FORM 2THE PATENT ACT 1970(39 OF 1970)&The Patent Rules, 2003COMPLETE SPECIFICATION(See Section 10 and Rule 13)1 TITLE OF THE INVENTION :A SYSTEM FOR MIXING OF COREX AND BLAST FURNACE GAS FOR PRE-HEATING OF BF AIR.2 APPLICANT (S)Name : JSW Steel Limited.Nationality : An Indian Company.Address : Jindal Mansion, 5-A, Dr. G. Deshmukh Marg ,Mumbai - 400 026, State of Maharastra, India.3 PREAMBLE TO THE DESCRIPTION COMPLETEThe following specification particularly descibes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The present invention relates to a system for mixing of BF gas with COREX gas and in particular to the system for mixing of high Calorific Corex gas (2000 Kcal/Nm3) with low calorific BF gas (700kcal/Nm3) directly in the main duct involving injection technology thereby avoiding the complexities of mixing such gases in mixing stations involving complicated circuit and huge capital investment. Thus by injecting high pressure COREX gas into low pressure BF gas duct, it is possible to on one hand ensure achieving a mixed gas for pre-heating of air for use in BF operation and advantageously on the other hand avoid the complexities of such mixing of gases in mixing stations. The system of the invention would favour utilizing BF gas effectively up to about 95% using said high pressure injection method involving selective valve systems which is simple, safe, reliable and cost effective and thus having enough merit to be widely used in industry in the related field of Blast furnace operation and the like.
BACKGROUND ART
The production of molten iron by chemical reduction of the oxide ores is conventionally carried out in the Blast Furnace (BF). The process of conversion of iron ore into molten iron takes place in the closed chamber of the furnace where a large amount of heat is produced and huge volume of various gases produced through chemical reactions taking place. The iron ore and the coke as the reducing agent are charged in appropriate proportions, are charged from the top and preheated air at about 1100°C is blown through the tuyeres at the bottom part of furnace to favor desired chemical reactions for extraction of iron from the ore. The preheated air reacts with coke to form reducing gases i.e. carbon monoxide at the lower part of the furnace. The ascending reducing gases undergoes chemical reactions with the descending charge of iron ore. After the complete reduction of the ore, the molten iron gets accumulated at the bottom bed of the hearth of BF and the slag being lighter, floats above the molten iron. The huge amount of BF gas is generated during the chemical reactions at the BF chamber, which is used for air preheating purpose. The BF gases are first cleaned in the Gas Cleaning Plant (GCP) and thereafter used as a fuel for heating air. Air preheating is done conventionally in a domed shaped structure, commonly known as stove. The air preheating process undergoes two-phase operations. In heating cycles, at first a fuel with high calorific value is combusted along with BF gases in the combustion chamber and the heat generated is transferred to checker chamber through convection. In

the second stage, high pressure atmospheric air is passed through it to pick up heat of combustion to meet the requirement of preheated air. BF gases alone cannot provide enough heat to attain air temperature up to desired level of about 1100°C, thus remains under utilized in terms of its heat generating potential.
In the existing system, mixing of two or more gases (or fuel) is done conventionally, in a mixing gas station. It works on the principle of supplying different gases from different sources into a common mixing vessel for thorough mixing. Since these gases are obtained at different volume flow rate and pressures, the existing system requires a large number of pressure switches, mass flow control valves, shut off valves, safety valves and thereby making the installation and maintenance of such system complex and highly expensive. The typical mixing of COREX gas having high calorific value with low calorific value BF gas comprising the above components in the circuit in a conventional mixing system is very much complicated and difficult and costly to maintain. The existing gas mixing system therefore is not only complicated in nature but also attracts huge capital investment. Moreover, it requires separate unit which is fitted with too many flow controllers, switches, pressure switches, various interlocks, making it susceptible to frequent failure/breakdown needing expensive maintenance in terms of repair/replacement and related manpower cost.
There has been therefore a persistent need to develop a system that is simple and less expensive yet safe and reliable and having the capacity to overcome the limitations observed in the existing gas mixing system for air preheating purpose for BF operation.
OBJECTS OF THE INVENTION
The basic object of the present invention is thus directed to a simple and less expensive system for mixing of COREX gas with BF gas for improved utilization of low calorific value BF gases up to about 95% by way of the mixed gases, used for air preheating up to desired temperature level to meet requirements of the BF operation.
A further object of the present invention is directed to a new system of mixing BF gases with the high calorific value COREX gas, by injection method wherein the high pressure COREX gas can be advantageously injected directly to the BF gas duct for obtaining the desired mixing.

