Sludge blanket of UASB reactor: Mathematical simulation

Blanket height is an important aspect of UASB reactor design. It regulates the solid concentration reaching the gas-solid separator (GSS) and, thereby, prevents sludge washout. The maximum organic load which a reactor can assimilate depends on proper proportioning of the reactor height into the bed and blanket. A condition of force equilibrium has been considered between the rising gas bubbles and the adjacent water mass. The negative pressure behind the bubble attracts the water mass and leads to the formation of a wake. Using diffusion concepts, solid particles moving along the wake due to concentration gradient have been equated to those settling down under the influence of gravity at steady state and solid concentration along the blanket height is ascertained. Computed values have been found to compare well with the scanty experimental observations available from the literature. Using this model, it is possible to size the reactor. (C) 1997 Elsevier Science Ltd.