A sensor using raman spectroscopy for on-line composition monitoring of distillation mixtures in real time

The goal of this project is energy conservation. All the discoveries made during the course of the research are incidental to this goal. Distillation is a notable example of a commercial process that can be dramatically improved through energy conservation. To efficiently operate a distillation column requires the ability to accurately monitor the composition of the distillation mixture. It has been found that Raman spectroscopy, a proven laboratory technique for composition analysis, can be applied to industrial composition monitoring. Practical implementation of Raman spectroscopy in an industrial setting is constrained by several competing limitations. The instrumentation must be housed in a benign environment, while the process, a hostile environment, must be monitored on-line with a hardened probe. This requires that the instrumentation and the probe be connected by optical fibers. Raman scattering is a weak effect, but only a small fraction of the available Raman energy can be coupled into the fibers. Consequently, in order to obtain usable spectra, stringent demands are imposed on the optical efficiency of the system. Finally, the instrumentation is expensive, but the market will not bear a high price for composition measurements. An acceptable cost per monitoring point can be realized by using time division multiplexing to allow the same instrumentation to monitor several points simultaneously. All the elements of a prototype composition monitoring system have been constructed and tested in the laboratory. The composition readings produced by the system are of sufficient accuracy to be used for efficient control of a distillation column. The computerized control system has been verified with the hardware. The system is ready to be applied to an actual distillation column.