Provided are apparatus and methods of gasification using a circulating fluidized bed reactor comprising a separate pyrolysis reaction chamber, one or more primary char gasification chambers, and one or more secondary char gasification chambers which comprise an internal vertical reaction volume suitable for containing a particle bed fluidized by a predominantly vertical upwards gas flow. The vertical reaction volume is advantageous in that this provides the possibility for increased retention time of particles, facilitating comparatively slow “productive” temperature moderation based on endothermic char conversion.