Claims:We Claim:

1. A method for reducing graphite electrode consumption in ladle furnaces and the like comprising :

carrying out intermittent electrode cooling operations by water spraying onto the electrode column surface such as to reduce consumption during arc generation by the electrode especially the side surface of the electrodes.

2.The method as claimed in claim 1 comprising carrying out said water spraying selectively based on the temperature distribution along the full length covering area around the bottom of the electrode, area along the middle of the electrode and area along the top part of the electrode and also the tip of the electrode .

3.The method as claimed in anyone of claims 1 to 2 wherein the water spraying is carried out to control the temperature along the full length of the covering area around the bottom of the electrode from 700-1000°C, area along the middle of the electrode from 400-500°C and area along the top part of the electrode from 100-250°C and at the tip of the electrode from from1000-1250°C .

4.The method as claimed in anyone of claims 1 to 3 wherein the water spraying is controlled such that water trickles down the electrode column and gets evaporated before leaving the bottom of the electrode involving spray nozzle based spraying of water under controlled water flow and pressure on the outer periphery of the electrode and thereby cooling of the electrode surfaces and wherein pressure and flow of water is maintained 2-6 kg in line and 40-90 lpm for each header connected to the nozzle spray system.

5. The method as claimed in claimed in anyone of claims 1 to 4 comprising stopping water flow and spraying during arcing and carrying out air flow through nozzle during arcing to prevent clogging of nozzles to achieve reduction in consumption of around 8-10%.
6. An electrode cooling system for reducing graphite electrode consumption due to required electric arcing while generating electric energy based required heat for liquid steel in furnace comprising:
said electrode cooling system comprising means for spraying water onto the outer periphery of the graphite electrode intermittently when not under arcing and thereby cooling the surface of the electrode;
said means for spraying of water being operatively controlled based on the surface temperature of the electrode involving water flow control and pressure regularizing means such that water trickles down the electrode column and gets evaporated before leaving the bottom of the electrode involving spray nozzle based spraying of water under controlled water flow and pressure on the outer periphery of the electrode and thereby cooling of the electrode surfaces;
an air flow mechanism to flow air through the spray means including nozzle when the arcing of electrode is under process when the water spray is not required.

7.The electrode cooling system as claimed in claim 6 comprising of a common water line connected to spray nozzles including pressure gauges, flow meter, pressure regulating valves and wherein each said electrode is independent cooled based on water spray operating branch header pipeline connected to said common pipeline also having flow valve and flow meters.

8. The electrode cooling system as claimed in anyone of claims 6 or 7 wherein said air flow mechanism includes air flow line operatively connecting to the spray means/nozzles through respective valve control and flow control means.

9. The electrode cooling system as claimed in anyone of claims 6 to 8 comprising controller means for selective operation of water spraying intermittently when the arcing is not active and flow of said air through said spray/nozzle means during arcing to avoid any nozzle clogging.
10. The electrode cooling system as claimed in anyone of claims 6 to 9 comprising means for temperature mapping of the full length and tip of the respective electrodes and said water spray flow control is based on the thus mapped electrode surface temperature and required cooling for reduced consumption of electrode.

Dated this the 12th day of March, 2021
Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)
IN/PA-199

, Description:FORM 2
THE PATENT ACT 1970
(39 OF 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)

1 TITLE OF THE INVENTION :
A METHOD TO REDUCE GRAPHITE ELECTRODE CONSUMPTION IN LADLE FURNACE AND A SYSTEM THEREOF.



2 APPLICANT (S)

Name : STEEL AUTHORITY OF INDIA LIMITED.

Nationality : Indian.

Address : Research & Development Centre for Iron & Steel,
Doranda, Ranchi, Jharkhand, India. PIN-834002.






3 PREAMBLE TO THE DESCRIPTION

COMPLETE

The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The present invention relates to an electrode cooling system for reducing graphite electrode consumption due to required electric arcing while generating electric energy based required heat for liquid steel in furnace and a method to reduce graphite electrode consumption in ladle furnace by water cooling onto the outer periphery of the graphite electrode through spray nozzles intermittently when not under arcing and carrying out air flow through nozzle during arcing to prevent clogging of nozzles.

