U.P.B. Sci. Bull., Series B, Vol. 79, Iss.

1, 2017 ISSN 1454-2331

CONTRIBUTION TO IMPROVING THE DURABILITY OF

THE REFRACTORY LINING OF THE STEEL LADLES

Adrian IOANA1, Nicolae CONSTANTIN2, Lucian PAUNESCU3, Cristian

DOBRESCU4, Gheorghe SURUGIU5, Massimo POLIFRONI6

The paper presents experimental results obtained in the iron and steel
industry with an own conception burner for drying and heating the steel ladles
masonry, using, as a solution to intensify the combustion, the oxygen enrichment of
combustion air. The main goal is to reach the maximum temperature of 1200 ºC
inside the refractory lining, according to the request of the refractory materials
manufacturers. The results obtained in ArcelorMittal Galati confirm the correctness
of the adopted solutions, the burner allowing to reach the required heating speed
and to respect the thermal parameters of diagram, that contribute to the significant
increase of the durability of the ladles wear layer.

Keywords: ladle, durability, refractory lining, burner, oxygen, temperature

1. Introduction

The modern processes of the liquid steel treatment in the ladle impose the
prior preheating the ladles refractory lining at high temperatures (1150 – 1200 ºC),
to diminish as much as possible the cooling process of the hot steel at the contact
with the ladle masonry. The technological process of drying-heating the layers
which compose the refractory lining has a special importance to ensure the
durability of material at the prolonged contact with the liquid metal. The diagrams
are designed so that the thermal conditions be achieved to totally eliminate the

1
Assoc. Prof., Science and Engineering Materials Faculty, Engineering and Management of
Metallic Materials Obtaining Department, University POLITEHNICA of Bucharest, Romania,
e-mail: adyioana@gmail.com
2
Prof., Science and Engineering Materials Faculty, Engineering and Management of Metallic
Materials Obtaining Department, University POLITEHNICA of Bucharest, Romania, e-mail:
nctin2014@yahoo.com
3
Senior researcher, Cermax 2000 Patents SRL Bucharest, Romania, e-mail:
lucian.paunescu.cermax@gmail.com
4
Lecturer, Science and Engineering Materials Faculty, Engineering and Management of Metallic
Materials Obtaining Department, University POLITEHNICA of Bucharest, Romania, e-mail:
cristiandobrescu@yahoo.com
5
Eng., State Inspection for Control of Boilers, Pressure Vessels and Lifting Installations,
Bucharest, Romania, e-mail: gsurugiu2000@yahoo.com
6
Assoc. Prof., University of Turin, Italy, e-mail: massimo.pollifroni@unito.it
202 A. Ioana, N. Constantin, L. Paunescu, C. Dobrescu, Ghe. Surugiu, M. Polifroni

refractory material moisture, as well as a high temperature inside the lining to

reduce the heat loss of the liquid steel into environment.
Generally, the methods of combustion intensifying are air combustion
preheating (by recovery the physical heat of waste gas resulted from the process)
and the oxygen enrichment of air. By the both methods it is obtained a significant
increase of the flame temperature and, implicitly, of waste gas resulted from the
combustion process, so that the transfer of thermal energy by radiation and
convection from gases to the first layer, which composes the refractory lining (the
wear layer), is much improved. Further, the heat is transferred by thermal
conductivity in all lining layers (intermediate and permanent layer), ensuring a
global heating of the refractory lining, superior in terms of heat compared to the
conventional heating processes.
Worldwide they are known the self-recuperative burners, which have
embedded the metal heat recuperator in the burner construction, which ensures a
very high heat exchange between waste gas and the combustion air, the air
reaching temperatures of over 600 ºC. Conceived and achieved by the British
company Hotwork Development Ltd. [1], this burner type is limited at thermal
power values of maximum 400 kW. The energy efficiency of the self-recuperative
burners is diminished with the increase of their thermal powers, because the heat
recuperator sizes would be very large to obtain a heat transfer as effective.
Therefore, in case of the steel ladles of high capacity (of over 65 t), that require
combustion installations with thermal powers of over 1000 – 1500 kW, the self-
recuperative burners have a very diminished efficiency. Generally, the high
capacity ladles are placed horizontally and the heating installation is installed on a
mobile wagon, equipped with a refractory lined vertical wall (with a ladle cover
role), a conventional burner and a waste gas / combustion air exchanger [2]. But
the horizontal position of ladle is not recommended in case of the new built ladle
and subjected to drying (especially, for refractory linings of dolomite blocks).
A high degree energy recovery (up to 0.90) in the heating process of steel
ladles masonry can be achieved [3 – 5] by use the self-regenerative burners. The
thermal power of this burner type varies in the range 300 – 4000 kW. The
regenerative heat exchanger uses balls and cylinders of refractory ceramic
material. Made by the British company Hotwork and then by the French
companies Stein-Heurtey and Hotwork France (after its license), the burners
operate in tandem. The combustion air is preheated at temperatures that can reach
900 – 1000 ºC. As the high thermal powers self-recuperative burners, the self-
regenerative burners involve the horizontal position of ladles subjected to drying
and, so, are not advisable in case of drying processes of new built ladles masonry.
The other method of combustion process intensifying, noted above, is
oxygen enrichment of combustion air. Effects of this method application are
significant: decrease of heating duration, optimal using of oxygen, increase of
 Contribution to improving the durability of the refractory lining of the steel ladles 203

