AN IMPROVED SEALING SYSTEM OF DUST- LEGS OF SINTER MACHINE
FIELD OF INVENTION
The present invention relates to an improved sealing system of dust-legs of
Sinter Machine. More particularly, the present invention deals with a leak-proof
and PLC governed double cone double acting valve with unique innovative
features and thereby replacing all the counter-weight flap valves.
BACKGROUND OF THE INVENTION
Research & Development Centre for Iron and Steel (RDCIS), Ranchi and
Rourkela Steel Plant (RSP), Rourkela have designed and installed an improved
sealing system of dust-legs of Sinter Machines at Sinter Plant - I, RSP.
Counter-weight operated manual flap valves, provided in each of the dust-hopper
discharges the accumulated material on to the conveyor. These valves are
normally kept in closed position by counter-weights, which act against the
material load in the hopper to prevent the unwanted entry of atmospheric air into
the wind-main. The flap valve opens to discharge the accumulated material from
the respective hopper, when the material load exceeds the weight of the counter-
weights of the valve. The flap of the valve again gets closed as soon as the
counter-weight exceeds the material load. This ensures sealing against the
unwanted entry of atmospheric air through discharge opening of the valves. The
photograph of the counterweight operated manual flap valve is depicted in Fig-1.
However, due to various reasons of mal-functioning, the manual valves remain in
open condition, even after completely discharging the material from the individual
hoppers. Due to the remote location of these valves, the open position of the
valves is normally unnoticeable. The valves in open condition help atmospheric

air to enter the wind-main easily, due to suction inside the wind-mains. This
affects heavily the necessary under-grate suction underneath the sinter bed. The
reduction in under-grate suction affects the speed of the sintering process, which
will finally lead to low productivity of the sinter machine. The presence of un-
wanted cold atmospheric air in the wind-main also overloads the exhauster and
increases its power consumption.
The atmospheric air sucked through sinter beds by exhausters, gets laden with
dust in the process of sintering. Dust hoppers are provided below the wind-main
to collect the coarse dust particles, which are separated from the dust-laden hot
air. The hot air with fine dust is vented out through chimney. The accumulated
dust from the dust hopper is discharged, on to a conveyor, by a counter-weight
operated manual flap valve, provided at the discharge end of the each hopper.
These manual flap valves are kept in closed condition by counter-weights, to
prevent entry of atmospheric air through the discharge openings. Entry of
atmospheric air into the wind-main, through dust hoppers, reduces the effective
suction underneath the sinter bed which leads to loss of productivity of sinter
machine. The malfunctioning of the counter-weight manual valves results in the
surrounding air being sucked into the system leading to reduction in effective
under grate suction. To eliminate suction loss due to entry of atmospheric air into
wind-main through the defect prone manual flap valves, it was decided to
introduce leak-proof Programmable Logic Controller (PLC) governed, "Double
Cone Double Acting Valves" (DCDAV) underneath the dust hoppers, in the place
of the existing counter-weight based manual flap valves.
To tackle this problem of entry of atmospheric air through dust-hoppers due to
un-necessary opening of the flap valve, a leak-proof and PLC governed double
cone double acting valve with unique innovative features has been designed and
installed by replacing all the counter-weight flap valves.

SUMMARY OF THE INVENTION
Therefore disclosed here is an improved system designed for effective sealing of
dust-legs against entry of atmospheric air through discharge opening of the dust
hoppers for effective under-grate suction below the sinter bed, by introduction of
double cone double acting valves with innovative features.
Such as herein described an improved sealing system of dust-legs of Sinter
Machine comprising of: at least one Double Cone Double Acting Valve (DCDAV),
at least one programmable logic controller (PLC) configured for the control for the
said DCDAV; and the said DCDAVs are driven through roller & cam-lever in
operation by a geared motor.
An object of the present invention is to provide a valve configured for preventing
of chamber wall puncturing of DCDAV.
Another object of the present invention is to provide an energy efficient dust
discharge system.
Yet another object of the present invention is to provide an improved material of
construction for valve-seat of DCDAV.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS.
Fig 1 illustrates the counter-weight operated manual flap valve (prior art) in
accordance with the present invention;
Fig 2 illustrates the double cone double acting valves, operated through
programmable logic controller in accordance with the present invention;

