Refractory tile for open-spaced boiler tubes

A refractory tile adapted for protecting boiler tubes from the corrosive and erosive effects of a hot gas stream comprises an elongated ceramic body covering only that side of a boiler tube upon which the hot gas impinges. The tile is hung on the tube with a threaded stud anchored on the tube and a nut threaded on the stud, urging the tile against the tube.

This invention is in the field of refractory shield materials, especially 
ceramic refractories for protecting water-containing boiler tubing from 
the corrosive and erosive effects of a hot gas stream in a furnace. 
BACKGROUND 
It is standard practice to protect the water or steam-carrying boiler tubes 
in a commercial furnace with refractory materials. In many cases such 
boiler tubing is disposed in closely spaced arrays, and these arrays can 
be protected with a substantially monolithic wall of refractory tile. 
Bailey, U.S. Pat. No. 1,719,642, discloses tile for use in such an array of 
closely spaced tubing Metal-backed, ceramic-faced tiles are hung from 
bolts anchored between the tubes. The tubing array is covered with a 
substantially monolithic wall of tile completely encircling the tubing. 
Lawson, U.S. Pat. No. 3,797,416, describes boiler tube protection for 
powdered coal-fired boilers. A substantially monolithic protective wall 
with tongue and groove connections between the protective parts completely 
encircles the tubing. 
Graham, et al., U.S. Pat. No. 3,828,735, discloses a substantially 
monolithic wall of tile to protect a closely-spaced boiler tube array. The 
tiles are hung from T-shaped anchors between the tubes. 
Fournier, et al., U.S. Pat. No. 4,809,645, discloses a closely-spaced 
boiler tube array covered with a substantially monolithic wall of 
individual refractory tiles held against the tubing by means of fins 
projecting from the tubing. 
Aiken, et al., U.S. Pat. No. 5,243,801, describes a substantially 
monolithic refractory tile wall to be hung on a closely-spaced array of 
boiler tubing by means of T-shaped anchors affixed between the tubes. 
Whereas closely spaced boiler tubes in a furnace can be protected 
economically with a substantially monolithic wall of refractory tile, when 
the boiler tubes are spaced a greater distance apart it may not be 
economically feasible to provide a complete wall of protection. Rather, it 
may be more desirable to protect each water tube individually. This 
situation arises in several different contexts. 
For example, Guskea, U.S. Pat. No. 3,914,100, describes protective ceramic 
tile for spaced apart water tubes in a steel mill reheat furnace. A pair 
of hollowed ceramic tiles interlock along their longitudinal edges to 
completely encircle the tubing. 
Also, Errington, U.S. Pat. No. 4,071,311, discloses refractory sheathing 
for horizontal water pipes in a steel mill reheat furnace; the sheathing 
consists of two layers which completely surround the tubing, a fibrous 
layer overlaid with refractory tile. 
Finally, Green, et al., U.S. Pat. No. 4,682,568, describes ceramic tile for 
protecting individual spaced superheater tubes. The shielding includes two 
interlocking semicylindrical refractory shapes which completely encircle 
the steam tube. The interlock between the halves of the tile requires that 
they be slid together about the tube by relative motion parallel to the 
tubing and, thus, that the tubing be accessible from all sides for initial 
installation or replacement. These conditions cannot always be met. To 
replace a single cracked or otherwise damaged tile, many of the tile on 
the tube must be removed to slide the damaged piece off. 
SUMMARY OF THE INVENTION 
This invention is directed to the spaced apart array of steam tubes found 
in the superheater section of a furnace. The invention is especially 
useful in a mass-fired municipal-refuse incinerator. Under the operating 
conditions found in such facilities, the overhead superheater section of 
the furnace is subjected to a high velocity hot air stream which contains 
both particulate and gaseous components that rapidly corrode and erode the 
steam tubing. Because of the desirability of efficient heat transfer from 
the hot gas to the tubing and because of the relatively wide spacing of 
the tubing perpendicular to the gas stream, it is not economically 
feasible to protect the superheater tubing with a complete refractory tile 
wall. 
Thus, it is one object of this invention to provide refractory tile adapted 
for protecting open-spaced boiler tubing against corrosion/erosion. It is 
another objective of this invention to provide refractory tile which are 
readily installed, removed from the tubing, and replaced. It is yet 
another objective of this invention to provide refractory tile which are 
light in weight and economical to use. 
In attaining these objectives it has been found that, contrary to the 
teachings of the prior art, refractory tile of this invention are 
effective in protecting the tubing even though only that side of the 
tubing facing the hot gas stream is covered. As a consequence, not only is 
the heat transfer from the hot gas to the tubing enhanced, the overall 
cost of protecting the superheater is reduced, because less ceramic 
material is required. Furthermore, the protective tile is lighter in 
weight than the tile of the prior art and so does not require as much 
reinforcement of the tubing to support the tile. 
Accordingly, the refractory tile of this invention includes a ceramic body 
elongated along the tubing and having a front face directed toward the hot 
gas stream and a back face contoured to contact no more than about 
one-half the tubing surface. A ceramic shield, which can be a part of the 
ceramic body or a separately molded article, projects from the front face 
of the ceramic body toward the incoming gas stream. 
A cavity is provided in the ceramic body and shield extending from the back 
face of the ceramic body through the front face of the shield. The cavity 
is elongated at the back face and enlarged toward the front face of the 
shield in a step. Tiles are hung on the tubing from threaded studs 
anchored thereon by fitting the tile to the tubing, passing the stud into 
the cavity and threading a nut onto the stud. Contact between the nut and 
the shoulder created by the step-wise enlargement of the cavity urges the 
tile against the tubing. 
In a preferred embodiment, a ceramic plug is fitted to the cavity at the 
front face of the shield, providing enhanced protection to the anchoring 
mechanism. 
The manner and means by which the refractory tile of this invention can be 
made and used will be clarified by reference to the drawings which 
accompany this specification and to the Detailed Description which 
follows.

