Iranian Journal of Chemical Engineering (IJChE)

Abstract Abstract
Gas to liquid (GTL) process involves heterogeneous catalytic chemical reactions that convert synthesis gas to hydrocarbons and water vapor. A three phase reactor, called Low temperature Fischer-Tropsch (LTFT) is commonly applied for GTL process. In this reactor the gaseous phase includes the synthesis gas, light hydrocarbons and water vapor, the liquid phase is a mixture of the heavy hydrocarbons, and the solid phase is composed of the catalyst and the waxy products. The presence of the liquid phase in LTFT reactor causes mass transfer restriction, affecting the reaction conversion. In this work a numerical simulation of the LTFT fixed bed reactor in trickle flow regime has been accomplished to understand the impact of the liquid phase on the reactor performance. For this purpose, we have developed an axisymmetric two-dimensional multiphase heterogeneous model, where contain carbon monoxide and hydrogen, are transferred into the liquid phase. The reactor consisted of a shell and a tube that was filled with the spherical cobalt catalyst. The reaction conditions were as follows: the wall temperature was 473 K, pressure was 20 bars and a gas hour space velocity (GHSV) was 111 Nml.g_cat^(-1).h^(-1). The numerical simulation results proved the negative impact of the liquid phase on the reaction conversion. The model predictions were evaluated against the reported experimental data and also compared with the result of a numerical pseudo-homogeneous model. It was found that applying the heterogeneous model instead of the pseudo-homogeneous model clearly decreases the deviation of the numerical results.

Abstract Enhanced design strategies in the industrial cracking furnaces are of practical interest for petrochemical industries. For such engineering purposes the exact simulation of temperature and flow fields in the furnace is mandatory. In this paper, a study was conducted to simulate 3D flue gas flow pattern and temperature field in the radiation section of an industrial cracking furnace in order to improve the design of the steam cracking furnaces, employing the computational fluid dynamics (CFD) technique. The steady-state Reynolds averaged Navier–Stokes (RANS) equations were solved, in a finite volume scheme for a turbulent premixed flow applying the renormalization group (RNG) version of the k
ε− model, together with global combustion kinetics for methane-hydrogen-air. Calculation of the Damkhöler number and optical-thickness was conducted to identify the appropriate methods for the numerical modeling of radiation and turbulence-chemistry interaction phenomena. The predicted results match the literature data quite well. The validated numerical procedure was then employed to investigate alternative design attributed to different burner locations. The alternative design resulted in a more uniform temperature profile on the reactor tubes as well as lower peak flame temperature.

Abstract Solid transport phenomena drastically affect rotary drying process. A change in any solid movement variable such as particle hold up or input flow rate results in a significant variation of heat and mass transfer rates. Therefore, in this research dynamic study of these phenomena was conducted both experimentally and theoretically. Several experiments was performed employing an industrial granule dryer. The dryer length and diameter were 5 and 1 m, respectively. In each experiment one of the solid movement variables was changed and the resulting dynamic change on the process was measured. The data was used to estimate the parameters of a dynamic distributed parameter model of the system using dynamic optimization method. The data were also employed to evaluate the model. The model predictions for solid hold up and outlet flow rate were compared with those of the experimental data. The average model error for solid hold up and outlet flow rate were 5.6% and 5.4 %, respectively.