US2750159A - Metallic recuperator - Google Patents

Description

June 12, 1956 EBNER METALLIC RECUPERATOR 3 Sheets-Sheet 2 Filed Aug. 21, 1952 OOOOO IN VEN TOR. 44 250 J. 5 A/. 6W, M

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June 12, 1956 A. J. EBNER 2,750,159

METALLIC RECUPERATOR Filed Aug. 21, 1952 3 Sheets-Sheet 3 1 0 I t-FO -2 P [WW HF In .b .b a b 2v M M4 wwzmmi United States Patent This invention relates to heat exchangers, particularly to heat exchangers for heating air, and more particularly to those heat exchangers known as metallic recuperators for preheating the combustion air of industrial furnaces.

f Metallic recuperators are well known in the art, and it will be understood that my present invention consists in certain new and useful improvements in the structure of such recuperators, to the end that the following structural features and advantages may be realized:

1. The essential tubes of my recuperator are relatively short, whereby the difiiculties encountered due to the thermal expansion of the tubes are minimized.

2. My tube arrangement is such that the air is easily passed through a plurality of tube stages, with the eifect that the heat transfer obtained is equivalent to that realized with tubes more than twice as long.

I 3. My recuperator structure is self-contained, whereby it may be applicable as a unit to any fuel-fired furnace.

4. My recuperator structure is independent of the furnace structure, and may be cut into and out 'of op-. eration at will, without loss of furnace operating time.

5. In the recuperator of my invention the cold air. is supplied under pressure, with the eifect that a hot fan is not required. recuperator structures the heated air is drawn through the recuperator by means of a fan, and the heat to which such fan is thus exposed requires a fan of special construction, a so-called hot fan that requires water cooled bearings, an alloy impeller, and other costly features of construction.

6. My recuperator structure is relatively inexpensive to build, and is readily accessible for repairs. Tube replacement is a simple operation. Indeed, a complete recuperator unit may be quickly replaced by a spare unit without substantial loss of furnace time, and required repairs madeto the defective unit when convenient.

7. Temperatures to which air is preheated in my recuperator may be readily controlled.

The invention will be understood upon reference to the accompanying drawings, in which:

Fig. 1 is a view of a recuperator unit embodying my invention, the view being shown in horizontal section on the plane I-I of Fig. 2;

Fig. 2 is a view of the recuperator in vertical section, as seen on plane II-II of Fig. 1;

Fig. 3 is a view in vertical section through the waste gas flue of an industrial furnace, showing incorporated therewith a plurality of recuperator units of my invention;

Fig. 4 is a diagrammatic view, illustrating in plan and to smaller scale the structure shown in Fig. 3; Fig. 5 is a diagrammatic plan view of a battery of four recuperator units, such as is shown in Fig. 3, illustrating a preferred arrangement of air ducts leading to and from the battery;

Fig. 6 is a view similar to Fig. 5, illustrating the arrangement of the air piping for a battery of two recuperator units;

Fig. 7 is a diagrammatic view, illustrating in plan a It will be-understood that in many.

modified arrangement of the recuperator units of a battery; Fig. 8 is a fragmentary view comparable withFig. 2,

illustrating a modification in the structural detail of the recuperator; Fig. 9 is a sectional view, showing tureof Fig. 8 to larger scale, the indicated at IX IX in Fig. 8;

Fig. 10 is a diagrammatic view, showing on the vertical broken plane X-X of Fig. 11 still another modification in the recuperator of this. invention; and t Fig. 11 is a view in top elevation of the structure of Fig. 10., f 7 Referring to Figs. 1 and 2 of the drawings a single a'detail of the strucplane of section being recuperator unit embodying the invention will be described in; detail. The recuperatorunit comprisesan inner wall 2 forming a duct which in this caseis of rectangular cross section (Fig- 1).. ,Thewall of such duct isfconstructed of four sections of heat-resisting alloy sheet or platesteel (a suitable composition of alloy steel being known to the art for; use in metallic recuperators), and

the edges of the four sections are united by means of grooved joiner strips 3, which are also formed of alloy 1 of alloy sheet steel, welded at'their inner edges to the steel. The edges of the sections are secured in the grooves of the joiner strips 3, and theunion is such that the edges may slide laterally in the grooves, to make accommodation for the expansion and'contraction of the structure under the varying temperatures of service, without. objection'able leakage of gasthroughthejoints, I

