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Tunable-Diode Laser-based moisture sensors help ensure long catalyst life, reduce operational costs, and offer the lowers overall cost of ownership.

Refineries and chemical plants have long been subjected – perhaps unwittingly - to high costs incurred from failure of conventional moisture analyzer to accurately read moisture intrusion in feedstocks and hydrogen recycle streams, vital to optimizing product yield and catalyst life.

Because typical analyzers, such as those based on surface absorption or adsorption, employ sensors that are exposed directly to harsh elements in the streams they monitor, timely and accurate moisture readings may be disrupted within a relatively short period of time. The disruptive operational life leads to substantial costs that can range from exorbitant consumables and maintenance to conceivably hundreds of thousands of dollars for premature catalyst recharging or untimely interruption of continuous processes.

The innovative employment of tunable diode laser (TDL) technology has enabled the development of a new moisture technology — the laser-based spectroscopy moisture analyzer. One such device, developed as a spin-off of NASA-JPL space technology by SpectraSensors, Inc. (San Dimas, CA), continuously samples reformer streams without coming into contact with them, thereby avoiding destructive contents such as hydrochloric acid, which can quickly damage (“poison”) a surface-absorption based sensor. Moreover, the surface based sensors may not be entirely disabled, or it may drift for a number of reasons and may continue to transmit inaccurate moisture readings until catalyst life has been compromised.

The TDL-based sensor can provide refineries and chemical processors with a high return on investment (ROI) based on avoidance of tangible costs, such as consumables, as well as extremely high intangible costs, such as catalyst recharging and process interruptions.

Tangible costs are greatly reduced through the use of the TDL based moisture analyzer. While initial purchase price is somewhat higher, the reduced operating costs of this technology are likely to overcome this initial investment quickly. These devices can run for years without requiring maintenance, recalibration or replacement. Therefore, costs such as analyzer technicians, repair or replacement of probes, as well as an inventory of spare sensor heads are eliminated.

During turnovers or other abnormal process events, moisture slugs can render conventional moisture sensors “blind” for hours or days. For this reason, refineries have resorted to building in redundant analyzers and the associated sample handling conditioning and stream switching. This can double or triple the installed costs!

Speed and reliable measurements characterize TDL-based moisture analyzers. They are about to detect moisture problems with extremely high accuracy and measurement intervals as frequent as within a second, enabling practically instantaneous response. This helps to eliminate the chance that moisture will get through “reading time gaps” that are often several minutes or hours in duration with conventional sensors.