9.1.Thermal Insulation of Torpedo Cars - Pyrotek

THERMAL INSULATION OF TORPEDO CARS
Jiang Hua, Bao Ji, and Li Jun, Baoshan Iron and Steel, Shanghai, 201900,
P.R. China
Song Li Ming, Northeastern Univ., No. 11 Sanxiang, Wenhua Rd. Shenyang,
Liaonning, P.R. China
En-Sheng Chen, Thermomechanical Designs, 6111 FM 1960 West, # 107,
Houston, Texas 77069, USA
Marc-H. Fréchette, Pyrotek, 2400 Lemire Blvd. Drummondville, Quebec,
J2B 6X9, Canada
Abstract
Baoshan Iron & Steel operates a
fleet of seventy (70) 320 tonne
torpedo cars. During liquid iron
transportation, they experience
significant heat loss through their
refractory linings. Therefore, a layer
of high strength insulating material
behind a safety lining was
considered. This paper summarizes
a study evaluating the thermal
behavior of the refractory lining with
and without this insulating layer. A
finite-element thermal analysis was
conducted, with representative
modeling of material properties and
processing conditions. It covered the
main process steps, including the
charging at the blast furnace, the
residence time, the different
treatments, emptying at the BOF
shop, and idling time. The benefits of
using the insulation layer, in terms of
heat conservation, lower shell
temperatures, the improvement of
liquid iron temperatures, and better
heat-flow regulation, are quantified.
KEYWORDS: Ironmaking, Torpedo
Car, heatloss, liquid temperature,
and simulation.
INTRODUCTION
In recent years, at Baoshan, the use
of high-conductivity ASC brick for
torpedo car linings, result in high
shell temperatures, high heat losses
through the lining system,
consequential degradation of the
shell strength and significant loss of
temperature of the liquid iron. While
extra lining insulation is necessary,
the proper selection of insulating
materials is vital to the linings
integrity and stability. A low density
insulating board, which usually
provides good insulation, may have
low strength and experience severe
crushing upon lining expansion. A
proper balance between thermal
properties and mechanical strength
requires careful evaluation of an
insulating board employed in a
specific T-Car lining shell system.
This study evaluated the thermal
behavior of a torpedo car lining using
a dense, high-strength insulating
board behind the safety lining taking

into consideration the two-stage
chemical treatment. The justification
of using the board had to be based
on achieving desirable shell
temperatures and improving liquid
metal temperatures while
maintaining its lining integrity as well
as its stability under a typical
operation during its complete cycle.
TORPEDO CAR CONFIGURATION
AND OPERATION
Baoshan Iron and Steel Co. Ltd. are
operating a fleet of seventy 320
tonne torpedo cars and each car is
lined with multi-layers of refractory
materials to protect the shell from the
liquid iron. The previous current
refractory practice is summarized in
Table 1.
Refractory Materials
ASC Brick
(5/10% SiC +
10/15°C)
65% Al2O3 Castable
50% Al2O3 Brick
Refractory Materials
ASC Brick
(75%Al2O3&22%SiC+C)
65% Al2O3 Castable
50% Al2O3 Brick
Slag
Zone
275 mm
20 mm
70 mm
Cylinder
275 mm
20 mm
70 mm
Impact
Pad
382
mm
20 mm
70 mm
Cones
275
mm
20 mm
70 mm
Table 1 : Previous Refractory Practice
Each vessel averages 2.6 cycles/day
(9 hours/cycle). The cycle begins at
the Blast Furnace where the liquid
metal is poured into the torpedo car.
The hot metal resides in the car for
approximately 4.5 hours for
transportation and treatment. After
1.5 hours, a two-stage chemical
treatment is conducted. Each stage
of the treatment lasts for about 30
minutes. During the residence
period, they are not using a lid to
cover the mouth of the vessel
therefore, a significant heat loss is
apparent. After it reaches the BOF
Shop, the vessel is emptied into a
transfer ladle for BOF charging.
Thereafter, the empty car returns to
the Blast Furnace Cast House for the
next charge. The average idling time
is 4.5 hours/cycle.
During the residence time,
substantial heat loss occurs through
the refractory lining, resulting in
significant temperature reduction of
the liquid iron. During the idling time,
the heat loss, through and from the
refractory lining contribute to further
reduce the overall lining
temperatures. This results, after the
subsequent charge, in a sudden heat
loss (Heatflow) from the iron bath
into the refractory lining. This
phenomenon is conducive to the
increase of the shell temperatures to
such a level that it becomes a major
concern as the lining is thinning
down toward the later stage of the
campaign.
INSULATING MATERIALS
To solve the above thermal problem,
an improved lining design using a
high density insulating board, 16mm

