| Microalgae has great potential for development.However,due to the fine particles and low concentration of microalgae and its culture medium,the traditional solid-liquid separation technology is directly used for microalgae harvest without economic competitiveness.How to provide a good hydraulic condition for the flocculation of microalgae under appropriate flocculant system and ensure the good growth of floc in order to facilitate the efficient process of subsequent harvesting process is one of the problems to be solved in the current microalgae harvesting research.The research system of microflora collected by spiral flocculation was designed,and the microalgae flocculation was realized under laboratory conditions.The CFD simulation technique was used to study the change of the flow field characteristics of the diameter of the pipe,the thread diameter and the flow velocity(flow rate).On the basis of this,the flocculation kinetic theory and flocculation experiment were used to analyze the effect of the above factors and spiral tube length on the flocculation efficiency of microalgae.The optimum flocculation conditions of microalgae in the spiral flow field under laboratory conditions were obtained.And the effect of hydraulic environment on flocculation effect was discussed.For the spiral flow field,the RNG k-? two-equation model and the near-wall enhanced wall treatment method were used for numerical simulation.The results shows that the increase of inlet flow will increase the velocity gradient of the flow field,and the turbulence kinetic energy and the turbulence dissipation rate will increase accordingly.The increase of the thread diameter increases the velocity gradient of the flow field and the turbulence kinetic energy is not obvious,but the analysis of the turbulent dissipation rate shows that the increase of the thread diameter will increase the effective energy consumption of the flocs.The effect on the flocculation of microalgae depends on the effect of the three combinations.The increase of the pipe diameter increases the velocity gradient in the flow field,and the turbulence kinetic energy and the turbulent dissipation rate also decrease to a certain extent.The more significant one of above factors is the main reason for the effect of pipe diameter change on the flocculation effect.The influence of different factors on the flow field in the spiral pipe was analyzed by single factor test on the inlet flow rate,spiral diameter,spiral length and coil diameter of the spiral flocculant.Under the experimental conditions,the recovery rate and fractal dimension decrease gradually when the pipe diameter increases,Under the test conditions,the recovery rate decreases with the decrease of the GT value.When the length of spiral pipe increases,the recovery rate increases and then decreases.The recovery rate is the highest at pipe length of 15 m,and the change of fractal dimension is the same as that of recovery.When the thread diameter increases,the recovery rate increases first and then decreases gradually after thread diameter reaching 30 cm.The fractal dimension gradually increases when the thread diameter increases.While the increase in the value of GT did not bring a direct increase in recovery,so the introduction of fluid angular velocity for analysis.The recovery rate increases with the increase of the GT value when the angular velocity is small.After the angular velocity continues to increase beyond the proper range,although the GT value increases,the recovery rate of the floc damage caused by the excessive angular velocity of the fluid decreases.When the inlet flow rate increases,the recovery rate increases gradually.And the fractal dimension of the flocs increases first while decreases after the flow reaches 150L/h.The range of GT is in the range of 1900-15000,and the recovery is positively correlated with the GT value within the range of the GT range under experimental conditions.The effects of inlet flow rate,helical diameter,spiral length and coil diameter on the flocculation recovery and fractal dimension of spiral flap were investigated by four-factor four-level orthogonal test.The experimental results show that the inlet flow rate,the pipe diameter and the length of the spiral pipe have a significant effect on the recovery,and the diameter of the spiral is not.The diameter of the spiral pipe diameter and the inlet flow have a significant effect on the fractal dimension of the floc,but the thread diameter and the length of pipe are both not.Under the test condition,recovery up to 95.88% under the condition of inlet flow of 200L/h,spiral pipe diameter of 8mm,pipe length of 25 m and thread diameter of 40 cm.The optimal combination of each factor is the spiral pipe diameter of 8mm,the inlet flow of 200L/h,the length of the spiral pipe of 15 m and the thread diameter of 30 cm when recovery as the indicator. |
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