FIELD OF THE INVENTION
The present invention relates to desulphurization of hot metal. The invention in
particular relates to external desulphurization of hot metal in a ladle. More
particularly, the present invention relates to a desulphurization system for
external desulphurization of hot metal in a ladle with less than 60 tons capacity.
BACKGROUND OF THE INVENTION
Sulphur, if present in hot metal is considered to be detrimental for its further use
in certain applications and therefore the hot metal needs to be desulphurized to
the extent required to suit the desired applications. Nevertheless an external
desulphurization solution exists for a hot metal ladle capacity of > 100 tons and
therefore the available technology is primarily being used by large integrated
steel plants aimed at meeting their specifications. However, the pig iron plants
with mini blast furnaces (MBFs) and mini steel plants (MSPs) are unable to adapt
this technology as their hot metal ladle size varied between 15 to 60 tons. And
this despite the fact that the need for pig iron with sulphur content as low as
0.015% existed in the market. Thus a need exists for development of an
improved desulphurization system which makes it possible for the MBFs and
MSPs having ladle capacity of 15-60 tons to go for the desulphurization process
to suit their needs.

SUMMARY OF THE INVENTION
Accordingly there is provided an improved process and system for external
desulphurization of hot metal for < 60 tons capacity ladle. The process uses
calcium carbide based DS compound for desulphurization of hot metal. There are
four major steps involved in the process which are as under:
• Silo charging : Conveying a DS compound from silo trucks to
a DS storage silo. Conveying gas used is nitrogen at a pressure of 2
to 2.5 bar. The silo has been suitably modified by reducing its
capacity to 30 tons (existing silos are all above 80 tons) to suit the
needs of mini blast furnaces and other producers with such capacity.
• ID charging: The DS compound from the silo is taken into an
Injection Dispenser (ID). The injection dispenser (ID) has further
been modified to reduce its capacity to 0.5 ton (the prior art
systems have IDs of 1.5 to 2 tons capacity) as required in case of
mini blast furnaces and other producers with such capacity. The
Injection Dispenser (ID) is located just below the silo so that the
DS compound falls into it under gravity and no carrier medium is
required. However, the prior art systems incorporate an
intermediate vessel between the Injection Dispenser (ID) and the

silo. The present invention thus eliminates the need for providing
an intermediate vessel. Capacity of the Injection Dispenser (ID)
and the time required to pressurize the vessel is so adjusted that
the cycle time is not subsequently affected, thus reducing capital
costs and technological complications.
• Injection: This involves injecting the DS compound into the hot
metal through a lance designed specifically for the purpose. For this
purpose the Injection Dispenser (ID) is pressurized to about 4 to
4.5 bar and the DS compound is injected through a flow controlling
valve and the lance into the hot metal. Nitrogen as a carrier gas is
used at pre-specified flow rates, controlled by a flow controller and
transmitter, during the injection process.
• Back Blowing : The invented system is provided with means
for conveying the DS compound from the injection dispenser vessel
back into the silo. This is known as back blowing and has been fully
automated as against prior art systems which involved manual
operations.
The improved system for external desulphurization of hot metal adaptable in
ladles less than 60 ton capacity, according to the invention, is characterized in
that:
• Size of the Injection Dispenser (ID) vessel has been reduced by
30% to 50% as compared to prior art systems which, interalia,

reduces the pressurizing time of the ID vessel and provides a
flexibility of pressurizing and depressurizing the ID vessel in each
injection cycle without substantially affecting the cycle time. Thus,
if required, the ID vessel can be charged after each injection cycle.
The nitrogen consumption for fluidization of the DS compound in
the ID vessel (a process requirement) is correspondingly reduced.
A PLC application program has been developed to implement the
process step.
• A simple and light weight lance for the injection process has been
developed for < 60 tons hot metal capacity ladles, which, interalia,
reduces the total weight of the lance carriage system including
making its operation much simpler.
• The injection parameters governing the injection process, for
example, pressure of the ID vessel, flow rate of the DS compound,
flow rate and pressure of the carrier gas have been optimized
corresponding to the 60 tons ladle size. This together with the
improved lance system ensures smooth injection with minimum of
splashing.
• Silo capacity has been designed to store 30 tons of the DS
compound to suit the mini-plant capacity.
• The system has been designed without an intermediate vessel
between the silo and the ID vessel.