thickness was implemented. In order
to reduce heat loss and shell
temperature while maintaining vessel
capacity, we have reduced the safety
lining thickness to accommodate the
insulating layer. The properties of the
insulating board are summarized in
table 2.
Chemical
Composition (%) :
SiO2
MgO
P2O5
Fe2O3
Al2O3
Bulk Density
(g/cm 3 )
Apparent Porosity
(%)
Cold Crushing
Strength (MPa)
Thermal
Conductivity
(W/°K.m)
36
24.6
11.8
8.7
6.8
1.3 +-
6%
53.5
15.1
0.31 @
600°C
Table 2 : Properties of the Insulating
Board.
MODELING AND ANALYSES
To evaluate the effectiveness of the
current design with the insulating
layer, a series of thermal analyses
was conducted. It adopted the
thermal analysis capability
developed exclusively for hightemperature
lining-shell systems and
verified with field data over years.
The analyses employ 3-D finiteelement
geometry modeling,
temperature-dependent material
modeling, thermal boundary
modeling, and transient analyses. A
paper in the related areas of heattransfer
analyses is also presented
in this symposium.
Figures 1 and 2, show the 3-D
geometry models on a quarter of the
torpedo car (assumed symmetry)
developed for the car with a new
lining condition and a worn lining
condition, respectively. Thermal
loads were properly applied to the
various boundaries of the torpedo
car and it's lining to simulate the
actual operating conditions, with the
following specifications:
(1) The residence period lasted
for 4.5 hours. The initial iron
temperature right after the
iron charging was 1560°C.
After 1.5 hours entering the
residence period, the two
stage chemical treatment
started. The first stage lasted
for 30 minutes and reduced
the average iron temperature
by 1°C/min and the second
one also lasted for 30 minutes
and reduced the average iron
temperature by 1.75°C/min.
The mouth opening would
allow heat loss into the
ambient environment.
(2) During the residence period,
the liquid iron did not fully fill
the interior space of the
torpedo car. High thermal
radiation was considered as
the heat transfer mechanism
in the space between the
lining and the liquid iron.

(3) After the resident period, the
liquid iron was tapped out at a
BOF site. The torpedo car
then became empty for 4.5
hours.
(4) The exterior surface of the
shell was considered a
convective and
radiative thermal boundary
with an ambient temperature
of 25°C.
Figure 1 : Finite element model / new
lining
Figure 2 : Finite element model /
worn lining
For each case with a specific
combination of lining design (with or
without insulating board) and
working lining condition (new or worn
linings), a multi-step, nonlinear heat
transfer analysis was conducted. An
initial steady-state condition was first
established, followed by an iterative
process to ensure the average
interior temperatures during the
residence period converged to the
average surface temperatures of the
liquid iron. During the empty period,
the iteration further converged the
average interior temperatures to the
average lining inside-face
temperatures. This iterative process,
although time consuming would
provide a realistic heat transfer
simulation for all components. The
heat loss caused by the chemical
treatment was modeled as a heat
sink in the liquid iron. The average
heat loss rates were imposed based
on the temperature drops specified
previously.
THERMAL BEHAVIOR DURING
RESIDENCE TIME
The use of the insulating board was
expected to significantly improve the
liquid iron temperatures during the
iron transport through heat-loss
reduction. Therefore, by evaluating
the heat loss and temperature in the
liquid iron, we could quantify and
contrast for the benefit of using the
insulating board.
Figures 3 to 4 shows the average
liquid-iron temperatures for the newand
worn-lining cases during the
residence period. Figures 5 to 6
shows heat losses during Residence
Period for the new and worn lining.

Temperature (oC)
1600
1580
1560
1540
1520
1500
1480
1460
1440
1420
1400
1380
with Board
without Board
1360
0 1 2 3 4 5
Time after Charge (Hours)
Figure 3 : Average liquid Iron
temperatures / new lining.
As these figures show, during the
early stage, heat escapes fast from
the liquid iron into the much cooler
lining, resulting in a fast drop of
liquid-iron temperatures. Afterward,
the heat-loss rates gradually stabilize
with steady heat flows through the
lining and the mouth opening, until
the chemical treatment starts.
Temperature (oC)
1600
1580
1560
1540
1520
1500
1480
1460
1440
1420
1400
1380
without Board
with Board
1360
0 1 2 3 4 5
Time after Charge (Hours)
Figure 4 : Average liquid Iron
temperatures/ worn lining
During the chemical treatment, the
liquid-iron temperatures drop
substantially. This brings the liquidiron
temperatures to a close range of
the temperatures near the lining hot
face. Therefore, the heat transfer
between the liquid iron and the lining
reduces significantly. This results in
a much slower temperature
reduction in the liquid iron right after
the treatment. However, toward the
later stage of the residence period,
the temperature reduction rates pick
up again.
Heat Loss (10 9 Joule)
28
26
24
22
20
18
16
14
12
10
8
6
4
2
without Board
with Board
0
0 1 2 3 4 5
Time after Charge (Hours)
Figure 5 : Heat losses during residence
period / new lining
Compared with the cases without the
use of an insulating board, the
introduction of the board can
significantly reduce the heat loss
through the refractory lining system
and thus maintain higher liquid-iron
temperatures and lower shell
temperatures. On the average, the

