JPH01266489A - Liquid film descending type heat exchanger - Google Patents

Abstract

PURPOSE:To provide heat medium in the lengthwisely upper and lower parts of a heat transfer tube wit different temperatures and improve beat exchanging performance, by a method wherein the heat medium is mixed with inert gas and the mixture is made to flow along the outer surface of the heat transfer from the part toward the upper part of the tube. CONSTITUTION:The mixed gas of water vapor and inert gas is used as heat medium. The heat medium flows into a cylinder 1 through a heat medium inlet nozzle 5 provided at the lower part of the cylinder 1, flows along the outer surface of a heat transfer tube 4 from the lower part of the cylinder 1 toward the upper part of the same and flows out of the cylinder 1 through a heat medium outlet nozzle 8 provided at the upper part of the cylinder 1. Condensed water flows out through a condensed water outlet nozzle 9 provided at the lower part of the heat medium inlet nozzle 5. The partial pressure of H2O in the heat medium on the outer surface of the heat transfer tube 4 is made higher at the lower part of the beat transfer tube 4 and is made lower at the upper part of the same. Plenty of water vapor remains yet in the fluid of the beat medium flowing out of the heat medium outlet nozzle 8. The pressure of the heat medium which flowed, out is increased and the heat medium is supplied again into the cylinder 1 through the heat medium inlet nozzle 5. Even when the total pressure is the same, the condensting temperature of water vapor is changed by the mixing ratio of the water vapor and the inert gas.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a descending liquid film heat exchanger used for concentrating solutions and the like.

[Conventional technology]

The conventional technology will be explained with reference to FIGS. 2 to 4. Second
The figure is a vertical cross-sectional view of a conventional descending liquid film heat exchanger - Figure 3 is an enlarged view of the part ■ in Figure 2 to explain its function, and Figure 4 shows the arrangement of peripheral equipment. It is a system diagram.

First, in Figure 2, 01 is the body, 02 is the upper tube plate, 03
is the lower tube plate. , 04 are a plurality of vertical heat exchanger tubes, which communicate the chamber above the upper tube sheet 02 and the chamber below the lower tube sheet 03. 05 is an inlet nozzle for water vapor as a heating medium, and 06 is an outlet nozzle for a brackish water mixed fluid of condensed water and uncondensed water vapor. 012 is the upper mirror, 013 is the heated solution inlet nozzle, and 014 is the heated solution inlet nozzle 013.
This is a solvent vapor outlet nozzle through which gas (resolved medium vapor) generated by heating the solution flowing in from the solvent vapor outlet nozzle flows out. 0
15 is a lower mirror, and 016 is an exit nozzle for liquid after gas has escaped due to heating (liquid<m-line solution). 07 is a plurality of baffle plates.

Next, in FIG. 3, the solution flowing from the heated solution inlet nozzle 013 spreads horizontally on the upper surface of the upper tube plate 02, and when the liquid level exceeds the height of the upper edge 04a of the heat transfer tube 04, it flows into the tube. Inflow. A liquid film is formed on the inner surface of the heat transfer tube 04 and flows downward due to one gravity. On the other hand, heat exchanger tube 04
Water vapor exists as a heating medium on the outer surface of the pipe, and the heat held by this heating medium (mainly the latent heat of condensation of water vapor) is given to the liquid film inside the pipe via the pipe wall, and the liquid film transfers the gas to the liquid film. (For example, water vapor in the case of an aqueous solution) is evaporated and released. This gas exits from the solvent vapor outlet nozzle 014. Heat exchanger tube 04
The liquid film inside moves from the top to the bottom and flows out from the concentrated solution outlet nozzle 016, but the composition and concentration of the liquid changes in the upper and lower parts of the υ tube due to the release of solvent vapor. In Figure 4, the heating medium is discharged from the heating medium inlet nozzle 05.
Although saturated steam is supplied, the pressure or temperature inside the shell 01 varies depending on the conditions of the liquid film. Brackish water mixed flow suspension Ronoznu 06
A brackish water mixture of condensed water and uncondensed steam flowing out from the brackish water separator 021 separates the condensed water, and the uncondensed steam is disposed of or diverted to other uses.

The pressure loss when water vapor moves inside the shell 01 to the shell 06 is extremely small, and the shell meat can be considered to have substantially equal pressure. In this way, heat is applied to the outer surface of the pipe 04 by the heat of condensation of the saturated steam at one constant pressure, and the steam temperature is substantially the same and the heat transfer coefficient is also large. In other words, the heat supply conditions are the same from the top to the bottom of the heat exchanger tube.

