Disposal and fuel costs are an important competitive factor in the steel industry. Industrial waste management company Diproinduca operates a highly productive recycling plant for waste from blast furnaces on the site of the ArcelorMittal steelworks in Mexico. Festo provided a complete solution spanning several levels of the automation pyramid for the plant.
In Lázaro Cárdenas – strategically important as Mexico’s largest seaport – ArcelorMittal, the world’s biggest steel manufacturer, produces steel slabs using the DRI-EAF method. This production method provides a uniform surface texture and improves the quality of the 3.8 million tonnes of slabs produced each year. An important ingredient in slab production is coke. It provides the required heat in the blast furnace during the production process; however, it must be recycled afterwards.
A slab is an ingot of cast steel, aluminium or copper whose width and length are many times its thickness. Slabs are produced by means of casting and rolling, and are the primary material for sheets and strips. The slab size is adapted to the dimensions of the required product.
One of the by-products of slab production is combustion residues from the blast furnace such as coke breeze and furnace sludge. These can be processed and subsequently returned to the combustion process. That is why the steelworks site is also home to a recycling plant, operated by Diproinduca, where this waste is recycled.
An international company headquartered in Canada, Diproinduca has made a name for itself over the past twenty years in the recycling of waste materials from industrial processes in mining and steel manufacturing. The company has recycling plants in Canada, Mexico, Venezuela and Trinidad. The specialists in recycling industrial waste transform the waste from the steel manufacturing process into briquettes that can be reused in the steelworks’ blast furnace. A crucial element in the production of the briquettes is the accurate mixing ratio for the individual ingredients. Water, cement and selected chemical additives to bind the individual substances are added to the waste.
In Lázaro Cárdenas, precise metering of the individual ingredients is performed by a Festo automation solution. “This is a truly complete solution, where everything from development of the technical concept through to delivery of the control technology was handled by the system solutions engineers from Festo Mexico”, explains Alexander Vargas, Head of Process Automation Product Management at Festo.
The integrated automation system features a weighing system equipped with load cells on the conveyors and on the cement hopper developed especially for the application. Other components include pre-mixer and mixer technology complete with electric motors as well as the metering technology for water and chemical additives together with the necessary pneumatic process valves. The weighing system measures out the exact quantity of waste materials for the specific batch at the raw material hopper. These are then transported to a pre-mixer, where they are homogenised. Next, water, cement and chemical additives are added in the mixer. Once the mixture has the appropriate composition, the mixer is opened and the entire batch is transported to the briquette machine, which shapes the briquettes.
Automated raw material hoppers The weighing system measures out the exact quantity of waste materials for the specific batch.
“The Mexican engineers put all of their expertise in process automation, including all the different levels of the automation pyramid, into developing the complete solution”, explains Vargas, who supervised the project from the start from Festo headquarters, offering expert assistance when requested. At the sensor/actuator level, all the applicable liquid media flows in the plant are controlled by various automated process valves such as the quarter turn actuator DAPS for opening and closing the butterfly valves.
At the field level, three distributed CPX terminals connected via PROFIBUS DP collect the signals from the field instruments. Well-protected in stainless steel control cabinets delivered ready to install, they can even withstand the tropical climate of the Mexican Pacific Coast when installed outdoors.
A CECX-X-C1 used as a PLC at the control level acts as the “brain” of the plant. A SCADA system visualises the various areas and equipment in the plant for the operator. Communication with the PLC and the SCADA system takes place via an Ethernet network. The PLC program together with the SCADA system monitors the entire manufacturing process, which can either be fully automatically or manually controlled. The PLC master in the form of the controller CECX-X-C1 processes the information and passes it on to the SCADA software. Four screen views show the general layout of the plant, parameters, events and reports relating to the plant.
“The Mexican system solutions engineers employed all their automation knowledge throughout all the steps of this project, from technical development through delivery of the control technology to after sales service”, emphasises automation expert Vargas. The integration of automation components from all four levels of the automation pyramid results in highly efficient recycling of coke, which is valuable as a fuel, and in the process helps the environment and improves the productivity of slab production.
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Area of business: Plant construction for industrial recycling
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Area of business: World’s biggest steel manufacturer with steelworks and iron ore mines around the world