FIELD OF INVENTION
The present invention relates to development of Rotary hearth furnace for reduction
of oxide ore in order to produce reduced products ranges from sponge to metal
nuggets at lower temperature range.
BACKGROUND OF THE INVENTION
Ferrochrome making process is highly energy intensive. Therefore, a novel route for
reduction of energy consumption by using low temperature solid state reduction route
is developed. As a process requirement in the technology development, a Rotary
hearth furnace is developed at R&D for conducting reduction experiments in
controlled atmosphere in variable heating and cooling cycles. This facility is used for
reduction of various oxide ores such as chromite ore, Iron ore, etc.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a development of rotary
hearth furnace for reduction of oxide ore which eliminates the disadvantages of
existing state of Art.
Another object of the present invention is to propose a development of Rotary hearth
furnace for reduction of oxide ore which generates multi-range product starting from
sponge to nuggets.
A further object of the present invention is to propose a development of Rotary hearth
furnace for reduction of oxide ore which consumes less energy.

A still further object of the present invention is to propose a development of Rotary
hearth furnace for reduction of oxide ore which is cost-effective.
An yet further object of the present invention is to propose a development of Rotary
hearth furnace for reduction of oxide ore which is eco-friendly.
SUMMARY OF THE INVENTION
The furnace shell is fabricated with mild steel plates and reinforced with M.S. channels
and angles. The furnace shell is fabricated such that all the joints will be fully welded
and will have total leak proof sealing. Gas sealing provided will be all around the
furnace so that leakage will be minimized. The gas sealing will consists of two no's
silicon rubber 'O' rings. Separate doors for charging and discharging are present. The
door will be operated electromechanically. Door opening and closing will be carried
out by a pneumatic cylinder and separate set of pneumatic cylinder for sealing the
door. The furnace has provision for purging different gas like N2 or Argon gas as per
the process requirement (Fig. 1). The max dimensions of sample trays for charging
samples are 150 mm Length, 150 mm Width and 30 mm Height and the capacity of
the furnace is 40-60 Kg/hr.
Heating Elements
The furnace has five heating zones and one cooling zone (Refer Fig. 1). The operating
temperature in each zone is given in following table:



All the terminals for the heating elements are designed for achieving the gas leak
proofness. The cooling zones will not have any heating element. The cooling zone has
water cooling out side the shell. And purging the gas in to the furnace can control the
cooling rate.
Control System
Thyrister power control is provided for heating elements in conjuction with PID
programmable temperature controllers. The whole furnace is controlled through
dedicated PLC. The PLC also provides fault alarms. A.C variable speed drive is
provided for control of hearth rotation.
Drive Mechanism
The rotation of hearth is achieved by means of motor and gearbox. The speed can be
varied to match process requirement. The hearth rotation can be stopped for loading
and unloading of alumina trays.
Gas Control
The gas panel have necessary rotameters and shut off valves. The gas control panel
also has pressure switches for indicating if the gas cylinder pressure has fallen or any
major leakage of gas. The furnace also provided with pressure switch to indicate that
furnace pressure has increased suddenly.
Safety Features

The furnace is designed with PLC based control system which will have two layer of
protection. The gas system will have pressure regulators and pressure switch and
solenoid valves. In case of sudden increase or decrease of pressure at any point the
system will stop the gas and alarm will be displayed on computer screen. Water
cooling jackets also provided with flow switch, which will give alarm incase of failure
in water flow. Temp controller will have open sensor protection and an excess temp
controller is provided for failure of main controller. The charging and discharging will
be done manually. The charge will align with door for easy operation and necessary
sensors are provided for the same. The heating element supply voltage should be low
voltage for no leakage of power and no risk of shocks. Outside wall temperature of
the furnace does not exceed ±40°C than atmospheric temperature.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1 shows a schematic diagram of Rotary hearth furnace
Fig.2 shows a schematic diagram of sectional front view and sectional top view of
Rotary hearth furnace
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE
INVENTION
As shown in Fig-1, the present invention relates to a rotary hearth furnace. The
furnace shell (18) comprising of a vertical cylindrical shaped casing which is fabricated
with mild steel plates and reinforced with m.s. channels and angles. High alumina
refractory bricks (12) are lined inside the shell. Around the inside circular periphery
the furnace comprises a plurality of heating zones viz. zone 1, zone 2, zone 3, zone 4,
zone 5 and one cooling zone (zone 6). A partition wall (9) is disposed inside the lining

