Note: Descriptions are shown in the official language in which they were submitted.
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-I TITLE: IMPROVED FLUIDIZED BED FURNACE HEATED BY Infrared
RADIATION
l BACKGROUND OF THE INVENTION
Heat treatment of metals in -Fluids boas with or
without a controlled atmosphere have been proposed for many
applications and the his-tory of fluidized beds and the various
techniques are well described in an article by ROW. Reynolds on,
published in the publication Heat Treatment of Metals, 1977.1,
entitled Control Atmosphere Fluidizied Bed -For Heat Treatment
of Metals. In this article, a fluidized bed furnace is shown
where internal resistance heating elements are place within a
fluidized bed for the batch treating of a product. The article
also refers to various types of combustion processes winch may
be carried out within and/or above a fluidized bed. Generally,
fluidized beds heated by combustion have an operating
temperature somewhere between 600 and 800C and are not
suitable for high temperature application.
In fluidized beds and in -the heat treating of any
product, it is important to provide uniform heating and it is
also important to provide a system which is capable of fast
start up.
A substantial amount of research has been undertaken
with respect to introducing of a combustible gas Jo a flossed
bed in a manner where the gas assists in the Fluidization of
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1 the bed while also providing the proper gas mixture to support
corrbustion within the bed. In cases where a controlled
atmosphere is required, the combustion process is still carries
out within a portion of -the bed which results in the heating of
particles which are stripped from the combustion gases anywhere
returned to the fluid be for heating of the remaining
particles of the bed and heating of the product being treated.
In this way, the product briny treated is isolator from tune
atmosphere required to support combustion. The portion of the
bed which does not have the combustible chases is fluidized by
an inert gas.
The demands placed on the heating source of -the
fluidized bed should be capable of rapidly raising the
temperature of the fluid bed from ambient to the heat treat
temperature, preferably up to about 1200C. In addition,
the heating source should be capable of providing uniform
heating of the bed once the bed has arrived at its operating
temperature. To date, the ability to rapidly raise the
temperature of the fluid bed to operating levels and -thereafter
2û maintain it in a manner such that the uniform heating of
products is accomplished, has been achieved with -fluids
beds, but problems occur with gas fired at tune upper
temperatures.
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We have found that it is possible -to provide uniform
and rapid heating of a bed of fluidized refractory particles in
a channel type furnace used for the heat treating of product
on a continuous basis by using high intensity infrared
radiation lamps exposed to the surface of the fluidized bed.
This system allows the fluidized gas to be separated from the
initial heating step as the energy is transmitted -to the
particles of the bed by radiation, resulting in efficient an
rapid heat transfer. The high intensity infrared radiation
lamps are capable of operating at maximum power to rapidly
raise the temperature of a fluidized bed and are capable of
operating at a reduced power setting to provide uniform heating
of the bed. The heating of the surface of the bed by infrared
radiation and the thermal transfer characteristics of the bed
cooperate to effect rapid and uniform heat transfer throughout
the length, width and depth of the bed. The radiation emitted
by the lamps can be controlled by adjusting the power input to
the lamps and preferably the lamps are disposed along the
length of the bed to initially expose the surface of the bed to
generally uniform radiation levels.
SUMMARY OF THE INVENTION
Apparatus according -to the invention is used for heat
treating of metal products such as wire, s-trip and special
section materials and the like on a continuous basis as the
product is passed through a fluids bed.
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1 The apparatus comprises a normal fluidized owed of
refractory particles suitably fluidized by a gas with a surface
of the bed being exposed -to high intensity infrared radiation
for heating thereof. Infrared radiation sources are positioned
above the bed and emit the radiation which is absorbed by tune
particles. The absorbed energy is quickly dissipate
throughout the bed due to the thermal -transfer characteristics
of fluid beds. This combination provides a heated fluid bed
which is highly temperature responsive to increasing levels of
radiation varied by controlling the input energy to the
radiation source. The product being treated is passed through
-the bed preferably out of direct contact with the emitted
radiation.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are shown in
the drawings wherein;
Figure 1 is a sectional view through fluidized bed
furnace; and
Figure 2 is a sectional view taken along line AA of
Figure 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The channel-type fluidized bed furnace generally
indicated as 2 has a fluidized bed generally indicated as 4,
including refractory particles or the like fluidized by tune yes
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1 flow generally indicated as 6. The fluidized gas will be
selected in accordance with the post processing surface
conditions sought to be obtained. This gas is introduce in
any of a number of known manners adjacent the base of the
refractory insulation material 10. Exterior to the insulation
material, is an exterior steel shell and section case which
includes suitable means for supporting the furnace. In this
case, a fluidizing gas inlet 12 is provided a-t the upper
surface of -the base of the refractory insulation material 10.