refractory lining durability, uniform heating of lining, decrease of energy costs,

reduction of CO2 and NOx volumes. Literature presents the Pyre Tron burner [6]
of the British company Air Liquide, having maximum flexibility in the proportion
of oxygen in combustion air, allowing to obtain flame temperatures in a very large
range, depending on needs. On the other hand, the burner (of acceptable sizes
regardless of its thermal power) placing is easily on the ladle cover and this can be
vertically placed.
Also, the burners with oxygen enrichment air of the Japanese company
Chugai Ro Ltd. [7] are recommended for rapid heating processes and at high
temperatures of the steel ladles.
If in terms of energy effects the burners operating with oxygen enrichment
air are superior compared to the self-recuperative and self-regenerative burners,
presented above, not the same thing can be said about the efficiency of the
technological heating process. Thus, in case of self-recuperative and self-
regenerative burners, a part of waste gas energy resulted from the process is
recovered by preheating the combustion air at high temperatures and is
reintroduced into system. In case of burners operating with oxygen enrichment
air, used in the heating process of ladles, waste gas heat is not recovered, although
their energy content is much higher than that of waste gas produced in the
combustion process of self-recuperative and self-regenerative burners. By placing
of some heat recuperators above the exhaust holes of the hot gases would increase
very much the weight of ladle cover. Certainly, there is also the possibility to
energy recovery in this case with condition of horizontal position of the ladle and
placing the recovery system on a mobile wagon [8]. As previously noted, the
horizontal position of the ladles is not suitable for those new built.
The aim of research presented in this paper is to achieve an own
conception installation with oxygen enrichment air, designed for drying and
heating processes of high capacity steel ladles masonry (180 t). The burner was
designed and achieved for the Converters Steelwork in ArcelorMittal Galati,
taking into account the technological and material concrete situation of the plant.
It is estimated that, by using the new combustion installation to achieve the
drying-heating diagrams required by the manufacturers of refractory materials,
that compose the wear layers, it will obtain a significant increase of the refractory
lining durability.

2. Refractory materials of the composition of steel ladles lining and

technical specifications of the manufacturers

Currently, in the Converters Steelwork of ArcelorMittal Galati the steel

ladles are built in several ways, two of which being the most used. A mode of
masonry construction consists of using magnesia bricks bonded with magnesium
204 A. Ioana, N. Constantin, L. Paunescu, C. Dobrescu, Ghe. Surugiu, M. Polifroni

spinel, as a wear layer (which comes in direct contact with slag and molten steel),
with thickness of 187 mm, silica – alumina bricks as a permanent layer (made on
the inner surface of the ladle metal shell), with thickness of 80 mm in the upper
area of ladle and 120 mm in the lower area and granulated dolomite bonded with
tar as an intermediate layer (between the wear layer and the permanent), with
thickness of 50 mm. The second mode of masonry construction is composed of
dolomite blocks as a wear layer, with thickness of 150 mm, high-aluminous
refractory concrete B90A as a permanent layer, with thickness of 80 mm in the
upper area and 120 mm in the lower area and granulated dolomite bonded with tar
as an intermediate layer, with thickness of 50 mm [9].
Between the ladle refractory lining layers, that on which it is focused the
entire attention during the drying-heating process, is the wear layer. Therefore, the
refractory materials, which influence the parameters of the drying-heating
diagrams used in the two ways of ladles masonry construction, are magnesia
bricks bonded with magnesium spinel, made in Tremag Tulcea and dolomite
blocks, made even in ArcelorMittal Galati, at the Bricks Plant.
The magnesia bricks manufacturer requires compliance with a heating
diagram with the total duration of 30 hours, characterized by a heating in the first
stage up to 1000 ºC in 25 hours (with the speed of 40 ºC/ h), continued by a
maintaining at this temperature for 2.5 hours and the final heating from 1000 ºC to
1200 ºC in 2.5 hours (with the speed of 80 ºC/ h). The measurement point of
temperature would be placed, according to the technical specification of
manufacturer, 50 mm from the inner surface of the ladle shell, i. e., practically, in
the permanent layer, at 450 mm from the bottom of ladle.
Literature recommends [10] for the magnesia masonry a drying-heating
diagram with the duration of 30 hours, but with a linear increase with the heating
speed of 40 ºC/ h, constant kept up to the end of process. The constant
maintaining at 1000 ºC, required by the Romanian manufacturer, has not a
motivation based on textural-structural transformation inside the magnesia bricks,
but only the need of the heat transfer homogenization and the stabilization of
dimensional variation of material in the entire volume of masonry. The need to
heat up to 1200 ºC is imposed by getting a denser refractory mass, with low
porosities, which does not allow the liquid steel infiltration during its stationing in
the ladle. Using the magnesium spinel (MgO·Al2O3) as a binder, aims, inter alia,
to diminish the effects of masonry dilatation, the coefficient of linear dilatation of
spinels being with about 40% lower than the magnesia on the entire temperature
range 20 – 1600 ºC [11].
The manufacturer (ArcelorMittal Galati-Bricks Plant) requires compliance
with a drying-heating diagram with the total duration of 16 hours, achieved in four
stages, according to table 1.
 Contribution to improving the durability of the refractory lining of the steel ladles 205

Table 1
Drying-heating diagram of dolomite blocks
Temperature range (ºC) 20 - 450 450 - 800 800 - 1060 1060 - 1145
Heating speed (ºC/ h) 215.0 87.5 38.5 26.1
Duration (hours, min.) 2.00 4.00 6.45 3.15

Literature recommends [10] a more compressed diagram, with the total

duration of only 12 hours, having only two heating stages, according to table 2.

