RU2294786C2 - Evaporation apparatus - Google Patents

Abstract

FIELD: chemical industry; atomic industry; milk industry; alimentary industry; pulp-and-paper industry; other industries; evaporation equipment.

SUBSTANCE: the invention is pertaining to the evaporation engineering and may be used in chemical, atomic, milk, alimentary, pulp-and-paper and other industries. The evaporation apparatus includes: the heating chamber containing the outer casing with the vertical heat-exchange pipes fixed in the tube plates; the separator; the upper solution chamber divided by the vertical partition into two isolated parts. In one of them - there are arranged: the device for inlet of the product for evaporation and the device for its uniform distribution in the form of the film into the heat-exchange pipes; and in the other part - there are arranged the device for withdrawal of the secondary vapor and the product into the separator, the connecting pipe for the vapor inlet, the connecting pipes for the condensate and the non-condensable gases feeding in and withdrawal. The heating chamber is divided by the vertical partition into two cavities isolated from each other with the equal number of the heat-exchange pipes. The connecting pipes for the vapor inlet are installed on the both parts of the heating chamber. The technical result of the invention is the increased reliability of operation of the evaporation apparatus due to elimination of the product sticking on the internal surface of the heat-exchange pipes, the decrease of the losses of the hydrodynamic head in the heat-exchange pipes.

EFFECT: the invention ensures the increased reliability of operation of the evaporation apparatus due to elimination of the product sticking on the internal surface of the heat-exchange pipes, the decrease of the losses of the hydrodynamic head in the heat-exchange pipes.

2 cl, 3 dwg

Description

The invention relates to evaporation technology and can be used in chemical, nuclear, dairy, food, pulp and paper and other industries.

Evaporation is one of the most common methods of initial dehydration or concentration of many products produced in the chemical, dairy and other industries.

Recently, vacuum-evaporation units equipped with film-type evaporators have been widely used both in foreign and domestic industries.

In these installations, the thickening is carried out in one pass of the product through the heat exchange tubes of the heating chambers of the evaporators, which significantly reduces the length of time the product stays in the apparatus (compared with circulating apparatuses) and at the same time allows you to control and regulate the duration of thermal exposure to the product. In this regard, vacuum evaporators of this type are most effective for thickening thermolabile solutions and are considered the most promising.

Film-type evaporators have high performance with relatively small volumes of the apparatus itself and the production area occupied by it, and are also characterized by the highest heat transfer intensity.

Distinguish evaporators with rising and falling film. In industrial practice, the most widely used are evaporators with a falling film, which consist of a heating chamber made in the form of a vertical shell-and-tube heat exchanger with steam heating of the separator, upper and lower solution chambers.

The operating experience of film-type evaporators has shown that having a number of undoubted advantages, which were mentioned above, these evaporators also have the following disadvantages:

1. Film-type evaporators installed on trailing steps in multi-body vacuum-evaporation plants operate at low values of the irrigation density of the heat exchange surface. This leads to exposure of the heat exchange tubes, burning of the product on the tubes and as a result to a decrease in the heat transfer rate, a decrease in the continuous operation time, an increase in the washing time and an increased consumption of detergents.

2. Evaporators of this type do not allow thickening of dairy products to high concentrations (more than 50-55%) and do not allow thickening of foaming products.

Thus, the improvement of evaporators in order to increase the efficiency of their work is relevant.

In modern evaporation technology for the dairy and food industries, these shortcomings are not eliminated. To prove this, consider the well-known modern technical solutions.

Known evaporation apparatus (Lipatov NN, Kharitonov VD. Powdered milk M .: Light and food industry, p.64-65) film type with a falling film. The apparatus consists of a heating chamber, a separator, lower and upper mortar chambers. The heating chamber includes a casing, heat exchange tubes, tube boards, as well as nozzles for the input of heating steam and the output of condensate and non-condensable gases. The upper solution chamber is equipped with devices for introducing the product to be evaporated and distributing it evenly through the heat exchange tubes. The lower solution chamber and the separator have nozzles for the output of one stripped off product. The separator is also equipped with a secondary steam outlet.