DETAILED DESCRIPTION 
With reference now to the Figures, boiler tube 20 carries protective tile 
30, which is hung on one side of the tube. Tile 30 includes ceramic body 
38 and shield 33. In an especially useful application, tube 20 will be a 
steam tube in the superheater section of a mass-fired municipal-waste 
incinerator, and the tile will be hung on that side of the tube facing the 
hot gas stream. In this application the hot gas stream will impinge upon 
front face 32 of the tile. In general, another tile 30 will be hung on the 
adjacent section of the same tube, as shown in FIG. 4. 
The joints between adjacent tiles can be of several different types, and 
the utility of the invention is not very dependent upon the type of joint 
selected. For example, butt to butt joints, optionally with refractory 
cement between the tiles, can be employed, as can other variations. 
Another type of joint, a shiplap joint, is illustrated in the Figures and 
is preferred. As most clearly shown in FIG. 5, in a shiplap joint, the 
butt end 31 of one tile is held beneath collar 40 of the adjacent tile. 
Front face 32 of the tile carries shield 33, which can be an integral part 
of the tile, or it can be produced separately and joined to ceramic body 
38 at the time the tile is affixed to the tubing. With reference now to 
FIGS. 2 and 3, it will be observed the back face 37 of tile 30 contacts no 
more than about one-half the boiler tube surface, i.e., the tile touches 
no more than about one-half the tubing circumference. The remainder of the 
tube, that portion opposite the impinging hot gas stream, is open. Thus, 
expensive refractory material is conserved, and the weight and cost of the 
tile are reduced correspondingly. 
Cavity 34 is provided, beginning with entrance 41 and extending from the 
back face 37 of the ceramic body 38 through the front face of shield 33. 
The cavity is enlarged stepwise toward the front face of the shield, 
producing shoulder 39. The cavity can be molded into the ceramic body and 
shield at the time of manufacture. The longitudinal elongation of entrance 
41 permits some longitudinal adjustability of the tile with respect to the 
means for anchoring the tile on tube 20 and provides for thermal 
expansion. 
Cavity 34 is sized back to front to pass threaded stud 21. Stud 21 can be 
made of stainless steel and can be anchored to boiler tube 20 by welding 
or other appropriate means. Tile can be affixed to the tube by first 
fitting the tile to the tubing by passing the stud into cavity 34 through 
entrance 41 and then threading a nut 22 onto the stud to press against 
shoulder 39, thereby urging the tile against the tube. If the ceramic body 
and the shield are separate articles, the shield will be placed against 
the ceramic body and the stud passed through the combination. When applied 
to the stud, the nut will hold the articles together. 
Although not a requirement, it may be desirable and so is preferred that a 
ceramic plug 35, sized to closely occupy and seal the cavity at the front 
face of the shield, be inserted. Refractory cement 36 can optionally be 
employed to enhance the seal, thereby protecting the tile attachment means 
from corrosion. It will be evident that this added protection ensures that 
the tile can be readily removed from the tube, if desired, and replaced. 
The tile of this invention can be produced from any of a number of 
different ceramic materials which are available in commerce. For example, 
a very satisfactory tile can be produced from REFRAX.RTM. 20 silicon 
nitride-bonded silicon carbide, which is available from The Carborundum 
Company, Niagara Falls, N.Y. 
It is not intended that the invention be confined to that specifically 
exemplified in this specification; the scope of the invention is limited 
only by the following claims.