Regulation of atmospheric deaerators. Atmospheric deaerators

Deaerator- technical device, which implements the process of deaeration of a certain liquid (usually water), that is, its purification from undesirable gas impurities present in it (oxygen and carbon dioxide). Being dissolved in water, these gases cause corrosion of the feed pipes and heating surfaces of the boiler, as a result of which the equipment fails. Thermal deaeration of water is used at steam turbine stations.

The principle of operation of thermal deaerators is based on the fact that the absolute pressure above the liquid is the sum of the partial pressures of gases and steam.

If we increase the partial pressure of steam so that with the simultaneous removal of steam (this is a mixture of gases released from the water and a small amount of steam to be evacuated from the deaerator), then as a result we get the total partial pressure of gases. Then, according to Henry's law (the equilibrium mass concentration of gases in the 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.

By appointment: deaerators for feed water of steam boilers; make-up water and return condensate from external consumers; make-up water of the heating network.

According to the pressure of the heating steam: high pressure (0.6-0.8 MPa) ( D); atmospheric (0.12 MPa)( YES); vacuum (7.5-50 kPa) ( DV).

According to the method of heating deaerated water: mixing type (with mixing of heating steam with heated water); superheated water deaerators with external preheating of water with selective steam.

By design (according to the principle of formation of an interfacial surface): with a contact surface formed in a turbulent mode (slender-bubbling, film type with a disordered nozzle, jet plate type); with a fixed phase contact surface (film type with an ordered packing).

circuit diagram deaeration plant.

Rice. Mixing type atmospheric deaerator: 1 - tank (accumulator), 2 - feed water outlet from the tank, 3 - water-indicating glass, 4 - pressure gauge, 5, 6 and 12 - plates, 7 - draining water into the drainage tank, 8 - automatic regulator supply of chemically purified water, 9 - steam cooler, 10 - steam outlet to the atmosphere, 11 and 15 - pipes, 13 - deaerator column, 14 - steam distributor, 16 - water inlet to the hydraulic seal, 17 - hydraulic seal, 18 - excess water outlet from a hydraulic seal

The deaerator consists of tank 1 and column 13, inside 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 to distribution plate 12; through another pipeline through the regulator 8 on the plate 12 is supplied as an additive chemically purified water; from the plate, feed water is distributed in separate and uniform streams around the entire circumference of the deaerator column and flows down sequentially through a row of intermediate plates 5 and 6 arranged 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 rest of the uncondensed steam, leaves through the wind 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 consumed to power the boilers. To avoid a significant increase in pressure in the deaerator, two hydraulic seals are installed on it, as well as a hydraulic seal 17 in case of vacuum formation in it. When the pressure is exceeded, the deaerator may explode, and when rarefied, atmospheric pressure can crush it. The deaerator is supplied with a water-indicating 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.

In industrial and heating boiler houses, to protect against corrosion of heating surfaces washed by water, as well as pipelines, it is necessary to remove corrosive gases (oxygen and carbon dioxide) from feed and make-up water, which is most effectively ensured by thermal deaeration of water. Deaeration is the process of removing gases dissolved in water 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 scheme of the boiler plant is carried out in special devices - thermal deaerators.

Purpose and scope

Two-stage atmospheric pressure deaerators of the DA series with a bubbling device in the lower part of the column are designed to remove corrosive gases (oxygen and free carbon dioxide) from the feed water of steam boilers and make-up water of heat supply systems in boiler houses of all types (except for pure hot water). Deaerators are manufactured in accordance with the requirements of GOST 16860-77. OKP code 31 1402.

Modifications

Symbol example:

DA-5/2 - atmospheric pressure deaerator with a column capacity of 5 m³ / h with a tank with a capacity of 2 m³. Serial sizes - DA-5/2; DA-15/4; DA-25/8; DA-50/15; DA-100/25; DA-200/50; DA-300/75.

At the request of the customer, it is possible to supply atmospheric pressure deaerators of the DSA series, with standard sizes DSA-5/4; DSA-15/10; DSA-25/15; DSA-50/15; DSA-50/25; DSA-75/25; DSA-75/35; DSA-100/35; DSA-100/50; DSA-150/50; DSA-150/75; DSA-200/75; DSA-200/100; DSA-300/75; DSA-300/100.

Deaeration columns may be combined with larger tanks.