This evaporator has the following disadvantages:

1. Evaporators of this type, installed on the closing steps of multi-case vacuum-evaporator installations, operate at low values of the irrigation density of the heat exchange surface. This leads to the possibility of exposing the heat exchange tubes, burning the product on the tubes and as a result, reducing the heat transfer rate, reducing the continuous operation time, increasing the washing time and increased consumption of detergents.

2. The operating experience of evaporators of this type and studies have shown that it was not possible to obtain condensed milk products with an increased content of the mass fraction of solids of more than 50-55% on the apparatus.

Some disadvantages are eliminated in the known evaporator [Vacuum evaporator. Prospectus of the company "A-RV ANHUDRO" A / 3 K-41SOV, 1986] film type with a falling film. The apparatus consists of a heating chamber, a separator, upper and lower mortar chambers. The heating chamber includes a casing, heat exchange tubes, tube boards, as well as nozzles for the input of heating steam and the output of condensate and non-condensable gases. The upper solution chamber is equipped with a device for introducing the product to be evaporated, distributing it evenly over the heat exchange tubes and a vertical partition adjacent to the tube plate of the heating chamber.

This evaporator differs from the previously considered one in that it is equipped with vertical partitions installed in the upper and lower mortar chambers. Partitions divide the device into two parts along the course of the product and allow you to use it as a two-way. In this case, the evaporator must be equipped with a transfer pump. These design features allow, due to the double passage of the product through the heat exchange tubes, to increase the density of irrigation with the product of the heat exchange surface and to eliminate some of the disadvantages characteristic of the evaporators discussed above.

However, this evaporator has the following disadvantages:

1. The presence of an additional pump leads to an increase in energy consumption and insufficient reliability.

2. The operating experience of this type of apparatus and the studies conducted also showed that it is not possible to obtain condensed milk products with a high content of the mass fraction of solids on the apparatus, i.e. more than 50-55%.

The closest to the claimed technical essence and the achieved result is an evaporator [RF Patent No. 2039438, op. 1995.07.20.], Including a heating chamber with vertical heat exchanger tubes placed in it, fixed in tube boards, a separator, an upper solution chamber divided by a vertical partition installed in it into two insulated parts, in one of which are placed devices for introducing the product to be evaporated, and its uniform distribution in the form of a film through heat exchange tubes, and in another, a device for removing secondary steam and product into the separator, a fitting for introducing steam, a pipe for removing from the separator separated from arivaemogo product nozzle for discharging condensate and input and noncondensable gas, wherein the upper tube sheet is divided by a vertical partition into two portions with an equal number of heat exchange tubes arranged specularly relative to the vertical partition, and the lower ends of the tubes disposed specularly interconnected channels.

The separation of the upper solution chamber by the vertical partition installed in it into two insulated parts, in one of which there is a device for introducing an evaporated product and its uniform distribution in the form of a film through heat exchange tubes, and in another - a device for introducing steam and product into the separator, allowed to intensify heat transfer on the walls of the tubes, and therefore, increase the efficiency of the evaporator.

The constant irrigation of the tube walls created in the apparatus by the evaporated product reduces the degree of sticking of the product to the tubes, thereby increasing the reliability of the apparatus while reducing capital costs.

However, experimental studies on a vacuum evaporator equipped with an evaporator of this type showed that, despite a number of advantages, it also has drawbacks.

To illustrate, we present one of the technological modes of the apparatus (see table). The evaporator under study was equipped with heat exchange tubes with a diameter of 32 × 2 mm and a length of 7000 mm; studies were carried out with the condensation of whole milk and other products.

