Development Of Shearing Aerator To Decrease Bubble Size And Promote Mass Transfer For CO₂ Fixation With Microalgae From Flue Gas

Microalgae have many advantages such as strong environmental adaptability,fast growth rate,high conversion efficiency and good biomass benefit.Therefore,using microalgae to fix coal-fired flue gas CO₂ is of great significance for China’s energy conservation and emission reduction and development of new energy.The aerator used in microalgae photosynthetic reactor often generates large size bubbles,resulting in poor gas-liquid mass transfer,which severely limits the conversion efficiency of the microalgae growth and CO₂ fixation.Thus,the high-efficiency aerators which can reduce the CO₂ bubble diameter,is crucial to improve the CO₂ fixation rate with microalgae.This paper revealed the influence of SO₂ impurities on the dissolution of 15% CO₂ in the process of CO₂ fixation from coal-fired flue gas by microalgae.A volute aerator was developed to generate shear force through water centrifugation to decrease bubble diameter and promote mass transfer for CO₂ fixation with microalgae.A three-stage shearing aerator was de veloped to reduce the bubble diameter and promote the microalgae growth.The study re veals the influence of SO₂ impurities on the dissolution of 15% CO₂ in the process of CO₂ fixation from coal-fired flue gas with microalgae.Through the visual experiment,when the p H value of the medium solution increased from 3 to 11,the final bubble dissolution diameter of 15% concentration CO₂ from flue gas decreased from 3.48 mm to 3.42 mm,so high p H value promoted the dissolution of 15% concentration CO₂ bubbles from the flue gas.When the SO₂ concentration in the flue gas increased from 0 mg/m3 to 300 mg/m3,the p H value of the medium solution became lower to inhibit the dissolution of CO₂.When the initial diameter of the flue gas CO₂ bubble containing SO₂ impurities reduced from 3.4 mm to 2.3 mm,the specific surface area of the bubble became high,resulting in the initial bubble dissolution rate in 30 s increased from 0.009 mm/s to 0.018 mm/s.When the microalgae cell density in the medium solution increased from 0.1 to 0.4,the initial bubble dissolution rate in 30 s increased from 0.023 mm/s to 0.027 mm/s because of microalgae photosynthesis reaction consumed CO₂ faster.A novel volute aerator was proposed to generate shear force and break gas flow through water centrifugation to decrease bubble diameter and promote mass transfer for CO₂ fixation with microalgae.When the CO₂ gas concentration is 99.99% and the flow rate is 100ml/min,the results tested by experiment were that the bubble generation time decreased by 60.10% to 3.33 ms and outlet bubble diameter decreased by 50.70% to 1.85 mm,compared with traditional strip aerator.The corresponding gas–liquid mixing time reduced by 15.63% and mass transfer coefficient increased by 42.19%,the biomass production increased by 50.70%.A three-stage sawtooth mechanical shearing aerator was de veloped which is suitable for fixing coal-fired flue gas CO₂ by microalgae.The 3D printing technology is used to optimize the parameters such as the air inlet diameter,the aerator angle,the pyramid height on the head part of aerator and so on to reduce the diameter of the bubble and enhance the mass transfer to promote the CO₂ fixation of the microalgae.When the air inlet diameter of the aerator decreased,the number and the height of triangles increased,the number of teeth in the cylinder and the number of teeth on the side of the cylinder increased,the bubble diameter decreased.However,when the aerator angle increased,the diameter of the bubble generated by the aerator decreased first and then increased.When the aerator angle was 55°,the bubble diameter became smallest.The experimental results show that when the aerator inlet diameter is 1mm,the aerator angle is 55 degrees,the pyramid height on the head part of aerator is 7mm,the number of cylindrical internal cutting tooth is 50,the pyramid number on the head part of aerator is 106,and the cutting teeth on cylindrical side is 70,the bubble diameter is reduced by 35.10% to 2.40 mm,the mass transfer coefficient is increased by 25.50%,and the biomass production is increased by 46.80% compared with the conventional strip aerator.