Rice. General form deaerator tank with an explication of fittings.

Technical specifications

Main specifications atmospheric pressure deaerators with bubbling in the column are shown in the table.

Deaerator				DA-50/15	DA-100/25	DA-200/50	DA-300/75
Nominal productivity, t/h
Working overpressure, MPa
Temperature of deaerated water, °C
Performance range, %
Productivity range, t/h
Maximum and minimum water heating in the deaerator,°C
The concentration of O 2 in deaerated water at its concentration in the source water, C to O 2, μg / kg: - corresponding to the state of saturation Not more than 3 mg/kg
Concentration of free carbon dioxide and deaerated water, С to О 2 , mcg/kg
Trial hydraulic pressure, MPa
Permissible pressure increase during operation protective device, MPa
Specific steam consumption at rated load, kg/td.v
Diameter, mm Height, mm Weight, kg
Useful capacity of the battery tank, m 3
Type of deaerator tank
Vapor cooler size
Type safety device

* - design dimensions of deaeration columns may differ depending on the manufacturer.

Design Description

The atmospheric pressure thermal deaerator of the DA series consists of a deaeration column mounted on an accumulator tank. The deaerator uses a two-stage degassing scheme: stage 1 - jet, stage 2 - bubbling, and both stages are placed in a deaeration column, the schematic diagram of which is shown in fig. 1. Flows of water to be deaerated are fed into column 1 through pipes 2 to the upper perforated plate 3. From the latter, water flows in jets to the bypass plate 4 located below, from where it merges with a narrow jet of increased diameter to the initial section of the non-failure bubbling sheet 5. Then the water passes through the bubbling sheet in the layer provided by the overflow threshold (the protruding part of the drain pipe), and through drain pipes 6 merges 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 gets under the bubbling sheet 5. Passing through the holes of the bubbling sheet, the area of ​​which is chosen in such a way as to exclude water failure at the minimum thermal load of the deaerator, the steam exposes the water to it intensive processing. With an increase in the heat load, the pressure in the chamber under the sheet 5 increases, the hydraulic seal of the bypass device 9 is activated, and excess steam is passed into the bypass of the bubbling sheet through the steam bypass pipe 10. Pipe 7 ensures that the hydraulic seal of the bypass device is flooded with deaerated water when the heat load is reduced. From the bubbling device, steam is directed through hole 11 to the compartment between plates 3 and 4. The vapor-gas mixture (vapour) is removed from the deaerator through gap 12 and pipe 13. Water is heated in the jets to a temperature close to the saturation temperature; removal of the main mass of gases and condensation of most of the steam supplied to the deaerator. Partial release of gases from water in the form of small bubbles occurs on plates 3 and 4. On the bubbling sheet, the water is heated to saturation temperature with slight condensation of steam and the removal of trace amounts of gases. The degassing process is completed in the accumulator tank, where the smallest gas bubbles are released from the water due to sludge.

The deaeration column is welded directly to the storage tank, except for those columns that have a flange connection to the deaerator tank. Relative to the vertical axis, the column can be oriented arbitrarily, depending on the specific installation scheme. Cases of DA series deaerators are made of carbon steel, internal elements - from stainless steel, fastening of elements to the case and among themselves is carried out by electric welding.

The delivery set of the deaeration unit includes (the manufacturer agrees with the customer on the completeness of the delivery of the deaeration unit in each individual case):

deaeration column;

a control valve on the line for supplying chemically purified water to the column to maintain the water level in the tank;

a control valve on the steam supply line to maintain pressure in the deaerator;

pressure gauge;

shut-off valve;

water level indicator in the tank;

manometer;

thermometer;

safety device;

vapor cooler;

shut-off valve;

drain pipe;

technical documentation.

Rice. 1 Schematic diagram of an atmospheric pressure deaeration column with a bubbling stage.

Scheme of switching on the deaeration unit

The scheme of inclusion of atmospheric deaerators is determined by the design organization, depending on the conditions of appointment and the capabilities of the facility where they are installed. On fig. 2 shows the recommended scheme of the deaeration unit of the DA series.

