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Tata Steel has cut the cost of iron production at its Scunthorpe plant by using medium-pressure oxygen in blast furnaces. Control systems developed and put in place by ABB have enabled the move.
The plant produces carbon steel by the basic oxygen method. Until now, a pressurised oxygen plant produced high-pressure oxygen at 42bar that was later reduced to 11bar and supplied to the site's three blast furnaces. Lowering the pressure of the oxygen was not cost-effective, so the company looked for another solution.
In partnership with BOC, Tata Steel built a new medium-pressure oxygen plant on site and a 4.5km pipeline to supply the three blast furnaces. Each furnace can take up to 20,000m3 per hour of oxygen to enrich its air supply at up to 11% by volume.
The blast furnaces have different control systems that have been installed progressively over their lifetimes during shutdown maintenance. But all use or part use a common controller, the ABB Master AC450.
ABB upgraded and expanded the AC450 controller with new hardware and software to enable the furnaces to use medium-pressure gas. The company installed a Modbus serial link to connect the three controllers to a PLC, which collects data about the operation of the furnaces, and provides information and reports for management.
ABB project manager Gopal Chopra says: “We also installed ABB S800 I/Os for the hard-wired signals for each furnace.”
The controllers keep pressure line and flow in check. The three separate control systems allow the furnaces to work independently on different production cycles. The new pipeline feeds the medium-pressure oxygen to the blast furnaces via a three-way valve station.
Controlling the oxygen flow to each furnace is a complex interplay between the needs of the three units. Each furnace must be able to react to the condition and oxygen demand of its counterparts.
Ian Render, project engineer with Tata Steel, says: “The result is a control system that allows us to make use of a lower-cost oxygen supply route. Overall, the project has been a big success.”
The project was undertaken as part of ABB’s Evolution programme, under which the company provides software updates following the initial installation.