Note: Descriptions are shown in the official language in which they were submitted.
1- ~331%82
HEATING VESSEL LID CONSTRUCTION
This application is a division of our application
serial number 570,754 filed June 29, 1988.
Back~round of the Invention
1. Field of the Invention
This invention relates to high temperature heating
vessels, and in particular, to technique for prolonging
the service life of a lid for a glass batch melting
furnace by protecting the inner exposed surface of the
lid. This invention also relates to a heat and wear
resistant lid for a glass melting furnace.
2a. Technical Considerations
One type of glass melting process entails feeding
of glass batch materials onto a pool of molten glass
contained in a tank type melting furnace and applying
thermal energy to melt the materials into the pool of
molten glass. The melting tank conventionally contains a
relatively large volume of molten glass so as to provide
sufficient residence time for currents in the molten glass
to effect some degree of homogenization beore the glass
is discharged to a forming operation.
U. S. Patent No. 4,381,934 to Kunkle and Matesa,
disclcses an alternative type of glass melting
arrangement, and more particularly an intensified batch
liquefaction process in which large volumes of glass batch
materials are efficiently liquefied in a relatively small
liquefaction vessel. This type of process, particularly
when using intensified heat sources such as oxygen flame
: 1331282
-- 2 --
burners, produces relatively small volumes of high
temperature exhaust gases.
During the heating and melting process, it is
believed that certain components of the batch material
vaporize. These vapors may be corrosive to exposed metal
and refractory surfaces and when combined with the hot
exhaust gas stream that circulates through vessels of the
type disclosed in U. S. Patent No. 4,381,934, corrode
exposed interior surfaces, and in particular the vessel
lid. In addition, the exhaust gas may entrain particulate
matter within the vessel which may act as an abrasive on
an exposed surface. This corrosive and abrasive gas
stream greatly reduces the service life of the vessel lid
which may result in increased costs and additional do~n
time for lid repair and replacement.
Due to the corrosive effects of the exhaust gas
stream within the vessel which are accelerated by the high
temperatures as well as any abrasive or erosive effects
from the entrained particulates, exposed surfaces within
the vessel, and in particular the vessel lid, must be
designed to withstand these deleterious conditions, so as
to reduce maintenance and/or replacement of the lid that
is necessitated by excessive wear along its inner surface~
The high temperatures within the vessel may also
pose additional processing problems. For example, heat
loss will affect the efficiency of the operation. The-
more heat that is lost during the liquefaction process
through uninsulated and/or exposed interior surfaces of
. ~
133~ 282
-- 3 --
the vessel, the less efficient the liquefaction process
becomes. This may require additional heat input to the
vessel in order to account for the amount of heat lost.
In particular, the removal of heat by cooling the vessel
lid in order to reduce heat degradation and prolong
service life reduces the overall heating efficiency of the
operation. If this heat loss could be controlled and
reduced, the overall efficiency of the operation would be
increased.
It would be advantageous to have a heating vessel
lid with a protective coating on its exposed inner surface
that both insulates the lid, thus reducing heat loss from
the heating vessell and protects the exposed inner surface
from a high temperature corrosive gas stream entrained
with abrasive particulates, so as to increase its service
life and decrease overall operating costs. In addition,
it would be advantageous to have a wear resistant lid
design that could withstand such operating conditions and
provide a prolonged operating life.
U. S. Patent No. 3,165,301 to Riviere teaches a
method and device for protecting refractory walls. A
burner positioned in the roof of an elongated horizontal
furnace flows a gaseous suspension of carbon particles
along the roof to protect the roof against heat radiating
from the flame formed by burners in the furnace. The
carbon particle suspension is circulated within the
furnace parallel to the roof and in a direction opposite
to that of the main burner flame. The arrangement
- 4 - ~ 3 3 1~ ~ 2
reguires additional gas to be added to the heating
system~ Furthermore, the carbon particles are an
additional contaminant in the heating operation.
U. S. Patent No. 4,021,603 to Nanjyo et al teaches
a cooled metal roof assembly for an arc furnace with
refractory liner to protect the interior roof surface from
high heat. Fire brick or other refractory material is
provided within grooves formed on the interior ~urface of
the roof to improve r~sistance to heat of the furnace roof
assembly. The refractory material must be periodically
replaced in order to ensure proper thermal insulation. In
addition, the center portion of the lid is a consumable
substructure that includes three holes for electrodes.
There is no protection provided to this portion of the lid.
U. S. Patent No. 4,182,610 to Mizuno et al teaches
a water cooled metal cover for steel making or smelting
furnace. Fins in the formi of a lattice structure extend
from the interior surface of an annular portion of the
cover to provide a surface to which slag resulting from
splashes within the furnace may adhere. The splashes of
slag that adhere to the fins insulate the lower surface of
the cover's cooling jacket. The center portion of the
cover which includes openings for electrodes, does not
have the lattice structure to accumulate the slag so that
there is no protection provided on this portion of the
lid. In addition, the random splashing of-the slag does
; not provide a uniform buildup of insulating material over
the entire cover surface.
, ~"
.- ~ ., . ~ ~ ,
_ 5 _ ~ 3~2~2
U.S. Patent No. 4,434,495 to Tomizawa et al.
teaches a cooling pipe structure for arc furnaces.
Wherein cooling pipes are embedded within refractory
blocks. The pipes are positioned adjacent to the surface
of the block facing the inside of the furnace to intensify
the cooling of the surface. Slag splashed against the
block surface will congeal and adh~re to the block to form
an insulating film.
U.S. Patent No. 3,765,858 to Settino teaches a
method of roll forming a ribbon of glass at high
temperatures by bringing the glass, while still molten,
into con~act with a roll faced with an iron-based alloy
which includes, among other components, 5.0 to 5.8 percent
chromium by weight. The patent discloses other roll
configurations wherein the rolls are provided with a
surface of AISI type 410 or 420 stainless steel.