• Nitrogen supply to the DS station is maintained at 6 - 10 kg/cm2
and fed from a station which is filled by liquid nitrogen from
tankers, intermittently. Thus the requirement of gas plants for
continuous nitrogen supply according to the prior art systems is not
necessary in the invented system, thereby saving capital
investments.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1: Shows a schematic diagram of a ladle injection system for
desulphurization of molten iron according to the invention.
Figure 2: Shows the desulphurization system according to the invention.
Figure 3: Shows the details of the injection dispenser vessel in a system of
Figure 2.
Figure 4: Shows the details of DS-chemical storage bin of the system of
figure 2.
Figure 5: Shows the 'lance' of the system of figure 2.
DETAIL DESCRIPTION OF THE INVENTION
As shown in figure 1 there are three nitrogen receivers (1, 2, 3) at different
working pressures. Nitrogen from the source (not shown) is received in the main

receiver (1) at a pressure of 7.5 to 8 bar, which is then distributed to the other
two auxiliary receivers (2, 3) after reducing the pressure. A first auxiliary
nitrogen receiver (2) is meant for process and a second auxiliary nitrogen
receiver (3) for instruments. The output pressure of the process nitrogen
receiver (2) is maintained at 4.5 to 5 bar and the instrument nitrogen receiver
(3) at 5.5 to 6.0 bar. This is done through a plurality of pressure regulating
valves (2a, 2b, 3a) at the input of the receivers (2, 3).
Since moisture is not acceptable in the nitrogen used in the system, a moisture
analyzer (4) is provided in the main receiver (1) for detection of moisture, if any,
present in the incoming nitrogen gas. The moisture analyzer (4) indicates the
dew point temperature of the nitrogen.
As shown in figure 2, nitrogen from the process nitrogen receiver (2) is used for
the following purposes:
• Lifting of the DS compound from the silo truck (5) to the storage
silo (6).
• DS compound injection into the hot metal (29) through the lance
(7).
• Back filing the DS compound from the ID vessel (11) to the silo (6).
• Fluidizing in the ID vessel (11) and storage.

• Inertisation in the storage silo (6).
All the pneumatically controlled valves and the instruments are supplied with
nitrogen from the instrument nitrogen receiver (3) at a pressure of 6 to 6.5 bar.
Pressure of nitrogen from the process nitrogen receiver (2) is further reduced to
2.5 bar and made available for the purpose of unloading of the silo truck (5). A
plurality of Solenoid operated pneumatically controlled valves (15) are installed in
the pressurizing line (14) to make the conveying process automatic and to
ensure safety. The material conveying line (14) leads the DS compound from the
silo truck (5) to the silo (6). Provision has been made to flush the material
conveying line (14) automatically whenever the line gets choked due to any
reason. For the purpose of fluidizing the DS compound in the silo (6) and to
' maintain a slight positive pressure inside it, a first nitrogen line (39) has been
provided which enters the silo (6) at multiple points through a number of
aeration pads (16) provided at the bottom conical part of the silo (6) at a
pressure of 2.5 bar. Maintaining a slight positive pressure inside the silo is
important to prevent any entry of moisture laden air/gases from the atmosphere
into the silo (6). A C2H2 (acetylene gas) sample probe (17) is provided at the top
of the silo (6) to acquire continuous samples of nitrogen inside the silo (6) and
analyze it for G2H2, and transmitting corresponding signal to a PLC which
indicates the percentage of C2H2 (formed when the DS compound comes in
contact with moisture) in the gases inside the silo (6). A bag filter (18) has been
provided at the silo top to filter the nitrogen before being emitted into the

atmosphere. At least three load cell-based device (40) is provided to indicate the
weight of the DS compound available in the storage silo (6). All the parametric
indications are displaced in operator's control screen also.
The bottom of the silo (6) is connected to the top of ID vessel (11) through the
expansion joints (19) and a manual gate valve (20), a solenoid gate valve (21)
and a dome valve (22), are installed between bottom of the silo (6) and the ID
vessel (11).
Ds compound from the ID vessel (11) is injected into the hot metal (29) in a
controlled manner by means of a flow control valve called Dosing Valve (23).
Nitrogen being used as carrier gas flows through another regulated line (26)
which meets the material line (14) carrying DS compound from the ID vessel
(11) to the lance (7). The flow of nitrogen in this case is controlled by a mass
flow controller and transmitter (27, 28). For the purpose of fluidizing the DS
compound in the ID vessel (11), a second nitrogen line (24) has been provided
which enters the ID vessel (11) at multiple points through said aeration pads
(16) at the bottom conical part of the vessel (11) at a pressure of 2.5 bar. Two
separate lines are connected to the ID vessel (11), one for pressurizing (13) to
extract the DS compound and another for depressurizing the ID vessel (11).
Similar to the silo (6), the ID vessel (11) is mounted on at least three load cell-
based device (not shown) through which parametric data, can be acquired and
transmitted to the operator's display.

