Operability analysis of a circulating fluidized-bed coupled dual-loop system for autothermal pyrolysis/gasification of coal

The study examines the operability of a pilot plant for autothermal pyrolysis/gasification of coal from the standpoint of system hydrodynamics. The plant, owned by ENEL and located at Bastardo (Italy), consists of a circulating fluidized bed dual loop system embodying a riser as coal pyrolyser/gasifier and a second riser serving as char combustor. The system has been modelled as a combination of mutually interconnected blocks (risers, cyclones, downcomers, L-valves) after proper selection of constitutive equations for each block. The operability of the system has been theoretically investigated by mapping hydrodynamic regimes establishing in the risers of the dual loop for different sets of design variables. Results are analyzed with the aim of identifying regions in the phase space of operating variables where stable and trouble-free operation of the system can be achieved.