US3430693A - Heat exchange element with condensate collector - Google Patents

Description

March 4, 1969 EG I WALL 3,430,693

HEAT EXCHANGE ELEMENT WITH CONDENSATE COLLECTOR FiledApfil 14, 1966 United States Patent 3,430,693 HEAT EXQHANGE ELEMENT WITH CONDENSATE COLLECTOR Gustaf C. Egenvall, Lidingo, Sweden, assignor to Johnson Construction Company AB, Stockholm, Sweden, 21 company of Sweden Filed Apr. 14, 1966, Ser. No. 542,659 Claims priority, application Sweden, June 16, 1965,

7,947/65 U.S. Cl. 165-166 4 Claims 1m. 01. F28f 3/00,- F28b 9/08; BOld 53/00 ABSTRACT OF THE DISCLOSURE Such heat exchange elements are previously known, being either square or rectangular in shape and adapted so that their inlet edges and outlet edges lie in the same horizontal plane. The heat exchange element is used particularly within the field of chemical technology. In many chemical processes it is desirable to cool and condense a gaseous medium both rapidly and uniformly and to lead the formed condensate away from the heat transfer surfaces as quickly and as effectively as possible. In order to cool the gases rapidly they must pass through the condensation channels in the heat-exchange element, at high speed and the volume of said channels must be relatively small. Uniform cooling of a gas requires all the gas particles to pass over equally large and uniform cooling surfaces at the same speed and that no dead space occurs in the heat exchange element. Effective removal of the condensate requires the heat exchange element to be so designed that the condensate formed is discharged in the channel-shaped collecting members and not allowed to run freely over the heating surface, towards the outlet. Present day embodiments of the above described heatexchange element have not fulfilled this requirement to any satisfactory degree, which must be considered a disadvantage.

It has now been shown that this disadvantage can be overcome, or at least substantially reduced if, in accordance with the invention, the inlet and outlet edges of the heat exchange lamellas lie in one plane, which inclines with respect to the horizontal. Due to the face that the gas flows at right angles to the horizontal plane and the condensate-flows are inclined with respect to the horizontal plane, the flow of gas automatically drives away the condensate collected in the channels, obliquely in relation to its own direction of flow.

According to one embodiment of the invention the inlet and outlet edges of the heat exchange element may be inclined in relation to the horizontal plane.

According to another embodiment of the invention the inlet and outlet edges of the heat exchange element may be horizontal but arranged in the form of steps in such a Way that an inclined inlet and outlet plane is formed.

The invention also includes a chemical apparatus for cooling and condensing purposes, said apparatus being built of the above disclosed heat exchange element. In this respect it is convenient to arrange several heat-exchanging elements in a column, or the like, so as to build a heat exchanger.

One chemical process in which it is important to provide for rapid cooling and condensing of gaseous mixtures, is the preparation of nitric acid by catalytic oxidation of ammonia and absorption of the formed nitrous gases. The gaseous product formed upon oxidation is a mixture of nitrous gases, elementary oxygen, nitrogen and steam. These mixtures are first cooled in a steam generator and thereafter in a heat exchanger. During the latter cooling process a large portion of the steam is condensed at the same time as the gases if they are allowed to partly dissolve in the condensate and form diluted nitric acid. So that the nitrous gases can be used as completely as possible the nitric acid must be formed in countercurrent; in this way the highest concentration of the produced acid is also obtained. If the condensate is allowed to form nitric acid in countercurrent, the content of nitrous gases in the gas mixture introduced into the absorption part of the absorption tower is reduced, which means that the concentration of the acid which leaves the tower at the same level is also reduced. Oxidation of nitrogen oxide (NO) to nitrogen dioxide (N0 also takes place during the cooling process, the oxygen present in the gas mixture being used. Since it is nitrogen oxide which is absorbed, it is important that oxidation occurs as closely in front of the discharge level of the acid-product as possible and that oxidation is kept to the lowest minimum possible during that par-t of the cooling process in which the condensate is formed.

For the purpose of preparing highly concentrated nitric acid a small-volume heat exchanger is required which cools the gases rapidly so that any oxidation taking place in the heat exchanger, where the condensate is formed, is irrelevant to the process. An additional requirement for such a heat exchanger is to remove the formed condensate as rapidly and as effectively as possible so that the nitrous gases have no time to be absorbed by the same.