Table 2
Drying-heating diagram of dolomite blocks recommended by Didier
Temperature range (ºC) 20 - 450 450 - 1175
Heating speed (ºC/ h) 215.0 72.5
Duration (hours, minutes) 2.00 10.00

The very high speed of the beginning process (215 ºC/ h) is imposed, inter
alia, by the need to avoid the unwanted phenomenon of dolomite hydration, which
modifies the thermal and structural characteristics of this material [12]. This can
occur, in significant measure, at temperatures of below 450 ºC, in conditions of a
low heating speed.
The explication of difference between technological requests of the two
manufacturers of dolomite blocks (ArcelorMittal Galati and Didier) must be
search, primarily, in the recognition of lower performances of the current
combustion installations which equip the ladle preparation sector of the Romanian
iron and steel industry and, implicitly, the impossibility to answer the requests
imposed by the drying-heating technology of this refractory material type.
Therefore, it is preferably to reach rapidly the temperature of 800 ºC, and then the
heating is conducted slowly up to 1145 ºC, with a speed obviously much lower
and in a greater time range. In this way, the heating in the range 800 – 1145 ºC,
during 14 hours, allows a good temperature homogenization inside the refractory
material.
Corresponding to the drying-heating diagram of magnesia bricks, the
measurement point of the masonry temperature is placed 50 mm from the inner
surface of the ladle shell and 450 mm from the bottom of ladle.

3. Own conception technical solutions adopted to design the

combustion installation

3.1. Technical requests imposed to the combustion installation

Because the technological conditions imposed by the magnesia bricks and

dolomite blocks manufacturers for the drying-heating process of ladles masonry
of 180 t in Arcelor Mittal Galati were impossible to achieve with the installations
206 A. Ioana, N. Constantin, L. Paunescu, C. Dobrescu, Ghe. Surugiu, M. Polifroni

existing in the plant, it was imposed to made a new burner with advanced
characteristics, capable to answer to the following requests:
- the flame developed through combustion to be radiant by self
carburizing, with a preponderantly central jet of natural gas, surrounded by
annular flame jets produced by the mixture between natural gas radial distributed
and the primary combustion air;
- the combustion efficiency to be very high, as that, by achieving an
intimate mixture between fuel and combustion air (distributed in three mixture
stages), the transformation of fuel chemical energy in thermal energy to take place
in maximum proportion;
- the real flame temperature would reach values of over 1700 ºC, achieving
by processes of combustion intensifying, noted previously;
- pollutants emissions in waste gas (CO, NO, NOx) to be below the
maximum levels allowed by the law.
Considering the superiority, in terms of energy effects, of the process of
combustion intensifying by using oxygen enrichment of combustion air [9], as
well as the easily installing this burner type on the cover, the ladle position being
vertically, it was adopted this intensifying variant.

3.2. Description of the constructive and functional solution adopted to

design the burner

To design the new combustion installation destined to the vertical drying-

heating stand of the steel ladles of 180 t, they are adopted the hourly flow rate of
natural gas of 250 m3N/ h and the maximum flow rate of oxygen (available at the
supply source of the stand area) of 150 m3N/ h.
To achieve the imposed technical requests, noted above, it was considered
the need to ensure a preponderantly central jet of natural gas (80% from the total
flow rate of fuel) through an axial central orifice with the diameter Ø 20 mm. The
remaining fuel (20%) is radial distributed through 24 orifices Ø 8 mm. The fuel
radial distributed meets a part of the instilled air amount (primary air), swirled
with more propellers welded on the body of natural gas pipe and, in this annular
cylindrical area it is produced the first mixture stage between fuel and air. The
secondary combustion air passes through an annular concentric route and exits
through oblique slits made in the head of piece, on its inner surface, which ensure
a rotary motion of air in opposite direction compared to the primary air motion. In
this area, it is produced the second mixture stage between the ignited fuel and the
secondary air. To cool the combustion chamber of the burner, made from
15SiNiCr250 refractory steel, a peripheral stream of tertiary air is instilled. This
enters in the combustion chamber and participates in a third stage of mixture at
 Contribution to improving the durability of the refractory lining of the steel ladles 207

the fuel combustion. The tertiary air role is, excepting the cooling of the
combustion chamber, to lengthen the flame.
The phased distribution of combustion air in the combustion process is one
of the well-known methods of reducing the nitrogen oxides concentration in waste
gas [13].
The introduction of technical oxygen to increase the volumetric proportion
of oxygen in the combustion air is achieved by the injection in the entry
connection of air in the burner body. The oxygen addition occurs simultaneously
with the reduction of the combustion air flow rate. By diminishing the nitrogen
volume in air, that is an inert element, which does not participate at the
combustion reaction of methane from the fuel, the flame temperature increases
significant due to the reduction of cold nitrogen in waste gas.
In Fig. 1 it is presented the constructive scheme of the burner for achieving
the drying-heating process of the steel ladles masonry in Arcelor Mittal Galati.

