Many problems can cause a loss of efficiency in a distillation column such as flooding, tray damage, weeping, and foaming. Scan measurements are a powerful tool that can be utilised to locate the origin and/or severity of these problems. A TRU-SCAN® across the active area of a fractionation tray can provide hydraulic conditions and/or mechanical status of the active area such as, weeping and tray froth heights. A scan through the tray downcomers provides hydraulic and/or mechanical status based on the level of liquid measured in the downcomers.
Advanced collection technology and data analysis, confirmed by Tracerco's recent research work on hydrocarbon system pilot plant towers, provide a new way of extracting quantitative information from gamma scan data to diagnose and characterise real-time performance of fractionation towers.
Tracerco has developed a new, patent-pending technology, FrothView™, that has been developed and tested whereby the total froth height on a tray is measured from TRU-SCAN® data. The total froth height and knowledge of the tray spacing provides a method of measuring the percentage of tray space occupied by tray froth and remaining capacity. The "percent tray space" has been shown to correlate very well with percent flood, making it a useful field measurement of the capacity of operating trays.
Stationary monitoring scan results include the determination of the incipient flood point, operational surges in distillation towers, monitoring and calibration of level instruments and liquid entrainment studies. For some complicated applications, several stationary monitoring points on a tower are needed to observe the dynamic changes at different locations simultaneously.
Enhanced Tower Scanning Results For Packed Bed Analysis
One of the major concerns with packed towers is liquid distribution. Common causes of liquid maldistribution include: design, manufacturing or installation defects in distributors or packed beds; damage or plugging; and process disturbances. The first step to identifying liquid maldistribution is to perform a Tru-Grid™ Scan to determine the quality of liquid distribution through the beds, i.e., liquid channeling down one side. Scan results from a Tru-Grid™ Scan showing maldistribution as a problem can provide customers with an understanding of the areas of most concern and an opportunity to plan and prepare for necessary repairs or modifications needed in advance of a shutdown.
Tracerco has introduced a new technique, PackView™, whereby gamma scan data is used to determine relative process densities through packing. Relative process densities can be converted into liquid holdup fractions, either of which can be used as a quantitative measure of liquid maldistribution.
A Tracerco™ ThruVision Scan offers additional information to that of a Tru-Grid™ Scan when applied to a packed tower. A Tru-Grid™ Scan may show what appears to be good liquid distribution when in fact there is liquid maldistribution, e.g. An annular flow pattern. In packed towers, liquid maldistribution can be classified as Chordal or Annular liquid maldistribution. Chordal liquid maldistribution occurs when one side (one chord) of a column has excess liquid and another side (chord) will have liquid deficiency. Annular liquid distribution occurs when liquid flow distribution is in an annular pattern such as liquid flow against the wall of a column or in the center of a column. Annular liquid maldistribution may appear as "uniform" liquid and density distribution on a Tru-Grid™ Scan but can be detected by TRACERCO Diagnostics™ ThruVision scan technology.
Baseline and Pre-Turnaround scan data provide valuable real-time data for analysis
Baseline scans provide a valuable reference that can be used to identify and monitor operating performance in a column over time. A baseline scan establishes a reference point, a historical marker for column performance. The baseline scan should be performed when the column is clean, known to be in good mechanical shape, and operating with no known problems. A baseline scan of a distillation column eliminates uncertainty on future column scans, and enhances their accuracy and sensitivity allowing more subtle operational changes to be determined. Baseline scans can also be used to evaluate the effects of tower revamps, and to document the start-up of a tower.
Scheduling a scan before a turnaround can provide valuable information to assist customers with managing turnaround costs and time. Results from a tower scan can prevent shutting down a column based upon the suspicion of tray or packing damage when the actual problem may be process related. Process systems with a history of fouling or tray damage benefit from pre-shutdown scans to verify the need to order tower internals and avoid tray manufacturers emergency charges or plan suitable wash chemicals to effectively purge solids from a system.
Continuous Improvement Provides Customers With The Highest Quality of Scan Safety
Tracerco offers the safest, highest quality, and most accurate process diagnostics® service available.
For actual case studies on tower troubleshooting or baseline studies reference our Tracerco Newsletter library or case studies section feature on this website.
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