FIELD OF THE INVENTION
The present invention relates to a system for automatic temperature control during
shutdown periods for desired reduced heating of the Pusher Type Reheating Furnace. More
particularly, the present invention relates to automation system involving expert system
based programmed delay strategy commensurate with the method for desired
temperature control for reduced heating through different zones of the reheat furnace
during a block/shutdown period. The invention also relates to a PLC program based control
system through PID control loop, which implement the actual zonal temperatures as
determined by the expert system. Thus the present invention involves two level
automation comprising automation determine the set temperatures of delay strategy for
the reheat furnace and automation for implementing the actual control on temperatures in
different zones of the pusher Type Reheat Furnace. Importantly, the present invention is
directed to saving the consumption of energy/fuel gas by reduced heating of the furnace
during shutdown or repair for long hours and favoring restarting furnace for resuming
operation without delay. The system and the method of the present invention for
automatic control of temperatures in different zones of the Pusher Type Reheat Furnace is
thus adapted for wide industrial application in the hot rolling mills in large steel plants with
significant economic advantage, enhanced furnace life and saving on man-hours.
BACKGROUND ART
It is well known in the conventional practice of temperature control of different Zonal
temperatures of pusher type Reheating Furnace during shutdown/repair period is achieved
by manually lowering of individual zonal set temperature as per the decision of furnace
operator. Such manual control does not ensure reliable performance and does not co-
relate to an established scientific method but heavily depends on one person's decision
guided by rule of thumb. Such decisions are thus most often not optimum. The other
known practice in the related art include manual closing of all the valves partially or
completely in order to reduce the furnace temperature and then to open them at the end
of shut-down period to restore operation.

The existing manual control system for zonal temperatures of reheat furnace is thus not
optimum on one hand and also subjected to high degree of unreliability and uncertainty in
relation to stability of temperature or minimizing time cycle for restoration of operation
after shutdown. The manual system is also labor intensive as operators have to manually
change the individual zonal set-points at the beginning and end of furnace shut-down.
Further, lowering or increasing the furnace temperature suddenly, as is done by way of
manual control, the said sharp temperature gradient impart thermal shocks to the
furnaces. These thermal shocks are very much detrimental for the life of furnace.
It has been also experienced in the related art that during shutdown/repair days or other
mill shutdowns, slab delivery from the furnace is stopped and there is no actual
requirement of maintaining the normal temperature inside the Reheating Furnace. There
has been thus a persistent need in the art to developing a programmable schedule for
heating/ temperature control system in order to conserve the heat/energy and ensure
optimum use of fuel gas for zonal heating of reheat furnace as well as to avoid abrupt
thermal shocks to the furnace and thereby to achieve economy in operation, which is very
much detrimental to its life. In view of above, the present invention provide means for an
expert system based delay strategy for zonal temperature control of reheat furnace in
slab/plate mill, which gradually lowers the zonal set temperatures, holds that temperature
for predefined time duration and again gradually restores the original temperature. The
invention is thus capable of ensuring safe and economic furnace operation, saving
consumption of fuel gases, optimum control by two level automation involving expert
system and PLC/PID control and an appropriate communicating interface so as to attain
high level of reliability, enhanced furnace life with reduced manpower.
OBJECTS OF THE INVENTION
It is thus basic object of the present invention to provide a system for automatic
temperature control for reduced heating of the Pusher Type Reheating Furnace during
shutdown periods/repair and a method for such controlled heating using said system,
wherein said automation system is based on an expert system based preprogrammed
heating schedule comprising selectively configured Delay Strategy commensurate with the

