Study of the influence of various types of biofuels on the raw pellets strength in the production of iron ore pellets

Abstract

Purpose. One of the ways to reduce CO2 emissions from pelletized iron ore production is to use biofuels, which also save more expensive fossil fuels. A particularly cost-effective effect is achieved when biofuels are used in pellet firing, which reduces natural gas consumption. Pellets with the addition of biofuels must meet the minimum requirements for mechanical strength in the wet and dry state for the possibility of further heat treatment, and in the annealed steel - for the possibility of using a blast furnace. The paper considers the peculiarities of using biofuels as solid fuels in the charge for pellet production. The purpose of this study is to determine the possibility of using sunflower husk, wheat straw, wood, and charcoal as solid fuels in pellet charge, namely to determine the effect of adding biofuels on the strength of raw and dry pellets. Methodology. Four types of plant-based fuels were selected for the study: sunflower husk, wheat straw, wood, and charcoal. To investigate the possibility of using plant-based fuels in pellet firing, a charge of the following composition was prepared: iron ore concentrate, bentonite, and one of the four types of plant-based fuels under study. The consumption of each biofuel ranged from 0 to 1 %. To reduce the influence of the shape, size, and molding conditions, cylindrical briquettes of the same size were formed from each of the obtained charge samples. The briquettes were formed on a hydraulic press with a force that corresponds to pelletizing pellets on industrial pelletizers. Findings. It has been found that the addition of straw causes a significant decrease in pellet strength, which can be explained by the fact that wheat straw has a high concentration of hydrophobic waxes on its surface. These waxes form a hydrophobic layer consisting of a corner coating and wax particles. The hydrophobic waxes create boundaries between the straw particles, which leads to a decrease in pellet strength. The best strength characteristics of wet and dry pellets are achieved when sunflower husk is added. When analyzing the properties of sunflower husk, it can be seen that sunflower husk has a lower lignin content compared to woody biomass. Lignin provides a hydrophobic surface that prevents moisture from interacting with cellulose. Instead, the cellulose and hemicellulose content of sunflower husk can generally exceed 80%. Cellulose and hemicellulose contain a significant amount of hydroxyl OH groups, which are hydrophilic groups and can increase the water retention capacity of raw pellets. Charcoal has carbon as its main component, so, like coke and hard coal, it is less wettable with water than iron ore materials and reduces the strength of raw pellets. Originality. The mechanism of influence of different types of biomaterials on the strength of raw pellets has been established. The relationship between the composition of the surface layers of biofuels and the possibility of their use in pelletizing iron ore pellets was determined. Practical value. From the results obtained in the work, it was determined that sunflower husk can be used as a fuel for pelletizing in an amount of up to 0.5% by introducing it into the charge for the production of pellets. The use of other types of biofuels considered in the study requires their preliminary preparation.