Analysis of Paddlewheel Mixing System for Algal Biomass Production in Raceway Ponds using Simulation Techniques

Abstract

Raceway Ponds (RWP) are single or multiple closed-loop, oblong and shallow re-circulating ponds with semi-circular ends. A paddlewheel mixer is installed at one end of RWP that enable the circulation and flow of suspended algae cells through the channel in the pond. The proposed RWP system had four inoculum ponds, two grow out ponds, flocculation pond and treatment pond. There was 33% scale up in volume of the inoculum pond 1 to the final grow out pond, step by step. The algal biomass production was targeted to 1 kg/m3 of pond volume. The power required for mixing algae was estimated based on the pond volume and the flow velocity of 0.3 m/s to be maintained. Numerical simulations of the RWP with rotating paddles were performed using CFD Software STAR CCM+ for the estimation of paddle power requirements and the flow velocities in the pond. RPM of the paddle wheel was adjusted to achieve the desired velocity in the RWP; simulation was carried out until the flow was established in the RWP. The power required for driving the paddle wheel was arrived for the RWP from simulations, which is in agreement with the estimated power from analytical methods.