8th International Congress on Science and Technology of Ironmaking - ICSTI 2018

Coke reactivity is one of the most important parameters that defines coke quality. Although coal parameters such as coal rank, maceral composition and ash chemistry are used as indicators of coke reactivity, they cannot fully predict it. It is well recognized that reactivity of coke is controlled by catalytic mineral matter and its porosity, particularly its nanoporosity (pores of nm in size). Our previous studies on coke gasification under chemically controlled conditions concluded that catalytic mineral matter plays a dominant role on the reaction rate at initial stages whereas nanoporosity controls the reaction rate at the later stages. Porosity in cokes consists of open and closed pores. Recently we found that closed nanoporosity occurs in large proportions in cokes, almost all pores less than 5 nm are closed, and the amount of closed porosity in cokes was influenced by the maceral composition of the parent coals. In this study we examined how the fraction of the closed pores in cokes (as a function of pore size) changes during gasification under chemically controlled conditions. The cokes along with cokes prepared from maceral concentrates have been reacted with CO2 to different burn-outs, namely 25%, 50% and 75%, using a fixed-bed reactor where the reaction is chemically controlled. The analysis of closed and open porosity in unreacted and reacted cokes was performed using Small Angle Neutron Scattering (SANS). Here we show that closed porosity down to sizes as small as 10 nm open gradually during gasification. Increased pore accessibility rather than pore growth may be the reason surface area of coke increases during the early stages of gasification. The influence of coal maceral composition and coal rank on pore opening in the product coke will be discussed.