Liquid heaters and vaporizers – Tube sheets
Reexamination Certificate
2001-10-22
2003-07-15
Lu, Jiping (Department: 3749)
Liquid heaters and vaporizers
Tube sheets
C122S00600B, C122S511000, C122SDIG001
Reexamination Certificate
active
06591790
ABSTRACT:
TECHNICAL FIELD
This invention concerns support fittings for supporting a heat-resistant assembly to protect boiler tubes which is mounted on an array of tubes belonging to a heat exchanger (or boiler) of a heat recovery boiler in a waste incinerator or a thermal power plant. More specifically, it concerns the support fittings for supporting a heat-resistant assembly to protect boiler tubes. The heat-resistant assembly is used on the heating side of the tubes facing the incinerator to protect the array of boiler tubes which constitute the plant's heat exchanger (i.e., boiler). This invention also concerns the array of boiler tubes on which the fittings are used.
TECHNICAL BACKGROUND
FIGS. 4 and 5
show a combined structure of boiler tubes and heat-resistant assembly.
10
is an array of boiler tubes in a heat-recovery boiler. A number of cylindrical tubes which constitute boiler tubes
11
are arranged in parallel. Each two of the cylindrical tubes are fixed in place by the flat rib
12
. In the center of each of the ribs
12
is welded a support fitting
100
, which is oriented vertically.
Support fittings
100
consist of a parallelogram with a vertical surface
100
a
, which is welded to flat rib
12
, and an oblique upper surface
100
b
, which will engage in a heat-resistant catch
19
. Generally, the vertical surface
100
a
is first placed in contact with the flat rib
12
, and then side foot portion
100
c
is welded by hand.
16
is the heat-resistant block. The tube assembly
10
, consisting of the boiler tubes
11
and the flat ribs
12
, must be protected from the heat and corrosive atmosphere of the exhaust gases from combustion. As can be seen in
FIG. 4
, tube assembly
10
is enclosed in such a way that a 180° portion on the bottom of each tube is entirely covered. Each two lead tubes, paired in the axial direction, are protected by a block whose cross section resembles two semicircular tubes joined by a flat rib surface
16
b
. This block extends for a given length along the longitudinal axis of the tubes. The block surrounds boiler tube assembly
10
and is fitted close to but not directly against it, with a specified gap left between the block and the tube assembly.
19
is a heat-resistant catch by which the heat-resistant block
16
is attached through the support fitting
100
to boiler tube assembly
10
in such a way as to be integral with the assembly. It is a rectangular projection from the surface of flat rib
16
b
in the heat-resistant block
16
. To insure that it has sufficient strength in the axial direction, the heat-resistant catch
19
should be no more than one third of the length of heat-resistant block
16
. The catch can be attached to the heat-resistant block in not only one place, but more than two places.
The heat-resistant block
16
and the heat-resistant catch
19
are formed by molding a material like SiC which has relatively good thermal conductivity.
A thin layer of mortar
14
is packed on the inner side of the heat-resistant block
16
and the catch
19
to enhance the cooling effect of the block
16
.
The boiler tube assembly
10
and the heat-resistant block
16
configured as described can be securely joined by means of support fitting
100
and heat-resistant catch
19
. According to the prior art, the support fitting
100
was hand-welded to the flat rib
12
which connects two boiler tubes
11
.
Because there are normally two semicircular boiler tube sections
11
in the location where the two facing surfaces must be hand-welded, the space into which the welding jig must be inserted is very small. In other words, the surfaces of the two boiler tube sections
11
interfere with the welding, making the welding task difficult and extremely time-consuming.
We therefore investigated the possibility of employing the comparatively simple procedure of stud welding instead of the hand welding. However, with both the arc and percussion stud welding, there were problems due to the non-rectangle shape of the support fitting
100
which made stud welding very difficult to perform.
Furthermore, the support fitting
100
does not have a round cross section like the stud bolt used in the prior art, but is tall and thin. It is difficult to achieve either the pressure or the temperature needed to weld it properly. When the long narrow fittings are to be stud-welded, they are frequently arc stud welded using a ferrule. To maintain the temperature for two-surface arc welding, a heat-resistant porcelain ferrule must be put on the end of the stud, and the welding must be executed while the periphery of the stud is covered by the ferrule.
The principle of arc stud welding using a ferrule can be explained simply with reference to FIG.
6
. Ferrule
20
is placed on the end of stud
110
. The end of stud
110
is placed in direct contact with a base metal. When the welder pulls the trigger of the welding electrode, a current flows between the stud
110
and the base metal
112
.
The lifting mechanism
111
of the welding electrode automatically pulls up the stud
110
. Inside the ferrule
20
, an arc
113
is generated between the stud
110
and the base metal
112
as indicated by the arrows. The arc
113
is maintained for a period determined by a timer. The stud
110
and the base metal
112
fuse, and after a given period of time, the stud
110
is pressed against the base metal
112
and the current is cut off.
With this technology, then, a deoxidizing conductive material
115
as flux which is attached to the end of stud
110
by various methods acts on the metals in such a way as to result in a welded portion
114
. The ferrule
20
mainly serves as a mold for the molten metals. When the welding is completed, it is removed as needed by a means such as breaking it.
However, when the support fitting
100
is welded by arc stud welding using a ferrule, the ferrule
20
cannot completely seal the welding surfaces of the materials as shown in FIG.
5
(B), so it cannot serve as a mold.
Since support fitting
100
is to engage with the heat-resistant catch
19
, it must have a stopper on its upper surface. This is why the surface which is to engage with the catch
19
slants upward. When the ferrule
20
is inserted onto the support fitting, as can be seen in FIG.
5
(B), the upper surface of the fitting
100
is not perpendicular to the welding surface of the base metal (i.e., it is not horizontal). The ferrule
20
, will be also oriented obliquely, so that its lower portion is not flush against the welding surface, making it difficult to maintain a uniform temperature.
Because the fitting
100
is long and narrow, it will be extremely difficult to insure that its contact with the base metal at the welding surface is uniform. If the arc is started from the lower end or the upper end where a considerable contact pressure is provided, a lopsided weld may result.
SUMMARY OF THE INVENTION
In view of the problems described above, the objective of this invention is to provide a support fitting for a heat-resistant block to protect boiler tubes which can be easily and reliably stud-welded without losing any of its function as a support fitting.
This invention concerns a support fitting for the heat-resistant block to protect boiler tubes, which protrudes upward at a right angle from the surface of the rib between two boiler tubes. The support fitting is welded on the rib and it has a catch to engage with the heat-resistant block on its end.
The support fitting according to this invention is distinguished by the fact that the welding surface of the support fitting to the rib is shaped narrower, and by the fact that a single globule of a deoxidizing conductive material used as flux is attached to the narrowed welding surface.
With this embodiment of the invention, even though the shape of the support fitting is long and narrow, the fact that its welding surface is narrowed makes it easier to achieve uniform contact with the base metal and increases the contact pressure on the welding surface. And because the deoxidizing conductive material used as f
Ike Minoru
Inoue Keita
Maruyama Ryuta
Yoshida Kenshi
Lu Jiping
Mitsubishi Heavy Industries Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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