Centrifuging Petroleum-refinery Emulsions

Abstract

The centrifuge has come into general use in the oil fields and in theestablishments where lubricating and fuel oils are used. Probably centrifugalmachinery will be found more useful in the refinery when the operators are morefamiliar with the principles of modern centrifugation and when centrifugalengineers better understand the refinery emulsion problems. It is not generally realized that centrifugal force and gravity have twodistinct functions: First, subsidence wherein the suspended globules arebrought into contact; second, coalescence (when this is possible) by rupturingthe films around the globules. In the case of a water-in-oil emulsion, anexercise of the former function alone would yield:oil, free, or as free asdesired, from water; anda concentrated water-in-oil emulsion-concentratedin the sense that it contains a relatively large percentage of the internalphase. An exercise of both functions will yield:water-free oil andoil-free water. Centrifugal force is much better than gravity for subsidence because, in thecase of industrial emulsions where the suspended globules are visible under amicroscope, subsidence is directly proportional to the force applied. Centrifugal force is only slightly better than gravity for coalescence. Aminute trace of a proper reagent will immediately do more to nullify theinterfacial surface tension opposing coalescence than an indefinite applicationof the highest attainable centrifugal force. No mathematical analysis has beenmade to explain the failure of high centrifugal force to induce a decidedlymore rapid and more complete coalescence than is obtained by gravity. The adjustment of the centrifuge rotor depends more on the extent ofcoalescence that is desired or is possible than on any other factor. One reasonfor this dependence is to be found in the curious relation between the specificgravity and the hydrostatic pressure of emulsions. AIME 070–61