Fig.1. Constructive scheme of the burner for drying-heating process of steel ladles in ArcelorMittal
Galati: 1 – burner body; 2 – primary air pipe; 3 – sealing piece; 4 – secondary air pipe; 5 – natural
gas pipe; 6 – oxygen pipe; 7 – combustion chamber; 8 – fastening system of the combustion
chamber; 9,11 – gasket; 10,12 – fastening system.

Burner body (1) is made by stainless steel. The role of the two air pipe, primary
(3) and secondary (4) is to ensure proper mixing between natural gas – air.
Combustion chamber (7) is made by refractory steel. Sealing burner is provided
by gaskets (9) and (11) with fastening system (12)
208 A. Ioana, N. Constantin, L. Paunescu, C. Dobrescu, Ghe. Surugiu, M. Polifroni

In table 3 they are presented the main technical and dimensional

characteristics of the burner designed for drying and heating installation of steel
ladles of 180 t.
Table 3
Technical and dimensional characteristics of the burner
Name Unit Value
A. Technical characteristics
Nominal flow rate of natural gas m3N/ h 250
Nominal pressure of natural gas mbar 75
Maximum flow rate of oxygen m3N/ h 150
Maximum pressure of oxygen bar 1.5
Coefficient of air excess - 1.02
Nominal flow rate of combustion air
- at the operation without additional oxygen m3N/ h 2428
- at the operation with oxygen enrichment of
combustion air (30%) m3N/ h 1190
Maximum temperature of the flame ºC 1890
B. Dimensional characteristics
Length mm 828
Diameter mm 300
Net mass mm 85.56

4. Experimental methodology

The burner experimentation was carried out directly in industry at the

Converters Steelwork in ArcelorMittal Galati on a drying and heating stand of
steel ladles of 180 t. The new burner was installed on a ladle metal cover, lined
with super aluminous refractory concrete. The cover has four equidistant holes Ø
200 mm for waste gas exhausting from the ladle. Two steel ladles built in the two
most used modes were dried and heated with the new burner.
The following parameters of the process were measured:
- hourly flow rate of natural gas, with a calibrated gas meter;
- natural gas pressure, with AFRISO FZM 15 digital manometer, with
measuring range of 0 – 150 mbar;
- hourly flow rate of oxygen, with a calibrated oxygen meter;
- oxygen pressure, with AFRISO FZM 15 digital manometer;
- refractory masonry temperature, determined manually with a Chromel-
Alumel thermocouple, with the measurement range of 0 – 1200 ºC, installed
in the posterior area of ladle, with the measurement point placed 50 mm
from the inner of the ladle, according to the requests of the refractory bricks
manufacturers;
 Contribution to improving the durability of the refractory lining of the steel ladles 209

- waste gas temperature at the exit from the ladle, determined with a Pt-Rh-Pt
thermocouple, with the measurement range of 0 – 1800 ºC, placed into one
of the exhaust holes of gases from the ladle cover;
- inner surface temperature of the refractory masonry, measured with a Rytek
type radiation pyrometer, with the measurement range of 800 – 1800 ºC;
- waste gas chemical composition, determined with an AFRISO-MAXILYZER
type gas analyser, with built-in printer for CO, NO, NOx, CO2 and O2, the
sampling performing with the capture probe introduced through one of the
waste gas holes of the ladle cover.

5. Experimental results and discussions

In table 4 it is presented the technical data sheet of the drying-heating

process of a steel ladle of 180 t new built in the first mode of masonry
construction used in ArcelorMittal Galati (magnesia bricks as a wear layer).
Table 4
The technical data sheet of the drying-heating process of a ladle built with magnesia
bricks
Duration Temperature, ºC Flow rate, m3N/ h Observations
hours, Inside Waste Inner Natural Combustion Oxygen
minutes the gas surface gas air
masonry of the
ladle
masonry
0.00 20 - - 150 1457 - Beginning
the drying
1.00 80 200 - 150 1457 -
2.00 130 270 - 130 1262 -
3.00 170 300 - 100 971 -
4.00 195 350 - 100 971 -
5.00 230 375 - 100 971 -
6.00 260 400 - 150 1457 -
7.00 300 440 - 150 1457 -
8.00 330 480 - 180 1748 -
9.00 390 550 - 190 1845 -
10.00 430 625 - 210 2039 -
11.00 485 660 - 170 1651 -
12.00 530 695 - 155 1505 -
13.00 550 720 - 155 1505 -
14.00 580 740 - 155 1505 -
15.00 600 770 - 152 1476 -
16.00 630 780 - 170 1651 -
17.00 695 840 - 170 1651 -
18.00 745 890 - 220 2136 -
19.00 780 945 - 200 1942 -
210 A. Ioana, N. Constantin, L. Paunescu, C. Dobrescu, Ghe. Surugiu, M. Polifroni

