Seal assembly in rotary regenerative heat exchanger

A seal assembly for providing seal between an end face of a cylindrical and rotatable heat-transferring member and an opposite surface of a stationary member of the heat exchanger, having a loop-shaped and cross-sectionally rectangular seal member of a heat-resistant and rigid material, a loop-shaped groove formed in the surface of the stationary member to loosely receive the seal member, a loop-shaped back-up member of a resilient material tightly received in the bottom of the groove such that the seal member is sandwiched with a compressive force between the back-up member and the end face of the heat-transferring member, and a loop-shaped auxiliary seal member of a resilient material arranged to provide seal between the outer surface of the seal member and the outer wall of the groove and press the seal member against the inner wall of the groove.

This invention relates to a rotary regenerative heat exchanger, and more 
particularly to a seal assembly for providing seal between a rotatable 
heat-transferring member and a stationary block member of the heat 
exchanger. 
A rotary regenerative heat exchanger for accomplishing heat exchange 
between two fluids, which are usually at different pressures as 
exemplified by a combustion gas and compressed air in a gas turbine, has a 
heat-transferring member which is rotatable and moves alternately through 
the two fluids. The heat exchanger has some seal assemblies to provide 
seal between the rotating heat-transferring member and a stationary member 
forming therein fluid passages for the respective fluids and prevent any 
leakage of the highly pressurized fluid into the other fluid in a heat 
exchange section of the apparatus. A seal assembly for this purpose 
includes a seal member which is made of a heat-resistant and rigid 
material and a back-up member of a resilient material which forces the 
seal member to be kept in contact with an end face of the 
heat-transferring member with an adequate compressive force. 
Conventional seal assemblies for this purpose involve some problems. 
Firstly, the back-up member tends to deteriorate and gradually lose its 
resilient property by the influences of the fluids subjected to heat 
exchange. Besides, the back-up member and the seal member are liable to 
lean in a certain direction with respect to the contact surface between 
the heat-transferring member by the effect of a pressure difference 
between the two fluids, so that the seal member suffers from a local and 
noticeable wear. These problems will be explained hereinafter more 
practically.

Referring to FIG. 1, a rotary regenerative heat exchanger has two fluid 
passages: a first fluid passage 10 for passing a relatively cold fluid 
such as compressed air indicated at A and a second fluid passage 12 for 
passing a heated fluid such as a combustion gas B which is usually at a 
lower pressure than the cold fluid A. These fluid passages 10 and 12 are 
generally isolated from one another by a stationary block member 14, but a 
partition wall of the block member 14 is cut to form a wide chamber which 
spreads over the two fluid passages 10 and 12 for the installation of a 
cylindrical and rotatable heat-transferring member 16 in this chamber. The 
heat-transferring member 16 revolves on its longitudinal axis 18 and moves 
alternately through the first and second fluid passages 10 and 12. 
Therefore, loop-shaped seal members 20 and 20' are secured to the end 
walls of the cylindrical chamber so as to be in slide contact respectively 
with the front and back end faces of the heat-transferring member 16 as 
seen in FIGS. 1 and 2. The function of the heat-transferring member 16, 
which is usually made of metal plates in spaced layers, will need no 
explanation. Since there is a pressure difference between the cold fluid A 
and the heated fluid B, a certain pressure balance measure is needed to 
allow the heat-transferring member 16 to revolve smoothly. Therefore, the 
pressurized and cold fluid A is introduced into a peripheral region of the 
cylindrical chamber so that the fluid pressure of this fluid A may be 
applied to the side surface of the heat-transferring member 16 in radial 
directions uniformly over the entire area. As a result, the outer surface 
of each seal member 20 or 20' is exposed to the pressurized fluid A and 
the inner surface is exposed to the heated fluid B. 
FIG. 3 shows the construction of a conventional seal assembly in the rotary 
regenerative heat exchanger of FIG. 1. The block member 14 has a surface 
14a as an end wall of the aforementioned cylindrical chamber. An end face 
16a of the cylindrical heat-transferring member 16 is partly opposite to 
and spaced from this surface 14a. The loop-shaped seal member 20 is 
fundamentally made from a heat-resistant material such as carbon and has a 
flat surface 20a over the entire length to be kept in slide contact with 
the end face 16a of the heat-transferring member 16. The seal member 20 is 
secured to a loop-shaped back-up member 24, which is made of a resilient 
and adequately heat-resistant material such as silicone rubber, such that 
a portion of the back-up member 24 over the entire length is inserted 
between the wall 14a and a surface 20b (reverse of the contact surfaces 
20a) of the seal member 20 and pressed against the wall 14a. 