U.S. Patent No. 4,216,348 to Greenberger teaches a
water cooled roof panel assembly for an electric arc
furnace. Copper sheets are brazed to a steel backing
having integral ducts to circulate cooling
fluid through the panel. An outer ring around the roof
assembly acts as both a water source and drain for the
panels.
U.S Patent Nos. 4,182,610 to Nizuno et al. and
25 4,197,422 to Fuchs et al. teach a water cooled furnace ~ -
cover having a plurality of cooling boxes or jackets that
provide a ducting arrangement such that coolant may
circulate through the cooling boxes to cool the ~urnace
~3~1282
cover. In Mizuno et al., fin-like members extend from the
lower surface of the furnace cover so that a slag layer
may adhere to the fins to form a heat insulating layer.
In Fuchs et al., a protective layer of refractory material
is disposed on the underside of the cooling boxes to
provide additional thermal protection for the cover.
U.S. Patent No. ~,453,253 to Lauria et al. teaches
a wall and roof construction ~or electric arc furnaces
that are made of graphite blocks with removably attached
fluid cooled panels. The panels contain conduits for
circulating a cooling fluid along the exterior surface of
the block to cool it.
The prior art teaches lid construction furnaces but
does not disclose controlling the cooling of the lid to
permit materials entrained in hot gases circulating within
the furnace to be deposited on the inner surface of the
lid to form a relatively uniform and continuous insulating
and protective layer herein thickness of the layer, and
its associated insulative properties may be adjusted by
varying the cooling of the lid. The prior art also does
not teach a heat and wear resistant vessel lid that is
subjected to high temperature, corrosive and abrasive
conditions.
An object of this disclosure is to provide a
protective layer on an exposed inner surface of a heating
vessel. Hot exhaust gas which circulates within the -~
vessel includes entrained particulate and molten :~
materials, which may corrode and thermally degrade exposed
"'','', ;
, ': ,~ '
`` ~3~ 32
-- 7
surfaces within the vessel. The surfaces are cooled such
that the particulate and molten material that contacts the
surface will condense and stick to the surface.
Additional entrained material build up on previously
deposited material so as to increase the material layer
thickness. This layer both thermally insulates the
sur~ace and protects it against corrosion from materials
within the circulating exhaust gas stream. As the layer
thickness increases, so does the insulative properties.
When the temperature within the heating vessel is
suf~iciently high, newly deposited material on the layer
will be melted off so as to maintain a relatively constant
layer thickness over the surface. The cooling rate of the
lid or the heating rate within the heating vessel may be
varied in order to change the thickness of the built~up
layer.
Another object is to provide a heating vessel lid
with a controlled cooling arrangement that allows
materials entrained in exhaust gas circulating within the
vessel to be deposited on an inner surface of the lid and
build up a protective, insulatlng layer.
The present disclosure also provides a heat and
wear resistant lid for a heating vessel whose interior
surface is subjected to high temperature, corrosive and
abrasive conditions during the heating operation. A main
support plate constructed ~rom ~or example, low carbo~
steel, is covered with a protective facing member to
- 8 - 133128~
increase the use~ul operating life of the lid. The lid
may be cooled so as to further reduce
the deleterious accelerating affect the high temperature
have on the corrosion of the lid.
In one particular embodiment of the invention, the
protective member is constructed from a chromium
containing alloy that is approximately 10 to 25 percent
chromium by weight. The protective member may be a
chromium steel alloy plate or weld overlay. The lid is
cooled to maintain a member temperature between
approximately 900F to 1200F (482C to 649C) so that
entrained materials within the circulating exhaust gas
adhere to and build up on the exposed surface of the
member and ~orm an insulating and protective layer.
Chromium alloy steel is used for the protective member
because of its high temperature and abrasive resistant
characteristics as well as its resistance to oxidization
and sulfidation.
Here also described is a lid module for a heating
unit having a rigid support plate, a protective facing
member overlaying the support plate and an arrangement to
independently support each module, interconnect the module
with adjacent modules, and cool each module. The
protective member is a chromium containing alloy and may
include a plurality of overlaying members.
Further described is a method of protecting an-- -
exposed, inner surface of a heating vessel from corrosive
gases. The exposed surface as provided with a protective
.- : -
~ 3312~2
_ 9
member whose temperature is maintained outside a range of
a temperature range within which it will crack.
Embodiments of the i~vention will now be described
with re~erence to the accompanying drawings wherein;
Figure 1 is a cross-sectional view of a
liquefaction vessel including a lid with a protective
insulating layer and embodying the invention.
Figure 2 is a graph showing the insulating
properties of a cooled metal lid used in a liquefaction
vessel as batch material adheres to the interior lid
surface.
Figures 3, 4 and 5 are enlarged cross-sectional
views of alternate embodiments of the present invention.
Figure 6 is a plan view of the expanded metal shown
in the embodiment illustrated in Figure 5.
Figure 7 is a cross-sectional of an alternate
liquefaction vessel embodying the present invention
including a heat and wear resistant lid.
Figure 8 is an enlarged top view of a lid module
for the heating vessel lid illustrated in Figure 7 with
portions removed for clarity.
Figure 9 is a cross-sectional view through line 9-9
of Figure 8 illustrating the protective facing members,
the batch build-up layer, the expanded metal anchors, the
cooling ducts and hanger support arrangement.
Figure 10 is a cross-sectional view through line
10-10 of Figure 8 illustrating the lid module
~-;
133~ 2~2
-- 10 --
interconnecting arrangement with portions removed for
clarity.
Figure 11 is a view similar to Figure 10
illustrating an alternate embodiment of the invention.
