Study On Hydrodynamics, Mass Transferand Nutrition Metabolism In Arectangular Airlift Loop Photobioreactor

Microalgae are one of the most promising biomass energy, and the key todevelop and use microalgae resources is to realize its high density cultivation. In thiswork, a novel rectangular airlift loop photobioreactor (RALPBR) for large-scalecultivation of microalgae is developed, and the gas-liquid flow, mixing and masstransfer in the reactor are studied. In addition, Chlorella vulgaris is cultivated in thereactor, and the parameters of growth and the metabolism of nutrients are alsomeasured.At first, influences of superficial gas velocity and top clearance on gas holdup,liquid circulation velocity, mixing time and mass transfer coefficient in the reactor areinvestigated, and empirical models for its rational control and scale-up of theRALPBR are also proposed. In addition, a novel technique based on volumeexpansion technique is also developed to determine the low gas holdup in theRALPBR. The results indicate that the superficial gas velocity plays a dominant rolein the performance of the reactor, and the top clearance is found to influence the gasholdup, the liquid circulation velocity, the mixing time and the mass transfercoefficient to some degree. Moreover, volumetric power in the PBR is analyzed with aclassic model. It shows that the designed PBR is a cost-effective reactor, andpromising for the mass cultivation of microalgae in the future.In this work, the bubble characteristics in the RALPBR are studied using aMATLAB codes with digital image technology (DIT), and the effect of superficial gasvelocity on the bubble characteristics is investigated. The pictures are treated withmany image analysis technologies, including binary image, hole filling, overlappingbubbles segmenting and so on. The results show that the gas holdup with the methodof DIT is consistent with experimental data obtained by using the developed volume expansion method. It is indicated that the DIT is feasible to acquire the gas holdup inthe reactor, and the details of bubbles (including shape, diameter, distribution andinterface of bubbles) can also be obtained. Through statistical analysis of all bubblesin the reactor, the changes of average bubble diameter with superficial gas velocityand height in the RALPBR are addressed.The influence of superficial gas velocity on the growth parameters of Chlorellavulgaris is investigated in this reactor, and the metabolic rate of nutrients in themedium are also measured. The results show that the dry weight grew from0.2g/L to4.34g/L after264hours of cultivation. When the superficial gas velocity is greaterthan5.56×10-4m/s, it had almost insignificant effect on the growth rate of microalgae.From the elemental analysis, it shows that N、P、Fe、Ca and Mg are the principalelements for the growth of Chlorella vulgaris.