'An outer wall or casing 4' envelo'psin spaced relation the vertical duct formed bythe wall 2.. The"oute'r wall' is formed in four sections unitedin bolted. joints'5,'-suchjoints permitting theouter casing to be'readilyopene'd for inspection, or repair, or renewal of the innerunit 2. Between the four joiner strips .3 of the inner wall and the four joints 5 of the outer wall, partitions 6 extend'throughoutso much of thevertical extent of the structure as is common to the inner and outer walls. The partitions 6 are yieldable under variations in temperatures towhich they are exposed in service, wherefore the partitions may be said'to be thermally yieldable. As shown herein the partitions are formed of corrugated or bellows-likewebs strips 3 and at their outer edges clamped in the bolted joints 5. Thus, the space'between the inner and outer walls is divided into four vertical chambers a, b, 'c, and d of right-angle shape, as viewed in horizontal cross section,

Fig. 1. In service the recuperator is installed in combina-.

tion with the duct system of an industrial furnace, so that the hot waste gases flowing from the furnace to the stack, pass upwardly through the duct formed by the inner' wall 2, as indicated by arrows 2, while the air for sustaining combustion in the furnace is. propelled under thepressure of a fan or blower (not shown) successively through the chambers a, b, c and d and a maze ofrelatively. short heat-exchange tubes traversing the interior space of the duct 2, the paths of air flow being indicated by dotted-line arrows. 7

The heat-exchange tubes are arranged in a plurality of vertically spaced flights or stages F-F' and SS'. Each flight is formed of. two groups of tubes arranged in a common horizontal plane, and each of the flights appearing in the line of sight in Fig. 2 comprises a group of five tubes S and five tubes S, while the tubes in the alternate or intervening flights appearing in side elevation in Fig. 2 comprise five tubes F and five tubes F. This will be understood upon comparing Figs. 1 and 2. 7

As in the case'of the parts 2, 3 and 4, the tubes are formed of a heat-resisting alloy. The ends of the tubes are welded or swedged in sealed joints in the opposite wall portions of the duct 2, after the manner that boiler tubes are united to the header plates or bulkheads of steam-generating boilers. The tubes are open at-their Patented June .12, 1956" opposite ends, whereby the air may flow in unimpeded streams, as described. As the tubes (under the varying temperatures to which they are exposed in service) expand and contract, the opposed wall sections (2), to which the tubes are at their ends united, are free to move apart or toward each other, by virtue of the slip-engagement of the edges of such wall sections with the grooves of the joiner strips 3.

The air to be preheated is introduced under fan pressure to a primary or air-inlet chamber a by way of an inlet duct 7, and from the chamber a the flowing air divides and passes part through the tubes into a secondary air chamber b and part through the tubes F into a secondary air chamber c. From secondary chamber b the air flows through tubes F into the tertiary or air outlet chamber d, and from secondary chamber 0 the air flows through tubes S into the said tertiary or outlet chamber.

The wall 2 of the inner duct and the criss-cross maze of tubes are exposed to the hot products of combustion rising through the duct, as indicated by the arrows e, and heat is transmitted through the walls of the tubes and the duct to the flowing air. The tortuous and turbulent flow of the hot products of combustion around and between the successive flights of criss-crossed tubes promotes an extraordinary transfer of heat to the streaming air, and the flow of the air in divided small streams through the successive, angularly disposed passes of tubes between the air chambers a to d insures prolonged exposure of the air to the heat. A highly efiicient heating of the air is obtained.

From the outlet chamber d the highly heated air is delivered through a duct 8 to the combustion system of the furnace.

The recuperator unit of the invention may be arranged individually or in a battery of two or more units, with the flue system of a furnace (not shown). In Figs. 3 and 4 the stack 9 of a furnace is fragmentarily indicated, as also is the flue 10 for leading the hot products of combustion from the furnace to the stack. In this case a battery of four recuperator units is installed in the flue system.

It will be noted that the outer casing or wall of the recuperator units may be formed as a single casing 40 for the four inner units or ducts 2. The four inner units or ducts 2 of the battery are supported on end upon the arch 11 and end wall 12 of the flue 10, and upon intervening and spaced rider arches 13. The hot waste gases of the furnace, streaming through the flue, rise through the units or ducts 2 into a stack flue 14 leading into the stack 9. It will be understood that suitable dampers may be provided to effect a distributed flow of the hot gases through the several units. In this case a damper 15 in the flue 10 and a butterfly valve 16 in the flue 14 are shown in exemplary way as means for controlling the draft of the stack and the flow of the hot waste gases of the furnace. This showing is deemed sufiicient .for those skilled in the art.

