A portable pulsed photoacoustic sensor for the monitoring of hydrocarbons in process water

During the operation of offshore production platforms, marine contamination can occur from leakage, spillage and from the overboard discharge of process water. For every 100 tonnes of oil extracted from North Sea reservoirs, 130 tonnes of contaminated process water are generated (1990 figures) and when discharged overboard, the current protocol limits the oil content of discharged water to 40 parts per million (ppm) averaged over a calendar month Thus with North Sea production approaching 100,000,000 tonnes per annum, an annual contamination of some 4,000 tonnes of oil could be discharged overboard from production platforms. This situation is replicated in most offshore facilities world-wide and represents a global threat to sensitive marine environments. The present methods for the detection of oil in discharge water are based either on chemical analysis of intermittent samples or bypass pipelines with instrumentation to detect either dissolved or dispersed hydrocarbons by a variety of optical techniques including absorption, scattering and fluorescence. Tests have shown that no single instrument entirely meets either the present needs or satisfies the requirements of the more stringent future legislation which may limit total hydrocarbon content to 30 ppm or less. To meet this need and to develop a new generation of systems for environmental monitoring, a completely novel type of in-line instrumentation is being developed based on the photoacoustic technique. The instrument has been designed primarily for the monitoring of oil in process water but may also find application in the oil detection in the open sea and in the detection of oil and other pollutants in rivers, estuaries, lochs and sewage.