Coke Oven By- Products
Coking is a process of heating the coal, resulting in a solid, porous, and carbonized residue, together with the evolution of a certain number of volatile products that escape the coking chamber.
In the coke ovens, the burden is heated in completely sealed chambers, except for the outlets for the volatile products. These coking chambers are elongated, heated by the fuel gas burning in channels or ducts set up on the silica brick walls, which separate one another. At ArcelorMittal Tubarão, these chambers are grouped in 3 batteries (totaling 147 furnaces), for a higher economy of heat energy and space.
The coal, when charged into the coking chamber, suffers a decomposition of its most complex molecules, by releasing the simpler and volatile compounds, and forming the carbonized residue: the coke. The gases released are mainly comprised of water vapor, light tar components, in addition to coal dust.
Most of these gases that are released during the heating process pass through the already formed coke, towards the heated walls of the coking chamber. The vertical flue pipes carry the heated gases from the coke oven individual chambers up to the common main collecting pipe. This gas is sucked by the exhausters through the collectors and primary coolers, where it is cooled at a temperature lower than 35ºC.
This gas contains a certain amount of tar (dragged or in vapor shape). During this cooling process, the tar is precipitated in tanks, through particles of coal that become sediments on the bottom of the tank. This mixture of tar and coal is taken out through the bottom and is called coal tar sludge. Then it is reutilized by mixing it with the coal that enters the coke oven, thus saving on the costs of imported coal. The rest of the tar that remains in the tank, which is already separated from the coal, is called Coal Tar. ArcelorMittal Tubarão commercializes it because of its economical value in the market, due to many products that are originated from its distillation.
By continuing the process, the coking is completed on an average between 17 and 18 hours. The doors are taken off, the drawing machine is put in place and, on the other side of the battery, the coke sledge car and the coke-oven charging car take their positions on their tracks. The drawing machine is a mobile structure that guides the pusher, which consists of a heavy beam of steel, with an edge section very similar to the one of the discharge door, which forces the coke out of the chamber. The coke sledge car performs the role of extending the walls of the coking chamber by being placed in front of the blast furnace door, thus reducing to a maximum level the loss of coke that is poured.
While the coke is being withdrawn from the furnace, there is a great production of dust that is collected by exhausters and put into silos. The coke-oven charging car collects the coke withdrawn from the furnace and travels to the CDQ tower (Coke Dry Quenching), where the bucket with incandescent coke is taken by a crane and is lifted to the top of the cooling chamber and then is dumped into it. As soon as it is dumped into the chamber, the incandescent coke is thrown against the flow of inert gas (Nitrogen - N2), and then cooled. That gas comes out of the chamber already heated (between 700 and 800 ºC) and carries with it the dusts produced in the process. This gas passes through a cooling process in order to be reutilized, and the dusts are separated and put into silos. Both the dusts that come up during the withdrawing process and the ones that arise during drying, have the same characteristics. This dust is called: CDQ Dust and is commercialized by ArcelorMittal Tubarão because of its applications such as, Soderberg paste and
foaming slag.
After being cooled, this coke is screened and classified according to ArcelorMittal Tubarão internal requirements. The blast furnace is its most important final destination. Part of the coke ranging from 0 to 25 mm (fine coke) is sent to an outside plant, where it undergoes a grinding and screening process in order to produce coke ranging from 4 to 7 mm and from 7 to 9 mm, which is used as recarburizer at ArcelorMittal Tubarão steelmaking plant.
However, there is also the production of coke ranging from 0 to 4mm, which is called Recarburizing Dust, and is also commercialized by ArcelorMittal Tubarão.
Siderúrgica produtora de placas de aço, aços planos, bobinas e laminados a quente.
