US1740145A - Air preheater - Google Patents

Description

'Dec. 17, 1929. H. H. BATES 1,7

AIR PREHEATER Filed May 6, 1,926 4 Sheets-Sheet l \LH. Safes WITNESSES: INVENTOR W 1. BY

ATTORNEY Dec. 17, 1929. H; H. BATES 1,740,145

AIR PREHEATER 'Filed May 6, 1926 4 Sheets-Sheet 2 H .H. Bates WITNESSES: INVENTOR ATTORNEY Dec. 17, 1929. H, H, BATES 1,740,145

AIR PREHEATER Filed May 6, 1926 4 Sheets-Sheet 3 Hj'l. Bates WITNESSES: INVENTOR BY CDJZLM ATTORNEY Dec. 17, I929. I H. H. BATES I 1,740,145

AIR PREHEATER Filed May 6, 1926 ,4 Sheets-Sheet 4 rmBateS WITNESSES: INVENTOR M w BY GPPQI AM ATTORNEY Patented Dec.- 17, 1929 a 1,740,145.

UNITED STATES PATENT FOFFICE' HARRY H. BATES, OF RIDLEY PARK, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY,'A CORPORATION OF PENNSYLVANIA AIR PREHEATER Application filed May 6, i926. Serial No. 107,276.

My invention relates to heat transfer apparatus, more particularly to air preheaters for furnaces, and has for an object the provision of apparatus of the character designated which shall be simple of design and eflicient of operation.

More particularly, my invention has for an object to provide an air preheater wherein the escaping gases of combustion are employed as a heating medium and wherein both the gases and the "passages through which the air to be heated flows, have heretofore been proposed.

also been proposed in many forms of heat exchange apparatus to employ the principle of contra-flow as between the heating medium and the medium to be heated. All such prior apparatus,

arran 'ement of battles for reversing the current ow of the heating medium, or the medium to be heated, or caused a considerable amount of eddies to form in the passages with consequent pressure losses in the media passing through said passages. These pressure losses have entailed, in turn, an increase in the power required to set up andmaintain the flow of gases or air through the preheater.

Another serious problem, which has heretofore confronted the designer of air preheaters, has been the difliculty of obtaining the greatest possible amount of heat transfer between the heating gases and the air to be heated while providing unimpeded passages for both of the media. Where baflles or tortuous passages are employed, the passages for the gas soon fill up with soot and the pasair to be preheated have free passages therethrough, unimpeded by bafiles and unobstructed by reduced flow areas.

A still further object of my invention is to provide an air preheater wherein the wellknown advantages of the contra-flow princi- 4 ple in heat exchange apparatus is obtained without impeding the flow of the heating medium or the air. Another object of my invention is to provide an air preheater utilizing waste flue gases as a heating medium and wherein an approximately constant. velocity of gas and air through the preheater is maintained.

' Apparatus embodying features of my invention is illustrated in the accompanying drawings, forming a part of this application,

' wherein: sages for the air to be heated soon become Fig. 1 is a diagrammatic view showing my obstructed with foreign matter drawn into improved air preheater installed with a furthepreheater with the air. Accumulations nace; 1 I of soot and dirt not only-entail serious draft Fig. 2 is a perspective vitw of the prelosses of the heating gases, and of the air to heater; .i be heated, but also impair the efficiency of Fig. 3 is a perspective view of a fragment the preheater as a heat exchange apparatus.

- The beforementioned and other difiiculties are overcome in accordance with my invention by the provision of an air preheater 'formed of a plurality of plane surfaced, spaced plates disposed in parallel relation and forming intervening straight assages. The individual plates are formed wit peaked ends and have one side of their peaks at each end joined to an adjacent plate thereof passages extending of the preheater with air and heating mes dium conduits removed so as to show arrange ment of passages;

- Fig. 4 isa perspective view of one of the preheater-forming members;

. Fig. 5 is a sectional viewtaken along the line VV of Fig. 2; I

Fig. 6 is a diagrammatic view illustrativeof the relative areas of passages and conduits leading thereto; and

Fig. 7 isa view similartoFig. 6 but showing a modified proportional arrangement of conduit and passage areas. gAir .preheaters employing the escaping gases of combustion as a heating medium utilizing-the gases by allowing them to by forming a plurality through the preheater, said passages opening only on one side of a peak. Preferably the plates are so joined that adjacent passages openon opposite sides of the peak at each end of the preheater. A conduit for the heating gases is connected. to one side of a 59 and flow through passages arranged adjacent to It has as known to me, has involved an both, and has thus measured'normal to its longitudinal axis.

By this construction, the area of the entry and exit passages of the heating gases and of the air is not reduced and there is an unimpeded flow of both air and gases through the preheater in service. With the arrangements just described, air may be readily passed through the preheater in a direction counter to the direction of flow of the heating gases, with the resulting well-known advantages of this principle.

