Moving to sustainability: Improving material flows in the iron casting industry.

摘要

Sustainable engineering solutions were developed to improve the sustainability of the iron casting process. These engineering solutions aimed to modify the material and energy flow in the iron casting industry in a manner that previously wasted energy and resources can be utilized to control the pollution and reduce energy and material cost for the iron foundries.;The first approach was to reclaim the thermal energy from cupola furnace exhaust gas to produce and regenerate porous carbons that could be employed to adsorb the volatile organic compounds from the iron casting process. Saturated porous carbons could further be reused in the green sand mold as the carbon additive. Therefore no extra cost will be posed to the iron casting to remove its VOC emissions. The pore structure developments of different coals under simulated thermal conditions were investigated. The adsorption of typical volatile organic compounds from the iron casting process on the in-situ porous carbons was also studied and compared with a commercial activated carbon from similar precursors.;The second approach was to replace expensive foundry coke by waste anthracite fines. The iron melting process was carefully investigated for the design of the alternative fuel. The thermal energy in the preheat zone of the cupola furnace was employed as free energy to create silicon carbide binding in-situ. The traditional material flow into the cupola furnace was also rearranged to assist the in-situ ceramic binding, minimize the change of chemistry in the cupola furnace, and eliminate the additional cost with silicon additives. Different Si-containing materials tested in this study showed different binding mechanisms at high temperature. Bindered anthracite with silicon powders had the highest post-pyrolysis strength provided by the nanowires generated in-situ at high temperature. The binding strength from the nanowires was further enhanced by decreasing the anthracite grain size which allowed more direct connections of the anthracite particles by individual nanowires. The post-pyrolysis unconfined compressive strength of anthracite pellets (2.86 cm in diameter and 1.875" in length) made from pulverized anthracite fines with 9% silicon powders reached as high as 3.6 Mpa (535 psi). Anthracite pellets made from 50% pulverized anthracite fines and 50% original anthracite fines were only slightly weaker than the anthracite pellets made from 100% pulverized anthracite fines. The nanowires generated between silicon powders and anthracite fines at high temperature are silicon carbide (3C-SiC or beta-SiC) nanowires with highly crystallized face-center cubic zinc-blender structures. These nanowires, which were grown though the vapor-solid mechanism by stacking the (111) lattice plane along the [111] direction, were typically 30--60 nm in the diameter and could grow tens of micrometers in length. In the lab-scale pyrolysis system used in this study, the silicon carbide nanowires started to form at temperature as low as 1100 °C. At 1400 °C the formation of silicon carbide was very fast and finished within 10 minutes. The replacement of foundry coke by waste anthracite fines could save significant amount of energy, greatly reduce carbon dioxide emission, and avoid other pollutions from the coking process.