Claims:WE CLAIM:
1. An auto changeover system for controlling blast furnace stoves operation comprising
server operatively connected to PLCs of blast furnace stoves for changeover of the blast furnace stoves by automatically and selectively control operational status of the blast furnace stoves in a cyclic manner engaged in generating hot blast temperature in a blast furnace;
communication interface for operatively connecting said server with the PLC of blast furnace stoves and receiving condition based inputs from blast furnace stoves via the PLC.

2. The auto changeover system as claimed in claim 1, wherein the server selectively control operational status of relevant blast furnace stoves to maintain optimum hot blast temperature and efficient fuel consumption.

3. The auto changeover system as claimed in anyone of the claim 1 or 2, wherein the server embodies a control module configured to generate command to the PLCs of the blast furnace stoves for selective control of the operational status of relevant blast furnace stoves based on the condition based inputs from blast furnace stoves and logics.

4. The auto changeover system as claimed in anyone of the claims 1 to 3, wherein the control module generated command to the PLCs of the blast furnace stoves to control operational status of relevant blast furnace stoves in a Heating-Bottle-Blast cycle includes

Gas to Bottle stage wherein said control module generates command based on set value of waste gas temperature/ fixed time elapsed;
Bottle to Blast stage wherein the stove, which is already bottled from Gas, goes for Blast due to generated command with operational time elapsed;
Blast to Bottle stage wherein said control module generates command position feedback of the mixed blast valve in the closing direction; and
Bottle to Gas stage wherein the stove, which was changed from Blast to Bottle, go for heating after operational time elapsed.

5. The auto changeover system as claimed in anyone of the claims 1 to 4, wherein the server is further interfaced with a display interface to display important parameters including current cycle of stove, waste gas temperature, air flow, gas flow, mixed blast valve position and like on a Human Machine Interface (HMI) station provided in control room of the Blast Furnace.

6. The auto changeover system as claimed in anyone of the claims 1 to 5, wherein the control module is configured to interface with PLC application programs of the blast furnace PLC to display of information in the HMI, taking input for auto-changeover including feedback from actual condition from stoves, set points of waste gas temperature, mixed blast valve position and like.

7. The auto changeover system as claimed in anyone of the claims 1 to 6, wherein the control module includes separate modules for individual control of anyone or more operations from taking feedback from individual stove, displaying set points to screen, logic of auto changeover based on the input values, generation of alarm during changeover and like.

8. The auto changeover system as claimed in anyone of the claims 1 to 7, further includes Ethernet network based safety modules for critical operations as well as monitoring applications.

9. The auto changeover system as claimed in anyone of the claims 1 to 7, wherein the server includes alarm annunciation means configured activate during fault and blast furnace stove change-over operation for operator awareness
, Description:FIELD OF THE INVENTION:
The present invention relates to controlling operation of blast furnace stoves. More specifically, the present invention is directed to an auto changeover system for blast furnace stoves which can automatically control stove operation for conventional Blast Furnaces of an integrated steel plant.

BACKGROUND OF THE INVENTION:
In an integrated steel plant, multiple Blast Furnaces are used to generate hot blast temperature around 8500C based upon refractory condition of the stoves. The hot blast temperature is a vital parameter that controls the reduction process and BF coke rate. The Blast Furnaces are normally operate in a cyclic order, wherein a stove tender (operator) manually initiate the stove operation through switches of a PLC based electro-hydraulic operation
The opening and closing of relevant stove valves during heating or blast cycle takes place with instrumentation and electrical interlocks. Average blast cycle is 1 hr 30 min and after this period, the stove operator, by noticing the HBT value from mixed blast valve closing position and computer HMI, has to initiate the switch for change over of the stoves. First, another stove is taken into blast and secondly, he bottles the stove which was in the blast to maintain steady blast temperature. But sometimes, it is observed being engaged in cast house operation like mud gun, drill machine and casting etc., stove operator normally makes a delay in changing stoves to the tune of 15-30 min. This adversely affects the furnace reduction process and result in increase of coke rate.
Normally, the heating cycle of a stove is 2 to 2 hr 20 min with the help of air-gas ratio combustion controller. Stove is heated with air and BF gas. Air is drawn by ID fan driven by a motor (110 kW, 975 rpm, squirrel cage induction motor). During the heating process, when the waste gas reaches 350 0C or the set value, through instrumentation controller interlock, BF gas stops. Noticing that, the stove operator should immediately bottle the stove. Suppose, there is a 20 min delay in a change over by the operator, due to reason mentioned earlier, BF gas is stopped but air fan motor will continue to supply air, which results in cooling of stoves. Due to that, dome temperature falls by significant extent. It results in wastage of thermal energy. Again, additional heating will be required which consumes extra BF gas which only optimally available from gas grid for the stove heating.
It is thus there has been a need for developing a new system which can automatically interchange blast furnace stoves operational status during heating or blast cycles without involving any human/operator interventions.