Partitions 6 are provided between the ducts 2 and the outer walls 40, and partitions 60 are provided between the opposing faces of the row of units, whereby each unit (2) has four air chambers a, b, c and d associated with it. In the battery as thus partitioned there are three primary air chambers a, each having an air inlet pipe 7; there are two secondary chambers b, and three secondary chambers c; and there are two tertiary or air outlet chambers d, each having an air delivery duct 8. The flow of air between the inlet chambers a and the outlet chambers d follows the same sequence through the tubes and chambers b and c as that described in connection with the single unit shown in Figs. 1 and 2, the only qualification being that middle one of the three air inlet chambers 11 (cf. Fig. 4) serves two of the units 2, each of the two chambers b serves two of such units, the middle one of the three chambers c serves two of the units 2, and each of the two outlet air chambers d serves two of the said units. The arrangement is shown diagrammatically in Fig. 5, and this figure of the drawing also indicates that the air inlet pipes 7 may stem from a single air supply main 70, and that the hot-air outlet pipes 8 may connect into a single duct leading to the combustion equipment of the furnace.

Returning to Fig. 4, it is to be noted that an auxiliary fiue 17 is arranged to by-pass the recuperator installation, so that the hot waste gases of the furnace may flow directly to the stack. This by-pass flue includes a damper 18. When it is desired to take the recuperators out of service for the renewal or repair of one or more of the units, the damper 15 is closed and damper 18 opened. In a few hours the recuperator installation and the by-passed portion of the flue will cool to the point where repair or maintenance men can work.

Fig. 6 illustrates diagrammatically how two recuperator units may be enclosed within a single housing 41, and two air inlet chambers a may be fed by pipes 7. A single outlet chamber d receives the air flowing from chambers a through the tubes (FF and S-S', Figs. 1 and 2) and chambers b and c, and from such outlet chamber the highly heated air is delivered by a duct 8 to the furnace combustion equipment.

In each of the recuperator arrangements described in the foregoing context it will be understood that the air to be heated flows through two passes of recuperator tubes between the inlet and outlet chambers of the installation. More particularly, half of the air entering chamber a flows to the intermediate or secondary chamber b and half to the intermediate or secondary chamber 0. This comprises the first pass. From both chambers b and c the air flows through the recuperator tubes into the outlet chamber d, and this flow comprises the second pass. This statement applies whether the recuperator installation embodies one or more of the recuperator units described. The two-pass recuperator installation will be found effective for preheating the combustion air for most industrial furnaces. In the event, however, that an extremely high preheat is desired, the number of passes of the installation may be increased as need be. Fig. 7 of the drawings diagrammatically indicates a four-pass installation.

As shown in Fig. 7, four recuperator units 2 may be arranged cornerwise in alignment within a single outer housing 42, and partitions 6 may be arranged betwen the units 2 and the outer casing 42, while partitions 60 are arranged between the adjacent corners of the successive recuperator units. The air to be preheated enters an inlet chamber a whence it flows through a primary pass, as indicated by the crossing arrows, into two intermediate chambers b. From the chambers b the air flows through a second pass, as indicated by the crossing arrows, into two chambers c, whence the air flows into two chambers d, such flow comprising the third pass. From the two chambers d, the air flows, as indicated by the crossing arrows, into a single outlet chamber this flow comprising the fourth pass. In flowing through these four passes the air for a given rate of flow, is exposed twice as long to the effects of the hot products of combustion as in the case of the recuperator installations first described. A high degree of preheat is obtained. The highly heated air is delivered by way of duct 8 to the combustion equipment to be supplied.

It may be noted that the outer walls or casing of the recuperator units may be provided with suitable insulation against heat loss, and also the delivery ducts (8 and 80) may also be insulated. This is a practice well known to the art and illustration is needless.

The four-pass heat-exchange effect described in connection with Fig. 7 can be obtained by modifying the recuperator unit of Figs. 1 and 2, as illustrated in Figs. 10 and 11. Specifically, the four vertically extending air chambers between the inner and outer casings or walls 2 and 4 are medially divided by a horizontal corrugated partition 61, thereby providing four top air chambers a, b, c and d, and four corresponding lower chambers. The cold air inlet duct 7 opens into top chamber a and flows sequentially through two passes of heat-exchange tubes in reaching top chamber a, all similar to the manner described in which the air flows from chamber a to d in the unit of Figs. 1 and 2. Upon entering top chamber d of the unit of Figs. 10 and 11, the partially heated air flows downwardly through openings 20 in the horizontal partition 61 into a lower air chamber a. From the latter chamber the air flows through two passes of tubes to the lower chamber d; that is, the air flows through a pass of tubes from chamber a into two lower chambers that lie directly below the top chambers designated b and c in Fig. 11, and from such lower chambers the air flows through a pass of tubes to a lower chamber d; whence the air enters the hot air delivery duct 8 leading to the combustion equipment of the furnace. The four passes through which the air flows atfords the desired prolonged exposure of the air to heat transfer from the hot products of combustion of the furnace. And it is note worthy that the air flowing through the tubes in the lower half of the unit is exposed to the effect of the waste gases in their hottest condition as they enter the recuperator from below. This gives the advantages of the well-known counterflow principle so eifective in heat exchangers.