Figur~ 12 is a view along line 12-12 of Figure 11
showing the exposed surface of the lid of the heating
vessel illustrated in Figure 7.
petailed Description of the Preferred Embodiments
This invention is suitable for use in a process
wherein a hostile environment adversely ef~ects the
exposed interior surface of a heating vessel~ It is
particularly well suited for use in a heating process
where high temperatures and additional conditions within
the heating vessel such as circulation o~ corrosive and
abrasive materials accelerate the wear of portions of the
lid or roof o~ the heating vessel. The invention is
described in connection with a glass liquefaction process
of the type taught in U. S. Patent No. 4,381,934 to
Heithoff but it is to be understood that the invention can y
be used in any heat related process where heat loss is to
be reduced or exposed surfaces such as heating vessel
walls reguire an insulating and/or protective coating.
With reference to Figure 1, the liquefaction vessel
10 is of a type similar to that disclosed in U. S. Patent
No. 4,381,934. The vessel 10 includes a steel drum 12
supported on a circular frame 14 which is in turn moun~ed
~or rotation about a generally vertical axis corresponding
to the center line of the drum 12 on a plurality of
. . - -
,. i~ -:
~` ~
1331~82
-- 11 --
support rollers 16 and aligning rollers 18. An outlet
assembly 20 below the drum 12 includes a bushing 22 with
an open center 24 leading to a collecting vessel 26. A
lid 28 is provided with stationary support by way of a
circular frame 30 including lid support blocks 31. The
lid 28 includes at least one opening 32 for inserting a
burner 34. The burner 34 is preferably a ~ulti-port
burner and is preferably fired with oxygen and gaseous
fuel, such as methane, but can be any type of heat source
that produces hot gases to heat batch material 36 within
the vessel lO, e.g., plasma torches.
Within the vessel 10, a layer of unmelted batch 36
is maintained on the walls of the drum 12 encircling a ~ ;
central cavity within which combustio~ and liquefaction
takes place. The heat from the flame of the burners 34
causes a portion 38 of the batch 36 to become li~uefied
and flow downwardly through the bottom opening 24. The
lique~ied batch 38 flows out of the liquefaction vessel 10 -~ ;
and may be collected in the vessel 26 below the
20 liquefaction vessel 10 for further processing as needed. ~ ~
The exhaust gases escape upwardly through an opening 40 in ~ -
the lid 28 into an exhaust duct (not shown~ or through an ;~
opening in the bottom of the heating vessel (not shown).
During the liquefaction process in the vessel 10,
various materials become entrained in the hot exhaust gas
from the burners 34. For example, in a typical ~
soda-lime-silica batch these entrained materials may
include vapors such as, but not limited to, sodium
- 12 _ ~331~2
hydroxide and particulates such as, but not limitad to,
sodium sulfate or sodium carbonate, all of which are
highly corrosive to metal and refractory materials. At
the elevated temperatures within the heating vessel 10 the
chemical attack on exposed interior surfaces of the vessel
10 is accelerated. In addition, abrasive particles within
the vessel 10 may combine with the hot exhaust gas to form
a corrosive and abrasive gas stream that circulates within
the vessel 10. The interior surface 42 of the lid 28
presents a large exposed surface within the vessel 10 that
is susceptible to this high temperature attack.
In general, the surface 42 is made of a corrosive
resistant steel such as, but not limited to, chrome alloy
steel. Although not limiting in the present invention, in
a praferred embodiment of the invention the lid 28 is
preferably a fluid cooled metal lid as shown in
` Figure 1. A cooling fluid, for example air or water,
enters the lid 28 through inlet 44 and flows into plenum
46. The fluid then passes through perforate plate 48 to
distribute the cooling fluid along inner surface 50 of the
exposed interior surface 42 of the lid 28. The fluid
circulates along the inner surface 50 and exits the lid 28
through outlet 52. The arrows in Figure l show the
circulation of the cooling fluid through the lid 28. As
the fluid circulates through the lid 28 it extracts heat
from the interior surface 42 so as to maintain a surface
temperature of surface 42 lower than that of the interior
of the vessel lO. The removal of excess heat through the
. .
: ~: , ., , ~ . .
. . - ~ . ~ . ~ . .
.... . .. . .
- 13 - 1 3 3 1 2 82
lid 28 in order to main~ain a relatively low temperature
of the lid 28 thus reducing heat degradation and
prolonging its service life may result in an inefficient
heating operation since additional heat must be added to
the system in order to affect the amount of heat lost or
removed.
In the embodiment of the invention illustrated in
Figure 1, the surface 42 is cooled to a temperature such
that material circulated by the hot exhaust gas within the
~0 vessel 10 will begin to adhere to it. In the initial
stages of the vessel 10 heatup, the exhaust gas with the :~
vessel 10 may include, but is not limited to, entrained
airborne particulates ~uch as sand grains, dolomite and
limestone, molten sodium carbonate, and molten glass
cullet particles. At a sufficiently low lid surface 42
temperature, material such as molten glass cullet and ;~
sodium carbonate will condense and '~freeze" on the lid ;~
surface 42 with additional glass cullet and sodium
carbonate, as well other solid particulate materials and
20 condensed vapors, building up thereon. This built-up ~:~
layer 54 has a coef~icient of thermal conductivity at
least an order of magnitude lower than the metal lid 28
and therefore provides an insulating effect so that more
heat stays within the vessel 10 and less is removed
through the cooled lid 2d. As the temperature within the
vessel 10 increases due to less heat loss, additional ~~-
particulates within the exhaust gas stream begin to soften
and also stick to the previously deposited batch layer 54
s~ -
~33~ 2~2
- 14 -
further increasing its insulating qualities. This in turn
further reduces the heat loss through the lid 28 and
increas~s the temperature within the vessel 10. In
addition, unsoftened particulates are captured by the heat
softenad layer, further adding to its thickness and
insulative properties. At a sufficiently high temperature
within the vessel 10, the deposited material in layer 54
will start to melt at the surface exposed to the interior
of the vessel 10 and drip back into the vessel 10, thus
limiting the thickness of the batch layer 54 buildup and
maintaining it at a generally constant layer thickness,
with a correspondingly reduced heat loss. At this steady ;~
state condition, the final batch layer 54 thickness will
directly relate to the types of material being heated and
the interior temperature within the vessel 10. As a
result, it is clear that the relationship between the
engineering of the vessel and type of material within the
vessel 10 requires balancing the cooling of the lid 28 and
the temperature within the vessel 10 so as to develop the
layer 54 thickness required for a specific heating process.
