Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1137302
-- 1 --
LADLE ~EATING SYSTEM
Technical Field
This invention relates to a ladle heating system wherein a
flame is directed into the chamber of a ladle and the hot gases are
exhausted from the ladle through a heat exchanger which heats the
oncoming air and fuel that forms the flame.
Background Art
In the ferrous and nonferrous molten metals industries,
ladles and similar metal receivers such as holding vessels and
vacuum furnace chambers, receive a charge of molten metal. The
receivers usually are lined with a refractory material, and it is
desirable to preheat the receiver before molten metal is received
in the receiver in order to avoid interface solidification of the
metal upon contact between the metal and the cold interior surface
of the receiver, and also to avoid thermal shock to the refractory
liner of the receiver, thus avoiding deterioration of the liner.
A preheated ladle also minimizes the heat loss from the molten
metal as the metal is transported in the ladle from the furnace to
the pouring position, thereby assisting in maintaining the molten
metal at a high enough temperature for use in a casting machine
or mold.
A common prior art method for heating ladles and other
molten metal receivers prior to charging them with molten metal is
to direct an open natural gas flame into the open chamber of the
ladle. The open flame heating method permits combustion gases from
within the ladle chamber to escape to the surrounding atmosphere.
This permits a substantial amount of the heat energy to escape with-
out effective use thereof, thus wasting an excessive amount of gas.
Moreover, it is difficult to uniformly heat a ladle with an open
flame, in that the ladle may be overheated in some areas and not
heated sufficiently in other areas. Additionally, after a ladle
has been initially heated, it is sometimes desirable to maintain
the ladle in its heated condition if the ladle achieves its desired
temperature before it is time to introduce the molten metal to the
ladle. In this situation the open flame hea~ing procedure continues
to waste energy and hot spots are more likely to be formed in the
ladle.
, , '~
11373(~2
Summary of the Invention
In one aspect the invention comprehends a method of heating
ladles and similar molten metal receivers comprising engaging the
rim of the ladle with a seal of refractory fiber modules positioned
substantially in a common plane with sufficient force to cause the
rim of the ladle to be pressed into the seal and compress the fibers
of the modules it e~gages, directing air through a heat exchanger
and through the seal into the ladle, mixing fuel with the air and
igniting the mixture as the mixture passes through the seal and
into the ladle, and exhausting the gases from the ladle through the
seal and through the heat exchanger.
Another aspect of the invention pertains to apparatus for
heating ladles and similar molten metal receivers wherein a seal
assembly is provided for movement into sealing abutment with the
rim of the ladle, the seal assembly comprising a support frame and
a layer of compressible refractory fiber material supported by the
support frame and arranged in a configuration to engage the rim of
the ladle and form a seal about the rim of the ladle.
The invention also comprehends an apparatus for heating
a ladle having an open end, inc'uding seal means comprising ceramic
fiber compaction material sized and shaped to engage the ladle about
its open end and defining an opening therethrough. A ceramic heat
exchanger defines an air inlet path and an exhaust outlet path for
communicating through the opening of the seal means with the interior
of the ladle. A fuel burner means is connected to the air inlet
path for directing hot combustion gases through the opening of the
seal means into the open end of the ladle. Variable fuel supply
means provide for mixing fuel with air from the air inlet path and
for supplying the mixture to the fuel burner means. Blower means
move air along the air inlet path to the burner means. Thus, the
seal means forms resilient contact with the open end of the ladle
and air from the blower means moves through the heat exchanger,
past the fuel supply means, through the fuel burner and through the
opening of the seal means and forms a flame to heat the inside sur-
faces of the ladle and the hot gases from inside the ladle move backthrough the seal means and through the heat exchanger to preheat
the air moving from the blower means through the heat exchanger.
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Still another aspect of the invention comprehends a method
of heating a ladle having an open end including the steps of
enclosing the open end of the ladle with a heat exchanger, the heat
exchanger defining an exhaust outlet path communicating with the
interior of the ladle and an air inlet path and heating air travel-
ing along the air inlet path by mixing the air with fuel and burning
the mixture in a fuel burner. The method further includes directing
the heated air into the ladle, further heating the air traveling
along the air inlet path with hot gases travelir.g in the exhaust
outlet path in the heat exchanger prior to mixing the air with the
fuel, measuring the amount of oxygen in the hot gases traveling
along the exhaust outlet path, and in response to the amount of
oxygen in the exhaust outlet path, regulating the fuel-air mixture
provided to the fuel burner to maintain the amount of oxygen in the
exhaust outlet path at a predetermined value. The invention also
comprehends the apparatus for carrying out the method.
The invention in still a further aspect pertains to an
apparatus for heating a ladle having an open end including a heat
exchanger defining an air inlet path and an exhaust outlet path,
and further defining an open end for matingly receiving and enclosing
the open end of the ladle, the exhaust outlet path and the air inlet
path communicating through the open end of the heat exchanger with
the interior of the ladle. A fuel burner means is in communication
with the air inlet path for directing hot combustion gases through
the open end of the heat exchanger into the ladle and variable fuel
supply means provide for mixing fuel with air from the air inlet
path and for supplying the mixture to the fuel burner means. Blower
means move air along the air inlet path to the burner means. The
heat exchanger comprises a ceramic heat exchange means for receiving
the hot combustion gases directly from the interior of the ladle.