On the other hand, the conditions of the liquid film inside the heat transfer tube 04 differ between the upper and lower portions of the tube and are not the same. Solvent vapor in the tube (e.g. water vapor)
Since the pressure in the upper and lower parts of the tube is the same, e, the evaporation of water from the membrane (increase in solute concentration) causes an increase in the saturation temperature (increase in the boiling point), and therefore the evaporation of gas from the peritoneum. The velocity is large at the top of tube 04.

It gets smaller at the bottom.

The pressure (temperature) of the heat medium steam is determined by II condensation solution outlet nozzle 01.
It is determined from the condition of the product to be taken out. Therefore, the liquid film rises violently in the upper part of the heat exchanger tube 04,
Maintaining a liquid film flow bottom layer may become impossible. That is, when the liquid film peels off from the inner surface of the tube at the upper part of the heat transfer tube 04, most of the peeling liquid falls down the center of the tube, leaving only a small amount of peritoneum at the bottom of the tube.

Or it will all disappear. This is a major factor in the deterioration of the performance of this food device.

(2) While flowing inside the shell 01, the pressure of the water vapor decreases, albeit slightly. Therefore, the pressure of the steam separated by the steam separator 021 is slightly lower than the pressure of the steam at the heat medium inlet nozzle 05.

The two cannot be mixed. In other words, the latent heat of condensation of uncondensed water vapor cannot be effectively utilized.

[Means to solve the problem]

As a means to solve the above-mentioned problems, the present invention evaporates the solvent of the solution flowing down as a liquid film on the inner surfaces of the plurality of vertical heat transfer tubes by heating the outer surfaces of the plurality of vertical heat transfer tubes with the latent heat of condensation of the heat medium vapor. In things.

In addition to mixing an inert gas with the heat medium vapor.

The present invention proposes a descending liquid film heat exchanger characterized in that the mixed gas is caused to flow from bottom to top along the outer surface of the heat transfer tube.

[Effect]

Since the present invention is configured as described above, it is possible to change the vapor partial pressure (that is, temperature) of the heat medium on the outer surface of the heat exchanger tube in the vertical direction of the tube. In other words, the heating medium vapor partial pressure is reduced (lower heating medium temperature) in the upper part where the solute concentration of the solution in the tube is small.
, the heat medium vapor partial pressure can be increased (heat medium temperature raised) in the lower part where the solute concentration is high.

Furthermore, in the present invention, uncondensed water vapor can be reused.

〔Example〕

An embodiment of the present invention is shown in FIG. In this figure, 1
2 is an upper tube sheet, 3 is a lower tube sheet, and 4 is a plurality of heat exchanger tubes. 5 is the heat medium inlet nozzle.

It is provided at the bottom of the body 1. 8 is a heat medium outlet nozzle;
It is provided on the upper part of the body 1. 9 is a condensed water outlet nozzle, which is also located below the heating medium inlet nozzle 5.

- located directly above the lower tube sheet 3; 12 is an upper mirror, 13 is a heated solution inlet nozzle, 14 is a solvent vapor outlet nozzle, 15 is a lower mirror, and 16 is a concentrated solution outlet nozzle. Also, 21 is a condensed water receiving tank.

22 is a steam ejector, and 23 is a mixer.

In this embodiment, a mixed gas of water vapor and inert gas is used as the heating medium. As the inert gas, nitrogen gas, argon, methane, etc. can be used, as it is necessary that it not react with water vapor and not corrode the constituent materials of the equipment.

The heat medium flows in from a heat medium inlet nozzle 5 provided at the bottom of the shell 1, flows from bottom to top along the outer surface of the heat transfer tube 4, and flows through a heat medium outlet nozzle provided at the top of the shell 1. It flows out from 8. The condensed water flows out from the heat medium inlet nozzle 5 as well as from the condensed water outlet nozzle 9 located further below.

The heat medium flowing out from the heat medium outlet nozzle 8 is supplied to the steam ejector 22, is pressurized, and is again fed into the shell 1 from the heat medium inlet nozzle 5. In this case, ejector 2
2 is supplied with working steam.

23 is a mixer. Add inert gas if necessary. Further, water vapor can be additionally added to adjust the water vapor level.

In this embodiment, assuming that a caustic soda aqueous solution is supplied from the heated solution inlet nozzle 13 and concentrated, the boiling temperature at an H20 partial pressure of 1 atm changes with the concentration. This is shown in Table 1.

For example, a 18-inch aqueous solution of NaOH is heated to evaporate water and concentrate to 40-inch solution. In this case, if the heating medium is to be supplied using the latent heat of condensation of water vapor in the heat medium, which has a calorific value equivalent to the latent heat of vaporization of water in the solution, it is preferable to vary the conditions of the heat medium in contact with the outer surface of the heat transfer tube 4 in the tube length direction. .