DS compound from the ID vessel (11) can also be fed back to the storage silo
(6) (instead of injecting through the lance into the hot metal). This process of
Back Blowing has been fully automated and utilized for emptying out the ID
vessel (11).
A WVF drive controlled lance carriage assembly (10) is provided to ensure
smooth vertical movement of the lance (7) into and out of the hot metal (29) in
the ladle (9).
A,hood (8) is provided at the top of the hot metal ladle (9) and connected to a
spark arrester (30) through a duct (31). The spark arrester (30) is also
connected to a bag house (32). The filtered gas passing through the bag house
(32) is emitted through a chimney (33). The suction at the hood (8) is connected
to at least one ID fan (34) installed next to the bag house (32) and before the
chimney (33).
Pressure in the nitrogen lines is controlled by means of a plurality of pressure
regulating valves, pressure transmitters and pressure switches are provided at a
suitable point to measure pressure at various points for indication as well as for
automation purpose.
LANCE DESIGN
As shown in figure 5, a lance (7) for the injection purpose has been designed to
suit the requirements of injection into < 60 tons hot metal ladle. The lower

portion 7(A) of the lance (7) is made of refractory material capable of working up
to a temperature of 2000°C. A steel pipe (7B) with T shape at the one end and
having a threaded portion 7(C) at the other is provided through out the lance
(7). The upper portion (7A) of the lance (7) is kept without refractory as it does
not come in contact with the hot metal (29). The DS compound with nitrogen
gas passes through this pipe (7B) during desulphurization.
THE PROCESS
The process comprises pneumatically (using N2 as carrier gas) conveying
desulphurization reagent through a monolithic lance (7) kept immersed in the
centre of the hot metal (29) in vertical position. The ladle (9) with hot metal (29)
is placed on the ladle car (35) which transfers the ladle (9) under the fixed
suction hood (8) at the desulphurization station. On receipt of chemical analysis
of data relating to the hot metal (29) from the control room, said data is entered
into the processor, which automatically calculates the amount of DS compound
to be injected into the hot metal (29) to achieve the desired sulphur level. Since
the system operation is completely PLC program based, the entire activities take
place in a sequence after giving the 'Group Start' command from the computer
apparatus.
The lance (7) is then lowered to be disposed at a first position (B) above the
level of the hot metal (29), the flow of gas will be maintained through the lance

(7) to keep it clear from the metal. As the lance tip will move into the hot metal
(29), reagent (DS compound) will start flowing automatically. When the lance (7)
will reach its lowest position (Q, the conveying gas and DS compound flow rates
will be regulated according to the preset value. When the total preset amount of
reagent is injected, the discharge valve (23) of the injection dispenser (11) will
close automatically and the lance (7) will be raised. Simultaneously, the gas flow
rate will increase to avoid lance (7) blockage due to ferrostatic pressure. When
the lance will emerge out of the hot metal (29), it will stop for a short time to
make sure that the conveying line (14) is completely free from the reagent. The
lance (7) will be withdrawn then to its highest position (A) and the temperature
measurement and sample collection will be repeated.
Gas generating agents in the desulphurization reagent will create the required
turbulence in the hot metal (29) and will provide optimum mixing of the liquid
and the solid phases across a wide reaction surface. The gases generated during
the desulphurization process will be drawn through the dust collecting hood (8).
The conveying operation of the material will be automatic to avoid human errors.
The C2H2 content in the DC silo (6) will be monitored continuously. The silo (6)
and the dispenser (11) will be kept under positive pressure (30 to
50 mm wc) and purged with nitrogen continuously to avoid acetylene generation.
NITROGEN LINE FOR MATERIAL CONVEYING
Nitrogen is made available for conveying of the DS compound from the silo truck

(5) to the silo (6) at a specified pressure (process nitrogen pressure regulated by
the pressure regulating valves). A flexible hose (41) and a coupling (42).have
been provided to connect the line to silo tanker (5). A solenoid operated
pneumatically controlled valve (15) is provided in the nitrogen line to make the
conveying process automatic and to ensure safety. A control panel (not shown)
is installed to control the process of DS compound conveying. A pressure
transmitter (36) in the nitrogen line transmits pressure readings in the DS control
room.
PS COMPOUND CONVEYING LINE
The DS compound conveying line (15) leads the DS compound from the silo
tanker (5) to the silo (6). As in the case of the nitrogen line (14) a flexible hose
(41) and a coupling (42) is provided to connect the line (15) to the silo tanker
(5). A pressure switch has also been installed in the line so as to get an
indication of line choke (pressure in the line going beyond that in the nitrogen
line for material conveying) in the DS control room (not shown) and also to open
the flushing line automatically in that case.
FLUSHING LINE (FOR MATERILA CONVEYING LINE)
A flushing line (37) has been provided which connects the DS compound
conveying (15) line at three points and opens automatically as soon as there is

any indication of choking in the DS compound conveying line (15). A solenoid
operated pneumatically controlled_valve (15) has been installed in the line (37)
to make the conveying process automatic and to ensure safety.
LANCE CARRIAGE SYSTEM
A specially designed lance carriage system (10) is provided which consists of a
3.7 kw motor with a braking arrangement, a VWF drive to control the speed of
the motor a 25.1 gear box, sprockets and holding arrangement for lance.
Three positions A, B and C have been marked for the vertical movement of the
lance by proving limit switches at these positions. 'A' is the parking position. NB' is
the intermediate position to which the lance moves when given command for
injection. Only of all the references are available, the lance (7) moves to the
injection position *C. The lance movement has been fully automated and
synchronized with rest of the injection process.
LADLE MOVEMENT SYSTEM
The hot metal ladle is brought to the injection position in a hot metal ladle car.
The correct position of the car is ensured by a limit switch provided at an
appropriate position and is linked to the injection process logic.

