In spite of the versatility of spouted beds of conventional geometry (cylindrical with conical base), there are situations in which the gas–solid contact is not fully satisfactory. In these situations, the process conditioning factors are the physical characteristics of the solid and the residence time of the gas. Thus, conical spouted beds have been used for drying suspensions, solutions, and pasty materials. Chemical reaction applications, such as catalytic polymerization, coal gasification, and waste pyrolysis, have also been under research and development.
In fast reactions, such as ultrapyrolysis, selectivity is the factor that conditions the design, so the optimum residence time of the gaseous phase can be as short as a few milliseconds. The spouting in conical beds attains these gas residence times, which can be controlled within a narrow range. Nevertheless, until the 1990s, the literature on the principles and hydrodynamics of the flow regimes in conical spouted beds was very scarce, and its diffusion was very limited, partially owing to the scant dissemination in the past of the research on such beds carried out in Eastern Europe.
Conditions for stable operation and design geometric factors
Operating in conical contactors is sensitive to the geometry of the contactor and to particle diameter, so it is necessary to delimit the operating conditions that strictly correspond to the spouted bed regime and allow for the gas–solid contact to take place stably.