Fluidized Bed Polymerization Reactor, Paper Numerical Validation, ANSYS Fluent Training

Description

This simulation is about a fluidized bed polymerization reactor via ANSYS Fluent software. We perform this CFD project and investigate it by CFD analysis. A reactor is a device for performing chemical reactions (conversion, composition, decomposition, etc.) using catalysts and, as a result, the conversion of raw materials into desired products.

Due to the economic aspects of the production of reactors, it is necessary to design reactors with higher efficiency but lower cost and lower energy consumption; therefore, in the design of reactors, parameters such as volume, temperature, pressure, particle concentration, particle residence time, heat transfer coefficient, and reaction rate are important.

Chemical reactors have different classifications, including continuous and discontinuous reactors, homogeneous and heterogeneous, pipe and tank reactors, and fixed bed and fluidized bed reactors. In fixed bed reactors, the solids are stationary inside the reactor as a catalyst, and the reactants pass through these materials, reacting and leaving the reactor. In these fluidized bed reactors, the solids are reactants or catalysts suspended in the flow under pressure.

The fluidized bed-type reactor has advantages such as a high heat transfer rate and high mass transfer rate, lower heat transfer surface, uniform temperature distribution, proper temperature control, and complete and rapid mixing of reactors and catalysts.

The main advantage of the fluidized bed type reactor compared to the fixed bed type is the ability to control the temperature and prevent the formation of hot spots, which is necessary for any reaction. Fluidized bed reactors have many industrial applications, including petrochemical, chemical, electricity generation, incinerator, etc. This problem will simulate a two-phase flow inside a fluidized bed reactor with simple geometry.

The results are compared and validated with a paper called “A fundamental CFD study of the gas-solid flow field in fluidized bed polymerization reactors.” The simulation process is such that in the initial state inside the chamber, the solid suspended particles are only up to a height of 20 cm from the chamber bottom with a volume fraction of 0.63 inside the gas flow. The operating pressure of the system is defined as 1400000 pa.

The gas flow enters vertically and upwards at a speed of 0.3 m/s, while no solid particles enter the reactor. The present study investigates the behavior of suspended solid particles in the gas flow over time and the pressure drop generated from the reactor inlet to the outlet. The geometry of the present model is drawn by Design Modeler software. The model is then meshed by ANSYS Meshing software. The model mesh is unstructured, and 938174 cells have been created.

Fluidized Bed Method

Since the performance of reactors is inherently based on the mixing of flows and particles as reactants and catalysts in the chemical reaction process, a multi-phase model has been used to define the fluid flow within the model.

Also, considering the present model is related to simulating the suspension of solid particles within a fluid flow like a fluidized bed model, choosing the Eulerian multi-phase flow model is the most appropriate option.

Therefore, the model includes a gas flow defined as the primary phase and suspended solids defined as the secondary phase. The present model is unsteady; because the model’s nature is such, the behavior of the particles in the model changes over time. The simulation process was performed for 4 s with a time step of 0.001 s.

Fluidized Bed Conclusion

After simulation, two-dimensional contours related to the mixture pressure, gas flow velocity and suspended solids, and volume fraction of the gas flow and solid suspended particles from zero to four seconds are obtained.

Also, the pressure value at the inlet and outlet is obtained. Therefore, the pressure drop in the model has been obtained at different times because the pressure drop is equal to the static pressure difference between the inlet.

So the pressure drop is presented as a function of time. The pressure drop at different times (every 0.2 seconds) was obtained using facet average and compared with the results in the article.

The diagram in Figure 6 of the article has been used to validate the present numerical simulation results. This plot shows the pressure drop within the model over 4 seconds. A comparison of the present numerical simulation results with the results of the numerical work of the article is presented.