desired temperature control for reduced heating through different zones of the reheat
furnace during a block/shutdown period.
Another object of the present invention is directed to a system of controlled heating of
reheat furnace during shutdown/repair and a method for carrying out said controlled
heating comprising development of Expert System based automation system for
determination of delay schedule for a given shut-down period.
A further object of the present invention is directed to a system of delay strategy
implementation for controlled/reduced heating schedule of furnace and said system for
implementing the method comprising developing a control system for controlling actual
furnace temperature through PLC program/PID loop based control following selectively
programmed delay schedule.
A still further object of the present invention is directed to a expert system based delay
strategy for reduced heating of the reheating furnace during shut-down period involving
automatically lowering all the actual zonal temperatures in a programmed fashion in order
to conserve the heating gas by controlling air/gas ratio.
A still further object of the present invention is directed to a system for reduced/controlled
heating of the reheating furnace wherein the method of gradual cooling/heating and
soaking involving said expert system directed to avoid abrupt thermal shocks to the
furnace and thus enhancing reliability of operation and enhancing life of the furnace.
A still further object of the present invention is directed to a system for reduced/controlled
heating of the reheating furnace involving said expert system based delay strategy to
gradually lower the zonal set temperatures, holding that temperature for desired time
duration and again gradually restoring the original temperature so that at the end of shut-
down furnace is ready for delivering the slabs for rolling.
A still further object of the present invention is directed to a system for reduced/controlled
heating schedule of the reheating furnace involving said expert system based delay
strategy the operator has been given a provision of enabling or disabling any zone for
implementation of scheduled delay strategy.

A still further object of the present invention is directed to a system for reduced/controlled
heating schedule of the reheating furnace involving said expert system based delay
strategy implementation achieved on receiving confirmation of the furnace operator via the
HMI screen based on data downloaded from expert system to level I automation PLC
program that starts reducing the actual zonal temperatures according to the set
temperatures based on level II program.
A still further object of the present invention is directed to a system for automatic
reduced/controlled heating schedule of the reheating furnace wherein the implementation
of the scheduled delay strategy enable saving energy and costs, reduce manpower
requirements and ensure reliable and longer furnace availability improving productivity.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is thus directed to developing a system of delay
strategy implementation of the pusher type reheating furnaces for reduced heating of
furnaces during shut-down period comprising:
means provided to furnace operator for selecting the furnace number and duration of shut
down;
means adapted to determine the appropriate values of 'TD' representing, the final drop in
zonal set temperature which is to be maintained for time 'thold', 'tlower' representing time in
which temperature will be dropped and 'theat' representing time by which original
temperature will be restored for all the zones;
means for obtaining confirmation from the operator downloading the values to a PLC based
system adapted for implementation of the said delay schedule.
A further aspect of the present invention is directed to said system of delay strategy
implementation of the pusher type reheating furnaces for reduced heating during shut-
down period wherein said system is adapted for automatically lowering all the zonal
temperatures in a programmed fashion in order to conserve the heating gas as well as to
avoid abrupt thermal shocks to the furnace.

Another aspect of the present invention is directed to said system of delay strategy
implementation for reduced heating of reheat furnace is adapted to gradually lower the
zonal set temperatures, holds that temperature for a time and again gradually restores the
original temperature, so that at the end of shut-down furnace is ready for delivering the
slabs for rolling.
A further aspect of said system of the present invention wherein the temperature lowering
or heating is done in steps and not continuously to give sufficient settling time to the
actual process variable i.e. zonal temperature as measured preferably by two S-type
thermocouples installed at every zone, to attain the new set temperature, the time At is
selected preferably as 5 minutes.
Another aspect of the present invention is directed to said system of delay strategy
implementation for reduced heating of reheat furnace which is adapted such that the
values of 'TD', 'tlower' , 'thold' and 'theat' depend on total duration of shutdown and zone
number in Reheating Furnace.
According to yet another aspect of the present invention directed to a system for delay
strategy implementation in different zones of the reheat furnace comprising means for
selectively enabling or disabling any zone for implementation of delay strategy.
A still further aspect of the present invention is directed to a system of delay strategy
implementation in the reheat furnace for reduced heating during shut-down period wherein
based on data downloaded, the PLC is adapted to start implementing the delay schedule
and start reducing the zonal set temperatures, it reduces the temperature by 'TD' °C in
time 'tlower' and holds the set temperature at this minimum value for time 'thold' and
gradually increases the temperature and restores the original value in time 'theat'.
A still further aspect of the present invention is directed to a system of delay strategy
implementation in the reheat furnace for reduced heating during shut-down wherein the
PLC is adapted for gas / air ratio control of individual furnace zones through PID control
loops such that as the set temperature changes as per delay schedule, the PID control

