US3373802A - Heat exchanger with removable tube groups of decreasing flow area - Google Patents

Abstract

1,119,772. Cooling liquids in bulk. BOLIDEN, A.B. 3 Dec., 1965 [7 Dec., 1964], No. 51404/65. Heading F4S. A liquid, particularly a highly corrosive liquid such as hot sulphuric acid, is cooled in an upright (cylindrical or oval) chamber by a fluid coolant such as sea water which circulates through groups of tubes 9 (either U-tubes or Field tubes being preferred) each group comprising a radial series of tubes interconnected through header compartments in a structure forming the top cover for the chamber, and the total tube crosssectional area of a group increasing progressively outwardly from the centre of the chamber. The cover structure comprises a lid 5 in which are formed sector-shaped openings. These are closed by header sections (See Fig. 2) from which the tubes extend into the chamber. Each section has its own inlet and outlet 11, 12 leading to main header 17, 18. The liquid to be cooled enters the chamber through an inlet 2. An impeller acting against the inlet stream, causes continuous recirculation of liquid within the chamber to somewhat reduce the temperature of the liquid before it contacts the tube surfaces. Contact by the corrosive liquid with the joints between the tube ends and the headers is prevented by the provision of a cylindrical baffle 6 extending downwardly from the lid 5. The baffle causes a gas pocket to be formed above the liquidas the level rises. Wave shaped inserts may be inserted into the tubes to create turbulence in the coolant. These inserts are preferably of a material more readily ionizable than that of the tubes whereby any tendency to galvanic corrosion, will erode only the inserts. The coolant is maintained at a higher pressure than that of the container liquid to prevent the entry of corrosive liquid into the tubes in the event of leakage. The tubes and headers are of stainless steel and may be lined with copper.

Description

March 19, 1968 w K U ET AL 3,373,802

HEAT EXGHANGER WITH REMOVABLE TUBE GROUPS OF DECREASING FLOW AREA Filed Dec. 5, 1965 Fig.1

7 INVENTOR UZHAM E k/l (L lJ/ D' MAENC L. Man/mom ATTORNEYI United States Patent Office 3,373,802 Patented Mar. 19, 1968 ABSTRACT OF THE DISCLOSURE A heat exchanger for passing a heated liquid in indirect heat transfer relationship with a coolant fluid and comprised of a container having an opening at its upper end closed by a closure member. The heated liquid is disposed within the container and has a liquid level spaced below the closure member. Partition means in combination with the closure member form a multiplicity of fluid chambers at the upper end of the container. The fluid chambers are positioned in a number of radially arranged groups and a plurality of U-shaped seamless tubes extend downwardly from the chambers into the body of liquid.

Each tube has its inlet connected to one fluid chamber and its outlet connected to the radially inner adjacent fluid chamber within the same group. The cross sectional area of the tubes interconnecting adjacent fluid chambers within the same group increases radially outwardly from the innermost pair of adjacent fluid chambers. The partition means and the closure member are arranged whereby individual groups of tubes can be removed from the container and replaced by another group with a minimum of effort and loss time.

The present invention relates to a heat exchanger for exchanging heat between two liquid fluids.

In case one or both of the fluids are corrosive the apparatus is easily attacked, if special regard is not taken to this fact in the design of the apparatus. Particularly, such types of damages as pitting, crack corrosion, tension corrosion and common corrosion may occur. Among these types of damages the pitting is the most diflicult one to control, especially if sea-water is used as coolant. This is often the case in cooling concentrated sulphuric acid in connection with its commercial manufacture.

In the manufacture of sulphuric acid the most common type of cooler is the trickling cooler. This cooler consists of horizontally positioned pipes of cast iron arranged one above the other and in which the acid is passed. Water is poured on to the outer surfaces of the pipes so as to flow from the upper pipes to the lower ones. This type of cooler requires a space of about 16 m? for a cooling effect of 1 million KcaL/hfand it is necessary to operate with relatively high acid temperatures in order to obtain a reasonable area of heat exchanging surface.

