Comparing the energy efficiency of different high rate algal raceway pond designs using computational fluid dynamics

High Rate Algal Ponds with long, shallow, looped channels and powered by paddlewheels have been used since the late 1970s for growing algae to produce nutraceuticals and to remediate wastewater. These high rate or raceway ponds are also being applied to other fields such as CO2 capture and biodiesel production, where there is an ongoing effort to find ways of minimizing operating and capital costs. One approach for minimizing costs is to improve the energy efficiency of raceway ponds as this would lower operating costs and allow the construction of larger ponds, which should also lower capital costs. A major component of energy loss in a raceway pond is the energy required to circulate the fluid around the raceway, particularly at the hairpin bends.In order to design a low-energy consumption bend for a raceway pond, a computational fluid dynamics (CFD) code was used to model different raceway bend configurations. These simulations assisted in the development of a novel bend design that can reduce the energy loss at a bend by around 87% relative to the energy consumed at a conventional bend. This new design can also remove or reduce the incidence of stagnation regions within the flow. Such a development should, potentially, improve the productivity of algae in raceway ponds.

► A 75% energy saving using the new raceway bend design relative to the standard raceway bend. ► Obtain an approximate doubling in length of the new raceway pond design for the same energy consumption of the shorter, standard raceway pond. ► The removal of separation regions in the flow, resulting in better mixing. ► The resulting economies of scale may reduce operating expenses by around 5%.