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 cooking technology wide range 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 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 coolant is necessary to heat the water in front of the vacuum deaerator. Coolant temperatures up to 90 °C are provided at most facilities where it is potentially possible to use vacuum deaerator.
The main difference between a vacuum deaerator and an atmospheric deaerator is in the vapor removal system 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.
The following can be used as a vacuum pump: vacuum water 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, the driving force for the deaeration process appears.
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 the battery tank located at the zero level. 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 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.
Because vacuum deaeration 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 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 the saturation pressure and obtain a superheated state of water can significantly increase the efficiency of the deaeration process and reduce the overall dimensions and weight of the vacuum deaerator.
For comprehensive solution the issue of installing a vacuum deaerator in a boiler room at zero level with a minimum overall height was developed, tested, and successfully introduced into mass production block vacuum deaerator BVD. 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.
An indispensable condition for the effective and economical operation of atmospheric deaerators is their proper configuration. Our article is about what requirements the operation of deaerators must satisfy, and how you can configure it yourself.
Typical malfunctions in the operation of deaerators
In practice, the most common are 2 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 removing dissolved gases whose residual levels are prescribed by regulations. But the operating efficiency of deaerators under such conditions is extremely low due to the large specific consumption steam for deaeration.
Criteria and conditions for high-quality operation of deaerators
When deaerating, 6-7 grams of dissolved gases are usually removed from 1 ton of water. It has been experimentally established that when operating atmospheric deaerators, the maximum amount of vapor should not be more than 22 kg per ton. Based on this, the cross-section of the outlet pipeline and the vapor cooler are selected. The optimal method of operation of the deaerator can be considered in which the required operating parameters are automatically provided both in the deaeration column and in the bubble tank with the minimum required amount of vapor.The main factors influencing the quality of deaerator operation are well known:
- water flow and its stability;
- temperature of chemically purified water;
- pressure in the deaerator;
- steam flow into the deaeration column;
- steam consumption for bubbling in the tank;
- water level in the tank.
Operating principle of the automatic deaerator control system
First let's look at how the system works automatic control in general (Fig. 1).As steam consumption increases, consumption increases feed water from the deaerator tank. In this case, a deviation of its level, measured by the sensor, from the specified value occurs. The level regulator acts on the control valve for the water supply 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.
Rice. 1
More quantity enters the deaeration column cold water accompanied by intense condensation of steam coming from the steam 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 control valve rod takes a new position, corresponding to a higher steam flow. But the pressure in the vapor space, nevertheless, will be slightly lower than the original one. This is how it should be with proportional regulation.
How will the temperature of the water in the tank change (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 “superheated” 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 through the steam space, will end up in the deaeration column.
Rice. 2
Now let's consider the opposite situation. What happens when the load decreases? There will be no special features in the operation of the level regulator and pressure regulator. The level regulator will restore it, while reducing water flow, and the pressure regulator will reduce the supply of steam to the steam space. The established pressure will be slightly higher than the initial one, and accordingly, after some time the water temperature will be slightly higher. After all, the boiling point (condensation) is clearly related to pressure. An example of temperature changes depending on the load is shown in Fig. 3.
Rice. 3
Unlike level and pressure regulators, the effect of the steam flow regulator on bubbling may have an unpleasant feature. And it is directly related to how correctly it is configured. The fact is that if the settings are careless, the set temperature may turn out to be less or the same as that established at increased pressure. In this case, there will be no reduction in the supply of steam to bubbling, but a complete cessation of steam. As a result, the deaeration regime will be disrupted.
Operating principle of automatic regulators
Now let's look at how each regulator works individually. Let's start with the pressure regulator, which determines the flow of steam into the deaeration column. Let us only note that it actually supplies steam to the steam space of the tank. From the tank, through the impulse tube, pressure is transmitted to the regulator drive diaphragm. In this way it is carried out Feedback. An example of the flow characteristic of a direct-acting valve is shown in Fig. 4.
Rice. 4
This controller has a proportional characteristic. With this characteristic, a larger difference between the current and set value of the parameter corresponds to a larger stroke of the rod. Range of change set pressure depends on the 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 determined mainly by the time it takes to fill or empty the drive cavity.
