U.S. patent application number 16/532410 was filed with the patent office on 2019-11-28 for process for the preparation of high alumina cement.
The applicant listed for this patent is KNAUF INSULATION. Invention is credited to Gerard DEMOTT, David DUCARME, Bostjan MAROLT.
Application Number | 20190359523 16/532410 |
Document ID | / |
Family ID | 52673969 |
Filed Date | 2019-11-28 |
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United States Patent
Application |
20190359523 |
Kind Code |
A1 |
DEMOTT; Gerard ; et
al. |
November 28, 2019 |
PROCESS FOR THE PREPARATION OF HIGH ALUMINA CEMENT
Abstract
High alumina cement is produced in a submerged combustion
melter, cooled and ground.
Inventors: |
DEMOTT; Gerard; (Majcichov,
SK) ; MAROLT; Bostjan; (Poljane, SI) ;
DUCARME; David; (Wavre, BE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KNAUF INSULATION |
Vise |
|
BE |
|
|
Family ID: |
52673969 |
Appl. No.: |
16/532410 |
Filed: |
August 5, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15545991 |
Jul 24, 2017 |
|
|
|
PCT/EP2016/051731 |
Jan 27, 2016 |
|
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16532410 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C04B 7/32 20130101; F27B
2014/104 20130101; F27B 14/143 20130101; F27B 14/0806 20130101;
F27B 2014/0837 20130101; F27D 2027/002 20130101; C04B 7/475
20130101; C04B 7/4484 20130101; F27D 15/0206 20130101; F27D
2099/0085 20130101 |
International
Class: |
C04B 7/32 20060101
C04B007/32; F27B 14/08 20060101 F27B014/08; C04B 7/47 20060101
C04B007/47; F27D 15/02 20060101 F27D015/02; C04B 7/44 20060101
C04B007/44 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 27, 2015 |
GB |
1501306.3 |
Claims
1. Process for the preparation of high alumina cement comprising:
introducing a solid batch material for preparation of high alumina
cement into a melter; melting the solid batch material in the
melter by submerged combustion to form a liquid melt; withdrawing
at least a portion of the liquid melt from the melter; cooling said
discharged liquid melt to obtain solidified melt; and grinding the
solidified melt to appropriate grain size.
2. The process of claim 1, wherein the melting chamber walls are
cooled comprising double steel walls separated by circulating
cooling liquid, and are not covered by a refractory lining.
3. The process of claim 1, wherein heat is recovered from the hot
fumes and/or from the cooling liquid.
4. The process of claim 1 wherein heat is recovered from the hot
fumes to preheat the raw materials.
5. The process of claim 1 wherein part at least of the melt is
withdrawn continuously or batchwise from the melter.
6. The process of claim 1 wherein the submerged burners of the
melter are controlled such that the melt volume is increased by at
least 8% compared to the volume the melt would have with no burners
firing.
7. The process of claim 1 wherein the submerged combustion is
performed such that a substantially toroidal melt flow pattern is
generated in the melt, having a substantially vertical central axis
of revolution, comprising major centrally inwardly convergent flows
at the melt surface; the melt moves downwardly at proximity of the
vertical central axis of revolution and is recirculated in an
ascending movement back to the melt surface, thus defining a
substantially toroidal flow pattern.
8. The process of claim 1 wherein the melting step comprises
melting the solid batch material, in a submerged combustion melter
by subjecting the melt to a flow pattern which when simulated by
computational fluid dynamic analysis shows a substantially toroidal
melt flow pattern in the melt, comprising major centrally inwardly
convergent flow vectors at the melt surface, with the central axis
of revolution of the toroid being substantially vertical.
9. The process of claim 8 wherein towards the melter bottom, the
flow vectors change orientation showing outward and then upward
components.
10. Production equipment for the preparation of high alumina cement
comprising (i) a submerged combustion melter (1) comprising melting
chamber (3) walls (19) and a melting chamber bottom, submerged
burners (21,22,23,24,25,26), and equipped with a raw material
discharge (10) or feeder and melt outlet (9), (ii) a melt cooling
station and (iii) a grinding station.
11. The production equipment of claim 10 wherein the melting
chamber walls (19) are cooled, comprising double steel walls
separated by circulating cooling liquid, and are not covered by
refractory lining.
