Fluidized bed apparatus and method using same

An apparatus is disclosed for heat treating a product. The apparatus includes a retort having a volume sized to receive a bed of fluidized particles having a predetermined elevation within the volume and a plurality of electrically powered infrared radiation sources. The sources are submerged within the bed of fluidized particles. Use of the apparatus to reclaim foundry sand is also disclosed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention pertains to improvements in controlled heat treating 
processes and apparatus. More particularly, this invention pertains to a 
fluidized bed heat treatment apparatus with submerged infrared radiation 
heating sources. The invention also pertains to a method of using such an 
apparatus for reclaiming foundry sand. 
2. Description of the Prior Art 
The use of fluidized bed furnaces for heat treating a product is well 
known. Such furnaces heat a bed of particles so as to develop an extremely 
hot bed of fluidizing particles such as, for example, aluminum oxide. The 
furnaces can be used for both the continuous processing of a product or 
the batch processing products. 
U.S. Pat. No. 4,752,061 teaches a fluidized bed furnace which uses infrared 
radiation as the heating source. One advantage of using infrared radiation 
as the heating source is that it permits the use of inert gases fluidize 
the particles within the furnace. As a result, a controlled atmosphere can 
be provided surrounding the product being heat treated within the furnace. 
The aforenoted U.S. Pat. No. 4,752,061 places the infrared lamps out of the 
bed behind a quartz wall or screen. As a result, the distance from the 
infrared lamps to the bed results in the development of a high temperature 
gradient within the bed with too little of the energy source contributing 
to the heating of the bed. This leads to a significant amount of energy 
inefficiency. In addition, the infrared lamps may be disposed in close 
proximity to the stainless steel retort. This could result in partial 
melting of the retort. 
SUMMARY OF THE INVENTION 
According to a preferred embodiment of the present invention, an apparatus 
is disclosed for heat treating a product. The apparatus includes a retort 
having walls defining a furnace volume. A bed of fluidized particles is 
disposed within the volume. A plurality of electrically powered infrared 
sources are provided in a submerged mode or manner within the bed. The 
application also discloses a method of reclaiming foundry sand using the 
novel apparatus. 
BRIEF DESCRIPTION OF THE DRAWINGS 
Various other objects, features, and attendant advantages of the present 
invention will become more fully appreciated from the following detailed 
description, when considered in connection with the accompanying drawings, 
in which like reference characters designate like or corresponding parts 
throughout the several views, and wherein: 
FIG. 1 is a side elevation view of a fluidizing bed furnace constructed 
according to the present invention, with a portion of an outer skin 
removed so as to expose certain interior elements of the furnace; 
FIG. 2 is an enlarged view of certain interior elements of the furnace of 
FIG. 1, with the bus plates shown removed; 
FIG. 3 is a side elevation view, shown partially in section, showing the 
connection of the infrared heating elements to the bus plates; 
FIG. 4 is a side elevation schematic representation of the furnace of the 
present invention; 
FIG. 5 is an end elevation view, shown schematically, of the furnace of the 
present invention; 
FIG. 6 is a top plan view, shown schematically, of the furnace of the 
present invention; and 
FIG. 7 is a schematic diagram of a processing system using the apparatus of 
the present invention within a processor for reclaiming foundry sand.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A. Description of the Apparatus 
Referring now to the various figures in which identical elements are 
numbered identically throughout, the description of the preferred 
embodiment will now be given with reference to a furnace of the present 
invention which is generally designated by means of the reference 
character 10. As is shown best in FIGS. 4 and 5, the furnace 10 includes a 
retort 12, which is preferably formed of R330 stainless steel or the like. 
The retort 12 includes a bottom wall 14, end walls 15, 16 and side walls 
17, 18. Walls 14-18 cooperate with each other so as to define a retort 
interior 20. A cover (not shown in the Figures) may be provided so as to 
cover the top of the retort 12. 
The furnace 10 also includes an outer shell 22 which is shown best in FIGS. 
5 and 6. Outer shell 22 includes a first outer shell wall 24 covering wall 
17, and a second outer shell wall 26 covering wall 18. In FIG. 1, a 
central portion of shell wall 24 has been removed so as to expose wall 17. 
Wall 24 and wall 17 cooperate with each other so as to define an exhaust 
plenum 28. Walls 26 and 18 cooperate with each other so as to define an 
inlet plenum 30. 