A projection 26 is formed on the wall 14a along the inner surface of the 
back-up member 24 to prevent the back-up member 24 and the seal member 20 
from being moved or deformed by the fluid pressure acting on the outer 
surfaces of the back-up member 24 and the seal member 20. The function of 
the seal assembly of FIG. 3 is satisfactory so long as the seal member 20 
and the back-up member 24 remain in the illustrated state. Since the end 
face 16a of the heat-transferring member 16 slides over the surface 20a of 
the seal member 20 which is pressed against the end face 16a, the seal 
member 20 serves as a lubricant when made of carbon and exhibits a good 
antiwear property. 
One of the disadvantages of this seal assembly is exposure of the back-up 
member 24 to a high temperature atmospheres. An inner portion 24a of the 
back-up member 24 is exposed to the heated fluid B of which temperature is 
usually about 300.degree. C when the heated fluid B is a combustion gas, 
so that the back-up member 24 is liable to be damaged by heat and/or 
chemical erosion. An outer portion 24b of the back-up member 24 is exposed 
to the "cold" fluid A, but the cold fluid A becomes a heated fluid upon 
contact with the revolving heat-transferring member 16. When the cold 
fluid A is compressed air, a temperature of about 200.degree. C is 
realized easily. The heating and/or erosion by the fluids results in that 
the back-up member 24 loses its resilience and cannot press the seal 
member 20 against the end face 16a of the heat-transferring member 16 with 
a satisfactorily large and uniformly distributed compressive force. 
Apart from high temperatures of the fluids, there is a pressure difference 
by about 3 kg/cm.sup.2, for example, between the compressed air and the 
combustion gas whereas the back-up member 24 is supported by the block 
member 14 only partly and unsymmetrically. When the back-up member 24 is 
pressed against the projection 26 due to the pressure difference, the 
back-up member 24 exhibits a certain deformation in a region adjacent the 
inner surface and is detached from the wall 14a in another region adjacent 
the outer surface as shown in FIG. 4. Then the surface 20a of the seal 
member 20 cannot be kept in contact with the end face 16a of the 
heat-transferring member 16 over the entire area of the surface 20a. As 
seen in FIG. 4, the surface 20a is detached from the end face 16a in an 
inner region but is pressed with an extremely strong force against the end 
face 16a in an outer region: the contact between the heat-transferring 
member 16 and the seal member 20 is established only over a very small 
area. Consequently both the heat-transferring member 16 and the seal 
member 20 are worn out noticeably in the thus limited and localized 
contact area. 
In regard to a rotary regenerative heat exchanger, it is an object of the 
present invention to obviate these drawbacks of conventional seal 
assemblies. 
It is another object of the invention to provide an improved seal assembly 
in association with a rotatable heat-transferring member of the heat 
exchanger in which a slide contact between the heat-transferring member 
and a seal member is maintained uniformly with a constant compressive 
force over a constant area even when the seal assembly is used for 
separating two different fluid pressures and a resilient back-up member is 
prevented from exposure to heated and/or pressurized fluids. 
In a rotary regenerative heat exchanger having a heat-transferring member 
which is cylindrical and rotatable on its longitudinal axis and a 
stationary block member having a surface opposite to and spaced from an 
end face of the heat-transferring member, a seal assembly according to the 
invention comprises: (a) a loop-shaped seal member of a heat-resistant and 
substantially rigid material having an outer surface, an inner surface, a 
flat front surface stretched between the outer and inner surfaces and a 
back surface; (b) a loop-shaped groove formed in the aforementioned 
surface of the block member to have a width larger than the width of the 
seal member; and (c) a loop-shaped back-up member of a resilient material 
tightly received in the groove such that the front surface and the back 
surface of the seal member are kept in contact with the end face of the 
heat-transferring member and the back-up member, respectively. The back-up 
member is sandwiched with a compressive force between the back surface of 
the seal member and the bottom of the groove when the front surface of the 
seal member is in contact with the end face of the heat-transferring 
member. The seal assembly further comprises (d) a loop-shaped auxiliary 
seal member of a resilient material arranged in the groove to provide seal 
between the outer wall of the groove and the outer surface of the seal 
member and keep the inner surface of the seal member in contact with the 
inner wall of the groove with a compressive force. 