Chemically purified water 1 is fed through the vapor cooler 2 and the control valve 4 to the deaeration column 6. The flow of the main condensate 7 with a temperature below the operating temperature of the deaerator is also directed here. The deaeration column is installed at one of the ends of the deaerator tank 9. The deaerated water 14 is drained from the opposite end of the tank in order to ensure maximum water holding time in the tank. All steam is supplied through the pipe 13 through the pressure control valve 12 to the end of the tank, opposite the column, in order to ensure good ventilation of the steam volume from the gases released from the water. Hot condensates (clean) are fed into the deaerator tank through pipe 10. The vapor from the unit is removed through the vapor cooler 2 and pipe 3 or directly into the atmosphere through pipe 5.

To protect the deaerator from an emergency increase in pressure and level, a self-priming combined safety device 8 is installed. Periodic testing of the quality of deaerated water for the content of oxygen and free carbon dioxide is carried out using a heat exchanger for cooling water samples 15.

Rice. 2 Schematic diagram of the inclusion of an atmospheric pressure deaeration unit:
1 - chemically purified water supply; 2 - vapor cooler; 3, 5 - exhaust into the atmosphere; 4 - level control 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 - removal of deaerated water; 15 - water sample cooler; 16 - level indicator; 17- drainage; 18 - pressure gauge.

Vapor cooler

To condense the gas-vapor mixture (vapour), a surface-type vapor cooler is used, consisting of a horizontal body in which a pipe system is placed (pipe material is brass or corrosion-resistant steel).

The vaporizer cooler is a heat exchanger in which chemically treated water or cold condensate from a constant source heading to the deaeration column. The vapor-gas mixture (vapour) enters the annulus, where the vapor from it is almost completely condensed. The remaining gases are discharged into the atmosphere, the vapor condensate is drained into a deaerator or a drainage tank.

The vapor cooler consists of the following main elements (see Fig. 3):

Nomenclature and general characteristics vapor coolers

Vapor cooler
Pressure, MPa In a pipe system In case
In a pipe system In case	steam, water	steam, water	steam, water	steam, water
Medium temperature, °С In a pipe system In case
Weight, kg

Safety device (hydraulic seal) of atmospheric pressure deaerators

To provide safe operation deaerators, they are protected from a dangerous increase in pressure and water level in the tank using a combined safety device (hydraulic trap), which must be installed in each deaerator installation.

The water seal must be connected to the supply steam line between the control valve and the deaerator or to the steam space of the deaerator tank. The device consists of two hydraulic seals (see Fig. 4), one of which protects the deaerator from exceeding the permissible pressure 9 (shorter), and the other from a dangerous increase in level 1, combined into a common hydraulic system, and expansion tank. Expansion tank 3, serves to accumulate the volume of water (when the device is triggered), which is necessary for automatic filling of the device (after the violation in the installation has been eliminated), i.e. makes the device self-priming. The diameter of the overflow water seal is determined depending on the maximum possible water flow to the deaerator in emergency situations.

The diameter of the steam hydraulic seal is determined based on the highest allowable pressure in the deaerator during operation of the device 0.07 MPa and the maximum possible steam flow into the deaerator in an emergency with a fully open control valve and maximum pressure at the steam source.

In order to limit the steam flow to the deaerator in any situation to the maximum required (at 120% load and 40-degree heating), a restrictive throttle diaphragm should be additionally installed on the steam pipeline.
In some cases (to reduce the construction height, install deaerators in the premises), instead of a safety device, safety valves are installed (to protect against overpressure) and a steam trap to the overflow fitting.

Combined safety devices are manufactured in six sizes: for deaerators DA - 5 - DA - 25, DA - 50 and DA - 75, DA - 100, DA - 150, DA - 200, DA - 300.

Rice. 4 Schematic diagram of the combined safety device.
1 - Overflow water seal; 2 – steam supply from the deaerator; 3 - expansion tank; 4 - water drain; 5 - exhaust into the atmosphere; 6 - pipe for controlling the bay; 7 - supply of chemically purified water for pouring; 8 - water supply from the deaerator; 9 - hydraulic seal against pressure increase; 10 - drainage.

Installation of deaeration plants

For execution installation work installation sites must be equipped with basic installation equipment, fixtures and tools in accordance with the project for the production of works. Upon acceptance of the deaerators, it is necessary to check the completeness and compliance of the nomenclature and number of places with the shipping documents, the compliance of the supplied equipment with the installation drawings, the absence of damage and defects in the equipment. Before installation, an external inspection and depreservation of the deaerator is carried out, and the detected defects are eliminated.