It should be noted that the surface 42 should be of
a material that is not early oxidized because the metal
oxide may combine with the material in the layer 54 to
~orm an interface layer having a lower melting point than
the layer 54. As a result the interface layer will be
loosened from lid 28, and the layer 54 will fall back into
the vessel 10 exposing the lid surface 42. In addition,
if the metal does become oxidized care must be taken that
', ~ ' ' ~' .,- - ' ' ;' ~' .
- 15 - ~33~282
any oxides formed on the lid surface 42 will not add any
color or any other detrimental contaminants to the
resulting glass if the oxides become incorporiated into the
glass.
The batch layer 54 thickness can be modified by
changing the heating rate within the vessel 10 or the
cooling rate of the lid 28. For example, if the amount of
heat provided by the burners 34 is reduced, the layer
thickness will increase since the temperature within the
vessel lO would be lower, thus allowing the layer
thickness to increase before the insulating properties of
the layer raise the internal temperature of the vessel lO
to that required to melt the exposed outer surface of the
layer 54. Conversely, by increasing the amount of heat
provided by the burners 34 the thicXness of layer 54 can
be reduced. As discussed, the thickness of the layer 54
can also be modified by changing the cooling rate of the :~
lid 28. Although not limited in the present invention, a
valve 55 at inlet 44 may control the flow of cooling fluid
in the lid 28 as shown in Figure l. In particular, by
increasing the cooling rate, the amount of heat removed
from the system through the insulating layer is increased ~:
thu~ cooling the layer 54 and allowing its thickness to
increase until the increased insulating effect of the
layer increases the internal temperature of the vessel to
that required to melt the exposed surface of the layer~54.
The batch layer 54 provides several interrelated
functions. The layer 54 protects the surface against
` ` 133~ ~82
- 16 -
abrasive particles circulating within the vessel. It is
contemplated that some of the particulates will get
"stuck" to the layer and become part of the layer 54
itself. The layer 54 further functions as an insulator
that both reduces the heat loss within the heating vessel
10 through the lid 28, and lowers the temperature of the
lid surface 42, thus reducing the effects of heat
degradation. The layer 54 also seals the lid surface 42
and protects it from chemical attack. Specifically, the
layer 54 provides a barrier between the surlace 42 of the
lid 28 and oxygen, moisture, and corrosive vaporous gases
that circulate within the vessel 10, such as, but not
limited to, sodium sulfate, all of which will attack and
corrode the lid surface 42. In addition, since chemical
reactions are generally accelerated at high temperatures,
the reduced temperature of the surface 42 of the lid 28,
due to the insulating layer 54, reduces the rate of any
chemical attack at the lid surface 42 by corrosive
materials and thus prolonqs the lid life.
Figure 2 illustrates the effects on a lid of batch
layer 54 buildup with respect to temperature and burner
gas usage for a liquefaction vessel similar to that shown
in Figure 1. In this example, the cooling gas was air. It
should be noted that the reduction in the burner gas usage
at elapsed time intervals of 30 minutes and 70 minutes was
made to maintain a generally constant internal tempera~ure
within the vessel 10 as the insulating layer 54 began to
buildup on the lid. Referring to Figure 2 prior to the
,. - .~ , .~, ,: - .,
..... ~ . , . :,
. " - -
: - i, - ~ -. .
17 13~1282
batch buildup on the lid, the metal temperature was
approximately 1140F ~616C), cooling gas enthalpy was
approximately 115 x 103 BTU's per hour, cooling air exit
temperature was approximately S50F (291~C) and the burner
gas usage was approximately 90 cubic feet per hour (CFH)
at approximately 85F (29JC) ambient temperature. After
about 100 minutes of allowing the batch layer to build up
on the lid, these values were 825F (441C), 6.5 x 103
BTU's per hour, less than 400~F (204C) and ~0 CFH,
respectively. As can be seen, the lid metal temperature,
cooling gas enthalpy, and cooling gas exit temperature
were all significantly reduced due to the batch layer
buildup on the lid. It is believed that the two peaks in
the metal temperature of the lid at elapsed times 55
15 minutes and 85 minutes as shown in Figure 2 may have been ;~
due portions of the built up layer falling off of the lid
surface 42 and the subsequent restabilization of the lid
temperature. In general, it is expected that maintaining ~-
a lid sur~ace 42 temperature of approximately 900F~150F
(481C+66C) in a liquefaction vessel 10 with an internal
vessel temperature sufficient to liquefy a typical
soda-lime-silica glass batch, will form an insulating and
protective layer between 1/8 inches to 3/4 inch (0.32 cm
to 1.91 cm) thick depending on heating and cooling
conditions and batch formulation.
As the layer 54 increases in thickness, it is ~
possible that a portion of the layer 54 may fall off
exposing an area of the interior surface 42 of the lid
.
- 18 - ~ 3 3 ~ 2 ~ 2
28. As a result, there may be a kemporary loss of
insulating effect requiring sudden change in heating and
cooling demands. This may lead to dif~iculty in ?
controlling internal vessel temperature and the amount of
5 coolant required for the lid 28. I* desired, the surface
42 of the lid may include anchoring devices such as, but
not limited to, grooves 56 to accommodate and hold the
batch. The grooves 56 may be on the order of 3/32 inches
(0.24 cm) deep. Referring to Figure 3, although not
10 limiting to the invention, the grooves 56 may be
dovetailed in shape to help secure the batch layer 54 to
the surface 42. The groovas 56 also provid~ additional
surface area for initial layer 54 built up and may
distribute and reduce surface-to-surface shearing ~orces
15 between the layer 54 and lid surface 42 due to temperature
change in the vessel 10. Referring to Figure 4, the
initial adhesion of the lid 54 to the surface 42 may be
enhanced by coating the surface 42, whether it be smooth
or grooved, with a refractory cement 58 which provides an
20 initial insulation in the vessel 10 and better adhesion of
the layer 54 due to the resulting higher temperature
formation of the initial portions of the layer 54.
