Combustion and gasification of coals in fixed-beds

Abstract Fixed-bed processes are commercially used for the combustion and conversion of coal for generation of power or production of gaseous or liquid products. Coal particle sizes in fixed-bed processes are typically in the mm to cm diameter range, being much larger than in most other coal processes. This review provides a broad treatment of the technology and the science related to fixed-bed systems. Commercialized and developmental fixed-bed combustion and gasification processes are explored, including countercurrent, cocurrent, and crosscurrent configurations. Ongoing demonstrations in the U.S. Clean Coal Technology program are included. Physical and chemical rate processes occurring in fixed-bed combustion are summarized, with emphasis on coal devolatilization and char oxidation. Mechanisms, rate data and models of these steps are considered with emphasis on large particles. Heat and mass transfer processes, solid flows, bed voidage, tar production and gas phase reactions were also considered. Modeling of fixed-bed processes is also reviewed. Features and assumptions of a large number of one- and two-dimensional fixed-bed combustion and gasification models are summarized while the details of a recent model from this laboratory are presented and compared with data. Research needs are also discussed.