Claims:WE CLAIM:

1. A system for monitoring electric arc furnace (EAF) and to detect water leakage condition in water cooled furnace roof of the EAF comprising

current measuring means operatively connected to roof of the EAF, said current measuring means continuously detects and measures leakage current from said EAF roof;

transducer cooperative to said current measuring means to generate a signal proportional to said leakage current; and

programmable logic controller to compare said signal with respect to a preset threshold value for detection of increase in the leakage current due to roof jam and accordingly generating an alarm for cleaning the roof jam to avoid the water leakages and propagation of leak water into the EAF from the roof due to the roof jam.

2. The system as claimed in claim 1, wherein the current measuring means comprises

earthing line connected to the EAF roof; and

a current transformer, whereby said earthing line is connected to ground by passing through said current transformer enabling the current transformer for continuously detection of the leakage current from the EAF roof and accordingly generation of a proportional current at output of the current transformer.

3. The system as claimed in claim 1 or 2, wherein the earthing line includes a flexible copper wire connected to the EAF roof near to its pivot point to draw leakage current from the EAF roof.

4. The system as claimed in anyone of claims 1 to 3, wherein the leakage current from the EAF roof is affected by the roof jam due to sticking of non-metallic slag and other deposits to the roof during EAF operation and abnormal variation of this leakage current from the EAF roof corresponds to an indirect indication of the roof jam which leading to the water leakage condition in the cooling water panels of the water cooled furnace roof of the EAF.

5. The system as claimed in anyone of claims 1 to 4, wherein the current transformer at its output is connected to the transducer for feeding of its output proportional current in the transducer and thus enabling the transducer to generate the signal proportional to the leakage current.

6. The system as claimed in anyone of claims 1 to 5, wherein the programmable logic controller embodies programming logic to initiate a signal to a hooter for generating the alarm when the leakage current reaches a preset threshold value and sound from the hooter notifies operating personal to clean the EAF roof jam to avoid water leakage from the EAF roof.

7. The system as claimed in anyone of claims 1 to 6, wherein the programmable logic controller is connected to a display interface for displaying the current values in real-time.

Dated this the 30th day of July, 2019 Anjan Sen
Of Anjan Sen & Associates
(Applicants Agent)
IN/PA-199
, Description:FIELD OF THE INVENTION:
The present invention relates to monitoring electric arc furnace (EAF). More specifically, the present invention is directed to develop a system for monitoring the EAF to detect water leakage from water cooled furnace roof of the EAF.

BACKGROUND OF THE INVENTION:
The electric arc furnace (EAF) is a versatile and most widely used instrument for making steel from a wide range of input iron bearing materials such as hot metal, DRI, steel scrap etc. The EAF utilises energy of electric arc for smelting and refining of metallic charge i.e. the iron bearing materials in the process of making the steel therefrom.

A typical EAF usually consists of a refractory lined dish shaped hearth or reaction chamber. The reaction chamber of the furnace is covered from the above with a removable water cooled roof with refractory lining which is held by steel shell and roof ring. The EAF is further equipped with three phase alternating or direct current supply and three graphite electrodes connected to said three phase alternating or direct current supply by flexible electrical water cooled copper cables. The reaction chamber of the furnace receives the metallic charge after opening the roof and the three electrodes are inserted into the melting chamber through small opening of the roof called delta. The electrodes generate a large amount of heat energy during operation by striking electric arc among each other and also with the metallic charge and thereby melt and refine the charge.

The water cooled furnace roof of the EAF forms outer perimeter of roof cage. This cage acts as part of lifting structure for the furnace roof. Water cooled panels are inserted into this roof cage and have a cylindrical opening at the centre. The refractory made delta is inserted to fill this opening. This delta section has minimum gap around the electrodes to avoid the risk of arcing between the electrodes and the water cooled panels. The cooling circuit connected to the water cooled panels typically consists of supply pumps, return pumps, filters, cooling tower cells and flow monitoring instrumentation.