A still further object of the present invention is directed to a method of mixing using a simple and less expensive device/systems whereby the high calorific value of the COREX gas such as 2000 kcal/Nm3 can be readily and simply mixed with the BF gas having low calorific value such as 700 kcal/Nm3 and thereby improve the heating capacity of the mixed gas for desired preheating of air up to required temperature of about 1100°C.
A still further object of the present invention is to eliminate use of complex flow/pressure control gadgets and instruments in the known systems for mixing of such gases in mixing stations and the like and minimizing the requirement of maintenance ensuring longer plant availability, making the method and system therefore such mixing more safe ,reliable and user friendly.
A still further object of the present invention is directed to a simple and cost effective system of mixing of COREX and the BF gas involving injection technology and selective size/diameter and length of such gas conveying ducts wherein said mixing by injection method can take place effectively ensuring proper mixing of the two gases in the network itself, providing desired uniform improved calorific value of mixed gas compared to that obtained from other existing mixing systems.
SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided a system for mixing of Corex and Blast Furnace gas for pre-heating of air in Blast Furnace route of producing molten iron comprising:
a main duct carrying the low pressure BF gas;
means for injecting the high pressure Corex gas into said low pressure BF gas main duct;
said Corex line adapted for said injection mixing with the BF gas line through a valve means to thereby favour effective mixing of the low calorific BF gas with the said high

calorific value Corex gas in the network itself comprising said duct line carrying the generated BF gas for its use in preheating of air.
A further aspect of the present invention directed to a system for mixing of Corex and Blast Furnace gas wherein said valve means for mixing of said Corex line with BF gas line comprises block and bleed valve systems.
According to yet another aspect of the present invention directed to a system for mixing of Corex and Blast Furnace gas wherein said valve means for mixing of said Corex line with BF gas line comprises selectively pneumatic regulating valve, shut-off valve and safety relief valve.
In the above system of the invention the said system for mixing of Corex and Blast Furnace gas advantageously also comprising a calorific value analyzer adapted to measure the resulting calorific value of the mixed gas prior to combustion;
According to an important aspect of the present invention the same is directed to the system for mixing of Corex and Blast Furnace gas by injection method wherein the dimensions of said Corex and BF gas lines are selectively determined to facilitate the proper injection mixing of said Corex gas with the BF gas.
According to yet another aspect of the present invention the same is directed a method for mixing of Corex and Blast Furnace gas for pre-heating of air in Blast Furnace route of producing molten iron comprising:
injecting the high pressure Corex gas into said low pressure BF gas main duct, said

injection mixing of said Corex gas with the BF gas line controlled through valve means to thereby favour effective mixing of the low calorific BF gas with the said high calorific value Corex gas in the network itself comprising said duct line carrying the generated BF gas for its use in preheating of air.
A still further aspect of the invention is directed to a method for mixing of Corex and Blast Furnace gas wherein said mixing of said Corex line with BF gas line is carried out involving block and bleed valve systems preferably selectively controlling pneumatic regulating valve, shut-off valve, safety relief valve and calorific value analyzer.
According to a further aspect of said method for mixing of Corex and Blast Furnace gas comprises selectively injecting Corex gas of high pressure of about 0.9 bar and high calorific value of about 2000kcal/Nm3 into BF gas duct of low pressure of about 0.07 bar and low calorific value of about 700 kcal/Nm3.
The present invention and its advantages and objectives are described in further details with particular reference to accompanying non-limiting illustrations.
BRIEF DESCRIPTION OF THE FIGURES
Figure 1: is the illustration of the conventional mixing gas station used to mix Corex gas with the BF gas presently known in the art;
Figure 2: is a schematic illustration of the gas mixing system in accordance with the present invention.
Figure 3: is the graphical representation of the actual versus predicted curve for mixed gases; and
Figure 4: is the graphical representation illustrating the effect on rise in dome temperature.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURES
As discussed hereinbefore, the present invention is directed to a simple and cost effective method of mixing of BF gas with COREX gas with the objective of achieving improved utilization of the low calorific value BF gas up to about 95% being mixed with high calorific value and high pressure COREX gas adopting an online gas injection system, and thereby favor obtaining preheating of air to desired temperature of about 1100°C, for use in BF operation more efficiently. The present invention involving gas mixing by injection method and the system for implementing such mixing eliminates the complexities and exceptionally high costs associated with the conventional mixing method in a separate mixing station, involving various flow/pressure control devices and costly measuring systems used in isolation for each of the gas manifolds and delivery line for the mixed gas.
Reference is first invited to the accompanying Figure 1 which illustrates the distribution network and mixing arrangement for BF gases and COREX gases in the existing system. The arrangement of ducting and accessories clearly shows that separate units for each type of gas with a substantial number of flow controllers, valves, switches, pressure switches, indicators, instruments and various interlocks, making the circuit too much complicated and prone to frequent failure and maintenance of the auxiliaries in such a system. It is apparent from the accompanying Figure 1, that the BF gas, usually at 0.07 bar, is carried through a 800NB duct, the flow parameters of which are monitored through a series of controllers and indicators/sensors such as the pressure indicator (PI), Calorific value transmitter (CVT), Pressure control Valve (PCV), Pressure transmitter(PT), Pressure indicator controller(PIC), Pressure alarm(PAL), Pressure safety limit (PSL), Supervisory control and data acquisition(SCADA), and the Flow indicator(FI), Flow transmitter(FT), Flow indication and regulation(FIR), Flow control valve(FCV), Flow indicator controller(FIC), Temperature element(sensor)(TE), Flow element sensor(FE), Solenoid operated valve(SOV), Calorific value analyzer(C);
Similarly, the COREX gas, usually at 0.9 bar, is carried through a 200 NB duct comprising similar flow and pressure control devices/switches and indicators/controllers;
The desired volumetric flow of the two types of gases is controlled and allowed to enter the mixing chamber which is a duct of 1000NB size and of selective length, at desired pressure