A stainless steel heat exchange means communicates with the ceramic
heat exchange means for receiving the hot combustion gases from the
ceramic heat exchange means, and a carbon steel heat exchange means
communicates with the stainless steel heat exchange means for receiv-
ing the hot combustion gases from the stainless steel heat exchangemeans.' The air inlet path extends from the blower through the car-
bon steel heat exchange means, then through the stainless steel heat
~r ^ - t,
~tr,~
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exchange means, and then through the ceramic heat exchange means to
the fuel burner means.
The invention also comprehends apparatus for heating ladles
and similar molten metal receivers having a lid assembly for move-
ment with respect to the ladle into sealing abutment with the rimof the ladle. The lid assembly comprises a support frame and a
layer of compressible refractory fiber material supported by the
support frame of a breadth greater than the rim of the ladle and
substantially covering the face of the lid. Conduit means extend
through the compressible refractory fiber material for exhausting
gases from the ladle, and a burner extends through the compressible
refractory fiber material for directing a flame into the ladle.
Thus, the lid assembly and the ladle are urged together with a force
sufficient to cause the rim of the ladle to indent the compressible
refractory fiber material and form a seal at the rim of the ladle.
A flame is directed from the burner into the ladle and gases are
exhausted from the ladle through the conduit means, the compressible
refractory fiber material shielding the lid assembly from the flame.
More particularly, the invention disclosed comprises an
improved system for preheating ladles and similar molten metal
receivers wherein a seal is applied to the rim of the ladle and air
is directed through a heat exchanger and through the seal and mixed
with a fuel to form a flame in the ladle chamber, and the gases from
the flame are exhausted back through the seal and through the heat
exchanger. The heat in the exhaust gases are partially recouperated
in the heat exchanger by being transferred to the oncoming air, and
the flame formed in the ladle chamber is controlled so as to wash
the inner surfaces of the chamber with heat in a manner that tends
to avoid hot and cold spots in the ladle. The exhaust gases are
directed through an exhaust opening in the seal which is approximate-
ly concentric with the ladle rim, thus further controlling the heat
applied to the ladle. In one embodiment of the invention the seal
formed against the ladle rim comprises a network of refractory fiber
modules each formed from a web of refractory fibers, with the webs
formed in an accordian fold, and the modules are arranged in a com-
mon plane with the folds of each module arranged at a right angle
with repect to the folds of the adjacent modules. The refractory
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fiber modules are maintained in compression by the seal support
frame, and when the seal is pressed into abutment with the rim of
the ladle, the modules tend to conform to the shape of the ladle
rim and form a seal about the rim. The ability of the seal to be
compressed tends to compensate for irregularities of the ladle rim
as might be caused by a build up of slag or by chips or rough sur-
faces present on the ladle rim.
In one embodiment of the invention the heat exchanger is
shielded from direct radiation from the flame in the ladle chamber,
and the heat exchanger comprises a multiple stage heat exchanger
with the first exchanger that receives the hottest gases being fab-
ricated of a material with a superior heat resistance than the sub-
sequent ones of the heat exchangers.
The system of the invention further includes a means for
sensing the temperature of the ladle and a means responsive to the
temperature sensing means for adjusting the output of the fuel
burner to maintain the ladle at a predetermined temperature. The
system also includes a means for sensing the amount of oxygen pass-
ing through the exhaust outlet path and a means responsive to the
oxygen sensing means for adjusting the composition of the fuel-air
mixture provided to the fuel burner by the variable fuel supply
means to minimize the amount of unburned oxygen in the exhaust out-
let path in order to maximi2e the efficiency of the combustion.
Such adjustments responsive to the temperature of the ladle and the
amount of un-burned oxygen are interrelated in the system according
to the invention so that the adjustment responsive to the unburned
oxygen is made at whatever intensity the operation of the burner
has been caused to assume by the adjustment means that is responsive
to the ladle temperature. The ladle heating system according to the
present invention thus has the advantages of energy efficiency re-
sulting from careful control of fuel consumption, recovery of waste
heat, and the ability to maintain a ladle at a desired elevated
temperature with a minimum of energy consumption.
Other aspects, features and advantages of the present inven-
tion will become apparent upon reading the following specification,when taken in conjunction with the accompanying drawings.
Brief Description of the Drawings
Fig. 1 is a perspective illustration of a ladle and the
ladle heater, with portions removed to illustrate the inside of the
ladle and the ladle heater, illustrating the first embodiment of the
`-` 11373~2
invention.
Fiq. 2 is a back view of the ladle heater
of Fig. 1, with the carriage removed.
Fig. 3 is a side elevational view of the
ladle heater of Fig. 1, with the carriage removed.
Fig. 4 is a front elevational view of the
ladle heater of Fig. 1, with the carriage removed,
showing the face of the seal assembly.
Fig. S is a detailed exploded perspective
illustration of several of the refractory fiber
modules and the upright seal support plate of the
ladle heater of Fig. 1. appearing with Figure 3.
