New Technology in Oil Content Monitors

Abstract

ABSTRACTInternational antipollution requirements have been legislated to regulate the oil content of bilge effluent from ships. In response to these standards, the U.S. Navy is currently in the process of installing pollution abatement equipment on all vessels. The equipment will consist of an oil‐water separator in the bilge discharge line, followed by an oil content monitor which makes the final decision on whether or not the water is clean enough to be pumped overboard. The monitor is required to make a real‐time measurement of oil concentration in the range 15 ± 5 to 100 ± 20 ppm for flow rates up to 50 gal/min. and possibly in the presence of interfering contaminants, such as rust.This paper presents the results of the current effort to develop a monitor which satisfies all of these requirements and is sufficiently rugged for fleet deployment. The monitor under development employs two fiber optic systems and a small microprocessor. The first optical system measures the concentration of particles in the flow as a function of their sizes, using small angle forward scattering. The second determines what percentage of the particles in the flow are oil, using large angle scattering. The microprocessor takes the data from the two optical systems and calculates the oil concentration in the flow. Since the particle size is measured by the monitor, no sample preparation is required and the monitor may be placed directly in the discharge line where it responds to changes in oil content in less than one second. In addition, this monitor can notify the operator of impending oil‐water separator failure associated with passing large oil particles.A demonstration monitor consisting of the forward scattering unit has been successfully tested at the NavSea oil pollution abatement test facility at the Naval Ship Systems Engineering Station at Philadelphia. The monitor agrees well with chemical means of measuring oil content. Results of this comparison and laboratory test of a prototype instrument that features contaminant discrimination will be presented.