DESIGN PROBLEMS IN BIOCHEMICAL ENGINEERING

The cost of the mixer plus the associated blower required, plus installation of both is 900/kW with an impeller diameter to tank diameter ratio of 0.35. 

By using large diameter impellers at slower speeds, the maximum impeller zone fluid shear rate can be changed, and the cost of the mixer/kW must be changed accordingly. The cost of die mixer can be approximated to change inversely proportional to the maximum impeller zone fluid shear rate to the 2.3 exponent 

The particular antibiotic requires 200 mols of oxygen for each kg of product produced. The total production cost of the antibiotic is estimated as 60/kg, of which 30 is a fixed cost, independent of productivity of the fermenter, and 30 is the cost associated with the actual fermentation tank itself 

At 20 g// cell concentration, the mixer is capable of transferring 6.4 mols of oxygen per MJ. 

It is proposed to increase the solids concentration in the system to 40 g//, which will effectively double the productivity of the fermentation tank itself The oxygen transfer activity of the mixer is lowered, due to the increased viscosity, to 4 mol of oxygen per MJ. 

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