US2665120A

US2665120A - Regenerative heat exchanger

Info

Publication number: US2665120A
Application number: US178411A
Authority: US
Inventors: Blomquist Uno Olof
Original assignee: Individual
Current assignee: Individual
Priority date: 1950-08-09
Filing date: 1950-08-09
Publication date: 1954-01-05
Anticipated expiration: 1971-01-05

Description

Jan. 5, 1954 U, o. BLoMQuls'r 2,665,120

REGENERATIVE HEAT EXCHANGER Filed Aug. 9, 1950 ATTORNEY Patented Jan. 5, 1954 UNITE-D lSTIA"1"'ES PATENT REGENERATIVE HEAT .EXCHANGER 'Uno v010i" :'Blomguist, Vasteras, Sweden 7 Claims.

This vinvention relates. to .rotary regenerative airpreheaters in `which arotorenclosed in. ashell is .provided ywith .heat accumulating velements through which ue gasesand air pass `inanalterhating manner. In air :preheaters of .this `type, there prevails a .considerable pressure .difference between the air duct-andthe-gas duct. Inorder to reduce this pressure difference, sealingA members have to be providedbetween the -rotor and the stationarypartsofthe preheater. .'Saidsealing members.usuallycomprisestrips arranged rae dially at the end facesof the rotor and adapted to slide on sector ,plates .which separate the .air side from the gasside, the sealing ,members -further comprising strips arranged circumferentially on the rotor andstrips disposed axially between the rotor and the shell. 'In spite `of various vimprovements, particularly ,of the axially llocated sealing strips, for instance by .making them externally adjustable, it was not possible to reduce the losses due to leakage to reasonable values. The major part of these'lossesjs `a result of .air leaking through the space between the rotor and the shell from theair side to the,gas side of the preheater. On account ofthe 'leakage losses, the power required for the iluergas fan is considerably increased, and cleaning of' the flue gases 'in gas lters and ash separators is rendered more dilicult.

The invention vhas for its object' to "provide means for eliminating, entirely 'or'in part, "leakage from the air side to thegas'jside. The invention is characterized 'by a vdraught'fan connected to the space between the rotor and theshell von the air side of the preheaterat a location upstream from the air discharge port of .the shell for reducingthe pressure prevailing in `said space. The Adraught fan is preferably devisedto reduce the pressure in said space down to the pressure which prevails on the .gas side in the spacebetween the rotor and the shell. Due to :this arrangement, leakage through said space is entirely eliminated. vSince the air .quantity which would leak throughsaid space constitutes the major portion of air leaking between theair side and the gas side, theeinciencyof the preheater isconsiderably increased due to the arrangementaccording tto the invention. The .discharge -conduit of the fan is preferablyconnected to the air duct in front of or lafter the preheaten In the last named alternative, the discharge conduit of the fan may have inserted therein aheat exchanger located in the gas duct. By means of this heat exchanger, the quantity of air Ipassing 'through the fan can tbe lpreheated substantia11yfto-:the

-samei'temperature as .the main air stream.

The invention will now be described morezclearly with referenceito a the two. embodiments thereof .illustratedinmthe annexed drawing. i-'Fig lshows lin .diagrammatic manneran elevation,'.'part1y in section, of4` a preheater embodying -this invention. FigZillustratesthe cooperation betweenia sector Vplate vand -radial sealing strips; and .Figure `3 :iis similarto Figure 1 but'zshowsa slightly modied embodiment of the invention.

`The air preheater illustrated `comprisesiza..rotor 2 fadaptedlto rotate;aboutsa .iveltticalfaxis l, said `rotor Vhaving .a--great number of ,capa-ratively 'thinwalled plates .which may vbe corrugated :as vindicated in Fig. `2. The air :duct is =indicatediat3 :and the direction of flow of air-through said 4ductis indicated by thefarrows '4. .The flue gases pass through the gasduct-S in .an opposite direction, as indicated by thefarrows .6. The airduct and the gas duct lare separated from reach other by meansof. sector-shapedplates 1 and 8, on a'nhousing `,enclosing :the rotor, Vand in .contact with :radially extending sealing strips 9 fand i0, respectively, secured tothe rotor. .-Itisto be understood,

