Study On The Stability Of Anaerobic Fermentation Kinetics Model Based On The Flow Ratio And Dilution Rate

With the continuous research on renewable energy,anaerobic fermentation technology is becoming more and more popular.At present,anaerobic fermentation technology has been applied to a certain extent in China,and the complex anaerobic fermentation kinetic process is often difficult to control.How to control the anaerobic fermentation process has become one of the key problems that need to be solved in anaerobic fermentation technology.Generally,the anaerobic fermentation process can be divided into three stages:hydrolysis,acidification and methane production.According to the mass balance model,a three step nonlinear model of anaerobic fermentation kinetics can be established.The stability of the nonlinear system is a very important problem and the most basic requirement for the system.In this paper,the stability of the anaerobic fermentation kinetic model,the influence of the system outflow rate(?)and dilution rate(D)on the stability of the fermentation system,the time distribution required for the system to stabilize under these two parameters,and the numerical simulation of the three step model with time-delay effect are studied.The main contents include the following aspects:(1)The stability of the hydrolysis and acidification kinetics model based on Monod model and Contois model was studied.The washout equilibrium point and positive equilibrium point were found to be stable.When the system shows the washout equilibrium point,the value of matrix substrates tends to be stable in the system is negatively correlated with a.When the system showed a positive equilibrium point,the stable value of matrix substrates and macromolecular monomer organics in the system was positively correlated with ? and D.while the stable value of acid-producing bacteria was negatively correlated w ith a and D.The attachment system with ?+D-1.2 had the shortest time to reach the stable state,and the system with Contois model showed better time distribution.(2)The stability of acidification and methane-producing stage kinetics models based on Monod model and Haldane model in anaerobic fermentation was studied.There were also washout equilibrium points and positive equilibrium points that could reach a stable state.When the system presented as washout equilibrium points,the stability values of each component in the system did not change with alpha and D.When the system showed a positive equilibrium point,the stable value of macromolecular monomer organics and acids in the system showed a positive correlation with alpha and D.and the stable value of acid-producing bacteria and methanogenic bacteria showed a negative correlation with alpha and D.It takes the shortest time for an accessory system in ?+D=1 to reach a stable state.(3)The stability of the three step anaerobic fermentation kinetics model based on Contois model,Monod model and Haldane model was studied.When the system presents as the washout equilibrium point,the stable value of methane generation in the system does not change with a and D.When the system presents a positive equilibrium point,the stable value of methane generation is positively correlated with D and negatively correlated with ?.The minimum time required for an accessory system to reach a stable state in ?+D=1;At the same time,the time required to reach the stable state in each stage of the system will gradually increase with the progress of the fermentation process.The steady state of the system produces periodic oscillation(?0<?<T1).so the time-delay effect model can better characterize the dynamic stable process of anaerobic fermentation.In this paper,the three step of anaerobic fermentation,a systematic study is made on the stability of dynamic model,analyzed the flow ratio and dilution rate effect the stability of the system,and get the parameters of the system to reach steady state when the fastest range.At last,the anaerobic fermentation kinetics model with time-delay effect is established,which can provide reference for future studies.In this paper,the research results can be applied to the control process of fermentation process,through the control of the system parameters,keep the fermentation system in the best running state.