A novel non-intrusive probe of particle motion and gas generation in the feed injection zone of the feed riser of a fluidized bed catalytic cracking unit

Abstract

The random impact of particles with diameters less than 500 μm at the wall of a gas fluidized bed or transfer line is a frequency independent “white noise” excitation source, for frequencies below 50 kHz, of the wall vibrational energy. In previous papers it has been demonstrated that the average acceleration power spectrum over the wall of a laboratory fluidized bed generated by such an “Acoustic Shot Noise” (ASN) source can supply the first quantitative data on the average mean squared particle fluctuation velocity, or granular temperature, T*, at the wall as a function of superficial gas velocity and particle diameter. In this paper we present and analyze the first experimental data on ASN excitation of the wall of 14 transfer lines with inner diameters ranging from 2–9 ft, carrying 10–80 tons of catalyst and coke particles per minute. Our focus is the first data on the particle normal velocity and density, derived from this data, along the wall of a Fluid Bed Catalytic Cracking Unit (FCCU) where gas generated by thermal and catalytic cracking of injected heavy oil at one location is the dominant source of particle motion along the entire transfer line. Simultaneous RMS acceleration measurements of the wall vibrational energy produced by acoustic shot noise are presented along the length of such “feed risers”, with inner diameters ranging from 12 to 68 in., before and after feed injection on four FCCUs converting 15 to 110 kbbl of heavy oil per day into lighter fractions that are appropriate for gasoline production. The data includes measurements of significant changes in the RMS acceleration along the feed riser on the same unit that result from changes in significant process variables. The field data demonstrates the power of the acoustic shot noise probe to detect changes in the chemistry and physics of gas generation and particle motion in the feed injection zone of a fluidized bed catalytic cracking unit, The direct acoustic shot noise data is a unique measure of the particle normal velocity and density at the wall. Estimates of the axial velocity and mean density of the particles are readily derived from this data using heuristic models. Both sets of data can serve as unique and critical boundary condition for validating computer flow codes, numerical simulations, and fundamental two phase theories of particle motion and density at the wall of such transfer lines which are major components of such significant processes as the catalytic cracking of oil into gasoline or fluidized bed coal combustion.