Sridhar Seetharaman

Characteristics of low temperature biomass gasification and syngas release behavior using hot slag

This study proposes an emerging method to prepare syngas using integrated low temperature biomass gasification combined with heat recovery from hot slag. A series of non-isothermal and isothermal gasification experiments were performed in the temperature range of 250–500 °C to determine the effect of the presence of slag on gasification. The results showed that the addition of slag remarkably increased the production of syngas in the temperature range of 425–500 °C and during the gasification at 450 °C, with a mass ratio of wheat straw to slag of 1 : 1, syngas with 0.149 L CO, 0.036 L H2 and 0.069 L CH4 can be produced per gram of wheat straw. The kinetic mechanism of biomass gasification changed from an Avrami–Erofeev model to a three-dimensional diffusion model with the addition of slag. Although the presence of slag altered the mechanism of gasification, it did not lower the degree of gasification, and therefore the waste heat from the hot slag can be used to produce syngas. Therefore, an industrial prototype plant composed of multiple systems was proposed, through which an energy saving equivalent to 19.1 million tons of standard coal and an emission reduction of 69.9 million tons of CO2 emission would be achieved in China.

Detection of Non-metallic Inclusions in Centrifugal Continuous Casting Steel Billets

In the current study, automated particle analysis was employed to detect non-metallic inclusions in steel during a centrifugal continuous casting process of a high-strength low alloy steel. The morphology, composition, size, area fraction, amount, and spatial distribution of inclusions in steel were obtained. Etching experiment was performed to reveal the dendrite structure of the billet and to discuss the effect of centrifugal force on the distribution of oxide inclusions in the final solidified steel by comparing the solidification velocity with the critical velocity reported in literature. It was found that the amount of inclusions was highest in samples from the tundish (~250 per mm2), followed by samples from the mold (~200 per mm2), and lowest in billet samples (~86 per mm2). In all samples, over 90 pct of the inclusions were smaller than 2μm. In steel billets, the content of oxides, dual-phase oxide–sulfides, and sulfides in inclusions were found to be 10, 30, and 60 pct, respectively. The dual-phase inclusions were oxides with sulfides precipitated on the outer surface. Oxide inclusions consisted of high Al2O3 and high MnO which were solid at the molten steel temperature, implying that the calcium treatment was insufficient. Small oxide inclusions very uniformly distributed on the cross section of the billet, while there were more sulfide inclusions showing a banded structure at the outside 25 mm layer of the billet. The calculated solidification velocity was higher than the upper limit at which inclusions were entrapped by the solidifying front, revealing that for oxide inclusions smaller than 8μm in this study, the centrifugal force had little influence on its final distribution in billets. Instead, oxide inclusions were rapidly entrapped by solidifying front.