Study of heat-treated Spanish lignites: Characteristics and behaviour in co2 and o2 gasification reactions

Six Spanish lignites (raw and demineralized) have been charred to 1113 K in a N₂ atmosphere. The surface area, porosity and mineral matter content of the char coals so obtained have been studied, as well as their reactivity in CO₂ flow in the range 1073–1113 K, and in dry air in the temperature range 733–773 K. The reactivities of the raw chars in CO₂ may be explained according to the different inorganic matter content that may act as catalyst. The demineralization process brings about a lowering in reactivity and an increase, in general, in the apparent activation energy that may be interpreted as being due to a fall in mineral matter content and/or an increase in the amount of feeder pores. With regard to reactivity and apparent activation energy, in the case of dry air three groups of raw chars have been established. The differences between these three groups may be due to the different inorganic impurities present in the raw chars that catalyse the reaction of carbon with O₂ more than the porous texture parameters. Demineralization brings about a lowering in the reactivity values and a levelling off of apparent activation energies. The catalytic effect of iron has also been studied by adding different amounts of this metal to a demineralized char. The burn-off versus time curves of the different char coals have been adjusted by using the τ_0.5 parameter.