Pi~. 6 is a perspective illustration,
similar to Fig. 1, but illustrating a second
lS embodiment of the ladle heater.
Fig. 7 is a perspective illustration of a
third embodiment of the ladle heater~ appearing with Fig. 4.
Fig. 8 is a schematic illustration of the
control svstem for controlling the operation of the
ladle heater of Figs. 1-7
Fig. 9 is a side elevational view, with
portions illustrated in cross section, of a fourth
embodiment of the ladle heater.
Fig. 10 is a side elevational view of a
fifth embodiment of the ladle heater.
Fig. 11 is a schematic representation of
the control system for controlling the operation of
the ladle heaters of Figs. 9 and 10.
Detailed ~escription
Referring now in more detail to the
drawings, in which like numerals indicate like parts
throughout the several views, Fia. 1 illustrates the
ladle heater 10 for heating ladles such as ladle 11.
The ladle 11 is illustrated as resting on lts side on
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support blocks 12 and shims 13, with its rim 14
facing to the side. The ladle 11 includes a chamber
15 lined with fire brick or other suitable heat
resistant material. The rim 14 typically is circular
in shape but can include a pouring spout or other non
circular shapes. In some instances a build up of
slag is present on the rim 14 of the ladle, or the
ladle rim may be chipped or cracked or otherwise
im~erfect in shape.
Ladle heater 10 includes a carriage 18
mounted on wheels 19 and the wheels are movable alonq
tracks 20. Seal assembly 21 is mounted on carriage
18, a heat exchanger 22 is also mounted on carriage
18, blower 24 is mounted on carriage 18, and air
conduit means 25 incl~des blower exhaust duct 26
which extends upwardly from blower 24, heat exchanger
tubes 29, a second heat exchanger header 30
positioned on the other side of the heat exchange
tubes 29, and branch conduit 31 and 32 extending
downwardly ~from heater 29 and turning inwardly
through seal assembly 21. Burners 35 and 36
communicate with the air conduit means 25 at the
intersection of the branch conduits 31 and 32 with
the seal assembly 21. A filter 34 is mounted on the
inlet of blower 24.
An exhaust gas conduit means 38 defines an
opening 39 through seal assembly 21 between burners
35 and 36 and duct work 40 that extends first in a
horizontal leg 41 from opening 39 and then in a
vertical leg 42 upwardly to heat exchanger 22, and
then an exhaust duct 44 extends upwardly from the
heat exchanger and directs the exhaust gases away
from the lade heater. A damper 45 is located in
exhaust duct 44 and is arranged to selectively block
1137;~Z
or restrict the movement of gases throuqh the exhaust
gas con2uit means. It will be noted that the heat
exchanger 22 is remotely located from opening 39 of
exhaust gas conduit means 38 whereby the flames in
the chamber 15 of ladle 11 do not directly radiate
heat to the heat exchanger. Also, the duct work 40
of the exhaust gas conduit means is heat insulated.
The framework 46 is mounted on carriage 18 and
includes various upright, horizontal and diagonal
support beams for supporting the seal assembly 21,
heat exchanger 22 and air conduit means and exhaust
gas conduit means and their related components.
As illustrated in Figs. 2 and 3, seal
assembly 21 comprises a support frame 48 that
includes upright side frame elements 49 and 50, upper
horizontal frame element 51 and lower horizontal
frame element 52. Upriaht steel support plate S4 has
its edges in abutment with frame elements 49-52.
Frame elements 49-52 are channel members, each have
one flange in abutment with the upright steel plate
54 and the outer flanges thereof located in a common
plane and forming a frame rim. A network of
refractory fiber modules or insulating blocks 55 are
mounted in support frame 48, forming a surface of
refractory fibers inside the frame elements. The
refractory fiber modules 55 that are adjacent frame
elements 49-52 are partially confined in the flanges
of the channel shaped beams 49-52, and each module 55
is attached to upright steel support plate 54.
Each refractory fiber module or batt 55
(Fiq. 5) is formed from a weh or blanket of
refractory fibers, and the webs are in the form of
elongated sheets. The sheets are folded in a zig-zag
or an accordion arrangement so as to include a series
~1373(~2
_ of layers 56 with exposed side edges 58 and folds 59
on a front surface and similar folds 60 on the back
surface of the modules. The modules 55 are
rectangular in shape and are each maintained in their
accordion folded configuration by bands wrapped
around the module until the modules are mounted in
the support frame 48, whereupon the bands are
removed. The bands tend to hold the modules in
compression until the bands are removed. The modules
each include support rods 61 extending between the
layers 56 at the folds 60 at the back surface of the
module with connecting tabs 62 extending therefrom
and projecting through the blanket at a fold 60. A
channel-shaped connector bracket 63 defines slots
therethrough for receiving the tabs 62 of the support
rods and when the tabs are inserted through an
opening they are bent so that the bracket 63 is
secured to the module. The channel of the channel-
shaped bracket is then attached to a p{ojection 64
mounted on the upright support plate 54 to secure the
module to the support frame 48. A more detailed
descriPtion of a similar insulating block is found in
U.S. Patent 4,001,996.