DETAILED DESCRIPTION
The improved sealing system for dust-legs of sinter machine has been designed
and installed in Sinter Plant - I of Rourkela Steel Plant. The system mainly
consists of double cone double acting valves, operated through programmable
logic controller for sequential operation of the system. The improved sealing
system of dust-legs through double cone double acting valve with innovative
features has completely replaced the existing manually operated, counter-weight
based flap valves.
There are 20 numbers of dust-legs for the common wind-main in each sinter
machines. The atmospheric air sucked through sinter bed by exhauster for
sintering process carries dust and small particles from the gaps of the grate-bars
of moving pallets, into the wind-main. From the wind-main, the dust and particles
of sinter-mix are accumulated in the dust-hoppers, provided below the wind-main
and the remaining hot air is vented out to atmosphere through electro-static
precipitator.
The accumulated dust and particles of sinter-mix in the dust-hoppers are
discharged on to a common belt conveyor, which in turn carries them for reuse
into the sintering process as return sinter.
As per the primary object of the present invention, the chamber wall puncturing of
DCDAV is prevented. The common phenomenon of chamber (space between
the cones) wall puncturing of DCDAV, caused by swirling of entrapped air inside
the valve due to suction after number of operation of the DCDAV has been
completely eliminated through introduction of an innovative solution of ensuring
some buffer level of material accumulation in the dust-hopper at all the time
through installation of level sensor in each hopper, so that the accumulated dust
in the hopper acts as seal against air entrapment into the chamber portion of the
valve.

To ensure the aforesaid object an algorithm is developed in the system software,
which ensures to stop the operation of the respective DCDAV, once the dust
level reaches the low / buffer level. The said innovative system improves the life
of the DCDAVs and hence increases the availability of the machine.
The sinter machine of RSP comprise of 18 dust hoppers in each sinter machine
(36 nos. in total) is provided with individual Double Cone Double Acting Valves
(DCDAV) to discharge the accumulated materials i.e. return sinter. These valves
are operated through geared motor of 0.55 kw capacity each.
The logic developed for the system ensures the valves are operated only when it
is actually required. The DCDAVs are grouped / clubbed in different groups
according to material accumulation rate in the respective hoppers. The operating
sequence of the independent group(s) can be modified, depending on the
continuously variable parameters, such as, health condition of the pallets, quality
of sinter-mix material & return sinter, dust accumulation rate, etc.
This intelligent logic provision prevents the un-necessary operation of the
DCDAV, which in turn saves electrical energy as discussed in the subsequent
objective of the present invention.
As per another objective there is provided Improved material of construction for
valve-seat of DCDAV. The material of construction of the "valve seat" of DCDAV
has been specifically changed to "Ni-hard material" (IS-4771-1985) for better and
improved life. Earlier the valve-seats were made of non-metallic PTFE seat ring
material but these valve-seats had poor life against constant wear due to softer
nature. The leak-proof condition of the valve is wholly dependent on the valve-
seat condition. The improved valve seat material ensures increased life of the
valve seats against wear and in turn increases the availability of the valve.

The newly introduced Ni-hard material valve-seats are highly wear resistant
against the material contact but possess optimum softness for prompt sealing
during DCDAVs operation. This innovative development shall also improve the
performance of the valve along with reduction in cost of operation of the valve.
The DCDAVs are driven through roller & cam-lever operation by a geared motor.
Each hopper has been provided with a Level Switch for sensing low level of the
stored material, which is interlocked with the motors of DCDAVs. The motors of
DCDAV will stop, when the level of material in the hopper is low and keep both
the cones of DCDAV in closed condition. This arrangement helps in preventing
the tendency of chamber wall puncturing by the entrapped air, inside the
DCDAV. The photograph of the DCDAV is shown in Fig- 2.
The DCDAV operations are automatic, with sequential control and interlock as
per control logic implemented through PLC. The algorithm of PLC programming
is taking care of various operating philosophy for operation of the valves. To
achieve sequential operation of the system, interlocking with status of the
position of the cones of the valve, is also taken into consideration.
MCC for the geared motors is located in the building (Electrical Room) at a
distance of approximately 80 m from the source of power supply room i.e., U 11.
This electrical room is also housing the PLC cum MIMIC panel with operating
facilities. One control desk cum MIMIC panel with operating facilities is installed
in the machine control room.
Independent Local Control Station (LCS) has been provided near each of the
DCDAVs, for provision of operating the valves locally. Each LCS is having start &
stop push buttons and a selector switch for operation of the valve in manual,
individual and auto mode.