liquid-iron temperatures at the end of
the residence time can be increased
by 23 and 26°C for the new and
worn lining cases, respectively. The
heat-loss reduction can achieve 12.8
and 14.0% for the new and worn
lining cases, respectively. The
average shell temperatures are also
reduced with lower levels of
temperature variation. This may help
reduce the levels of local stress
development. The maximum
temperatures in the insulating board
are generally below 800°C, even in
the worn-lining case. This
temperature level should be within
the application rages of the board
and thus helps maintain reasonable
strength and integrity of the board.
Heat Loss (10 9 Joule)
28
26
24
22
20
18
16
14
12
10
8
6
4
2
without Board
0
0 1 2 3 4 5
Time after Charge (Hours)
with Board
Figure 6 : Heat losses during
residence period / worn lining
Based on thermal analyses and the
behavioral evaluation, the benefits of
using the insulating board for the
torpedo car are defined and found
quite appreciable. Therefore, the
board was recommended for field
installation and implementation.
INSTALLATION
The torpedo lining consists of
rectangular shapes (416 x 101 x
16mm) and conical shapes (416 x
(101/91) x 16mm). Baoshan used
the rectangular shapes in the
horizontal cylinder and a ratio of
rectangular and conical shapes in
the cones.
The first installation took place in
April 2002. For the first lining,
Baoshan installed the insulating
layer in the entire vessel, continued
with the installation of the safety
lining and completed with the wear
lining. They proceeded as follow:
• Horizontal cylinder: Starting
from both ends, they worked
towards the center to make
one cut to close the last ring.
They worked with 2 crews.
• Cones: They worked in both
cones simultaneously with
one crew in each cone.
Each crew consists of two brick
masons.
They have used an air set refractory
cement to glue the tiles against the
shell as well as in all horizontal and
vertical joints.
However, for the future installations,
Baoshan will include the insulating
board to their regular installation
practice. They will install all the
different refractory layers in the lower
section (cylinder and cones) of the
vessel before installing the
scaffolding and completing with the
installation of the

different refractory layers in the
upper section of the vessel.
PRELIMINARY RESULTS
After adequate pre-heating, the first
insulated torpedo car went in
service. Baoshan have monitored
the liquid iron temperature in the
insulated torpedo car as well as in a
non-insulated torpedo car for
comparison purposes.
The first series of measurements
were taken at the BOF, after 151
cycles (or 42,300 tonnes) and they
have noticed an improvement of the
liquid iron temperature ranging from
20°C to 25°C.
When we refer to the average
campaign of 600,000 tonne, we
recognize that the first set of
measurements were taken at an
early stage in the life of the torpedo
car. However, Baoshan will be taking
other measurements on a regular
basis throughout the campaign to
confirm the preliminary results.
SUMMARY AND CONCLUSIONS
An analysis study was conducted to
evaluate the thermal behavior of a
torpedo car using a dense, highstrength
insulating board behind the
safety lining. Based on the analysis
results, it clearly demonstrates that
the insulating board can:
1. Substantially reduce the shell
temperatures after the wear
lining worn down.
2. Reduce the heat loss from hot
liquid iron and improve liquid
iron temperature at the end of
residence time.
The trial preliminary results, at
Baoshan, support the use of the
insulating board for the torpedo car
application with similar lining designs
and operational practice.
We wish to extend our gratitude
toward Mr. Jiang Hua, Mr. Bao Ji,
and Mr. Li Jun of Baoshan and Song
Li Ming of Northeastern University
for their cooperation and contribution
for which this trial would not have
been possible.
REFERENCES
(1) E.S Chen and M.H. Fréchette,
"Thermal and Thermomechanical
Evaluation of High-Strength
Insulation in Steelmaking Ladle",
ISS Steelmaking Conference,
1996.
(2) E.S. Chen, "Thermal Analysis
of Refractory Lining Systems", 4 th
International Symposium on
Refractories, 2003.