in between cooling zone (zone 6) and heating zone 1. Each zone is heated by
inserting heating element (11) inside the furnace and zone 1 maintains a temperature
40-800°C, zone 2 maintains a temperature range 800-1300°C, zone 3 maintains a
temperature range 1300-1600°C, zone 4 maintains a temperature range 1300-
1600°C. Each zone having a peep hole (1) for visual observation and a provision for
CCT camera for on line sample image capturing. Each zone is provided with one port
(2) for sample thermocouple and one port (3) for gas sampling.
The gas flow is controlled through a solenoid valve (10). The oxide ores are fed into
the furnace by means of an aluminium tray (4) through charge inlet (6) and after
metallization charge are taken out through outlet (8). A separate doors (7) for
charging and discharging are present. The doors are operated electrochemically. Door
opening and closing are carried out by a pneumatic cylinder and separate set of
pneumatic cylinders for sealing the door. Two numbers of silicon rubber 'O' ring are
used for gas sealing around the furnace. There are two platforms (4), one for
charging oxide ore near charging inlet and one for charging outlet. The rotary hearth
furnace rotates by means of an electrical motor (17) and bearing (16) arrangement.
The furnace has also provision for purging different gas like N2 or Argon as per the
process requirement. The furnace is covered with special water jacket at the bottom
for avoiding air infiltration in the furnace from outside atmosphere.



WE CLAIM
1. A development of rotary hearth furnace for efficient reduction of oxide ore to
produce reduced products ranges from sponge to metal nuggets at low
temperature comprises:
- a vertical cylindrical shaped fabricated steel structure with mild steel plates,
channels and angles and lined inside with high alumina refractory bricks;
- a plurality of heating zones (1,2,3,4,5) and one cooling zone (6) are disposed
inside the hearth;
- a partition wall is disposed between cooling zone (6) and heating zone (1);
- a plurality of peep holes are disposed in all the zones around the outside
periphery for observation and for provision of CCT camera for online;
- a plurality of ports for mounting thermocouple in all the heating zones;
- a plurality of ports are disposed in the zones for gas sampling;
- at least one charge inlet and at least one charge outlet through sample tray
are provided around the outside periphery;
- The furnace hearth rotates by means of gear and motor arrangement.
2. The rotary hearth furnace as claimed in claim 1, wherein the capacity of the
furnace is 40-60 kg/hr.
3. The rotary hearth furnace as claimed in claim 1, wherein the heating elements
can work in highly reducing and oxidizing atmosphere.
4. The rotary hearth furnace as claimed in claim 1, wherein separate sliding door
for charging and discharging duct in order to avoid air infiltration in furnace
during handling of sample.

5. The rotary hearth furnace as claimed in claim 1, wherein a platform is provided
outside of charging and discharging doors.
6. The rotary hearth furnace as claimed in claim 1, wherein provision is made for
hot sampling from hearth in each zone.
7. The rotary hearth furnace as claimed in claim 1, wherein aluminium trays are
used for material transport on the hearth for avoiding sticking to hearth after
metallization.
8. The rotary hearth furnace as claimed in claim 1, wherein Ar and N2 gas are
used for controlling the atmosphere in the furnace chamber.
9. The rotary hearth furnace as claimed in claim 1, wherein no heating elements
are used in cooling zone.
l0.The rotary hearth furnace as claimed in claim 1, wherein special water jacket is
disposed at the bottom of furnace for avoiding infiltration in the furnace from
outside atmosphere.

The furnace shell is fabricated with mild steel plates and reinforced with M.S. channels
and angles. The furnace shell is fabricated such that all the joints will be fully welded
and will have total leak proof sealing. Gas sealing provided will be all around the
furnace so that leakage will be minimized. The gas sealing will consists of two no's
silicon rubber 'O' rings. Separate doors for charging and discharging are present. The
door will be operated electromechanically. Door opening and closing will be carried
out by a pneumatic cylinder and separate set of pneumatic cylinder for sealing the
door. The furnace has provision for purging different gas like N2 or Argon gas as per
the process requirement (Fig. 1). The max dimensions of sample trays for charging
samples are 150 mm Length, 150 mm Width and 30 mm Height and the capacity of
the furnace is 40-60 Kg/hr.