RU2392230C1 - Jet vortex deaerator - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: deaerator includes vertical case with side pipe of heated water feed, swirler with spiral channels, mounted coaxially in the top case part, and cowling mounted coaxially in the bottom case part. Spiral channels in external surface of swirler feature alternate cross-section converging from inlet to outlet. Swirler is hollow, with axial channel for vapour removal. Channel inlet has bell shape and is lowered against outlet edges of spiral channels so that external surface of bell, together with internal surface of case wall, forms annular sudden expansion chamber converging towards cowling. Cowling is mounted in the case by support with water drainage holes, so that an annular diffuser is formed between external surface of the cowling and internal case surface. Cylindrical rotation chamber with shaped internal surface is formed between bottom edge of swirler and top edge of cowling.

EFFECT: enhanced efficiency of fluid drop separation from vapour flow, reduced residual oxygen content in deaerated water, reduced spray entrainment.

2 cl, 3 dwg

Description

The invention relates to devices for thermal deaeration of water and can be used in small-sized heating and block-modular boiler rooms to remove corrosive gases from feed water for steam and hot water boilers, as well as from make-up water for heating networks.

Known cyclone deaerator (patent No. 2102329), which contains a housing placed vertically. The nozzle for supplying heated deaerated water is located tangentially in its upper part. A funnel with a pipe of deaerated water is located in the lower part of the housing. The vapor pipe is installed coaxially inside the housing. A crushing unit containing a crushing grid is cut into the nozzle for supplying heated deaerated water. Also known is a cyclone deaerator (patent No. 12407), containing a vertically placed housing with nozzles for supplying heated deaerated water in its upper part, a vapor pipe installed coaxially inside the housing, and a drain nozzle for deaerated water in the lower part, characterized in that it is additionally not equipped less than one tubular insert, while the tubular insert is installed coaxially inside the housing with the separation of the housing cavity around the vapor pipe into annular sections, in addition, each nozzle of the heated supply is deaerated of water is made with a prechamber, and the prechamber from the side of the vapor pipe is bounded by the upper part of one of the existing inserts or the side wall of the housing, the part into which nozzle devices with a tangentially oriented slot are mounted.

The main disadvantage of the known devices is the inability to implement with their use (when working in a vacuum mode) compact layout solutions. When working under vacuum, these deaerators should be located at a height of 9-10 m above the battery capacity into which water is drained to ensure free drainage and to prevent the possibility of suction of deaerated water by the ejector through an evaporator pipe. However, this is not possible in the limited construction space of a modular boiler room.

The second disadvantage of the known devices is the entrainment of deaerated water through the vapor pipe. In the deaerators (No. 2102329) and (No. 12407) the vapor pipe is placed vertically, in connection with which water enters it from the outside, freely flows down and is carried off from the bottom edge of the pipe by an ascending vapor stream. To reduce the mudguard it is necessary to reduce the speed of the vapor by increasing the internal volume of the device, which negatively affects the overall dimensions of the deaerator. Thus, these devices do not allow to achieve the minimum weight and size characteristics in the absence of mud spray, since these conditions are mutually exclusive.

As the closest analogue, a centrifugal deaerator (patent No. 2246446) may be adopted, comprising a cylindrical body, a swirl mounted at the inlet of the deaerator, a vapor pipe, the start of which inside the body is a hollow body of revolution, the outer surface of which together with the inner surface of the cylindrical body forms nozzle with tapering to a minimum section and then expanding part. Rectifier blades mounted longitudinally on the vapor pipe.

