On Energy Balance and Production Costs in Tubular and Flat Panel Photobioreactors

Reducing mixing in both flat panel and tubular photobioreactors can result in a positive net energy balance with state-of-the-art technology and Dutch weather conditions. In the tubular photobioreactor, the net energy balance becomes positive at velocities < 0.3 ms-1, at which point the biomass production cost is 3.2 €/kg dry weight. In flat panel reactors, this point is at an air supply rate < 0.25 vol vol-1 min-1, at which the biomass production cost is 2.39 €/kg dry weight. To achieve these values in flat panel reactors, cheap low pressure blowers must be used, which limits the panel height to a maximum of 0.5 m, and in tubular reactors the tubes must be hydraulically smooth. For tubular reactors, it is important to prevent the formation of wall growth in order to keep the tubes hydraulically smooth. This paper shows how current production costs and energy requirement could be decreased.