12. The production equipment of claim 10 wherein submerged
combustion burners (21,22,23,24,25,26) are arranged at the melter
bottom in a substantially annular burner zone.
13. The production equipment of claim 10 wherein the burners
(21,22,23,24,25,26) are arranged with a distance between adjacent
burners of about 250-1250 mm.
14. The production equipment of claim 10 wherein each burner axis
and/or a speed vector of the melt moving upwards over or adjacent
to the submerged burners (21,22,23,24,25,26) is slightly inclined
from the vertical, by an angle which is .gtoreq.1.degree.,
.gtoreq.2.degree., .gtoreq.3 or .gtoreq.5 and/or which is
.ltoreq.30.degree., towards the center of the melter.
15. The production equipment of claim 1 wherein each central burner
axis is inclined by a swirl angle with respect to a vertical plane
passing through a central vertical axis of the melter and the
burner center, the swirl angle being .gtoreq.1.degree.,
.gtoreq.2.degree., .gtoreq.3.degree., .gtoreq.5 and/or
.ltoreq.30.degree., .ltoreq.20.degree., .ltoreq.15.degree. or
.ltoreq.10.degree..
Description
[0001] The present invention relates to an improved process for the
preparation of high alumina cement.
[0002] High alumina cement, also called aluminous cement or calcium
aluminate cement, is produced by fusing a mixture of limestone and
bauxite at high temperatures comprised between 1400 and
1600.degree. C., hence obtaining a melt which after cooling is
ground to fine cement. The fusion may be performed in shaft
furnaces, like blast furnaces, or in rotary kilns.
[0003] In typical formulations for the preparation of high alumina
cement, the content of SiO2 may vary from 0.4 to 10.0% by weight,
Al2O3 may vary from 25 to 85% by weight and CaO from 15 to 50% by
weight. High alumina cement may be used as hydraulic binder for the
preparation of concrete intended for construction purposes or in
the manufacture of refractory elements. It may also be mixed with
other cements for the preparation of cement blends showing specific
properties. High alumina cement is known for its rapid strength
development.
[0004] The production of high alumina cement requires high energy
inputs, and there is an ever increasing need for improvement of the
energy efficiency of the manufacturing process.
[0005] Moreover, because of the highly corrosive nature of the raw
materials and melt to be treated, the refractory lining of the
furnaces in which the high alumina cement is treated needs to be
repaired or replaced after relatively short time periods. There is
hence a need to find a way to overcome that technical problem.
[0006] It has been found that high alumina cement may
advantageously be prepared in a submerged combustion melter. The
invention process hence comprises introducing solid batch material
for preparation of high alumina cement into a melter, melting the
solid batch material in the melter by submerged combustion,
discharging a liquid melt, cooling said discharged liquid melt to
obtain solidified melt and grinding the solidified melt to
appropriate grain size. The grinding step is known to the person
skilled in the art and may be adapted to product quality demand and
requirements of the market place.
[0007] The preparation of the high alumina cement may be carried
out using a method and/or melter disclosed in any of WO
2015/014919, WO 2015/014920 or WO 2015/014921, each of which is
hereby incorporated by reference.
[0008] Submerged combustion melters are known. These melters are
characterized by the fact that they have one or more burner nozzles
arranged below the surface of the melt, in a lance, in the melter
walls and/or melter bottom, preferably in the melter bottom, such
that the burner flame and/or combustion products pass through the
melt and transfer energy directly to the melt.
[0009] Submerged combustion melters are known to generate high
turbulence or agitation in the melt caused at least partially by
the injection of combustion gas under high pressure into the melt
and by the convective movements within the melt. The high
turbulence ensures efficient mixing in the melt, and homogenizes
the melt in terms of temperature profile and composition, leading
to a high quality cement product. It also favors the absorption of
raw material into the melt and improves heat transfer to fresh raw
material. This reduces required residence time in the melter prior
to withdrawal for downstream treatment. It is preferred, however,
that the burners are controlled such that the melt volume is
increased by at least 8%, preferably at least 10%, more preferably
at least 15% or 20%, compared to the volume the melt would have
with no burners firing. It is understood that the gas injection
reduces the density of the melt, hence increases its volume,
compared to what it would be when no gas is being injected.