ranges favoring homogenous mixing of the two gases in the chamber. The mixed gas then flows through the duct comprising the pressure, flow and temperature indicator/display means and data acquisition system to execute necessary control, manual or computerized, on flow parameters through another 800NB duct to the air preheating plant. Because of the complexities of the circuit as detailed in the Figure 1, the existing gas mixing system not only suffer from frequent failure/repair and downtime but also attracts high initial cost of equipments and accessories and the preventive maintenance costs are of high magnitude. Moreover such a complex system required more manpower for its operation and up keeping.
Reference is now invited to the accompanying Figure 2, wherein the present system of high pressure based injection of COREX gas in the low pressure BF gas has been illustrated. It is apparent from the figure that the present system involve much less number and variety of flow /pressure control equipments and display/indicator means, and thus making the system much simple and less expensive yet safe and reliable. It is apparent from the accompanying Figure 2, that such a system rely on injection mixing in the main duct itself and involves selective size/diameter of the ducts conveying the two types of gases e.g. the 300NB duct carrying the COREX gas at 0.9 bar pressure and having higher calorific value in the order of 2000kcal/Nm3 through a circuit such that the high pressure COREX gas is injected by way of sudden expansion on its entry into a 1000NB duct carrying the low pressure(0.07 bar) BF gas at selective right angled bend of the later duct, enlarged view of which is shown in inset, through a block and bleed valve system which includes pneumatic regulating valve, shut off valve(SOV) and safety relief valve, as clearly illustrated in the ducting layout in Figure 2. Importantly, a by-pass route is connected to the down stream side of the COREX entry point on the BF gas duct via a flow control valve (FCV) for controlled volumetric ratio of the two gases in the mix such as to favor high calorific value COREX gas supplement and maintain desired resulting Calorific value of the mixed gas delivered from the system while maintaining stable pressure by operation of a safety relief valve, said calorific value being measured online by a Calorific value analyzer(C) mounted on the ducting prior to entry of the duct conveying mixed gas, into the dome for combustion.
As already described, the actual mixing of the high pressure and high calorific value containing COREX gas with low pressure and low calorific value BF gas using injection technique ensures proper mixing of the two in the main duct itself. Given with the flow rates and proportions vis-a-vis the calorific values of the fuel gases, the theoretical