Installation of the deaerator at the facility is carried out in the following order:

install the storage tank on the foundation in accordance with the installation drawing of the design organization;

weld a spillway to the tank;

cut off the lower part of the deaeration column along the outer radius of the deaeration tank body and install it on the tank in accordance with the installation drawing of the design organization, while the plates must be located strictly horizontally;

weld the column to the deaerator tank;

install the vapor cooler and the safety device according to the installation drawing of the design organization;

connect pipelines to the fittings of the tank, column and vapor cooler in accordance with the deaerator piping drawings made by the design organization;

install shut-off and control valves and instrumentation;

conduct hydraulic test deaerator;

install thermal insulation at the direction of the design organization.

Specifying Security Measures

During the installation and operation of thermal deaerators, the safety measures determined by the requirements of Gosgortekhnadzor, the relevant regulatory and technical documents, job descriptions etc.

Thermal deaerators must be subject to technical examinations (internal inspections and hydraulic tests) in accordance with the rules for the design and safe operation of pressure vessels.

Operation of DA series deaerators

1. Preparing the deaerator for start-up:

make sure that all installation and repair work is completed, temporary plugs are removed from the pipelines, hatches on the deaerator are closed, bolts on flanges and fittings are tightened, all gate valves and control valves are in good order and closed;

Maintain the nominal flow rate of flash steam from the deaerator in all modes of its operation and periodically monitor it using a measuring vessel or according to the balance of the flash cooler.

The main malfunctions in the operation of deaerators and their elimination

1. An increase in the concentration of oxygen and free carbon dioxide in deaerated water above the norm can occur for the following reasons:

a) the determination of the concentration of oxygen and free carbon dioxide in the sample is incorrect. In this case it is necessary:

check the correctness of the performance of chemical analyzes in accordance with the instructions;

check the correctness of water sampling, its temperature, flow rate, absence of air bubbles in it;

check the tightness of the pipe system - sampling cooler;

b) the steam consumption is significantly underestimated.

In this case, it is necessary:

check the compliance of the surface of the vaporizer cooler with the design value and, if necessary, install a vaporizer cooler with a larger heating surface;

check the temperature and flow rate of the cooling water passing through the vapor cooler and, if necessary, reduce the temperature of the water or increase its flow rate;

check the degree of opening and serviceability of the valve on the pipeline for the removal of the steam-air mixture from the vapor cooler to the atmosphere;

c) the temperature of the deaerated water does not correspond to the pressure in the deaerator, in this case it should be:

check the temperature and flow rate of the flows entering the deaerator and increase the average temperature of the initial flows or reduce their flow rate;

check the operation of the pressure regulator and, if the automation fails, switch to remote or manual pressure control;

d) supply of steam with a high content of oxygen and free carbon dioxide to the deaerator. It is necessary to identify and eliminate the centers of contamination of steam with gases or take steam from another source;

e) the deaerator is out of order (clogging of the holes in the trays, warpage, breakage, breakage of the trays, installation of the trays with a slope, destruction of the bubbling device). It is necessary to take the deaerator out of operation and repair;

f) insufficient steam flow to the deaerator (average water heating in the deaerator is less than 10°C). It is necessary to reduce the average temperature of the initial water flows and ensure that the water in the deaerator is heated by at least 10°C;

g) drains containing a significant amount of oxygen and free carbon dioxide are sent to the deaerator tank. It is necessary to eliminate the source of contamination of the drains or feed them into the column, depending on the temperature, on the upper or overflow plates;

h) the pressure in the deaerator is reduced;

check the serviceability of the pressure regulator and, if necessary, switch to manual regulation;

check the pressure and sufficiency of heat flow in the power source.

2. An increase in pressure in the deaerator and the operation of a safety device can occur:

a) due to a malfunction of the pressure regulator and a sharp increase in steam flow or a decrease in the flow of source water; in this case, you should switch to remote or manual pressure control, and if it is impossible to reduce the pressure, stop the deaerator and check the control valve and the automation system;

b) with a sharp increase in temperature with a decrease in the flow rate of the source water, either reduce its temperature, or reduce the steam flow rate.

3. An increase and decrease in the water level in the deaerator tank above the permissible level may occur due to a malfunction of the level controller, it is necessary to switch to remote or manual level control, if it is impossible to maintain a normal level, stop the deaerator and check the control valve and automation system.

