Background of the Invention

The present invention relates to rotary regenerative air preheaters which employ a rotor post for rotation of the rotor and more particularly

to novel rotor post headers for mounting the rotor diaphragms.

A rotary regenerative air preheater transfers sensible heat from

the flue gas leaving a boiler to the entering combustion air through regenerative heat transfer surface in a rotor which turns continuously through the gas and air streams. The rotor, which is packed with the heat transfer surface, has a rotor post which is supported through a

lower bearing at the lower end of the air preheater and guided through a bearing assembly located at the top end for most vertical flow air

preheaters. Some vertical flow air preheaters use a top support bearing

and a lower guide bearing. The rotor is divided into compartments by

a number of radially extending plates referred to as diaphragms.

Generally, the bottom inboard edge of the diaphragms are set on a ledge on the lower rotor post header and an upper diaphragm tongue is pinned

within an annulus in the upper rotor post header.

In a typical rotary regenerative heat exchanger, the hot flue gas and the combustion air enter the rotor shell from opposite ends and pass in opposite directions over the heat exchange material housed

within the rotor. Consequently, the cold air inlet and the cooled gas outlet are at one end of the heat exchanger, referred to as the cold end,

and the hot gas inlet and the heated air outlet are at the opposite end of the heat exchanger, referred to as the hot end. As a result, an axial temperature gradient exists from the hot end of the rotor to the cold end of the rotor. In response to this temperature gradient, the rotor

tends to distort and to assume a shape similar to that of an inverted

dish (commonly referred to as rotor turndown). This distortion causes

the diaphragm tongues to move up their mounting pins, imposing a

tensile stress on the diaphragm tongue, the pin and the flanges on the

upper rotor post header that define the annulus. Consequently, the upper rotor post header comprises a massive structure to provide an

annulus having a sufficient height to allow movement of the diaphragm tongue and flanges having sufficient thickness to withstand the tensile

stress imposed by the rotor distortion. Such a structure is expensive to

manufacture and imposes a large weight burden on the rotor bearing.

Summary of the Invention

The present invention provides an arrangement of means in an air preheater for mounting rotor diaphragms on the rotor post wherein the

mounting means is free to move axially on the rotor post. This reduces the tensile stress on the mounting means, allowing the mass of the mounting means to be reduced.

Brief Description of the Drawings

Figure 1 is a general perspective view of a conventional rotary regenerative air preheater.

Figure 2 is a cross-section view, partly broken away, a prior art

rotor post and rotor diaphragm of the air preheater of Figure 1 .

Figure 3 is an enlarged cross-section view, partly broken away,

of the rotor post, the upper and lower rotor post headers and a rotor

diaphragm in accordance with the present invention.

Figure 4 is an enlarged top plan view of a portion of the upper rotor post header of Figure 3 and portions of a plurality of rotor

diaphragms.

Figure 5 is a cross-section view, partly broken away, of an

alternate embodiment of the diaphragm and lower rotor postheader of Figure 3.

Description of the Preferred Embodiments

Figure 1 of the drawings is a partially cut-away perspective view of a typical bi-sector air preheater 10 showing a housing 12 in which

the rotor 14 is mounted on a drive shaft or post 16 for rotation as indicated by the arrow 18. The housing is divided by means of the flow

impervious sector plates 20, 22 into a flue gas side 24 and an air side

26. Corresponding sector plates are also located on the bottom of the unit. In a trisector air preheater (not shown), the rotor housing is

divided into three sectors by the sector plates and include the flue gas

sector, the primary air sector, and the secondary air sector. The hot

flue gases enter the air preheater 10 through the gas inlet duct 28, flow through the sector where heat is transferred to the heat transfer surface

in the rotor 14 and then exit through gas outlet duct 30. As this hot

heat transfer surface then rotates through the air side 26, the heat is

transferred to the air flowing through the rotor from the air inlet duct connector 32. The heated air stream forms a hot air stream and leaves

the air preheater 10 through the duct connector section 34. Consequently, the cold air inlet and the cooled gas outlet 30 define a

cold end of the heat exchanger and the hot gas inlet 28 and the heated air outlet define a hot end of the heat exchanger.

The rotor 14 is composed of a plurality of sectors 36 with each sector containing a number of basket modules 38 and with each sector

being defined by the diaphragms 40. The basket modules 38 contain the heat exchange surface. The inboard end 42 of the diaphragms 40

are supported on upper and lower rotor post headers 44, 46. When the air preheater 10 is put into service, an axial temperature gradient

develops from the hot end of the rotor 14 to the cold end of the rotor 14 as the preheater progresses from a cold non-operating condition to

a hot operating condition. This axial temperature gradient causes the rotor 14 to distort. As a result, the upper portion 48 of the inboard end

42 of the diaphragms 40 moves axially upward.

