Modelling of a laboratory-scale bubbling fluidised-bed gasifier with feeds of both char and propane

A previous mathematical model developed for a bubbling fluidised-bed coal gasifier was modified for simulating the performance of a laboratory-scale gasifier with feeds of both Yallourn char and propane by incorporating propane decomposition and combustion reactions and reaction kinetics. Model predictions of the in-bed axial gas concentration profiles for O2, CO, CO2, CH4, and C3H8 compared well, except for the minor gas species of both C2H4 and C3H6, to the experimental data at operating bed temperatures of 850 and 950 °C, respectively. In contrast, the predicted gas species show a poor agreement with the experimental data, particularly for the carbon oxide species at 750 °C. Most importantly, the addition of propane to simulate the volatile matter released from coal devolatilisation process results in an increase in the proportion of oxygen consumed by homogeneous combustion. This leads to an increase in an availability of char for char gasification reactions, subsequently showing an increase in carbon conversion due to gasification over the sole gasification of char. The specific energy of the syngas gas has been shown to increase due to the enhancement of the char gasification reactions in the presence of volatiles. This further demonstrates the importance of incorporating homogenous combustion into the model for correctly predicting the gasifier performance, particularly for the in-bed feeding of coal with high volatile content.