4. Water hammer must not be allowed in the deaerator. In case of water hammer:

a) due to a malfunction of the deaerator, it should be stopped and repaired;

b) when the deaerator is operating in the “flooding” mode, it is necessary to check the temperature and flow rate of the initial water flows entering the deaerator, the maximum heating of water in the deaerator should not exceed 40 °C at 120 °C on the load, otherwise it is necessary to increase the temperature of the source water or reduce its consumption.

Repair

Current repair of deaerators is carried out once a year. At current repair inspection, cleaning and repair work is carried out to ensure normal operation of the plant until the next repair. For this purpose, deaeration tanks are equipped with manholes, and columns with inspection hatches.

Scheduled overhauls should be carried out at least once every 8 years. If it is necessary to repair the internal devices of the deaeration column and it is impossible to do it with the help of hatches, the column can be cut along a horizontal plane in the most convenient place for repair.

During the subsequent welding of the column, the horizontality of the plates and the vertical dimensions must be maintained. After finishing repair work a hydraulic pressure test of 0.2941 MPa (abs.) (3 kgf/cm2) must be performed.

An indispensable condition for the efficient and economical operation of atmospheric deaerators is their competent adjustment. About what requirements the work of deaerators must satisfy, and how you can configure it yourself - our article.

Typical violations in the operation of deaerators

In practice, the most common typical mistakes regulation of the operation of atmospheric deaerators: operation without bubbling 1 and operation without a deaeration column.
Both of these methods can be successful in terms of removing dissolved gases, the residual content of which is prescribed by the rules. But the efficiency of deaerators under such regimes is extremely low due to the high specific steam consumption for deaeration.

Criteria and conditions for high-quality operation of deaerators

During deaeration, 6-7 grams of dissolved gases are usually removed from 1 ton of water. It has been experimentally established that during the operation of atmospheric deaerators, the maximum amount of vapor should not exceed 22 kg per ton. Based on this, the section of the outlet pipeline and the vapor cooler are selected. Optimum can be considered such a method of operation of the deaerator, in which the required operating parameters are automatically provided both in the deaeration column and in the bubble tank at a minimum required quantity vapor.

The main factors affecting the quality of the deaerator are well known:

• water consumption and its stability;
• temperature of chemically purified water;
• pressure in the deaerator;
• steam consumption in the deaeration column;
• steam consumption for bubbling in the tank;
• water level in the tank.

Usually, as a result of adjustment work, it is possible to establish the values ​​of operational parameters that provide effective degassing over the entire range of operating loads. To automate the operation of deaerators, automatic control systems are used, consisting of direct-acting valves and temperature and level control systems.

The principle of operation of the automatic control system for the operation of the deaerator

First, let's consider how the automatic control system works in general (Fig. 1).
With an increase in steam consumption, the consumption of feed water from the deaerator tank increases. In this case, there is a deviation of its level, measured by the sensor, from the specified value. The level controller acts on the control valve for supplying water to the deaerator column so that its flow increases and the level is restored. In this case, the valve stem takes a new position corresponding to a higher flow rate.

Rice. one

Entering the deaeration column more cold water accompanied by intense condensation of steam coming from the vapor space of the tank. As a result, the pressure in the vapor space decreases. This leads to a change in the control action in the direct acting pressure regulator. In this case, the stem of the control valve occupies a new position corresponding to a higher steam flow. But the pressure in the vapor space, however, will be somewhat lower than the original. This is how proportional control should be.

How will the water temperature in the tank change in this case (Fig. 2)? It is obvious that it will quickly drop to a new value corresponding to the established pressure in the vapor space. This will happen partly due to the entry of water with a lower temperature from the column, partly due to the evaporation of a small amount of "overheated" water accumulated in the tank. A decrease in water temperature will increase the opening of the steam supply valve for bubbling. The steam consumption for bubbling will increase, part of it will condense in the water volume, and part, having passed the steam space, will fall into the deaeration column.

Rice. 2

Now consider the reverse situation. What happens when the load is reduced? There will be no peculiarities in the operation of the level regulator and the pressure regulator. The level regulator will restore it, while reducing the water flow, and the pressure regulator will reduce the steam supply to the steam space. In this case, the established pressure will be slightly higher than the initial one, respectively, the water temperature will also be somewhat higher after a while. After all, the boiling point (condensation) is uniquely related to pressure. An example of temperature change depending on the load is shown in fig. 3.