Now let's take a closer look at how the steam flow regulator for bubbling works. We will call it a flow regulator, although such a system is usually used as a temperature regulator. This controller also has a proportional characteristic. The range of change of the task 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 stroke of the rod.
The control action in our case will be determined by the difference between the temperature corresponding to the operating pressure in the deaerator (103-105 ºС) and the temperature specified by the adjustment handle. But it must be borne in mind that the result of this influence, in the general case, has a nonlinear form. Let's explain what's going on here.
Full speed ahead the pusher rod is 10 mm and corresponds to a change in the temperature of the liquid in the sensitive element by 10ºС. The full stroke of the valve plunger, depending on the diameter, ranges from 3 to 9 mm. In this case, when the valve stem moves from 0 to 20%, the flow rate increases from 0 to 75% of the total flow rate. This is a feature of the flow characteristics of the quick opening valve. Thus, the flow rate will change linearly only if the current movement of the valve plunger does not go beyond the linear portion of the flow characteristic.
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 mounting the sensor. The longest delay time will be when using a dry sleeve. The smallest value is when installed without a protective sleeve. It is important to note that in any case, the delay time of the flow regulator is significantly longer than that of the pressure regulator. Therefore, when regulators work together, their mutual influence does not lead to mode fluctuations.
Let's look briefly at the operation of the level controller. The correctness of its operation is determined by compliance with the configuration steps prescribed in the instructions. As a result of the adjustment, PID parameters are set that correspond to the integral quality criterion.
Conditions for successful completion of work on setting up the deaerator
It is necessary to say about the most important conditions, without which any attempts to adjust the operation of deaerators are like wandering in the dark.- To monitor the performance of the deaerator, you must have a reliable oximeter (oxygen meter) and a pH meter. It is desirable that the oximeter operates in the microgram range and provides continuous monitoring. 2
- Control points must be equipped with samplers. Flow-through sampling refrigerators are most suitable. They must ensure the sample temperature does not exceed 50ºС at a flow rate of 2 to 50 l/h. The presence of several samplers greatly simplifies the commissioning work. The supply tubes must be metal, which eliminates secondary contamination with oxygen. The use of non-metallic tubing is not recommended.
- adjust the water flow regulator;
- adjust the pressure regulator;
- set the steam flow regulator to bubbling;
- adjust the pressure regulator setting and check the pressure range;
- adjust the setting of the steam flow regulator for bubbling;
- check the operation of the deaerator at the operating points using the readings of the oximeter and PH meter.
Thermal deaerators are usually classified according to operating pressure and the method of organizing phase contact.
Based on operating pressure, the following types of deaerators are distinguished:
Vacuum, operating at an absolute pressure in the housing from 0.075 to 0.5 atmospheres;
Atmospheric, the absolute pressure in which varies in the range from 1.1 to 1.3 atmospheres;
High pressure, operating at absolute pressure from 5 to 12 atmospheres.
The method of organizing phase contact is determined by the design of the deaerator. Since the same deaerator, as a rule, uses deaeration devices that differ from each other in operating principles, modern deaerators are usually combined. In this case, the following main types of deaeration devices (or individual elements of deaerators) are distinguished:
Jet, in which the phase interface is formed by the surface of water jets freely falling in a steam flow;
Bubblers, in which the heating fluid in the form of steam bubbles is distributed in the water flow;
Film, where the phase interface is formed by the film flow of water in a steam flow;
Drip systems, in which water is distributed in the steam stream in the form of drops.
The interface between the phases can be conditionally fixed, as, for example, in film deaerators with an ordered packing, or unfixed, as in deaerators with a disordered packing, jet, drip and bubbling. The scope of application of deaerators in thermal circuits of energy facilities, as a rule, is determined by the operating pressure, deaerators high blood pressure are used exclusively as feedwater deaerators of thermal power plants with high, ultra-high and supercritical initial steam pressure;
Deaerators atmospheric pressure used as feedwater deaerators of power plants and boiler houses with low and medium initial steam pressure, additional water deaerators of the cycle of heating power plants (CHP) with a higher initial steam pressure, make-up water deaerators of heating networks closed type(less often - for heating networks open type using deaerated water coolers), feedwater deaerators of evaporation and steam conversion units of power plants;
Vacuum deaerators are used as deaerators of make-up water in heating networks, in circuits of evaporation and steam conversion plants, and less often - as deaerators of additional water in power plants and boiler houses.
