JPH0147715B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an immersion tube-type direct-fired high-temperature regenerator, and particularly to an immersion-tube-type direct-fired high-temperature regenerator (hereinafter referred to as a regenerator) used in an absorption refrigeration cycle.

This type of regenerator heats and concentrates a dilute lithium bromide (hereinafter referred to as LiBr) solution that has absorbed refrigerant vapor generated in the evaporator of an absorption refrigeration cycle.
This is to obtain concentrated LiBr liquid and refrigerant vapor.

1 and 2 are diagrams showing the structure of a conventional regenerator. In the figure, 10 is a regenerator main body, 12 is a furnace tube that defines the combustion chamber 14, 16 is a burner, 18 and 20 are solution tubes arranged almost vertically in the combustion chamber 14, and 22 is a furnace tube 12. 24 is a chimney for guiding high-temperature combustion gas attached to the side wall of the chimney. Further, the solution tube 20 is arranged downstream of the solution tube 18 in the gas flow direction,
This solution tube 20 is provided with fins 21 for heat transfer.

High-temperature combustion gas 26 obtained by burning gas, kerosene, etc. in the burner 16 travels straight horizontally within the furnace tube 12 and flows around the smooth solution tube 18 and the finned solution tube 20 for heat exchange. Afterwards, it is discharged from the chimney 24. On the other hand, the LiBr solution 28 is heated and boiled in the furnace tube 12 and the solution tubes 18 and 20 to be concentrated.

A regenerator with this type of structure has the advantage of being small and compact because it is a direct-fired type, but on the other hand, because the high-temperature combustion gas is sent directly into the regenerator,
It has the disadvantage that uniform heating is difficult and local temperature increases are likely to occur. This local increase in temperature is a very important problem for regenerators of absorption refrigeration cycles that use LiBr liquid, which is highly corrosive, as the absorption liquid for the following reasons.

In other words, in the regenerator, the liquid temperature is generally kept at about 160℃.
heat to a LiBr concentration of 60-65%.
Concentrate the LiBr solution. Figure 3 is a graph showing the relationship between the concentration of LiBr solution and the corrosion rate of metal;
% LiBr solution is in a static state, and c indicates a case where a LiBr solution with a LiBr concentration of 65% is in a fluid state. From this figure, it is clear that the corrosion rate of a LiBr solution with a LiBr concentration of 60 to 65% increases rapidly when the temperature reaches 165 to 175°C, especially in a stationary state. Therefore, in a regenerator where the LiBr concentration is 60 to 65%, significant corrosion will occur in areas where the liquid temperature locally becomes 160° C. or higher or where the liquid flow stagnates.

For the above reasons, in the regenerator, avoid local increases in liquid temperature, maintain a uniform temperature and keep it below a certain temperature (e.g. 160℃), and prevent local concentration of liquid due to the occurrence of liquid stagnation areas. Therefore, by uniformly flowing the liquid, local corrosion can be prevented, and the limit temperature and concentration of the regenerator can be raised, so the thermal efficiency of the refrigeration cycle can also be improved.

Therefore, the inventors investigated various corrosion conditions on the inner walls of solution tubes in actual regenerators, and found that in all models, corrosion was greater in the lower part of the pipe than in the upper part of the pipe. I found that some places were particularly intense.

Based on this fact, we measured the wall temperature distribution inside the tube using a single tube heating device in order to understand the boiling flow situation of the LiBr liquid inside the tube. The results are shown in FIG. Figure 4b shows the tube inner wall temperature T _W in the tube axis direction x using the heat load q (kcal/m ² h) as a parameter.
Figure _4a shows the boiling flow situation of the _LiBr liquid in the tube estimated from this temperature distribution. In the figure, F represents a boiling region, and M represents a non-boiling region.

The temperature distribution (Fig. 4b) shows that from the bottom of the tube
It was discovered that there is a maximum value (max) of wall temperature at mm, and although the maximum value increases with heat load, its position does not change.

This is a unique phenomenon that occurs when a liquid with high specific gravity boils under low pressure.As the liquid depth (depth from the free interface of the liquid) increases, the atmospheric pressure is low and the liquid specific gravity increases. As a result, the liquid pressure can no longer be ignored, and the saturation temperature (the temperature at which liquid can boil at that liquid pressure) increases.Even if the liquid temperature is the same, even if the liquid boils at the top of the tube (small liquid depth), it will boil at the bottom of the tube (large liquid depth). This is presumed to be due to the phenomenon that boiling does not occur.

Therefore, the LiBr liquid rises inside the tube while remaining unboiled in the lower part of the tube, and boiling starts from the liquid near the inner wall surface of the tube when it reaches the saturation temperature, and the entire liquid gradually reaches the saturation temperature, resulting in uniform saturated boiling.

