CLIAMS:WE CLAIM:
1. A method for controlling fuel flow rate and energy in reheating furnaces selectively based on slab dimensions, product details and discharge temperature matrixes comprising:
i) subjecting slab to reheating in reheating furnace with charging temperature;
ii) obtaining slab dimensions, discharge temperature matrix and product details ;
iii) discharging slab from the reheating furnace at discharging temperature;
iv)generating subsequent roughing mill exit temperature at multiple locations alongwith required correction factor;
v)controlling fuel flow selectively based on slab dimensions, discharge temperature matrix, product details , model value, correction factor from roughing mill exit temperature matrix.

2. A method as claimed in claim 1 wherein the thickness varies from 1.6 mm to 25.4mm and width varies from 900 mm to 2150mm.

3. A method as claimed in anyone of claims 1 or 2 comprising :
measuring the exit slab temperature from furnace and roughing mill exit temperature from rougher using a pyrometer for wide range of product thickness ranging from 1.6 mm to 25.4 mm and width ranging from 900mm to 2150mm and grade;
developing slab drop-out temperature matrix based on said slab dimensions alongwith roughing mill exit temperature matrix for different product dimensions.

4. A method as claimed in anyone of claims 1 to 3 wherein said product dimensions and roughing mill exit temperature matrix is developed for product head end, middle and tails end.

5. A method as claimed in anyone of claims 1 to 4 comprising development of said correction factor involving roughing mill exit temperature matrix wherein said
correction factor = [(Average rough mill exit temperature)-(Derived look up roughing mill strip exit temperature value0]/( Pacing X number of slabs in a furnace).

6. A method as claimed in anyone of claims 1 to 5 wherein said correction factor is used to generate feedback to the pre-heating and heating zones of the reheating furnace and roughing mill exit tail-end and head-end correction factor generates feedback to the furnace soaking zone.
7. A method as claimed in anyone of claims 1 to 6 wherein said product details obtained include thickness and properties.

8. A method as claimed in anyone of claims 1 to 7 wherein said slab leaving furnace alongwith discharge temperature is at 12000C.

9. A system for controlling fuel flow rate and energy in reheating furnaces selectively based on slab dimensions, product details and discharge temperature matrixes involving the method as claimed in anyone of claims 1 to 8 comprising:
reheating furnaces;
means for air and fuel flow;
a fuel flow controller operatively connected to a roughing means and finishing mill operation controller;
controller for controlling said air and fuel flow in said reheating furnace based on inputs received from said roughing means and finishing mill operation controller.

10. A system as claimed in claim 9 comprising:
reheating furnaces;
descaler to remove scale ;
said roughing mill for breaking cast structure operatively connected to roughing mill controller;
means for measuring the exit temperature of the bars after roughing operation;
finishing mill for achieving final product dimensions operatively connected to finishing mill controller;
a controller unit for controlling said roughing means controller and said finishing mill controller;
said controller unit operatively connected to controller for controlling said air and fuel flow in said reheating furnace based on inputs received from said controller unit’
a computer means for overseeing the operating parameters and trends.

Dated this the 27th day of November, 2013
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)
,TagSPECI:FIELD OF THE INVENTION

The present invention relates to a method and system for fuel and energy saving in reheating furnaces in hot strip mills involving controlled energy efficient reheating of slabs. More particularly, the present invention is directed to a method and system for controlling fuel flow rate and energy in reheating furnaces based on slab dimensions, product details and discharge temperature matrixes so as to reheat the slabs to a desired temperature in reheat furnace avoiding overheating for desired mechanical properties in the end product while reducing fuel consumption per ton of slabs reheated, in a reliable manner improving furnace life and productivity.

BACKGROUND ART

It is well known that in the steel plants Reheating furnace(RHF) is used to reheat cast slabs before rolling whose main function is to reheat the slabs to a desired temperature for achieving better mechanical property in product. Generally the slabs of width(900 mm to 2150 mm) and thickness 220 mm were charged into the reheating furnace(RHF). To keep reheating furnace exit temperature (1200±10)0C the fuel consumption was observed 322MCal/MT. It has resulted in less utilization and productivity of reheating furnace as well as mill.

Present fuel flow rate control system for all slab dimensions and discharge slab temperature is based on single value from furnace model and single value from roughing mill exit temperatures. It has resulted in over heating of critical grades and narrow width of slab resulted into poor product quality and increased miss rolls. Higher fuel consumption in the furnace results into deterioration of furnace healthiness in terms of lesser utilization and productivity.

There has been thus a need in the related art of reheating of slabs in reheating furnace to developing a method and system for controlled heating of slabs in reheating furnaces which would control fuel flow as per the specific slab dimensions in terms of width and thickness , product specification(thickness, properties) and discharge temperature matrix, so that fuel consumption is optimized while ensuring improved quality of end products and enhanced furnace utilization/productivity.