Figures 5 and 6 illustrate an additional embodiment
o~ the present invention. In order to further anchor
25 layer 54 to lid 28, foraminous members 62, such as
expanded metal, perforated plates, or screening are
secured to surface 42 of the lid 28. The foraminous
members 62 must be heat resistant and adequately attached
. ~ ... .
~L331282
-- 19 --
to the 28 so as to help support ~he layer 54 as it builds
on the lid surface 28. Although not limiting in the
present invention Figure 6 illustrates an expanded metal -
configuration that may be used. In one particular
embodiment of the invention, No. 16 expanded metal
fabricated from 410 stainless steel is tack welded at
approximately 2 to 3 inch centers (5.08 to 7.62 cm) to the
lid 28.
It should be appreciated to ~hose skilled in the
art that the benefits attributable to the batch layer 54
in the cooled metal lid 28 are equally attributable to a
: ~ :
lid of any construction, for example, refractory blocks.
The layer 54 will help seal and insulate the lid, maintain
lower heat loss within the vessel 10, provide protection
against accelerated chemical and abrasive attack and keep
the refractory surface at a lower temperature and thus
increase its effective service life. In addition, the new
structure may be used to protect exposed portions within
this vessel 10 other than the lid 28. For example, it may
be used to provide a protective layer on the inner surface
60 of lid support blocks 31. Furthermore, blocks 31 may
be constructed in a manner similar to that of the lid 28
shown in Figure 1 i.e., fluid cooled, metal construction,
so that the cooling rate of the blocks 31 may be
controlled to vary the thickness of a built-up protective
layer.
Figure 7 illustrates an alternate liquefartion
vessel 110 similar to the type disclosed in ~.S Patent No.
133 12~2
- 20 -
4,668,272 to Newcamp et al. A steel drum 112 is suspended
from a circular frame 114 by struts 116, which is mounted
on a plurality of support rollers 118 and aligning rollers
120, for rotation about a generally vertical axis
corresponding to the center line of the drum 112. An
outlet 122 below the drum 112 includes a bushing 124 with
an open center 126. Lid 128, which is the subject of this
invention, is provided with a stationary support by way of
a frame 130 which is mounted independently from and aboye
the rotating drum 112 as shown in Figure 7. The lid 128
includes one or more openings 132 for inserting a high
temperature burner 134 into the vessel 110.
Within the liquefaction vessel 110, a stable layer
of unmelted batch 136 is maintained on the walls of the
drum 112 and encircling the central cavity within which
combustion and melting takes place. The heat from the
burners causes a surface portion 138 of the batch to
become liquefied and flow downwardly toward and through
the bottom opening 126. The liquefied batch then flows
out of the liquefaction vessel 110 and may be collected in
a vessel 140 below the liquefaction vessel 110 ~or further
processing as needed, for example as shown in U.S. Patent
Number 4,381,934 to Kunkle et al. Exhaust gases escape
either upwardly through an opening in the lid 128 and into
an exhaust outlet 142 or downwardly through the bottom
opening 126 at the bushing 124. ~ -
During the melting process in the liquefactionvessel 110, various matarials become entrained in the hot
,, . ~ . . . . ,~, .. .. . .
` ~33~2
- 21 -
exhaust gas stream. For example, in a typical
soda-lime-silica glass batch, these entrained materials
may include vapors such as, but not limited to, sodium
oxide and particulates such as, but not limited to, sodium
sulfate or sodium carbonate, all of which are highly
corrosive. The vapors and particulates combine with the
hot exhaust gas to form a corrosive and abrasive gas
stream that will corrode inner surface 144 of the lid 128
that is exposed to the gas. In particular, the inner
surface 144 is subjected to oxidation and sulfidation in
the high temperature environment. The high temperature
within the liquefaction vessel 110, which typically is in
the range between approximately 2400F to 2600F (1316C
to 1427~C) near the lid surface 144, accelerates this
corrosion and wear. In addition, particulates entrained
in the gas stream may further erode the surface 144. It
has been observed that this mechanical and chemical attack
may wear alumina/zirconia/silica refractory at a rate in
excess of one quarter inch (O.64 cm) per 24 hour elapsed
time period.
one method of reducing the wearing action of the
exhaust gas on exposed portions of vessel 110, and in
particular on lid 128, is to direct a high velocity gas
from a gas jet between the exhaust gas and the exposed
25 portion as taught in U.S. Patent No. 4,675,041 to Tsai. -~
The high velocity gas minimizes contact between the
exhaust gas and the exposed portions of the vessel so as
to reduce wear due to corrosive degradation.
. i . . :- . : :
\~
- 22 - 1 3 3 1 2 8 2
The present disclosure permits another way to
protect the exposed portions of the vessel from the
circulating exhaust gas. Referring to Figures 8 through
10, the lid 128 is constructed from a plurality of lid
5 modules 146 each including a main base plate 148 and a
high temperature, wear resistant overlayment 150 on the
hot face 144 of the lid 128. The term "wear resistant" as
used herein includes, but is not limited to, resistance to
corrosion, abrasion, oxidation or any other surface
depletion mechanism that will reduce the effective
operating life of the lid 128. The overlayment 150 is
preferably a plate or a weld overlay as will be discussed
later. Although not limited in the present invention, in
the preferred embodiment of the invention, the overlayment
150 is a chromium alloy stainless steel. The surface of a
chromium alloy steel will oxidize leaving a chromium oxide
layer that protects and seals the underlying steel against
further oxidation and chemical attack. Chromium alloy
steels are also abrasion resistant.