The modules 55 are pac~ed within the
confines of the support frame. After they have been
properly positioned and packed in the support frame,
their straps (not shown) are removed, and the modules
tend to remain in compression due to their abutment
with one another. It will be noted that the folds 59
of each module 55 are oriented at a right angle with
respect to the folds of the next adjacent modules.
Thus, a parket or alternating fold effect is created
across the network of the seal assembly. The layers
56 are each approximately cube-shaped and are, in the
~1373C~Z
o
_ disclosed embodiment, approximately one foot square.
However, other dimensions and other shapes can be
utilized if desired.
When the ladle heater 10 and a ladle 11 are
moved into engagement with each other as shown in
Fig. 1, the rim 14 of the ladle moves into abutment
with the seal assembly 21. Since the seal assembly
21 includes a network of refractory fiber modules 55
each formed in an accordion arrangement as
illustrated in Fig. 5, the rim 14 tends to penetrate
or move into the surface of the seal assembly formed
by the folds 59 of the refractory fiber webs. As the
rim is forced against the modules 55, an indentation
is made in the refractory fibers. The rim and seal
assemhly are moved together with a force in excess of
2 pounds per square inch, preferably with a force
between 4 and 10 pounds per s~uare inch, so that the
rim tends to penetrate the surface of the seal
asembly and a good seal is made about the ladle rim.
The desired depth of indentation in the seal
assembly is about three inches. The density of the
refractory fiber modules is approximately 8 pounds
per square inch. Thus, a firm seal is made about the
ladle rim 14 and a substantial thickness of the
refractory fiber material remains between the ladle
rim and the upright steel plate 54 which supports the
fiber modules 55.
~hose modules 55 that are not directly
engaged by the rim o~ the ladle remain uncompressed
3~ by the rim and tend to retain all of their heat
resistance characteristics, thus closing off the
ladle opening inside the rim of the ladle, so that
the seal assembly functions as a lid or closure wall
with respect to the chamber 15 of the ladle except
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_ for exhaust opening 39, and the openings through
which the burners 35 and 36 are temperature probes or
other elements project. By this arrangement the
refractory fiber web material of the modules 55
shields the other components of the ladle heater from
direct heat radiation from the flame inside the
ladle.
Preferably, the ladle 11 and the seal
assembly 21 will be positioned so that the opening 39
of the exhaust gas conduit means 38 is coaxially
positioned with respect to the rim 14, thereby
directing the exhaust gases out of the chamber 15 of
the ladle through the middle of the opening formed by
the ladle rim 14. Since the burners 35 and 36 are
located on opposite sides of opening 39, the flames
will be projected into the chamber on opposite sides
of the exhaust opening 39. Preferably the burners 35
and 36 are constructed and arranged to direct the
flames toward the central portion of the bottom of
the ladle chamber 15, with the flames merging with
each other at the bottom wall of the ladle, thus
tending to completely wash the bottom surface of the
ladle with flame. This tends to apply the hottest
heat to the thicker bottom wall of the ladle, and the
flame and gases of combustion tend to wash-back along
the annular side wall of- the ladle and ultimately
exit through the exhaust opening 39 and on through
the exhaust gas conduit means 38. This tends to
uniformly heat the ladle and the heat not transferred
from the flame and gases to the ladle is moved with
the gases through exhaust opening 39.
Reversible motor 53 is mounted on carriage
18 and is in driving relationship with respect to the
wheels 19 of the platform and thus functions as a
113730Z
12
_ means for urging the seal assembly and the rim of the
ladle in compressive relationshiP wtih respect to
each other.
Heat exchan9er 22 is located at the upper
portion of the ladle heater 10 where it is accessible
for inspection and repair. This location of the heat
exchanger also places it in a remote location with
respect to the flame applied within the chamber 15 of
the ladle 11, so that the heat exchanger is not in
direct heat radiation with respect to the flame in
the chamber. This protects the heat exchanger from
the additional heat of radiation, while the heat
exchanger is fully exposed to the heat of convection
from the exhaust gases moving through the exhaust gas
conduit means. The heat exchanger 22 is fabricated
from ceramic materials so that it is capable of
withstanding temperatures in excess of 2000F.
When the heating of the ladle has been
accomplished by the ladle heater 10, the usual
2~ procedure is to extinguish the flame within the
chamber 15 of the ladle by terminating the flow of
fuel and air to the burners 35 and 36, to close
damper 45 in the exhaust duct 44 and to move the
ladle 11 and ladle heater 10 apart, whereupon the
ladle can be turned to an upright attitude and
transported to a position for filling with molten
metal, etc. ~hen the damper 45 is closed,
atmospheric air is substantially prevented from
flowing through exhaust gas conduit means 3~ and
through heat exchanger 22. This avoids rapid cooling
of the heat exchanger 22, and thereby reduces the
hazard of damage to the heat exchanger due to rapid
contraction. Also, if the ladle heater 10 is to be
used again within a short period, the heat exchanger
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13
22 will retain a substantial amount of its heat for
its next cycle of operation.
