MIXING EFFECTS IN COAL PROCESSING BIOREACTORS

In the bioprocessing of high-volume, low-value products like coal it is important to minimize the size and cost of the bioreactor. Optimum reactor design requires attention to the degree to which mixing should be induced or prevented. An analysis of a simple bioprocess in plug-flow and stirred-tank reactors shows that the amount of mixing required depends critically on the amount of microorganisms available from the inoculum and from cell growth. A mixed reactor is preferable when microbes are scarce and is the only possible solution when none are available to inoculate the coal entering the reactor. However, when sufficient cells are available (usually from cell recycling) a plug-flow reactor may be an order of magnitude smaller. The best solution may be a stirred-tank reactor feeding a plug-flow reactor and reactor size estimates for this system are given. © 1990.