Unisoma implements a Production Planning Optimization tool for CST’s sinter and blast furnace unit
With the support of AIMMS’ robust and flexible platform, Unisoma was able to develop the SISCAF system in less than a year. SISCAF is the Raw Material Mix Optimization System for Sintering Plant and Blast Furnaces at CST.
The steel production comprises one of the most important basic industrial activities in the world today. China has accomplished an industrialization effort, which has been giving rise to adaptations in the industries of many countries, in particular, in the Brazilian steel production.
The steel production process can be visualized along some phases, which involve the preparation of some intermediate products such as hot metal, sinter, pellets, briquette, coke, pulverized coal and many others. At CST, the management of these materials is accomplished in different areas such as the Coke Plant, Sinter Plant, Blast Furnaces, Storage Yards and supply lines.
CST produces pig iron, and the associated slag, in blast furnaces using raw materials such as iron ore, pellets, sinter, scrap, fluxes, coal, and lime. A homogeneous stack of mineral ore is processed, using complete train cargoes from CRVD (Companhia do Vale do Rio Doce), the sole mineral ore supplier to CST. These raw materials are classified according to granularity. Thin ores are transformed into pellets and supplied by CRVD. Medium size ores are transformed into sinter at CST, and thicker ores are fed directly to the blast furnaces.
Internal discussions were made involving personnel from Sinter Plant/Blast Furnaces (Technical & Commercial Division), with a view to gather the needs for SISCAF. One important topic was the construction of a third Blast Furnace; how to plan the buy and stock of the required new mix of raw materials and how to deal with the new offers of coke, anthracite and pulverized coals with changes mainly caused by China. Are the new operational conditions reaching the emission limit of sulfur on the environment? Is it worth to improve the quality of sinter using more costly lime expecting a possible cost reduction of pig iron? Is it using the right amount of quartz in pig iron production?
CST, an Arcelor Brasil S.A. Company (an Arcelor Mittal subsidiary) is a world leader in the steel slab market, responsible for 20% of worldwide sales volume, and is one of the largest companies in Brazil. Strategically located in the city of Vitória, the capital of Espírito Santos State, in eastern Brazil, CST has established itself as a supplier of high-quality semi-finished steel products (slabs and hot-rolled coils) for the automotive industry.
The motivation for the project was to develop and implement a system capable of simulating various charging scenarios, integrating the Burden Calculations of the Sinter Plant & Blast Furnaces.
Internal discussions were made involving personnel from Sinter Plant/Blast Furnaces (Technical & Commercial Division), with a view to gather the needs for the model.
The project developed by Unisoma involves the integrated planning of raw material preparation, sintering, and operations at the blast furnaces. An optimization model, implemented in AIMMS using a customized heuristic that sequentially solves basic MILP (mixed integer linear programming) and NLP (nonlinear programming) sub-problems, determines the quantities of raw material inputs for the production of pig iron. Nonlinear constraints are included in the model in order to compute the fuel mix for the sintering plant and for the blast furnaces, as well as the distribution of sinter among the blast furnaces. Integer variables were included in order to represent whole train cargoes of mineral ore and the use made of pulverized coal injection.
To support CST’s planning process, Unisoma developed SISCAF, an AIMMS-based system. This system has been developed always aiming to minimize the burden cost and simultaneously fulfilling the:
- Quality Requirements of the Sinter Plant & BF;
- Environmental Conditions;
- Process and Productivity Conditions.
We also tried to optimize the application through:
- Interface with CST’s Database and Coke Plant Optimization System;
- Interface with the user;
- Comparative between cases;
- Various Applications/Standardization.
The results may be used in the decision-making to:
- Purchase raw materials;
- Change the fusion bed;
- Assess environmental impacts;
- Assess future scenarios.
This system allows for a simple and effective utilization, facilitating the undertaking of comparative analysis, even inputting utilities data. It makes available in one single tool, information for burden planning aiming to minimize the cost of hot metal, also respecting the quality requirements, process and the environment.
How did AIMMS add value?
The robust environment provided by AIMMS allowed us to develop a set of integrated mathematical programming models. Different sequences of model calls were implemented for various complex objective functions. AIMMS’ graphical interfaces were very helpful to compose several sophisticated pages with results.
“SISCAF is an integrated system that has been used for CST’s technical and purchase staff to evaluate new sources of raw materials, new scenarios of production and prices, optimizing the burden costs and supporting the decision of the company, maintaining the quality of the products with low variability”.
Raw Material Purchase Executive at the
Iron Making Department of CST
Eduardo M. Milanez, Unisoma