Heating of the fluidized bed is accomplished by an
infrared radiation source generally indicated as 14. This
radiation source includes high intensity infrared radiation
lamps 16 positioned generally immediately above the surface of
the fluid bed 4. The lamp end tips 18 have been located within
cooling conduits 22 for cooling of the lamp ens. A cooling
gas is circulated through the conduits 22 to maintain the lamp
end tips at a lower temperature to increase the life of the
lamps. Above the lamps 16 and intermediate the cooling
conduits 22 is a top panel 24 which has a lower surface exposed
on to the infrared radiation lamps and is preferably of a
material and shape to redirect radiation emitted by the lamps
which strikes the panel, downwardly to the surface of the fluid
bed 4.
The channel-type fluid bed furnace 2 has an entrance
generally indicated as 30 and a exit generally indicated as
for introducing and withdrawing a product from the fluid bed.
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l In some cases, submerged rollers or other devices may be
required to maintain the introduced product submerged and out
of direct contact with emitted radiation as it is passed
throughout the length of the furnace 2.
The product which is passed through the fluid bed
furnace may be wire, strip and the like and can be pushed or
pulled through the furnace depending upon the actual product.
The product is heated as it is moved from the entrance MU to
the exit 32 to leave -the fluid bed furnace at an approximate
lo given temperature. The fluidized be of particles serves -tug
isolate the product being treated from the emit-ted radiation of
the infrared radiation source 14. It can be appreciate
treating of` other products are possible and -the application is
not limited to strip and wire.
The fluid bed particles are preferably aluminum or
zirconium oxide particles, although other refractory particles
may be suitable. The fluid bed particles in addition to the
normal characteristics required in any fluidized bed
application should tend to absorb infrared radiation impinged
thereon and should not be highly reflective to this radiation.
The spacing of the high intensity infrared radiation
lamps 16 along the length of the fluid bed furnace can vary
depending upon the maximum temperature capability of the
furnace, however, it has been found that if lamps extend across
US the bed and are spaced from one another approximately one to
four inches along -the length of the bed, rapid heating of the
fluid bed from ambient to operating -temperatures is possible.
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l With the system described above, the infrared
radiation lamps directly heat the surface of the fluid bed and
the absorbed infrared radiation is quickly transmitted
throughout the fluid bed due to the thermal transfer
characteristics of the bed. It has been found that tune
infrared radiation lamps and particularly high intensity
electrically powered shortwave infrared radiation lamps are
capable of rapidly raising the temperature of the bed to an
operating temperature in the range of a maximum of about
lo 1200C and thereafter the power supplied to the lamps can be
reduced to a level of radiation sufficient -to maintain the bed
at the desired temperature. The response characteristics of
the infrared radiation lamps in accordance with the electrical
power supply to the lamps is thus used to result in a fluidized
bed furnace which can be quickly raised to the aerating
temperature and thereafter maintained to provide even uniform
heat distribution throughout the fluid bed. Ail the lamps may
be controlled in unison or in groups by varying the electrical
input in accordance with a sensed be temperature. Such a
system has improved operating characteristics and reduced
operating costs.
In Figure l, the infrared radiation source is movable
to a service position exposing the upper surface of the fluid
bed and exposing the infrared radiation lamps for inspection
and service as shown in broken line. Preferably, one of the
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1 cooling conduits 22 is hingidly attached to -the exterior steel
shell and section case 8 to allow convent positioning of the
infrared radiation 14 for service. A quartz limiting member 20
is shown in Figure 1, and serves to isolate the lamps 16 from
the hot gas flow 6 and fluid bed particles at the surface of
the bed. This limiting member may not be required in all
cases, however, in high temperature applications the life of
the lamps can be increased.
The apparatus and method have been described with
respect to a continuous process, however, the heat treating of
products on a batch basis is also possible.
Although various preferred embodiments of the present
invention have been described herein in detail, it will be
appreciated by those skilled in the art, that variations may be
made thereto without departing from the spirit of the invention
or the scope of the appended claims.
