Ensuring contact of the liquid with the air is a prerequisite for maintaining the operability of many engineering installations, process tanks and heating systems. This process is called aeration. But the reverse technology is also applied, which involves the removal of air from technological liquid media. Deaeration of water is usually used as a way to eliminate unwanted gas inclusions.
The principle of operation of the device
In water, air bubbles and gas mixtures can be present in the form of dissolved molecules, as micro bubbles or as compounds that gradually break down. The task of a typical deaerator is to organize the process of mass transfer between pro-gas mixtures and liquid. Technically, this procedure can be carried out in different ways, differing in the degree of degassing. In small installations of deaeration of water, a certain proportion of the output of gases is achieved by irradiating the liquid with ultrasound. Intensive exposure to ultrasonic waves is effective especially in cases where coagulation of the vesicles is required.
There is also the concept of vapor - this is the mass of gas removed from the liquid, which must be removed from the deaerator itself. The optimum performance of these devices is ensured with steam flow rates of at least 2 kg / t. If the liquid contains carbon dioxide, then this standard indicator increases to 3 kg / t.
Appointment classification
Special deaerator models are available for various fields of application and working conditions. According to the signs of structural performance, it is worth highlighting horizontal and vertical devices designed for specific conditions of a technical installation. According to the purpose, two broad groups of deaerators are distinguished - devices for utility networks and related equipment, as well as systems for maintaining the supply of water in boiler units, thermal equipment, etc. In the first case, corrosion is protected by the removal of air bubbles, and in the second is the optimization of capacitive pressure. At the same time, water deaeration for boiler rooms and heating networks is also performed by different devices.
In the case of boiler equipment, for example, it is advisable to use vacuum apparatuses operating at low temperatures of the order of 50-100 degrees Celsius. Atmospheric deaerators are more oriented towards servicing evaporative equipment and heating networks - their temperature is also low and slightly exceeds 100 degrees Celsius. Against this background, high pressure installations designed to work with energy boilers differ. The temperature in this case can be about 200 degrees Celsius, and the pressure - 9-10 MPa.
Disk deaerators
Such installations are usually horizontal in design with a vertically positioned tank. Air from the boiler enters from above and exits through the bottom row of perforated plates. For the deaeration process, reduced pressure steam is used, which is directed upward through the plate openings. The mechanics of mixing liquid with steam can be realized not only due to perforated elements, but also using a filtration system with membranes and gaskets. They provide a large phase interface for mass transfer. Dissolved gases during water deaeration pass into the vapor phase, after which the vapor-gas mixtures are discharged into the pipe of the ventilation system.
This is how standard evaporation occurs, but in some systems condensation of steam is provided with the return of heat from the gas mixture.
Spray Deaerators
Devices of this type are also mainly performed in a horizontal form factor with separate zones for heating and deaeration, which are separated by a special plate. Working steam passes into the tank area through the comb. During spray deaeration, the liquid is heated with steam to a boiling point. As the temperature rises, gas mixtures are removed through ventilation. To save thermal energy, spray deaeration of water may include recovery through heat exchange designs. They perceive the heat of the exhaust gases, passing it to the working equipment. Another way of saving involves the initial heating of water to a temperature close to the boiling point.
Features of thermal deaeration
This group of deaerators has a number of fundamental differences from heat exchangers. Such devices are mixing or surface. Heating and deaeration zones are also separated by partitions. Important is the very method of creating phase contact between the media. In this sense, thermal deaeration of water may include film, inkjet and bubbling contours of the direction of the working medium.
The first two in the basis of the design contain columns - these are devices through which liquid flows to the tank, while the heating steam rises up to the point of evaporation. During this process, condensate is released. Small designs of such deaerators may allow the tank and instrument housing to be combined into one system. As for bubbling deaerators, in them the steam is directly fed to the water surface and is crushed into small bubbles. The advantages of such devices include the modest dimensions of the structure and high deaeration performance.
Atmospheric deaeration
Nutrient water contains oxygen and carbon dioxide. When dissolved, these gas mixtures adversely affect the walls of the equipment. Moreover, the provoked corrosion processes intensify when exposed to steam under high pressure, which limits the use of some deaeration methods. The solution is atmospheric water treatment, which provides positive processes of chemical degassing. The optimal solution in this case is deaeration of feed water in a non-scale mode. The principle of operation of such a device is to break down the flow of water into small jets with parallel heating to a boiling state. Ultimately, you can achieve an effect in which the carbon dioxide content is reduced to 2 mg / l, and oxygen - to 0.01 mg / l.
Makeup fluid deaeration
Vacuum degassing technology is used to prepare make-up water. It is often used in the maintenance of hot water systems using nozzle deaerators. It should be noted that such a treatment scheme is allowed only if the alkali content in the liquid is low.
Deaeration is carried out with automatic regulation of water pressure in steel and cast iron structures. The temperature of the boiler can vary from 70 to 150 degrees Celsius. In order to minimize energy consumption, it is recommended to activate the mode of constant support of a low temperature threshold. This will increase the time of the procedure, but deaeration of the make-up water will give a higher effect. Alternatively, atmospheric deaeration can be used, which will use steam instead of the hot medium.
Conclusion
In choosing the appropriate method of eliminating water from gases and air, it is equally important to choose the right communication infrastructure. Modern means of water deaeration allow for regulation through automation, comparing performance with the characteristics of the equipment being serviced. The selection of power equipment with protective systems is also responsible. It will not be superfluous to acquire a powerful pump to support pressure, fuses and sensors to monitor critical performance indicators.