Pelletizing is the industrial process of transforming iron ore fines into spherical pellets. They are formed by agglomeration and gain mechanical strength after firing and sintering in ovens at high temperatures. These linear ovens are of great length and have more than 40 natural gas or liquid fuel burners. The pellet format is used in blast furnaces for the production of steel in steel mills or in direct reduction systems for the production of iron. The stacking of pellets in the blast furnace allows air circulation between the free spaces and must have a mechanical resistance to support the weight of the upper layers. In the pelletizing furnaces there are drying, pre-burning, burning, post-burning and cooling regions. The duration of each step, given by the speed of the grid cars, and the temperature to which the pellets are subjected have a strong influence on the quality of the pellet. That is why it is important to study the combustion processes and temperatures throughout the furnace and their distribution within each car.
The emissions of CO, CO2, NOx and SOx produced by burning fuels and pellets are also of interest. All companies are interested in reducing their environmental footprint, operating within the restrictions of legislation and having the least impact on the environment. For this they study different types of fuels and design different types of burners. Generally, the improvement in emissions is accompanied by an increase in the efficiency of parts of the process. It is an opportunity to rethink your current equipment and burner design to improve your operation. For this it is interesting to have the support of ATS for research and development to design innovative equipment with the lowest possible operational or experimental cost. ATS uses simulation with CFD++ to reduce prototype testing and fabrication costs as it is able to build an accurate digital twin of the plant's combustion process.
ATS has developed a long-term work for Samarco to understand the physical processes of its pellet furnaces. Furnaces 1,2,3 and the newest 4 were worked on. Various parts of the furnace were simulated as combustion chambers and cooling zone, including the fan air supply manifold. The aerodynamics of the combustion chamber and the burners were studied in a study on natural gas flame deflection, which was generating a deposit of molten material and an increase in the furnace maintenance rate. Cooling zone wall temperatures were also studied to verify the type of refractory material and operational limits. Finally, the flow rates and speeds of each car in the burning and cooling zone were studied to verify the homogeneity and the consequence for the quality of the product. The flow distribution of the cooling zone air distribution manifold was also studied. Finally, an erosion analysis was carried out at the points of highest velocity near the walls of the cooling zone. These analyzes used Metacomp Technologies' CFD++ software.
Also for Samarco's pelletizing furnaces, an analysis of the deposit of particles in expansion joints was carried out in some air pipes. The oven air, after passing through the grid cars, has small particles of iron oxide. These particles can impinge on surfaces or walls, but they can also be deposited in curves or cavities. ATS performed the simulations to approve a new expansion joint project made by AGE Engenharia.
For Vale, a new type of burner was studied, with low NOx nitrogen oxide emission technology (called Low Nox) for its pellet furnaces. More than fifteen configurations and design options were studied before the prototype was made. An ideal configuration was found through the application of the CFD++ tool considering a chemical kinetic model of combustion and thermal NOx generation. ATS specified and ordered a stand for measuring pressure, temperature and flow. It was made especially for the test that was carried out in Vale's real oven in Vitória. This was a three-year research and development work and had great success and results for the customer, who developed a low-cost solution, with little testing and with the manufacture of only one prototype. With the project carried out by ATS, Vale will be able to specify burners and modes of operation to reduce NOx emissions.
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