Figs. 8 and 9 illustrate a modification in a detail of construction. Whereas in Figs. 1 and 2 the four sections of steel plate that form the duct 2 are united by slotted joiner strips 3, in modification the joiner strips may be replaced by lengths of tubing 19 formed of the same heatresisting alloy as the plate of which the wall 2 is formed. Each length of tubing may be slotted as at 20 to receive in slip-fit the edges of the plate sections to be united, and then the interior of the tube may be filled with sand or other suitable comminuted refractory material. The corrugated alloy partitions 6 may be welded to the tube section 19 and secured in the joints of the opposing outer wall or casing 4 of the recuperator unit.

The recuperator structure illustrated and described herein, is susceptible to many structural variations and modifications, without departing from the spirit of the invention defined in the appended claims.

I claim:

1. A recuperator for an industrial furnace comprising spaced inner and outer walls formed of sections of heatresisting metal plate united at their edges, grooved joiner elements engaging the meeting edges of the sections of the inner wall in a slip-joint that provides for movement of the engaged edges as the recuperator structure expands and contracts under varying temperatures in service, the recuperator structure having partitions traversing the space between the walls to form at least two air chambers, an air inlet opening into one of said chambers and an air outlet opening from the other, said inner wall comprising a metal duct for the passage of hot waste gases of said furnace, and a multiplicity of metal tubes traversing the.

line of flow of the waste gases through said metal duct, with the bores of the tubes in open communication at one end with one of said air chambers and at opposite end with the other chamber.

2. A recuperator for an industrial furnace comprising spaced inner and outer walls formed of sections of heatresisting metal plate united at their edges, the sections of the outer wall being united in readily disengageable bolted joints, grooved joiner elements engaging the meeting edges of the sections of the inner wall in a slip-joint that provides for movement of the engaged edges as the recuperator structure expands and contracts under varying temperatures in service, the recuperator structure having partitions traversing the space between the walls to form at least two air chambers, an air inlet opening into one of said chambers and an air outlet opening from the other, said inner wall comprising a metal duct for the passage of hot waste gases of said furnace, and a multiplicity of metal tubes traversing the line of flow of the waste gases through said metal duct, with the bores of the tubes in open communication at one end with one of said air chambers and at opposite end with the other chamber.

3. A multiple air pass recuperator for an industrial furnace comprising spaced inner and outer walls formed of sections of heat-resisting metal plate united at their edges, grooved joiner elements engaging the meeting edges of the sections of the inner wall in a slip-joint that provides for movement of the engaged edges as the recuperator structure expands and contracts under varying temperatures in service, the recuperator structure having partitions traversing the space between the walls to form an inlet air chamber, an outlet air chamber and an intermediate chamber, an air inlet opening into said inlet chamber, an air outlet opening from the outlet chamber, said inner wall comprising a metal duct for the passage of hot waste gases of said furnace, a plurality of flights of metal tubes traversing the line of flow of waste gases through said duct with tubes of certain of said flights having their bores in open communication at one end with said air inlet chamber and at opposite end with said intermediate air chamber, and the tubes of other of said flights having their bores in open communication with said intermediate air chamber and at opposite end with said outlet air chamber.

4. A multiple air pass recuperator for an industrial furnace comprising spaced inner and outer walls formed of sections of heat-resisting metal plate united at their edges, the sections of the outer wall being united in readily disengageable bolted joints, grooved joiner elements engaging the meeting edges of the sections of the inner wall in a slip-joint that provides for movement of the engaged edges as the recuperator structure expands and contracts under varying temperatures in service, the recuperator structure having partitions traversing the space between the walls to form an inlet air chamber, an outlet air chamber and an intermediate chamber, an air inlet opening into said inlet chamber, an air outlet openin g from the outlet chamber, said inner wall comprising a metal duct for the passage of hot waste gases of said furnace, a plurality of flights of metal tubes traversing the line of flow of waste gases through said duct with tubes of the flights spaced apart laterally of one another and longitudinally of the duct, the tubes of certain of said flights having their bores in open communication at one end with said air inlet chamber and at opposite end with said intermediate air chamber, and the tubes of other of said flights having their bores in open communication with said intermediate air chamber and at opposite end with said outlet air chamber.

References Cited in the file of this patent UNITED STATES PATENTS 1,067,689 Spotts July 15, 1913 1,547,986 Whitacre July 28, 1925 1,914,604 Keenan et al June 20, 1933 2,240,203 Armacost Apr. 29, 1941 2,336,879 Mekler Dec. 14, 1943 2,468,903 Villiger May 3, 1949 FOREIGN PATENTS 775 Great Britain Feb. 11, 1911 168,609 Great Britain Sept. 2, 1921 367,026 Great Britain Feb. 15, 1932

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