Now while the EAF is operational and as the steel batch-wise processed in the EAF, the cooling water panels suffer from thermal fatigue due to continuous heating and cooling cycles during arcing and non-arcing process. This thermal fatigue contributes to initiation and propagation of micro cracks in the cooling water panels and pipes resulting water leakages which can propagate and cause water leakage into the furnace which may sometimes lead to explosion. This leads to personal and structural damage, unplanned plant shut downs and production losses.

At present, water leakages from the cooling panels of EAF roof are detected by visual inspection and it is totally dependent on the operator’s expertise and skill. Recently, different automated water leakage detection systems have been reported in the art which are based on measurement of pressure, flow or analysis of exhaust gases from EAF. However, these systems detect only large water leaks and their response time is also less. These systems also do not give prior indication of the micro cracks in the cooling water panels to stop the furnace operation and take necessary repair actions before occurrence of the water leakage in the EAF.

It is thus there has been a need for developing a system for water leakage detection or pre-alarm system for the EAF by continuous monitoring of leakage current from the EAF roof to detect water leakage from water cooled furnace roof of the EAF.

OBJECT OF THE INVENTION:
The basic object of the present invention is to develop a system for water leakage detection or pre-alarm system for the EAF by continuous monitoring of leakage current from EAF roof to detect water leakage into the EAF from the EAF roof.

Another object of the present invention is to develop a system for continuous monitoring the EAF which would be adapted to detect the water leakages in cooling water panels in the water cooled roof of the EAF and generating an alarm to indicate the necessity of instant actions for EAF roof jam cleaning.

A still further object of the present invention is to develop a system for continuously monitoring the EAF which would be adapted to actuate an alarm for the EAF roof jam cleaning to prevent propagation of the water leakage into the EAF from the water cooled EAF roof.

SUMMARY OF THE INVENTION:
The primary aspect of the present invention is to provide a system for monitoring electric arc furnace (EAF) and to detect water leakage condition in water cooled furnace roof of the EAF comprising

current measuring means operatively connected to roof of the EAF, said current measuring means continuously detects and measures leakage current from said EAF roof;

transducer cooperative to said current measuring means to generate a signal proportional to said leakage current; and

programmable logic controller to compare said signal with respect to a preset threshold value for detection of increase in the leakage current due to roof jam and accordingly generating an alarm for cleaning the roof jam to avoid the water leakages and propagation of leak water into the EAF from the roof due to the roof jam.

In a preferred embodiment of the present system for monitoring electric arc furnace (EAF), the current measuring means comprises

earthing line connected to the EAF roof; and

a current transformer, whereby said earthing line is connected to ground by passing through said current transformer enabling the current transformer for continuously detection of the leakage current from the EAF roof and accordingly generation of a proportional current at output of the current transformer.

In a preferred embodiment of the present system for monitoring electric arc furnace (EAF), the earthing line includes a flexible copper wire connected to the EAF roof near to its pivot point to draw leakage current from the EAF roof.

In a preferred embodiment of the present system for monitoring electric arc furnace (EAF), the leakage current from the EAF roof is affected by the roof jam due to sticking of non-metallic slag and other deposits to the roof during EAF operation and abnormal variation of this leakage current from the EAF roof corresponds to an indirect indication of the roof jam which leading to the water leakage condition in the cooling water panels of the water cooled furnace roof of the EAF.

In a preferred embodiment of the present system for monitoring electric arc furnace (EAF), the programmable logic controller embodies programming logic to initiate a signal to a hooter for generating the alarm when the leakage current reaches a preset threshold value and sound from the hooter notifies operating personal to clean the EAF roof jam to avoid water leakage from the EAF roof.

In a preferred embodiment of the present system for monitoring electric arc furnace (EAF), the programmable logic controller is connected to a display interface for displaying the current values in real-time.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig. 1 shows the existing earthing connection system to the EAF upper and bottom shells along with a clamp meter to measure leakage current from the same.