As the LiBr liquid rises inside the tube, an unboiled zone occurs at the bottom of the tube, so there is no agitation of the liquid due to bubbles generated at the bottom of the tube, and the wall temperature rapidly increases due to poor heat transfer from the tube wall. rise to As the liquid rises, boiling begins near the wall surface, and the bubbles generated stir the liquid and promote heat transfer, so the wall temperature gradually decreases. Thereby,
In the temperature distribution, the maximum value of wall temperature occurs at the position where boiling starts near the wall surface.

Also, the reason why the maximum position does not change due to heat load is that liquid flow in the pipe occurs due to the bubble pump action of generated steam bubbles, and as the heat load increases, the amount of liquid transported also increases. It is presumed that this is because the overall temperature rise is almost the same.

From the above, it is clear that LiBr with high specific gravity is used as a regenerator.
When liquid is boiled in a tube under low pressure and the liquid is made to flow by the bubbles generated, the liquid flow in the tube is caused by an unboiled (convection) zone at the bottom of the tube, so Since the maximum value of the pipe inner wall temperature occurs in this zone, there is no liquid stirring by bubbles in this zone, so it was discovered that at the same time as a local rise in liquid temperature occurs, liquid stagnation occurs and corrosion is likely to occur.

An object of the present invention is to provide a new direct-fired high-temperature regenerator that eliminates the corrosion caused by localized temperature increases and poor liquid flow that occur specifically in the above-described conventional direct-fired high-temperature regenerators.

In order to achieve this object, the first invention introduces gas at a lower temperature than the combustion gas into the combustion chamber around the lower part of the solution tube to reduce the temperature rise ΔT at the lower part of the solution tube. .

That is, △T is generally expressed by the following formula, △T=Q/(h・A)......(1) △T: Temperature rise (℃) Q: Heat transfer amount (kcal/
h) h: Heat transfer coefficient (kcal/m ² h℃) A: Heat transfer area (m ² ) This first invention lowers the combustion gas temperature only at the lower part of the tube, lowers Q, and reduces ΔT. This is how it was done.

In addition, the second invention provides bubble nucleation means on the inner circumferential surface of the lower part of the solution tube to promote boiling in the lower part of the solution tube, and the development of a temperature boundary layer is promoted by the stirring action of the generated water vapor bubbles. Prevents and heat transfer coefficient (above
By increasing h) in equation (1), the temperature rise (same, △
T) is made small.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 5 is a configuration diagram of an embodiment of the first invention.
In this embodiment, the hottest combustion gas 26 passes;
The lower part of the tube at the front of the tube group (A
A part of the air 50 supplied to the burner 16 is introduced from the part) to mix and cool the high-temperature combustion gas 26 to provide a temperature distribution in the axial direction of the solution tube 18,
By lowering the gas temperature at the bottom of the pipe, the amount of heat transmitted there Q
It is designed to locally lower the

FIG. 6 is a diagram showing an example of the distribution of the gas temperature T and the amount of heat transfer Q in the tube axis direction in the embodiment shown in FIG. 5, where the solid line relates to the embodiment and the broken line relates to the conventional example. As shown in FIG. 6, in this example, T and Q are lowered at the lower part of the solution tube.

FIGS. 7 and 8 are configuration diagrams of another embodiment of the first invention, in which comparatively low-temperature combustion exhaust gas 60 at the outlet of the tube group is employed as the gas used for mixed cooling. In this case, by passing the combustion exhaust gas 60 through the solution, the gas is cooled to a lower temperature by the solution, increasing the mixing cooling effect of the high-temperature combustion gas, and using the thermal energy of the combustion exhaust gas as a source for preheating the solution. There are some effects that can be achieved.

In addition, the introduction position of the cooling air is the place where the temperature of the combustion gas is high or the amount of heat transfer Q is the largest. Therefore, as shown in FIG.
It is effective to introduce the solution tube at a position (section B) where the amount of heat Q rapidly increases as the solution tube changes from the smooth tube 18 to the finned tube 20. FIG. 9 is a diagram showing an example of the distribution of the gas temperature T and the amount of heat transfer Q in the gas flow direction in the embodiment shown in FIG.

Next, with reference to FIGS. 10 to 14, the second
An embodiment of the invention will be described.

In the second invention, as shown in FIG. 10, a bubble nucleation means is provided on the inner peripheral surface of the lower part 100 of the solution tube 18 or 20.
Various types of bubble nucleation means can be employed.

FIG. 11 shows that metal is sintered to form a metal sintered layer 102 on the inner peripheral surface of the lower part 100 of the solution tube, and the voids in the layer are used to promote the generation of nuclei of bubbles 200. This is how it was done. Also the first
In FIG. 2, a fine space 104 is formed on the inner peripheral surface of the lower part 100 of the solution tube by machining or the like. Furthermore, FIG. 13 shows the solution tube lower part 100
A fine vertical groove 106 is formed on the inner circumferential surface of the groove. Further, in FIG. 14, a Teflon film 108 is pasted on the inner circumferential surface of the lower part of the solution tube 100 to make the inner circumferential surface of the tube difficult to wet with liquid and to promote the generation of nuclei.

