploset” of the Krasnogorsk region, allows you to degas water without alterations to the deaerator without steam supply and without the disadvantages of vacuum deaeration.
Thermal deaeration
Water always contains dissolved aggressive gases, primarily oxygen and carbon dioxide, which cause corrosion of equipment and pipelines. Corrosive gases enter the source water as a result of contact with the atmosphere and other processes, for example, ion exchange. Oxygen has the main corrosive effect on metal. Carbon dioxide accelerates the action of oxygen and also has independent corrosive properties.
To protect against gas corrosion deaeration (degassing) of water is used. The most widespread is thermal deaeration. When water is heated at constant pressure, the gases dissolved in it are gradually released. When the temperature rises to the saturation (boiling) temperature, the concentration of gases decreases to zero. Water is freed from gases.
Underheating of water to the saturation temperature corresponding to a given pressure increases the residual content of gases in it. The influence of this parameter is very significant. Underheating of water even by 1 °C will not allow achieving the requirements of the “Rules...” for feed water of steam and hot water boilers.
The concentration of gases dissolved in water is very low (on the order of mg/kg), so it is not enough to separate them from the water, but it is also important to remove them from the deaerator. To do this, it is necessary to supply excess steam or vapor to the deaerator, in excess of the amount required to heat the water to a boil. With a total steam consumption of 15-20 kg/t of treated water, evaporation is 2-3 kg/t. Reduced evaporation can significantly degrade the quality of deaerated water. In addition, the deaerator tank must have a significant volume, ensuring that water remains in it for at least 20 ... 30 minutes. Long time necessary not only for the removal of gases, but also for the decomposition of carbonates.
Atmospheric deaerators with steam supply
For deaeration of water in boiler rooms with steam boilers Mostly 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 having two or more perforated plates, or other special devices, thanks to which the source water, breaking into drops and jets, falls into the accumulator tank, encountering steam moving countercurrently on its way. In the column, water is heated and the first stage of its deaeration occurs. Such deaerators require the installation of steam boilers, which complicate the thermal circuit of the hot water boiler house and the chemical water treatment circuit.
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 disadvantages: high metal consumption, a large number of additional auxiliary equipment ( vacuum pumps or ejectors, tanks, pumps), the need to be located at a significant height to ensure the operability of make-up pumps. The main disadvantage is the presence of a significant amount of equipment and pipelines that are under vacuum. As a result, air enters the water through the shaft seals of pumps and fittings, leaks in flange connections and welded joints. In this case, the deaeration effect completely disappears and it is even possible to increase the oxygen concentration in the make-up water compared to the initial one.
Atmospheric deaeration without steam supply
Recently, a large number of steam boilers have been switched to hot water mode. An effective way deaeration in boiler houses with such boilers was developed and passed a long test at the AP "Teploset" of the Krasnogorsk region.
The water after the sodium cation exchanger is heated to 106-110 °C and injected into the head of the atmospheric deaerator, where water droplets boil due to a decrease in pressure. When boiling, corrosive gases are removed from water along with steam, more actively than in deaerators with steam supply. The scheme was implemented on equipment that was operated in a steam boiler house with three DKVR 10/13 boilers, when switched to water heating mode with coolant parameters of 115/70 °C. In this case, the DSA type deaerator does not require modifications. To heat the make-up water, steam network heaters were used, modified to operate on heating water with a temperature of 110-113 °C, and not on steam. On technical solutions, used in boiler houses of the Krasnogorsk region, a patent of the Russian Federation was received.
This scheme eliminates the disadvantages of vacuum deaeration and deaeration with steam supply. The advantage of the new deaeration scheme is its simplicity and reliability, allowing it to operate stably in any hot water boiler house.
Besides
When switching DKVR 10/13 boilers with coolant parameters of 115/70 °C to water heating mode according to the TsKTI scheme, we encountered a decrease in the heating output of the boiler unit (it does not decrease with the 150/70 schedule). Such a reduction was unacceptable in terms of the load on the heating network, so we developed and implemented changes to the TsKTI scheme. Structurally, the changes are not significant, but they made it possible to improve circulation in the rear screens and increase the heating output of the boiler to the required level. The pattern of water movement in the boiler circuit is patented. The boilers have been in operation for 10 years without any complaints.