JPS5834734B2 - Evaporator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an evaporator, and more particularly to an evaporator that supplies a fluid at or below a saturation temperature, that is, a subcooled liquid.

In this specification, the term "evaporator" is not limited to evaporators in the narrow sense used in refrigeration equipment, etc., but is used in petroleum refining plants, general chemical industry plants, gas industries, etc. Refers to a device that is a type of heat exchanger that has the function of heating and evaporating.

Generally, in conventional evaporators, the subcooled liquid is supplied into the evaporator from below the tube bundle through which the heating medium flows, so the subcooled liquid is transferred through the tube bundle. The evaporator must be designed with natural convection heat transfer between it and the hot surface, and therefore the heat transfer coefficient must be underestimated, which necessarily increases the heat transfer area and It has the disadvantage of being large.

That is, as shown in FIGS. 1 and 2, the horizontal evaporator 1 has a heating medium intake chamber 3 button and a heating medium extraction chamber 4 which are opened vertically by a partition plate 2, and these chambers 3, 4. and a cylindrical evaporation chamber 6 created by a tube plate 5 between the
The subcool liquid inlet in the evaporation chamber 6 is formed by a plurality of U-shaped tubes connected at both ends to the heat medium intake chamber 3''J? and the heat medium extraction chamber 4 and extending in the length direction of the evaporation chamber 6. It is heated by the heat dissipation of the tube bundle 8 consisting of 7.

The sub-cooled liquid A is supplied from a sub-cooled liquid intake port 9 opened at the middle part in the longitudinal direction of the evaporation chamber 6, and is influenced by the convection phenomenon in the evaporation chamber 6 as shown by arrow B in FIG. As a result, the subcooled liquid A is heated and boiled while passing through the tube bundle 8.

Therefore, the boiling liquid rises to the liquid surface C and forms a foam layer D.
The foam layer separates into steam and boiling point liquid, and the steam is taken out from a steam outlet 10 provided above the liquid level C.

In other words, since the above-mentioned evaporation phenomenon also includes natural convection heat transfer or a phenomenon similar to it, the heat calculation when designing the evaporator is based on the fact that the heat exchange between the subcooled liquid and the heat transfer surface of the tube bundle 8. It is calculated as being carried out between.

To explain this concretely, consider the case where normal butane at room temperature, that is, 20°C, is supplied and steam of W = 10'kg per hour is generated under the condition of 21kg/cm2g. -The boiling point of butane is 120°C.

Therefore, the specific heat cp is 0.72 Kcal/~℃, and the sensible heat exchange heat amount Qs is Qs = WCp (T2-T1) = 10' X O,
72X (120-20) = 72X10' (Kcal
/hr) ""The formula (1) is obtained.

The latent heat of normal butane at 120℃ is λ=
52 KcalA9, so the latent heat exchange heat amount QL is also the temperature difference △tL in the latent heat region is △tL = 158-120 = 38℃... (5
), respectively.

However, the natural convection heat transfer coefficient of normal butane is h
s"3 Xi 02Kcal/m2hr 'C1 boiling heat transfer coefficient h b = 3 X 103Kcal/m2h
r °C, the heat transfer coefficient of steam is h" = 10'Kcal
/m2hr℃, dirt, the sum of the two-factor director and pipe wall resistance is r
=4X10'm2hrY'Kcal, the overall heat transfer coefficient Us, UI, in the sensible heat region and the latent heat region is given by the following formula, and the heat transfer area of the tube bundle 8 becomes a considerably large value, and as a result, The size of the evaporator is increased because a large heat transfer area is required for convective heat transfer with a relatively small amount of heat exchange.

In view of the above-mentioned deficiencies in the conventional evaporator structure, the present invention provides an evaporator structure in which the heat transfer phenomenon between the subcooled liquid and the tube bundle can be considered as heat transfer accompanied only by boiling. By obtaining this, it is intended to reduce the heat transfer area of the evaporator.

Hereinafter, the principle of the present invention will be explained in detail using the third solidification and kettle type evaporator shown in FIG.

