Oxidative pyrolysis of mixed solid wastes by sand bed and freeboard reaction in a fluidized bed

Abstract

Oxidative pyrolysis of mixed solid wastes by both sand bed and freeboard reaction in a fluidized bed reactor was investigated. Air was the fluidizing gas (i.e. primary air, injected into the dense solids region) and secondary gas (i.e. injected into the freeboard). The effects were examined of (1) pyrolysis temperature (in both main and secondary combustion chambers) and (2) dimensionless air factor (defined as ratio of actual air flow rate to stoichiometric air flow rate) on the formation of liquid hydrocarbons (gasoline, diesel, fuel oil and residue), BTX concentration and H C ratio of the gasoline fraction. The results indicated that (1) the operating temperature can be correlated with the air factor, (2) introducing air into the freeboard forms a quasi-vortexing fluidized bed similar to a cyclone freeboard capable not only of reducing sand elutriation but also of mixing the primary volatiles uniformly with the secondary air and the reactive agent, (3) a high operating temperature can produce lower-boiling-point oils (i.e. gasoline or diesel), a lower temperature tending to form high-molecular-weight hydrocarbons (i.e. fuel oil or heavy oil), and (4) the gasoline derived from oxidative pyrolysis has a sulfur content ranging from 0.25 to 0.35% wt%.