This example uses the phenomenon that the condensation temperature of water vapor changes depending on the mixing ratio of water vapor and inert gas, even if the total pressure is the same, as shown in Table 2. be.

The gas mixtures in Table 2 are as follows: C1aseA1 in Table 2;
The conditions are such that the N2 ratio is large. This mixed gas comes into contact with the outer surface of the heat exchanger tube 4, and gives heat to the liquid inside the heat exchanger tube 4 due to the latent heat of condensation of the water vapor in the mixed gas, and the mixed gas itself converts into H2O by the amount that the water vapor it possesses is condensed and liquefied. Pressure decreases. While this phenomenon continues, the mixed gas moves upward and flows out from the heat medium outlet nozzle 8. Of course.

The condensed and liquefied water flows downward along the outer surface of the heat transfer tube 4 and is taken out from the condensed water outlet nozzle 6.

In this way, the temperature condition (
820 partial pressure) is increased at the bottom of the heat exchanger tube 4.

It can be made smaller at the top.

When water vapor is mixed with an inert gas such as nitrogen and used as a heat transfer fluid, a film on the outer surface of the heat transfer tube 4 is formed as the water vapor condenses and liquefies, resulting in a partial pressure decrease of υ1 (20). 4 The 820 partial pressure at the outer surface is controlled by the ratio of the diffusion supply amount to the condensation and liquefaction amount. This diffusion supply amount is determined by the fluid flow rate (
The total pressure of the heat transfer fluid in this example, the flow f (flow velocity), and the upper 20/N2 ratio of the inlet and outlet are , determined on a case-by-case basis depending on the requirements.

In other words, in this embodiment, the entire amount of heat held by the water vapor in the heat medium fluid that has flowed in from the heat medium inlet nozzle 5 is not supplied to the liquid in the heat transfer tube 4 .

A large amount of water vapor still remains in the heat medium fluid flowing out from the heat medium outlet nozzle 8.

In this embodiment, in order to reduce heat loss by reusing the water vapor in the heat medium flowing out from the heat medium outlet nozzle 8, water vapor is further added to the heat medium and the water vapor is caused to flow in from the heat medium inlet nozzle 5 again. That is, the steam ejector 22 is used as a means for boosting the pressure.

The steam used to drive the ejector is also effectively used as a heat medium. Additionally, water vapor is added to the mixer 23 in order to adjust the water vapor partial pressure of the heat medium fluid flowing in from the heat medium inlet nozzle 5 . In the mixer 23, liquid water can also be injected (sprayed) in order to adjust the degree of dryness.

Although the above embodiment describes the case of concentrating a caustic soda aqueous solution, the present invention can also be applied to the use of removing substances other than water from the liquid inside the heat transfer tube 4.

〔Effect of the invention〕

In the present invention, by mixing an inert gas with the heating medium and flowing it from bottom to top along the outer surface of the heat transfer tube, the temperature of the heating medium is changed in the longitudinal direction of the heat transfer tube, that is, at the top and bottom. It is possible to improve heat exchange performance. In the case of evaporative concentration of a liquid with a large increase in boiling point,
The effect is particularly strong.

[Brief explanation of the drawing]

Figure g1 is a diagram showing an embodiment of the present invention, Figure 2 is a vertical cross-sectional view of an example of a conventional liquid film descending heat exchanger, and Figure 3 is a diagram showing the example of Figure 2.
FIG. 4, which is an enlarged view of the section, is a system diagram showing the arrangement of peripheral devices. 01.1...Body 02.2...Upper tube plate 03.3...Lower tube plate 04.4...Heat transfer tube 05.5...Heat medium inlet nozzle 06...Brackish water mixed fluid Outlet nozzle 07...Living plate 8...Heat medium outlet nozzle 9...Condensed water outlet nozzle 012.12...Upper mirror 013.13...Heated solution inlet nozzle 014.14
... Solvent vapor outlet nozzle 015.15 ... Lower mirror 016.6 ... Concentrated solution outlet nozzle 021 ... Brackish water separator 21 ... Condensed water receiving tank 22 ... Steam ejector 23 ... Mixing Representative Patent Attorney Akira Sakama and two others Figure 2

Claims (1)

[Claims] In a device that evaporates the solvent of the solution flowing down as a liquid film on the inner surface of the heat transfer tube by heating the outer surface of a plurality of vertical heat transfer tubes with the latent heat of condensation of the heat transfer tube, an inert gas is added to the heat transfer tube. A descending liquid film heat exchanger characterized in that the mixed gas is mixed and is caused to flow from bottom to top along the outer surface of the heat transfer tube.