Energy Consumption Analysis And Performance Optimization Studies Of Air-forced Type Low-pressure Jet Aeration

With the gradual increase in the number of sewage treatment plants in China and the gradual increase in the volume of sewage treatment,the problem of water pollution has been greatly eased.At the same time,the energy consumption of sewage treatment plants has gradually been concerned by researchers.In the sewage treatment process,the aeration system is one of the main energy-consuming units,and its power consumption accounts for about 50%to 70%of the total power consumption of the sewage treatment plant.Because the traditional fine bubble aeration equipment has high oxygen mass transfer efficiency,it has the problems of easy plugging and large power consumption.Therefore,the development of a new type of aeration equipment with high efficiency and low energy consumption has become an important issue for wastewater treatment.The jet aerator is an aeration device between the mechanical aerator and the fine bubble aerator.It uses the two functions of bubble diffusion and hydraulic shear to achieve the purpose of aeration and gas-liquid mixing,with oxygen transmission.The advantages of high mass efficiency,low clogging,large service area and long service life have been widely used in the treatment of urban domestic sewage and various types of industrial wastewater.In this paper,FLUENT numerical simulation software is used to perform three-dimensional modeling and numerical simulation of first-generation of low-pressure jet aerator for gas supply.The gas-liquid two-phase distribution change,two-phase flow velocity and pressure distribution inside the aerator are obtained during the work process.The flow field properties such as the turbulence intensity of gas-liquid two-phase flow,theoretically reveals the feasibility and advantages of the addition of diffusion orifices,double-pipe inlets,and changes to the mixing chamber structural parameters in the mixing chamber.For the influence of the aerator performance,the five structural parameters such as the position of the orifice plate,the number of the inlet tubes,the orifice size and number of openings of the orifice plate,the primary nozzle diameter and the secondary nozzle diameter are used for the gas in the aerator have great influence on the mixing effect of liquid two phases and turbulent intensity.While the three structural parameters of the length of the mixing chamber,the diameter of the mixing chamber and the inlet angle of the inlet pipe have little effect on the performance of the aerator.The final result is that when the diffuser plate installed in front of the inlet pipe has 19 holes,the aperture is 15 mm,the double pipe inlet works together,the primary nozzle diameter is 36 mm,and the secondary nozzle diameter is 55 mm,the length of the chamber is360 mm,the diameter of the mixing chamber is 90 mm,and the inlet angle of the inlet pipe is 90°,the gas-liquid mixing effect of the second-generation air-supply type low-pressure jet aerator is better and it provides reference for aerator design and research work.The results show that the second-generation jet aerator has better gas-liquid mixing effect than the original aerator,with stronger turbulent intensity and stable two-phase flow structure.Thewateroxygenationexperimentisperformedonthe first-generationand second-generationjet aerators through the oxygenation performance study device,and the clean water oxygenation performance parameters of the two generations of aerators are calculated and compared to optimize and save energy for the gas-supply low-pressure jet aeration equipment.Consumption provides theoretical and technical support.Through experiments,under the condition of the same circulating water volume,as the gas-water ratio increases from 2:1to 4:1,the standard oxygen total mass transfer coefficient(K_Las)and the standard oxygen mass transfer rate?SOTR?also increase.Large,while the standard oxygen transfer efficiency?SOTE?and standard aeration efficiency?SAE?are reduced.At the same time,when the same amount of circulating water and air supply are provided,the second-generation aerator's K_Lasas can increase the by 16 to 18%compared with the first-generation aerator,the SOTE can increase by 15 to 20%and the average SAE can increase by about 20%,and the second generation jet aeration has a maximum SOTE of 29.22%and an SAE of 3.043kg/?k W·h?.It is proved that the second-generation improved aerator has better oxygenation capacity and lower energy consumption than the first-generation aerator.In the depth range of 3 m to 5 m,with the increase of water depth,the oxygenation performance of the jet aerator gradually increases,indicating that the water depth has a great influence on the oxygenation performance of the jet aerator,and only when the water depth is deep enough can show the outstanding oxygenation performance of the jet aerator.At the same time,through the oxygenation performance research device,the fine bubble aerator for aerobic water oxygenation experiment is conducted to compare the water oxygenation performance parameters of the fine bubble aerator and the second-generation jet aerators.The results shows that with the flow rate of the air supply gradual increase,the standard oxygen transfer rate?SOTR?of second-generation jet aerators and fine bubble aerators tends to increase,and the standard oxygen transfer efficiency?SOTE?and standard aeration efficiency?SAE?both show a downward trend.Due to the unique oxygenation mechanism of the jet aerator,the SOTR of the second-generation jet aerator is always higher than that of the fine bubble aerator when the air supply flow is the same.But the circulating water pump and the blower are needed at the same time when the jet aerator operates,the jet aerator SAE is smaller than the fine bubble aerator,but the SAE gap between the second-generation jet aerator and the fine bubble aerator is reduced.