Steel Converter Slag as an Oxygen Carrier-Interaction with Sulfur Dioxide

Steel converter slag, also called Linz-Donawitz (LD) slag, has been considered as an oxygen carrier for biofuel chemical looping applications due to its high availability. In addition to its content of iron which contributes to its oxygen-carrying capacity, LD slag also contains a significant amount of calcium. Calcium, however, is known to interact with sulfur, which may affect the usability of LD slag. To get a better understanding of the interaction between sulfur and LD slag, batch scale experiments have been performed using solid and gaseous fuel with or without sulfur dioxide, together with LD slag as an oxygen carrier. The reactivity and sulfur interaction were compared to the benchmark oxygen carrier ilmenite. Sulfur increases the gasification rate of biofuel char and the conversion of CO for both LD slag and ilmenite. However, no effect of sulfur could be seen on the conversion of the model tar species benzene. The increased gasification rate of char was suspected to originate from both surface-active sulfur and gaseous sulfur, increasing the reactivity and oxygen transfer of the oxygen carrier. Sulfur was partly absorbed into the LD slag particles with calcium, forming CaS and/or CaSO4. This, in turn, blocks the catalytic effect of CaO towards the water gas shift reaction. When the SO2 vapor pressure was decreased, the absorbed sulfur was released as SO2. This indicates that sulfur may be released in loop-seals or in the air reactor in a continuous process.

Automated summary

Steel converter slag, also known as LD slag, is a potential oxygen carrier for biofuel chemical looping. However, the interaction between calcium and sulfur in LD slag may affect its usability. Experimental results show that sulfur increases the gasification rate and CO conversion for both LD slag and ilmenite, but has no effect on the conversion of benzene. Sulfur is partially absorbed into LD slag particles with calcium, forming CaS and/or CaSO4, which inhibits the catalytic effect of CaO on the water gas shift reaction. The absorbed sulfur is released as SO2 when the SO2 vapor pressure is decreased.