Abstract

Iron & steelmaking and slagging gasification processes utilize carbon feedstock such as coal and petroleum coke (petcoke) in the production of metal, power, and/or chemicals; but they also generate large quantities of greenhouse gases (high in CO2) and slag as by-products. The chemistry of slags, whenever possible, is adjusted to maximize refractory service life.  Other uses for slag beyond refractory service life need to be considered in the future, especially those that may reduce greenhouse gases.  Typical iron & steelmaking slags are rich in calcium oxide while petcoke slags from gasification are rich in trivalent vanadium oxide. This study discusses a potential method to simultaneously use gasification and metallurgical slags to generate gaseous fuels (CO and/or H2) by utilizing strong chemical affinity of calcium oxide to vanadium oxide under certain conditions. If metallurgical and gasification slags were mixed at a specific ratio in the presence of industrial process waste including H2O and CO2, then the calcium would influence valence of vanadium changing from 3+ to 5+, forming calcium orthovanadate (3CaO·V2O5) while converting waste gases to H2 and CO. The vanadate formation is expected to occur by removing oxygen from the surrounding gases, following:

3CaO + V2O3 + 2[(H2O)1-x + (CO2)x] → (CaO)3(V2O5) +  2[(H2)1-x + (CO)x] + excess heat

Excess heat generated from the reaction can be used in other processes such as ore reduction, gas turbine power generation, and synthetic liquid/gaseous fuel production. In the present work, in-situ experiments were conducted using a synthetic slag mixture of calcium rich metallurgical slag and vanadium rich petcoke slag in a CO2 rich environment. Conversion of CO2 to CO rapidly occurred between 1400 °C and 1450 °C with a CO2 conversion rate of 97%. H2 is expected to be generated from H2O using the same mixed slag approach. The final slag volume would decrease to about 30% of the original volume, lightening burden imposed on landfill sites, and would reduce process emissions of CO2.

Thermodynamic computational simulations are discussed to explore optimal conditions for the conversions, including temperature, slag composition, and slag/gas ratios. It was found that appropriate compositions of the slag mixtures needed to maximize the conversion will alter slag chemistry – potentially impacting refractory service life and/or producing a slag of different viscosity.