Referring now to the drawings for a betterunderstan'ding of my. invention, I show inFig. 1, at 10, a boiler furnace having associated therewith a well-known form of stoker 11. An up-take for the escaping gaseous products of combustion is shown at 12. A1313 I show my improved air preheater, which is placed in series as. to fluid flow with the uptake 12 and through which I the gaseous products of combustion flow in a generally upward direction. Air for the preheateris supplied by a blower 14 which may be of any well-known design and which preferably forces the air to be heated through a duct 16 from whence it flows into the preheater and passes th'erethrough in a generally downward direction and out through a duct 17 to the'furnace 10 in a manner well understood m the art. At 18 is shown a duct for carrying away the gaseous products of 'combustion after passing through the preheater and which is connected to the upper portion of the preheater.

Referring nowto Fig.- 2,'it maybe seen that the preheater is comprised of a body portion having peaked ends and that the ducts 12, 16, 17 and 18 are in communication with the peaked ends by means of hoods- 12', 16', 17 and 18 which are detachably connected to the sides of the respective peaks as shown. d 1

While any suitable cleaning means for the preheater may be employed, I preferably make the body thereof in a. plurality of sections and provide means whereby a section' may be cut out of operation and removed bodily for cleaning while retaining other sections in service. To this end, I provide, in

all the hoods, dampers such as21 and 22 in the hood 16'. and a-dividing member 23 betweenthe dampers 21 and 22. Similar dampers 24 and 26, with a similar d vid g Thus the heatingmember 25, are shown in the hood 12 and 'arealso provided in the hoods 17 and 18 so that it is to be understood that the structural makeup of the hoods 16' and 12', where they jointo the preheater, is representative of the other two hoods.

The two sections of the body of the preheater are held in position by means of angle irons such as shown at 27 and 28, together with a suitable number of screws. as at 29 and 31 which screws enter the body portion of the preheater and hold it firmly to thehoods. As will be understood from the drawing, the hoods, in their juncture with the body portion of the preheater, have triangular shaped ends in cross section as at 35-35 in the drawing.- To better facilitate removability,

these ends are preferably welded to the body of the preheater and the hoods divided along parallel lines drawn through the boundaries of the widest part of the body portion. The

preheater is then held in place with respect to the hoods by means of suitable strap iron members at 33, 34, 36, 37, 39 and 41, said strap iron members being provided on the hoods at the upper and the lower ends of the preheater along the dividing lines thereof, the adjoining strap iron members being bolted together by bolts 42-42 as may be clearly seen from the drawing.

Whenever it is desired-to remove a sec tion of the preheater for cleaning purposes, the screws 29 and 31 and the bolts 42 of the section are removed, the dampers in the respective hoods leading to the particular section of the preheater are closed and the section may then be lifted bodily out of position by means of a ring 43 provided in the top of the preheater section.

Referring now to Figs. 3 and 4, there is shown a fragmentary portion of the preheat er body illustrating the arrangement of the passages therein and a plate element which goes into the make-up of the preheater body.

Each section of the preheater body is comprised of a plurality of relatively thin sheet metal plates such as illustrated at 46 in Figs. 3 and 4. The plates are of an elongatedhex agonal shape and are arranged in spaced parallel relation so as to formlong straight relatively narrow passages therebetween. Each of the plates 46 comprises a central web portion 46' and'side flange portions 47 and 48, which .flange portions arejoined to the next adjacent plate to close the sides of each of the passages. The joining together may conveniently be accomplished by electric I welding.

At the peaked ends of each of the plates there is provided turned over portions as at 49, 51, 53 and 54. The portions 49 and 54 are preferably turned over in onedirection toward an adjacent cooperating plate and the portions 51 and 53. areturnedpver in the opposite direction. In thus forming the plates,

7 all of the side flange portions 47 and 48 may be turned in the same direction. The turned over portions of the peaks however, are alternately reversed from that shown in Fig.-

4 so that, for example a turned over-portion 56 as shown in Fig. 3, meets a turned over "portion 49 in a small peak toclose the pasportioned as to meet in a line to form an outwardly extending wedge-shaped closure.

By forming the plates in the manner just described, they may be assembled with alternate passages as 57 and 58 opening on one side of a peak of the preheater and closed on the opposite side. Furthermore, the juncture of the plates as 49 and 56 in an'outwardly extending wedge-shaped closure, minimizes to the greatest possible degree the obstruction to flow of gases or air through the preheater. From' the structure described, it will be seen that the heating gases enter the lower end of the preheater from the up-take 12 and hood 12 on one side of a peak and pass through alternate passages in substantially straight lines upwardly through the preheater and out through the hood 18 and duct 18. At the same time, air is forced into the preheater through the duct 16 and hood 16' on one side of the peak at the upper end thereof and flows through alternate passages in substantially straight lines downwardly through the preheater and out through the hood 17' and duct 17. Itwill be apparent that I thus obtain the well-known advantages of the contra-flow principle in heat exchange I hoods 16' and 18,

apparatus and that the method of joining the plates together minimizes to the greatest degree the obstruction to flow of gases and air through the preheater. vBy this means the greatest possible heat exchange efliciency is obtained, together with the minimum of power required to force the air and gases through thepreheater.

