Heat exchange – With protector or protective agent
Reexamination Certificate
1999-10-27
2002-07-02
Lazarus, Ira S. (Department: 3743)
Heat exchange
With protector or protective agent
C165S081000, C122S512000
Reexamination Certificate
active
06412548
ABSTRACT:
TECHNICAL FIELD
This invention concerns a heat-resistant assembly for the water tubes of a heat-exchanger in a boiler to protect them from an atmosphere of super-heated gases, as well as a method of assembling this device.
TECHNICAL BACKGROUND
The water tubes which conduct heat in waste-heat boilers are protected from the heat conducted by the combustion gases and from their corrosive atmosphere by a heat-resistant block.
FIGS. 19 through 21
show several examples of heat-resistant assemblies for the water tubes of a waste-heat boiler taken from the prior art.
The design shown in
FIG. 19
was proposed in Japanese Patent Publication (Kokai)
9-184602
. In this drawing,
11
are boiler tubes and
13
are flat ribs to lend strength to tubes
11
by connecting them in either a horizontal or a vertical array. 26 are heat-resistant blocks of a ceramic material which are placed so as to protect the tubes
11
from combustion gases
50
. The tubes
11
are protected from the heat of the combustion exhaust gases and their corrosive atmosphere
50
by these heat-resistant blocks
26
.
23
a
is a bolt for affixing the heat-resistant block
26
onto one of the flat ribs
13
. The bolt
23
a
extends from the flat rib
13
through heat-resistant block
26
. When nut
23
b
is tightened on bolt
23
a
, the heat-resistant block
26
is fastened to tubes
11
and ribs
13
.
20
is mortar which fills the spaces between heat-resistant block
26
and ribs
13
or tubes
11
.
27
is a cap which is placed on top of nut
23
b
in order to protect the top of the bolt
23
a
, the portion of the bolt on which nut
23
b
engages, from combustion gases
50
.
FIGS. 20 and 21
show a design proposed in Japanese Patent Publication (Kokai) 9-236203.
FIG. 20
is a cross section taken orthogonally with respect to the axes of the tubes.
FIG. 21
is a cross section taken along line A—A in FIG.
20
. In
FIGS. 20 and 21
,
11
are the tubes;
13
are the flat ribs which lend strength to the tubes
11
by connecting them;
36
is the heat-resistant block which protects the tubes
11
and ribs
13
from combustion gases
50
; and
20
is the mortar which fills the spaces between the heat-resistant block
36
and ribs
13
or tubes
11
.
38
is an arm which fixes the block
36
to its rib
13
. Arm
38
protrudes from the appropriate portion of the rib
13
. When indented portion
37
engages with the arm
38
, the heat-resistant block
36
is securely attached to tubes
11
and ribs
13
.
Although we do not include drawings, designs for these sorts of heat-resistant assemblies for protecting boiler tubes are proposed in Japanese Utility Patent Publication (Kokai)
1-106706
(Title of invention: Water-cooled Wall) and Japanese Patent Publication (Kokai) 7-225016 (Title of invention: Configuration of Incinerator Walls and Heat-resistant Bricks).
The design proposed in Utility Patent Publication 1106706 features supportive fittings which slant upward on the ribs (or fins) between the tubes and are fixed so that they protrude at specified intervals along the length of the tubes. Indentations are provided on the heat-resistant blocks into which the fittings engage. The spaces between the fittings and indentations are filled with mortar.
In the design proposed in Patent Publication 7-225016, the heat-resistant block (in this case, heat-resistant brick) consists of a number of mantles which have an arc-shaped cross section so that they conform to the contour of the tubes and connective portions which link the mantles. A number of projections are provided on the heat-resistant block at specified intervals along the axes of the tubes so as to maintain the necessary space between the block and the exterior surfaces of the tubes which is to be filled with mortar. Mounting holes are provided in the heat-resistant block into which fittings can be inserted to mount the tubes to the connective portions.
However, the designs described above have the following failings.
In the design proposed in the Patent Publication 9184602, which is shown in
FIG. 19
, bolt
23
a
becomes hot when the boiler is operating and undergoes thermal expansion, causing cap
27
to jut out toward combustion gases
50
and separate from the bolt. This results in both the bolt
23
a
and the nut
23
b being exposed to combustion gases
50
, which are likely to corrode them. If this corrosion continues over time, heat resistant block
26
will be damaged, or it will separate from the tubes.
And because the heat-resistant block
26
is fastened to boiler tubes
11
and rib
13
by bolt
23
a
, which is fixed to rib
13
and immobilized, it is constrained when the bolt
23
a
is tightened. In addition, the thermal expansion differential between tubes
11
and block
26
causes thermal distortion. When this constraint or distortion occurs, the resulting thermal stress and that caused by the temperature differential between the interior and exterior of block
26
will damage the block.
The design proposed in Patent Publication 9-236203, which is pictured in
FIGS. 20 and 21
, has the potential to solve the problems of the prior art shown in FIG.
19
. However, in this device heat-resistant block
36
is supported solely by arm
38
, which protrudes obliquely upward from rib
13
and is forced into indentation
37
in the block. This makes it difficult to securely fasten block
36
to tubes
11
and rib
13
, and the block
36
has a tendency to slip off the tubes.
With the design proposed in Utility Patent publication 1-106706, just as with that in Publication
9-236203
, the heat-resistant block is supported on the tubes solely by a fitting which protrudes obliquely upward from the rib and is engaged in an indentation in the block. This makes it difficult to securely fasten the block to the tubes, and the block has a tendency to become detached.
In the design proposed in Patent Publication 7-225016, just as in that proposed in Publication 9-184602, the end of the fitting which mounts the tubes to the connective portion of the block is exposed to the combustion gases, so it corrodes. If this corrosion is allowed to continue, the block will be damaged or detached from the tubes.
With the prior art designs discussed above, for example that of Patent Publication 9-236203, shown in
FIGS. 20 and 21
, the heat-resistant block
36
must have an obliquely slanted indentation
37
into which arm
38
of tube
11
can engage. If the angle of inclination of this indentation becomes too large, it will be impossible to remove the block from the mold, and it will not be possible to form the block
36
using a press. Also, in order to attach the block securely, the angle of inclination must be very large. However, a large angle requires that a special mold be used, thereby increasing the production time and the cost.
Such a block
36
is manufactured by pouring the raw material into a metal mold. A molded block is inferior to a pressed block with respect to both strength and durability.
Furthermore, in prior art designs, for example in the design in Patent Publication 9-236203, the space between metal arm
38
, which is fixed to tubes
11
, and heat-resistant block
36
is filled with mortar to attach the arm
38
to block
36
.
The temperature of the area between the arm
38
and block
36
which is filled with mortar rises to 250° C. to 500° C. The rate of thermal expansion differs widely between metal arm
38
and mortar
20
. In prior art devices, then, the differential in thermal expansion between the arm
38
and mortar
20
would damage the mortar, which would have an adverse effect on the durability of the heat-resistant assembly.
With the prior art designs discussed above, the mortar for fastening the tube assembly to the heat-resistant block was introduced into the space between the two. When it approached the required thickness, the worker would use a hand tool such as a trowel to finish filling the mortar to the required thickness according to his own intuition. With prior art designs, then, the final thickness of the mortar would vary with the worker. Thi
Ike Minoru
Inoue Keita
Nakagawa Yuji
Terashima Yasuhiro
Duong Tho Van
Lazarus Ira S.
Mitsubishi Heavy Industries Ltd.
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