A fluidized bed membrane reactor for steam methane reforming: experimental verification and model validation

• Main Author: Adris, Alaa-Eldin M.
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/6980

Steam reforming of light hydrocarbons, especially natural gas, is an industrially important chemical reaction and a key step for producing hydrogen and syngas for ammonia and methanol production, hydrocracking and hydrotreating, oxo-alcohol and Fischer-Tropsch synthesis and other essential processes in the petroleum and petrochemical industries. However, industrial fixed bed steam reformers suffer from several problems which seriously affect the operation and performance of these reactors: low catalyst effectiveness due to mass transfer resistance, low heat transfer rates, large temperature gradients and thermodynamic equilibrium constraints. These problems with conventional reformers can be alleviated by using a new fluidized bed membrane reactor (FBMR) system. The FBMR system combines the several advantages of fhiidized beds as catalytic chemical reactors, in particular catalyst bed uniformity, improved heat transfer and virtual elimfriation of diflhsional limitations, with advantages offered by permselective membrane technology, in particular shifting the conventional thermodynamic equilibrium and the in-situ separation and removal of a desirable reaction product. A pilot scale reforming plant was designed, constructed and commissioned to prove the concept of the new reactor system and to study its properties. The pilot reactor system had a hydrogen production capacity of 6 m³[STP]Ih and was designed to withstand temperatures up to 750 C and pressures up to 1.5 MPa. The reactor had a main body of inside diameter 97 mm and length 1.143 m, in addition to an expansion section of inside diameter 191 mm and length 0.3 05 in. The reactor was provided with thin-walled palladium-based tubes as hydrogen permseleotive membranes. The work presented in this thesis shows the reforming catalyst to be fluidizable, when the proper particle size range is used, and able to withstand the mechanical environment of the fluidized bed reactor to a reasonable extent. The investigation also indicates that fluidized bed process with hydrogen removal via permselective membrane tubes is feasible from a technical point ofview. Advantages of the new process demonstrated by this study include major decreases in the reactor size and in the amount of catalyst required, withdrawal of a very pure hydrogen product, operation beyond normal conversion limits imposed by thermodynamic equilibrium and suppression of undesirable (backward) reactions in the freeboard region. The shifi of the reaction equilibrium reduces the reforming reactor energy requirements and is advantageous from an environmental point ofview. Economic feasibility ofthe new reactor system will improve as technical improvements are made in membranes to allow, for example, thin uniform layers of palladium or nickel on a porous ceramic or sintered metal substrate.