As is best shown in FIGS. 4 and 6, interior divider walls 31 and 32 are 
provided within the interior 20. Walls 31, 32 extend upwardly between side 
walls 17 and 18 and are disposed parallel to end walls 15 and 16. The 
divider walls 31, 32 extend from floor 14 and terminate beneath partially 
toward the top of the retort 12. Walls 31, 32 divide retort interior 20 
into a fluidizing chamber 20a, a first overflow chamber 20b, and a second 
overflow chamber 20c (see FIG. 4). 
A plurality of quartz tubes 36 extend between and through walls 17 and 18. 
As shown, the tubes 36 are disposed in parallel alignment with respect to 
each other are generally perpendicular to side walls 17, 18 and are 
parallel to the floor 14 of the retort 12. The tubes 36 are disposed 
within the fluidizing portion 20a of interior 20, and are located beneath 
a predetermined elevation 38 (see FIG. 4) of the fluidizing particles to 
be retained within the chamber 20a. 
FIG. 3 shows the attachment of each the tube 36 to the side wall 17. The 
quartz tube 36 is similarly attached to side wall 18. As shown in FIG. 3, 
the tube 36 extends through side wall 17, and is connected to the side 
wall 17 by means of a steel mounting clamp 40. The clamp 40 houses a 
plurality of ceramic washers 42. The clamp 40 is attached to side wall 17 
by means of bolts 44. 
An infrared lamp 46 is disposed within each one of the tubes 36, as best 
shown in FIGS. 2, 3, 5 and 6, (for clarity, the lamps are not shown within 
the tubes 36 in FIGS. 1 and 4). Each lamp 46 is completely contained 
between walls 17, 18, and is retained in coaxial alignment within its 
respective tube 36 by means of a mounting clip 48. 
In order to provide electrical energy to the plurality of lamps 46, a 
plurality of bus bar plates 50 are provided. (For clarity purposes, the 
bus bar plates are not shown in FIGS. 1 and 4.) As shown in FIG. 2, nine 
bus bar plates are provided for each side wall 17, 18 of the retort 12. In 
the schematic representation of FIG. 6, eight bus bar plates are shown for 
each side wall. 
The bus bar plates 50 are electrically conductive plates of metal. Each 
plate 50 is connected to a separately controllable source (not shown) of 
electrical power for energizing the particular plate 50. 
The plates 50 are secured to the walls 17, 18 by means of bus bar plate 
mounts 52 (see FIG. 3), which are preferably ceramic. A lead 54 connects 
each infrared lamp 46 to one of the bus bar plates 50. The lead 54 is 
connected to the bus bar plate 50 by means of a nut and bolt combination 
56. 
As best shown in FIG. 2, a plurality of lamps 46 are covered by means of a 
predetermined bus bar plate 50. In the expanded view of FIG. 2, each of 
the bus bar plates 50 is removed from covering the lamps 46 and tubes 36. 
The positioning of the bus bar plates 50 over the lamps 46 in FIG. 2 is 
shown in phantom lines. As a result of having a plurality of lamps 46 
covered by means of a plurality of different bus bar plates 50, the length 
of the fluidizing chamber 20a can be divided into a plurality of zones. 
Each bus bar plate 50 with its associated lamps 46 constitutes a given 
zone. By separately regulating the current supplied to each bus bar plate 
50, the intensity of the lamps connected to such bus bar plate 50 can be 
separately controlled. As a result, a temperature gradient can be created 
across the length of the chamber 20a. 
As is shown in FIGS. 1, 4 and 5, a stainless steel screen 60 is placed 
above the lamps 46 and quartz tubes 36. The screen 60 prevents a product 
that is being heat treated within the furnace from falling onto the quartz 
tubes 36 and possibly damaging them. 
Fluidizing tubes 62 are disposed between the floor 14 and the quartz tubes 
36. The tubes 62 are connected by means of a conduit 64 to a source (not 
shown) of a fluidizing gas. The fluidizing gas may be air or any inert gas 
such as, for example, nitrogen. The fluidizing tubes 62 may be such as 
those shown and described in U.S. Pat. No. 4,752,061 and indicated by 
means of reference numeral 98 in FIG. 5 of that patent. 
A coolant mechanism is provided for conducting a cooling fluid (preferably 
air) through the tubes 36 so as to cool the infrared lamps 46. A blower 70 
is connected to inlet plenum 30. An exhaust fan (not shown) may be 
connected through means of an exhaust conduit 72 to exhaust plenum 28. As 
a result, cooling air may be forced from plenum 30 through each of tubes 
36 into plenum 28 and out exhaust conduit 72. 