Another type of cooler commercially used is made from acid resistant steel and has a spirally shaped cooling surface. In view of the attack on the material it is necessary to limit the temperature of the entering acid to about 55. Therefore the cooling surface must be about as great as that of a trickling cooler for a given cooling effect. The space demand is, on the other hand,

only about a fourth of that needed for a trickling cooler.

In want of water in any useful form, air coolers made from acid resistant material are employed. Very great cooling surfaces must in such a case be resorted to.

In case of deficiency in a cooler of the above mentioned performances it is necessary to interrupt the stream of acid, which mostly has a detrimental influence upon the acid production and in certain cases necessitates stopping of the production during repair or replacement of the defective cooler.

The object of the invention is to provide a heat exchanger in which the above disadvantages are eliminated. It shall also provide the advantage that the space demand for a given cooling effect is extremely limited, e.g., about 2 square meters per 10 KcaL/h. It is further an object to eliminate working conditions known to favour corrosive attacks of the above mentioned types except for common corrosion. Moreover, it is an object, for instance by powerful back-mixing of acid entering the apparatus,

to make feasible to keep a high temperature of the enter ing acid without subjecting the structure material to too high stresses. Further objects and advantages will be evident from the following description.

The main object of the invention is obtained by a heat exchanger comprising an upright container having a bottom and a substantially vertical wall enclosing a liquid space and having inlet and outlet for said liquid connected to said liquid space, and a cover structure on top of said container, inlet and outlet for said fluid connected to said structure, a plurality of submerging tubes suspended from said structure so as to submerge into said liquid space, each submerging tube being seamless at least in the region submerging into said liquid space and adapted for one passage of said fluid down and up, said sumberging tubes being interconnected in said structure so as to form at least one passage way for fluid from said inlet to said outlet, said cover structure comprising a plurality of chambers connected in series, adjacent chambers being interconnected by at least one of said submerging tubes. Although a submerging tube may consist of an outer tube suspended from the cover structure and an inner tube inserted therein so that fluid can pass downwards in the interspace between the outer and inner tubes and upwards in the inner tube, or vice versa, the'subtnerging tubes are preferably U-shaped seamless tubes. Thereby the cooling can be more effectively controlled and the cooling surface be better dimensioned with regard to effective heat. exchange and appropriate streaming properties as well as to mechanical strength. This is so especially if all tubes are of equal diameter, which moreover facilitates the manufacture and keeping spare tubes in store. The tubes should be long so that the effective cooling surface submerging into the liquid be great relative to the surface of tube portions between the liquid surface and the attachment of the tubes to the cover structure. It is possible to make this effective su face about 9:10 of the total surface.

In order to prevent, possibly corrosive, liquid from entering into the tube system in case of leakage the pressure of the fluid in the tube system should be kept higher than that prevailing in the liquid in the container. In case of cooling sulphuric acid with water, such as seawater, or generally a heavy liquid with a'lighter fluid, consideration must also be taken to the difference in density. According to the invention the higher pressure can be attained by pumping the fluid against a resistance at the end of the tube system, for instance in the form of choking means, such as a constriction in the passageway near the fluid outlet.

In a preferred embodiment of the invention the total cross-sectional open area of the submerging tubes which interconnect two of said adjacent chambers, partof one of said passageways, is smaller for two adjacent chambers situated nearer said fluid outlet than for those situated further therefrom, at least close to said outlet. That means that in the passageway of the tubes, in case the tubes have equal diameter, the number of tubes decrease successively in the direction of flow of the fluid.

One advantage with the decreasing sectional area of flow in the tube system is that the increased flow resistance consequential to high speed of flow is obtained only at the latter portions of the passageway for the fluid, where it is especially required, since the fluid has there become heated and thus less effective in cooling capacity which is compensated by its increased speed. Giving the fluid high speed also in the earlier portions of the passage way would mean waste of pumping power.