[0010] In connection with the above, the melt volume (no submerged
burners firing) may be calculated as a function of the temperature
and the raw material batch composition. The level and hence volume
of the agitated melt (submerged burners firing) may be measured
with laser scanners or similar measuring devices that allow to
measure and average melt level over a given period of time.
[0011] While submerged combustion has a tendency to cause foam
formation at the top of the melt, that is over the melt level, it
is preferable to operate the submerged combustion melter without
foam or at reduced foam level, as the foam level may be
disadvantageous with respect to the heat transfer.
[0012] Furthermore, the melting chamber walls are preferably
cooled; for example, they may comprise double steel walls separated
by circulating cooling liquid, preferably water.
[0013] Particularly in the case of a cylindrical melting chamber,
such assembly is relatively easy to build and is capable of
resisting high mechanical stresses. A cylindrical shape of the
melter facilitates balance of stresses on the outside wall. As the
walls are cooled, for example water cooled, melt preferably
solidifies and forms a protective layer on the inside of the melter
wall. The melter assembly may not require any internal refractory
lining and therefore needs less or less costly maintenance. In
addition, the melt is not contaminated with undesirable components
of refractory material normally eroded from an internal refractory
lining. The internal face of the melter wall may advantageously be
equipped with tabs or pastilles or other small elements projecting
towards the inside of the melter. These may help in constituting
and fixing a layer of solidified melt on the internal melter wall
generating a lining having thermal resistance and reducing the
transfer of heat to the cooling liquid in the double walls of the
melter.
[0014] The melter may be equipped with heat recovery equipment. Hot
fumes from the melter may be used to preheat raw material or the
thermal energy contained in them may be recovered.
[0015] Similarly, the thermal energy contained in the cooling
liquid circulating between the two walls of the melter may also be
recovered for heating or other purposes
[0016] Overall the energy efficiency of submerged combustion
melters is significantly improved compared to conventional shaft
melters or rotary kilns.
[0017] The raw materials may be loaded through an opening in the
melter wall, above the melt surface. Said opening may be opened and
closed, for example by a piston, to minimize escape of heat and
fumes. Raw material may be prepared and loaded into an intermediate
chute and subsequently fall into the melter, in an opposite
direction to escaping fumes, onto the melt surface. This
countercurrent flow may advantageously preheat the raw materials.
In the alternative, the raw materials may be charged below the
level of the melt, by way of a screw feeder or a hydraulic
feeder.
[0018] Melt may be withdrawn continuously or batch wise from the
melter. Where raw material is loaded close to the melter wall, the
melt outlet is preferably arranged opposite the material inlet. In
a preferred embodiment of the invention, the melt is withdrawn
through a discharge opening controlled by, for example, a ceramic
piston. The piston may open or close a sliding door covering or
uncovering the discharge opening.
[0019] The submerged burners preferably inject high pressure jets
of combustion products into the melt that is sufficient to overcome
the liquid pressure and to create forced upward travel of the flame
and combustion products. The speed of the combustion and/or
combustible gases, notably at the exit from the burner nozzle(s),
may be .gtoreq.60 m/s, .gtoreq.100 m/s or .gtoreq.120 m/s and/or
.ltoreq.350 m/s, .ltoreq.330 m/s, .ltoreq.300 or .ltoreq.200 m/s.
Preferably the speed of the combustion gases is in the range of
about 60 to 300 m/s, preferably 100 to 200, more preferably 110 to
160 m/s.
[0020] The temperature of the melt may advantageously be between
1400.degree. C. and 1600.degree. C.; it may be at least
1450.degree. C. or 1480.degree. C. and/or no more than 1600.degree.
C. or 1550.degree. C. or 1520.degree. C.
[0021] According to a preferred embodiment, the submerged
combustion is performed such that a substantially toroidal melt
flow pattern is generated in the melt, having a substantially
vertical central axis of revolution, comprising major centrally
inwardly convergent flows at the melt surface; the melt moves
downwardly at proximity of the vertical central axis of revolution
and is recirculated in an ascending movement back to the melt
surface, thus defining an substantially toroidal flow pattern.
[0022] The generation of such a toroidal flow pattern ensures
highly efficient mixing of the melt and absorption of raw material
into the melt, and homogenizes the melt in terms of temperature
profile and composition, thus leading to high quality final
product.
