Influence of additives on cokemaking from a semi-soft coking coal during microwave heating

Abstract

Coke was produced from a Waterberg semi-soft coking coal using microwave heating and selected microwave susceptors. Waterberg semi-soft coking coal is poorly susceptible to microwave heating, especially below 500°C, and therefore requires microwave susceptors. Susceptors were selected from ferroalloy fines and their respective ores. Various batch experiments were performed on compressed discs utilizing a resonant microwave cavity at a constant 915 MHz frequency to heat a batch of about 5 to 7 kg of the semi-soft coking coal (sscc) to obtain coke. Materials were characterized using Inductive Coupled Plasma (ICP) analysis and coke strength tests. Dielectric property results showed that chrome and manganese ores, as well as their respective high carbon ferrochrome and ferromanganese alloys, are suitable microwave susceptors to enable rapid coke formation during microwave heating. Coke formation was completed within 2 to 3 hours up to 1 100°C compared to 21 hours for a commercial plant since microwave heating reduces the "cold centre" in a coke oven. Obtained coke strengths were slightly lower than for a commercial coke but still of a high quality. It was also shown that the admixture of chrome ore resulted in its partial reduction which will be advantageous to the ferrochrome industry since this method allows for recycling of fines without additional pelletisation. The results also showed that microwave energy has the potential to be employed during commercial coke formation, either on its own or as a hybrid technology. © 2012 ISIJ.