OBJECT OF THE INVENTION:
It thus the basic object of the present invention is to develop an automatic changeover system which would be adapted to automatically interchange blast furnace stoves operational status during heating or blast cycles in a blast furnace of an integrated steel plant without involving any human/operator interventions.

Another object of the present invention is to develop an automatic changeover system which would be adapted to automatically control changeover blast furnace stoves operational status to maintain optimum hot blast temperature and efficient fuel consumption in a blast furnace of an integrated steel plant.

Yet another object of the present invention is to develop an automatic changeover system which would be adapted to implement a new scheme of air and gas combustion control during stove heating for substantial electric energy saving.

SUMMARY OF THE INVENTION:
Thus according to the basic aspect of the present invention, there is provided an auto changeover system for controlling blast furnace stoves operation comprising
server operatively connected to PLCs of blast furnace stoves for changeover of the blast furnace stoves by automatically and selectively control operational status of relevant blast furnace stoves in a cyclic manner engaged in generating hot blast temperature in a blast furnace;
communication interface for operatively connecting said server with the PLC of blast furnace stoves and receiving condition based inputs from blast furnace stoves via the PLC.

In a preferred embodiment of the present auto changeover system, the server selectively control operational status of relevant blast furnace stoves to maintain optimum hot blast temperature and efficient fuel consumption.

In an embodiment of the present auto changeover system, the server embodies a control module configured to generate command to the PLCs of the blast furnace stoves for selective control of the operational status of relevant blast furnace stoves based on the condition based inputs from blast furnace stoves and logics.

In an embodiment of the present auto changeover system, the control module generated command to the PLCs of the blast furnace stoves to control operational status of relevant blast furnace stoves in a Heating-Bottle-Blast cycle includes
Gas to Bottle stage wherein said control module generates command based on set value of waste gas temperature/ fixed time elapsed;
Bottle to Blast stage wherein the stove, which is already bottled from Gas, goes for Blast due to generated command with operational time elapsed;
Blast to Bottle stage wherein said control module generates command position feedback of the mixed blast valve in the closing direction; and
Bottle to Gas stage wherein the stove, which was changed from Blast to Bottle, go for heating after operational time elapsed.

In an embodiment of the present auto changeover system, the server is further interfaced with a display interface to display important parameters including current cycle of stove, waste gas temperature, air flow, gas flow, mixed blast valve position and like on a Human Machine Interface (HMI) station provided in control room of the Blast Furnace.

In an embodiment of the present auto changeover system, the control module is configured to interface with PLC application programs of the blast furnace PLC to display of information in the HMI, taking input for auto-changeover including feedback from actual condition from stoves, set points of waste gas temperature, mixed blast valve position and like.

In an embodiment of the present auto changeover system, the control module includes separate modules for individual control of anyone or more operations from taking feedback from individual stove, displaying set points to screen, logic of auto changeover based on the input values, generation of alarm during changeover and like.

A preferred embodiment of the present auto changeover system further includes Ethernet network based safety modules for critical operations as well as monitoring applications.

In an embodiment of the present auto changeover system, the server includes alarm annunciation means configured activate during fault and blast furnace stove change-over operation for operator awareness.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 shows heating cycle of the stoves in a typical Blast Furnace.
Figure 2 shows Control Desk of present auto changeover system showing the status of valves (close/ open) & the HMI of Auto changeover system for display of various important parameters of stoves along with the current cycle of operation.

DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS:
In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and illustrate the best mode presently contemplated for carrying out the invention. In the present invention, a fully automatic server based auto changeover system for automatically control operational status of the blast furnace stoves in a Heating-Bottle-Blast cycle by commanding PLC of the blast furnace stoves has been implemented. Also, the present invention discloses a new scheme of air and gas combustion control during stove heating with the help of VFD drive for substantial electric energy saving.
The present auto changeover system includes server embodying control module operatively connected to PLC of blast furnace stoves through communication interface to command the PLC of the blast furnace stoves based upon logics, without switch initiation by stove operator. The server generates output command and forward the same to the PLC, taking condition based inputs from instrument panel/DCS via PLC panel through relevant communication interface.
Based on the predefined conditions, the changeover of the Blast furnace stoves operations in the Heating-Bottle-Blast cycle is being carried out. This further ensures the efficiency of blast furnace operation by maintaining optimum hot blast temperature and help in efficient fuel consumption.
The control module which is embedded in the server generates the command for auto change in four sequential stages viz. (i) Gas to Bottle, (ii) Bottle to Blast, (iii) Blast to Bottle, and (iv) Bottle to Gas based on the pre-defined logic etc. In the Gas to Bottle, the control module generates command based on set value of waste gas temperature/ fixed time elapsed. In the Bottle to Blast, the stove, which is already bottled from Gas, goes for Blast due to generated command with operational time elapsed. In the subsequent Blast to Bottle stage, the control module generates command the position feedback of the mixed blast valve in the closing direction. Finally in the Bottle to Gas stage, the stove, which was changed from Blast to Bottle, go for heating after operational time elapsed.
In order to provide the stove operator a better view of the ongoing blast furnace stove conditions the server may be interfaced with a display interface which display important parameters like current cycle of stove, waste gas temperature, air flow, gas flow, mixed blast valve position etc. on a Human Machine Interface (HMI) station provided in the Control Room of the Blast Furnace. The present system also comprises Auto/ Manual change over switch provided on the control desk for operators to switch between auto and manual modes thereby giving the flexibility to the operator to change mode of stove operation based on the need.
The control module is also configured to interface with PLC application programs to display of information in the HMI, taking input for auto-changeover like feedback from actual condition from stoves which include set points of waste gas temperature, mixed blast valve position and like.
In the present invention, the control module is configured or developed in modular manner wherein separate modules are developed for individual control of various operations like taking feedback from individual stove, displaying set points to screen, logic of auto changeover based on the input values, generation of alarm during changeover etc. PLC software gives the status of the stoves along with various other parameters, which in turn displayed at the HMI. In addition to the PLC application program, HMI screens (one of the HMI Screen shown in Fig. 2) are designed and software developed for monitoring the process status.
The server computer of the present invention and the PLC based control enable easy and reliable implementation of auto changeover algorithm. The new control scheme further established so that an Ethernet network based module could be successfully implemented for critical operations as well as monitoring applications provided the design is robust and all safety interlocks are considered. The server computer also includes alarm annunciation facility during fault and hooter ringing during change-over operation for operator awareness.
Extensive trials were carried out off-line as well as on-line during stove operation. Each and every mechanism, where interlocks are used, required lot of trials so that the new system runs trouble free and safely.
The implemented system yields benefits are as follows:
• It maintains stable hot blast temperature by arresting 15-20 oC loss of HBT. This helps in reduction of coke rate and stabilizing the thermal regime of the furnace
• It reduces the thermal energy wastage at stoves by optimizing the heating cycle and also making optimum use of BF gas
• Delay of stove change over by operator is avoided
• Efficient utilization of manpower

Similar schemes can be implemented in stoves of various conventional blast furnaces of any integrated steel plant. The new system will have distinct advantages over the manual changeover mechanism with respect to ease of operation, maintaining stable hot blast temperature, reduction in thermal energy waste, arresting delay in stove changeover by minimizing manual intervention and maintainability. The chances of unintentional errors will be less and any change in operation logic will be easy to implement through soft logic. Moreover the user interface supports dynamic editing of set values based on the stove conditions.