Rice. 3

Unlike level and pressure regulators, the result of the action of the steam flow regulator on bubbling can have an unpleasant feature. And it is directly related to how well it is configured. The fact is that with a careless setting, the set temperature may be less than or the same as that established at elevated pressure. In this case, there will be no reduction in the supply of steam for bubbling, but its complete cessation. As a result, the deaeration regime will be violated.

The principle of operation of automatic regulators

Now let's look at how each regulator works separately. Let's start with the pressure regulator, which determines the flow of steam into the deaeration column. We only note that in fact it supplies steam to the vapor space of the tank. From the tank, pressure is transmitted through the impulse tube to the regulator drive diaphragm. This is how feedback works. An example of a flow characteristic of a direct acting valve is shown in fig. 4.

Rice. 4

This regulator 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. The set pressure range depends on the area of ​​the diaphragm and the range of the spring. The control deviation in our case is the difference between the pressure of 0.2 bar, corresponding to the operating pressure in the deaerator, and the current pressure, corresponding to the operating point on the flow characteristic of the valve. The regulator responds to pressure changes almost instantly. The delay time is mainly determined by the time the drive cavity is filled or emptied.

Now let's take a closer look at how the steam flow regulator for bubbling works. We will call it a flow controller, although such a system is usually used as a temperature controller. This regulator also has a proportional characteristic. The range of change in the reference depends on the volume of liquid in the sensing element and its coefficient of volumetric expansion. With this characteristic, a larger difference between the current temperature value and its set value corresponds to a larger stroke.
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 set by the setting knob. But it must be borne in mind that the result of this action, in the general case, has a non-linear form. Let's explain what's going on here.

The full stroke of the pusher rod is 10 mm and corresponds to a change in the temperature of the liquid in the sensing element by 10ºС. The full stroke of the valve plunger, depending on the diameter, is from 3 to 9 mm. In this case, when the valve stem is moved from 0 to 20%, the flow increases from 0 to 75% of the total flow. This is a feature of the flow characteristic of the quick opening valve. Thus, the flow will change linearly only if the current movement of the valve plug does not go beyond the linear section 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 installation of the sensor. longest time there will be delays when using a dry sleeve. The smallest - when mounting without a protective sleeve. It is important to note that in any case, the delay time of the flow controller is significantly longer than that of the pressure controller. Therefore, when the regulators work together, their mutual influence does not lead to mode fluctuations.

Let us dwell briefly on the operation of the level controller. The correctness of its operation is determined by the observance of the procedure for setting up, prescribed in the instructions. As a result of tuning, PID parameters are set corresponding to the integral quality criterion.

Conditions for the successful completion of work on setting up the deaerator

It is necessary to say about the most important conditions, without which any attempt to set up the work of deaerators is like wandering in the dark.

1. To control the result of the operation of the deaerator, it is necessary to have a reliable oximeter (oxygen meter) and a PH meter. It is desirable that the oximeter operate in the microgram range and provide continuous monitoring. 2
2. Control points should be equipped with samplers. Flow type sampling coolers are most suitable. They should ensure that the sample temperature does not exceed 50ºС at a flow rate of 2 to 50 l/h. The presence of several samplers greatly facilitates the implementation of adjustment work. The supply tubes must be metal, which excludes secondary oxygen contamination. The use of non-metallic tubing is not recommended.

In conclusion, we briefly outline the sequence of actions when setting up a deaerator.

• adjust the water flow regulator;
• adjust the pressure regulator;
• set the steam flow controller to bubbling;
• adjust the pressure regulator setting and check the pressure range;
• adjust the setting of the steam flow controller for bubbling;
• check the operation of the deaerator at sensitive points according to the readings of the oximeter and PH-meter.

A deaerator is a technical device that implements the process of deaeration of a certain liquid (usually water or liquid fuel), that is, its purification from unwanted gas impurities present in it. On many power stations also plays the role of a regeneration stage and a feed water storage tank.

The deaerator device is intended:

* To protect pumps from cavitation.

* To protect equipment and pipelines from corrosion.

* To protect the system from air entering it, which disrupts the hydraulics and the normal operation of the nozzles.

Fig.2.