[0023] Advantageously, the melting step comprises melting the solid
batch material, in a submerged combustion melter by subjecting the
melt to a flow pattern which when simulated by computational fluid
dynamic analysis shows a substantially toroidal melt flow pattern
in the melt, comprising major centrally inwardly convergent flow
vectors at the melt surface, with the central axis of revolution of
the toroid being substantially vertical.
[0024] At the vertical axis of revolution of said toroidal flow
pattern, the flow vectors have a downward component reflecting
significant downward movement of the melt in proximity of said
axis. Towards the melter bottom, the flow vectors change
orientation showing outward and then upward components.
[0025] Preferably the fluid dynamics model is code ANSYS R14.5,
taking into consideration the multi-phase flow field ranging from
solid batch material to liquid melt and gas generated in the course
of the conversion, and the batch-to-melt conversion.
[0026] A toroidal melt flow pattern may be obtained using submerged
combustion burners arranged at the melter bottom in a substantially
annular burner zone imparting a substantially vertically upward
directed speed component to the combustion gases. Advantageously,
the burners are arranged with a distance between adjacent burners
of about 250-1250 mm, advantageously 500-900 mm, preferably about
600-800, even more preferably about 650-750 mm. It is preferred
that adjacent flames do not merge.
[0027] Each burner axis and/or a speed vector of the melt moving
upwards over or adjacent to the submerged burners may be slightly
inclined from the vertical, for example by an angle which is
.gtoreq.1, .gtoreq.2, .gtoreq.3 or .gtoreq.5 and/or which is
.ltoreq.30.degree., preferably .ltoreq.15.degree., more preferably
.ltoreq.10.degree., notably towards the center of the melter. Such
an arrangement may improve the flow and directs melt flow away from
the outlet opening and/or towards a center of the melter thus
favoring a toroidal flow and incorporation of raw material in to
the melt.
[0028] According to a one embodiment, each central burner axis is
inclined by a swirl angle with respect to a vertical plane passing
through a central vertical axis of melter and the burner center.
The swirl angle may be .gtoreq.1.degree., .gtoreq.2.degree.,
.gtoreq.3.degree., .gtoreq.5.degree. and/or .ltoreq.30.degree.,
.ltoreq.20.degree., .ltoreq.15.degree. or .ltoreq.10.degree..
Preferably, the swirl angle of each burner is about the same.
Arrangement of each burner axis at a swirl angle imparts a slightly
tangential speed component to the upward blowing flames, thus
imparting a swirling movement to the melt, in addition to the
toroidal flow pattern.
[0029] The burner zone is defined as a substantially annular zone.
Burner arrangements, for example on an elliptical or ovoid line
within the relevant zone are possible, but the burners are
preferably arranged on a substantially circular burner line.
[0030] Preferably, the flow pattern comprises an inwardly
convergent flow at the melt surface followed by a downwardly
oriented flow in proximity of the central axis of revolution of the
toroid. Said central axis of revolution advantageously corresponds
to the vertical axis of symmetry of the melter. By axis of symmetry
is meant the central axis of symmetry and, if the melter shows a
transversal cross-section which does not have any single defined
axis of symmetry, then the axis of symmetry of the circle in which
the melter section is inscribed. The downwardly oriented flow is
followed by an outwardly oriented flow at the bottom of the melter
and a substantially annular upward flow at proximity of the
burners, reflecting recirculation of melt toward the burner zone
and in an ascending movement back to the melt surface, thus
defining a substantially toroidal flow pattern.
[0031] The inwardly convergent flow vectors at the melt surface
advantageously show a speed comprised between 0.1-3 m/s. The
downward oriented speed vectors at proximity of the vertical
central axis of revolution are preferably of significant magnitude
reflecting a relatively high speed of material flowing downwardly.
The downward speed vectors may be between 0.1-3 m/s. The melt
and/or the raw materials within the melter, at least at one portion
of the melter and notably at the melt surface (particularly
inwardly convergent flow vectors at the melt surface) and/or at or
proximate a vertical central axis of revolution, may reach a speed
which is .gtoreq.0.1 m/s, .gtoreq.0.2 m/s, .gtoreq.0.3 m/s or
.gtoreq.0.5 m/s and/or which is .ltoreq.2.5 m/s, .ltoreq.2 m/s,
.ltoreq.1.8 m/s or .ltoreq.1.5 m/s.
