Validation of a fluid dynamic model in a cold riser measuring catalyst concentration by gamma ray attenuation

Simulated and experimental data of a cold riser were compared to validate a fluid dynamic model and a good agreement was found. The mathematical model described the fluid dynamic behavior of the riser in a FCC - fluid catalyst cracking type unit. In the circulating fluidized bed, air and catalyst were the components, the riser is a glass tube of 2.3 m long and 0.032 m in diameter. A computational CLP controls the unit operation and the maintenance of a steady state working regime. Measurements of the air flow, pressure drop and catalyst are continuously taken for monitoring the process variables. The solid concentration in circulating flow was determined by gamma attenuation measurements with a 241Am source and a NaI(Tl) detector coupled to a multichannel analyzer. Volumetric fraction measurements were taken using a Beer-Lambert based equation. Fluid dynamic models were selected from literature according to the basic equations formulated to describe the behavior of a solid-gas system. Three one-dimensional models were initially adopted and simulation tests with literature data were carried out. By means of a program written in the MATLAB software language the solution of the equations were obtained. One model was finally validated comparing the calculated data with experimental for the fluid dynamic variables: volumetric fraction (axial profile), solid and gas velocity and slip ratio between the two components. The results are given in graphics for the correlations of experimental and simulated data. The calculated values approximation was evaluated following the validation criterion of a maximum 10 % error. The validated model shows a good agreement for the experimental conditions: catalyst density of 2 - 5 kg/m3, gas velocity of 3 - 6 m/s and slip ratio values between 1 and 2. Under these conditions it can be stated the a one-dimensional model can satisfactorily describe the fluid dynamic behavior of a small diameter riser as in the cold model studied. (author)