To obtain a compact apparatus requiring but a small floor surface the invention provides a heat exchanger in which the container is substantially circular, possibly oval, and the fluid inlet is arranged at the periphery and the fluid outlet near the centre of the container. If the number of tubes decrease in the flow direction the tubes may be so arranged as to be evenly distributed in the liquid space of the container, which is advantageous for the efliciency of the heat exchange.

The invention comprises a heat exchanger in which said submerging tubes form an assembly of sections, each section comprising at least one of said passageways for the fluid and being easily removable from said assembly, so as to become replaceable for repair or inspection. Preferably, the cover structure comprises a support frame work, and each of said sections comprises a bottom plate, openings in said frame work, each opening accommodating one of said sections thereby being closed by the bottom plate of said section. By these arrangement it is possible to run the apparatus without or with only very short interruptions, also if a tube has to be replaced. One or more sections can be kept in spare and rapidly replace a defective section.

The ends of the tubes are passed through and liquid and air tightly secured to the bottom plate of the cover structure, care being taken partly to avoid local electrolytic elements and partly to warrant an attachment of sufficient mechanical strength for resisting the bending forces that may arise as a result of the movements of the liquid in the container, which, under circumstances, may have a horizontal component.

In an improved embodiment of the invention the cover structure is air-tightly attached to the wall of said container and at its central portion has a vertical plate airtightly secured to it and projecting at least downwards a limited extent so as to form a central shaft, said submerging tubes being located between the wall of the container and said vertical plate, an air-tightly enclosed gas space being thereby formed to house a gas cushion at the places where said tubes are attached to said cover structure. The extent to which said plate shall project downwards is determined by the requirement that a protecting gas cushion shall be formed; usually one or a conple of decimeters will do, and about one-tenth of the depth of the tube may be reasonable. By this arrangement the sensitive attachment of the tubes to the cover structure are protected even if the supply of corrosive liquid should vary considerably and occasionally be excessive. Also overflow arrangements can be avoided so that the liquid can be transported away from the container by the aid of the propelling means used for feeding the liquid to the container.

The sulphuric acid to be cooled has usually a temperature of over 80 C., sometimes even up to about 100 C. So hot an acid is strongly corrosive, particularly with regard to the tube material. In an embodiment of the invention for eliminating this drawback the inlet of the container for the liquid opens centrally at the bottom of the container, a propelling means being arranged centrally in said container and so as to counteract the inflow of liquid through said inlet. Thereby the entering hot liquid is effectively mixed with already cooled liquid and the mixture becomes less attacking. The temperature of the liquid at the heat exchanging surface will thus be lower than would otherwise have been the case and consequently the differential tem eratur at i rf be reduced. This would normally be considered less attractive from a heat exchanging point of view. However, in practice sea-water is often used as coolant and, owing to its salt contents it is strongly corrosive at temperatures over about 35 C. This is also a reason for keeping the temperature of the liquid in the container at a relatively low value. Nevertheless, and in spite of the fact that the invention can not utilize countercurrence, the heat exchanging capacity is surprisingly high. This is partly due to the fact that the speed of flow of the cooling fluid is increased as the fluid passes through the tube system.

Moreover, the heat transfer can be increased by the introduction of wave-shaped inserts in the tubes which increase the turbulence of the fluid and consequently the heat transmission from fluid to tube wall.

The inserts should be arranged so as to contact the tube at several places and made of a metal that is more easily ionized than the metals of the tube material, so that the metal of the insert will rather go into solution than those of the tube. The insert then acts as an offer electrode. This is of particular importance if in emergency case the circulation of coolant ceases while the hot liquid is still in the container.

On the attached drawing the invention is illustrated diagrammatically by way of an example of the heat exchanger and FIG. 1 shows a vertical section while FIG. 2 shows a horizontal section thereof.