A bed of fluidizing particles (preferably granular aluminum oxide) is 
provided within the retort 12. A first layer 80 of coarse particles 
(preferably of 12 grit size) is provided for covering the fluidizing tubes 
62 and such layer terminated beneath the quartz tubes 36. Finer aluminum 
oxide sand (preferably of 100 grit size) rests on top of the coarser sand 
80, and terminates at level 38. The coarser sand 80 diffuses the 
fluidizing gas from the fluidizing tubes 62, and distributes it evenly to 
the quartz tubes 36. 
In operation, the infrared lamps 46 may be heated from 
0.degree.-4000.degree. F. The aluminum oxide will heat from 
0.degree.-2100.degree. F. A controller 100 (schematically shown in FIG. 2) 
is connected through means of control lines 102 to each of the bus plates 
50. Through means of the operation of controller 100, the potential upon 
each one of the bus plates 50 may be separately controlled. Accordingly, 
the plurality of infrared lamps 46 are divided into a plurality of 
separately controllable zones. 
In operation, the lamps 46 heat the aluminum oxide. The fluidizing gas from 
tubes 62 fluidizes the aluminum oxide. The divider walls 31, 32 capture 
within chambers 20b and 20c any aluminum oxide which spills out of the 
fluidizing chamber 20a. 
Each one of the lamps 46 and tubes 36 comprise a lamp assembly 37 (shown 
numbered in FIGS. 3, 5 and 6). As previously indicated, a cooling gas is 
passed through the lamp assemblies 37. In operation, the temperature of 
the apparatus can be quite high. For example, the temperature surrounding 
the assemblies 37 will commonly exceed 2,100.degree. F. At temperatures in 
excess of 1,500.degree. F., the quartz tubes 36 may deteriorate. For 
example, from 1,500.degree. to 1,800.degree. F., quartz softens and sags. 
The air passing through the quartz tubes 36 cools the quartz tubes 36 so as 
to prevent sagging. However, the air flow can adversely affect the 
efficiency of the infrared lamps 46. Accordingly, air flow through the 
quartz tubes 36 must be balanced to provide sufficient cooling of the 
lamps so as to prevent the quartz tubes 36 from sagging while minimizing 
the adverse impact upon the efficiency of the lamps 46. 
In order to achieve the desired balancing, air flow through the quartz 
tubes 36 is preferably only provided when the temperature of the fluidized 
bed 38 exceeds a predetermined temperature in accordance with a preferred 
embodiment, the predetermined temperature being, for example, 
1,500.degree. F. 
The amount of air flow through the tubes 36 is selected so as to balance 
the thermal energy impressed upon the tubes 36. Namely, the bed draws 
thermal energy from the tubes 36. If the thermal energy drawn from the 
tubes 36 is insufficient to maintain the temperature of the tubes 36 below 
the predetermined temperature, air flow is passed through the tubes 36 at 
a rate selected to draw energy away from the tubes 36. The amount of air 
flow is a function of the length of the tubes 36, the voltage across the 
lamps 46 and the ambient temperature (that is, the temperature of the bed 
within the immediate vicinity of the tubes 36). The actual amount of air 
flow is empirically derived for a given apparatus 10 and will vary with 
the operating process in which it is used. 
In order to achieve the balancing, a thermocouple 101 (schematically shown 
only in FIG. 5) is provided for sensing the temperature within bed within 
the vicinity of the tubes 36. Thermocouple 101 provides a signal to a 
controller 103. The controller 102 also receives an input signal from a 
voltage sensor 104 which senses a voltage across the lamps 46. Comparing 
the voltage upon the lamps 46 and the temperature within the bed, the 
controller 103 operates blower 70 so as to force coolant gas through the 
quartz tubes 36 when the temperature within the bed exceeds the 
predetermined temperature. The air flow through the quartz tubes 36 is 
selected so as to be an increasing function of the voltage across the 
lamps 46 and to be increasing with the increased temperature measured by 
means of the thermocouple 100. The increasing function is selected for the 
air flow to be the minimum air flow necessary to prevent deterioration of 
the quartz tubes 36. 
The preferred embodiment discloses use of air cooled lamp assemblies 37. A 
further embodiment may replace the assemblies with resistance type silicon 
carbide heating elements (also called glow bars). These elements may be 
electrically energized so as to be heated and generate infrared radiation. 
These elements may be used in direct contact with the bed and do not 
require quartz conduits (such as tubes 36) or air cooling. Such elements 
are commercially available such as, for example, those marketed by 
Smith-Sharpe of Minneapolis, Minn. 