of course, .thatthe vhousing .has axially aligned air .inletand outlet Iports with which the `inlet= and Outlet portionslof theair duct 3 communicate; and gas inlet andoutletfports likewise communicatingwith the gas inlet and outlet'portions of the fgasduct `ii. Therotor further has vcircumferentiallyextending sealingstrips H andaxially extendingsealingstrips, not shown, between the periphery ,of .the-rotor and .-a shell 1.2.-whichsurrounds therotor andconstitutes part of the rotor housing. Thatportion of the rotor .which during the .rotation of the rotor is. passed by :Huid gases, accumulates heatfrom the gases andupon-.continued rotation transfers'heat to the air vpassing in a counteriiow direction through the -air duct. As willappear from Fig. 2, the sector plate .1 extends substantially diametrically Aover the end face .of the rotor. 'The angular distance between consecutive sealing strips '9 is somewhat smaller than 'the sector angle of the plate '1. IConsequently, at any time, atleast one sealing strip'9 will slide on'the plate T on either sides ofthe axisof rotation so as to act as a sealing member'between the air side vandthe gas side of thepreheater. Before a sealing strip comes out'of engagement with the platel, the next following sealing striphas already engaged thejplate. 'Betweenthetwo sealing"strips,-the plate 1 and-the endfaceof the-rotor, 4there is temporarily -formed'a vclosedY space, and the air quantity enclosed in said space Lis 4conveyed to the gas side. Similar conditions prevail at the lower face of the rotor where closed spaces are formed between the plate 8 and the sealing strips I0.

In the operation of the air preheater, the pressure prevailing in the inlet part of the air duct may amount to, for instance, +3 inches of water, in the outlet portion of the air duct after the preheater to +1", in the gas duct before the preheater to -1.5", after the preheater to -4, in the space I3 between the rotor and the shell on the air side to -3/4 and in the corresponding space I4 on the gas side to 1.5". On account of the pressure difference between the spaces I3 and I4, which difference according to the example amounts to .75" of water, part of the air will ilow over to the gas side along the periphery of the rotor. The leakage losses resulting therefrom can be entirely eliminated by reducing the pressure prevailing in the space I3 substantially to the pressure prevailing in the space I4 so as to stop the flow from the air side to the gas side.

To this end, the space I3 is by means of a conduit I5 connected to a draught fan I6 which maintains the pressure in the space I3 at substantially the same value as the pressure prevailing in the space I4 on the gas side. As indicated in Figure 3, the air quantity withdrawn from the space I3 may be returned to the inlet portion of the air duct 3 by a conduit I'I. However, it is deemed more suitable to discharge said air quantity to the outlet portion of the air duct, as indicated in Figure 1. In order to avoid a decrease in temperature of the main air stream by the air quantity withdrawn by the fan, said air quantity may be supplied, through a conduit i3, to a heat exchanger 20 provided in the gas duct 5. 1n this heat exchanger, the air quantity withdrawn by the fan can be heated to substantially the saine temperature as the main air stream and is then united with the main air stream by means of a conduit 2I opening into the air discharge portion of the air duct.

As a result of the arrangements described, the volume flowing through the gas duct after the preheater is reduced by the quantity of air which otherwise would leak from the space I3 to the space I4. The practical importance of this advantage will be evident from the fact that said air quantity may amount up to 15% of the total air quantity. Consequently, the power required for the ilue gas fan will be materially reduced, and the devices for cleaning the nue gases can be made in a more simple manner. The power required for the fan I6 is compensated for by a corresponding reduction of the power required for the fan for the main air stream.

It may be suitable to provide additional sealing means between the rotor and the shell I2 along a plane at right angles to the plane of Fig. 1 and through the axis of rotation I. For instance, such sealing means may consist of two sealing strips located on opposite sides of the axis of rotation for separating the air side from the gas side and reducing the power required for the fan I6.

As indicated by

conduits

22 and 23 of Figure 1, the suction conduit I5 of the fan may also be connected to the spaces between the sector plates 'I, 8 and the cooperating sealing strips 9, I0 so as entirely or in part to eliminate the quantity conveyed through said spaces from the air side to the gas side.

What I claim is:

1. An air preheater of the regenerative type comprising a rotor with a number of axial passages therethrough provided with heat accumulati-ng elements and rotatable in a housing the interior of which has an air side and a hot gas side, said housing having axially aligned air inlet and outlet ports at its air side and axially aligned hot gas inlet and outlet ports at its hot gas side, and said rotor being rotatable about an axis intermediate and parallel to those of the air and hot gas ports of the housing to carry said elements successively through the hot gas and the air sides of the housing, said rotor having a side wall cooperating with the adjacent wall of the housing to dene a circumferential space around the rotor, said rotor at the ends of its passages, being imperfectly sealed from said space so that air and hot gas from the rotor passages may enter said circumferential space at the air side and the hot gas side of the housing, respectively, at a pressure diierential which promotes their intermingling, said preheater being characterized by: a suction fan communicated with said space at the air side of the housing for withdrawing air from the space at the air side of the housing at a rate such as to maintain the pressure of the air therein substantially equal to the pressure of the hot gases in the space at the hot gas side of the housing, irrespective of the hot gas and air pressures which obtain in the rotor passages.

