By Nick Basta
Our feature this month about optical remote sensing (ORS) offers a snapshot of where this technology has been and where it is going. There are active and successful implementations, but there is also a sense among its proponents that there is unmet potential. Why is this?
ORS truly offers some near-magical capabilities. By shining filtered light across a path, or even from a source and measuring the reflected light that returns, one can determine the chemical composition of the air in parts-per-billion sensitivity. ORS has been used in climatological studies of the atmosphere; in geological studies of volcanoes; in national or regional surveys of ambient air conditions; and as so-called fenceline monitoring systems that can observe the emissions of a process plant, pipeline or remediation site. In a somewhat different configuration (the remote part drops out), the technology can be used to measure chemical reactions, gas concentrations in storage vessels, or stack emissions.
Having demonstrated all these capabilities, one would expect the technology to occupy a prominent place in the repertoire of instrumentation and environmental engineers. It generated considerable excitement in the early 1990s, but then receded to the background as more of a developmental tool. Even its advocates concede that the early applications of the technology were overpromised and underdelivered. Now, at least according to its proponents, it is poised for a comeback.
Technology developers have put a lot of hard work into lowering the cost of the systems, making them reliable and requiring little routine maintenance. The interfering presence of water vapor or CO2 has been solved. New software automates what had been the complex process of filtering and analyzing the optical signals the instruments generate. Some also offer comprehensive environmental-monitoring programs to ease the acquisition, analysis and reporting of air-emissions data.
The application that ORS fans point to is fenceline monitoring of chemical process plants, either as part of a regular monitoring system, or as an emergency response system in case of upsets. As they properly point out, plant managers know where their potential emissions could occur, and have point-source monitors already in place. But they dont know and dont monitor where unplanned emissions could occur.
A related situation occurs during site remediation, where point monitors are required to measure gas releases. But these releases could bypass the monitors if the wind changes, or if the distance between monitoring points is too large. ORS systems now have the capability newly developed to map a plume in two or three dimensions, providing a near-ironclad confirmation of what is occurring during the remediation.
But these applications are neither unmet needs of the industry, nor are they unaddressed by more conventional technology. ORS might be unequivocally better, but existing point-source sniffers or related instrumentation can meet some of the need. And advances in risk-management practices, as well as development of risk-management plans, address much of the need for preparing for unexpected process upsets or gas releases.
Environmental managers and ORS proponents point to regulatory agencies, specifically EPA, as being part of the holdup of advancing this technology. But there, too, the picture is more nuanced. EPA has funded development of new ORS capabilities, and also funds an Environmental Technology Verification Program where instrument vendors can obtain third-party validation of their systems. There is a comparable program but different enough to make cross-validation impossible in Europe, run by the TUV organization in Germany.
When you put all these pieces together, what you have is a technology struggling to make its place in the toolkit of industrial and environmental management. There might also be as-yet-unknown process-control or reactor applications that could be a real benefit to manufacturers running gas-phase processes. From one perspective, ORS has made it in the sense of having been developed to the point where it can be a drop-in choice for air monitoring. From another, its still struggling to meet its initial expectations. Its hard to say where ORS is going to end up, but if nothing else, it gives testimony to the persistence and determination of the researchers and entrepreneurs who have been working on it for more than a decade.
Nick Basta is editor at large for Chemical Processing magazine. E-mail him at Nbasta@putman.net.