Study On Flow Field Of Gas-liquid And Design Of Multi-stage Internal Circulation Anaerobic Reactor Based On CFD

Nowadays,water pollution is increasingly serious,sewage treatment market is gradually expanding,The need for low-cost,high-efficiency of waste water treatment technology is urgent.Anaerobic reactor has been a good choice.Anaerobic reactors have undergone several replacements,so far to the third generation of anaerobic reactors.Anaerobic reactors are updated in the third generation of enhancing the effect of mass transfer between mud and water every time,and the nature is proposing to improve the flow field inside the reactor.A new type of anaerobic reactor-Multi-stage Internal Circulation Anaerobic Reactor has been developed by our team,and use the CFD to simulate flow field of the reactor with different sizes of structure.The principle of design is the three stages of acid production,hydrogen and acetic acid production,methane production stage in three different reaction stages,each reaction conditions in the reaction zone are adjusted to the the microorganisms in each reaction zone,and thus the maximum efficacy of the microorganisms can be exhibited.While in each reaction chamber,the internal circulation system is automatically formed by the self-produced biogas from the methane-producing stage,and the internal circulation system keeps the microorganisms in the reactor,so that the granular sludge is in the state of expansion and fluidization,The mixture can be fully exposed,the full contact with mud to achieve good mass transfer,greatly improve the efficiency of sewage treatment.Previously,a large number of scholars have studied anaerobic reactors,but most of the previous studies focused on the experimental study of the process,few people study the flow field within the reactor mechanism,and the most of studies is to rely on empirical formula to create the reactor,so there is a certain blindness in the design and it can not make full use of the reactor internalspace,it is difficult to achieve the best mass transfer effect.The numerical simulation method can replace the pilot experiment in the reactor,which greatly saves the research time and expense,and can solve the problems that can not be solved in the pilot experiment.The simulation result can predict the operation effect and state of the reactor in a short time.Combined with the particularity of the multi-stage internal circulation anaerobic reactor,the FLUENT software of CFD was used to simulate the operation of the reactor.By changing the three factors,such as the size of intake air volume,height/diameter and aeration the height of plate installation,The optimal process parameters of the reactor are designed so as to optimize the mass transfer effect of the mud and water inside the reactor,to improve the treatment effect;to decrease the proportion of the dead space inside the reactor and to improve the space utilization rate;to shorten the hydraulic retention time and speed up its Processing efficiency.The numerical simulation results show that:(1)If the gas flow rate is too large or too small,there will be a large are of dead zones in the reaction zone,and the flow field in the reaction zone is favorable only when the inlet velocity is maintained at 2.68 m / s or 3.75 m /s.However,the larger the velocity of gas entering,the more violent the speed of liquid entering the gas collecting pipe.The speed of liquid is too high to be conducive to the formation of anaerobic granular sludge.Therefore,the optimum process is 2.68 m / s;(2)The height /diameter has significant influence on the shape of the flow field,and the height /diameter is chosen as the variables.The results show that the velocity distribution More uniform,axial and radial velocity extension,thus contributing to the muddy mixed mass transfer,and the high aspect ratio,the reaction zone velocity changes more gentle,the final formation of a flat flow state is conducive to anaerobic granular sludge form.Therefore,the simulation resultsshow that the reactor can achieve the best condition with the height / diameter of1.75;(3)The height of aeration disk installation is an important factor which influence the flow field inside the reactor.The aeration disk is the source of the reactor power,and the installation height will influence the flow field in the reactor.I chosed several experimental variables such as 40,60,80,100,and 120 mm.The results show that the lower the installation height of the aeration disk,the more favorable the mixed mass transfer of mud and water,when the height of the aeration disk is low,The smaller the viscous resistance of the hood wall,the more favorable is the radial expansion of the liquid velocity,so the dead space ratio in the reactor can be reduced,and the utilization space of the reactor is greatly improved.Finally,20 mm is selected as the best installation height;...