FUMES/DUST EXTRACTION SYSTEM
The dust laden fumes generated during the injection process are sucked through
the hood (8) placed directly above the ladle (9) which is connected to a spark
arrester (30) and the bag house (32). Fumes are filtered at the bag house (32)
before being exhausted through a chimney (33). The suction is created by an
induced draft fan (34) provided at the outlet of the bag house (32) and the
chimney inlet (33). The spark arrester (30) is provided to arrest the spark, if any.
A temperature measuring device (38) is installed near the spark arrester (30) to
measure the temperature of the gas entering the spark arrester (30). If the
temperature goes beyond a certain specified limit, a dilution air damper (39)
provided at the spark arrester (30) inlet sucks the air to dilute the incoming gas
and thus lowers its
temperature. A damper (43) is further provided at the fan inlet to regulate the
draft provided by the fan (34). All the dust collected in the bag house (32) and
the spark arrester (30) in taken out through a plurality of rotary air lock valves
(44) provided at the bottom of the spark arrester (30) and the bag house (32).
The system doesn't allow any dust particles to go into the atmosphere and hence
clean air is emitted to the atmosphere.

KEY WORDS
• Hot Metal: Liquid metal produced in blast furnaces at a temperature of
around 1350°C - 1400°C.
• Pig Iron: Hot metal cast in a particular shape called 'pig' and hence
the name. ,
• Flow Controller and Transmitter: An instrument designed to control flow
of nitrogen and to transmit the same to PLC panel.
• Dew Point: Temperature to which air must be cooled to reach saturation
at a constant atmospheric pressure. At this temperature dew begins to
form and water vapour changes to liquid form.
• Inertisation: To keep without any reaction.
• Solenoid Valves: Electrically operated valves.
• Dome Valve: A specially designed valve to provide sealing for the ID
vessel.
• Ferrostatic Pressure: Pressure exerted by a bed of hot metal at a
particular point.

WE CLAIM:
1. An improved system for external desulphurization of hot metal for < 60
tons capacity ladle, comprising :
• a storage silo having reduced capacity (6) for receiving DS-compound
conveyed from a cargo-carrying truck;
• an injection dispenser vessel having reduced capacity (11) situated below
the silo (6) so thatwithout the need of any carrying medium the DS-compound can
be transported from the silo to the ID vessel by gravity;
• a lance (7) applicable for the lower capacity ladle including a lance carriage
means (10) provided for vertical movement into the hot metal ladle; and
• a ladle (9) with hot metal (29) including the carriage means transportable
and disposable below the lance for desulphurization of the hot metal, the flow rates
of the DS compound and the conveying gas including vertical movement of the
lance in hot metal ladle being regulated based on an on-line measurement of the
operational parameters and comparing the parameters with a preset value.

2. The system as claimed in claim 1, comprising a PLC-based control and
monitoring apparatus.
3. The system as claimed in claim 1, wherein a plurality of conveying lines(14)
equipped with control means are provided for conveying of the DS compound
including the conveying gas within the system.

4. The system as claimed in claim 1, comprising control means for discharge
of dust laden fumes generated during the operation, which is filtered and exhausted
to the atmosphere.

ABSTRACT

TITLE "AN IMPROVED SYSTEM FOR EXTERNAL PESULPHURIZATION OF HOT
METAL FOR < 60 TONS CAPACITY LADLE"
The invention relates to an improved system for external desulphurization of hot
metal for < 60 tons capacity ladle, comprising a correspondingly modified
storage silo for receiving DS-compound conveyed from a cargo-carrying truck; an
injection dispenser vessel (ID vessel) modified in registration of the modification
incorporated in the storage silo, and being disposed below the silo such that the
DS-compound without the need of any carrying medium can be transported from
the silo to the ID vessel by gravity; a lance applicable for the lower capacity ladle
including a lance carriage means provided for vertical movement into the hot
metal ladle; and a ladle with hot metal including the carriage means
transportable and disposable below the lance for desulphurization of the hot
metal, the flow rates of the DS compound and the conveying gas including
vertical movement of the lance in hot metal ladle being regulated based on an
on-line measurement of the operational parameters and comparing the
parameters with a preset value.