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Upgraded control systems help cut the cost of iron production

28 November 2011

Tata Steel’s Scunthorpe steel plant produces carbon steel by the basic oxygen method. The existing pressurised oxygen plant produced high pressure oxygen at 42 Bar for steel production, but the three operating blast furnaces only require an 11 Bar supply. Producing oxygen at 42 Bar and then reducing it to 11 Bar was not cost-effective which led the company to look for a more efficient solution.

In partnership with BOC, the company built a new medium-pressure oxygen plant on the site, together with a 4.5 km pipeline to serve the three blast furnaces. Each furnace can take up to 20,000 m3/hr of oxygen to enrich its air supply at up to 11% by volume.
 
The three operating blast furnaces each have an individual control system, based on ABB Advant, ABB 800xA and MasterView respectively. These control systems were installed progressively over the lifetime of the furnaces as each was shutdown for maintenance.
Because the blast furnaces already had an ABB AC450 controller, to allow the furnaces to use the medium pressure oxygen supply, they were upgraded/expanded the controllers with new hardware and software and linked by a Modbus serial link to a PLC, which collects data about the operation of the furnaces and provides information management and reports for all three. ABB S800 I/O was also installed for the hardwired signals for each furnace.

The three separate control systems allow the furnaces to work independently on different production cycles. The new medium pressure pipeline feeds the blast furnaces via a three-way valve station. Control of the oxygen flow to each furnace is a complex interplay between the needs of the three units, with each furnace needing to react to the condition and oxygen demand of its counterparts. Pressure line control and flow control are both performed by the controllers.

Developing the system threw up a number of challenges. To develop the software, ABB made use of its software specialists in India who have experience of control systems for the metals industries. Gopal Chopra, ABB project manager, said: “We found during testing on site that some of the EEPROMS needed changing as the new controller was not compatible with the existing system hardware. We have a policy of dealing with any such problems straight way and the customer was able to see that we addressed the issue promptly.”


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