In the area of glass melting, ferritic stainless
steel is preferred over austenitic stainless steel because
the former has little or no nickel. If nickel from the
lid 128 gets into the melted glass, it will form a nickel
sulfide stone defect in the final glass ribbon. In the
following discussion reference to the properties of
chromium steel will be to ferritic steel but it should~be
appreciated that similar problems may occur with
austenitic stainless steels.
~: .;- . . :, . : -
- `
` ~3312~2
~ 23 -
Generally, the higher the chromium content in the
steel the greater its oxidation and corrosive resistance,
but the use of chromium steels present additional
problems. For example, chromium steels containing more
than about 15% chromium by weight and exposed to sustained
temperatures in the range of about 750F to 1050F (399DC
to S66C) may increase in hardness with a corresponding
decrease in ductility. This embrittlement ~ncreases with
increasing chromium and time at temperature. As a res~lt,
even though a lid surface 144 exposed directly to an
intense heat of greater than 1000F (538C) is constructed
of chromium steel with a high content of chromium, if the
temperature gradient through the overlay thickness is such
that portions of the overlay are maintained within a
critical predetermined temperature range, the lid 128 may
develop internal cracking.
~ o prolong the useful life of the lid 128, the
temperature of the lid 128, and more particularly, the
overlayment 150, is controlled to avoid embrittlement. In
the particular embodiment of the invention illustrated in
Figures 8 through 10, each module 146 of the lid 128 is
cooled by circulating coolant, preferably water, through a
series of ducts 152 formed, for example, by pipe members
divided along their longitudinal axis and welded to the
cold face 154 of the base plate 148. This cooling
arrangement is easily fabricated and avoids the need ~o-
form base plate 148 with integral ducts. Individual
inlets 156 and outlets 15~ allow the amount of coolant
" . .: :-, .: ` . . ' . ' ~ ' ; ;, ''' ~ . : -
- 1331282
- 24 -
circulating through the ducts 152 to be varied so as to
provide individual temperature control of each module 146
of the lid 128, if required. In addition, the inlets 156
and outlets 158 allow a single module 146 to be removed
from the lid 128, as will be discussed later, without
affecting the coolant circulation to the other modules 146.
The use~ul life of the lid 128 may be prolonged
further by providing a protective cover for overlayment
150. In the preferred embodiment of the invention, the
lid 128 is cooled to a temperature such that material
circulated by the hot exhaust gas within the vessel 110
will begin to adhere to it in a manner similar to that
taught in U.S. Patent 4,789,390 to Kunkle et al issued 6
December 1988.
In the initial stages of the vessel 110 heatup, the
exhaust gas with the vessel 110 may include, but is not
limited to, entrained airborne particulates ~uch as sand
grains, dolomite and limestone, molten sodium carbonate,
and molten glass cullet particles. At a sufficiently low
hot face 144 temperature, material such as molten glass
cullet and sodium carbonate will condense and "freeze" on
the hot face 144 with additional glass cullet and sodium
carbonate, as well as other solid particulate materials
and condensed vapors, building up thereon. This built-up
layer 160 has a coefficient of thermal conductivity at
least an order of magnitude lower than the metal lid r28
and therefore provides an insulating effect so that more
heat stays within the vessel 110 and less is removed
133~2
- 25 -
through the lid 128. As the temperature within the vessel
llO increases due to less heat loss, additional
particulates within the exhaust gas stream begin to soften
and also stick to the previously deposited batch layer 160
further increas~ng its insulating qualities. This in turn
further reduces the heat loss through the lid 128 and
increases the temperature within the vessel 110. In
addition, unsoftened particulates are captured by the heat
softened layer, further adding to its thickness and
insulative properties. At a sufficiently high temperature
within the vessel 110, the deposited material in layer 160
will start to melt at the surface exposed to the interior
of the vessel 110 and drip back into the vessel llO, thus
limiting the thickness of the batch layer 160 build-up and
maintaining it at a generally constant layer thickness,
with a correspondingly reduced heat loss. At this steady ~-
state condition, the final batch layer 160 thickness will
directly relate to khe types of material being heated and
the interior temperature within the vessel llO.
The batch layer 160 provides several interrelated
functions. The layer 160 protects the surface against
abrasive particles circulating within the vessel. It is
contemplated that some of the particulates will get
"stucki' to the layer and become part of the layer 160
itself. The layer 160 further functions as an insulator
that both reduces the heat loss within the heating vessel
110 through the lid 128, and lowers the temperature of the
hot face 144, thus reducing the effects of heat ~-
... ~ .. . . .... .... ..
., " ~. , . :~ . ., .. :
. . ~ . ~ , ,
~331282
- 26 -
degradation. The layer 160 also seals the face 144 and
protects it from chemical attack. Specifically, the layer
160 provides a barrier between the face 144 of the lid 128
and oxygen, moisture, and corrosive vaporous gases that
circulate within the vessel 110, all of which will attack
and corrode the lid hot face 144. Since chemical
reactions are generally accelerated at high temperatures,
the reduced temperature of the hot face 144 of the lid
128, due to the insulating layer 160, reduces the rate of
any chemical attack at the ~ace 144 by corrosive materials
and thus prolongs the lid life. However, it should be
noted that the batch layer 160 itself is corrosive due to,
for example, the sulfur content in the layer 160 which
results in sulfidation attack, so that the hot face 144 of
the lid 128 must still be resistant to chemical attack.
As the layer 160 increases in thickness, it is -~ -
possible that a portion of the layer 160 may fall off
exposing an area of the hot face 144 of the lid 128. As a
result, there may be a temporary loss of insulating effect
requiring sudden change in heating and cooling demands.
