Refineries and chemical plants have long been subjected – perhaps unwittingly – to high costs incurred from failure of conventional sensors 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 contaminants 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. Developed as a spin-off of NASA-JPL space technology by SpectraSensors, Inc., this advanced optical device 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 moisture analyzer can provide refineries and chemical processors with a high 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 quickly 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. The aggregate savings on tangible costs can easily amount to tens to hundreds of thousands of dollars per year, depending on the number of measurement points.
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!
Intangible cost savings vary widely according to applications and extent of moisture intrusion. It is reasonable to assume that these costs may range from tens of thousands of dollars to hundreds of thousands for lost product or due to a degraded catalyst.
The timely detection of excess water from feed streams enables refiners to lengthen the intervals between catalyst recharges in some instances. Lengthening the useful lifetime of catalyst represents a savings of hundreds of thousands of dollars or more, depending on specific plant requirements.
Historically, in cases where catalysts require recharging or replacement, consequential process interruptions have resulted in cascading costs of millions of dollars. Even discounting the savings of such catastrophic failures (e.g. moisture slugs), it may be assumed that, by enabling the maintenance of catalyst quality and efficiency, the TDL-based moisture analyzer can save many times its purchase price in a short period of time.
Speed and reliable measurements characterize TDL-based moisture analyzers such as those offered by SpectraSensors. They detect moisture problems with high accuracy in as quickly as one second, enabling practically instantaneous response. This eliminates the chance that moisture will get through ‘reading time gaps’ that are often several minutes or hours in duration with conventional sensors.
The costs associated with unreliable moisture measurements can easily be derived by examining operational costs over the life of an analyzer. These include probe replacement, technician labor and overhead associated with maintenance and downtime. The costs associated with redundant systems are equally straightforward to compute. Additionally, the intangible costs of analyzer failure can be examined. Although the probability of events such as catalyst failure or reduced efficiency or contaminated production may be low, the costs of these events are extremely high. For these reasons, the value of a reliable and fast measurement point goes far beyond the initial purchase price.