Study On Hydrogen Production By Methane Catalytic Decomposition In A Fluidized Bed Reactor

Because its combustion product is none but H2O, and no pollution on the environment, hydrogen is a perfect fuel in the future and attracts more and more attentions from the researchers in the recent years. A great deal of carbon oxide will be produced when steam methane reforming is employed to produce hydrogen, which is the most widely used method in the industry. Catalytic direct decomposition of methane is a good option to produce high-purity hydrogen because its product does not contain carbons oxide, which means that no further process, such as shift reaction, separating carbon dioxide, needs to be carried out. So an experimental investigation about methane decomposition was carried out in a fluidized bed reactor, and the main contain of this work includes: gas-solids flow structure under ambient temperature; hydrodynamics of gas-solids under high temperature; methane direct decomposition with presence of Ni-basis catalyst in a fluidized bed reactor.The solids concentration signals obtained by the optical fiber probe were analyzed by the wavelet analysis method for the investigating the axial and radial structure of gas-solids flow in a circulating fluidized bed, and these signals were decomposed into 15 scales by db4 wavelet. The results indicate that the particles in axial distribution is dense section in the bottom and dilute section in the top, the particles in radial distribution is a core-annular structure. The power fraction of the high frequency, medium frequency and low frequency is about 10%, 60% and 30%, respectively, which implies that the most particles are in the cluster or aggregates in the riser. The velocity, volume fraction and power fraction of the particles in radial distribution all presents a typical core-annular structure, which is uniform in the major portion of the riser, while varies significantly near the wall of the bed. The influence of the operation conditions on the gas-solids flow structure in the bottom dense section is different from that in top dilute section of the riser. The solids flux has a visible effect of the gas-solids flow in the bottom dense section of the riser, while in the top dilute section, the superficial gas velocity has a significant influence.A bubble fluidized bed that can endure high temperature up to 6000C was built up to study the hydrodynamics of gas-solids flow under high temperature. The initial fluidization velocity of 15Ni/Al₂O₃, 15Fe/SiO₂ and activated carbon particles have been tested from 400℃to 600℃. The effect of supports such as activated alumina, silica gel and activated carbon and promoters such as copper, iron, magnesium and zinc in nickel-based catalyst for methane decomposition were studied in a fluidized bed reactor. The results indicate that the supports have a great influence on the activity of the catalyst, and the highest catalytic activity is activated alumina, then silica gel, and activated carbon is the lowest one among three supports. The activation energy ( Ea) of these three nickel-based catalysts(content of Ni is 15%) is 64.9 KJ/mol,75.6 KJ/mol,104.2 KJ/mol, respectively. The metallic promoters such as Mg,Fe,Cu,Zn could improve the conversation of methane during the initial reaction time, and their effects ranking over the catalyst active capability is Fe>Zn>Cu>Mg on activated alumina, Fe>Zn>Mg>Cu on silica gel, Cu>Fe>Mg>Zn on activated carbon. With increasing of the mass proportion of active substance, the activity of catalyst increases. Higher temperature and lower space velocity will conduce the improvement of methane conversion rate.