Preferably, the back-up member and/or the groove are shaped such that a 
loop-shaped space is formed in the groove partly defined by the inner wall 
of the groove and an inner extreme region of the back surface of the seal 
member so that an inner corner portion of the back-up member may not be 
pinched between the inner wall and the seal member. 
Other features and advantages of the invention will become apparent from 
the following detailed description of preferred embodiments with reference 
to the accompanying drawings. 
A seal assembly according to the invention is used at the same places in 
the heat exchanger as the conventional seal assembly described 
hereinbefore with reference to FIGS. 1-3. In a first embodiment of the 
invention shown in FIG. 5, a seal member 30 is formed as a loop like the 
seal member 20 of FIG. 20 and has a rectangular cross section. This seal 
member 30 is made of a usual material comprising porous carbon as a 
fundamental component. Two parallel sides 31 and 32 of the rectangle are 
given respectively by outer and inner side surfaces of the loop-shaped 
seal member 30, and one (33) of the remaining two parallel sides 33 and 34 
is given by a front surface to be kept in contact with the end face 16a of 
the heat-transferring member 16. A groove 40 is formed in the surface 14a 
of the block member 14 to have the same loop-shape as the seal member 30 
and a rectangular cross section. The width of the groove 40, i.e., the 
distance between outer and inner walls 41 and 42, is slightly larger than 
the width of the seal member 30, i.e., the distance between the outer and 
inner surfaces 31 and 32. A resilient back-up member 50, which also has 
the same loop-shape as the seal member 30 and a rectangular cross section, 
is tightly received in the groove 40 so that a surface 54 of the back-up 
member 50 is pressed against the bottom wall 43 of the groove 40. The 
width of the back-up member 50 is nearly equal to the width of the groove 
40 so that outer and inner surfaces 51 and 52 of the back-up member 50 are 
respectively in intimate contact with the outer and inner walls 41 and 42 
of the groove 40 at least when the back-up member 50 is pressed against 
the bottom wall 43. The depth of the groove 40 is larger than the 
thickness of the back-up member 50 but is smaller than the total thickness 
of the seal member 30 and the back-up member 50. The seal member 30 is 
received in the groove 40 such that the back surface 34 is in contact with 
the exposed surface 53 of the back-up member 50. In this state, the front 
surface 33 of the seal member 30 is out of the groove 40 and in contact 
with the end face 16a of the heat-transferring member 16. The seal member 
30 provides an effective seal between the heat-transferring member 16 and 
the block member 14 since the surface 33 of the seal member 30 is always 
pressed against the end face 16a with an adequate compressive force 
resulting from a repulsive action of the compressed back-up member 50. The 
inner surface 32 of the seal member 30 is kept in contact with the inner 
wall 42 of the groove 40, so that a gap 60 is formed between the outer 
surface 31 of the seal member 30 and the outer wall 41. To prevent the 
back-up member 50 from being exposed to the fluid A passing through the 
first fluid passage 10 of FIG. 1, a loop-shaped auxiliary seal member 70 
is installed in this gap 60 to provide seal between the outer surface 31 
and the outer wall 41. A groove 35 may be formed in the outer surface 31 
to secure the auxiliary seal member 70. 
Both the back-up member 50 and the auxiliary seal member 70 are made of a 
resilient and adequately heat-resistant material such as silicone rubber. 
The block member 14, at least in a portion forming therein the groove 40, 
is preferably made of a metal such as aluminum which has a good heat 
conductivity so that the back-up member 50 and the auxiliary seal member 
70 may be relieved from being heated excessively. 