2. In an air preheater of the regenerative type comprising a rotor with a number of axial passages therethrough provided with heat accumulating elements, and a housing in which the rotor is rotatable and the interior of which has an air side at one side of the rotor axis, with air inlet and outlet ports aligned on an axis parallel to that of the rotor, and a hot gas side at the opposite side of the rotor axis with hot gas inlet and outlet ports aligned on an axis parallel to that of the rotor, said rotor also having a circumferential wall cooperating with the housing to define a circumferential space around the rotor whichvspace, at the hot gas and air sides of the housing, receives hot gas and air, respectively, from the rotor passages due to imperfect seals at the ends of the rotor passages, means for precluding intermingling of such hot gas and air in said space which results from the air therein having a greater pressure than that of the hot gas, said means comprising: a suction conduit connected to the housing in communication with the air side of said space; and a suction fan in said conduit for withdrawing air from said space at a rate such as to maintain the pressure of the air therein substantially equal to the pressure of the .hot gases in the hot gas side of Said space, irrespective of the hot gas and air pressures which obtain in the rotor passages.

3. The air preheater of claim 2, further characterized by an air outlet duct communicated with said air outlet port; and further characterized by duct means communicating said conduit with said air outlet duct for passing the air withdrawn from said space into said air outlet duct.

4. The air preheater of claim 3, further characterized by a heat exchanger in said duct means for heating the air withdrawn from said space before the same is fed into said outlet duct.

5. The air preheater of claim 4, further characterized by a hot gas outlet duct communicated with said hot gas outlet port; and further characterized by the fact that said heat exchanger is located in said hot gas outlet duct, so that air withdrawn from said space is passed in heat exchange relationship with hot gas which has emerged from the air preheater, and is thereby preheated before being fed to said air outlet duct.

6. The air preheater of claim 2, further characterized by an air inlet duct communicated with said air inlet port; and further characterized by duct means communicating said conduit With said air inlet duct for conducting air withdrawn from said space back into said air inlet duct.

7. In a rotary air preheater of the regenerative type comprising a rotor with a number of axial passages therethrough provided with heat accumulating elements, and a housing in which the rotor is rotatable and the interior of which has an air side at one side of the rotor axis, With air inlet and outlet ports aligned on an axis parallel to that of the rotor, and a hot gas side at the opposite side of the rotor axis with hot gas inlet and outlet ports aligned on an axis parallel to that of the rotor, said rotor also having a circumferential Wall cooperating with the housing to dene a circumferential .space around the rotor, and said housing having sector-like end plates extending substantially diametrically across the end faces of the rotor, defining an intermediate zone in the housing and cooperable with radially extending sealing members on the end faces of the rotor to temporarily form closed compartments in the rotor as each rotor passage is carried through said intermediate zone during rotor rotation and in which compartments air is carried from the air side of the housing to the hot gas side thereof; means for t precluding intermingling of hot gas and air which respectively occupy the hot gas and air sides of said circumferential space around the rotor and which are received into said space from the rotor passages due to imperfect seals at the ends of the rotor, said means comprising a suction conduit connected with the housing and communicated with the air side of said space, and a suction fan in said conduit for Withdrawing air from the air side of said space at a rate such as to maintain the pressure of the air therein substantially equal to the pressure of the hot gases in the hot gas side of said space; and means for substantially preventing air in said compartments carried from the hot gas side of the housing through the intermediate zone from being transferred to the hot gas outlet port of said housing, said means comprising a second suction conduit connected with one of said sector-like end plates and communicated with said intermediate zone in the housing and with said rst named suction conduit, at the suction side of said fan, for withdrawing air from each of said closed compartments as the compartment moves through said intermediate zone during rotor rotation.

UNO OLOF BLOMQUIST.

References Cited in the le 0f this patent UNITED STATES PATENTS Number Name Date 2,229,691 Boestad Jan. 28, 1941 2,468,826 Karlsson et al. May 3, 1949 2,471,995 Yerrick et al May 31, 1949 FOREIGN PATENTS Number Country Date 106,546 Australia May 25, 1927