As illustrated in Fig. 6, wherein a second
embodiment of the invention is disclosed, the heat
exchanger can be formed as a multiple stage heat
exchanger wherein a first stage 65 is located
relatively low in the exhaust gas conduit means 38
and one or more additional heat exchangers are
located in sequence therewith. In the embodiment
illustrated, an intermediate or second stage heat
exchanger 66 is located above the first staqe heat
exchanger, and an upper or third stage heater
exchanger 67 is located above second staqe heat
exchanger 66. The exhaust gases are directed in
lS sequence through the first, second and third heat
exchangers, with the first stage 65 receiving the
hottest gases of combustion. The air from blower 24
passes first through the upper or third stage heat
exchanger 67, then through duct 68 to the second
stage heat exchanger 66, then through duct 69 through-
the first stage heat exchanger 65, and then through
branch conduits 31 and 32 to the burners 35 and 36.
Exhaust blower 24A is located above third stage heat
exchangers 67 and induces a flow of hot gases from
the ladle across the heat exchangers.
Preferably, first stage heat exchanger 65
is fabricated from ceramic materials which are
capable of withstanding temperatures in excess of
2000F. The second and third heat exchangers 66 and
67 are fabricated from stainless steel and carbon
steel respectively which are mateirals which are not
capable of withstanding the high temperatures that
the ceramic materials can withstand. For example,
the ceramic heat exchanger is fabricated to withstand
li37302
14
_ temperatures up to 2600-F, the stainless stee~ heat
exchanger is fabricated to withstand temperatureS up
to 1800F and the carbon steel heat exchanger is
fabricated to withstand temperatures up to 1000F.
It is anticipated that the temperature of the gases
exhausted from the third stage heat exchanger will be
approximately 600F. The air moved from blower 24-is
expected to be received in third stage heat exchanger
67 at a temperature of approximately lOO~F, will exit
from the third stage heat exchanger and enter the
second stage heat exchanger 66 at a temperature of
approximately 5~0-F, and will exit from the second
stage exchanger 66 and enter the first stage heat
exchanger 55 at a temperature at approximately
1300F. The temperature of the air as it leaves the
first stage heat exchanger 65 and approaches the
burners will be approximately 2000F. While specific
materials are disclosed from which the best
exchangers can be fabricated, other materials can be
used and different sizes, types and numbers of heat
exchangers can be utilized, if desired.
As illustrated in Fig. 7, the seal assembly
of the ladle heater can be reoriented from a vertical
attitude to a horizontal attitude to engage the rim
of an upright ladle. seal assembly 70 comprises a
support ~rame 71 and a network of refactory fiber
modules (not shown) similar to those illustrated in
Figs. 4 and 5 are supported in the horizontal support
frame. The support frame is movably mounted on
upright threaded jack screws 72 and 73 and the
exhaust gas conduit means 75 comp~ises duct work 76
that extends from the opening (not shown) in the seal
assembly 70 to the heat exchanger 74, and exhaust
duct 78 directs the exhaust gases from the heat
.
''` 11373~Z
_ exchanqer 74 away from the ladle heater. Blower 7g
directs air through conduit 80 to the upper header 81
of the heat exchanger, and the air is then directed
down through the heat exchanger 74, lower header 82
and then through branch conduits such as conduit 84
to burners such as burner 85. The ladle heater of
~ig. 7 is mounted on a carriage 86 and carriage 86 is
mounted on wheels 88 for movement along a track or
the like. The reversible motor 89 is mounted on
platform 18 and is arranged to drive the wheels of
the ladle heater so that the ladle heater can be
moved along the tracks 20 toward or away from a
ladle. In the alternative, the ladle heater of Fig.
7 can be mounted in a stationar~ position if desired.
The jack screws function as a means for urging the
seal assembly and the rim of the ladle in compressive
relationship with respect to each other.
As illustrated in Fig. 8, a control system
is provided for controlling the operation of the
ladle heater illustrated in Figs. 1-4. Similar
control systems are provided for ladle heaters of the
type illustrated in Figs. 6 and 7. Air is directed
from blower 24 through the air conduit means 25,
through heat exchanger 22 and to burners 35 and 3~
and through seal assembly 21 to the ladle 11. Air
control valve 90 regulates the flow of air from
blower 24 through the air conduit means, and position
controller 91 controls the position valve 90.
Position controller 91 is actuated by thermocouple 92
which detects the temperature of the exhaust gases
moving through exhaust gas conduit means 38. Thus,
when the temperature of the exhaust gases is higher
than desired, position controller 91 and air control
valve 90 function to reduce the amount of air movin~
11373(~2
16
to the ladle.