BACKGROUND OF THE INVENTION
The bulk of plain carbon steel is produced either in integrated or in mini steel plants through conventional basic oxygen furnace (BOF) or through electric-arc furnace (EAF) routes. Production of alloy and special steels was made possible in these steel plants only after development of the AC-arc ladle furnaces, popularly known as LF/LRF. Among the diverse secondary steelmaking process existing today, ladle furnaces with electrode heating system have occupied an important position in steelmaking owing to the flexible and versatile applicability. The electric power requirement in LF is quite moderate (compared with EAF for steel melting) providing a heating rate 3 - 5 °C min-1 max. The required heating energy not only depends on the desired temperature increment but also on the amount and thermal properties (specific heat) of the alloys which are added in the ladle. In addition to heating, ladle furnace is an excellent place to make desulfurization with slag, Ca-treatment, and other alloying and trimming additions.

Graphite electrode, a conductor that releases electric energy in the form of an electric arc, is used to heat the liquid steel in ladle furnace. They are currently the only products with high electrical conductivity and are able to maintain extremely high heat generation. Graphite electrode has irreplaceable performance advantages that plays an indispensable role in the high temperature manufacturing field such as in iron and steel smelting, electrolytic aluminum, ferroalloy, calcium carbide, industrial silicon and yellow phosphorus smelting.
Main factors affecting graphite electrode consumption in Ladle Furnace:
1. The main reasons of loss and consumption of graphite electrodes are overload and timeout operation.
2. The increased feeding times lead to higher probability of electrode bottom damage and fracture.
3. Ladle furnace power supply equipment not matching the electrode specifications.
4. The selection of power curve & gear, the voltage & current control of starting and stabilizing arcs, the use of long, medium and short arcs and the configuration of water cooling system are important to the service life and consumption of electrodes.
5. The quality of the graphite electrode itself affects the consumption ratio. Nowadays, the processes of ladle furnaces have higher requirements on the anti-oxidation performance and thermal shock resistance of graphite electrodes.
Due to the above factors the consumption of the side surface of the electrode which can be considered a real loss is very huge which leads to increased electrode unit consumption resulting in higher production cost. There has been thus a need to develop a system and method to reduce the electrode consumption in ladle furnace used for steel production.
OBJECTS OF THE INVENTION
The basic object of the present invention is directed to a method for reducing graphite electrode consumption in ladle furnaces and a system to carry out such method.
A still further object of the present invention is directed to a system and method for reducing electrode consumption in ladle furnace by water cooling onto the outer periphery of the graphite electrode intermittently when not under arcing and carrying out air flow through nozzle during arcing to prevent clogging of nozzles.
A still further object of the present invention is directed to a system and method for reducing electrode consumption in ladle furnace wherein gradual sublimation of tip of the electrode by the arc due to very high temperature, narrowing of electrode tip diameter or fall down of electrode tip due to thermal shock and at the same time, consumption due to oxidation of the side surface of the lower part of the electrode in high temperature atmosphere can be substantially reduced.

A still further object of the present invention is directed to provide a system and method for reducing electrode consumption in ladle furnace favouring enhanced electrode life and reducing cost of production of steel.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to a method for reducing graphite electrode consumption during arcing operations in ladle furnaces and the like comprising :

carrying out intermittent electrode cooling operations by water spraying onto the electrode column surface such as to reduce consumption during arc generation by the electrode especially the side surface of the electrodes.