The present invention is characterized in that newly supplied subcooled liquid is sprayed onto the surface of the foam layer, and the generated steam preheats this subcooled liquid.

That is, the subcooled liquid intake 9 described with reference to FIGS. Two subcooled liquid supply pipes 20.2 extended to
1 is provided.

Further, a plurality of spray nozzles 23 are suspended from the sub-cooled liquid supply pipe 20.21, and the spray nozzles 23 are equally distributed in the length direction, and the sub-cooled liquid is sprayed onto the foam layer from these spray nozzles 23. It's Nishide.

Therefore, the sub-cooled liquid ejected from the spray nozzle 23 at a temperature below the saturation temperature reaches the foam layer while exchanging heat with the steam, absorbs latent heat from the steam through the foam layer, and reaches a temperature at or near the boiling point. reach

This heated anchor flows into the tube bundle 8 due to the convection phenomenon occurring in the evaporation chamber 6, but since the temperature of the liquid is already at or near the boiling point, it immediately boils.

Therefore, since most of the heat exchange between the liquid and the tube bundle is boiling heat transfer, the boiling heat transfer coefficient with high heat transfer efficiency can be used to calculate the heat transfer area of the tube bundle 8. Therefore, the heat transfer area of the tube bundle 8 is much smaller than that of the conventional tube bundle, and the size of the evaporator can be reduced, and the materials used therein can also be significantly reduced.

To facilitate understanding of such advantages, if the case according to the present invention is applied to the thermal calculations described above for the cases of Figs. 1 and 2, the temperature difference △t between the heat exchange medium will be Since it is given by the difference from the boiling point of the liquid, and the heat transfer coefficient can be considered only as the boiling heat transfer coefficient hb, it becomes as follows.

Therefore, as can be understood by comparing equations (7) and (8), according to the present invention, the heat transfer area of the tube bundle 8 can be reduced by about a factor of 42.

In order to apply the above principle to a known thermosyphon type evaporator, it is constructed as follows.

That is, a thermosiphon-type evaporator includes a vertical or horizontal heat exchanger containing a tube bundle supported at both ends by tube plates, and an accumulator for performing gas-liquid separation.

Therefore, a subcooling liquid supply pipe equipped with a plurality of spray nozzles is arranged in the vapor layer inside the upper part of this accumulator.

The evaporator operates as follows.

The liquid at or near the boiling point is supplied from the bottom of the accumulator to the bottom of the heat exchanger, and heat exchange occurs while it flows upward inside the heat exchanger tube in the case of a vertical type, and on the outside of the tube in the case of a horizontal type. It is heated by a heat medium supplied to the outside or inside of the tube, and a portion of it vaporizes to form a gas-liquid mixture with the saturated liquid, and is returned to the liquid level of the accumulator from the upper part of the heat exchanger.

The separated steam rises toward the outlet provided above.

A subcooled liquid is sprayed into this rising steam from a spray nozzle.

This subcooled liquid comes into direct contact with the steam and gains latent heat due to the condensation of the steam, increasing its temperature, reaching the foam layer, reaching a temperature at or near the boiling point, and is stored in the accumulator along with the saturated liquid returned from the heat exchanger. The heat exchanger flows into the heat exchanger once again due to the thermosiphon effect.

Therefore, as clarified by the above explanation of the principle, the heat transfer area of the tube bundle in the evaporator can be reduced, and the evaporator can be made smaller and the manufacturing cost can be reduced.

[Brief explanation of drawings]

Figure 1 is an axial cross-sectional view of a conventional evaporator, and Figure 2 is a cross-sectional view of a conventional evaporator.
3 is an axial sectional view of a kettle-type evaporator for explaining the present invention in detail, and FIG. 4 is a sectional view taken along line IV-IV in FIG. 3. FIG.

Claims (1)

[Claims] 1. In a thermosiphon type evaporator in which a gas-liquid separation section and a heat transfer section having a tube bundle are connected, a subcooled liquid is newly supplied by spraying a subcooled liquid onto the foam layer of the gas-liquid separation section. An evaporator whose purpose is to preheat subcooled liquid to a temperature at or near the boiling point.