Atmospheric pressure deaerators
The most common type of atmospheric deaerator is the jet-bubble deaerator. In such deaerators it is usually used two-stage scheme deaeration, including jet and bubbling stages. It should be noted that the deaeration stage is usually understood as one or more deaeration elements connected in series through the water, operating according to the same principle. For example, two jet compartments located one below the other belong to one jet stage.
The designs of such deaerators are somewhat different from each other for devices of different capacities from the standard range. Most of the standard designs of jet-bubbling atmospheric deaerators were developed by NPO TsKTI im. I.I. Polzunov. Currently, both outdated models of such deaerators (type DSA) and their modern analogues (types DA and DA-m) are used. A standard range of standard sizes of such deaerators has been developed, differing in nominal capacity for deaerated water: 1, 3, 5, 15, 25, 50, 100, 200 and 300 t/h.
Atmospheric deaerators typically consist of a deaeration column mounted on a horizontally located cylindrical deaerator tank. The deaerator tank as part of the deaerator performs two important functions. Firstly, it serves as a means of creating a supply of deaerated water for technological scheme. If, for example, the deaerator is used as a feedwater deaerator for steam boilers low pressure, then it is necessary to create a supply of water in the deaerator tank to ensure uninterruptible power supply these boilers in emergency situations. Secondly, as shown above, the deaeration tank allows you to increase the time the water is kept at a temperature close to the saturation temperature, which helps to increase the efficiency of deaeration.
In relation to devices with low productivity (1 and 3 t/h of deaerated water), the deaerator can perform the indicated functions without a deaerator tank, since the necessary supply of water can be created directly in the body of the deaeration column, the dimensions of which will not be too large. IN standard designs Such deaerators are not distinguished between a deaeration column and a deaerator tank, but rather refer to the deaerator body as a whole. Such deaerators are called columnless.
Deaerators with higher productivity are equipped with deaerator tanks of various capacities. Domestic power engineering plants produce deaerator tanks of standard sizes with a capacity of 2, 4, 8, 15, 25, 35, 50 and 75 m 3, and each deaerator tank is designed for a deaeration column of a certain capacity. However, at the customer's request, as a rule, it is possible to supply selected deaeration columns with tanks of a different capacity from the standard range.
In addition to the deaerators developed by NPO TsKTI im. I.I. Polzunov, a number of designs of atmospheric deaerators developed by other organizations are used. Among such deaerators, we note the bubbling deaerator designed by Uralenergometallurgprom.
Currently, atmospheric deaerators are produced by the following main domestic factories:
Neftekhimmash Equipment LLC, Biysk Boiler Plant OJSC, Sibenergomash OJSC, Belenergomash OJSC, Teploenergokomplek CJSC, TKZ-Krasny Kotelshchik OJSC, Sarenergomash OJSC.
Below we will consider the main design solutions used in atmospheric pressure deaerators and their piping elements: vapor coolers and safety drain devices.
Let's consider the design diagram of columnless deaerators with a capacity of 1 and 3 t/h (Fig. 3.1), developed by NPO TsKTI im. I.I. Polzunov.
Rice. 3.1. Structural diagram columnless deaerators DA-1 and DA-3: 1 - source water supply fitting; 2 - perforated water distribution manifold; 3 - jet-forming plate; 4 - water intake tray; 5 - sectioning threshold of the jet-forming plate; 6 - limiting threshold of the jet-forming plate; 7 - bubbling device; 8 - bubble sheet; 9 and 10 - partitions; 11 - fitting for draining deaerated water; 12 - heating steam supply fitting; 13 - steam line; 14 - steam receiving box; 15 - vapor transfer window; 16 - steam inlet window; 17 - inlet window of the built-in vapor cooler; 18 - vapor outlet fitting; 19 - hatch; 20 and 21 - fittings for connecting the safety-drain device for steam and water, respectively; 22 - drainage fitting.
energy desorption bubbling hydrodynamic
The deaerator DA-1 or DA-3 is a vertical cylindrical vessel with elliptical bottoms and deaeration devices located inside it.