As shown in Figure 2, a tongue 50 radially extends from the

upper portion 48 of the inboard end 42 of the diaphragm 40 in

conventional air preheaters. The tongue 50 is received in an annulus 52 in the upper rotor post header 44 and is pinned in place. As the air

preheater 10 progresses from a cold condition to a hot condition on

startup, the resulting deformation causes the tongue 50 to move axially upward on the pin 54. Such movement is opposed by friction between

the tongue 50 and the pin 54, imposing a tensile stress on the

diaphragm tongue 50, the pin 54 and the flanges 56, 58 on the upper

rotor post header 44 that define the annulus 52. Consequently, the upper rotor post header 44 must include sufficient structure to provide an annulus 52 having a height that will allow movement of the

diaphragm tongue 50 and flanges 56, 58 having a thickness sufficient to withstand the tensile stress imposed by the rotor distortion.

In the present invention, the upper rotor post header 60 comprises a floating tensile ring having an interior opening 62 for

receiving the rotor post 16. (Figures 3 and 4) A plurality of circumferentially spaced radially extending slots 64 are disposed in the

outer peripheral portion 66 of the upper rotor post header 60. The outboard portion 68 of each slot 64 defines a gap 72 in the peripheral

surface 73 of the header 60. The inboard portion 70 of each slot 64 defines a pair of shoulders 74, wherein the slot has a T-shape. The upper portion 78 of the inboard end 80 of each diaphragm 76 comprises

a box-shaped lug 82 which is received in the inboard portion of one of

the T-shaped slots 64. The shoulders 84 defined by the lug 82 engage

the shoulders 74 defined by the inboard portion 70 of the slot 64 to prevent radial movement of the diaphragm 76. Each diaphragm 76 has

a notch 86 disposed below the lug 82. The height H of the notch 86

is at least as great as the thickness T of the upper rotor post header 60.

The diaphragm 76 is mounted to the upper rotor post header 60 by inserting the outer peripheral portion 66 of the upper rotor post header

60 into the notch 86, positioning the lug 82 of the diaphragm 76 over the inboard portion 70 of the slot 64 , and lowering the diaphragm 76

such that the lug 82 is disposed in the inboard portion 70 of the slot

64.

During startup, the rotor deformation causes the upper rotor post header 60 to move axially upward on the rotor post 1 6. The radial

force imposed on the upper rotor post header 60 by each diaphragm 76 is offset by the radial force imposed by one or more diaphragms 76 mounted on the opposite side of the upper rotor post header 60. Therefore, the rotor post 1 6 remains substantially centered within the

interior opening 62. As an example, the thickness T of the upper rotor

post header is six (6) inches for a given size and weight rotor. Such a

header has a mass that is approximately fifty to sixty percent (50-60%) less than the mass of a comparable traditional upper header 44 for the same size and weight rotor, has sufficient mechanical strength to

withstand the tensile stress imposed by the diaphragms 76, and may be

smaller in diameter than the traditional upper header 44.

Preferably, the lower rotor post header 88 is mounted to the rotor by a weld 90. The lower segment 92 of the outer peripheral portion 98

of the lower post header 88 radially extends beyond the upper segment

94 of the outer peripheral portion 90 to define a shelf 96. The lower

portion 100 of the inboard end 80 of each diaphragm 76 rests on the shelf 96, whereby the diaphragms 76 are supported by the lower rotor

post header 88. In one embodiment (Figure 5), the upper segment 94' of the outer peripheral portion 98' of the lower post header 88' comprises a plurality of T-shaped slots 102 and the lower portion 100' of the inboard end 80' of each diaphragm 76' defines a box-shaped lug

104' which is received in a slot 102 to lock the diaphragm 76' to the rotor post 1 6. The bottom surface of each lug 104 rests on the shelf

96' of the lower post header 88'.

The relative thermal growth that occurred in the mounting connection of the traditional design between the diaphragms 40 and the upper post header 44 is eliminated by accommodating such growth between the bore of the floating tensile ring 60 and the post 16. The floating tensile ring 60 is centered on the post 16 by controlling the

diameter of the post 1 6 and the opening or bore 62 of the ring 60 while allowing for thermal growth therebetween with no need for

consideration of the actual total weight of the rotor 14 or the individual sectors 36.

The lower support header 88 of the present invention may be designed almost entirely based upon the dead weight of the rotor 14

since the excess axial load over and above the dead weight due to the

relative thermal growth in the upper mounting connection has been

reduced or eliminated. As a result, this excess axial loading on the lower header 88 is reduced by approximately eighty to ninety percent (80-90%). Consequently, for a given size and weight rotor 14, the required mass of the lower post header 88 of the present invention is reduced in excess of fifty percent (50%). In the present invention, the rotor post shell and connecting welds may be designed based on

overturning moment reactions due to air and gas pressure drop through the heat transfer surfaces and radial pressure due to air to gas pressure

differentials.