[0032] The preferred toroidal flow pattern ensures highly efficient
mixing and homogenizes the melt in terms of temperature profile and
composition. It also favors the absorption of raw material into the
melt and improves heat transfer to fresh raw material. This reduces
required residence time in the melter prior to withdrawal, while
avoiding or at least reducing the risk of raw material short
cutting the melt circulation.
[0033] In one preferred embodiment, the burners are arranged at a
distance of about 250-750 mm from the side wall of said melting
chamber; this favors the preferred flow described above and avoids
flame attraction to the melting chamber side walls. Too small a
distance between burners and side wall may damage or unnecessarily
stress the side wall. While a certain melt flow between burner and
wall may not be detrimental and may even be desirable, too large a
distance will tend to generate undesirable melt flows and may
create dead zones which mix less with the melt in the center of the
melter and lead to reduced homogeneity of the melt.
[0034] The distance between submerged burners is advantageously
chosen such as to provide the desired toroidal flow pattern within
the melt but also to avoid that adjacent flames merge. While this
phenomenon depends on many parameters such as temperature and
viscosity of the melt, pressure and other characteristics of the
burners, it has been found advantageous to select a burner circle
diameter comprised between about 1200 and 2000 mm. Depending on
burner type, operating pressure and other parameters, too large a
diameter will lead to diverging flames; too narrow a diameter will
lead to merging flames.
[0035] Preferably at east 6 burners are provided, for example
arranged on a burner circle line, more preferably 6 to 10 burners,
even more preferably 6 to 8 burners, depending on the melter
dimensions, burner dimensions, operating pressure and other design
parameters.
[0036] Each burner or each of a plurality of a group of burners,
for example opposed burners, may be individually controlled.
Burners close to a raw material discharge may be controlled at
different, preferably higher gas speeds and/or pressures than
adjacent burners, thus allowing for improved heat transfer to the
fresh raw material that is being loaded into the melter. Higher gas
speeds may be required only temporarily, that is, in the case of
batch wise loading of fresh raw material, just during the time
period required for absorption of the relevant load into the melt
contained in the melter. It may also be desirable to control
burners that are located close to a melt outlet at a lower gas
speed/pressure in order not to disturb the outlet of the melt.
[0037] The melting chamber is preferably substantially cylindrical
in cross section; nevertheless, it may have an elliptical cross
section or polygonal cross section showing more than 4 sides,
preferably more than 5 sides.
[0038] It has been found that the melt for the preparation of high
alumina cement shows a tendency to crystallize rather quickly. It
may thus be desirable to discharge the melt quickly for downstream
solidification and grinding. Such discharge may preferably be
carried out through an outlet opening which may be opened and
closed by a sliding door controlled by a piston.
[0039] The composition of the melt produced may typically
comprise:
TABLE-US-00001 Possible melt composition (% weight) SiO.sub.2 4.0
Al.sub.20.sub.3 39.4 CaO 38.4 Fe.sub.2O.sub.3 (total iron) 16.4 MgO
1.0 Na2O 0.1 K2O 0.2 TiO2 1.9 other Rest to 100%
[0040] The discharged melt is allowed to cool at suitable
temperature for storage and/or grinding. Grinding may be operated
in several stages as is known per se. A first grinding step may
break the cooled solidified melt particles down to a particle size
suitable for supply into a grinder that will finally reduce the
particle size such that 100% thereof pass a 90 .mu.m screen in a
dry circuit, possibly in several stages. Equipment for carrying out
said grinding operations are known in the art.
[0041] An embodiment of a melter suitable for use in accordance
with the present invention is described below, with reference to
the appended drawings of which:
[0042] FIGS. 1a and 1b are schematic representations of a toroidal
flow pattern in a submerged combustion melter;
[0043] FIG. 2 shows a vertical section through a submerged
combustion melter;
[0044] FIG. 3 is a schematic representation of a burner layout for
a melter of FIG. 2; and
[0045] FIG. 4 schematically shows a production line according to
the invention.
[0046] With reference to the figures, a toroidal flow pattern is
preferably established in which melt follows an ascending direction
close to submerged burners 21, 22, 23, 24, 25, 26 which are
arranged on a circular burner line 27, flows inwardly towards the
center of the circular burner line at the melt surface, and flows
downwards in the proximity of the said center. The toroidal flow
generates agitation in the melt, ensures good stirring of the melt,
and absorption of raw material into the melt. Furthermore, it has
been determined that the flow as generated also reduces foam
generation at the top of the melt; the gas or foam bubbles being
entrained back into the melt, thus reducing its density.