The water sent for deaeration enters the deaerator through fitting 1 and the perforated water distribution manifold 2. From the holes of the water distribution manifold 2, water flows in the form of jets onto the jet-forming plate 3, perforated in the part located above the water receiving tray 4. The jet-forming plate 3 is sectioned by a threshold 5 in such a way that that with a low hydraulic load, water flows in the form of jets into tray 4 only through holes located up to threshold 5 in the direction of water movement. With an increased hydraulic load, the water level on the jet-forming plate 3 rises, the water flows over the threshold 5 and all the holes of the jet-forming plate are put into operation. This sectioning of the jet-forming plate 3 is made so that, at low hydraulic loads of the deaerator, there is no misalignment (“distortions”) between the flows of water and heating steam, leading to a deterioration in the conditions of heat exchange and deaeration. The maximum hydraulic load of the deaerator is limited by the height of the limiting threshold 6: with increased hydraulic load, the water level on the jet-forming plate increases and if water overflows over threshold 6, the efficiency of water heating and deaeration sharply deteriorates.
In the jet stream inside tray 4, the main heating of water occurs when it comes into contact with heating steam and the degassing process begins. The water draining from tray 4 in the form of a stream into the water volume of the deaerator, under most operating modes of the deaerator, remains underheated to the saturation temperature corresponding to the pressure in the steam space of the deaerator, and contains gases both in dissolved and dispersed form.
After a certain exposure of water in the water volume of the deaerator, the duration of which is determined by the hydraulic load and the water level in the deaerator, water enters the bubbling device 7. This device is made in the form of a channel of rectangular cross-section, limited at the top and sides by solid partitions and having a perforated bubbler at the bottom sheet 8. When steam is bubbling through a layer of water in the bubbling device 7, the water is heated to a saturation temperature corresponding to the pressure in the bubbling device. This pressure is greater than the pressure in the steam space of the deaerator above the water surface by the pressure of the water column of height H, therefore the water temperature in the bubbling device becomes greater than the saturation temperature at the steam pressure above the water surface in the deaerator. In the bubbling device 7, due to the water reaching the saturation temperature, most of the dissolved gases transform into a dispersed state in the form of small gas bubbles; here, partial thermal decomposition of hydrocarbonates and hydrolysis of carbonates occurs with the formation of free carbon dioxide, which, in turn, also transforms into dispersed state.
Having left the bubbling device 7, water mixed with the non-condensed part of the heating steam enters the channel formed by partitions 9 and 10 and moves upward along this channel. During this movement, the pressure of the medium continuously decreases from the pressure in the bubbling device to the steam pressure above the surface of the water in the deaerator. Accordingly, water, which turns out to be overheated relative to the saturation temperature, boils in volume, which is accompanied by the transition of most of the gases still in dissolved form into a dispersed state. In the upper part of the water volume, phase separation occurs: water flows through partition 10 and falls towards the deaerated water outlet fitting 11, and steam with gases released from the water moves towards the jet deaeration stage.
It should be noted that the leakage of the steam-water mixture from the bubbling device 7 directly into the deaerated water outlet fitting 11 is unlikely. The flow of the medium in the gap between the partitions 9 and 10, due to the presence of steam, has a lower density than the flow of water descending in the channel formed by the partition 10 and the wall of the housing, which causes only the lifting movement of the medium between the partitions 9 and 10. Meanwhile, the gap between the partition 10 and the housing in the lower part is necessary to allow some circulation of water around the partition 10. Such circulation increases the frequency of water treatment with steam and increases the available time of the deaeration process, which increases the efficiency of removing gases from water.
All the heating steam is supplied to the deaerator through fitting 12 and through the steam line 13 enters the steam receiving box 14 under the bubble sheet 8. A steam cushion is created under the bubble sheet 8, preventing water from falling through the holes of the bubble sheet. Such bubble sheets are called non-sinking sheets.
