FIELD OF INVENTION
The present invention relates to an improved reactor for the desulphurization
of hot metal by directly generating magnesium utilizing the heat available in the hot metal
and a process for the same.
BACKGROUND OF THE INVENTION
Most of the conventional processes for the desulphurization of hot metal
employ discharging metallic magnesium with or without additives into the liquid metal. In a
typical desulphurization process employed in the steel industry, powder magnesium along
with calcium carbide is injected into the hot metal using nitrogen as a carrier gas, through a
submerged lance. Magnesium injected into the metal reacts with sulphur in the bath and
forms magnesium sulphide. The latter is removed in the slag phase. The efficiency of the
process depends on the degree of mixing of the magnesium in the bath, the particle size of
magnesium metal, the kinetics of reaction between magnesium and sulphur dissolved in the
hot metal etc. The efficiency of utilization of magnesium is very low in this process. Since
magnesium reacts violently in the liquid bath, mono injection of magnesium is rarely
practiced. Instead, it is always injected along with lime, calcium carbide etc. In a
modification of the process, such as the Kambara Reactor, mechanical stirring is employed
instead of deep injection. In this process, either lime or calcium carbide is added to the
surface of the liquid metal in the transfer ladle. A paddle or impeller is introduced into the
bath and is rotated using overhead motors causing stirring of the bath and mixing of the
reactants. However, this process does not make use of magnesium which has approximately
twenty times the capacity of lime to remove sulphur. The traditional processes involve the
production of magnesium metal in an industrial operation and subsequent utilization of the
metal in desulphurization. A process that can directly generate magnesium from the same
raw materials utilizing the heat available in the hot metal can considerably reduce the cost of
operation since it eliminates the need for an additional step involving external heating. If
magnesium vapour can be generated directly in the metal
bath, it will improve the efficiency of utilization of magnesium since the vapour can react
faster than solid magnesium which is currently used in the conventional desulphurization
processes.
Magnesium is traditionally produced by the reduction of its oxide with an
appropriate reducing agent such as ferro-silicon, aluminium etc. at a temperature ranging
from 1200-1300°C. The metal which is deposited in the form of crowns in the cooler parts of
the reactor is melted and refined. The refined metal is cast into ingots. This metal is milled to
fine size and collected as a powder. This powder is subsequently charged into the bath of
liquid iron for desulphurization using an inert gas as a carrier. Considerable amount of
energy is consumed during reduction, remelting and communition to fine powder. In addition
magnesium is lost during refining leading to a low level of recovery.
OBJECT OF THE INVENTION
Therefore, it is an object of the invention to propose an improved reactor for
the desulphurization of hot metal by directly generating magnesium utilizing the heat
available in the hot metal which is capable of producing magnesium vapour directly in the
process and bubbled into the hot liquid metal for desulphurization.
Another object of the invention is to propose an improved reactor for the
desulphurization of hot metal by directly generating magnesium utilizing the heat available in
the hot metal which is capable of producing hot liquid metal with low sulphur at low cost.
A further object of the invention is to propose an improved reactor for the
desulphurization of hot metal by directly generating magnesium utilizing the heat available in
the hot metal which is able to reduce the number of process steps required for the
desulphurization of hot liquid metal.
A still another object of the invention is to propose an improved reactor for the
desulphurization of hot metal by directly generating magnesium utilizing the heat available in
the hot metal which substantially reduces the time taken for desulphurization and thus make
the process economical.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Fig. 1 (a) - Shows the reactor according to the invention.
Fig. 1 (b) - Shows a top flange of the reactor.
Fig. 2 - Shows an equipment for desulphurization according to the invention where
the reactor is dipped inside the liquid metal bath.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
The present invention provides an improved reactor for the desulphurization of
hot metal using magnesium vapour instead of magnesium powder. The magnesium vapour is
produced by reducing magnesium oxide with aluminium powder at the temperature of the
hot metal, say around 1250-1400°C and is injected into the hot metal using an inert gas such
as Argon as the carrier gas.
Accordingly, the present invention provides a design of a reactor and a process
for the desulphurization of hot metal which involves: process for the production of titanium
oxide and metallic iron from llmenite, which comprises:
i) Fabrication of a graphite reactor (1) which is cylindrical in shape and
about 500 mm long (4); 29 mm I.D. (5) (inner diameter); 56 mm O.D. (6)
(outer diameter); 14 mm thick (3) with a flange (2) diameter (7) of 120
mm and flange thickness (8) of 14 mm, according to figure (lb) enclosed.