1 - tank (accumulator), 2 - outlet of feed water from the tank, 5 - water-indicating glass, 4 - pressure gauge, 5, 6 and 12 - plates, 7 - draining water into the drain, 8 - automatic regulator supply of chemically purified water, 9 - steam cooler, 10 - steam outlet to the atmosphere, 11 and 15 - pipes, 13 - deaerator column, 14 - steam distributor, 16 - water inlet to the hydraulic seal, 17 - hydraulic shutter, 18 -- release of excess water from the hydraulic seal

The thermal deaerator is based on the principle of diffusion desorption, when the liquid in the system is heated to the point of boiling. During such a process in a thermal deaerator, the solubility of gases is zero. The resulting vapor carries gases out of the system, and the diffusion coefficient increases.

In a vortex deaerator, hydrodynamic effects are used that cause forced desorption, that is, they lead to liquid rupture in the weakest places - under the action of a density difference. In this case, there is no heating of the liquid.

By pressure, thermal deaerators are classified into:

* Vacuum (DV)

* Atmospheric (YES).

* High blood pressure(DP).

Atmospheric deaerator - used in the smallest wall thickness. Under the action of excess pressure above atmospheric - steam is removed from the walls by gravity. Atmospheric deaerator DSA is designed to remove corrosive gases from the system of steam boilers and boiler plants. Atmospheric deaerators are installed both outdoors and indoors. The numbers marked on the atmospheric deaerator DSA 75 and deaerator DA 25 - determine the performance of the device.

Vacuum deaerator - are used in conditions when boiler rooms do not have released steam. Vacuum deaerators DV - are forced to work in conjunction with devices for suction of vapor. The DV feed water deaerator has a large wall thickness, and also allows the decomposition of bicarbonates at low pressure. Depending on the performance, they are indicated by numbers (Example: Vacuum deaerator DV 25).

Deaerators DP ( high pressure) - have a large wall thickness, but the DP deaerators allow you to use the vapor as a light working environment for condenser ejectors. Also, excess high pressure deaerators can reduce the amount of metal-intensive HPH.

Deaerator device and principle of operation

In the deaerator column, water is heated and treated with steam. After passing through two stages of degassing (1st stage - jet, 2nd - bubbling), water flows from the column in jets into the BDA deaerator tank.

The design of the deaerator ensures the convenience of the internal inspection of the deaeration column. The material of the perforated sheets of the internal devices of the deaerator column is corrosion-resistant steel.

The deaeration tank houses the third stage of degassing after the deaeration column in the form of a flooded bubbling device.

In the deaerator tank, tiny gas bubbles are released from the water due to sludge.

The deaerator vapor cooler serves only to recover the vapor condensation heat. Chemically purified water passes inside the tubes of the vapor cooler and is directed to the deaeration column. A vapor-gas mixture (evaporator) enters the annular space, where the steam from it is almost completely condensed. The remaining gases are discharged into the atmosphere, the vapor condensate is drained into a deaerator or drainage tank

Tube material - brass or corrosion-resistant steel.

The operation of the deaerator is carried out automatically. The pressure in the deaerator is constantly regulated at the level of 0.02 MPa. The water level in the deaerator is also constantly maintained. Deaerators are started and stopped manually

Fig.3.

The deaeration plant consists of:

· Vacuum deaerator;

· HVV (vapour cooler, shell-and-tube heat exchanger designed to condense the maximum amount of steam and utilize its thermal energy);

· EV (water-jet ejector, air-suction device).

The DV uses a two-stage degassing system. 1st stage jet, 2nd - bubbling, non-failing perforated plate.

A vacuum deaerator is used to deaerate water if its temperature is below 100 °C (the boiling point of water at atmospheric pressure).

The area for the design, installation and operation of a vacuum deaerator are hot water boilers (especially in a block version) and heat points. Vacuum deaerators are also actively used in Food Industry for deaeration of water necessary in the technology of preparing a wide range of beverages.

Vacuum deaeration is applied to the water flows going to make up the heating network, the boiler circuit, the hot water supply network.

Features of the vacuum deaerator.

Since the process of vacuum deaeration occurs at relatively low water temperatures (on average from 40 to 80 °C, depending on the type of deaerator), the operation of a vacuum deaerator does not require the use of a coolant with a temperature above 90 °C. The heat carrier is necessary for water heating in front of the vacuum deaerator. The coolant temperature up to 90 °C is provided at most facilities where it is potentially possible to use a vacuum deaerator.