Here it is advisable to dwell in more detail on the limiting operating mode of a non-failing bubble sheet - the “flooding” mode or injection mode. If the velocity of steam in the holes of the sheet is too high, the steam coming out of the holes of the bubble sheet will capture all the liquid, crush it and carry it away in the form of spray. It is for this reason that the maximum steam pressure under the bubble sheet must be limited. In the considered deaerators DA-1 and DA-3, for this purpose, a steam bypass window 15 is made in the partition 9, which bypasses part of the steam in addition to the holes of the bubbling sheet 8 when the steam pressure under this sheet increases above that required for the effective operation of the bubbling device.
After separating the water and the steam-gas mixture in the upper part of the channel formed by partitions 9 and 10, this mixture enters through the steam inlet window 16 into the jet compartment of the deaerator, where most of the steam condenses, heating the water flow. The remaining part of the steam mixed with gases washes the jet-forming plate 3 and enters the built-in contact vapor cooler. The vapor cooler is a jet stream of water flowing from the water distribution manifold 2, through which passes the vapor-gas mixture entering through window 17. Here, water vapor is additionally condensed on jets of relatively cold water. The remaining small part of the steam and non-condensable gases are removed from the deaerator through the vapor outlet fitting 18.
Deaerators DA-1 and DA-3 are equipped with hatch 19, which provides access to the inside of the housing for inspection and repair, as well as fittings 20 and 21 for connecting a safety drain device and drain fitting 22.
An atmospheric deaerator with a capacity of 5 t/h or more (Fig. 3.2) consists of a deaeration column 7 installed on a deaerator tank 10. The column includes several (in in this example two) jet compartments formed below the upper 8 and lower 9 perforated plates, and can also be supplemented with a bubble sheet. The water to be deaerated is supplied through a water distribution system to the upper jet-forming plate 8, from where it flows onto the plate 9 located below and then onto the bubble sheet (if present) or directly into the deaerator tank (as in the example under consideration). Jet trays have special thresholds that ensure the maintenance of a certain water level on them, as well as the overflow of water in addition to the jet zone when the trays are overfilled. Bubbler sheets are usually made non-sinking (the dynamic action of the steam flow does not allow water to “fall” through the holes of the sheet), since the operation of a sinking bubble sheet is effective only in a narrow range of water and steam flow rates through it.
Fig.3.2.
1 - water supply; 2 - vapor cooler; 3, 6 - vapor to the atmosphere; 4 - supply of third-party condensate (for example, condensate of steam from production extraction of turbine units); 5-level regulator; 7 - deaeration column; 8, 9 - upper and lower jet-forming plates; 10 - deaerator tank; 11 - safety drain device; 12 - supply of bubbling steam; 13 - pressure control devices; 14 - pressure regulator; 15 - main steam supply; 16 - drainage of deaerated water; 17 - level indicator; 18 - drainage; 19 - supply of hot condensate.
Steam is usually supplied to the above-water space of the deaerator tank (and in this case is called the main steam 15), ventilates it, ensuring the removal of gases released from the water in the tank, and enters the deaeration column. Here the steam interacts with the downward flow of water, providing its heating and deaeration.
The vapor containing gases and water vapor released from the water is discharged from the deaerator into the atmosphere through pipe 6 or to the vapor cooler 2, where the thermal potential of this flow is used, for example, to heat the source water in front of the deaeration column. In this case, gas blowing 3 is carried out from the steam space of the vapor cooler. It is possible to supplement the specified design with a bubbling device for the deaerator tank. The most commonly used devices are the TsKTI system (in this example) or perforated bubble collectors mounted at the bottom of the tank along its generatrices. In this case, bubble steam 12 is supplied through a special pipeline, since the pressure of this steam must be greater than the pressure of the main steam by at least the pressure of the water column in the deaerator tank. The deaerator is equipped with a safety drain device 11; level glass 17; connections for connecting the deaerator to the steam and water equalization lines; drainage pipeline 18; deaerated water outlet pipe 16.
Experience in operating atmospheric deaeration plants shows that, regardless of the reason for the deterioration in the efficiency of water deaeration, the use of steam bubbling in the water volume of the deaeration tank allows this efficiency to be increased.
Even if the deaeration column provides the required quality of deaerated water, the bubbling device of the deaerator tank acts as a barrier, reducing the likelihood of dissolved gases leaking into the deaerated water and expanding the permissible range of changes in the hydraulic and thermal loads of the deaerator while maintaining the required quality of deaerated water. In this case, steam bubbling in the deaerator tank provides some overheating of the water relative to the saturation temperature and thereby protects the water from reinfection gases.