[0047] The illustrated melter 1 comprises: a cylindrical melting
chamber 3 having an internal diameter of about 2.0 m which contains
the melt; an upper chamber 5; and a chimney for evacuation of the
fumes. The upper chamber 5 is equipped with baffles 7 that prevent
any melt projections thrown from the surface 18 of the melt being
entrained into the fumes. A raw material feeder 10 is arranged at
the upper chamber 5 and is designed to load fresh raw material into
the melter 1 at a point 11 located above the melt surface 18 and
close to the side wall of the melter. The feeder 10 comprises a
horizontal feeding means, for example a feed screw, which
transports the raw material mix to a hopper fastened to the melter,
the bottom of which may be opened and closed by a vertical piston.
The bottom of the melting chamber comprises six submerged burners
21, 22, 23, 24, 25, 26 arranged on a circular burner line 27
concentric with the melter axis and having a diameter of about 1.4
m. The melt may be withdrawn from the melting chamber 3 through a
controllable outlet opening 9 located in the melting chamber side
wall, close to the melter bottom, substantially opposite the
feeding device 10. The melt withdrawn from the melter may then be
allowed to cool and subsequently ground as required.
[0048] The temperature within the melt may be between 1400.degree.
C. and 1600.degree. C., preferably 1450.degree. C. and 1550C,
depending on the composition of the melt, desired viscosity and
other parameters. Preferably, the melter wall is a double steel
wall cooled by a cooling liquid, preferably water. Cooling water
connections provided at the external melter wall allow a flow
sufficient to withdraw energy from the inside wall such that melt
can solidify on the internal wall and the cooling liquid, here
water, does not boil. The internal melter wall is not lined with
any refractory material.
[0049] The submerged burners 21,22,23,24,25,26 comprise concentric
tube burners operated at gas flows of 100 to 200 m/s, preferably
110 to 160 m/s and generate combustion of fuel gas and oxygen
containing gas within the melt. The combustion and combustion gases
generate agitation within the melt before they escape into the
upper chamber and then through the chimney. These hot gases may be
used to preheat the raw material and/or the fuel gas and/or oxidant
gas (eg oxygen, industrial oxygen have an oxygen content
.gtoreq.95% by weight or oxygen enriched air) used in the burners.
The fumes are preferably filtered prior to release to the
environment, optionally using dilution with ambient air to reduce
their temperature prior to filtering.
[0050] With reference to FIG. 4, raw material from a raw material
storage 30 is charged into the furnace 1 as described above, and
withdrawn thereof for cooling 32 and further downstream treatments
known per se. The discharged melt is allowed to cool at a
temperature suitable for further downstream operation, including
grinding 34 to appropriate grain size and/or storing 36,38. The
grinding is advantageously effected in several stages, including a
first stage 39 that reduces the particle size of the solidified
melt to a size suitable for downstream fine grinding 40 which in
turn may be carried out in a manner known per se, in several
stages, in order to reach a particle size as is common in the
cement manufacturing industry. Mostly the final grain size is a
powdery grain size. For example, it is such that 100% of the
particles pass a 90 .mu.m screen in a dry circuit. The production
line further comprises dryers as appropriate and as is known per
se; these devices have not been shown in the figures.
[0051] With respect to the exemplified melter, it has been found
that the turbulent aerated melt showed almost no foam floating at
the top of the melt, and it has been determined that the turbulent
aerated melt showed a volume (averaged over a 1 minute time period)
of 30-50% higher than that calculated on the basis of the raw
material fed into the melter and maintained at the same
temperature. The volume was.
[0052] The high alumina cement obtained is of high quality. The
above described production process is less energy demanding then
known processes, because of the choice of submerged combustion
melters that allow for improved energy transfer to the melt,
shorter residence times and thus less heat loss, and because the
high stirring leads to a more homogenous melt at reduced melt
viscosity, which in turn may allow for operation at reduced
temperatures. Furthermore, submerged combustion may advantageously
be performed in water-cooled melters which are easier and less
costly to maintain and repair and which further allow for recycling
of the energy withdrawn from the cooling fluid.
* * * * *