The main disadvantage of this device is the dependence of the quality of deaeration on the height of the deaerator above the battery capacity. The lower the deaerator is located above the battery capacity, the higher is the working back pressure. The pressure in the gas cavity of the deaerator remains constant and equal to the saturation pressure at the temperature of the deaerated water. The greater the difference between the pressure in the cavity of the deaerator and the back pressure, the more the thickness of the rotating layer of water inside the deaerator increases. Considering that due to the action of centrifugal forces, the pressure in the core of the rotating water flow (i.e. between the deaerator wall and the interface between the liquid and gaseous phases) is always greater than the pressure of saturated vapors in the gas cavity, only surface boiling of water occurs at the interface. When boiling, the gas cavity is filled with water vapor, in connection with which the partial pressure of oxygen above the surface of the water decreases in proportion to its molar fraction in the vapor-gas mixture. This leads to a violation of the equilibrium concentration of oxygen in water and to diffusion of oxygen through the free surface of the liquid into the gaseous medium. That is, oxygen desorption occurs. In this case, only the surface layer of the fluid flow is effectively deaerated. The deaeration of the core of the fluid flow occurs less efficiently as the fluid particles making up the core of the flow enter the surface layer due to convective mixing during movement. However, with an increase in the thickness of the rotating water layer, the conditions of convective mass transfer in the core of the water flow deteriorate and the molecular oxygen diffusion rate through the surface boundary layer decreases simultaneously. As a result, the mass transfer coefficient between the liquid-gas phases decreases, oxygen desorption worsens, and the residual oxygen content in the flow core increases. In addition, the part of the fluid flow directly adjacent to the inner surface of the casing wall and forming the wall laminar boundary layer does not mix at all with the turbulent core of the flow; therefore, the oxygen concentration in this layer remains equal to the initial concentration. In practice, this leads to the fact that with the compact arrangement of this deaerator at the same level as the capacity in the temperature range of the deaerated water to 75 ° C, it is impossible to reduce the oxygen content to the declared value of 50 μg / L.

The second disadvantage of this device is the incomplete exclusion of mud spray through the vapor pipe, due to the selected location of the gas-vapor mixture inlet to the vapor pipe at the end of the rotation chamber (from the outlet of water from the deaerator). Since the main quantity of vapor is explosive at the exit from the spiral channels to the rotation chamber, a large number of fine droplets are formed, and a significant part of the droplets has an axial velocity component directed directly towards the entrance to the channel to remove the vapor, which is the reason for the increased spraying.

The third disadvantage is the periodic drawdown of water into the vapor pipe, due to the shape of the spiral channels. Since the swirl of this device has channels formed by spirally wound ribs on a cylindrical body of revolution, the cross section of each channel is constant over the entire length. It is known that during the flow of water in an extended narrow channel of constant cross section, local narrowing of the flow occurs at the channel inlet. In accordance with Bernoulli's law, the narrowing of the flow is accompanied by a local increase in flow velocity and a decrease in static pressure in the flow. And since to ensure boiling, the pressure at the outlet of the swirl channel (in the rotation chamber) must be equal to the pressure of saturated vapor of the liquid, then in the zone of local narrowing, the pressure in the channel decreases below the pressure of saturated vapor. This is especially evident when working in the temperature range of more than 85 ° C. This leads to local boiling of the liquid inside the channel and to the occurrence of a slug flow of a two-phase medium in the channel, which in turn is the cause of the uneven flow of liquid into the rotation chamber and the appearance of mechanical pulsations in the rotating fluid flow. In addition, due to the action of viscous friction forces between the layer of rapidly rotating water and the stationary inner surface of the casing, the water flow is decelerated intensively, therefore, closer to the exit from the deaerator, the peripheral water velocity is much lower than at the beginning of the rotation chamber. It is known that centrifugal force is directly proportional to the square of the peripheral speed and inversely proportional to the radius of the circle. A decrease in peripheral velocity leads to a decrease in the radius of the vortex and an increase in the thickness of the rotating layer of water closer to the exit from the deaerator. Therefore, the thickness of the rotating layer of water from the outlet side always turns out to be greater than from the inlet side. In this case, the inner boundary of the water layer comes too close to the edge of the entrance to the channel to remove the vapor, which is located at the end of the rotation chamber. And since the internal boundary of the water layer during mechanical operation of the deaerator undergoes mechanical pulsations caused by the uneven flow of water through the swirl channels, this circumstance contributes to the periodic drawing of water into the pipe to remove the vapor.