The main difference between a vacuum deaerator and an atmospheric deaerator is in the system for removing vapor from the deaerator.

In a vacuum deaerator, vapor (vapor-gas mixture formed during the release of saturated vapors and dissolved gases from water) is removed using vacuum pump.

As a vacuum pump, you can use: vacuum water ring pump, water jet ejector, steam jet ejector. They are different in design, but based on the same principle - a decrease in static pressure (creation of a rarefaction - vacuum) in a fluid flow with an increase in flow rate.

The fluid flow rate increases either when moving through a converging nozzle (water jet ejector) or when the fluid swirls as the impeller rotates.

When steam is removed from the vacuum deaerator, the pressure in the deaerator drops to the saturation pressure corresponding to the temperature of the water entering the deaerator. The water in the deaerator is at the boiling point. At the water-gas interface, a difference in concentrations arises for the gases dissolved in water (oxygen, carbon dioxide) and, accordingly, the driving force of the deaeration process appears.

The quality of the deaerated water after the vacuum deaerator depends on the efficiency of the vacuum pump.

Features of the installation of a vacuum deaerator.

Because the water temperature in the vacuum deaerator is below 100 °C and, accordingly, the pressure in the vacuum deaerator is below atmospheric - vacuum, the main question arises in the design and operation of a vacuum deaerator - how to supply the deaerated water after the vacuum deaerator further to the heat supply system. This is the main problem of using a vacuum deaerator for water deaeration at boiler houses and heating stations.

Basically, this was solved by installing a vacuum deaerator at a height of at least 16 m, which provided the necessary pressure difference between the vacuum in the deaerator and atmospheric pressure. Water flowed by gravity into the storage tank located at the zero mark. The installation height of the vacuum deaerator was chosen based on the maximum possible vacuum (-10 m.a.c.), the height of the water column in the accumulator tank, the resistance of the drain pipeline and the pressure drop necessary to ensure the movement of deaerated water. But this entailed a number of significant disadvantages: an increase in the initial construction costs (a 16 m high stack with a service platform), the possibility of freezing water 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 period.

For block boiler houses that are actively designed and installed this decision on applicable.

The second solution to the issue of supplying deaerated water after a vacuum deaerator is to use an intermediate deaerated water storage tank - a deaerator tank and pumps for supplying deaerated water. The deaerator tank is under the same vacuum as the vacuum deaerator itself. In fact, the vacuum deaerator and the deaerator tank are one vessel. The main load falls on the deaerated water supply pumps, which take the deaerated water from under vacuum and feed it further into the system. To prevent the occurrence of cavitation in the pump for supplying deaerated water, it is necessary to ensure that the height of the water column (the distance between the water surface in the deaerator tank and the pump suction axis) at the pump suction is not less than the value indicated in the pump passport as NPFS or NPFS. The cavitation reserve, depending on the brand and performance of the pump, ranges from 1 to 5 m.

The advantage of the second version of the layout of the vacuum deaerator is the ability to install the vacuum deaerator at a low height, indoors. Deaerated water supply pumps will ensure that deaerated water is pumped further into storage tanks or for make-up. To ensure a stable process of pumping deaerated water from the deaerator tank, it is important to choose the right pumps for supplying deaerated water.

Improving the efficiency of the vacuum deaerator.

Since vacuum deaeration of water is carried out at a water temperature below 100 ° C, the requirements for the technology of the deaeration process increase. The lower the water temperature, the higher the coefficient of solubility of gases in water, the more difficult the deaeration process. It is necessary to increase the intensity of the deaeration process, respectively apply Constructive decisions based on new scientific developments and experiments in the field of hydrodynamics and mass transfer.

The use of high-speed flows with turbulent mass transfer when creating conditions in the liquid flow to further reduce the static pressure relative to 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 complete solution the issue of installing a vacuum deaerator in the boiler room at zero with a minimum overall height, a block vacuum deaerator BVD was developed, tested, and successfully put into mass production. With a deaerator height slightly less than 4 m, the block vacuum deaerator BVD allows efficient deaeration of water in the performance range from 2 to 40 m3/h for deaerated water. The block vacuum deaerator occupies no more than 3x3 m space in the boiler room (at the base) in its most productive design.