The reactor (1) contains perforations (9) at the bottom, on the cylindrical
surface about 50 mm from the bottom surface.
ii) Fabrication of a top flange (14) made of steel to match the dimensions of
the flange of the graphite reactor with a port (11) for passing argon
through the reactor (fig. 2)
iii) Thorough mixing of magnesium oxide and aluminium powder, in the mass
ratio 2:1, and making tablets (10) of the mixture using a hydraulic pres;
each tablet (10) shall be about 25 mm diameter and 5 mm thick.
iv) Taking about 100 g of the tablet (10) in the graphite reactor (1).
v) Assembling the top flange (14) with the graphite reactor (1) using
appropriate means, such as, C-clamps for fastening the two.
vi) Connecting the gas port in the top flange to a source of inert gas (15)
such as argon
vii) Holding the reactor assembly (graphite reactor connected to the top
flange) above the bath of hot metal for about 20 minutes for preheating,
passing argon through the reactor during the period of pre-heating.
viii) Lowering the reactor into the bath of hot metal (17), maintaining the flow
of argon, at an appropriate flow rate.
ix) Holding the reactor in the bath of hot metal (17) maintaining the flow of
argon, for 15-20 minutes
x) Withdrawing the reactor from the bath of hot metal (17) at the end of the
period of holding.
In an preferred embodiment of the present invention, the height of the graphite
reactor is of 500-600 mm. This height can be varied depending upon the quantity of hot
metal to be desulphurised and the depth of the vessel in which the metal is held.
The graphite reactor is having an inner diameter of 29 mm which can be varied
according to the amount of reactant tablets taken in the reactor.
The perforations in the reactor can have diameter of 0.1-1 mm and the number
of perforations made can be 1-10.
The perforations can be uniformly distributed on the surface of the reactor or
they can be placed in a staggered manner.
In the present invention the magnesium oxide may have the following
composition : MgO : 90-100% and the reducing agent may be aluminium powder with a
purity of 96-100%
The magnesium oxide and aluminium powder can be mixed in the ratio 2:1, by
weight.
In the present invention the oxide can be reduced in situ in the liquid metal bath
utilizing the sensible heat available in the bath. The magnesium vapour released during
reduction of the oxide can be directly bubbled into the hot liquid metal for desulphurization.
This will considerably reduce the cost of production of magnesium for desulphurization. In
addition, magnesium is injected into the liquid metal in the form of a vapour which has a
considerably larger reactivity compared to the powder magnesium.
The novelty of the process lies in the reduction of magnesium oxide inside the
hot metal in situ using the sensible heat available from the metal and the utilization of the
freshly generated magnesium vapour for desulphurization combined with the use of a
cylindrical reactor of appropriate design for desulphurization of hot metal.
The following examples are given by way of illustration of the working of the
invention in actual practice and therefore should not be construed to limit the scope of the
present invention.
Magnesium oxide in the following examples was 96% pure. Tablets of MgO and
Al were made by pressing a mixture of the two components in a die at 2 tonnes load in a
hydraulic press. Each tablet measured 25 mm diameter and 5 mm thickness. Each tablet
contained about 5 g of the material. To ensure uniformity in composition, about 10 g of MgO
was thoroughly mixed with 5 g of Al. Three tablets were made from this mixture. MgO
of 96% purity and aluminium of 99% purity were used. The particle size of MgO was 200 urn
and that of Al was 75 urn. A graphite reactor was used for the reduction of MgO and the
generation of magnesium vapour. The reactor measured 500 mm in length and had 29 mm
ID. The outer diameter was 56 mm. The flange (2) of the graphite reactor measured 120
mm diameter. This was fastened to a flange (14) made of mild steel (M.S.) with asbestos
sheet as gasket material. Fig. 1 gives the dimenstions of the reactor (1) and those of the
flange. There was a port in the M.S. flange (14) for passing argon. Six perforations at the
bottom of the reactor, each measuring about 1 mm diameter, served exit ports for the
carrier gas as well as the magnesium vapour generated during the reduction of MgO. The
argon inlet (11) was connected to a cylinder of argon gas via a rotameter(12). A pressure
gauge (13) was fitted in a parallel line to measure the pressure of the gas. Each tablet was
broken into four pieces before being charged into the immersion tube. This increased the
surface area of the tablets and the packing density of the tablets in the reactor. 100 g of the
tablets were taken in the reactor. The reactor containing the tablets was fitted to a holder
which was fitted to a trolley which could be moved along one axis on a pair of rails. The
holder could be moved in the vertical direction. This helped in controlling the depth of
immersion of the immersion tube in the hot metal.
