Research Of Fluidized Bed Reactor For Methanol-to-Olefins Process

Methanol-to-olefins process is the most hopeful new process instead of petroleum route process, so research of fluidized bed reactor for methanol-to-olefins process is of importance for continuous development and improvement of the process. The dissertation gives some results about reaction-regeneration process of methanol-to-olefins in fluidized bed and micro-structure of catalysis. Cold model experimental facility of gas-solid circulating fluidized bed for methanol-to-olefins process is established and flow behavior in gas-solid circulating fluidized bed is studied. Computational fluid dynamics model of gas-solid fluidized bed is established and gas-solid flow behavior is simulated by software FLUENT by means of modified drag coefficient model. Mathematical model of fluidized bed reactor for methanol-to-olefins process is founded combining with cold model experiments in the gas-solid circulating fluidized bed, reaction kinetics and transport process principles. The model equations are programmed using software MATLAB.Experimental equipment of reaction-regeneration fluidized bed for methanol-to-olefins process is established and optimized operating conditions of reaction-regeneration process are obtained according to the research of reaction-regeneration process for methanol-to-olefins process in the experimental equipment. In order to study the process of methanol-to-olefins, the SAPO-34 is used as the main active component in a fluidized bed reactor with dimensions of 030 mm×320 mm for its dense section and 068 mm×160 mm for its thin section. The effects of reaction temperature, WHSV and feed composition on ethylene, propylene selectivity and methanol conversion are investigated; at the same time, the deactivated catalyst after use is regenerated in the fluidized bed and the catalytic performances of the regenerated catalyst is investigated too. The results indicate that, under optimal conditions for proceeding operation methanol-to-olefins:i. e. temperature of 450?, WHSV of 3 h1a and feed methanol composition of 99.5%(mol), the total selectivity of ethylene and propylene can reach 92.06%. The catalyst SAPO-34 and the regenerated catalyst are characterized by means of XRD, SEM, BET, NH3-TDP and TGA, respectively. It is found that, after regeneration, the microstructure and the catalytic performance of the regenerated catalyst has no evident change, and it can be used repeatedly. The TGA characterization indicates that the 600?is the optimal regeneration temperature.Flow behavior in gas-solid circulating fluidized bed is studied in cold model experimental facility of gas-solid circulating fluidized bed for methanol-to-olefins process via a PC-6D solid concentration analyzer and a PV-6D particle velocity analyzer. Solid concentration and particle velocity distribution in cold model experimental facility are studied with a mixture of sand ranging from 154 to 180?m diameter used as the fluidizing particles, different superficial gas velocities ranging from 0.3930 to 0.7860 m/s and different initial bed height ranging from 600 to 1200mm using air as the fluidizing gas. Local solid concentrations and particle velocity under 10 operating conditions are measured at 10 radial positions (r/R=0.0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9) on 10 axial levels (500,600,700, 800,900,1000,1100,1200,1400,1600mm),4 initial bed height (600,800,1000,1200mm) and 4 superficial gas velocities (0.3930,0.4912,0.5895,0.6877,0.7860m/s). Solid concentration and particle velocity distribution in cold model experimental facility are discussed with four types of distributors employed in the experiment:5%o circle distributor,5%o branched pipe distributor,2.5%o branched pipe distributor and 2.5%o circle distributor. Particle cycle flux is studied with different superficial gas velocities ranging from 0.3930 to 0.7860 m/s, different initial bed height ranging from 600 to 800mm and 5%o branched pipe distributor used. Optimized operating conditions of particle cycle flux for reaction-regeneration process are obtained.Computational fluid dynamics model of gas-solid fluidized bed is established according to analysis of flow behavior in gas-solid fluidized bed and theory of gas-solid flow. Gas-solid flow behavior in fluidized bed is simulated by software FLUENT by means of multi fluid model for two phase and 3d unsteady state algorithm. Syamlal & O'Brien model is modified based on minimum fluidization velocity and modified Syamlal & O'Brien model is added in software FLUENT via C programming language. Flow behaviors in gas-solid fluidized bed are discussed under different operations and models, the simulated results are compared with experimental results. Effects of meshing, drag models, particle shear viscosity, particle coefficient of restitution and virtual mass force on predictive power of computational fluid dynamics model are discussed. Simultaneously the flow behaviors using different particle diameters are studied. The results indicate that flow behaviors can be simulated by computational fluid dynamics model. the result with modified Syamlal& O'Brien drag model,3d mesh, Syamlal particle shear viscosity, regard of virtual mass force can simulate the flow behavior of gas-solid fluidized bed better. The effect of particle coefficient of restitution on the simulated result is small.Mathematical model of fluidized bed reactor for methanol-to-olefins process is founded combining with cold model experiments in the gas-solid circulating fluidized bed, reaction kinetics and transport process principles, the results of methanol-to-olefins reactions using catalysis SAPO-34 in relative steady period are simulated. Effects of operated conditions on product distribution and pressure drop are discussed. The results indicate that high temperature can increase the selectivities of ethylene and propylene, methanol conversion and pressure drop; high operated pressure can increase methanol conversion and decrease pressure drop; high space velocity can increase pressure drop and decrease methanol conversion; effects of nitrogen on results of reactions are unconspicuous.