This may lead to difficulty in controlling internal vessel
temperature and the amount of coolant required for the lid
128. If desired, the hot face 144 of the lid may include
anchoring devices such as, but not limited to, foraminous
members 162, such as expanded metal, perforated plates, or
screening secured to face 144 of the lid 128 to hold the
layer 160, as shown in Figures 7, 9 and 10. The
foraminous members 162 must be heat resistant and
:`~
- 27 - 1331282
adequately attached to the lid 128 for sufficient cooling
and to help support the layer 160 as it builds on the hot
~ace 144.
In the particular embodiment of the invention
illustrated in Figures 8 through 10, the lid 128 is
fabricated from a 1 1/2 inch (3.~I cm~ thick base plate 48
of low carbon steel, for example AISI 1010 steel, a 1/4
inch (0.64 cm) thick intermediate plate 164 of chrome
steel having approximately lo to 16 percent chrvmium
lo content by weight and a 1/4 inch to 3/8 inch (0.64 to 0.95
cm) sxposed inner plate 166 of chrome steel with
approximately 16 to 27 percent chromium content by
weightO The preferred coolant is water which is
circulated through the ducts 152 to maintain the lid
surface 144 at temperatures between 900F to 1200F ~482C
to 649C). If required, chromium steel side plates 168
may be added to protect the side faces of the base plate ;
148, as illustrated in Figures 8 through 10. No. 16
expanded metal mesh fabricated from 410 stainless steel is
tack welded at approximately 2 to 3 inch centers (5.08 cm
to 7.62 cm) to plate 166 of the lid 128.
As discussed above, if the plate 166 is too thick,
a portion of the plate may be cooled by a combination of ::
the water cooling and/or the layer 160 build-up, to a
temperature range within which cracking may occur due to
the temperature gradient through the plate thickness. ~For
example, if the plate 166 is constructed from chromium
steel that is 125 percent by weight chromium and the plate
- 28 - ~ 3 3 ~ 2 ~ 2
166 is cooled so that the temperature gradient from the
surface 144 through the plate 166 results in a portion of
the plate thickness being maintained at a temperature
within its embrittlement range, there is a possibility
that internal cracking may occur in the inner plate 166.
By including an intermediate plate 164 of chromium steel
that has a lower chromium content than the e.~osed lnner
plate 166, and establishing the thicknesses of plates 164
and 166 so th~t under a predetermined set of operating .
parameters, the temperature gradient through the
overlayment l5o is such that the entire thickness of plat~
166 is maintained above the embrittlement temp rature -
range of 25% chromium content chromium steel, the plate
166 will not crack due to embrittlement. The lower
chromium content steel can be maintained within the
temperature range of the temperature gradient that will
cause e~brittlement of the 25% chromium content steel
because, due to its lower chromium content, the
embrittlement temperature range is lower. As a result,
the intermediate plate 164 will not e~perience the same
adverse affects within the embrittlement temperature range
of the 25% chromium content steel so that the risk o~
embrittlement in either plate of the overlayment 150 is
reduced.
It should be appreciated that a single plate of
chromium steel having an embrittlement temperature range
outside the temperature range of the temperature gradient
through the overlayment 150 may be used so as to eliminate
- ~: - - .: , : i . .
1331~82
- 29 -
cracking due to embrittlement. ~ low chromium content
chromium steel may have an embrittlement temperature range
below the tamperature gradient temperature range so that
cracking due to embrittlement will not occur, but low
chromium content chrome steel is less wear resistant than
higher chromium content steels. On the other hand, a high
chromium content chrome steel with an embri~.tlement range
above the temperature gradient temperature range, may
provide adeguate wear resis~ance but is more expensive
than lower chromium content chrome steel.
As an alternative, the overlayment 150 on the hot
face 144 may be constructed from multiple layers of the
same chromium content chrome steel. With this
arrangement, using high chromium content steel, the steel
15 plates positioned between the main plate 148 and exposed ;
outermost chromium steel plate may crack without the crack
propagating through the overlayment 150 to the hot face
144 of lid 128. If lower chromium content steel is used,
the exposed outermost plate may crack but the interior
plates will not, so that the main plate 148 is protected.
The plates 164 and 166 may be secured to the main
plate 148 in a number of ways well known in the art, such
as conventional welding, explosion welding and roll
bonding. It should be noted that the integrity of a
conventionally welded system is limited by the defects
that are inherent in the welding process, for example-
microcracking, voids, etc. In addition, conventional
weldin~ may not provide the degree of heat transfer
- 30 - ~ 3 3 ~ 2 ~2
between metal plates as is required in a high temperature
operation. For the high temperature applications,
explosion welding is the preferred method since it
provides the continuous, intimate contact between plates
that is necessary for good thermal conductivity through
the lid. If explosion welding is used for fabrication,
care must be taken to be sure that the impact strength of
the plate materials is high enough to withstand the
explosion welding techniques.
It should be appreciated that although in the
preferred embodiment of this invention, the overlayment
150 is chromium steel, other alloys may be used, e.g.,
Alpha IV* which is an aluminum and chromium alloy
available from Allegheny Ludlum Corp., Pennsylvania, and
Stellite 6* which is a cobalt and chromium alloy available
from Cabot Stellite Division, Indiana.
As an alternative, the overlayment 150 may be a
weld overlay, i.e., a series of weld beads deposited side
by side covering the entire hot face 144 of the lid 128.
In the particular embodiment of the invention illustrated
in Figures 11 and 12, chromium steel weld beads 170 are
applied to the base plate 148 by any of a number of well
known welding techniques, such as submerged arc welding,
which is preferred, and metal insert gas weldings. The
weld area 172 i9 preferably kept small to reduce
distortion of the base plate 148 which may warp or bow-if
long weld beads 170 are used. After one layer 174 of weld
overlay is applied, subsequent weld overlay layers 176 may
*Trade-mark
-
- 31 _ 1 3 3 ~ 2 ~ 2
be added, with the additional layers having a di~ferent
chromium content if required, to avoid embrittlament as
already discussed.
