Variations in the design of dual fluidized bed gasifiers and the quality of syngas from biomass

Fluidized bed reactors are the most popular mode of reactors for gasification to produce syngas at medium- to large-scale applications. Fluidized bed gasification is either carried out conventionally in a bubbling fluidized bed or in a circulating fluidized bed. However, the recent development on the use of indirectly heated gasifiers to produce high energy syngas has resulted in a number of possible combinations of fluidized beds, involving combinations of bubbling fluidized beds and circulating fluidized beds. The present work attempts to compile the different designs that are in various stages of development, addressing its operations and merits. In addition, an attempt has been made to compile and analyze the work reported in the literature, based on syngas quality in terms of carbon monooxide (CO) to hydrogen (H2) ratio, which is critical for downstream processing, along with the heating value of the syngas.