João Batista Ferreira Neto

An analysis of Brazilian sugarcane bagasse ash behavior under thermal gasification

BackgroundAshes from sugarcane were analyzed by X-ray fluorescence, ash content, X-ray diffraction, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). FactSage 6.4 database software was used to estimate viscosity at high temperatures (900 - 1550°C) of them.ResultsThe results showed that although ashes from sugarcane bagasse contain silica, most of its SiO2 is from soil contamination. Higher and lower silica samples treated at 1350°C for 20 minutes showed that the fine portion of fraction of the ashes melted at this temperature.ConclusionsThe melting phase could act as sticking flux for the coarse silica particles on the gasifier bottom wall, which could compromise the gasification process.Graphical Abstract(a) Nanoparticles of SiO2 absorbed by sugarcane bagasse, (b) microparticle of SiO2 in the fibers of bagasse after processed in the mill, and (c) particles of SiO2 from the soil not melted, and glass phase formed by the reaction of nano SiO2 and other nutrients elements of the plant such as K, Na, Ca, P, and Fe at 1350 oC/20 min.

Silicon refining by a metallurgical processing route

Directional solidification experiments were carried out in a Bridgman furnace to remove carbon and metallic impurities from silicon. For carbon removal, solidification was achieved by extracting the mold from the hot into the cold zone of the furnace, while for the removal of metallic impurities, solidification occurred by cooling the furnace with a motionless mold. In the experiments of carbon removal, a mold extraction rate of 5 µm/s results in an ingot with columnar grain structure aligned in the ingot axial direction and a macrosegregation of carbon and SiC particles to the ingot top regions. However, at a mold extraction rate of 80 µm/s, the grain structure consisted of columnar grains aligned in the radial direction and SiC particles were observed throughout the ingot, showing lower macrosegregation with a carbon concentration still larger at the ingot top. In the metallic impurities removal experiment, an ingot with a columnar grain structure aligned in the ingot axial direction was obtained and the concentration profiles showed significant metallic impurities macrosegregation to the ingot top.

SOLIDIFICATION OF BOF SLAGS MODIFIED BY PYROMETALURGY AND SUBMITTED AT DIFFERENT COOLING RATES

In a scenario of blast furnace slag shortage, the use of BOF slag (Blast Oxygen Furnace) as a partial substitute in cement production is a low cost alternative. In this paper, BOF (Blast Oxygen Furnace) slag samples were melted in an experimental electric arc furnace (EAF), with different modifiers materials (Al top dross reject, slag from FeSi iron alloy production, et al.) with different rates of additions, subject to differentiated cooling in specifically designed experimental apparatus. The objective was to search the formation of different phases formed during a process of BOF slag modification, for different materials additions containing Al2O3 and SiO2 and subjected to different cooling conditions. Modified slags, with basicity (CaO/SiO2) below 1.1 and Al2O3 contents less than 5%, subjected to cooling rates up to 21°C/s, favor the formation of crystalline phases; no amorphous phases were detected in this trial. Modified slag tests with basicity below 1.2 and Al2O3 content between 10.0% and 12.5% favor both the formation of crystalline (majority) and amorphous phases (between 25% and 30%). The influence of the cooling rate up to 21°C/s on amorphous phase formation in this trial was not conclusive.

Modification of BOF Slag for Cement Manufacturing

The use of metallurgical slags in cement manufacturing depends on the phases that compose such slags, which are affected by changes in slag chemical composition as well as by cooling rates adopted during solidification. Two different slags were produced in a pilot scale metallurgical reactor by mixing additives into 300 kg of re-melted BOF slag followed by natural cooling or by adding of steel balls to it. Quantitative XRD, SEM and Raman analysis of slag samples revealed the relationship among cooling conditions and crystalline phases.

Treatment of Molten Steel Slag for Cement Application

Steel slag can be an alternative in cement mineral admixture, partially as a substitute for blast furnace slag. A pyrometallugical process has been investigated to promote the chemical composition modification of molten steelmaking slag in a metallurgical reactor. Experiments were conducted by remelting 300 kg of steel slag followed by chemical modification of liquid slag. The modified slags were naturally cooled in the metallurgical reactor or cooled by steel balls. XRD and SEM analysis of slag samples revealed the relationship among chemical composition, cooling conditions and amorphous and crystalline phases. Cement samples were produced by mixing 25% of treated steelmaking slag with 75% of Portland cement, resulting in more than 280 J/g of accumulated hydration heat in 72 h, expansion lower than 0,1% in the autoclave tests and compressive strength higher than 42 MPa after 28 days. The process indicates potential to be applied as a steelmaking slag treatment.