It has now been shown that this desideratum can be realized in an extraordinarily advantageous manner if an apparatus which includes the above described heatexchange element is used to cool the gaseous mixture formed on oxidation of ammonia. In this context several elements are suitably arranged in layers, one above the other.

In fractionation and fractional condensation it is desirable to accurately control the cooling process of a gaseous mixture so that the distillate obtained is as uniform as possible. This can only occur in a heat exchanger where each particle of gas is allowed to travel at the same velocity over a heat-transfer surface of the same temperature and shape. An additional requirement is that the formed condensate is removed so effectively that it does not run to one side or forms obstructions which could disturb the flow of gas. This presupposes a heat exchanger of small volume and without a dead space" Where the gas may be delayed, and arrangements which remove the formed condensate effectively and uniformly over the whole heating surface.

Even this desideratum can be satisfied in an extraordinarily advantageous manner by means of the heat-exchaning elements according to the invention.

The accompanying drawing shows, diagrammatically, several embodiments of heat exchanging lamellas in which the idea of the invention is adapted.

FIG. 1 shows diagrammatically a side view of a heat exchanging lamella according to the invention obliquely cut away;

FIG. 1a shows very diagrammatically an end view of the heat exchanging element according to the invention, arranged in steps and cut away at right angles,

FIG. 2 diagrammatically illustrates, with the assistance of a vertical section, how zig-zag shaped flow channels are formed between two heat exchanging lamellas provided with a corrugated surface;

FIGS. 3 and 4 illustrate various types of heat exchanging elements to which the invention can be adapted;

FIG. shows diagramma ically how several heat exchanging elements are arranged in layers, one above the other in a column, to build a heat exchanger;

FIG. 6 shows how channel-shaped collecting members intended for the condensate are adapted integrally with the heat exchanging lamellas in FIG. 2;

FIG. 7 shows a portion of a heat exchanging element with channel-shaped collecting member integral with heat exchanging elements included in the heat-exchanging lamellas and FIG. 8 shows how channel-shaped collecting members are arranged between two heat exchanging elements and how the guide members are arranged to lead the flow of gas-condensate down into the channels.

Referring to the accompanying drawing, FIG. 1 shows very diagrammatically a heat exchanging lamella, both vertical side edges of which are indicated by the reference numerals 1 and 2, each inlet edge intended for the medium to be cooled by the reference numeral 3 and each outlet edge for the cooled medium with numeral 4. In the shown lamellas comprised of thin-sheet sections presenting heat transfer surfaces and either welded together i pairs or defined by packings, the edges 3 and 4 are inclined with respect to the horizontal plane. In this Way gas or steam flowing parallel to the side edges 1 and 2 drives the formed condensate more effectively into a condensate trap arranged parallel to the outlet edge 4.

FIG. 1a shows very diagrammatically a heat exchange element comprising rectangular heat exchanging lamellas arranged in steps, two vertical side edges being indicated by reference numerals 1a and 2a and the inlet surface for the medium to be cooled, with numeral 3a whereas the outlet surface for the cooled medium is indicated by numeral 4a. Each of the lamellas in the heat exchanging element shown in FIG. 1a is comprised of two welded lamella sections provided with heat transfer surfaces, or defined by packings; the edges of said lamella sections being obtained at right angles and the inlet and outlet plane caused to slope by virtue of the step-like arrangement of the lamellas.

FIG. 2 shows diagrammatically, in vertical section,

how heat exchange lamellas can be manufactured by pressing corrugated plates and how by displacing the lamellas 5 and 6 in relation to 7 and 8 zig-zag-shaped gaps 9 and 10 of uniform area are obtained for the condensing medium. The inside channels of each heat exchanging lamella are intended for the cooling medium, which can be led parallel or in series within each lamella. The lower edge slopes in relation to a plane at right angles to the drawing in a manner shown in FIG. 1.

FIG. 3 shows diagrammatically a cut-away view of three heat exchanging lamellas 1'1, 12 and 13 arranged side by side in such a way that a gap for condensed medi um appears between two adjacent lamellas. In a similar way to FIG. 1 the outlet edge on each lamella is designed to slope in relation to a plane at right angles to the plane of the drawing or arranged in the form of steps as in FIG. 1a. Spacers 14 are disposed in the interior of each lamella, said spacers being so adapted that they impart a certain desired movement, forwards and backwards, to the cooling medium in a plane at right angles to the plane of the drawing.

FIG. 4 shows diagrammatically, in a cut-away view, three heat exchanging lamellas, 15, 16, .17 which are held apart by external spacers 18 designed as filler members.

