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.

Factors affecting the microwave coking of coals and the implications on microwave cavity design

“…Coetzer and Rossouw have used microwave treatment to produce high quality cokes from a Waterberg semi-soft coking coal in 2 -3 hours using microwave receptors to heat the coal indirectly [24]. However, according to the theory presented above, some or even all coals could be heated to coking temperatures without the addition of microwave receptors.…”

Formation of Metallurgical Coke within Minutes through Coal Densification and Microwave Energy

“…Similar studies have not demonstrated such rapid coking potential. Coetzer and Rossouw 24 produced lump coke from a semi-soft coking coal with microwave susceptors over a period of 2-3 hours, while…”

“…8,20 Several studies have used susceptors to increase the microwave absorbance of coal. [21][22][23][24] However, Lester et al 8 and Binner et al 20 showed that it is possible to produce coke with a similar vitrinite reflectance to that of conventional cokes without the use of susceptors, although the cokes formed were only in powdered form. The physical structure of coke is a key feature of blast furnace operation, 25 as it provides the bed support and permeability for the liquid phase drainage and upward flow of blast furnace gases.…”

Dynamic Dielectric Properties of a Wood Liquefaction System Using Polyethylene Glycol and Glycerol

“…It has been reported that large values of ε′ and ε″ will result in surface heating and low penetration depth. 33,34 At the initial liquefaction stage, most liquefaction solvent was not able to penetrate into wood particles and remained "free" in the system. Therefore, the liquefaction system had high ε′ and ε″ values close to that of the liquefaction solvent.…”

“…It was observed that the range of temperatures for the higher penetration depths overlapped with the range of temperatures for the phase transition in the liquefaction system, specifically when the liquid/solid mixture transformed into a viscous liquid between 90 to 110 °C. It has been reported that large values of ε′ and ε″ will result in surface heating and low penetration depth. , At the initial liquefaction stage, most liquefaction solvent was not able to penetrate into wood particles and remained “free” in the system. Therefore, the liquefaction system had high ε′ and ε″ values close to that of the liquefaction solvent.…”