blocks changes the zonal gas / air flow ratio to achieve the desired actual zonal
temperature.
A still further aspect of the present invention is directed to a system of delay strategy
implementation in the reheat furnace for reduced heating during shut-down wherein the
communication between Delay Program and PLC Program is accomplished through an OPC
(OLE for Process Control) based software.
The present invention and its objects and advantages are described in greater details with
reference to the accompanying non limiting figures and embodiment.
BRIEF DESCRIPTON OF THE ACCOMPANYING FIGURES
Figure 1: is the schematic illustration of the cross-sectional view of the Pusher Type
Reheating Furnace showing its different zonal heating sections, air/gas flow directions and
different control points for controlling air/gas ratio for desired heating/temperature control.
Figure 2: is the illustration of the graphical representation of the typical trend for reduced
furnace heating schedule delineating the implementation of delay strategy involving expert
system/PLC control system according to the present invention.
Figure 3: is the illustration of the interfacing HMI screen for the furnace operator for
monitoring and confirming implementation of control of zonal temperature according to the
programmed set temperatures of heating schedule involving with specified delay strategy.
Figure 4: is the illustration of the graphical presentation of the result of delay strategy
implementation during a 60 minute plant shut-down for actual trend of top heating zone
temperature vis-a-vis programmed delay schedule as of the invention.
Figure 5: is the illustration of the graphical presentation of the result of delay strategy
implementation during a 60 minute plant shut-down depicting the trend for soaking zone
temperature, vis-a-vis programmed delay schedule as of the invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING FIGURES
As already described, the present invention is directed to a method of reduced heating of
the reheating furnace in hot rolling mills during shut down or repair according to an
automatic heating schedule with preprogrammed delay strategy whereby the cooling and
then soaking and further heating to operating temperature of the heating zones of the
reheat furnace is achieved thereby saving waste of energy/fuel and enhance furnace life
through safe and reliable operation of the furnace. The automatic control of the different
zonal temperatures according to the programmed heating schedule involving selective
delay strategy is carried out in two levels-viz. the level II automation through an Expert
System for the programmable heating schedule developed using higher level language
(VC++) while the implementation of said schedule including the delay strategy is carried
out at the level I automation through PLC control and PID controller to control the air/gas
ratio at different zones of the furnace and thus controlling the respective temperatures.
Advantageously also, a Human machine Interface (HMI) further provide flexibility in
operation whereby the operator decides and monitor the implementation of the
programmed heating schedule involving the delay strategy in respect of each of the
different zones of the reheating furnace. The bidirectional data communication between
expert system and Level - I PLC has been achieved through an OPC(OLE for Process
Control) client software developed in VC++ and is an integral part of expert system.
According to an preferred embodiment of the present invention directed to an expert
system based delay strategy for reheating furnaces during downtime essentially comprise
an expert system implemented in a PC platform interfaced with an appropriate software
written in VC++ (Microsoft Visual Studio.Net). The PLC based control system is envisaged
through a Rockwell Automation make Control Logix processor. The bidirectional data
communication between expert system and Level - 1 PLC has been achieved through an
OPC (OLE for Process Control) client software developed in VC++ and is an integral part of
expert system. Rockwell Automation make RS-Linx has been used as OPC server. A
furnace operator selects the furnace number and duration of shut-down. Based on this, the
expert system determines the appropriate values of TD', 'tlower', 'thold' and 'theat' for all the
zones. On confirmation from furnace operator, the expert system downloads the values to
PLC, which subsequently takes care of implementation of delay schedule. The particular
manner of implementation of the different elements of the system for executing the