20.00 810 980 925 200 1942 -

21.00 850 1025 970 200 1942 -
22.00 880 1060 1000 227 2204 -
23.00 920 1105 1050 227 1374 50 Beginning
the oxygen
supply
24.00 990 1150 1100 221 1400 30
25.00 1000 1175 1110 221 1400 30
26.00 1000 1175 1110 227 1442 30
27.00 1000 1170 1105 230 1461 30
27.45 1000 1175 1110 238 1108 150
28.00 1060 1200 1150 238 1108 150
29.00 1145 1300 1245 250 1190 150
30.00 1200 1375 1305 (250)* (1190)* (150)* Stopping the
burner
Total consumption (m3N) 5,400 46,120 500
Note: The natural gas, air and oxygen flow rates noted with *) correspond to the moment of
burner stopping at the end of process.

Based on the data from table 4, in Fig. 2 it is presented the diagram of

drying-heating process of ladle, containing the time evolution of temperature
value measured inside the masonry (50 mm from the ladle metal shell) compared
to the recommended values of manufacturer, on the inner surface of ladle
masonry, as well as the evolution of waste gas temperature at the exit from the
ladle through the cover holes.

Fig. 2. Diagram of the drying-heating process of a ladle built with magnesia bricks as a wear layer
1 – waste gas temperature at the exit from the ladle; 2 – temperature on the inner surface of ladle
masonry; 3 – temperature inside the masonry measured in the point indicated by manufacturer; 4 –
temperature inside the masonry according to the diagram required by manufacturer.
 Contribution to improving the durability of the refractory lining of the steel ladles 211

Also, it is showed the variation during the process of the hourly

consumptions of natural gas and oxygen used to enrich the combustion air.
The final masonry temperature in the measurement point indicated by
manufacturer, of 1200 ºC, was reached after 30 hours of combustion installation
operation. The heating speed of 40 ºC/ h up to the constant maintaining at 1000
ºC, according to the diagram imposed by manufacturer, was easily maintained, in
conditions of the burner operation without contribution of supplementary oxygen.
The slightly non-uniformity of the increasing slope of masonry temperature is due
to the absence, at the date of experiments, of the automatic control equipment of
the process. The continuation of the heating process over 1000 ºC was possible
only with oxygen addition in the combustion air. The volumetric proportion of
oxygen in air was maintained at the value of 30%.
Analyzing the graphs from Fig. 2, it can be observed that the waste gas
temperature at the exit from the ladle is higher with about 150 ºC than the
temperature measured inside the masonry, reaching 1375 ºC at the end of process.
The total natural gas consumption during the drying-heating process is
5400 m3N and the total oxygen consumption is 500 m3N.
In table 5 it is presented the technical data sheet of the drying-heating
process of a steel ladle of 180 t new built in the second mode of masonry
construction used in ArcelorMittal Galati (dolomite blocks as a wear layer).
Table 5
The technical data sheet of drying-heating process of a ladle built with dolomite blocks
Duration Temperature, ºC Flow rate, m3N/ h Observations
hours Inside Waste Inner Natural Combustion Oxygen
the gas surface gas air
masonry of the
ladle
masonry
0 20 420 - 250 2428 - Beginning
the drying
1 275 720 - 240 2330 -
2 450 900 - 245 2379 -
3 515 960 - 245 2379 -
4 590 1000 - 245 2379 -
5 690 1075 975 245 2379 -
6 800 1160 1100 245 2379 -
7 845 1260 1175 245 2379 -
8 855 1270 1190 245 2379 -
9 880 1290 1200 245 1632 10 Beginning
the oxygen
supply
10 970 1350 1295 230 1496 20
11 1000 1400 1340 230 1496 20
12 1025 1425 1355 235 1530 20
212 A. Ioana, N. Constantin, L. Paunescu, C. Dobrescu, Ghe. Surugiu, M. Polifroni

13 1085 1450 1400 235 1496 30

14 1100 1480 1425 235 1428 50
15 1150 1570 1480 240 1122 150
16 1200 1640 1550 (240)* (1122)* (150)* Stopping the
burner
Total consumption (m3N) 3,850 31,611 300
Note: The natural gas, air and oxygen flow rates noted with *) correspond to the moment of burner
stopping at the end of process.

Fig. 3, based on the data from table 5, shows the diagram of the drying-
heating process of ladle, containing the time evolution of temperature value
measured and, respectively, required by manufacturer, of the inner surface
temperature of ladle masonry and of waste gas temperature at the exit from ladle.
Also, it is presented the evolution during the process of the value of hourly flow
rates of fuel and supplementary oxygen.