OBJECTS OF THE INVENTION

It is thus the basic object of the present invention to provide for a method for controlling fuel flow rate and energy in reheating furnaces based on slab dimensions, product details and discharge temperature matrices and a system to implement such method.

A further object of the present invention is directed to a system and method for controlling fuel flow rate and energy in reheating furnaces which would economize fuel consumption and enhance furnace productivity.

A still further object of the present invention is directed to a system and method for controlling fuel flow rate and energy in reheating furnaces wherein requirement of heat energy input per ton of slabs extracted from furnace could be substantially reduced.

A still further object of the present invention is directed to a system and method for controlling fuel flow rate and energy in reheating furnaces wherein slabs are reheated based on slab dimensions and grade so as to ensure improved product quality avoiding overheating and miss rolls.

A still further object of the present invention is directed to a system and method for controlling fuel flow rate and energy in reheating furnaces wherein to implement said control slab temperatures are precisely measured at furnace exit and rougher exit for different product dimensions and grade using pyrometer.

A still further object of the present invention is directed to a system and method for controlling fuel flow rate and energy in reheating furnaces wherein separate controller is used to control the operation of roughing mill, operation of finishing mill and air and fuel flow in reheat furnace.

A still further object of the present invention is directed to a method for controlling fuel flow rate and energy in reheating furnaces wherein desired control could be achieved by involving a correction factor based on inputs from roughing mill exit temperature matrix and which could enable generation of feedback to the pre-heating and heating zones of the reheating furnace and roughing mill exit tail-end and enable generation of head-end correction factor.
SUMMARY OF THE INVENTION

Thus according to the basic aspect of the present invention there is provided a method for controlling fuel flow rate and energy in reheating furnaces selectively based on slab dimensions, product details and discharge temperature matrixes comprising:

i) subjecting slab to reheating in reheating furnace with charging temperature;
ii) obtaining slab dimensions, discharge temperature matrix and product details ;
iii) discharging slab from the reheating furnace at discharging temperature;
iv)generating subsequent roughing mill exit temperature at multiple locations alongwith required correction factor;
v)controlling fuel flow selectively based on slab dimensions, discharge temperature matrix, product details, model value, correction factor from roughing mill exit temperature matrix.

A further aspect of the present invention is directed to said method wherein the thickness varies from 1.6 mm to 25.4mm and width varies from 900mm to 2150mm.

A still further aspect of the present invention is directed to said method which comprises:
measuring the exit slab temperature from furnace and roughing mill exit temperature from rougher using a pyrometer for wide range of thickness ranging from 1.6 mm to 25.4 mm and width ranging from 900mm to 2150mm and grade;
developing slab drop-out temperature matrix based on said slab dimensions alongwith roughing mill exit temperature matrix for different product dimensions.

According to yet another aspect of the present invention directed to said method wherein said product dimensions and roughing mill exit temperature matrix is developed for product head end, middle and tails end.

Importantly also said method comprises development of said correction factor involving roughing mill exit temperature matrix wherein said
correction factor = [(Average rough mill exit temperature)-(Derived look up roughing mill strip exit temperature value)]/( Pacing X number of slabs in a furnace).

A further aspect of the present invention is directed to said method wherein said correction factor is used to generate feedback to the pre-heating and heating zones of the reheating furnace and roughing mill exit tail-end and head-end correction factor generates feedback to the furnace soaking zone.

Also in said method, said product details obtained include thickness and properties and said slab leaving furnace alongwith discharge temperature is at set temperature(1200oC).

A further aspect of the present invention is directed to a system for controlling fuel flow rate and energy in reheating furnaces selectively based on slab dimensions, product details and discharge temperature matrixes involving the method as described above comprising:
reheating furnaces;
means for air and fuel flow;
a fuel flow controller operatively connected to a roughing means and finishing mill operation controller;
controller for controlling said air and fuel flow in said reheating furnace based on inputs received from said roughing means and finishing mill operation controller.

Yet another aspect of the present invention is directed to said system comprising:
reheating furnaces;
descaler to remove scale ;
said roughing mill for breaking cast structure operatively connected to roughing mill controller;
means for measuring the exit temperature of the bars after roughing operation;
finishing mill for achieving final product dimensions operatively connected to finishing mill controller;
a controller unit for controlling said roughing means controller and said finishing mill controller;
said controller unit operatively connected to controller for controlling said air and fuel flow in said reheating furnace based on inputs received from said controller unit;
a computer means for overseeing the operating parameters and trends.

The objects and advantages of the present invention are described hereunder in greater details with reference to the following accompanying non limiting illustrative drawings.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:

Figure 1: is the flow chart showing the steps involved in the conventional method of fuel flow control in reheating furnace with higher fuel and energy consumption per ton of slab processed.

