Research On Key Scientific Issues And Scale-up Rules Of IC Anaerobic Reactor

As a new generation of high-efficiency anaerobic reactor,the Internal Circulation Anaerobic Reactor(IC reactor)shows the advantages of large processing capacity,small floor space,good operation stability and low investment cost in wastewater treatment.The core technology for this apparatus has been monopolized by some foreign countries,which we still do not master,and the information on its operating rules and design criteria are rarely reported.The anaerobic biological treatment process involves rather complex flow behaviors of gas,liquid and solid.Properly modeling and predicting of this process become the technical key to understand the operation law of the reactor and to establish the scaling up rules.In this work,a novel multi-scale method was developed from single granule scale,mesoscale scale of granule swarm as well as macroscopic reactor scale.The three-phase flow characteristics of IC reactor was systematically studied for the first time by this method.The flow characteristics of each phase in IC reactor were recognized and the scale-up rules of IC reactor were established.This research should be crucial for the design and development of industrial scale IC reactors.The flow behaviors of anaerobic granular sludge were difficult to predict because of its porous and permeable properties.The key issue was lack of suitable drag coefficient model.Firstly,the Discrete Element Method(DEM)was applied to establish the granular sludge geometry model.The Computational Fluid Dynamics(CFD)method was used to investigate detailed fluid flow and surface forces in and around the anaerobic granular sludge.The results showed that the drag coefficient model obtained by the simulation agreed well with the experimental results,indicating that the granular sludge geometric model constructed by DEM could well express the porous permeable characteristics of anaerobic granular sludge.The drag coefficient model for a single anaerobic granular sludge was also developed by introducing the porosity as a correction term.Since the IC reactor has a rather high sludge concentration,the flow behaviors of anaerobic granular sludge swarms were difficult to predict.The key issue was lack of suitable drag coefficient model for granular swarms.The unit cell model for a granular swarm was firstly constructed in the present study and the porous medium method was used to describe each granule.The drag force of a granular swarm was studied and analyzed by combining with the drag force coefficient model of single granule.The drag force coefficient model describing a granular swarm was corrected.By comparing with the experimental results,it was determined that the corrected model could accurately predict the expansion height of the anaerobic granular sludge bed.As the main reaction zone of the IC reactor,the three-phase flow including gas,liquid and solid was very complex and thus the accurate description for this process is rather difficult.Based on the obtained drag coefficient model for granule swarms,the flow field characteristics in the first reaction chamber of IC reactor were predicted and analyzed.It was found that the pneumatic stirring effect provided by self-produced gas was very important for the uniform mixing of granular sludge,which is useful for improving the treatment efficiency.When the gas production amount became larger,the granular sludge distribution was also more uniform.The accurate prediction of internal circulation should be beneficial to design the IC reactor.However,the accurate description of the multi-phase flow was still difficult.The Multiple Flow Regimes(MFR)was adopted to study the effects of immersion ratio and riser's tube diameter on the internal circulation,gas holdup and frictional resistance drop.Based on the detailed study,the key parameter models for the design of IC reactor,namely the gas holdup and frictional pressure drop,were improved.Based on the detailed study,the key parameter models were applied for the design of IC reactor,namely the gas holdup and frictional pressure drop,were improved.The calculation accuracies for the gas holdup model and frictional pressure drop model were improved by 36.5% and 58.5%,respectively.Based on the research results in this work,the scale up rules of IC reactor were summarized,and some design criteria of the reactor were proposed,which could provide the theoretical guidance to design industrial IC anaerobic reactor.