IMPROVED THERMAL EFFICIENCY OF SOLID HEARTH REHEATING FURNACE
BY INCORPORATING DIFFERENTIAL GASEOUS FUEL FLOW
FIELD OF INVENTION
This invention relates to a solid hearth reheating furnace with improved efficiency by
maintaining differential gaseous fuel flow and further to a method of controlling a
batch type reheating furnace for heating blooms or the like. More particularly the
present invention deals with an improved arrangement and control of the gas flow in
the reheating furnaces for achieving improved efficiency and better control of the
blooms heating in the furnace.
BACKGROUND ART
Reheating furnace is the heart of any hot rolling mills in Iron and Steel industries.
Semi finished steel products like blooms, billets or slabs are heated in reheating
furnaces for improving the plastic properties of steel. It is essential for plastic working
of the steel product in rolling mills. For smooth operation of the rolling mills, the
reheating furnace plays a very vital role. Their design, features and operating
parameters determine the quality of final rolled products, material yield, energy
consumption, pollution and finally the cost of the products. All efforts are made to
bring improvement in the performance of reheating furnace aiming to achieve
increase in productivity, quality steel products, optimum energy consumption and the
life of furnace elements. For the production of quality rolled products, quality heating
is a pre-requisite.
There are different types of reheating furnaces such as batch type furnace,
continuous pusher type furnace, walking beam furnace, walking hearth furnace, solid
hearth furnace, etc. which are in operation in different Iron and Steel industries. Solid
hearth has been provided in the existing old reheating furnace for supporting the
charge. Billets as charge are placed on the solid hearth of the existing reheating
furnace for heating. As given as prior art and shown in Fig 1, the existing reheating
furnace is equipped with two regenerators. These two regenerators are installed, one
at each end of the furnace. Each regenerator is divided into two parts and connected

to1st chimney through two separate flue tracks. Front divided in two parts and
connected to 1st chimney through two separate flue tracks. Front part of regenerator
is connected to burner # 1, 2 & 3 (say front burners) through flue track called as near
end (NE). The back part of regenerator is connected to the burner # 4, 5 & 6 (say
back burners) through flue track called as far end (FE). There are two dampers
provided in each flue track line to control the air distribution between front and back
burners. There are two reversals valves for changing the firing sequence of the
furnace. Reversal time is about 10 minutes during the normal operation of the
furnace as well as mills and during rolling delay; it is about 5 minutes to avoid over
heating of blooms lying inside the furnace.
When the heating of blooms/slabs in reheating furnaces is controlled, it is generally
required to heat blooms/slabs uniformly to a temperature suitable for rolling them and
simultaneously heat the blooms/slabs to the required final temperature in accordance
with a speed required for their rolling mill following the continuous reheating furnace.
In the control of the type referred to, there has been a procedure to control the
temperature of the atmosphere disposed in batch type reheating furnaces to a single
value set uniformly in a plurality of control zones into which the furnace is divided.
This is because it is extremely difficult to control temperature of a multitude of slabs
different in loading, for example, which differ in size from one another respectively
resulting in the employment of a single temperature in spite of the differences in the
loading or size of the slabs.
SUMMARY OF INVENTION
Accordingly, it is an object of the present invention to provide a solid hearth reheating
furnace with improved thermal efficiency by incorporating differential gaseous fuel
characterized by modified gas pipelines which are bi-furcated to achieve the
differential gas flow rate between front and back end burners which includes two
control valves and a controller configured for regulating the control valves and
installed in bifurcated gas pipelines, one on each side of the furnace for back end
burners.

As per another object of the present invention is to provide a method of reheating a
metallic work piece in a reheating furnace with improved thermal efficiency by
incorporating differential gaseous fuel flow comprising the steps of passing off a gas
rich in combustibles and at a high temperature from the front and back end of the
furnace through modified gas pipelines which are bi-furcated to achieve the
differential gas flow rate between front and back end; and controlling the control
valves installed in bifurcated gas pipelines, one on each side of the furnace for back
end burners to achieve differential gas flow rate between front and back end burners
and to avoid air ingress during mill delay
Accordingly, it is an object of the present invention to provide a novel and improved
method of controlling the heating of blooms/slabs in a batch type-reheating furnace
with a high efficiency.
As per another object of the present invention which has provided a differential
gaseous fuel flow rate which is maintained between front-end burners and back end
burners of the batch type reheating furnace
As per yet another object of the present invention, a thermocouple has been
installed in the back wall which facilitates in maintaining proper temperature in back
wail to avoid overheating / burning of back end of blooms.
As per yet another object of the present invention, the temperature is measured by
radiation pyrometer at roughing stand that helps to maintain proper thermal regime of
the furnace.
A further object of the present invention is to provide an arrangement for the
measurement of the furnace pressure at the back wall, which is being used for
maintaining slightly positive pressure inside the furnace to avoid ingress of cold air.
As per yet further object of the present invention, the pipeline modification is
designed and made very simple in construction and cost effective.

