Biocoke: Carrying capacity of coking coals for sugarcane bagasse char in terms of viscoelastic behaviour during co-carbonization

Abstract

Sugarcane bagasse was pyrolyzed to various temperatures and blended with three coking coals comprising two medium volatile bituminous (MVC 1 and MVC 2) and one high volatile bituminous (HVC 1) to assess carrying capacities and mechanisms behind fluidity loss during co-carbonization.

MVC 2 showed no fluidity loss when blended with 10 wt% char pyrolyzed to 600 °C and 800 °C. However, with higher char additions (20 and 25 wt%), fluidity loss progressively worsened due to reduced amount of coal-derived liquid filling voids, causing volatiles to exhaust the system more easily. Complete fluidity loss occurred at 30 wt% char addition. Conversely, for MVC 1, despite having similar properties to MVC 2 in terms of rank and volatile matter, a 10 wt% 800 °C char addition caused fluidity loss. MVC 2 swells to a greater extent than MVC 1 and it is hypothesized that char addition disrupts the bubble growth phase, promotes bubble coalescence, and exacerbates volatile release. Further, it is hypothesized that higher swelling coals, such as MVC 2, can better incorporate char, negating its effects on bubble growth and thereby retaining liquid.

For HVC 1, the addition of 5 wt% 800 °C char caused substantial fluidity loss which is attributed to the limited swelling behaviour of the coal alone, with bubble coalescence dominating over bubble growth early in the softening phase. The premature loss of volatiles caused by the addition of the char inhibits fluidity development and renders the blend unable to carry biochar. These results suggest that a coking blend’s carrying capacity for char may depend on its swelling behaviour, with greater swelling being advantageous.