After fixing the reactor in the holder, the trolley was placed at a position away
from the induction furnace. About 30 kg of pig iron was melted in the furnace The charge
was completely melted in about 45 minutes. After melting was complete, the reactor was
held above the surface of the bath for pre-heating the reactor. Flow of argon through the
reactor was commenced about 10 minutes before the start of pre-heating. Pre-heating was
carried out for about 15 minutes. Following this, the crucible containing the molten metal
was covered with a brick with a central hole through which the reactor could be lowered into
the bath. Bubble of gas could be seen emanating from the bath after the immersion of the
reactor. Argon flow through the reactor was maintained at the desired rate. The reactor was
kept immersed in the bath for the desired period of time and gradually withdrawn from the
bath at the end of this period. It was then moved away from the bath at the end of this
period. It was then moved away from the furnace by moving the trolley. The metal was then
poured into a pre-heated crucible. Samples were collected from the top, middle and bottom
of the metal bath during pouring. These samples were analysed for sulphur and carbon. The
temperature of the bath was measured using a disposable sensor and optical pyrometer.
Experimental Results:
Example 1
30 kg of iron from blast furnace was melted in the crucible in the induction
furnace as described above. The desulphurization trial was carried out as described above.
Argon was passed through the reactor at a flow rate of 14-16 litres per minutes. The reactor
was held in the liquid metal bath for 40 minutes. The reactor was immersed to a depth of
150 mm in the liquid metal bath. The temperature of the liquid metal was 1401-1500°C. The
sulphur level in the bath decreased from an initial level of 0.075% to 0.053%, at the end of
the desulphurization period.
Example 2
30 kg of iron from blast furnace was melted in a crucible held in an induction
furnace, as described above. The desulphurization trial was carried out as described above.
Argon was passed through the reactor at a flow rate 16-20 litres per minute. The reactor
was held in the liquid metal bath for a period of 40 minutes. The reactor was immersed to a
depth of 130 mm inside the bath. The temperature of the liquid metal was 1326-1442°C. The
sulphur level decreased from an initial level of 0.077% to 0.044%, at the end of the
desulphurization period.
Example 3
30 kg of iron from blast furnace was melted in a crucible in the induction
furnace as described above. The desulphurization trial was carried out as described above.
Argon was passed through the reactor at a flow rate of 10 litres per minute. The reactor was
held in the liquid metal bath for a period of 40 minutes. The reactor was immersed to a
depth of 180 mm in the bath. The temperature of the hot metal was 1233-1265°C. The level
of sulphur decreased from an initial level of 0.075% to 0.027% at the end of the
desulphurization period.
Example 4
30 kg of iron from blast furnace was melted in a crucible in an induction
furnace as describe above. The desulphurization trial was carried out as described above.
Argon was passed through the reactor at a rate of 10 litres per minute. The reactor was held
in the liquid metai bath for a period of 40 minutes. The reactor was immersed in the
bath to a depth of 200 mm. The temperature of the bath was 1320-1360°C. The sulphur
level decreased from an initial level of 0.072% to 0.042%, at the end of the desulphurization
period.
Example 5
30 kg of iron from blast furnace was melted in a crucible in an induction
furnace as described above. The desulphurization trial was carried out as described above.
Argon was passed through the reactor at a flow rate of 7 litres per minute. The reactor was
held in the liquid metal bath for a period of 40 minutes. The reactor was immersed in the
bath to a depth of 190 mm. The temperature of the bath was 1330-1350°C. The sulphur
level decreased from an initial level of 0.083% to 0.046% at the end of the desulphurization
period.
Example 6
30 kg of iron from blast furnace was melted in a crucible in an induction
furnace, as described above. The desulphurization trial was carried out as described above.
Argon was passed through the reactor at a flow rate of 7 litres per minute. The reactor was
held in the bath for a period of 20 minutes. The reactor was immersed in the liquid metal
bath to a depth of 190 mm. the temperature of the liquid metal was 1320°C. the sulphur
decreased from an initial level of 0.082% to 0.071% at the end of the desulphurization
period.
Example 7
30 kg of iron from blast furnace was melted in a crucible in an induction
furnace as described above. The desulphurization trial was carried out as described above.
Argon was passed through the reactor at a flow rate of 7 litres per minute. The reactor was
held in the liquid metal bath for a period of 40 minutes. The reactor was immersed in the
bath to a depth of 190 mm. the temperature of the liquid metal was 1350 C. the sulphur
level decreased from an initial level of 0.073% to 0.046% at the end of the desulphurization
period.
From the above we observe that the best parameters of the process for
desulphurization is achieved in Example -3 where the level of sulphur decreased from an
initial level of 0.75% to 0.027% at the end of the desulphurization period.