In the mimic cum control desk installed in the machine control room, facilities for
sequential operation of the valves in a group or in sequence has been provided.
The MIMIC panel is having LED indications of start, stop, trip for geared motors'
operations, low-level indication for the hoppers and selection status. The
networking of PLC's in electrical room and machine control room is achieved
through appropriate communication system with remote I/O facilities. Standalone
PLCs are provided for each machine.
The system can be operated from Control desk cum MIMIC panel in auto mode,
i.e. Sequential operation of these valves or in a group for each machine. For
individual / manual operation of these valves, the same can be achieved through
LCS located near the drives. Suitable selector switches to achieve the said
operations are incorporated in the system. In maintenance mode of operation,
the individual motors of each DCDAV can be operated from MCC without
powering up of PLCs or during failure of PLCs
The installed system has been suitably interlocked with their respective existing
belt conveyors i.e. 84 A & 84 B, such that the proposed DCDAVs are not
operated, whenever their respective belt conveyors are not operating.
The following design parameters were taken into consideration in designing the
improved sealing system for dust-legs.



Equipment specifications
a) Double Cone Double Acting Valve (DCDAV):
The valves have both end flanged and are driven by a geared motor of
0.55 KW. The cone and seating of the valve is Ni-hard construction. The
valves specification is as follows:

b) Accessories:
Inlet chute / adaptor of mild steel structure is provided to match the
existing flange of the hopper with the flange of the DCDAV at site.
c) MCC Panel:
The MCC of non-compartmental type is conform to IS 8623 (Part-1)-1993,
(Part-2)-1993. It will cater to all the geared motors for the DCDAV. Control
circuit voltages for MCC are 240V AC. The control transformer has MCB
protection on primary side as well as secondary side. The contactor used
in MCC module is conforms to IS 13947(part4/sec1): 1993. The contactor
rating is 30 / 32amps. The MCC panel has 40 nos. of feeders (36 nos. for
motors + 4 spares). The contactor coil rating is 240V AC without any
resistance in the coil circuit. Additional 20% spare terminal in the terminal
block has been provided for future use. Earthing terminals of 2 nos. is also
provided at the two opposite ends of the MCC for connection with external
earth connector. The MCC receives power of 415V 30, 50Hz, 3 wire
(without neutral) supply from the power source from the electrical room.
Incoming power is drawn from the U 11 room. The incomer has voltmeter,
ammeter with selector switch and wattmeter. The feeders to motors have
ammeter without selector switch. The indicating instrument conforms to IS:
1248(part-1)-1993 (part2)-1983 & IS: 2419-1979. The MCC is located in
electrical room.



d) PLC cum MIMIC Panel:
The PLC system consists of central processing unit, memory, power
supply module, communication module, interface module, input/output
module, racks, connector, interposing relays with DO modules, etc. as
required to make the PLC system complete in all respects functionally.
The PLC system has its own power supply system within the module. In-
comer, power equipment, isolating transformer etc., is segregated from
CPU, memory, I/O and other sensitive module. The internal wiring is of
650/1100V graded insulated copper wire of adequate cross-section with
PVC /Teflon insulation. The cross-section of insulated wire is of 1.5mm2.
Terminal blocks are of 650 /1100V grade rated for 10A. Separate terminal
blocks are provided for l/O's. Proper identification of voltage level is also
made on terminal block. 20% spare terminals are provided. A continuous
copper grounding bus of 25 x 3 mm size has been provided along the
bottom of PLC panel. Metallic parts of all components will be effectively
earthed.