It is a further object of this invention to provide means for reheating ferrous work in
such a way that a high degree of efficiency and economy is achieved.
It is a still further object of this invention to provide means and methods for fully
utilizing the heat content in fuel within a reheating furnace through complete
combustion.
A controller configured for regulating the control valves wherein the gas pipelines are
bi-furcated to achieve the differential gas flow rate between front and back end
burners with the help of two control valves installed in bifurcated gas pipelines, one
on each side of the furnace.
Gas pipelines are modified and the differential gas flow rate between front and back
end burners are maintained, and it helps to avoid burning of blooms during mill delay.
Further objects will appear from the following portion of the specification and the
drawings, wherein:
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig 1 illustrates the existing gas supply pipeline (prior art) in accordance with the
present invention;
Fig 2 illustrates the modified scheme for the gas supply line in accordance with the
present invention,
Fig 3 illustrates the P.I. Diagram for controlling the gas supply for back end burners in
accordance with the present invention.
DETAILED DESCRIPTION
Reheating furnaces in integrated steel plants invariably use the by-product fuels, in
most of the reheating furnaces, mixture of coke oven gas and blast furnace gas
(mixed gas) having calorific value ~ 1500-1550 Kcal/Nm3 is used as fuel. Coke oven
gas and blast furnace gas are generated as by-product fuels in the Coke Ovens and

Blast Furnaces of Iron and Steel industries respectively. Selection of gaseous fuel for
different type of reheating furnaces in Iron and Steel industries depends upon the
heat load requirement.
In this reheating furnace, high calorific value combustible gas (Coke Oven gas) is
used as fuel. There is common supply line with a control valve to regulate gas flow
rate. It is divided into two lines for feeding gas on both sides of burners. Each furnace
is equipped with 12 numbers of burners, 6 on each side of the furnace across the
width. Presently, there is no control valve to regulate the gas flow distribution
between front and back burners.
The existing gas supply line for feeding the burners of both sides of the furnace has
been shown in Fig.-1 (prior art). Originally, the burners were designed to fire mixed
gas as fuel at the rate of 3500 Nm3/hr with a calorific value of 3000 Kcal/Nm3 Gas is
supplied at a pressure of about 150mmwc through 6 burners and air is supplied
through uptake of the checker with a preheat temperature of 450-500°C. Presently
the furnaces are using coke oven gas as fuel with a calorific value of 4200 Kcal/Nm3
There is a facility provided to measure the gas flow rate to the furnace. There are two
thermocouples (TC) provided in the middle of the furnace roof. One TC is located in
front side of roof to measure front temperature of furnace and 2nd is located in back
side of roof furnace to measure of inner portion of furnace.
The furnaces are charged with both cold and hot blooms. About 80% blooms are
charged directly from primary mill in hot condition. Temperatures of hot blooms are in
the range of 600-800°C. The heating duration for hot & cold charge is about 45 and
120 minute respectively. The rated capacity of furnaces is 40 T/Hr and 15 T/Hr for hot
blooms and cold blooms respectively.
Over heating and large temperature gradient along front and back ends of blooms
are occurring while heating in furnace. This is resulting in generation of defects in the
rolled product. Cock oven gas supply is common for all 6 burners on each side. It is
essential to have differential gas flow rate between front and back end burners to
avoid air ingress during mill delay. The existing gas pipelines have been bi-furcated