B. Novel Method for Foundry Sand Reclamation Using the Novel Apparatus 
The apparatus 10 described above has been illustrated for heat treating a 
product within a fluidized bed. In addition to such beneficial uses, we 
have determined that the apparatus 10 is surprisingly useful for 
reclaiming foundry sand. 
In the foundry industry, various types of sands are used so as to form 
moldings from which metal castings are made. These sands include so-called 
"no-bake" sands and so-called "green" sand. A no-bake sand includes an 
organic binder which is air-cured so as to bind the sand into a sand 
casting. Green sand includes an inorganic binder which is baked so as to 
bind the sand into a casting. 
Government agencies (such as, for example, the U.S. Environmental 
Protection Agency) have severely restricted the disposal of foundry sand. 
For example, foundry sand cannot be readily disposed of within landfills 
since it is considered a hazardous material. 
Various methods have been devised to reclaim foundry sand. No-bake sand is 
reclaimed through means of a mechanical method of passing the sand through 
a crusher and a scrubber so as to reclaim approximately 80% of the sand. 
The foundry industry has been experimenting with various methods to reclaim 
sand through means of various temperature applications (referred to in the 
industry as "killing" the sand at elevated temperatures). For example, the 
industry has used gas fired fluidized beds to thermally reclaim the sand. 
An example of such a method is found in U.S. Pat. No. 4,478,572. 
In order to reclaim green sand, the sand must be heat treated to 
temperatures in excess of 1,400.degree. to 1,500.degree. F. When natural 
gas is used as the heat source, a substantial amount of gas is required. 
In addition, the capital cost of such equipment is very high. 
We have found that our apparatus is particularly suitable for reclaiming 
foundry sand including green sand. In order to accomplish this, the 
foundry sand is used as the fluidized bed within the furnace 10 instead of 
using the granular aluminum oxide previously described as the preferred 
fluidized bed material. 
FIG. 7 shows, in schematic format, the use of the apparatus 10 to reclaim 
green sand. As shown in FIG. 7, a reclamation system 199 includes feed 
hopper 200 for passing sand to a crusher 201. Crusher 201 crushes the sand 
and passes it to a magnetic separator 202 so as to separate out 
ferromagnetic material. A metering hopper 206 collects sand from separator 
202 and feeds the separated sand (by means of a conduit) 205, to the 
furnace 10. The fully reclaimed sand is passed from apparatus 10 through 
means of a discharge conduit 208. 
The hot reclaimed sand is passed from discharge conduit 208 to a cascade 
cooler 220. A blower 222 blows cooling air into cooler 220 and the air is 
exhausted through means of a conduit 224 to main exhaust conduit 226 from 
which it passes to filters and scrubbers (not shown). 
A blower 230 forces air into the fluidizing tube 62. In use of the 
apparatus 10 for foundry sand recovery, the fluidizing gas is 
oxygen-containing (preferably air) with the oxygen reacting with the sand 
binder. Resulting product gas (such as, for example CO, CO.sub.2) and dust 
are drawn off through means of main conduit 226. 
Use of the furnace 10 to reclaim foundry sand has been operated with 
no-bake sand at 750.degree. F. with a reclamation rate of approximately 
94% by weight, of the sand. In addition, 94% of green sand has been 
reclaimed when operating the furnace at a fluidized bed temperature of 
1,400.degree. to 1,600.degree. F. The latter is of substantial 
significance to the foundry industry which, prior to the present 
invention, was not capable of economically reclaiming green sand. 
The present apparatus has numerous advantages for use in reclaiming foundry 
sand. It has a much lower capital cost than prior thermal treatment 
apparatus for foundry sand. It operates at a much lower energy cost than 
prior thermal treatment apparatus and has a fast through-put rate. 
The actual physics and chemistry by means of which the apparatus 10 is so 
effective in reclaiming sand is not fully understood. However, it is 
believed that the submergence of an infrared heat source within the bed of 
sand causes individual sand grains to experience momentary periods of very 
high temperature. For example, while the bed may have an average 
temperature of approximately 1,400.degree. F., individual grains of sand 
come into momentary close proximity to submerged heat sources (that is, 
the IR lamps or glow bars) which may have very high temperatures. It is 
suspected that the momentary very high temperature makes the sand binders 
brittle and burn off. As a result, the sand reclaimed through means of the 
novel method requires very little scrubbing as compared to sand reclaimed 
through means of prior art techniques. 
Through the foregoing detailed description of the present invention, it has 
been shown how the invention has been obtained in a preferred manner. 
However, modifications and equivalents of the disclosed concepts, such as 
those which will readily occur to one skilled in the art, are intended to 
be included within the scope of this invention which is defined by means 
of the appended claims.