Blast furnace model for optimal charge distribution
The charging of a blast furnace
Using the scatter model we can control the gas flow in the blast furnace. Good control of the gas flow in the blast furnace ensures greater productivity and a longer life span of the installation.
Figure 1: a blast furnace is charged with layers of coke and layers of sinter
The blast furnace is charged at the top with alternate layers of coke and sinter. Hot air is blown in at the bottom of the blower openings. This incinerates the coke. The resulting CO gas rises and works its way through the layers of coke and sinter to the top of the blast furnace. The close contact of the hot CO gas with the sinter reduces the iron oxide in the sinter to iron, heats it up and melts it. The liquid hot metal is collected at the bottom of the blast furnace and drawn off.
The gas is the driving force of the blast furnace process. We therefore tightly control the gas flow through the layers, and adjust it if necessary. To ensure this, most modern blast furnaces also have a complex Paul Wurth charging installation.
The Paul-Wurth charger
Figure 2: schematic depiction of a Paul Wurth charging installation
With this charging installation the material is brought to the top of the blast furnace using a charging car in two feed bunkers . The material is then dumped by a rotating chute in the blast furnace.
Figure 3: the Paul Wurth rotating chute
The angle at which this rotating chute deposits the material is adjustable. Figure 4 shows three possible positions of the rotating chute. Changing this angle also changes the shape of the material layers.
Controlling the gas flow
Figure 4: changing the angle of the rotating chute allows the shape of the material layers to be controlled
Changing the shape of the material layers allows us to send the gas in a certain direction. Indeed, coke consists of larger pieces than sinter. The gas encounters much less resistance from a layer of coke than from a layer of sinter. When we want a lot of gas in a certain place in the blast furnace, it is sufficient to dump more coke than sinter. In places where we want less gas, we make the layers of sinter somewhat thicker. In this way, we keep the gas flow well under control.
Model for charge distribution
We can also influence the gas flow by means of segregation. As soon as the material is deposited, it rolls further down the mound and the larger pieces are automatically separated from the smaller ones (segregation). The smaller pieces are inclined to remain in the place where they first fell into the blast furnace, while the larger pieces roll further to the middle.
Because the larger pieces offer less resistance to the gas, they again help us to send the gas in a certain direction.
The working of the blast furnace is very sensitive to small changes to the shape of the layers, the so-called charge distribution. So, at ArcelorMittal Gent we developed a model that helps the blast furnace operator to choose the best charge distribution in all conditions. The model takes account of the diameters of the deposited material, of the separation of the different diameter fractions during the charging of the blast furnace (segregation), and obviously the shape of the layers themselves. The model also immediately calculates the gas flow resistance, and how it varies across the radius of the blast furnace.
Figure 5: the interface of the model for charge distribution
When calculating the shape of the layers, we obviously also take account of the physical laws: conservation of energy, friction with the rolling down of material or the influence of the gas flow on the rolling down of material. For a number of points we do, however, rely on measurements during a maintenance shut-down.