Fig. 2 shows earthing connection to EAF roof and roof leakage current continuous detection and monitoring system for the detection of water leakages in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS:
As stated hereinbefore, the present invention discloses a system for monitoring the EAF to detect water leakage from water cooled roof of the EAF. The present invention basically describes a system that continuously monitors leakage current from roof of the EAF and actuates a signal if measured current reaches a preset threshold value. Leakage current from the EAF roof increases due to roof jam which causes water leakage from water cooled panels in EAF roof and thus leakage current is a good indicator of indirect assessment of the water leakage condition in the EAF roof which may further propagates within the EAF leading to dangerous explosion if this water leakage is not arrested in early stage.

Reference in this context, first invited from the accompanying Fig 1 which shows the schematic diagram of a typical EAF comprising roof (1), top shell (2), bottom shell (3), an earthing connection to bottom shell (4), clamp meter connected to earthing connection of bottom shell (5), earthing connection to top shell (6) and clamp meter connected to earthing connection of top shell (7). The portable type clamp meters are connected to EAF top and bottom shell eathing connections (5 & 7) whenever required to measure leakage currents from top and bottom shells. The portable type clamp meter is basically a hand held portable current measuring device used to measure instantaneous current when connected across the line. Clamp meter measure and display current when it is connected and does not have any provision for data saving, transmission or connection to controller and therefore not suitable for continuous monitoring of leakage current. In the existing EAF earthing system, there is no separate earthing connection from EAF roof and therefore, leakage current from EAF roof is not measured in the current operational or maintenance practice.

Reference is now invited from the accompanying Fig 2 which shows the schematic diagram of present EAF monitoring system involving new earthing connection and means for continuous monitoring of leakage current from EAF roof and thereby prediction of water leakages from the EAF roof. As shown in the Fig 2, the present EAF monitoring system comprises a leakage current measuring means having earthing connection from EAF roof (8) and a current transformer (9); a transducer (10) connected to the current measuring means, a programmable logic controller (PLC) (11) connected to the transducer, a hooter (12) to sound alarm and a HMI (13) to store and display real-time current values.

Earthing connection to the EAF roof is exhausting as the roof is rotatable about a pivot point and also exposed to high temperature during EAF operation. In the present invention, a flexible copper wire is connected to EAF roof near to its pivot point to draw leakage current from the roof as the movement of EAF roof is minimum near to this pivot point.

As shown in the referred Fig 2, the EAF earthing is designated with an additional electrical earthing connection from roof (8) which its one end is connected to the EAF roof and the other end is connected to the ground by passing through the current transformer (9). This enables the current transformer (9) to continuously detect the leakage current from the EAF roof and accordingly generate a proportional current at its output. The leakage current from the EAF roof is affected by the sticking of non-metallic slag and other deposits to roof (called roof jam) during EAF operation. Abnormal variation of this leakage current from EAF roof is an indirect indication of roof jam and leads to water leak into furnace from water cooled roof panels if not cleaned in time.

As shown in the referred Fig 2, output current from the current transformer (9) is connected to the transducer (10) that generates signal proportional to the input current (i.e. also the leakage current) which is fed to the programmable logic controller (PLC) (11).

The PLC (11) is embodied a programming logic to compare the signal from the transducer with respect to a preset threshold value for the detection of an increase in the leakage current. The increase in leakage current from EAF roof is indications of the roof jam which may lead to the water leakage and the PLC by comparing the signal from the transducer with respect to the preset threshold value initiate a signal to the hooter (12) when the leakage current surpasses a preset threshold value.

The sound from hooter notifies operating personal to clean roof jam to avoid the roof jam related water leakage from the EAF roof. The signal from PLC is also connected to HMI (13) to continuously display the leakage current in the control room. This new system thus facilitates operating personal to take timely decisions to clean roof jam and to avoid subsequent water leakage into the furnace (EAF).

In a typical EAF, arresting of the water leakage generally takes 60 to 120 minutes and this delay directly reduces the productivity of the EAF. With the implementation of present system, the instances of the water leakages in the EAF are reduced from 7 times per month to 1 or zero. This increased the EAF availability and reduced the production delay from average 440 minutes per month to less than 90 minutes per month.