Fuel is directed through f~el line 94 from
a supply under pressure and passes through high
temperature shutoff valve 95 and flame out safety
shut off solenoid valves 96 and 97 to burners 35 and
36. Ther~ocouple 99 senses the temperature of the
exhaust gases flowing throu~h exhaust gas conduit
means 38 and regulates shutoff valve 95. For
example, when the temperature of exhaust gases is too
hi~h, v21ve 95 is closed and the flames from both
burners 35 and 36 are extinguished. Fuel regulator
valve 100 is also positioned in fuel line 94. Fuel/
air regular 101 regulates the fuel valve 100, and its
sensing conduit 102 communicates with air supply
conduit means 25. Sensing conduit 102 includes a
bleed line 104, and valve 105 regulates the bleed
through bleed line 104. Position controller 106
- regulates bleed valve 105, and position controller
106 is regulated by oxygen sensor 108 and by oxygen
transmitter 109. When an excessive amount of oxygen
is detected in exhaust gas conduit means 38, oxygen
~ransmitter 109 causes position controller 106 to
close valve 105, causing fuel air regulator 101 to
further open fuel valve 100.- - This supplies
additional fuel to burners 35 and 36, thus tending to
provide sufficient fuel to complete the combustion of
the oxygen supplied by the air to the ladle.
When the seal assembly 21 and ladle 11 are
separated, differential pressure sensor 112 detects a
change in pressure in exhaust gas conduit means 38,
and differential pressure transmitter 114 activates
position controller 115 to close exhaust damper 45,
to prevent atmospheric air from passing through heat
exchan~er 22.
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_ Ultraviolet sensors 118 and 119 are mounted
on each burner 35 and 36 and each functions to acuate
its solenoid valve 120 or 121 in response to a flame
out in its burner, thus immediately terminating the
flow of fuel to its burner.
Referring now to Fig. 9, wherein another
embodiment is illustrated, ladle 212 is placed on a
support stand 218 with the ladle tippled 90 from its
normal vertical orientation such that the open end
216 of the ladle opens in a horizontal direction. The
ladle 212 can be a conventional ladle which includes
a steel outer wall 214 and a refractory inner lining
215, which can be in the form of bricks.
The ladle heating system 210 according to
this embodiment of the invention includes a heat
exchanger and burner assembly 220 also having a
refractory or otherwise heat-resistant inner lining
221. The heat exchanger and burner assem~ly 220 has
an open end 222 defined by a mouth 224 opening in a
horizontal direction at the side of the heat
exchanger. The mouth 224 defines a mating opening
for receiving the open end 216 of the ladle 212, and
holds a circular seal 225 comprising a ceramic fiber
compaction material. The material of the seal 225
gives somewhat when engaged by the open end 216 of
the ladle 212 to prevent excessive leakage between
the interior of the ladle and the outside
atmosphere.
Ambient air is directed along an air inlet
duct 228 by means of a blower 230 into the assembly
220. The air inlet duct 228 splits into two branches
before entering the assembly 220, and the volume of
air delivered by the blower 23n is reg~lated by a
variable orifice valve 231 located prior to the
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18
branchinq of the duct 228. After entering the heat
exchanger and burner assembly 220, the branches of
the air inlet duct 228 are connected to a pair of
heat exchange units 228 within the heat assembly 220,
only one of which is visible in Fig. 9. ~ach heat
exchange unit 229 includes an air inlet path and an
exhaust outlet path. The air inlet path is connected
to one of a pair of fuel burners 233 which are
located within the assembly 220 and oriented to
project a flame and combustion gases into the ladle
212 to uniformly heat the refractory lininq 215 of
the ladle 212. The exhaust outlet path defined
within each heat exchange unit 22g is open at 232 to
the interior of the ladle 212. Within the openig 232
are located a conventional temperature probe 234,
such as a thermocouple, and a conventional oxygen
probe 235 which detects the amount of oxygen in the
gases surrounding the probe by measuring the change
in the electrical resistance of the gases. The
exhaust outlet path defined within the heat exchange
units 229 is also connected to an insulated exhaust
duct 36 which communicates with the surrounding
atmosphere either directly or through a filter or
other pollution control device.
The boundaries between the air inlet path
and the exhaust outlet path of the heat exchange
units 229 must be constructed of material sufficient
to withstand the heat of the com~ustion gases
produced by the burners 233, which can be in excess
of ~000F. A suitable heat recuperator for this
purpose is a single pass cross-flow shell and tube
heat exchanger with the interior components
constructed of ceramic materials. A suitable burner
for use in all the embodiments of the present
1~37~C~Z
19
invention is manufactured by Hague International,
Inc. under the product designation "HI 'TRANSJET'
Model 300", usina natural gas as a fuel and capable
of a heat output of 5.8 x 16BTU/Hr. The burners
233 are supplied with natural gas from a gas supply
238 (shown diagramatically in Fig. 11) through a fuel
supply line 239 which includes a main fuel control
valve 240 and an oxygen responsive control valve 241
downstream from the main valve 240.