method of reduced optimal heating cycle for the reheat furnace is described in details with
reference to the accompanying drawings.
Reference is first invited to the accompanying Figure 1 that schematically illustrates a
cross sectional view of the different zones of the pusher type Reheating Furnace that plays
a crucial role in hot rolling mills, in which semi-finished steel in the form of blooms, billets
or slabs are heated to an elevated temperature for improving the steel plastic properties,
which make it susceptible for rolling. The basic requirement of Reheating Furnace is to
heat the metal stock up-to desired level of temperature within permissible accuracy.
The present invention is implemented in Double row, Five Zone Pusher Type Reheating
Furnaces of Plate Mill. The cross sectional view of this type of furnace as illustrated in the
accompanying Figure 1 shows this different zones and the respective supply points for
control of air/gas ratio according to the programmed heating schedule. The heating in five
zone furnaces are divided in - Preheating zone -Top and Bottom, Heating Zone -Top &
Bottom and Soaking Zone. The slabs in plate mill are delivered from continuous caster.
The length range of slabs are around 5.6 to 10.2 m. These slabs are further cut to smaller
plates by flame cutting machines. So long the plates are in cold condition, they cannot be
rolled. In order to subject them to rolling, plates are heated in Reheating Furnaces. Mixed
gas such as a mixture of blast furnace gas and coke oven gas having a calorific value
around 2500 KCal/m3 is used as fuel gas. Air for combustion is supplied through natural
draft. Air before reaching burners are preheated in multi-cellular cross parallel flow type
metallic recuperator. The programmed heating schedule provides the basis for control of
the heat generation in respective zones of the Reheating furnace by controlling the air/gas
ratio burnt through the burners in the respective sections/zones of the furnace such that
slow cooling to a predefined temperature is reached within over predefined time
interval/delay, this temperature is on hold for certain time duration and then again the
slow heating of the furnace to predefined temperature is reached through incremental
steps such that thermal shock on furnace is avoided and its life is enhanced.
During normal operation, the plates are pushed one by one in to the furnace from the
charging side. The plates moves on after another on water cooled skid pipes inside the
furnace. The skid pipes are cooled by evaporating cooling system. The plates on the
delivery side are pushed to pre-determined position by pusher and then it is extracted by
plate extractors. The plate extractors places the plates on roll table from where it is send

for roughing / rolling. The burnt up waste gases leave the furnace through an exhaust pipe
at the extractor side.
A significant amount of gas is wasted during shutdown periods in these furnaces and there
is an ample scope of saving this scarce source of energy during these periods. The
invention relates to an expert system which determines a programmed scheduling of
furnace temperature during shutdown / repair period. It also relates to a PLC based control
system, which actually controls the zonal temperatures as determined by expert system.
Reference is now invited to the accompanying Figure 2, that shows graphically a typical
trend delineating the implementation of delay strategy according to the Expert system
based programmed heating schedule of the invention.
During the time of shutdown/repair, slab delivery from the furnace is stopped and there is
no actual requirement of maintaining the normal temperature inside the Reheating
Furnace. This necessitates automatic lowering of all the zonal temperatures in a
programmed fashion in order to conserve the heating gas as well as to avoid abrupt
thermal shocks to the furnace that deteriorate the life of the furnace. In view of the above,
an expert system based delay strategy has been configured, that enables gradually
lowering the zonal set temperatures, holds that temperature for a time and again
gradually restoring the original temperature, so that at the end of shut-down furnace is
ready for delivering the slabs for rolling.
It is clearly apparent from the accompanying Figure 2, that the programmed heating
schedule with built in delay strategy based on the expert system of the invention involves
very small increment or decrement steps of heating and/or cooling through very small
steps and over small duration prefixed through the Level II automation and the Level I
automation and control derived there from through PLC/ PID based controller of valve
operation/flow control to burners to thereby controlling the desired air/gas ratio at
respective burners and thus providing automatic control of respective zonal temperatures
maintaining the programmed heating schedule including the delay strategy involving
selective time components at each stage of cooling, soaking and heating.
It may be noted from said Figure 2 that TD' represents, the final drop in zonal set
temperature which is to be maintained for time 'thold' Similarly 'tlower' represents time in
which temperature will be dropped while 'theat' represents time by which original