Figure 2: is the flow chart showing the steps involved in the method of fuel flow control and energy saving in reheat furnace according to the present invention with substantial saving in fuel flow rate and energy consumption per ton of slab processed.

Figure 3: is the schematic view of the system for implementing the method for controlling fuel flow rate and energy in reheating furnaces based on slab dimensions, product details and discharge temperature matrices according to the present invention showing the different components involved.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS:

The present invention is directed to a method for controlling fuel flow rate and energy in reheating furnaces based on slab dimensions, product details and discharge temperature matrices and a system to implement such method to economize fuel consumption and enhance furnace life and improved productivity.

The conventional fuel flow rate control system is common for all slab dimensions and discharge slab temperature based on single value from furnace model and single value from roughing mill exit temperatures. It has resulted in over heating of critical grades and narrow width of slab resulted into poor product quality and increased miss rolls. Higher fuel consumption in the furnace results into deterioration of furnace healthiness in terms of lesser utilization and productivity. The steps of conventional system for fuel flow control in reheat furnace is shown in the flow chart of Figure 1.

An improved fuel flow control and energy saving has been proposed by way of the present invention to overcome the limitations of the prior art. The details of the fuel flow control steps according to the present invention has been shown in the accompanying Figure 2. As the rolling schedule is based on the wide range of thickness(1.6mm to 25.4 mm), width(900mm to 2150 mm) and grade, which required different slab drop-out temperature for rolling. The exit slab temperature from furnace was noted by using pyrometer and same slab temperature was noted by using pyrometer after rougher exit for wide range of thickness(1.6mm to 25.4mm), width(900mm to 2150mm) and grade. Slab drop-out temperature matrix has been developed based on slab dimensions and similarly roughing mill exit temperature matrix has been developed for different product dimensions. Product dimension and roughing mill exit temperature matrix has been developed for product head end, middle and tails end. Development of correction factor using roughing mill exit temperature(roughing mill exit) matrix. Correction factor=[(Average rough mill exit temperature)-(Derived look up roughing mill strip exit temperature value)]/(Pacing x number of Slabs in a furnace). Correction factor gives feedback to the pre-heating and heating zone of the reheating furnace and roughing mill exit tail-end and head-end correction factor gives feedback to the furnace soaking zone. Based on the correction factor, slab dimension and temperature matrix the furnace fuel flow rate has been controlled.

Comparison of the gas flow and heat energy in put per ton of slab processed as per the present method over the conventional reheating in reheat furnace are shown in Table-1 below. It can be seen from the table that the Heat energy per MT(Mcal/MT) has been reduced from conventional 322MCal/MT to 269MCal/MT (10-15%) by the application of the fuel flow control and energy saving method according to the present invention. Nearly 10-15% energy is saved per ton.
Table-1:
Conventional fuel flow control
Month Total gas consumption(Nm3) Slab extracted from Furnace, Tonnage Heat energy per MT(Mcal/MT)
Oct 53040351 311126 323
Nov 45820917 258925 330
Dec 47724626 271352 335
Jan 54512817 325187 320
Feb 36734224 236925 302
Total 237832935 1403515 322

Fuel flow control according to the present invention
Month Total gas consumption(Nm3) Slab extracted from Furnace, Tonnage Heat energy per MT(Mcal/MT)
Mar 44307404 311501 268
Apr 34306426 294989 256
May 33927154 256518 271
Jun 43103265 315641 266
Jul 41716170 293029 283
Total 197360419 1471678 269

Accompanying Figure 3 shows the schematic view of the system for implementing the method for controlling fuel flow rate and energy in reheating furnaces based on slab dimensions, product details and discharge temperature matrices according to the present invention showing the different stages/components involved. It can be seen in figure 3 that slabs are reheated in reheating furnace 1,2 & 3. Slabs are taken out after achieving the desire slab drop-out temperature and passed through descaler(4) to remove scale. After descaler slabs are passed through roughing mill(5) for breaking the cast structure. The exit temperature measures of the transfer bar after roughing operation (5). Transfer bar then processed through finishing mill for achieving final product dimensions(6). Roughing mill operation and control done through controller(8) and finishing mill operation and control done through controller (7). Both are manually controlled through controller(9). Reheating furnace(1,2&3) air and fuel flow is controlled through controller(11) by taking information from controller(9). Desktop(10) is used to see the operation parameter trends.

It is thus possible by way of the present invention to providing a method for controlling fuel flow rate and energy in reheating furnaces in hot strip mill based on slab dimensions, product details and discharge temperature matrices and a system to implement such method to economize fuel consumption and enhance furnace life with improved productivity avoiding overheating and miss rolls ensuring desired quality of end products.