Fig. 3. Diagram of the drying-heating process of a ladle built with dolomite blocks as a wear layer:
1 – waste gas temperature at the exit from the ladle; 2 – temperature on the inner surface of ladle
masonry; 3 – temperature inside the masonry measured in the point indicated by manufacturer; 4 –
temperature inside the masonry according to the diagram required by manufacturer.
 Contribution to improving the durability of the refractory lining of the steel ladles 213

Analyzing the experimental data presented in table 5 and graphically

represented in Fig. 5, it results that, in case of drying-heating process of the ladle
built with dolomite blocks as a wear layer, respecting the diagram imposed the
burner operation at its nominal capacity without supplementary oxygen up to the
temperature of 880 ºC inside the masonry. Then, it was necessary the oxygen
enrichment of air to maintain the increasing slope imposed by the heating diagram
and to reach the final temperature of 1200 ºC in the recommended time range.
From the experimental data results that waste gas temperature at the exit
from ladle is higher with about 400 ºC than the temperature measured inside the
masonry, reaching 1640 ºC at the end of process. The high difference between
waste gas temperatures resulted in the drying-heating process of dolomite blocks
and magnesia bricks and the temperatures measured inside the refractory lining of
the ladles built with these materials, of about 400 ºC and, respectively, 150 ºC, in
conditions of obtaining the same final temperature values inside the ladle masonry
(1200 ºC), confirms that there is a significant difference between the values of the
coefficients of heat transfer by thermal conductivity of the two refractory lining
types. Thus, the thermal energy distribution and, implicitly, the heat accumulation
in the dolomite masonry mass are achieved more difficult comparable with the
same distribution and accumulation in the magnesia masonry mass.
The total consumption of natural gas during the process was 3,850 m3N
and the total consumption of supplementary oxygen was 300 m3N.

6. Technical parameters of the drying-heating process and the

refractory linings durability of ladles

The use of the new burner in the drying-heating process of the steel ladles
led to significant modifications of the process parameters and the increase of the
refractory linings durability of ladles, compared to the results of the reference
combustion installation. Thus, though the reference fuel consumption is higher for
the two main masonry construction modes of the ladles (7,500 m3N compared to
5,400 m3N, in case of ladles with magnesia bricks and, respectively, 5,900 m3N
compared to 3,850 m3N, in case of the ladles with dolomite blocks), the maximum
heating temperature cannot exceed the value of 1050 ºC, while, using oxygen
enrichment of air (in a volumetric proportion of 30%), the final temperature of
process reaches 1200 ºC.
In table 6 they are presented, by comparison, the technical parameters of
process and the ladles durability for the two variants of masonry construction
obtained by the modification of the combustion installation [9].
214 A. Ioana, N. Constantin, L. Paunescu, C. Dobrescu, Ghe. Surugiu, M. Polifroni

Table 6
Technical parameters of the process and the ladles masonry durability
Name Unit Value
Refractory Refractory
lining with lining with
magnesia dolomite
bricks blocks
Refractory material mass built for one steel kg 15,100 12,300
ladle
Number of steel casting of a cycle
- during the experiment - 59 62
- reference situation - 45 40
Liquid steel amount casting in ladle
- at one discharge t/ charge 170 170
- at the total cycle for:
· dried and heated experimental ladle t/ cycle 10,030 10,540
· reference situation t/ cycle 7,650 6,800
Total natural gas consumption during the
drying-heating process
- during the experiment m3N/ charge 5,400 3,850
- reference situation m3N/ charge 7,500 5,900
Electricity consumption of the air fan
- during the experiment kWh/ charge 202.5 135
- reference situation kWh/ charge 225 140
Oxygen consumption during the test m3N charge 500 300
Duration of the drying-heating process
- during the experiment hours 30 16
- reference situation hours 30 16
Final heating temperature
- during the experiment ºC 1200 1200
- reference situation ºC 1050 1050

7. Economic effects

7.1. Calculus of specific consumption of the refractory materials

Knowing the mass of magnesia bricks (15100 kg) and dolomite blocks
(12300 kg) which constitute the wear layer of refractory lining of ladles built in
the first and, respectively, the second mode of masonry construction, as well as
the steel amounts casted in the two ladle types during the experiment and,
respectively, in the reference situation (10,030 t and 10,540 t, respectively, 7.650 t
and 6,800 t), they are calculated the specific consumptions of magnesia bricks and
dolomite blocks in table 7. Considering the prices of the two refractory natural
types (€900/ t magnesia bricks and €350/ t dolomite blocks) [9], they are
calculated the specific consumptions values, being indicated in the same table.
 Contribution to improving the durability of the refractory lining of the steel ladles 215

Table 7
Specific consumption and the value of refractory materials used at the masonry construction
of the ladles wear layer
Specific consumption of refractory Specific consumption value of
materials, kg/ t steel refractory materials, €/ t steel
Magnesia bricks Dolomite blocks Magnesia bricks Dolomite
blocks
Experimental 1.51 1.17 1.36 0.41
ladles
Reference 1.97 1.81 1.77 0.63
situation
Economy 0.46 0.64 0.41 0.22

