Optimizing Flow Fields Of Flashing Light Bioreactors To Improve CO₂ Fixation With Microalgae From Coal-fired Flue Gas

Microalgal energy has been extensively investigated in the context of reduction of CO₂ emission and new energy development because microalgae undergo rapid growth and exhibit high utilization efficiency of energy from sunlight.CO₂ capture and utlization from coal-fired power plant with microalgae has the good economic efficiency and stong industrial application prospect.High efficient and low cost of photosynthetic reactor is the key factor for the development of CO₂ capture and utlization industry with microalgae cultivation.Computational fluid dynamics?CFD?,particle imaging velocimeter?PIV?system,high-speed photography system?HSP?and online dissolved oxygen/pH probes were used to systemically analyze the flow field structure,bubble dynamic generation process,mass transfer mixture and the characteristics of CO₂ capture with microalgae when baffles were used.Novel up-down chute baffles were developed to increase microalgal growth rate with an enhanced flashing light effect in the raceway pond.CFD simulation indicates that the L/D cycle period decreased by 24%?from 5.1 s to 3.9 s?,and vertical fluid velocity increased by 75%when up-down chute baffles were used with paddlewheel speed of 30 r/min.The probability of L/D cycle period of 3 s increased by 52%from 0.29 to 0.44 with the up-down chute baffles.Vortexes flow field were developed and experimental measured when the novel up-down chute baffles were used in the raceway pond.Flashing light effect was enhanced between the bottom dark area and the top light area.The up-down chute baffles decreased the liquid mixing time and increased the mass transfer coefficient by 41%and 25%,respectively.Besides,the vertical liquid velocity increased from-0.5 cm/s to-6.1 cm/s.As a result,the dark-light cycle period was reduced to 1/12.This enhanced flashing light effect with up-down chute baffles increased biomass yield by 32.6%in the same raceway pond.A novel gas aerator was proposed based on the oscillating flow field to generate smaller aeration bubbles and enhance mass transfer coefficient.The optimized oscillating gas aerator decreased bubble diameter and generation time by 16.5%and 41.8%,respectively,when solution velocity inside the gas aerator was 0.41 m/s with an aeration diameter hole of 0.3 mm.Solution mass-transfer coefficient increased by 15%and mixing time decreased by 32%when the solution velocity was 0.2 m/s.Novel horizontal baffles were developed to increase microalgal growth rate with an enhanced.flashing light effect on the horizontal direction in a flat-panel photobioreactor.CFD calculation results showed that the light/dark?L/D?cycle period decreased by 17.5%and that the horizontal fluid velocity increased by 95%when horizontal baffles were used with an air aeration rate of 0.02 vvm and a microalgal concentration of 0.85 g/L.The probability of the L/D cycle period within 5-10 s increased by 65%to 0.43.Vortexes flow field were developed and experimental measured when the novel horizontal tubes and triangular prism?HTTP?baffles were used in a flat-panel photo-bioreactor.Micraogal growth rate and CO₂ fixation rate were increased with the enhanced flashing light effect on the horizontal direction.The mixing time decreased by 21%and solution mass-transfer coefficient increased by 30%when HTTP baffles were used.The solution velocity between dark and light areas increased from-0.9 cm/s to-3.5 cm/s,resulting in a decreased dark-light cycle period to one-fourth.This enhanced flashing light effect with the HTTP baffles dramatically increased microalgae biomass yield by 70%.Photosynthetic reactor flow field optimization technology were applied to a microalgal CO₂ capture and utlization demonstration project with 100,000 square meters in Shandong yantai.Based on a large-scale raceway reactors?1191 m2?,CO₂ removal rate of the culture system from flue gas and CO₂ fixation ratio between microalgal biomass and culture solution were investigated.Average daytime sunlight intensity and solution temperature were optimized to improve microalgal growth rate and to enhance the efficiency of GO₂ fixation.CO_2fixation rate in the microalgal biomass increased from 18.4 g/m2/d to 40.7 g/m2/d when the average daytime sunlight intensity increased from 39,900 lux to 88,300 lux.