Studies have shown that in the evaporator there are significant losses of hydrodynamic pressure during the movement of a two-phase flow (evaporated solution and secondary steam) in heat transfer tubes. Moreover, the main part of the hydrodynamic pressure loss (about 90%) is observed in the second half of the heat exchange tubes, in which there is a two-phase flow from bottom to top. It is trivial that in this regard, there is a change in pressure along the length of the heat exchange tubes, while the rate of change of pressure increases as the film of solution moves through the heat exchange tubes. It is known that the boiling point of a solution is a function of pressure; this causes a change (decrease) in the boiling temperature as the solution moves through the tubes. Given that the heat exchange tubes are in the same heating chamber and the steam entering the chamber condenses on all the tubes at the same temperature, the useful temperature difference also changes along the length of the heat transfer tubes, reaching maximum values at the solution outlet from the tubes.

In this regard, the specific heat load also varies along the length of the tubes and reaches significant values in the second half of the heat exchange tubes. Moreover, as noted above, when the solution moves in heat transfer tubes, a boiling point decreases, which leads to self-evaporation of the solution and the formation of an additional amount of secondary steam.

It is clear that in the second half of the heat exchange tubes, the self-evaporation process occurs most intensively.

Thus, in the second half of the tubes, in which there is direct flow of the two-phase flow from the bottom up, conditions are created for intensive vaporization both due to heat transfer through the wall and due to self-evaporation of the solution. This leads to the formation of an additional amount of secondary vapor, an increase in its speed, and under certain conditions, a change in the structure of the two-phase flow occurs. Namely, if an annular structure is observed in the first half of the heat exchange tubes: separate direct-flow flow of the annular liquid layer and the vapor stream along the axis of the tube, then in the second half of the heat exchange tubes, drops drop off the surface of the solution, which are distributed in the vapor stream, as the velocity of the secondary steam increases. , and there is a transition from the ring structure of the flow to the dispersed-ring one. Subsequently, as the liquid film becomes thinner, due to intensive vaporization, the stability of the film flow decreases, and the dispersed-ring structure becomes dispersed, in which the continuous phase is vapor and the dispersed liquid phase is distributed in the continuous phase in the form of droplets. With a dispersed-ring and dispersed structure of a two-phase flow, conditions are created for exposing the inner surface of the tubes and burning the product on this surface.

The experiments also showed that a decrease in the useful temperature difference in the heating chamber will not solve the above problems, since in this case there was a “choking” (violation of the ring structure) of the two-phase flow in the lower parts of the heat transfer tubes and its unstable operation.

The basis of the invention is the task of improving the reliability of the evaporator by eliminating product burning on the inner surface of the heat exchanger tubes, as well as reducing the loss of hydrodynamic pressure in the heat exchanger tubes of the evaporator.

The problem is solved in that in the evaporator, including a heating chamber, containing an outer casing with vertical heat exchanger tubes placed in it, fixed in tube boards, a separator, an upper solution chamber divided by a vertical partition installed in it into two insulated parts, in one of which contains devices for introducing the evaporated product and its uniform distribution in the form of a film through heat exchange tubes, and in another, a device for introducing secondary steam and product into sep an ator, a nozzle for introducing steam, a nozzle for discharging the separated evaporated product from the separator, a nozzle for discharging and introducing condensate and non-condensable gases, while the upper tube plate is also divided by a vertical partition into two parts with an equal number of heat exchange tubes, mirror-mounted relative to the vertical partition, and the lower ends of the mirrored tubes are interconnected by channels, according to the invention, the heating chamber is divided by a vertical partition into two isolated rods with an equal number of heat transfer tubes fixed in the upper and lower tube boards, respectively, and on the inner surface of the casing, combined with the vertical partition of the upper solution chamber and located with it in the same plane, the fitting for the introduction of steam, for the removal of condensate and non-condensable gases are installed on one part of the heating chamber and are connected with the corresponding cavity of the heating chamber, while the evaporator is equipped with additional fittings for introducing steam, for draining condensate and non-condensing gases respectively mounted on another part of the heating chamber and connected to its corresponding cavity.