A further aspect of the present invention is directed to said method comprising carrying out said water spraying selectively based on the temperature distribution along the full length covering area around the bottom of the electrode, area along the middle of the electrode and area along the top part of the electrode and also the tip of the electrode .
A still further aspect of the present invention is directed to said method wherein the water spraying is carried out to control the temperature along the full length of the covering area around the bottom of the electrode from 700-1000°C, area along the middle of the electrode from 400-500°C and area along the top part of the electrode from 100-250°C and at the tip of the electrode from1000-1250°C.
A still further aspect of the present invention is directed to said method wherein the water spraying is controlled such that water trickles down the electrode column and gets evaporated before leaving the tip of the electrode involving spray nozzle based spraying of water under controlled water flow and pressure on the outer periphery of the electrode and thereby cooling of the electrode surfaces and wherein pressure and flow of water is maintained 2-6 kg in line and 40-90 lpm for each header connected to the nozzle spray system.
A still further aspect of the present invention is directed to said method comprising stopping water flow and spraying during arcing and carrying out air flow through nozzle during arcing to prevent clogging of nozzles to achieve reduction in consumption of around 8-10%.
Another aspect of the present invention is directed to an electrode cooling system for reducing graphite electrode consumption due to required electric arcing while generating electric energy based required heat for liquid steel in furnace comprising:
said electrode cooling system comprising means for spraying water onto the outer periphery of the graphite electrode intermittently when not under arcing and thereby cooling the surface of the electrode;
said means for spraying of water being operatively controlled based on the surface temperature of the electrode involving water flow control and pressure regularizing means such that water trickles down the electrode column and gets evaporated before leaving the bottom of the electrode involving spray nozzle based spraying of water under controlled water flow and pressure on the outer periphery of the electrode and thereby cooling of the electrode surfaces;
an air flow mechanism to flow air through the spray means including nozzle when the arcing of electrode is under process when the water spray is not required.

Yet another aspect of the present invention is directed to said electrode cooling system comprising of a common water line connected to spray nozzles including pressure gauges, flow meter, pressure regulating valves and wherein each said electrode is independent cooled based on water spray operating branch header pipeline connected to said common pipeline also having flow valve and flow meters.

A further aspect of the present invention is directed to said electrode cooling system wherein said air flow mechanism includes air flow line operatively connecting to the spray means/nozzles through respective valve control and flow control means.

A still further aspect of the present invention is directed to said electrode cooling system comprising controller means for selective operation of water spraying intermittently when the arcing is not active and flow of said air through said spray/nozzle means during arcing to avoid any nozzle clogging.

A still further aspect of the present invention is directed to said electrode cooling system comprising means for temperature mapping of the full length and tip of the respective electrodes and said water spray flow control is based on the thus mapped electrode surface temperature and required cooling for reduced consumption of electrode.
The above and other objects and advantages of the present invention are described hereunder in greater details with reference to following accompanying non limiting illustrative drawings.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: Full length temperature mapping of electrode during treatment of Heat No 1.
Figure 2: Temperature mapping at electrode Tip of Heat No 1.
Figure 3: Schematic arrangement of Electrode cooling system according to present invention.
Figure 4: Electrode cooling System during operation.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS
Graphite electrodes are used in Ladle Furnace and they are clamped by an electrode holder to be inserted through hood of the ladle furnace having approach to liquid steel when ladle is in treatment position. Arc is generated between the tip of the electrode and the liquid steel to raise the temperature of the liquid steel. The tip of the electrode is sublimated by the arc gradually due to very high temperature and at the same time, the side surface of the lower part of the electrode is oxidized and consumed in high temperature atmosphere. Gradually with use, electrode column changes its shape from cylinder to pencil, the diameter of the bottom of the electrode decreases to about 65-75% as compared to the original electrode diameter. The above-mentioned electrode consumption can be broken down, in term of figures, into 30-40% by arc, 3-5 % by fall-down of the tip by thermal shock, 40-60 % by oxidized side surface and 3-5 % by other causes. The consumption of the side surface of the electrode which can be considered a real loss is very huge which leads to increased electrode unit consumption resulting in higher production cost.
Temperature mapping of electrode just after arcing
There are several steps of activity for saving the graphite electrode during use to have less consumption. One of the methods is to reduce side oxidation by the water spray cooling of electrode columns that lower the surface temperature. Water flow is controlled in a way that water trickles down the electrode columns and gets evaporated before leaving bottom of electrode. In this work, reduction in electrode consumption by designing a suitable electrode cooling system was targeted.
Temperature measurement of electrodes at different surface locations was conducted using Thermo vision camera (FLIR). Thermal imaging was carried out for Electrode no. 1 & 2 as shown in Figure 1. Temperature mapping was done for full length as well specifically for electrode tip so that temperature of whole body electrode could be measured. Temperature mapping of electrode tip is shown in Figure 2. This practice was done for heats of Ladle Furnace in which this system has been installed and its temperature distribution is shown below.
During measurement, full length of electrode was divided into three areas namely Area-1(Ar1), Area-1(Ar2) and Area-1(Ar3). Area-1 is the area around bottom of electrode whereas Area 2 and Area 3 are the middle and top part respectively. This has been shown in Table 1 and Table 2.
Table 1: Full length temperature distribution of electrode
Area Electrode-1 Electrode-2
Heat No 1 Heat No 1
Area-1 Max. Temperature Temperature 987.20 857.20
Avg Temperature 884.20 819.10
Area-2 Max. Temperature 848.90 826.50
Avg. Temperature 756.20 761.30
Area-3 Max. Temperature 618.30 732.80
Avg. Temperature 559.70 598.40