The illustrated heat exchanger consists of a cylindrical, internally lined container 1 having a central inlet opening 2 for the hot acid at the bottom and one or more outlet openings 3 for the cooled acid in the side wall of the container. The upper portion of the container is provided with a flange 4, on which the carrier structure 5 rests. This is provided with a vertical plate forming a central piece of tube or shaft 6, from which arms 7 extend radially to the periphery of the container. Sections 10 of a cover structure are inserted in the openin-gs between the arms and carried thereby and cooling elements in the form of U-shaped tubes 9 are suspended from sections 10 so as partly to submerge into the hot acid. These hair pin shaped tubes are made of acid resistant steel and both ends of the tubes are secured to a bottom wall plate 8 of the section 10 and resting on the flange 4. The tubes are passed through and rigidly secured to the plate. The cover structure 10 is subdivided into a number of chambers by vertical partition walls 13 and has studs 11 and 12 for the admission and extraction, respectively, of cooling water, which is forced to pass down and up through the hair pin tubes by means of said partition walls in the cover. The number of tubes connecting two adjacent chambers is reduced from the periphery towards the centre, which renders the cooling water an increasing speed of flow as it is heated. The subdivision of section 10 of the cover structure permits the removal of individual groups of chambers and tubes 9. In order to cathodically protect the acid resistant steel an iron plate or rod is inserted in each tube, bent in a sinus-shaped curvature so that metallic contact is obtained with the inner surface of the tube at an arbitrary number of points. The end chambers of structure 10 are connected via studs 11 and 12 to inlet and outlet water conduits 14 and 15, respectively, which are provided with closing valves 16 and are connected to annular inlet and outlet main conduits 17 and 18, respectively.

The tube piece 6 carries a centrally positioned driving device 20 for an agitator 19 which is rotated so as to counteract the in-flow of liquid through inlet 2 and cause the entering liquid to be mixed wit-h already cooled liquid. The direction of flow is substantially vertical downwards in the centre and upwards in the region of tubes 9. Depending on the shape of the propelling means there may be some degree of rotation of the liquid about the axis of the container.

The shaft or tube piece ,6 is extended downwardly to some extent whereby a gastight space is formed in the upper portion of the container above the acid level between the shaft and the wall of the container, and a gas cushion is formed when the acid level rises above the lower edge of the shaft. This arrangement warrants that even at too high a level of acid in the container the acid does not come into contact with the attachment of the tubes to the plate 8 of the cover structure 10.

In operating a heat exchanger as described and illustrated and with a total effective cooling tube surface of 184 sq. m. sulphuric acid in an amount of 6.6 cu. m./ min. was cooled from 90 C. to 63 C. (measured at the inlet and outlet of the container) with sea-water that was heated from 10 C. to 25 C.(measured at the inlet and outlet of the cover structure). The tubes were provided with inserts and the agitator worked as back-mixer. That means that 5 million KcaL/h. were transmitted in the heat exchanger. A K-value of 720 has been obtained.

The invention is not limited to the described embodiment but comprises every kind of execution where the principles of the invention are applied. Thus, the tubes or the cover structure or both may be made of compound material, such as stainless steel outside and copper inside. The tubes may be secured to the bottom plate of the cover structure under the intermediation of an electrically insulating material, such as a bushing of plastic material, so as to prevent corrosion by formation of electric local elements.

We claim:

1. A heat exchanger for passing heated liquid in indirect heat transfer relationship with a coolant fluid comprising a container open at its upper end, a closure member disposed across and closing the open end of said container, said container adapted to hold a body of liquid therein and to have a liquid level in its upper portion spaced below said closure member, a liquid inlet into said container disposed below the liquid level, a liquid outlet from said container disposed below the liquid level, wall means in combination with said closure member forming a multiplicity of fluid chambers at the upper end of said container, said fluid chambers arranged in a number of radially extending sector-like shaped groups, each of said groups containing at least three of said fluid chambers, a plurality of tubes disposed within said container and extending downwardly from said closure member into the body of liquid, each of said tubes having an inlet opening secured to one of said fluid chambers and an outlet opening secured to another said fluid chamber disposed within the same said group and positioned radially inwardly from and adjacent to the fluid chamber containing the inlet opening, a fluid inlet to each of said groups of fluid chambers secured to the radially outermost fluid chamber in each group, a fluid outlet from each of said groups secured to the radially innermost fluid chamber in each of said groups, and in each of said groups the total cross-sectional flow area of said tubes interconnecting adjacent fluid chambers increases outwardly from the innermost pair of adjacent fluid chambers, whereby said fluid chambers within each group in combination with said tubes secured to said fluid chambers within said group form a radially inwardly directed flow path for the coolant fluid as it flows in indirect heat transfer relationship with the heated liquid contained within the container.

2. A heat exchanger, as set forth in claim 1, where-in said fluid chambers and said tubes connected thereto within each of said groups are removable as a unit from the container whereby a replacement can be inserted in place of the removed group without disturbing the operation of the heat exchanger.

3. A heat exchanger, as set forth in claim 1, wherein said tubes have a U-shaped configuration.

4. A heat exchanger, as set forth in claim 1, wherein each of said tubes within one of said groups has the same diameter.

5. A heat exchanger, as set forth in claim 2, wherein said closure members comp-rises a plurality of radially extending arms disposed in angularly spaced relationship forming therebetween openings in said closure member, and said wall means comprise a plurality of cover sections supported by said arms and closing the openings in said closure member, and partitions arranged on said cover sections and forming in combination therewith a plurality of said fluid chambers whereby said cover sections are selectively removable from said closure member for removing the tubes secured therewith from within the container.

6. A heat exchanger, as set forth in claim 5, wherein said tubes are integrally attached in sealed relationship to said cover sections.

7. A heat exchanger, as set forth in claim 5, wherein a tubular member is connected to said closure member and extends downwardly into said container to a point above the liquid level therein, said tubular member spaced centrally Within said closure member inwardly from the innermost fluid chambers within said groups of fluid chambers and tubes, said closure member secured in fluidtight relationship to said container whereby a gas space is formed within said container between the liquid level therein and the surface of said closure member within said container whereby the tube connections to said fluid chambers are spaced from the body of liquid within said container.

8. A heat exchanger, as set forth in claim 1, wherein said liquid inlet is disposed centrally in the lower end of said container and said liquid outlet is positioned in the side of said container at a location intermediate the liquid level therein and the lower end of said container.

9. A heat exchanger, as set forth in claim 8, wherein stirring means are provided within the liquid space in said container for circulating the liquid therein.

10. A heat exchanger, as set forth in claim 9, wherein said stirring means comprises a dependently supported shaft extending downwardly into said body of liquid from said closure member, a bladed member located at the lower end of said shaft, and means for rotating said shaft and said bladed member mounted on said closure member, whereby a stirring effect is imparted to the liquid within said container causing it to flow downwardly from the bladed member along the lower portion of the container then upwardly along its sides to the upper surface of the liquid level and then returning downwardly along the center of the body of liquid to the bladed member for recirculation.

References Cited UNITED STATES PATENTS 801,489 10/1905 Uthemann l65134 X 2,122,256 6/1938 Leach l6578 X 2,590,465 3/1952 Ris l65134 X 2,729,433 l/1956 Berg -103 2,764,476 9/1956 Etter 16 5-409 X 2,774,575 12/1956 Walter l65l58 X 2,800,307 7/1957 Putney l65108 2,875,027 2/1959 Dye l65l09 X 3,126,949 3/1964 Boni et al. l65l58 3,187,807 6/1965 Ammon l65l58 X 1,770,320 7/1930 Morterud l65147 2,589,730 3/1952 Rathkey 165/146 EDWARD 1. MICHAEL, Primary Examiner.

ROBERT A. OLEARY, Examiner.

A. W. DAVIS, Assistant Examiner.

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