In the embodiment of FIG. 5, the back-up member 50 is cut at a corner 
region between the surfaces 52 and 53 over the entire length, so that a 
space 80 is formed in the seal assembly. This space 80 is partly defined 
by the wall 42 of the groove 40 and the inner surface 32 of the seal 
member 30 and has a far smaller cross-sectional area than the back-up 
member 50. The space 80 is formed for the purpose of preventing the 
occurrence of incomplete sealing between the wall 42 and the inner surface 
32 of the seal member 30 as the result of intrusion of the corner region 
of the back-up member 50 when the back-up member 50 is compressed by the 
seal member 30. 
As seen from the foregoing description, the back-up member 50 is kept 
isolated from the two fluids A and B passing through the heat exchanger. 
Accordingly, the back-up member 50 exhibits little deterioration by heat 
and makes no detachment from the bottom wall 43 of the groove 40 even if 
there is a great pressure difference between the two fluids A and B. In 
addition to the provision of seal between the wall 41 and the outer 
surface 31 of the seal member 30, the auxiliary seal member 70 causes the 
seal member 30 to be in contact with the block member 14 at the inner 
surface 32 and make no lateral movement (viewed in FIG. 5). In other 
words, the seal member 30 which is a practically rigid member is supported 
by the block member 14 which also is a rigid and stationary member against 
a fluid pressure acting on the surface 31. The seal member 30, therefore, 
does not lean inwards to cause a decrease in the contact area between the 
surface 33 and the end face 16a of the heat-transferring member 16 even 
though the outer surface 31 of the seal member 30 is partly exposed to the 
pressurized fluid A. Even if the pressurized fluid A leaks into the space 
between the auxiliary seal member 70 and the back-up member 50, neither 
the back-up member 50 nor the seal member 30 cannot easily lean to any 
direction to cause an ununiform contact between the seal member 30 and the 
heat-transferring member 16. If the contact surface between the surface 34 
of the seal member 30 and the surface 53 of the back-up member 50 is 
forced to let in the leaked fluid A, the intruded fluid A will not remain 
in the groove 40 and cause leaning of the seal member 30, but will flow 
out of the groove 40 through the contact surface between the two surfaces 
32 and 42 of the two rigid members 30 and 14. 
Thus, the back-up member 50 in a seal assembly according to the invention 
is protected against deterioration by heat and erosion resulting from 
exposure to a reactive fluid such as a combustion gas and accordingly can 
exert an adequate compressive force on the seal member 30 for a prolonged 
period of time. Any leaning of the seal member 30 with respect to the end 
face 16a of the heat-transferring member 16 is precluded, so that the seal 
member 30 can provide a constant contact area with an almost constant 
compressive force without exhibiting any ununiform wear. 
The seal member 30 of the seal assembly according to the invention is not 
fundamentally different from the seal member 20 in the conventional seal 
assembly as described hereinbefore. It is necessary, however, that the 
inner surface 32 of the seal member 30 can be brought into intimate 
contact with the inner wall 42 of the groove 40 in the seal assembly of 
the invention. Since the seal member 30 is made of a practically rigid 
material, it is difficult to realize an intimate contact between the seal 
member 30 and the wall 42 over the entire length if the seal member 
consists of a single member. In practice, the seal member 30 consists of a 
plurality of pieces which may be considered as the result of dividing a 
loop transversally into a plurality of sections. These pieces are shaped 
and sized that the individual pieces can move radially of the loop when 
arranged in a row within the groove 40. The lengths of the dividual pieces 
are determined precisely so that the lateral and narrow gaps between the 
adjacent pieces may practically disappear when the auxiliary seal member 
70 is assembled with these pieces to press them together against the wall 
42. 
FIG. 6 shows a slightly modified embodiment in regard to the space 80 in 
FIG. 1 for preventing the back-up member 50 from being pinched by the wall 
42 and the seal member 30. In the seal assembly of FIG. 6, the back-up 
member 50 is not cut at any corner region but has a slightly smaller width 
than the width of the groove 40. A shoulder 45 is formed at an extremely 
inner region of the bottom wall 43 of the groove 40 so that a space 80A of 
a rectangular cross section is defined by the surface 34 of the seal 
member 30, the inner surface 52 of the back-up member 50, the shoulder 
portion 45 of the wall 43 and the inner wall 42 of the groove 40 over the 
entire length of the loop-shaped groove 40. In other respects, the seal 
assembly of FIG. 6 is identical with the seal assembly of FIG. 5.