The problem to which this invention is directed is to improve the conditions of convective mass transfer in the core of a water stream, increase the mass transfer coefficient between the liquid and gaseous phases, increase the efficiency of separation of liquid droplets from the vapor stream, and eliminate mechanical pulsations of the inner boundary of the vortex.

The technical result achieved by using the proposed design of a jet vortex deaerator is to reduce the residual oxygen content in deaerated water, reduce the size of the spray nozzle, and prevent water from being drawn into the vapor pipe. This technical result is achieved due to the following technical solutions.

1. The inner surface of the rotation chamber is profiled using plates welded into the chamber wall. This makes it possible to destroy the wall laminar boundary layer adjacent to the surface and increase the convective mass transfer in the flow core; therefore, the surface boundary layer is updated more intensively; therefore, the diffusion rate of oxygen through the surface boundary layer increases and the residual oxygen content decreases.

2. The vapor from the deaerator is removed from the water inlet side. For this, the swirl is made hollow with an axial channel to remove the vapor. The diameter of the axial channel is chosen so as to ensure the speed of the vapor in the narrowest section of the channel 30-50 m / s.

3. At the entrance to the channels, a receiving chamber is made for uniform distribution of the flow through the channels. The spiral channels on the outer surface of the swirl adjacent to the inner surface of the cylindrical body are cut so as to ensure a continuous narrowing of the channel section from entrance to exit.

4. At the exit from the spiral channels, a sudden expansion chamber is made. For this, the entrance to the vapor channel is made in the form of a bell and is shifted in depth of the rotation chamber relative to the output edges of the spiral channels by at least 1 diameter of the axial channel. In this case, an annular cavity is formed between the outer surface of the socket and the inner surface of the cylindrical body, tapering towards the exit. The exit cross section of the sudden expansion chamber is selected so as to provide a vapor velocity of 100-150 m / s at the camera exit.

The design of the jet vortex deaerator is disclosed in more detail in the drawings, which show:

figure 1 - deaerator in top view;

figure 2 - deaerator in a side view in section along the line aa in figure 1;

figure 3 - camera rotation in section along the line BB in figure 2.

Figure 2 shows that the jet vortex deaerator consists of a vertical cylindrical body 1 with a side pipe 2 and a flange 3 for connecting a pipe supplying heated water. In the upper part of the casing, a swirler 4 is coaxially mounted. On the outer surface of the swirl adjacent to the inner surface of the cylindrical casing, spiral channels 5 are cut with a continuously tapering section along the entire length of the channels. In the zone of location of the side pipe between the inner surface of the casing and the outer surface of the swirler, a prechamber 6 of annular cross section is formed, which is necessary for even distribution of water at the entrances to the spiral channels. For removal of the vapor, the swirl has an axial channel 7. The entrance to the vapor channel is made in the form of a socket 8, which is offset at least one diameter of the axial channel relative to the output edges of the spiral channels. In this case, between the outer surface of the socket 8 and the inner surface of the cylindrical body 1, a sudden expansion chamber 9 is formed, having an annular section and tapering in the direction of the axial movement of the flow. A cowl 10 is mounted coaxially in the lower part of the body, having a support, the outer surface of which, together with the inner surface of the cylindrical body, forms an annular diffuser 11. A cylindrical rotation chamber 12 is formed in the body between the lower edge of the swirler 4 and the upper edge of the cowl 10. As shown in FIG. 3 , the inner surface of the rotation chamber is profiled using plates 13 welded into the chamber wall. The cowling support is provided with openings 14 for discharging water. The housing has a lower flange 15 and an upper flange 16, to which pipes are connected to drain the deaerated water and to remove the vapor.

The device operates as follows.