computed/predicted value of the calorific value of the mixed gas can be obtained for any flow rates and the same can also be measured online by a calorific value analyzer, such that when the computed values are plotted against the actual measured value, it fits a straight line indicating reasonably good agreement between the computed/predicted and the real life data for the steady state calorific value of the mixed gas, that ensure reliability in operation.
The rise in dome temperature is continuously measured/monitored and the same(in °C) is illustrated in accompanying figure 4 which is observed to rise steadily, against time in minutes, in stove corresponding to a fixed Air/Gas ratio, such as 0.70, and no fluctuation in dome temperature is observed during the heating cycle, indicating the stability and reliability in operation of the present system. The air at desired mass flow rate is fed to the dome for heating by combustion of mixed gases, such that the preheated air for BF operation is obtained at the outlet from dome/stove at favored temperature range through heat recovery by way of effective utilization of the BF flue gases being selectively mixed with COREX gas and used as fuel for heating said air.
It is thus possible by way of this invention to achieve a method of mixing the BF gases with the COREX gas such that the large volume of BF gas having low calorific value is effectively utilized up to about 95%, in a simple and cost effective system involving injection of high pressure COREX gas in to low pressure BF gas directly in the main duct of selective size, such as to obtain mixed gas of higher calorific value at desired flow rate and pressure required to preheat air up to desired temperature range to favor reducing chemical reactions in BF operation. Thus the present system for mixing of BF gas with COREX gas and in particular to the system for mixing of high Calorific Corex gas (2000 Kcal/Nm3) with low calorific BF gas (700kcal/Nm3) directly in the main duct involving injection technology would avoid the complexities of mixing such gases in mixing stations involving complicated circuit and huge capital investment. Thus by injecting high pressure COREX gas into low pressure BF gas duct, it is possible to on one hand ensure achieving a mixed gas for preheating of air for use in BF operation and advantageously on the other hand avoid the complexities of such mixing of gases in mixing stations. The invention would enable better and advantageous utilization of BF gas effectively up to about 95% using said high pressure injection method which is found to be simple, safe, reliable and cost effective and thus having wide scale applicability in Blast furnace operation and the like.

WE CLAIM:
1. A system for mixing of Corex and Blast Furnace gas for pre-heating of air in Blast
Furnace route of producing molten iron comprising:
a main duct carrying the low pressure BF gas;
means for injecting the high pressure Corex gas into said low pressure BF gas main duct;
said Corex line adapted for said injection mixing with the BF gas line through a valve means to thereby favour effective mixing of the low calorific BF gas with the said high calorific value Corex gas in the network itself comprising said duct line carrying the generated BF gas for its use in preheating of air.
2. A system for mixing of Corex and Blast Furnace gas as claimed in claim 1 wherein said valve means for mixing of said Corex line with BF gas line comprises block and bleed valve systems.
3. A system for mixing of Corex and Blast Furnace gas as claimed in anyone of claims 1 or 2 wherein said valve means for mixing of said Corex line with BF gas line comprises selectively pneumatic regulating valve, shut -off valve and safety relief valve.
4. A system for mixing of Corex and Blast Furnace gas as claimed in anyone of claims 1 to 3 comprising calorific value analyzer.
5. A system for mixing of Corex and Blast Furnace gas as claimed in anyone of claims 1 to 4 wherein the dimensions of said Corex and BF gas lines are selectively determined to facilitate the injection mixing of said Corex gas with the BF gas.
6. A method for mixing of Corex and Blast Furnace gas for pre-heating of air in Blast Furnace route of producing molten iron comprising:
injecting the high pressure Corex gas into said low pressure BF gas main duct, said injection mixing of said Corex gas with the BF gas line controlled through valve means to thereby favour effective mixing of the low calorific BF gas with the said high calorific value

Corex gas in the network itself comprising said duct line carrying the generated BF gas for its use in preheating of air.
7. A method for mixing of Corex and Blast Furnace gas as claimed in claim 6 wherein said mixing of said Corex line with BF gas line is carried out involving block and bleed valve systems preferably selectively controlling pneumatic regulating valve, shut-off valve, safety relief valve and calorific value analyzer.
8. A method for mixing of Corex and Blast Furnace gas as claimed in anyone of claims 6 or 7 comprising injecting Corex gas of high pressure of about 0.9 bar and high calorific value of about 2000kcal/Nm3 into BF gas duct of low pressure of about 0.07 bar and low calorific value of about 700 kcal/Nm3.
9. A system for mixing of Corex and Blast Furnace gas for pre-heating of air in Blast Furnace route of producing molten iron and a method of carrying out such injection mixing of Corex with BF gas substantially as hereindescribed and illustrated with reference to the accompanying figure 2.

ABSTRACT
A SYSTEM FOR MIXING OF COREX AND BLAST FURNACE GAS FOR PRE-HEATING OF BF AIR.
A simple system for mixing of Blast Furnace gas with COREX gas by injecting high pressure COREX gas into low pressure BF gas duct line itself, of selective dimensions. The method of mixing also ensure achieving a mixed gas for pre-heating of air for use in BF operation, comprising mixing of high Calorific value (CV) COREX gas having CV in the order of 2000 kcal/Nm3 with BF gas having low calorific value of 700 kcal/Nm3 and thereby utilizing BF gas effectively up to about 95% using said high pressure COREX gas injection method, selectively controlling pneumatic regulating valve, shut-off valve(SOV), safety relief valve and online calorific value analyzer( C ). The present system of mixing of BF gas with the COREX gas is simple, safe, reliable and cost effective and thus having enough merit to be widely used in industry in the related field of Blast furnace operation and the like. Figure 2.