A weld overlay provides the intimate bond with the
base plate 148 that is required for good thermal
conductivity between base plate 148 and layer 174, but
welding presents additional concerns that must be
addressed~ When a chromium alloy bead is applied to base
plate 148, the two metals combine and the chromium content
in the resulting bead is diluted, i.e., the chromium
content will be approximately the average chromium content
of the base material and the overlay material. For
example, if the base material has no chromium and the weld
overlay material is 20% chromium by weight, the resultant
bead will be approximately 10% chromium i.e., (0% chromium
in base plate + 20~ chromium in overlay material)/2. lt
should be noted that successive passes of chromium
overlayment material to build up the overlayment 150
thickness will result in less dilution since the
underlying material will contain ohromium. Continuing
with the previous example, if a second layer of the same
weld overlay material is added over the first layer, the
resulting chromium content in the second layer will be
approximately 15%, i.e., (10~ in fir~t layer + 20~ in
second layer)/2. It is obvious that the greater the
number of weld passes, the less the chromium content -
- 32 - 1331282
reduction and thus the higher the resulting chromium
content.
In addition, the type of base plate 148 material
may influence the effectiveness of the weld overlay. It
has been found that when the carbon content o~ the base
plate 148 is too high, for example, as in cast iron, the
chromium in the overlay material combines with the carbon
to form chromium carbide. This co~bination reduces or
eliminates the chromium available to form the chromium
oxide protective lay~r as discussed earlier. To a~oid
this situation, low carbon and/or low carbon chromium
steel base plate materials should be used. As an
alternative, if the base plate carbon content is too high,
a weld overlay layer of low carbon content material, such
as pure iron, may be positioned between the base plate 148
and the chromium alloy steel weld overlay to act as a
buffer and reduce chromium depletion from the weld overlay.
In the particular embodiment shown in Figures 11
and 12, 1/8 inch (0.32 cm) thick beads 170 of 25% chromium
content alloy steel are applied in approximately 6 inch by
6 inch (15.24 cm by 15.24 cm) weld areas 172 to cover a 2
1/2 inch (6.35 cm) thick low carbon steel base plate 148.
Two 1/8 inch (0.32 cm~ thick layers of weld overlay 178
protects the sides of the base plate 148. Stainless steel
expanded metal 180 may be used to cover the hot face 144
and support the batch layer 182 which may be formed as
discussed earlier.
_ 33 _ ~ 3 3 1 2 g 2
The thickness of the base plate 148 and overla~ment
150 and the cooling arrangement in any embodiment of the
present invention are all interrelated and depend on the
operating conditions of the vessel 1107 The temperature
at the hot face 144 of the lid 128 depends on the
temperature within the vessel 110 and the amount of
cooling in the lid 128. Cooling, in turn, depends on the
thickness of the base plate 148 and overlayment 150 and
their respective coefficients of the thermal conductivity
and the spa~ing of the cooling ducts 152 on the cold face
154 of base plate 14B, as well as the desired temperature ; :~
at hot ~ace 144. Also, as discussed earlier,
embrittlement of the chromium overlayment 150 will
determine layer thickness.
In the preferred embodiment of this invention, each
individual module 146 is supported such that it may be
removed without affecting the operation of the remaining
modules 146 in a manner similar to that disclosed in U.S.
: Patent 4,704,155 to Matesa et al. issued 3 November 1987.
In the particular embodiment of the invention illustrated
in Figures 7 and 9, modules 146 are supported from beam
184 of support frame 130 via tie rod 186 and hanger 188.
Clevis member I90 of tie rod 186 is pinned to hanger 18
while the upper end of rod 186 is removably secured to
beam 184.
: Each module 146 is preferably interconnected in- any
convenient fashion with adjacent modules to form a unitary
lid structure. In the particular embodiment of the
_ 34 _ 1331282
invention illustrated in Figure 10, bolt 192 extends
through opposing ends of tie plate 194 and into bolt hole
196 of main plate 148. Collars 198 maintain tie plate 194
in spaced relation from main plate 148.
Positioning plates 200, similar in construction to
hangar 188, may be provided ~or handling the module 146 as
it is moved into and out of position in the lid 128 by a
lifting mechanism, e.g., overhead hoist ~not shown). The
hoist may lower an assembly (not shown) to connect to
positioning plates 100. The hoist cable is then tensioned
so as to support the module 146 as the tie rod 186 and tie
plates 194 are disconnected and the inlet 156 and outlet
158 are uncoupled from the coolant supply ~not shown).
The hoist then lifts the lid module 146 out from the lid
128, transfers it to an unloading site and returns to the
opening in the lid 128 with a new lid module 146. As an
alternative, the modules 146 may be lifted directly by the
tie rod 186.
It should be appreciated that although the
embodiments of the invention disclosed in Figure 7 through
12 illustrate a flat lid with rectangular removable
modules, other lid and/or module configurations may
be used. For example, the lid 12~ may be domed and/or the
modules 146 may be wedge shaped as taught in U.S. Patent
25 4,704,1~5.
The modular construction of lid 128 allows the-use
of modules with different thickness of overlayment 150 at
different locations. For example, the overlayment 150 for
:~ '
" ? .. `: . . ~
r ~ ~
_ 35 _ 133128~
modules 146 at potential problem areas, such as in the
vicinity of a material loading chute (not shown) or an
exhaust outlet 142, may be thicker than other lid portions.
In addition, the lid design described may be
combined with other lid or roof configurations wherein
only selected portions o~ the roof require continual
monitoring and replacement due to temperature and/or
corrosive and/or abrasive conditions within the heating
vessel. Fox example, a roof may be a continuous, one
piece structure over a majority of the vessel with
replaceable modules 146 at potential problem areas.
~ he forms of this invention shown and described in
this disclosure represent illustrative embodiments and it
is understood that various changes may be made without
departing from the scope of the invention.