The main advantages of the present invention are:
1. It reduces the number of process steps required for the
desulphurization of liquid iron.
2. It utilizes sensible heat available in the liquid metal and therefore
reduces the energy consumption in the process.
3. It produced magnesium vapour which reacts faster than powder
magnesium with sulphur dissolved in the liquid iron.
4. It reduces the overall cost of desulphurization of liquid iron.
5. In the conventional process of desulphurization solid particles of
magnesium are injected into the melt, instead of vapour. These
particles take time to melt and react with the melt. Since vapour is
directly produced in the present invention, the time taken for
desulphurization is substantially reduced.
WE CLAIM
1. An improved reactor for the desulphurization of hot metal by directly generating
magnesium vapour in the liquid molten bath utilizing the heat available in the hot
metal comprising;
a fabricated graphite reactor (1) with a flange (2);
a rotameter (12) connecting the argon inlet (11) to the argon cylinder (15);
a pressure gauge (13) for measuring the pressure of the gas
at least one asbestos sheet as gasket material between the flanges (11, 2);
characterised in that,
a fabricated top flange (14) matching the dimension of the flange (2) of the
graphite reactor (1) with a port (11) for passing argon through the reactor (1) is
clamped to the flange (2) of the reactor wherein a plurality of perforations are
disposed at the bottom of the reactor for serving as exit ports for the carrier gas
as well as magnesium vapour generated during the reduction of MgO for flowing
to the metal hot liquid bath wherein an immersion tube is disposed in the reactor
for carrying the tablets of magnesium oxide and aluminium.
2. The improved reactor as claimed in claim 1, wherein the height (16) of the
graphite reactor (1) is of 500-600 mm having 29 mm inner diameter (5), 56 mm
outer diameter (6), and 14 mm thickness (3).
3. The improved reactor as claimed in claim 1, wherein the flange (2) on the top of
the reactor is having an outer dia (7) of 120 mm and thickness (8) of 14 mm.
4. The improved reactor as claimed in claim 1, wherein the reactor is cylindrical in
shape.
5. The improved reactor as claimed in claim 1, wherein the reactor contains a
plurality of perforations on the cylindrical surface about 50 mm from the bottom
surface.
6. The method of desulphurization of hot metal by the improved reactor claimed in
claim 1, comprising;
mixing magnesium oxide and aluminium powder in the mass ratio 2:1 to make
tablets of the mixture in a hydraulic press;
disposing a pre fixed amount of the tablet in the graphite reactor (1);
assembling the top flange (14) with the graphite reactor (1) by 'C' clamps or any
other fastening means;
connecting the gas port (11) in the top flange (14) to a source of inert gas cylinder
(15);
holding the reactor assembly of graphite reactor (1) with top flange (14) above
the bath of hot metal for about a desired time period to preheat the assembly
when Argon is passed through the reactor during the pre-heating maintaining an
appropriate flow rate of Argon when the reactor (1) is held in the bath of hot
metal for a pre-fixed time period when the magnesium vapour released during
reduction of the oxide inside the hot metal utilizing the sensible heat available
from the metal is directly bubbled into the liquid metal bath for desulphurization
and then the reactor is withdrawn from the bath of hot metal (17) at the end of
the period of holding.
7. The method of desulphurization as claimed in claim 6, wherein the magnesium oxide
(MgO) is having a purity of 90-100%.
8. The method of desulphurization as claimed in claim 6, wherein the aluminium
powder is having a purity of 96-100%.
9. The method of desulphurization as claimed in claim 6; wherein the prefixed amount
of tablet is 100 g and each tablet is 25 mm in diameter and 5 mm in thickness.
10. The method of desulphurization as claimed in claim 6, wherein the reactor is held
in the hot bath for 15-20 minutes.

ABSTRACT

Magnesium oxide and Aluminium powder in the mass ratio of 2:1 is mixed and
made to tablets in a hydraulic press. A prefixed amount of tablets are disposed in the
fabricated graphite reactor (1) having a flange (2). A top flange (14) is fixed to the flange
(2) of the reactor (1) by 'C' clamps. A gas port (11) in the top flange is connected to a
source of inert gas cylinder (15). The reactor assembly of graphite reactor (1) with top
flange (14) is held in the bath of hot metal for about 15-20 minutes when Argon is passed
through the reactor when magnesium vapour released during reduction of the oxide inside
the hot metal utilizing the sensible heat available from the metal is directly introduced into
the liquid metal bath for desulphurization and then the reactor is withdrawn from the bath
of hot metal (17) at the end of the period of holding.