The areas of each of the passages through the preheater where it opens into its associated hood should be at least equal to the area of a passage measured normal to the direction of flow therethrough in the body of the preheater. Fol-example, in Fig. 6 the area of the passages in the preheater leading into the measured along the planes indicated at a. and a, is-equal to the area of [a passage extending through the preheater areas of the passages where the hoods 12' and measured along the plane I). Likewise', the

17 join to the lower end of thepreheater, is indicated as a and c' andis equivalent to the area of a passage measured in a plane in the direction of the line (i.

In Fig. 7 I show diagrammatically a modification of my improved preheater wherein the areas of the passages through the preheater, and wherethe preheater joins on to the hoods, is modified in proportion to the increase in volume of the air as it is heated and the decrease in volume of the gases as they give up their heat to the air. In accordance with this modification the area of the passages where they join to the hoods 16' and 18 is, as shown in Fig. 6, at a and a measured across the plane I) and the passages where the preheater joins to the hoods 12 and 17 at the lower end thereof is as 0 and c" vmeasured across the plane d. In this modification, however, the lower end of the passages is made wider so that the general area thereof is greater at the bottom of the preheater than at the top. The air entering through the hood l6 and passing outwardly through the hood 17, is heated and its volume increased, and the area of the passages in the lower end of the preheater is made sufliciently large to compensate for the increased volume of the air. The gases entering through the hood 12' are relatively hot and in their passage through the preheater give up their heat to the air passing in a direction counter thereto so that upon leaving the preheater they have been reduced in volume, in approximately the same proportion .as the volume of the air is increased. The area of the passage at a in the hood 18 is therefore made considerably less than the passage at a in Fig. 7 to compensate for the decrease in volume of the gases as they are cooled in the preheater. By proportioning the areas of the passages in accordance, with the' changing volume of fluids flowingtherethrough, a uniform velocity of heating medium-and air may be maintained through the preheater.

From the foregoing it will'be apparent that I have devised an improved air preheater capable-of the highest efficiency as a heat exchange apparatus and wherein there is a minimum of draft loss and obstruction to flow of air and heating medium. 7

While I have shown my invention in two forms, it will be obvious to those skilled in the art thatit is not so limited, but is susceptible of various other changesand modifications, without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are imposed by the prior art or as are specifically set forth in the appended claims. I What I claim is 1. An air preheater comprising a plurality of plane surfaced, spaced plates forming an elongated body portion having peaked ends with a plurality of passages extending through the body-portion between the plates said passages conforming-in area to the change in volume of theair ,being heated,

means closing all the passages along the sides of the body portion, outwardly extending wedge-shaped means closing alternate pas sages on both sides of each of the peaks so as to provide a structure having alternate passages extending therethrough and open at the ends on one side of the peak only, a conduit for passing a heating medium connected to one side of each of the peaks, and a conduit for the air connected to the other side of eachof the peaks. v

2. An air preheater for a furnace and utilizing'thewaste gaseous products of combustion as a heating medium, comprising a plurality of plates of plane surfaced sheet metal disposed in parallel relation and forming a plurality of passages therebetween, means for passing the gaseous produc'ts of combustion in substantially straight lines through alternate passages between the plates, and means for similarly passing air to be heated in a counter direction through the remaining passages, the passages through the preheater increasing in area in the direction' of flow of the air in proportion to the increased volume of the air as it is heated.

3. In an air preheater for a furnace, a plurality of sections each comprising a series of parallel plates forming passages thereb'etween, means disposed in an acute angular relation with respect to the longitudinal axial plane of the preheater for-closing alternate passages on each side of said plane at each-end of the preheater, the passages closed on one side being" open on the, adjacent side, air ducts connected to opposite ends of the preheater and bridging the sections, means for closing off all the ducts from any one of the sections and means for removably attaching each of the sections to the ducts. I

4. Inan air preheater, an elongated body portion having peaked ends and comprising a plurality of sections, an air conduit connected at each end of the preheater to one. side of a peak, each. of said conduits bridging all of the sections, a heating medium conduit similarly connected at each end of the preheater on the other side of'the eak at each end thereof, means dividing eac of'the conduits into passages each equal in width to the width of a section, a damper in each of the passages effective for closing ofi the flow of air or gas therethrough, and means for detachably connecting the preheater to the conduits along the prolongation of parallel lines drawn through the boundaries of the widest part of the body portion, whereby a section may be removed for cleaning without disturbing the operation ofadjacent sections.

5. In heat exchange apparatus, the combination of a pair of separable sections arranged in si'de-by-side relation, each section comprising a plurality of plate members also arranged in side-by side relationwand having marginal flange portions-extending towards and firmly joined at their free edges with adjacent plate members to provide a plurality of passages, an inlet and an outlet conduit disposed at one end of both of said sections, a second inlet and a second'outlet conduit disposed at the other end of both said sections, the inlet conduit at one end and the outlet conduit at the other end being in communication with alternate passages in said sections,

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