A device for introducing steam and product into the separator can be made in the form of separate nozzles, each of which is fixed at one end to the upper end of the corresponding heat transfer tube, and the other is tangentially connected to the separator.

The supply of the heating chamber with a vertical partition dividing it into two equal cavities, as well as the supply of the heating chamber with additional fittings for introducing steam, condensate and non-condensable gases, made it possible to feed part of the heating chamber into the cavity, in which two-phase flow moves in the heat exchange tubes from the bottom up heating steam having lower parameters in temperature and pressure. Thus, the necessary thermal conditions (useful temperature difference and heat flux) are created under which there is no transition from the ring structure of a two-phase flow to a dispersed-ring or dispersed one. In this regard, conditions are not created in the evaporator for exposing the inner surface of the heat exchange tubes and for burning the product on this surface.

In addition, a decrease in the heat load in the second part of the heating chamber allows lower secondary steam velocities to be present in the heat exchange tubes of this part of the chamber, which means that the hydrodynamic pressure losses in these tubes and the evaporator as a whole can be reduced.

Figure 1 presents a General view of the inventive evaporator in section;

figure 2 is a section of the upper solution chamber in the context;

figure 3 is a General view of the inventive evaporator with a device for introducing steam and product into the separator in the form of separate pipes.

The evaporator consists of a heating chamber 1, a separator 2, an upper solution chamber 3. The heating chamber 1 contains an outer casing 4, heat transfer tubes 5 fixed in tube boards 6 and 7. The upper solution chamber 3 is divided into two insulated vertical baffle 8 installed in it between each other.

One of the parts of the upper solution chamber 3 is made in the form of a chamber 9, in which there is a device 10 for introducing an evaporated product and spraying it in a chamber 9, as well as a device 11 for uniformly distributing a solution in the form of a film through heat transfer tubes 5.

Another part of the upper solution chamber 3 is made in the form of a device 12 for introducing the evaporated product and the secondary steam into the separator 2.

The upper tube plate 6 is also divided by a vertical partition 8 into two parts with an equal number of heat transfer tubes 5, which are mirrored relative to the vertical partition 8.

The heating chamber 1 is divided by a vertical partition 13 into two separate cavities 14 and 15 with an equal number of heat transfer tubes 5, mounted in the upper and lower tube boards 6 and 7, respectively, and on the inner surface of the casing 4 is aligned with the vertical partition 8 and is located with it in one plane.

The evaporator contains a fitting 16 and 17 for supplying steam to the heating chamber 1, a fitting 18 and 19 for draining condensate and a fitting 20 and 21 for removing non-condensable gases. In this case, the fittings 16, 18 and 20 are installed on one part of the heating chamber 1 and are connected with the cavity 14, and the fittings 17, 19 and 21 are installed on the other part of the heating chamber 1 and are connected with the cavity 15.

The separator 2 is equipped with a fitting 22 for outputting one stripped off product and a device 23 for removing secondary steam.

The lower ends of the mirrored tubes 5 are interconnected by channels 24.

The device 10 consists of a fitting 25 and a nozzle 26. The device 11 consists of an upper switchgear 27 and a lower switchgear 28.

The devices 27 and 28 are made in the form of flat plates having holes 29 and 30, respectively.

The device 12 for introducing steam and product into the separator can be made (see figure 3) in the form of separate nozzles 12, each of which is fixed at one end to the upper end of the corresponding heat transfer tube 5 (second half of the tube bundle), and the other tangentially connected to separator 2.

The evaporator operates as follows. The initial product, for example, a wash water solution, is sent for evaporation to the evaporator and is continuously fed through the nozzle 25 to the nozzle 26 of the device 10 located in the upper part of the chamber 9. Using the nozzle 26, the solution is sprayed in the chamber 9 and enters the upper distribution device 27, in which there are openings 29 evenly distributed over the entire surface of the plates. The product flows through the openings 29 to the lower distribution device 28 and is evenly distributed on the surface of its plates. The product through openings 30 located coaxially with the first half of the heat exchange tubes 5 of the heating chamber 1 is discharged into these tubes 5, in which it is evenly distributed along the perimeter and flows down in the form of a film.