Table 2 : Temperature distribution at Tip of Heat No 1.
Area Electrode-1 Electrode-2
Electrode Tip Area Max. Temperature 1206.70 1235.40
Avg Temperature 892.80 1046.50

Effect of water spray cooling on graphite electrode
A cooling apparatus for ladle furnace electrodes was designed in which nozzles spray the outer periphery of graphite electrode and cool the surfaces of electrodes. Water flow was controlled in such a way that water running down the electrode columns evaporated before leaving the electrode tip to enable maximum graphite saving. Figure 3 shows the schematic diagram of electrode cooling system that was planned for installation at Ladle furnace. The system includes the mechanism for controlling water flow and pressure to regularize the flow. Moreover, provision for air flow was also included in the system so that during arcing when water flow is stopped then air flow will prevent the clogging of nozzle.
Figure 4 shows the electrode cooling system in running condition. During spray water trickles down on its surface and gets vaporized before reaching the tip of the electrode. Several hit and trial methods were adopted to optimize water pressure and flow. The value of optimized pressure and flow of water 2-6 Kg in line and 40-90 lpm for each header. The vaporization of water also acted as a blanket to prevent the ingress of air near the electrode surface.
Temperature taken during trial for different portion of surface of electrode. Data for more than 30 heats were recorded for this purpose. The average value of trial result and their relative temperature reduction is shown in Table 3.
Table 3: Temperature of different portion and % reduction after spray cooling
Temp of Electrode before Spray Temp of Electrode
after Spray Temperature Reduction,%
Tip Middle Top Tip Middle Top Tip Middle Top
Average 1300-1450 500-700 200-300 1100-1250 300-400 100-200 8-12 25-35 40-60

Based on above, consumption data was also recorded in which trial was conducted. While comparing the data without water cooling of electrode, a reduction in electrode consumption to the tune of 8-10% was observed.

Usefulness of the invention
Graphite electrode is a costly and consumable item used for heating of liquid steel in ladle furnace. Through this work, an effort has been given to reduce electrode consumption in ladle furnace by minimizing surface oxidation loss.

Industrial Applicability
This method of cooling the graphite electrode surface can be used for any ladle furnace in steel industry. This system has been installed and has been regularly used at Ladle Furnace of Bhilai steel plant.
It is thus possible by way of the present invention to provide the following benefits:
I. A METHOD TO REDUCE CONSUMPTION OF GRAPHITE ELECTRODE IN LADLE FURNACE
? A method has been developed to reduce the graphite electrode consumption at ladle furnace. In this method, the electrode surface is cooled down by spraying water at specified flow rate and pressure so that water trickles down on its surface and gets vaporizes near the tip. This system is used after processing of ladle containing liquid steel.
II. A METHOD TO UTILIZE WATER BY UTILIZING OUTLET OF WATER COOLED TRANSFORMER
? A method has been developed which requires the water usage at rate of 40-90 lpm and this requirement was fulfilled by utilizing the water from different outlet sources of equipment including that of transformer cooling water of ladle furnace, Vacuum arc degasser etc.