An investigation of the reactivity of chars formed in fluidized bed gasifiers: the effect of reaction conditions and particle size on coal char reactivity

Coal-derived chars formed during air-blown gasification processes may rapidly lose reactivity, and this can limit the extent of their conversion. To study this effect, a laboratory-scale fluidized bed reactor has been modified to enable char samples to be prepared under strictly controlled conditions of temperature, pressure, particle size, gaseous environment, and residence time. This has been used to gain an insight into the deactivation of the chars as they form and during their subsequent residence time in the bed of the gasifier. The work shows that the char reactivity declines rapidly during its formation as part of the pyrolysis of the coal. This is thought to result from the rapid deposition of secondary, unreactive char within the pores of the material. In this work, it has been shown to occur within the initial 10 s in the reactor, but in reality, this effect probably occurred within 1 s. Temperature, pressure, and particle size have an impact on this process. Subsequently, and over a longer tim...