7.2. Calculus of the specific consumptions of natural gas and

electricity

The total natural gas and electricity consumptions for the cycle of using
the ladles wear layer has been presented in table 6, both for the experimental
ladles and for the reference situation. The electricity consumptions include the
consumption at the combustion air fan and the indirect consumption necessary to
produce the technical oxygen (0.65 kWh/ m3N). The average price of natural gas is
€250/ 1000 m3N and the average price of electricity is €90/ MWh [9].
The calculus results of energy consumption value (natural gas and
electricity) corresponding to a cycle of using the wear layer of ladles, as well as
the cumulated specific consumptions value of energy, are presented in table 8.
Table 8
Calculus the value of cumulated specific consumptions of energy
Type of Value of energy consumption Value of cumulated specific
material in €/ cycle consumption
the wear layer Natural gas Electricity €/ cycle €/ t steel
Experimental Magnesia 1350 47.5 1397.5 0.14
ladles bricks
Dolomite 962.5 29.7 992.2 0.09
blocks
Reference Magnesia 1875 20.3 1895.3 0.25
situation bricks
Dolomite 1475 12.6 1487.6 0.22
blocks
Economy Magnesia - - 497.8 0.11
bricks
Dolomite - - 495.4 0.13
blocks
216 A. Ioana, N. Constantin, L. Paunescu, C. Dobrescu, Ghe. Surugiu, M. Polifroni

According to the data from table 8, it results that the value of cumulated
specific consumption of energy (natural gas and electricity), in case of masonry
construction with magnesia bricks, is diminished from €0.25/ t steel to €0.14 / t
steel, resulting an economy of €0.11/ t steel and, in case of masonry construction
with dolomite blocks, is reduced from €0.22/ t steel to €0.09/ t steel, resulting an
economy of €0.13/ t steel.
Analyzing the distribution of energy consumption values between the two
components (natural gas and electricity), it can be observed that, in case of
experimental ladles, the values of electricity consumptions increased over twice,
explicable by the supplementary consumption of oxygen. But, it is important to
decrease the values of natural gas consumptions at the experimental ladles, even
more as the final lining temperature of these ladles (1200 ºC) is obviously higher
than the final temperature obtained in the reference situation (only 1050 ºC).
Moreover, the increase in value of electricity consumptions is compensated by the
significant reduction of the value of natural gas consumptions, so that the value of
the cumulated consumption of energy indicates economies in the two modes of
ladles masonry construction.

7.3. Calculus of the net economies resulting by the increase of ladles

durability

According to the data from table 6, the durability of the experimental

ladles lining increased obviously from 45 to 59 casting/ cycle at the ladles with
magnesia bricks and from 40 to 62 casting/ cycle at the ladles with dolomite
blocks, leading to the significant increase of the steel amounts casted in the two
ladle types. Considering that the layers’ masses of magnesia bricks and,
respectively, dolomite blocks are not modified, it results that, by reporting to
greater steel amounts, the specific consumption of refractory materials and,
implicitly, their values are diminished.
This economic advantage is obtained by amplifying the energy requests of
the combustion installation, that makes the drying and heating ladles lining. To
highlight clearly the efficiency of using the new combustion installation achieved
and applied industrially it is necessary to summon the consumption values of
natural gas and refractory materials (from table 7) and the consumption values of
natural gas and electricity (from table 8) corresponding to the reference and
experimental ladles. Subtracting from the total value of the material and energy
consumptions of the reference ladles, the total value of the same type
consumptions of the experimental ladles, it is obtained the net economy value due
to the innovative solution. The results of these calculations are presented in table
9.
 Contribution to improving the durability of the refractory lining of the steel ladles 217

According to the data from table 9, the cumulated values of refractory

materials and energy consumptions economies are €0.52/ t steel, for the ladles
built with magnesia bricks and, respectively, €0.35/ t steel, for the ladles built
with dolomite blocks.
Table 9
Calculus of efficiency applying the technical solutions
Refractory lining Specific Value of the Total value of
type consumption energy consumptions
value of the consumption at €/ t steel
refractory the ladle drying
material and heating
€/ t steel €/ t steel
Experimental Magnesia bricks 1.36 0.14 1.50
ladles Dolomite blocks 0.41 0.09 0.50
Reference Magnesia bricks 1.77 0.25 2.02
situation Dolomite blocks 0.63 0.22 0.85
Economy Magnesia bricks 0.41 0.11 0.52
Dolomite blocks 0.22 0.13 0.35

The values of these economies are not high, but it must be considered that
there is an obvious difference between the maximum limits of temperature
reached in the experimental ladles masonry (1200 ºC) and the reference ladles
masonry (1050 ºC).

8. The impact on environment

During the drying-heating experimental process they are carried out

determinations of waste gas composition, corresponding to the both masonry
construction types of ladles [14]. The CO concentration in waste gas is in the
range 19 – 31 mg/ m3N, below the maximum limit of 100 mg/ m3N allowed by the
MAPPM Order no. 462/ 1993 [15].
The concentration of nitrogen oxides NO and NOx has values comprised in
the range 210 – 265 mg/ m3N, at the operation without oxygen enrichment of air
and 200 – 246 mg/ m3N, at the operation with oxygen enrichment of air, in
conditions in which the maximum limit allowed by law is 350 mg/ m3N [15].
Determinations of the pollutants concentration in waste gas resulted in the drying-
heating processes achieved with the reference combustion installations indicate
high exceeding of the maximum limit allowed for CO (160 – 200 mg/ m3N) and
values close to the maximum limit allowed for NO and NOx (310 – 350 mg/ m3N).
218 A. Ioana, N. Constantin, L. Paunescu, C. Dobrescu, Ghe. Surugiu, M. Polifroni