In addition, it is necessary to remember that the part of the gases remaining in the water after the deaeration column is contained in dispersed form and represents a multitude of tiny gas bubbles, the sizes of which are so small that they do not ensure their independent ascent due to the action of the buoyant force. In a deaerator without bubbling in the water volume of the tank, these bubbles will fall into the deaerated water. Steam bubbling, which provides intensive mixing and turbulization of the water volume in the tank, promotes the release of part of the gases in dispersed form from the water, increasing the efficiency of deaeration as a whole.
Thus, a flooded bubbling device in a deaeration tank is often necessary even when using modern two-stage deaeration columns.
Let us consider, as an example, the bubbling device of the TsKTI system (Fig. 3.2.).
Rice. 3.2. Schematic diagram bubbling device of the deaerator tank of the TsKTI system: 1 - bubbling sheet; 2 - top shelf; 3 - lifting shaft; 4 - drainage of deaerated water; 5 - deaeration column; 6 - deaerator tank; 7 - supply of bubbling steam; 8 - main steam supply; solid lines indicate the direction of water movement; dotted lines - directions of steam movement
Water passes through the channel formed by the surface of the bubble sheet 1 and top shelf 2, and during this movement it is treated with steam coming out of the holes of the bubble sheet. The steam-water mixture, leaving the channel, enters a specially organized lifting movement shaft 3, in the upper part of which the steam and gases released from the water are separated from the water and discharged into the above-water space of the deaerator tank and mixed with the flow of the main steam, and the water is lowered in the water volume of the tank to the deaerated water outlet pipe 4.
The deaerator tanks themselves (see example in Fig. 3.4) are horizontally located cylindrical vessels with elliptical, less often conical, bottoms, mounted on two supports. Moreover, for tanks with a useful capacity of 25 m 3 or more, one of the supports is movable (roller), providing compensation for temperature expansion of the tank during starts and stops of the deaerator. Tanks with a useful capacity of 8 m 3 or more are equipped with special belts that provide the required rigidity of the body.
Rice. 3.4. General form deaerator tank with a useful capacity of 75 m 3: A - fitting for the deaeration column; B - connection fitting for the safety-drain device for steam; B - main steam supply fitting; G - drainage fitting; D - deaerated water drainage fitting; E - connection fitting for the water safety drain device; F - fittings for connecting a level indicator; C- union for discharge from the separator continuous blowing boiler; T-fitting for introducing feed water from the recirculation line feed pumps; U - fitting for the input of superheated condensates; F - fitting for introducing the steam-air mixture from the steam space of the heaters; C- fitting for supplying steam to the submerged bubbling device of the deaerator tank; Ch- reserve fitting
Columns are connected to deaerator tanks, usually by welding. In the designs of modern deaerators, the column is located near one of the ends of the deaerator tank; deaerated water is removed from the tank from the opposite end. This achieves the maximum possible time for the given geometric characteristics to hold water in the deaeration tank at a temperature close to the saturation temperature, and, accordingly, the greatest deaeration efficiency.
Deaerator tanks are equipped with a hatch that provides access to the inside of the tank for inspection and repair, as well as inspection and repair. lower devices deaeration column, fittings for connecting a safety drain device for steam and water (the latter is mounted inside the tank and ends in an overflow funnel, the height of the upper edge of which determines the maximum water level in the tank). There are fittings for connecting the deaerator to the steam and water equalizing lines, necessary for the parallel operation of several deaerators, a fitting for draining deaerated water, supplying main and bubbling steam, a drain fitting, as well as a number of fittings for discharging high-potential flows, the temperature of which is higher than the saturation temperature at operating pressure in the deaerator, or introducing streams of already deaerated water. If streams overheated relative to the saturation temperature in the deaerator are directed not into the deaerator tank, but into the deaeration column, then the steam formed during their boiling can disrupt the normal ventilation of the steam space of the deaerator, which, in turn, will lead to a deterioration in the efficiency of water deaeration.
