Investigating the hydrodynamic performance of carbonation sumps in High Rate Algal Pond (HRAP)raceways using computational fluid dynamics (CFD)

Abstract

The production of microalgae requires carbonation and deoxygenation which is commonly supplied through a sump. This needs to be designed to minimise the energy loss to ensure a high net energy gain from the biofuel. Computational fluid dynamics was used to evaluate different sump designs and flow velocities in terms of energy loss and flow distribution to find the optimum configuration. It was established that increasing the radius of curvature of the corners to 0.1 m and the implantation of one flow deflector resulted in a reduction in hydraulic power of 73% compared to the basic setup. It was apparent that the central baffle resulted in considerable energy loss and when this was removed than a power saving of 95% was possible. There was, however, a much reduced flow around the sump leading to shortened contact time between the gas and fluid which could in turn decrease the carbonation of the fluid. It was also apparent that the use of standard formulas for the calculation of head loss was not applicable.

Microalgae-based wastewater treatment systems at demonstrative scale : gravity harvesting and thickening of biomass, and advanced design of bioreactors

“…The crater curvature should match the path of the blades, thus reducing leakage. Specific studies have shown that an optimal design of the paddlewheel can increase the efficiency from 10% to 60% (Musgrove, Heaven and Muller, 2017). According to these considerations, the paddlewheels of the HRAPs presented in this manuscript were designed with 8 aluminium paddles, a gap of 2.5 cm between the paddles and the floor, and a crater of 10 cm depth and 1 m length.…”

“…6.5) only refers to the energy needed for water flow, but not to the engine consumption, the type of wheel and the gearbox used, which are directly related to energy consumption. (Musgrove et al, 2017) reported that the total power required can be 5 times the calculated hydraulic power, which should be taken into account for the selection of the corresponding engines. The parameters used for the hydraulic sizing are shown in Table 6.3.…”