Case Studies

TRACERCO Diagnostics™ FCCU Study

Operating Problems Identified

A fluidised catalytic cracking unit (FCCU) had a problem producing and maintaining an even fluidisation of catalyst and gas between the catalyst regenerator and the reactor. This fluidisation was accomplished by arrays of nozzles along the standpipe from the regenerator and along the catalyst riser to the reactor. When the conversion efficiency fell, engineers began to question the fluidised catalyst density and the density profile across the pipe from the regenerator. Tracerco were called to carry out a TRACERCO Diagnostics™ FCCU Study to provide information on the fluidised catalyst density.

Scanning positions were chosen at several key places between the regenerator and reactor. At each position, a rigid frame was erected around the pipe with a gamma ray source on one side of the pipe and a gamma ray detector on the other. A series of scans were taken across the pipe; a second series was taken at right angles to complete the matrix of readings.

Fluctuations in the mean density were monitored versus time by recording the detector response continuously by means of a chart recorder. Results from this study showed significant variations in catalyst density along the standpipes and this was correlated to the positions of the aerating nozzles and the amount of aeration. The fluctuations in density at any one position indicated either pockets of air passing along the pipe or catalyst lumps crossing the scan line. By performing the matrix study in several positions, the locations and extent of the problems areas were determined and corrective action taken at those locations. Gamma ray scanning was then repeated in order to confirm the improvement.

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