9. Conclusions

1. The combustion installation for drying and heating the steel ladles masonry of
180 t was conceived, achieved and industrial tested at the Converters
Steelwork in ArcelorMittal Galati.
2. The main aim of research presented in the paper is the increase of maximum
heating temperature of the refractory lining of new built steel ladle up to
1200 ºC by techniques of intensification of the combustion process.
3. The installation is based on intensification solutions of combustion by oxygen
enrichment of combustion air of 30% to ensure energy conditions need to
reach the final temperature of 1200 ºC (the measurement point being
situated inside the masonry 50 mm from the metal shell, in the posterior
area of ladle) and to achieve the heating speeds required by the refractory
materials manufacturers.
4. The own conception burner is characterized by the distribution of a
preponderantly central jet (80%) of natural gas, surrounded by annular
jets of flame produced by the mixture between the radial distributed fuel
and the primary combustion air. They are provided three mixture stages
between fuel and air, the secondary and tertiary air coming later in
contact with the ignited fuel. Thus, the flame is radiant by self-
carburizing and the phased contact system between fuel and air ensures
low emissions of nitrogen oxides. The oxygen for enrichment of air is
injected in the air stream in the supply connection area.
5. The industrial experimentation of the burner confirmed the correctness of
selection the solutions of combustion intensification, the diagrams of
drying and heating ladles masonry being achieved according to the
requests of the refractory materials manufacturers.
6. Due to respect the drying-heating diagrams, the durability of the wear layer of
ladles (magnesia bricks or dolomite blocks) increased significantly from
45 and, respectively, 40 steel castings/ cycle, up to 59 and, respectively,
62 castings/ cycle.
7. At the technical advantage of the new heating system, represented by the
difference between the maximum temperature values inside the masonry
(1200 ºC compared to 1050 ºC), it is added the economic advantage
constituted by the cumulated material and energy economies between
€0.35 – €0.52/ t steel.
8. The new system of combustion intensifying in the drying-heating process of the
steel ladles, according to the authors’ design, was applied for the first
 Contribution to improving the durability of the refractory lining of the steel ladles 219

time in the Romanian iron and steel industry and is used at all drying and
heating stands at the Converters Steelwork in ArcelorMittal Galati.

REFERENCES

[1]. *** The energy savers, Hotwork Development Ltd., 1978.

[2]. *** Increasing Productivity by Using Recuperators in Ladle Heating, Steel Times no. 10,
October 1988.
[3]. P.J. L’homme,”Les brûleurs régéneratifs”, Revue de Métallurgie-CIT, no. 7/8, 1989.
[4]. P. Leblanc,”Les brûleurs régéneratifs en céramique. Première realization en France des
brûleurs céramiques régéneratifs chez Legrand Isoceram”, Revue de Métallurgie-CIT, no.
4, 1988.
[5].*** Regenerative Burner Type Ladle Preheater, Chungai Ro Co. Ltd. http://www.chungai.co.jp
[6]. *** Ladle Preheating, Air Liquide Company. http://www.uk.airliquide.com
[7]. *** Oxygen Burner Type Rapid and High Temperature Ladle Preheater, Chungai Ro Co. Ltd.
http://www.chungai.co.jp
[8]. C.E. Baukal Jr., Oxygen-Enhanced Combustion, 2010.
http://books.google.ro/books?isbn=1420050257
[9]. L. Păunescu Eficientizarea fluxurilor tehnologice funcţie de natura căptuşelilor refractare ale
oalelor de turnare din industria oţelului (Technological Flows Efficiency in Correlation
with Refractory Linings Nature of Casting Ladles from Steel Industry), Teză de doctorat,
Universitatea Valahia Tȃrgovişte, septembrie 2011.
[10].*** Basic Ladle Lining for Secondary Metallurgy, Didier Werke AG, Information no. 2,
1984.
[11]. F. H. Norton, Refractories, Mc Graw-Hill Book Company, New York, 1968.
[12]. N. Angelescu and L. Păunescu,”Cercetări în vederea diminuării pierderilor de căldură prin
izolaţia termică a oalelor de turnare” (“Research in Order to Diminish the Heat Loss
through the Insulation of Ladles”), Proceeding la Al VI-lea Simpozion cu participare
internaţională “Mecatronică şi Inginerie Mecanică, Microtehnologii şi Materiale Noi”,
Tȃrgovişte, 7 – 8 nov. 2008.
[13]. R.T. Waibel, D.N. Price and M.L. Halprin, “Advanced Burner Technology for Stringent NOx
Regulations”, Presented at the American Petroleum Institute Midyear Refining Joint
Meeting of the Subcommittee on Heat Transfer Equipment, Orlando, Florida, May 8, 1990.
220 A. Ioana, N. Constantin, L. Paunescu, C. Dobrescu, Ghe. Surugiu, M. Polifroni

[14] M. Angelescu, I. Butnariu, D. Angelescu, Own Experiments and Pollution Analysis on Flow
Technology Components Sequences in Old 1 Section, U.P.B. Sci. Bull., Series B, Vol. 78,
Iss. 2, ISSN 1454-2331, 2016, pp. 223-232.
[15]. *** Ordinul nr. 462, Ministerul Apelor, Pădurilor şi Protecţiei Mediului, Bucureşti, 1 iulie
1993. http://www.legex.ro/Ordin-462-1993-4195.aspx