Evaluation of power consumption of paddle wheel in an open raceway pond

Abstract

Open raceway ponds are widely adopted in microalgae cultivation. Paddle wheels consume the most part of power during the process of cultivation in open raceway ponds. The configuration of blades directly determines power consumption for paddle wheels. In this work, power consumption of four blades configurations was determined in a bench-scale open raceway pond of 2.2 m(2). The effect of blades configuration, the influence of filling levels from 5 to 15 cm and influence of rotational speeds from 7 to 15 r min(-1) on shaft power consumption (P(S)), fluid velocity (U(c)) and paddle wheel efficiency (η) was investigated. Results demonstrated that flat blades were the most efficient configuration. Higher culture depth led to larger U(c), more P(s) and larger η, especially when blades were not totally immerged in water. Under the same filling level and rotational speed, the value of P(S) decreases in the order: zigzagged, flat, forward-curved and back-curved, respectively. The zigzagged blades led to a larger U(c) at the culture depth of 5 cm, while flat and forward-curved blades drove a larger U(c) when culture depth was higher than 5 cm. The maximum value of η was 0.50 with flat blades at 11 r min(-1) and 15 cm of culture depth. Empirical correlations of non-dimensional numbers related to operation parameters and blades geometry for four paddle wheel blades were also proposed.

Hydrodynamic Characterization in a Raceway Bioreactor With Different Stirrers

“…It can be mentioned the Froude Number (Fr) which represents the type of flow presented into the channel, when Fr < 1 the flow is subcritical or slow, Fr=1 is a critical flow or normal and when Fr >1 is supercritical or fast (Mott, 2006). The Power Number (N P ) (Li et al, 2014), which is directly related to the energy required to move the paddlewheel; the flow number (N Q ) or pumping capacity also relates to the stirrer and hydraulic efficiency (McCabe et al, 2005;Uribe Ramírez et al, 2012). The determination of velocity profiles and dead zones localization is also a important part in the Raceway ponds characterization.…”

“…However, until now the stirrer's geometry has not been considered in studies where full mixing is sought. For example, (Li et al, 2014) studied three agitators (zigzaged, curved forward and curved back) but they focus only in turbulent kinetic energy. (Zeng et al, 2015) studied a paddlewheel at different degrees of inclination, however they focus on biomass production but not on hydrodynamics.…”

Optimal integration of microalgae production with photovoltaic panels: environmental impacts and energy balance

“…Electricity consumption: around 0.07 kWh m −3 Nutrients/water loss pumping system: 24 units (22 for raceways and 2 for inoculum ponds), time functioning: 12 h day −1 . Electricity consumption: negligible[23, 24, 32–34]Algae harvesting (dewatering)Settlers ponds: 22 units, energy demand: negligible, efficiency: 90%, outlet concentration: 10 g/L. Capacity: 364.1 m 3 .…”

Challenges and opportunities for microalgae‐mediated CO2 capture and biorefinery

“…Estimates of land and water usage, net energy usage and carbon dioxide emission from stages of growth, harvesting, dewatering, and drying for a typical microalgal CCU. Current best-case scenario (5% photosynthetic efficiency in fresh water medium) and a potential case of microalgae grown in municipal wastewater with 10% photosynthetic efficiency are presented in (1) and (2) (Andersen, 2005;Ferreira et al, 2013a;Li et al, 2014). Here, we have considered water circulation energy of 0.5 W/m 2 and the energy consumed for providing necessary pressure drop across sparger is less than 1% of the TPS capacity (Perry and Green 1984).…”