Heading:Hello dear customers of the MetalExportProm enterprise and those who are interested in our products. Today I want to tell you in detail what are deaerators dp - high blood pressure, which are rare, but still used and represent technically complex and critical containers. Everyone who works with such equipment is familiar with an atmospheric or vacuum deaerator, but not many people know the devices I’m talking about now. And so on 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, this is nine times more than aspirated. Accordingly, the walls of blood vessels are much thicker. If you are interested in immediately looking at the technical characteristics, then go to nuclear power plants, or read further.
The device itself belongs to capacitive equipment, you can see more about the containers, but since heat exchange processes also take place inside it, it can also be classified as 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, the symbol KDP, starting from KDP-80 to KDP-6000, stands for KDP - high-pressure deaerator column, and the numbers next to it are the nominal productivity measured in tons per hour or t/h, i.e. There are from 80 to 6000 tons per hour. The performance of a deaerator is the amount of prepared water leaving it, i.e. how much water it can process and produce 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 either vertical or horizontal, depending on the design of the device. Now let’s look at what function the column performs. To do this, let's start from the very beginning, why is the dp deaerator itself needed at all 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 boilers operating, 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 higher, just like them themselves. Let's look further to make the water treatment process itself clearer, since the entire capacitive and heat exchanger That's what it's designed for.
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. Where does it come from? It is produced by a generator, which drives a turbine, which requires steam to operate, and the steam is produced by a steam generator or the steam boiler itself, depending on the design of the station. But steam must be generated from somewhere, and it is obtained by evaporation of 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 exchange, 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 operating efficiency, but can also cause an emergency. To prevent this, we need water treatment and water purification, which in our case is directly involved in, 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 works for many months, but the second circuit works a little differently, read on. There are also single-circuit ones, then the coolant water goes through a 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 under 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 occurs in the steam generator, but this is not so strong.
Processes occurring in nuclear power plants
Let's consider all processes from start to finish using the example of an atomic power station, but only those related to our topic. So. There is the heart of the station - this is the reactor block, inside of which there are rods in which the nuclear reaction takes place. This releases a huge amount of heat. This container is located inside another container, between which there is water. Those. the two tanks represent a nuclear boiler, inside which a nuclear reaction takes place and heats the water in between.
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 circuit. And he is closed, i.e. water is poured there and circulates for a long time, of course sometimes being replenished.
But there is also a second circuit. Almost boiling water is pumped into the heat exchanger-steam generator by a pump and it already boils in it turning into steam, which is part of the generator. The steam comes out and hits the turbine blades, causing it to move, and 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 liquid.
You can familiarize yourself with capacitors in more detail.
Water treatment
The condensate leaving the condenser enters the deaeration column from above. The other part of the steam at the turbine outlet from the second extraction is also supplied to the column only from below. Condensate moves downwards, and steam moves towards it. As a result of this process, corrosive gases and their mixture, called vapor, oxygen, nitrogen and others rise to the top and exit into the vapor cooler, which is a shell and tube heat exchanger with a set of brass or stainless steel heat exchange pipes. The steam condenses and enters the tank, and the gases are discharged into the atmosphere. This is what the water purification process looks like, which is closely related to deaeration.
You can familiarize yourself with columns for atmospheric deaerators. The principle of its operation and purpose are also discussed in detail there.
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 pumps it into the heat exchanger and steam generator. The water inside rises and is heated by the primary circuit water and enters the evaporator.