In the embodiments shown in FIGS. 10 to 14, the boiling of the solution in the lower part of the solution tube 100 has the effect of making the heat transfer coefficient uniform and increasing, so that, for example, the thermal efficiency is improved. Also, the heat transfer area can be reduced, and the device can also be made smaller.

Furthermore, various experiments have shown that the unboiling zone is approximately 1/3 of the pipe length from the lower part of the pipe, even if the pipe diameter and pipe length are changed.
It has been confirmed that it occurs in
In particular, it is effective to make only that part a boiling promoting structure.

As described above, according to the present invention, local overheating in the lower part of the solution tube is eliminated and corrosion is prevented. Furthermore, the limit temperature and concentration of the regenerator can be increased, and the thermal efficiency of the refrigeration cycle can also be improved.

Note that the present invention is not limited to high-temperature regenerators, but also has similar effects when used in general evaporators having a vertical tube type evaporation structure under reduced pressure (vacuum) or using high specific gravity liquids. .

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional view showing the configuration of a conventional regenerator, Fig. 2 is a sectional view along the line shown in Fig. 1, and Fig. 3 is a sectional view along the line shown in Fig. 1.
The figure is a diagram showing the corrosivity of LiBr solution, Figure 4a
is a diagram showing the boiling flow situation of LiBr liquid in the tube, Figure 4b is a diagram showing the distribution of (T _W − T _L ) in the tube axis direction,
FIG. 5 is a longitudinal sectional view showing the configuration of the regenerator according to the embodiment of the first invention, FIG. 6 is a diagram showing the distribution of T and Q in the regenerator of FIG. 5, and FIGS.
9 is a longitudinal sectional view showing the configuration of a regenerator according to another embodiment of the first invention, FIG. 9 is a diagram showing the distribution of T and Q in the embodiment of FIG. 8, and FIG. 10 is a diagram showing the distribution of T and Q in the embodiment of FIG.
FIGS. 11 to 14 are cross-sectional views showing the solution pipe structure of the regenerator according to the second embodiment of the invention. 10... Regenerator main body, 12... Furnace tube, 14...
Combustion chamber, 18, 20...solution tube, 28...LiBr
Solution, 100... Lower part of solution tube, 102... Metal sintered layer, 108... Teflon membrane.

Claims (1)

[Claims] 1. Immersion tube type direct firing high temperature in which a large number of solution tubes are arranged almost vertically in a combustion chamber, and the solution rising inside the solution tubes is heated by the combustion gas flowing outside the solution tubes. An immersion tube type direct-fired high-temperature regenerator characterized in that the regenerator is configured to introduce gas at a lower temperature than the combustion gas into the combustion chamber around the lower part of the solution tube to prevent the lower part of the solution tube from overheating. vessel. 2. The immersion tube type direct-fired high-temperature regenerator according to claim 1, wherein the gas having a lower temperature than the combustion gas is air. 3. The immersion tube type direct-fired high-temperature regenerator according to claim 1, wherein the gas having a lower temperature than the combustion gas is the combustion exhaust gas discharged from the combustion chamber. 4 The solution tubes on the downstream side in the gas flow direction are provided with fins for heat transfer, and the gas at a lower temperature than the combustion gas is transferred to the upstream portion of any solution tube and the solution tube with fins. The immersion tube type direct-fired high-temperature regenerator according to any one of claims 1 to 3, characterized in that the regenerator is configured to be introduced from an upstream portion. 5. In an immersion tube type direct-fired high-temperature regenerator in which a large number of solution tubes are arranged almost vertically within a combustion chamber, and the solution rising inside the solution tubes is heated by combustion gas flowing outside the solution tubes, the solution 1. An immersion tube type direct-fired high-temperature regenerator, characterized in that a bubble nucleation means is provided on the inner circumferential surface of the lower portion of the tube to prevent overheating of the lower portion of the solution tube. 6. The immersion tube type direct-fired high-temperature regenerator according to claim 5, wherein the bubble nucleation means is a sintered metal layer. 7. The immersion tube type direct-fired high-temperature regenerator according to claim 5, wherein the means for forming bubble nuclei is a fine unevenness. 8. The immersion tube type direct firing high temperature regenerator according to claim 5, wherein the bubble nucleation means is a Teflon membrane. 9. Any one of claims 5 to 8, characterized in that a bubble nucleation means is provided for 1/3 of the length of the solution tube from the bottom of the solution tube.
The immersion tube-type direct-fired high-temperature regenerator described in .