At the same time, through the fitting 17, heating steam is supplied into the cavity 15 of the heating chamber 1. Steam, moving from top to bottom and giving off heat to the surface of the heat exchange tubes 5, condenses. Condensate on the outer surface of the tubes 5 flows down, collects on the lower tube plate 7 and is removed from the cavity 15 of the heating chamber 1 through the fitting 19.

Non-condensable gases are removed from the cavity 15 of the heating chamber 1 through the fitting 21.

The solution, flowing down in the form of a film on the inner surface of the tubes 5 due to the heat given off by the steam, boils and concentrates. The secondary steam generated during the boiling of the foaming solution, together with the solution moves down. The evaporated solution together with the secondary steam leaves the heat exchange tubes 5, passes through the arcuate channels 24, changes the direction of movement and enters the lower ends of the second half of the heat exchange tubes 5, when entering the lower ends of the tubes 5, the partially condensed solution due to the secondary steam moving upward with high speed, is evenly distributed around the perimeter of the heat transfer tubes 5 and rises in the form of a film.

At the same time, through the fitting 16, heating steam is supplied to the cavity 14 of the heating chamber 1, having lower parameters in pressure and temperature compared to the steam entering the cavity 15. The steam, moving from top to bottom and giving off heat to the surface of the heat exchange tubes 5, condenses. Condensate on the outer surface of the tubes 5 flows down, collects on the lower tube plate 7 and is removed from the heating chamber through the fitting 18.

Due to the favorable hydrodynamic conditions (high speed of the vapor and the film of the solution), the solution boils intensively and further secondary steam forms, which in turn further contributes to an increase in the speed of the two-phase flow and the intensification of heat transfer.

When exiting the heat exchange tubes 5, a two-phase flow (a mixture of secondary steam and one stripped off solution) through a device 12 connected tangentially to the separator 2 enters directly into the separator 2. In the separator 2, due to centrifugal forces, the secondary vapor and one stripped off are separated. One stripped off solution is removed through the nozzle 22, and the secondary steam through the device 23.

One stripped off product may be directed to further thickening or to drying.

Claims (2)

1. Evaporator, including a heating chamber, containing an outer casing with vertical heat exchange tubes placed in it, fixed in tube boards, a separator, an upper solution chamber divided by a vertical partition installed in it into two insulated parts, in one of which there are input devices the product to be evaporated and its uniform distribution in the form of a film through heat exchange tubes, and in the other, a device for introducing secondary steam and product into the separator, a fitting for introducing steam, a pipe for I withdrawal from the separator of the separated evaporated product, the nozzle for the removal of condensate and non-condensable gases, while the upper tube plate is divided by a vertical partition into two parts with an equal number of heat transfer tubes, mirror-mounted relative to the vertical partition, and the lower ends of the mirrored tubes are connected by channels, characterized in that the heating chamber is divided by a vertical partition into two cavities isolated between each other with an equal number of heat transfer tubes, located in the upper and lower tube boards, respectively, and on the inner surface of the casing, combined with the vertical partition of the upper solution chamber and located with it in the same plane, the steam inlet fitting, for the removal of condensate and non-condensable gases, are installed on one part of the heating chamber and are connected with the corresponding cavity of the heating chamber, while the evaporator is equipped with additional fittings for introducing steam, for the removal of condensate and non-condensable gases, installed respectively on the other part of cutting chamber and associated with its corresponding cavity. 2. The evaporator apparatus according to claim 1, characterized in that the device for introducing secondary steam and product into the separator is made in the form of separate nozzles, each of which is fixed at one end to the upper end of the corresponding heat exchange tube, and the other tangentially connected to the separator.

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