Flow Field Analysis And Optimization Of An Expanded Granular Sludge Bed (egsb) Reactor For Biohydrogen Production

Hydrogen is a clean, effetive and renewable energy, and is a satisfactory alternative for fossile hydrocarbon fuels in the future. Biohydrogen from waste is attactive due to energy recovery and environmental cleanup at the same time. Improving hydrogen-producing capacity and reducing the cost are the key factor to realize industrialization of biohydrogen production. There have been many publications on both Biohydrogen producing mechanisms and microorgamisms. However, the physical characteristics of Biohydrogen production reactors are not so well described. Understanding how a Biohydrogen production reactor functions is a necessary precursor for successful reactor design and operation. For a chosen bioprocess, the bioreactor should provide optimum conditions of shear stress,mass transfer, mixing, control of pH, temperature and substrate concentrations. Various types of Biohydrogen production reactors have been designed and developed, but most of these reactors were designed by means of semi-empirical correlations, and quantitative study on the fluid dynamics of such reactors are scarcely reported.In the light of above, an attempt was made for the first time in this paper to use CFD simulation to establish two models, one is expanded granular sludge bed (EGSB) reaction zone three-phase hydrodynamics model, the other one is EGSB full reactor three-phase hydrodynamics-reaction kinetics coupled model, and used these two model to analyze hydrodynamics information in an EGSB reacotr for biohydorgen production.In this paper, it clearly indicates that controlling an appropriate hydraulic retention time (HRT) is a critical factor in biohydrogen-production. When the liquid filows upward with a moderate velocity to obtain an appropriate HRT, axial pulsation and disturbances between granules of sludge are small, but compared with the velocity of lower fluid levels, the turbulent motion and velocity distribution are greater. The simulation indicated that the gas-liquid-solid system exhibits a more heterogeneous structure, with particle clusters forming and dissolving dynamically. The sludge cluster formation, which may involve gas-sludge, sludge-sludge, and sludge-wall interactions, is currently too complex to be well understood. Bubble movement, bursting, and size change are key factors affecting particle circulation and cluster formation in the reactor. Furthermore, it demonstrates that 0.5mm/s can be used to control the value of liquid upflow velocity in the EGSB operating process. Under this condition, it is good for sludge mixing and mass transfer between liquid and sludge granular, which can accelerate the reaction process and help Biohydrogen bubbles escape from the sludge; under such statement, predicted maximum potential biohydrogen production rate was 1.052(L/L·h). predicted effective Biohydrogen production rate could achieve at 0.815(L/L·h). Last but not least, the application and limitation of the models mentioned above have been discussed, and suggestions have been stated for further study.