A schematic diaqram of the ladle heating
system of the invention including the control system
utilized to operate the ladle heating system 210 of
the present invention is shown in Fig. 11. Signals
are received from the temperature probe 234 at a
temperature controller circuit 248. The construction
of a controller circuit 248 to perform the functions
required is within the capability of those skilled in
the art, and is commercially available. The circuit
248 monitors the temperature signal from the
temperature probe 234 and compares it to a
predetermined temperature. The predetermined
temperature is arriaved at by correlating empirical
measurements of the actual temperature of the ladle
212 and the temperature measured by the probe 234 at
the opening 232 to the exhaust outlet path of the
heat exchan~e unit 229, so that the predetermined
temperature represents a ladle temperature e~ual to
the temperature to which it is desired to heat the
ladle prior to being char~ed with molten metal. The
desired ladle temperature can range from 1600-2600F
depending on the type of molten metal to be placed in
the ladle. When the temperature measured by the
probe 234 exceeds the predetermined temperature, the
controller circuit 248 initiates a starter 256 to
11373~2
operate a motor 257 for a short ?eriod of time. The
motor 257 is mechanically linked bv a linkage 258 to
both the air inlet valve 231 and the main fuel valve
240, and thus causes the valve 231 to decrease the
amount of air traveling in the air inlet duct 228 and
also causes the valve 240 in the fuel line 239 to
decrease the amount of fuel being delivered to the
burners 233. The temperature of the burner output is
thereby decreased. Similarly, when the temperature
measured by the temperature ~robe drops below the
predetermined temperature, the control circuit 250
causes the valves 231 and 240 to increase the supply
of air and fuel to the burners 233 by operating the
motor 257 in a reverse direction.
The oxygen probe 235 located in the opening
232 of a heat exchange unit 299 sends a signal to an
oxy~en controller circuit 249, which is operable to
adjust the oxygen responsive valve 241 in the fuel
line 231 in response to the oxygen probe 235. The
oxygen controller circuit 249 is also within the
capability of those skilled in the art, and is
commercially available from ~aque International, Inc.
under the product desiqnation "OxSenn. Whenever the
amount of oxygen in the combustion gases as measured
by the oxygen probe 235 rises above a predetermined
valve representina efficient combustion, the
controller circuit 249 causes a starter 254 to
operate a motor 255 for a short period of time. The
motor 255 is connected via a mechanical linkage 259
to the valve 241 which is thereby mechanically opened
somewhat to slightly increase the amount of fuel
being delivered along the fuel supply line 239 to be
mixed with air from the air inlet duct 288 and burned
in the burners 233. Likewise, if the oxygen measured
11373~Z
by the probe 235 indicates that the fuel-air mixture
is too rich relative to the predetermined value of
oxygen content, the controller circuit 249 causes the
valve 241 to decrease the amount of fuel supplied to
the burners 233 by operating the motor 255 in a
reverse direction.
The heat exchanger and burner assembly 220
also includes a flame out safety fuel shutdown
system. An ultraviolet sensor 237, shown
diagrammatically in Fig. 11, is located within the
assembly 220 in suitable position to monitor the
radiation emitted by the burners 233 when in
operation. If for any reason the burner flame is
extinguished while fuel is being supplied, the
absence of radiation is sensed by the ultraviolet
sensor 237 and a signal is received from the sensor
237 at a solenoid controller circuit 250. The
circuit 250 is operatively connected to a solenoid
operated valve 242 in the fuel supply line 239 and
closes the valve 242 in response to the flame out
signal from the sensor 237. The controller circuit
250 is of conventional construction and is
commercially available.
The assembled heat exchanger and burner
assembly 220, blower 230 and ducts 288 and 236 are
mounted on a motorized transporter 244 which runs on
wheels 245 along rails 246. The assembly 220 is
selectively moved horizontally along the rails 246 by
a propulsion means (not shown) of any conventional
type known to those skilled in the art. Travel of
~he transporter 244 along the rails 246 is limited by
an end stop 247.
In operation of the ladle heating system
210, a ladle 212 is first placed on its side on the
113730Z
22
stand 218 at the end of the rails 246 by any
conventional means such as an overhead crane. The
transporter 244, initially located in spaced relation
from the end stop 247, is then moved horizontally
until the transporter 244 rests against the end stop
247 and the seal 225 within the mouth 224 of the heat
exchanger and burner assembly 220 is enqaged with the
open end 216 of the ladle 212. At such time the
~operation of the blower 230 is initiated to deliver
air along the inlet duct 228. After traveling
through the inlet air path of the heat exchange units
229, the air is mixed with fuel from the fuel line
239 and the mixture is ignited in the burner. Flame
and combustion gases from the burners 233 heat the
refractory lining 215 of the ladle 212. The hot
combustion gases escape from the interior of the
ladle 212 through the opening 232 of the heat
exchange units 229 into the exhaust outlet path of
the heat exchange units 229.
While passing through the heat exchange
units 229, the hot exhaust gases transfer heat to the
inlet air passing through the inlet air path of the
heat exchange units 229. Preheating of the inlet air
before mixture with fuel for combustion makes the
operation of the burners 233 more efficient. After
passing through the exhaust outlet path of the heat
exchange units 229, the hot combustion qases are
exhausted through the exhaust conduit 236.
As the combustion gases pass over the
oxygen Drobe 23~, the amount of oxygen in the
combustion gases is monitored by the probe, and a
signal providing such information is transmitted from
the oxygen probe 239 to the oxygen controller circuit
249. I~ the amount of oxygen measured by the probe
`- 113~ 2
23
235 is higher than a predetermined value, the
controller circuit 249 causes the oxygen responsive
valve 241 to allow more fuel to be mixed with the
inlet air in order to more fully burn the oxygen in
the inlet air. If the amount of oxygen measured by
the probe 235 becomes too small, the fuel-air ratio
is decreased to maintain optimum combustion condition
in the burners 233.
