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Numerical Simulation of Flow Field in CSTR Hydrogen Bio-Production Reactor

Author: WangBo
Tutor: DingJie
School: Harbin Institute of Technology
Course: Environmental Science and Engineering
Keywords: hydrogen bio-productio reactor Computational Fluid Dynamics(CFD) numerical simulation k-mode
CLC: X703
Type: Master's thesis
Year: 2009
Downloads: 96
Quote: 3
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Abstract


The hydrogen bio-productio reactor has been being the focus of the bioreactor research for its high efficient hydrogen production.While its structure choosing, designing and scale-up are still depended only on experimental validation and expert experience, lacking in support of theories and consuming much money and time. Now CFD technology is regarded more and more in the fields of the reactor designing and optimization. Being used to analyze the flow, mixing and mass transfer characters of fluid, Computational Fluid Dynamics(CFD)can not only save a lot of resource, but also get some important local data that cannot be gathered in experiment. In this thesis,numerical simulation method is used to simulate the fluid field of the hydrogen bio-productio reactor. Combining theory of Microbial fermentation,Characteristic of fluid field in this reactor is analyzed,which Provide useful refrence gist for how to further optimize the reactor.The flow fields under different ratios of impeller radius to tank radius and angular velocity of impeller was simulated. The influence of flow field on hydrogen bio-producing process was analyzed.According to analyzed result,PBT impeller,whose ratio impeller radius to tank radius is 0.6,can provide rational velocity distributing along the radial for sufficient contact btween the biomass and the substrate.Most of the turbulence energy aye generated and dissipated in impeller region.The flow pattern is suitable for hydrogen bio-produeting process.Through the operation of hydrogen bio-productio reactor:in the reactor configurated with PBT impeller, the average biogas yield reached a peak value 29.2L/d when imepller speed was 100rpm. A maximum hydrogen production rate of 11.8L/d was obtained when impeller speed was 120rpm. Comparatively, the reactor configurated with RT impeller obtained high biogas yield 32.1L/d at 60rpm. Biogas yield decreased acutely along with the increase of impeller speed. Combination of flow field simulation results of correlation analysis, it can be found that although the increase in impeller speed brought about by the velocity field inside the reactor to improve the uniformity and speed of improvement, which means that the stagnation zone and the reactor reduce the effective and increase in volume, but gas production has not followed the rise. Based on previous studies, high shear stress on the microbial cells and sludge floc damage, and the gas volume fraction of the increase in hydrogen production will inhibit the fermentation reaction. It is precisely because of shear stress and the gas volume fraction is increased with the stirring speed increases, the average gas production at a high speed under the conditions of decline. The hydrodynamics behavior brought by RT impeller with the speed of 60rpm is more suitable for bio hydrogen production. The most optimal operation of water conditions, uniform distribution of the velocity field, the appropriate shear stress and smaller volume fraction of the gas will help improve reactor efficiency.All the researches show that the new style impeller has boosted the fluid field. Velocity distributing along the radial and Velocity distributing along the axial were controled. Energy dissipation was distributed reasonably. The purpose of high-efficiency flocculation is executed.

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CLC: > Environmental science, safety science > Processing and comprehensive utilization of waste > General issues > Wastewater treatment and utilization
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