Process Design of Microalgae Slurry Pump

Abstract

Microalgae are a renewable source of dietary supplements, bioactive compounds, and potential energy. Once harvested, the microalgal medium is dewatered to form a slurry for downstream processing. This article outlines a process design for pumping the microalgae slurry. The pump requirements for delivering the Chlorella slurry with 5, 10 or 20 wt% solids at one tonne per hour (1,000 kg/h) and 10 bar were calculated. The 5 wt% microalgae slurry is a Newtonian fluid with a viscosity of 1.95 mPas. The 10 wt% and 20 wt% microalgae slurries are non-Newtonian fluids, whose viscosity depends on the shear rate (). The viscosity of 10 wt% and 20 wt% microalgae slurries is 1.504 ( = 50 s -1 )/1.155 ( = 100 s -1 ) and 1.844 ( = 50 s -1 )/1.219 ( = 100 s -1 ) mPas, respectively. The pump power requirements are mainly governed by the delivery pressure. The effect of the pipe length and the number of elbows is negligible. The effective power of the pump is calculated as 0.267-0.275 kW. To fulfill this duty, a ZGB type single-stage single-suction centrifugal slurry pump can be selected, which would provide enough shear rate to reduce the viscosity of the microalgae slurry and give required shaft power.