Water heated to a temperature of 70-90 ° C, through the pipe 2 enters the prechamber 6 and is evenly distributed at the entrances to the spiral channels 5. Passing through continuously narrowing spiral channels, the water gradually accelerates and swirls around the axis of the deaerator. As the speed increases, the static pressure in the channels decreases. In the outlet section of the channels, water acquires maximum speed and minimum pressure. When leaving the canals, water enters the chamber of sudden expansion 9, where the flow instantly boils up. In this zone, the bulk of the vapor is extracted from the core of the water stream, which leads to a significant decrease in the partial pressure of oxygen in the gas phase and ensures the desorption of oxygen from the water stream to the vapor. The resulting vapor, as a lighter phase, is displaced closer to the axis under the action of centrifugal forces, and the water is pressed against the wall of the housing 1. However, the part of the fluid flow directly adjacent to the inner surface of the housing wall and forming a wall laminar boundary layer cannot boil, since due to the action of centrifugal forces, it is under a pressure higher than the saturated vapor pressure. In addition, the fluid constituting the parietal boundary layer moves laminarly, that is, does not mix with the core of the flow, therefore, the oxygen concentration in this layer remains equal to the initial concentration. In the rotation chamber 12, due to the profiled surface, the parietal laminar boundary layer is destroyed and intensive mixing of the flow is ensured. In this case, convective mass transfer in the flow core is enhanced and the rate of molecular diffusion of oxygen through the surface boundary layer to the vapor stream increases. The vapor released in the sudden expansion chamber 9 contains a large amount of water in a finely divided drip state. Due to the narrowing formed between the outer surface of the socket 8 and the inner surface of the housing 1, the gas phase is accelerated in the axial direction at the exit from the sudden expansion chamber 9. Moreover, at the entrance to the rotation chamber 12, the axial velocity of the vapor stream reaches 150 m / s and is directed along the surface of the flow of rotating water from the swirl to the fairing. Closer to the cowling, the vapor stream changes its direction and moves in the axial zone from the cowling to the swirl in the direction of entry into the vapor pipe. Since the density of the liquid phase is more than 1000 times higher than the density of the gas phase, when the direction of movement of the vapor stream is reversed under the influence of inertia, the droplets of liquid separate from the vapor stream. Therefore, the axial flow of the vapor is drained and contains significantly fewer drops of liquid. Thus, a gas-liquid vortex with a complex structure is formed in the rotation chamber. The peripheral parietal region of the vortex is occupied by a stream of water moving along the wall in a spiral in the direction from the swirl to the fairing. The central near-axis region is occupied by a drained vapor stream moving axially from the cowl 10 to the swirl 4. The boundary region between the liquid stream and the dried vapor stream is occupied by a two-phase droplet stream moving at a high speed along the phase boundary from the swirler 4 to the cowling 10. From the chamber rotation 12 deaerated water enters the neck of the annular diffuser 11, which provides a smooth expansion of the water flow, leading to a decrease in speed and the restoration of static pressure. Deaerated water leaves the deaerator body through openings in the support 14 and is discharged through a pipe connected to the lower flange 15. The vapor is discharged through a pipe connected to the upper flange 16.

The proposed design of a jet vortex deaerator provides high-speed deaeration of heated water from an initial content of corrosive gases of the order of 3000-5000 μg / L to a residual content of 15-50 μg / L.

Claims (2)

1. A jet vortex deaerator containing a vertically placed housing with a side nozzle for supplying heated water, a swirl with spiral channels, mounted coaxially in the upper part of the body, and a cowling, mounted coaxially in its lower part, characterized in that the spiral channels on the outer surface of the swirl a variable section, tapering from entrance to exit, and at the entrance to the housing between the outer surface of the swirl and the inner surface of the wall of the housing formed by the annular receiving chamber, while swirl l is hollow with an axial channel to remove the vapor, the entrance to which is in the form of a bell and is shifted downward relative to the output edges of the spiral channels so that the outer surface of the bell, together with the inner surface of the wall of the body, form an annular chamber of sudden expansion, tapering towards the cowl, and the cowl is fixed in the casing by means of a support with openings for discharging water so that an annular diffuser is formed between the outer surface of the fairing and the inner surface of the casing, while between the lower edge A swirl is taken and a cylindrical rotation chamber with a profiled inner surface is formed by the upper edge of the fairing. 2. The jet vortex deaerator according to claim 1, characterized in that the profiling of the inner surface of the cylindrical rotation chamber is made using plates welded into the chamber wall.

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