Optimization And Research On Structure Of CSTR Reactor For Biohydrogen Production From Corn Straw Based On CFD Flow Field Analysis

The problems caused by the depletion of fossil fuels and environmental pollution have gradually become a major problem faced by all countries in the world.The search for clean new energy has become a priority nowadays.Straw crops are widely cultivated around the world,and the use of straw bio-fermentation for hydrogen production has become one of the effective ways to alleviate this problem.However,the hydrogen fermentation technology of straw-like biomass biofermentation is faced with many problems,such as low hydrogen production efficiency,lack of reactor design parameters,and the influence of the flow field characteristics in the reactor on the hydrogen production efficiency.Based on this,the continuous stirred tank reactor(CSTR)for biological fermentation of corn straw was selected as the research object,and the multiphase flow field characteristics in the reactor and the hydrogen production efficiency for the fermentation process were simulated by the combination of CFD simulation and experiment.The study of the influence laws is intended to reveal the relationship between the reactor structure,operating conditions,flow field characteristics,and the hydrogen production efficiency from the microscopic level.By optimizing the reaction structure,the fluid mixing performance is improved and the straw biomass is realized.The improvement of hydrogen production efficiency provides basic data and theoretical basis for the design and amplification of biofermentation CSTR reactors.(1)Based on the previous studies,the CFD modelling of the fluid flow field characteristics in a biofermentation CSTR reactor was performed.Three kinds of shell models were proposed to improve the uniformity of material and liquid mixing in the CSTR reactor,and the proposed shell model was physically modeled.The single-phase numerical simulation of the CSTR reactor was performed by Fluent 18.0,and analyszd the flow field characteristics of the internal fluid in the CSTR reactor with theories.It was found that in the reactor model d with 4 vertical baffles,the axial and radial velocity distributions of the fluid were improved,the flow field distribution in the reaction zone was uniform,and the formation of stagnation zones was effectively avoided,which increased the uniformity of the liquid mixture in the CSTR reactor.(2)Carried out numerical simulation and optimization to the flow field in the established CSTR reactor model d.After mesh independence verification,the number of meshes in the d model of the CSTR reactor was determined to be 852,057.Investigated the fluid flow characteristics of feed liquid in the CSTR reactor at different paddle types,different slot ratios,and different rotation speeds.Then analyzed it combine with theory of hydrogen production from biological fermentation.The best operating conditions after comparison were as follows: a 45-degree oblique-blade turbine impeller was used as a rotating device,the ratio of the diameter of the paddle and groove was 0.53,and the rotation speed of the paddle was 120 rpm.Under this condition,In the CSTR reactor model d,the key fluid flow field characteristics such as flow velocity,shear force,turbulent kinetic energy and gas phase volume fraction are all superior.(3)In order to determine the effect of the optimal operating parameters and flow field characteristics of the reactor on hydrogen production from biofermentation of corn stover,based on the CFD simulation and previous research results,the verification experiment of biohydrogenation of corn straw was performed in a 5 L CSTR reactor.when the other process parameters are the same,the experiment of hydrogen production from corn straw bio-fermentation is carried out according to the parameters of the stirring paddle type,the ratio of the diameter of the paddle and groove was 0.53,and the rotation speed obtained by CFD simulation,then analyzed the effect of reactor operating parameters and flow field characteristics on the hydrogen production efficiency,Combined with the flow field simulation results in the reactor.The results show that the configuration of 45 ° oblique blade turbine impeller in the 5 L CSTR reactor is significantly better than that of the double-blade impeller;The 45 ° oblique blade turbine impeller with the ratio of the diameter of the paddle and groove is 0.53,at 120 rpm can get better hydrogen production,which increased hydrogen production by 16.5% over previous research;the analysis of the homogeneous mixing of feed and liquid in the main reaction zone was beneficial to increase the hydrogen production,and the ability of hydrogen production by microorganisms was reduced when the shear force and hydrogen volume fraction were higher.