Case Studies

TRACERCO Diagnostics™ Distribution Study

Technique identifies design flaw

In the development of a new reactor design for a speciality chemical process, engineers spent considerable time debating methods for the rapid mixing of the reactants and the subsequent flow distribution throughout the reactor. Product yield and quality depended on the degree of mixing, so a sophisticated baffle arrangement was chosen to insure that no stagnant regions would occur in the reactor. During the start-up it became evident that the reactor was unable to achieve either the theoretical yield or even those demonstrated in the pilot plant. After eliminating many alternative reasons for the poor yield, engineers suspected inadequate mixing in the reactor, despite the care taken during the design stage. Tracerco was called in to perform a mixing and flow distribution study on the reactor as part of the investigation of the problem.

Using the TRACERCO Diagnostics™ Distribution Study, a small amount of an organic radioisotope liquid was injected into one of the reactant streams. The form of the isotope was chosen to be non-reactive in the process. It would follow the flow patterns of the fluids in the reactor. Twelve external detectors were mounted strategically around the reactor, plus one at the inlet and one on the product exit pipe. These inlet and exit detectors provided information about the residence time in the reactor. The shape of the exit curve was used to determine the mixing characteristics as defined by stirred tank equivalents (STE). The twelve detectors mounted around the reactor provided information about flow distribution through the reactor. By careful calibration of these detectors their responses can be compared to clearly indicate any bias in the flow throughout the reactor. The results of the test showed that the reactor had a 20 second mean residence time and that good mixing was occurring in the reactor, as indicated by the STE value of 1.2. However, the twelve detectors placed around the vessel did not have similar responses. The pattern was such that the front end of the reactor was not being effectively used, probably caused by the way the reactant streams were introduced. The inlet reactor baffles were redesigned to use the whole vessel more effectively, resulting in an increase in the product yield to the expected level. The process was then successfully commissioning to the design specifications.

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