temperature will be restored. The temperature lowering or heating is carried out in small
incremental/decrement steps and is not continuous. This procedure provides sufficient
settling time for the actual process variables. The zonal temperature are measured by two
S-type thermocouples installed at every zone, to attain the new set temperature. The time
At is selected as 5 minutes. It is found that actual zonal temperature smoothly follows the
delay cycle with this value of Δt.
The expert system has been implemented through a computer program developed in
VC++. The values of 'TD', 'tlower', 'thold' and 'theat' depends on total duration of shutdown and
zone number in Reheating Furnace and is determined by expert system.
Advantageously, the operator has been provided with the option for enabling or disabling
any zone for implementation of delay strategy. The system provides for a Human Machine
Interface (HMI) Screen as illustrated in the accompanying Figure 3, On confirmation from
furnace operator, the program downloads the values to the Level-1 PLC program. Based
on data downloaded from expert system, the PLC program starts implementing the delay
schedule and starts reducing the zonal set temperatures. It reduces the temperature by
'TD' °C in time 'tlower'. The program holds the set temperature at this minimum value for
time 'thold' and gradually increases the temperature and restores the original value in time
'theat' The HMI thus interfaces the furnace operator to allow/disallow or induce minor
adjustment in the programmed parameters such as the delay time, starting temperature,
holding temperature, temperature drop for individual each Furnace and for each of the
preheating, heating and soaking zone at the implementation stage based on field
data/assessment of exact requirements depending on breakdown/repair time that is
necessitating suspending furnace charging operation.
The same PLC program is also responsible for gas / air ratio control of individual furnace
zones through PID control loops. As the set temperature changes as per delay schedule,
the PID control blocks changes the zonal gas / air flow ratio to achieve the desired actual
zonal temperature.
Importantly also, the communication between Delay Program and PLC Program is
accomplished through an OPC (OLE for Process Control) based client software.
The plotting of the set temperatures as determined by the heating schedule involving the
delay strategy vs the actual zonal temperatures on a time scale has been illustrated in the

accompanying Figure 4 corresponding to air/gas ratio maintained to communicate with
the set temperatures. The result of delay strategy implementation during a 60 minute
plant shut-down is shown in accompanying Figure 4 representing the trend of top
heating zone temperature set points developed through the programmed heating
schedule. Likewise, the accompanying Figure 5 depicts trend for soaking zone
temperature. Curves marked (A) in these trend plots indicate the zonal set temperature as
programmed through delay strategy while curves marked (B) represents the actual zonal
temperature of the furnace. It is evident from Figure 4 and Figure 5 that actual zonal
temperature tracks the set temperature within a close variability range of ± 10 °C .
It is thus possible by way of the present invention to develop an effective and efficient
method for automation in establishing programmed heating schedule for reduced heating
for pusher type reheating furnace in hot rolling mill during furnace breakdown/repair,
involving selective delay strategy wherein selective rate of cooling to a temperature,
soaking at a predefined reduced temperature and then heating in very small incremental
steps to the desired furnace operating temperature so that detrimental thermal shock on
furnace is avoided, scarce gaseous fuel is saved, energy expenditure is economized and
manpower is rationalized. The inventive features of the invention thus ensure
determination of programmed schedule for reduction in Reheating Furnace temperature for
a given shut-down period by expert system. The present invention further flexibly
incorporates modification of furnace zonal set temperature and gas flow rate in gas/air
ratio PID control loops as per aforesaid schedule by Level I PLC based control system.
More advantageously, said level II and level I automation are communicated for optimal
performance using special OPC (OLE for Process Control) based driver software and
provides for actual operational flexibility wherein data entry and monitoring through a user
friendly Human Machine interface (HMI) console is effected as needed. The method of the
invention for reduced heating of reheating furnaces in hot rolling mills during
shutdown/repair is thus adapted to achieve economy in operation, enhance furnace life,
reduce down time costs and resultantly improve productivity in slab/plate rolling mills at
reduced cost of operations and hence favoring wide industrial application in large steel
plants/rolling mills.

