Fluidized bed hearth floor

A fluidized bed hearth floor comprises a supporting metal sheet provided with fluidization-gas injection nozzles. The supporting sheet is made of refractory metal, and is covered with a plurality of flat elements made of refractory metal, each flat element being fixed to the supporting sheet by welding in a localized zone, e.g., substantially at a point.

FIELD OF THE INVENTION 
The present invention relates to a fluidized bed hearth floor. 
More precisely, it concerns a fluidized bed hearth floor comprising a 
supporting metal sheet provided with through fluidization-gas injection 
nozzles and coated with a coating of refractory material. 
BACKGROUND OF THE INVENTION 
In this zone of the hearth, the fluidized solids subject the coating to 
high levels of stress by erosion because of the high speeds imparted to 
them by the fluidization gas being ejected. Moreover, because of the large 
temperature differences between the inside of the hearth and the 
fluidization gas at the outputs of the injection nozzles via which the gas 
is injected, this zone of the hearth is subjected to high levels of 
thermal stress. 
It is known that the supporting sheet can be protected by a layer of 
refractory material of the refractory concrete type. 
Such a layer must be very thick, i.e. greater than 100 mm. That thickness 
increases both the total height of the furnace, and also the lengths of 
the feed means for feeding the fluidization nozzles. 
Such a layer is also subjected to continuous wear and tear which makes it 
necessary for periodic repair work to be performed. At floor level in the 
hearth, the concentration of solids is very high, i.e. in the approximate 
range 500 kg/m.sup.3 to 1,200 kg/m.sup.3. 
Furthermore, with wear, chips of the layer come away and mix in with 
fluidized combustion solids, thereby disturbing fluidization. 
OBJECTS AND SUMMARY OF THE INVENTION 
The present invention solves those problems by providing that the 
supporting sheet is made of refractory metal, and the coating is made up 
of a plurality of flat elements made of refractory metal and covering said 
supporting sheet, each flat element being fixed to the supporting sheet by 
being welded in a localized zone, e.g., substantially at a point. 
The resulting coating protects the supporting sheet so that it is capable 
of withstanding heat, erosion, and thermal shocks. By being welded in a 
localized zone substantially at a point, it is possible for each of the 
flat elements to deform freely so as to allow for differential expansion. 
In this way, they are not stressed by forces that might tend to damage 
them. 
Preferably, the flat elements are disposed adjacent to one another. 
In a preferred embodiment, each flat element is provided with an opening in 
which the weld is performed that bonds it to the supporting sheet. 
Advantageously, the opening is situated substantially at the center of the 
flat element. 
The flat elements may be substantially rectangular. The nozzles may be 
disposed in rows and columns extending in the two directions of the 
supporting sheet, and they may be situated at the corners of the flat 
elements, which corners are scalloped. Both the supporting sheet and the 
flat elements are preferably made of refractory steel.

MORE DETAILED DESCRIPTION 
FIG. 1 shows the supporting metal sheet 1 of the floor of the hearth, which 
sheet is made of a refractory metal, and preferably a refractory steel 
such as "Incoloy 800 HT". The sheet 1 is reinforced by stiffening means 
constituted by cross-pieces welded discontinuously under the sheet 1, e.g. 
by two continuous cross-pieces 2 and by two perpendicular stiffeners made 
up of cross-piece segments 3, 3', 3" disposed so that they form a grid 
with the continuous cross-pieces. Vertically above each intersection of 
the grid, the sheet 1 is provided with an opening 4 enabling the hearth 
floor to be assembled on site as described below. 
The sheet 1 is provided with through holes 5, for accommodating the feed 
pipes to the fluidization gas injection nozzles 10, as shown in FIGS. 2 
and 5. Through holes 5 are disposed in rows and columns extending in the 
two directions of the supporting sheet 1 in a uniform grid. 
Advantageously, each one of openings 4 in the supporting sheet 1 is 
disposed equidistant from four through holes 5 for the nozzles 10. 
A plurality of flat elements 6 that are 15 mm thick and that are made of a 
refractory metal, preferably a refractory steel such as "Incoloy 800 HT", 
are disposed adjacent to one another and cover the supporting sheet 1, 
each flat element 6 being fixed to the supporting sheet by being welded in 
a localized zone, e.g., substantially at a point. Most of the flat 
elements 6 are square with sides that are substantially equal to the 
distance between nozzles 10, rectangular flat elements 6 being provided 
along the edges of the sheet 1. 
Each flat element 6 is provided with an opening 7 situated substantially at 
the center of the flat element 6 and in which the weld 8 is performed. 
Advantageously, the weld is a weld commonly referred to as a plug weld 
made up of a weld fillet extending around the edge of the opening 7 and 
connecting the flat element 6 to the supporting sheet 1. The corners of 
the flat elements 6 are scalloped so as to surround the through holes 5. 
The flat elements 6 are welded as shown in FIG. 3 in the factory, except 
for the four elements 6' which are to be disposed around each one of 
openings 4 in the supporting sheet 1, and which are welded on site as 
shown in FIG. 4. 
On site, once the supporting sheet 1 equipped with flat elements 6 welded 
in the factory has been put into place, and the injection nozzles 10 have 
been installed, the four flat elements 6' are welded. A round flat piece 9 
is welded in each one of the openings 4 onto a tube 11 fixed to the 
carrying structure 12, serving to support the sheet 1 and to prevent it 
from bending. For that purpose, the tube 11 is provided with passages 
through which the stiffening cross-pieces 2, 3, 3', 3" can pass. Flat 
elements 6' are welded to the round flat pieces 9 by means of welds such 
as 8 in the respective central openings 7 of flat elements 6'. 
Flat elements 6' have their corners scalloped to a greater extent than the 
other flat elements 6, so that they can be inserted between the heads of 
the nozzles 10 that are already installed and that are of greater diameter 
than through holes 5. 
By way of example, the length of a side of each of the square flat elements 
6 may be about 240 mm, and the diameter of the central opening 7 may be 
about 30 mm. 
Such a configuration may be used for any fluidized bed hearth floor such as 
the floor of a main hearth, the floor of an external fluidized bed 
associated with a main hearth, or the floor of a fluidized bed inside a 
main hearth, as described in Patent Application FR-2 690 512 filed on Apr. 
27, 1992 by the Applicant.