Techno-economic benefits
The PLC operated DCDAV for improved sealing system for dust-legs was
successfully implemented in both the machines of SP-I. Both the systems are
working satisfactorily in both auto and individual modes.
Trials were conducted to ascertain the performance of both the systems. Some
significant improvements in various sintering process parameters are mentioned
below:
> Increase in under-grate suction by 65-70 mm WC in both the machines.
> Increase in Burn Through Point (BTP) temperature by 50 C average.
> Increase in machine speed from 600 rpm to 650 rpm.
> Improvement in productivity by 5% from the level of 0.88 to 0.92 t/m2/hr.
> Improvement in energy consumption by 9%.
Although the foregoing description of the present invention has been shown
and described with reference to particular embodiments and applications
thereof, it has been presented for purposes of illustration and description and is
not intended to be exhaustive or to limit the invention to the particular
embodiments and applications disclosed. It will be apparent to those having
ordinary skill in the art that a number of changes, modifications, variations, or
alterations to the invention as described herein may be made, none of which
depart from the spirit or scope of the present invention. The particular
embodiments and applications were chosen and described to provide the best

illustration of the principles of the invention and its practical application to
thereby enable one of ordinary skill in the art to utilize the invention in various
embodiments and with various modifications as are suited to the particular use
contemplated. All such changes, modifications, variations, and alterations
should therefore be seen as being within the scope of the present invention as
determined by the appended claims when interpreted in accordance with the
breadth to which they are fairly, legally, and equitably entitled.

We claim:-
1. An improved sealing system of dust-legs of Sinter Machine comprising of:
at least one Double Cone Double Acting Valve (DCDAV);
at least one programmable logic controller (PLC) configured for the control
for the said DCDAV; and
the said DCDAV's are driven through roller & cam-lever in operation by a
geared motor.
2. An improved sealing system of dust-legs of Sinter Machine as claimed in
claiml, wherein each hopper is provided with a Level Switch for sensing low level
of the stored material, which is interlocked with the motors of DCDAVs.
3. An improved sealing system of dust-legs of Sinter Machine as claimed in
claim 2, wherein the level switch comprise of sensor of RF (Radio Frequency)
type which is flange mounted with canopy arrangement alongwith controller
connected through RF cable.
4. An improved sealing system of dust-legs of Sinter Machine as claimed in
claiml, wherein the PLC system consists of central processing unit, memory,
power supply module, communication module, interface module, input/output
module, racks, connector, interposing relays with DO modules, etc as required to
make the PLC system complete in all respects functionally.
5. An improved sealing system of dust-legs of Sinter Machine as claimed in
claiml, wherein an inlet chute / adaptor made up of mild steel structure is
provided to match the existing flange of the hopper with the flange of the DCDAV
at site.
6. An improved sealing system of dust-legs of Sinter Machine as claimed in
claim 3, wherein the wall puncturing of DCDAV is eliminated by ensuring some

buffer level of material accumulation in the dust-hopper at all the time through
installation of level sensor in each hopper, so that the accumulated dust in the
hopper acts as seal against air entrapment into the chamber portion of the valve.
7. An improved sealing system of dust-legs of Sinter Machine as claimed in
claim 4, wherein the logic developed for the system is configured such that it
ensures the valves are operated only when it is actually required, there by saves
electrical energy.
8. An improved sealing system of dust-legs of Sinter Machine as claimed in
claiml, wherein the DCDAVs are grouped / clubbed in different groups according
to material accumulation rate in the respective hoppers and the operating
sequence of the independent group(s) are configured, depending on the
continuously variable parameters, such as, health condition of the pallets, quality
of sinter-mix material & return sinter, dust accumulation rate, etc.
9. An improved sealing system of dust-legs of Sinter Machine as claimed in
claiml, wherein the material of construction for valve-seat of DCDAV is "Ni-hard
material" (IS-4771-1985) for better and improved life.
10. An improved sealing system of dust-legs of Sinter Machine, substantially
as herein described with particular reference to accompanying drawings.

The present invention relates to an improved sealing system of dust-legs of
Sinter Machine comprising of: at least one Double Cone Double Acting Valve
(DCDAV); at least one programmable logic controller (PLC) configured for the
control for the said DCDAV; and the said DCDAV's are driven through roller &
cam-lever in operation by a geared motor.