WE CLAIM:
1. A system of delay strategy implementation of the pusher type reheating furnaces for
reduced heating of furnaces during shut-down period comprising:
means provided to furnace operator for selecting the furnace number and duration of shut
down;
means adapted to determine the appropriate values of 'TD' representing, the final drop in
zonal set temperature which is to be maintained for time 'thold', 'tlower' representing time in
which temperature will be dropped and 'theat' representing time by which original
temperature will be restored for all the zones;
means for obtaining confirmation from the operator downloading the values to a PLC based
system adapted for implementation of the said delay schedule.
2. A system as claimed in claim 1 adapted for automatically lowering all the zonal
temperatures in a programmed fashion in order to conserve the heating gas as well as to
avoid abrupt thermal shocks to the furnace.
3. A system as claimed in anyone of claims 1 or 2 which is adapted to gradually lower the
zonal set temperatures, holds that temperature for a time and again gradually restores the
original temperature, so that at the end of shut-down furnace is ready for delivering the
slabs for rolling.
4. A system as claimed in anyone of claims 1 to 3 wherein the temperature lowering or
heating is done in steps and not continuously to give sufficient settling time to the actual

process variable i.e. zonal temperature as measured preferably by two S-type
thermocouples installed at every zone, to attain the new set temperature, the time At is
selected preferably as 5 minutes.
5. A system as claimed in anyone of claims 1 to 4 which is adapted such that the values of
'TD', 'tlower' , 'thold' and 'theat' depend on total duration of shutdown and zone number in
Reheating Furnace.
6. A system as claimed in anyone of claims 1 to 5 comprising means for selectively
enabling or disabling any zone for implementation of delay strategy.
7. A system as claimed in anyone of claims 1 to 6 wherein based on data downloaded, the
PLC is adapted to start implementing the delay schedule and start reducing the zonal set
temperatures, it reduces the temperature by 'TD' °C in time 'tlower' and holds the set
temperature at this minimum value for time 'thold' and gradually increases the temperature
and restores the original value in time 'theat'.
8. A system as claimed in anyone of claims 1 to 7 wherein the PLC is adapted for gas / air
ratio control of individual furnace zones through PID control loops such that as the set
temperature changes as per delay schedule, the PID control blocks changes the zonal gas
/ air flow ratio to achieve the desired actual zonal temperature.
9. A system as claimed in anyone of claims 1 to 8 wherein the communication between
Delay Program and PLC Program is accomplished through an OPC (OLE for Process
Control) based software.

10. A system of delay strategy implementation of the pusher type reheating furnaces for
reduced heating of furnaces during shut-down period substantially as herein described and
illustrated with reference to the accompanying figures.

A system for automatic temperature control of the Pusher Type Reheating Furnace for
desired reduced heating during shut-down. The invention particularly involve an Expert
System based programmed Delay Strategy for reduced heating through different zones of
the reheat furnace during a block/shutdown period to thereby saving on fuel consumption
and resulting in economy in operation. Thus the present invention involves two level
automation comprising control on set temperatures during shutdown/repair for the delay
strategy for heating schedule achieved through the automation in stages for implementing
the actual temperatures in different zones of the pusher Type Reheat Furnace through PLC
program and PID control loop based on operative Gas/Air ratio control commensurate with
the heating schedule/set temperature built in the delay strategy. The communication
between Delay Program and PLC Program is accomplished through an OPC (OLE for
Process Control) based client software.