FIG. 5 shows diagrammatically the arrangement of a number of heat exchanging elements of the same design as the heat exchanging lamellas illustrated in FIG. 1 or in a rectangular design or arranged in steps as in FIG. 1a. These elements are disposed in layers one on top of the other. The gaseous medium to be condensed is introduced at an upper inlet edge and passed up and down the elements of the heat exchanger. Two condensate traps are arranged between two heat exchanging elements (cg. between 20 and 21 and between 21 and 22) each parallel to the outlet plane of said heat exchanging element.

FIG. 6 shows condensate traps 23 and guide plates 23a manufactured integrally with the heat exchanging lamellas.

According to FIG. 7 the condensate traps '24 are each manufactured integrally, with a corresponding heat exchanging lamella.

FIG. 8 shows diagrammatically the way the condensate traps are secured between two heat exchange elements positioned one on top of the other, and each comprising heat exchanging lamellas, one lamella in the upper element being indicated by the reference numeral 25 and the lower element with 26. A number of channels intended for the condensate are disposed between the heat exchanging element, the one situated on the far right being indicated with reference numeral 27 and guide plates 28 on to which the condensate formed in the gaps between the lamellas 25 falls and is then led down into the traps 27. The guide plates and condensate traps are situated between the outlet and inlet edges of the lamellas in such a way that the gas-steam condensate mixture from the upper element can, without unnecessary drop in pressure, leave the gaps in this element and be divided, uniformly, in the gaps between the lamellas of subsequent elements.

What I claim is:

1. A heat exchange apparatus for cooling and condensation purposes comprising a plurality of lamellas disposed in side-by-side spaced relationship to one another, each of said lamellas being defined by a pair of lamella sections secured to one another to define an interior channel for cooling medium, each of said lamellas including opposite generally parallel vertical side edges and opposite generally parallel inlet and outlet edges, said inlet and outlet edges being disposed obliquely to horizontal whereby each of said lamellas defines a generally rhomboid shape, the inlet edges of said lamella all lying in a first plane and the outlet edges of said lamella all lying in a second plane, each of said planes extending obliquely to horizontal, the spaces between adjacent lamellas defining flow channels for receiving the medium to be condensed, and channel-shape condensate trap means positioned below and spaced from said lamellas for collecting condensate formed in said flow channels disposed thereabove, each of said condensate trap means being disposed ina plane which extends substantially parallel with the plane in which the outlet edges of said lamellas lie whereby the flow of the medium to be condensed through the apparatus in a direction substantially parallel with the side edges of said lamellas will cause formed condensate to be driven away in an oblique direction.

2. Apparatus as defined in claim 1 including an additional plurality of spaced lamellas similar to said first lamellas and positioned below and spaced from said condensate trap means and having the inlet and outlet edges thereof all disposed in planes extending oblique to horizontal, and havinng substantially vertical side edges.

3. Apparatus as defined in claim 1 wherein said condensate trap means defines upwardly opening channels, and guide plates defining downwardly opening channels, said condensate tra-p means being spaced from one another, and said guide plates spanning the space between said condensate trap means for directing condensate into said condensate trap means, whereby the condensate can be separated out without an undue drop in pressure.

4. A heat exchange apparatus for cooling and condensation purposes including a heat exchange element comprising a plurality of generally rectangular heat exchanging lamellas disposed in spaced substantially parallel relationship to one another to define flow channels therebetween, each of said lamellas comprising a plurality of lamella sections secured to one another, the lamellas being disposed in stepped relationship to one another, said lamellas having generally parallel vertical side edges, the upper edges of each of said lamellas defining an inlet edge and the lower edges of each of said lamellas cooperating to define an outlet edge, all of the inlet edges defining a first plane and all of said outlet edges defining a second plane, said planes being disposed substantially parallel with one another and being disposed oblique to horizontal, and channel-shaped condensate trap means positioned below said heat exchange element for collecting condensate formed in said flow channels, said condensate trap means being disposed in a plane which is substantially parallel to the first and second planes of said heat exchange element whereby the flow of medium to be condensed through the apparatus in a direction substantially parallel with the side edge of said lamellas will cause formed condensate to be driven away in an oblique direction.

References Cited ROBERT A. OLEARY, Primary Examiner.

T. W. STREULE, Assistant Examiner.

US. Cl. X.R.

Stack 1-65166

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