Technical characteristics of deaerators for nuclear power plants
| Name | Nominal productivity, t/h | Absolute operating pressure, MPa (kgf/cm2) | Column | Number of columns | Column diameter, mm | Tank capacity, m 3 | Tank useful capacity mm 3 | Tank diameter, mm | Deaerator length, mm | Deaerator height, mm | Weight, kg | Weight of deaerator with water, mm |
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| dp-2000-2x1000/120-A | 2000 | 0.7(7.0) | KDP-10A vertical | 2 | 2400 | 150 | 120 | 3400 | 17000 | 8300 | 43200 | 227200 |
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| dp-3200-2x1600/185-A | 3200 | 0.69(0.7) | KDP-1600-A vertical | 2 | 3400 | 210 | 185 | 3400 | 23415 | 11160 | 93000 | 361000 |
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| dp-3200/220-A | 3200 | 1.35(13.8) sliding | KDP-3200-A horizontal | 1 | 3000 | 350 | 220 | 3800 | 32180 | 7900 | 230000 | 710000 |
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| dp-6000/250-A | 6000 | 0.82(8.4) | KDP-6000-A horizontal | 1 | 3000 | 400 | 250 | 3800 | 32180 | 7900 | 190000 | 74000 |
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| dp-6000/250-A-1 tables above. In industrial and heating boiler houses, to protect heating surfaces washed by water, as well as pipelines, from corrosion, it is necessary to remove corrosive gases (oxygen and carbon dioxide), which is most effectively achieved by thermal deaeration of water. Deaeration is the process of removing gases dissolved in it from water. When water is heated to saturation temperature at a given pressure, the partial pressure of the removed gas above the liquid decreases, and its solubility decreases to zero. Removal of corrosive gases in the boiler installation circuit is carried out in special devices - thermal deaerators. Specifications
Design and principle of operationThe DA series atmospheric pressure thermal deaerator consists of a deaeration column mounted on an accumulator tank. The deaerator uses a two-stage degassing scheme: stage 1 is jet, stage 2 is bubbling, both stages are located in a deaeration column, the schematic diagram of which is shown in Fig. 1. Streams of water to be deaerated are fed into column 1 through pipes 2 onto the upper perforated plate 3. From the latter, water flows in streams onto the bypass plate 4 located below, from where it flows in a narrow beam of a jet of increased diameter onto the initial section of the non-failing bubble sheet 5. Then the water passes along the bubble sheet in the layer provided by the overflow threshold (the protruding part of the drain pipe), and through drain pipes 6 is discharged into the accumulator tank, after holding in which it is discharged from the deaerator through pipe 14 (see Fig. 2), all steam is supplied to the accumulator the deaerator tank through pipe 13 (see Fig. 2), ventilates the volume of the tank and falls under the bubble sheet 5. Passing through the holes of the bubble sheet, the area of which is selected in such a way as to prevent the failure of water at the minimum thermal load of the deaerator, the steam exposes the water to without intensive processing. As the thermal load increases, the pressure in the chamber under the sheet 5 increases, the water seal of the bypass device 9 is activated and excess steam is released into the bypass of the bubble sheet through the steam bypass pipe 10. Pipe 7 ensures that the water seal of the bypass device of deaerated water is filled with a decrease in the thermal load. From the bubbling device, steam is directed through hole 11 into the compartment between plates 3 and 4. The vapor-gas mixture (vapour) is removed from the deaerator through gap 12 and pipe 13. In the jets, water is heated to a temperature close to the saturation temperature; removal of the bulk of gases and condensation of most of the steam supplied to the deaerator. Partial release of gases from the water in the form of small bubbles occurs on plates 3 and 4. On the bubble sheet, the water is heated to saturation temperature with slight condensation of steam and micro quantities of gases are removed. The degassing process is completed in the battery tank, where tiny gas bubbles are released from the water due to sediment. The deaeration column is welded directly to the battery tank, with the exception of those columns that have flange connection with deaerator tank. The column can be oriented arbitrarily relative to the vertical axis, depending on the specific installation scheme. The housings of the DA series deaerators are made of carbon steel, the internal elements are made of of stainless steel, fastening of elements to the body and to each other is carried out by electric welding. Schematic diagram of an atmospheric pressure deaeration column with a bubbling stage. Contents of deliveryIncluded in delivery deaeration plant included (the manufacturer agrees with the customer on the scope of delivery of the deaeration unit in each individual case):
SchemeSchematic diagram of switching on an atmospheric pressure deaeration unit: 1 - supply of chemically purified water; 2 - vapor cooler; 3, 5 — exhaust into the atmosphere; 4 — level adjustment valve, 6 — column; 7 — main condensate supply; 8 - safety device; 9 — deaeration tank; 10 — supply of deaerated water; 11 - pressure gauge; 12 — pressure control valve; 13 — hot steam supply; 14 - drainage of deaerated water; 15 — water sample cooler; 16 — level indicator; 17 - drainage; 18 - pressure and vacuum gauge.
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