to achieve the differential gas flow rate between front and back end burners as
shown in Fig - 2. The gas rate will be regulated only in back end burners. Two control
valves have been installed in bifurcated gas pipelines, one on each side of the
furnace for back end burners. Control valves installed on gas supply line along with
other instruments has been shown in Fig - 3. Both control valves will regulate the gas
flow rate of all three burners of back end only. A Pt-Pt/Rh-10% thermocouple has
been installed in the middle of back wall, which measures temperature of back wall of
the furnace and it will be the input of the controller to regulate gas flow for the back
end burners. The existing air control damper has been provided with electrical motor
for easier control of combustion airflow rate. A radiation pyrometer has also been
installed at roughing stand to measure the temperature of blooms on the roller table.
This temperature is being displayed at three places one each at furnace control panel
and the third near the roller table to maintain proper temperature regimes to avoid
overheating of blooms. A furnace pressure transmitter has been installed in middle of
back wall to measure furnace pressure. This helps in maintaining positive furnace
pressure inside the furnace, which reduces ingress of cold air into the furnace.
As per one of the aspect of the present invention, there is provision for an
independent Local Confrol Station (LCS) connected through wire near the furnace for
operating the valves locally. Back end valve are controlled by the LCS which helps
for operation of the valves in manual or auto mode. The output reading of the
thermocouple is fed to the controller to regulate gas flow to the back end burners and
to maintain proper temperature regimes to avoid overheating of blooms.
The modification incorporated in the existing gas pipelines has helped in efficient
operation of the reheating furnace resulting in reduction in specific fuel consumption
by about 24-25% and increase in productivity by 8-10%. This design of new pipeline
is very simple in construction but very efficient in operation. It is observed during cold
de-slagging of the furnace that slag deposit on the hearth has reduced as compare to
the earlier level of slag deposit. The profile of slag deposit indicates that there is less
accumulation of slag near the back end of the furnace. This is due to reduction in
furnace back end temperature and maintaining positive pressure inside the furnace.
By maintaining proper thermal regime of the reheating furnace, scale formation has

reduced by 1 %. Presently this modified pipeline is being used in reheating furnace of
Heavy Structural Mill of IISCO Steel Plant, Burnpur.
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. A solid hearth reheating furnace with improved thermal efficiency by incorporating
differential gaseous fuel characterized by modified gas pipelines which are bi-
furcated to achieve the differential gas flow rate between front and back end burners
which includes two control valves and a controller configured for regulating the
control valves and installed in bifurcated gas pipelines, one on each side of the
furnace for back end burners.
2. A reheating furnace as claimed in claim 1, wherein the control valves are
configured for regulating the gas flow rate of all burners of back end only.
3. A reheating furnace as claimed in claim 1, wherein the furnace further includes
thermocouple being installed in the middle of back wall, which measures temperature
of back wall of the furnace and configured for inputting the data to the controller to
regulate gas flow for the back end burners.
4. A-reheating furnace as claimed in claim 1, wherein the furnace further includes air
control damper with electrical motor controller for easier control of combustion airflow
rate.
5. A reheating furnace as claimed in claim 1, wherein the furnace further includes a
radiation pyrometer installed at roughing stand to measure the temperature of blooms
on the roller table.
6. A reheating furnace as claimed in claim 1, wherein the temperature inside the
furnace is being displayed at three places one each at furnace control panel and the
third near the roller table to maintain proper temperature regimes to avoid
overheating of blooms.
7. A reheating furnace as claimed in claim 1, wherein the furnace further includes
furnace pressure transmitter installed in middle of back wall to measure furnace
pressure for maintaining positive furnace pressure inside the furnace, which reduces
ingress of cold air into the furnace.

8. A method of reheating a metallic work piece in a reheating furnace with improved
thermal efficiency by incorporating differential gaseous fuel flow comprising the steps
of.
passing off a gas rich in combustibles and at a high temperature from the front and
back end of the furnace through modified gas pipelines which are bi-furcated to
achieve the differential gas flow rate between front and back end; and
controlling the control valves installed in bifurcated gas pipelines, one on each side of
the furnace for back end burners to achieve differential gas flow rate between front
and back end burners and to avoid air ingress during mill delay..
9. A method of heating a metallic work piece in a reheating furnace as claimed in
claim 8, wherein the control valves are configured for regulating the gas flow rate of
all burners of back end only.
10. A method of heating a blooms, a reheating furnace as claimed in claim 8, wherein
the controlling of the control valves is carried out with an externally with local control
system (LCS).

The present invention relates to a solid hearth reheating furnace with improved
thermal efficiency by incorporating differential gaseous fuel characterized by modified
gas pipelines which are bi-furcated to achieve the differential gas flow rate between
front and back end burners which includes two control valves and a controller
configured for regulating the control valves and installed in bifurcated gas pipelines,
one on each side of the furnace for back end burners, and a method of reheating a
metallic work piece in said reheating furnace with improved thermal efficiency by
incorporating differential gaseous fuel flow.