The hot combustion gases also pass over the
temperature probe 235 which monitors the temperature
of the gases as they enter the heat exchange units
229. In response to the measured temperature rising
above a predetermined value, the temperature
controller circuit 248 lowers the output of the
burners 233 by simultaneously gradually closing the
blower valve 231 and the main fuel valve 240 in the
fuel line 239. Thus, when the burners are initially
ignited, they can run at full capacity and the
relatively cool ladle 12 will rapidly absorb the heat
of the combustion gases. As the ladle becomes
heated, it will less readily absorb heat and the
temperature probe 234 will rise. For example, an
unheated 55 ton ladle would accept heat initially at
a rate of about eleven million BTU/Hr, but would
eventually reach a stabilized condition. In such a
condition only about two million BTU/Hr are required
to maintain the elevated temperature of the ladle.
By maintaining the temperature of the
combustion gases at the predetermined value, the
control system of the present invention heats the
ladle 212 at the maximum rate possible, while
maintaining energy efficiency by operating the
burners 233 to provide the maximum level of heat
which ~he ladle 212 can absorb at any particular time
1137~0Z
24
_ during the heating of the ladle. The intensity of
the burners it thus gradually throttled down from
maximum output to minimum output, during the course
of a typical ladle heating operation. If, during a
holding period after the ladle has been heated to the
required temperature for receipt of molten metal, the
temperature of the combustion aases drops below the
predtermined value, the controller circuit 248 causes
the valve 231 and 240 to increase the intensity of
the burner and thereby maintain the ladle in its
heated state.
It will be seen that the control system is
designed so that the fine tuning of the fuel-air
ratio provided by the oxygen controller 249 operates
effectively at whatever `level of intensity the
burners 233 assume in response to the temperature of
the combustion gases as measured by the temperature
probe 235 and regulated by the temperature controller
248.
When the ladle has reached the desired
temperature and is needed to receive a charge of
molten metal, the transporter 244 is moved
horizontally along the rails 246 to remove the heat
exchanger 220 from engagement with the open end 216
of the ladle 212. The ladle 212 may then be removed
from the stand 218 and delivered to a station for
receiving molten metal from a furnace. It should be
understood that the ladle heating system 210 could
alternatively be fixed in position, and that the
transporter would be located to convey the ladle 212
between the position shown in Fig. 9 engaging the
heat exchanger, and a position spaced apart from the
fixed system for enaagement by an overhead crane or
the like. Moreovert the ladle heating system 210 can
11373(~Z
alternatively be oriented vertically so as to receive
a ladle in upright position; suitable manipulating
apparatus would be required to move the system and/or
the ladle into and out of contact.
Another embodiment of the present invention
is shown in Fig. 10, which depicts a ladle heating
apparatus 260. The ladle heating apparatus 260 is
similar in all respects to the apparatus shown in
Fig. 9, ~ith the exception that two additional heat
exchangers, a stainless steel heat exchanger 252 and
a carbon steel heat exchanger 253, are included in
the system. Thus, the blower 230 delivers air
through an inlet conduit 228a to an inlet air path
within the heat exchanger 253, through a connecting
inlet duct 228b to an inlet air path within the heat
exchanger 252, and thereafter through an inlet air
duct 228c to the ceramic heat exchanger and burner
assembly 220 which includes the burners 233 and
engages the ladle 212. After heating inlet gases in
the assembly 220, the hot combustion gases pass
through an exhaust duct 236a to the exhaust path of
the stainless steel heat exchanger 252, through
exhaust ducts 236b and 236c to the exhaust path
within the carbon steel heat exchanger 253, and
thereafter are exhausted to atmopshere through a duct
262. The three heat exchangers of the embodiment
shown in Fig. 10 cooperate to recuperate as much
waste heat as possible from the combustion gases
leaving the ladle 212. The ceramic heat exchanger
and burner assembly 220 is constucted of materials
capable of withstanding the combustion gas
temperatures, which are in excess of 2000F, and
transfers heat ~rom such gases to the inlet air
stream. The stainless steel heat exchanger is
1137302
26
capable of withstandinq the exhaust gases of
intermediate temperature after heat has been
extracted therefrom by the ceramic heat exchanger.
Similarly, the carbon steel heat exchanger 253 is
efficient in transferring heat from the relatively
low temperature exhaust gases prior to exhausting
said gases to the atmosphere. Operation of the
embodiment of the invention shown in Fig. 10 is
essentially similar to that described for the
embodiment shown in Fig. 9.
Now that the ladle heating system according
to the invention has been described in detail, it
will be understood by those skilled in the art that
the principles of waste heat recuperation and heating
control may be applied to systems utilizing heat
sources other than natural gas flame burners.
Although the foregoing description realtes to
apparatus and methods of heating ladles, it should be
understood that various other objects can be heated
with the disclosed apparatus and method. It should
~e understood, of course, that the foregoing relates
only to preferred embodiments of the present
invention and that numerous modifications or
alterations may be made therein without departing
from the spirit and scope of the invention as set
forth in the appended claims.
