Moving gamma scanning forward – quantitative analysis of tray capacity

Improving process operating margins can include maximising production of higher value products and/or minimising production costs. Process plants depend heavily on fractionation towers to produce products meeting customer specifications. Tower gamma scanning is well established in the process industries as a qualitative tool to help troubleshoot fractionation towers. Using new measurement detector technology and innovative analysis of gamma scanning data Tracerco is now able to offer quantitative information about the useful capacity of fractionation towers, both trayed and packed.

Trayed Towers - FrothView™
Up to now there are few practiced methods for measuring a liquid or froth level on a tray from gamma scan data. However; no matter the practitioner the conventional methods allocate a tray’s aerated liquid height somewhere in the middle of the layer. This method is adequate for diagnosing tray damage – whether a tray is capable of holding liquid or not. But beyond this determination, conventional tray liquid level measurement has no correlation to any other operating variable. Additionally, to characterise remaining tray space above this position that is seen to be denser than “clear vapour”, subjective terms such as slight entrainment, moderate entrainment or heavy entrainment are typically used. This method is illustrated in Figure 1a.

For trayed towers a new methodology, FrothView™, has been developed and tested whereby the total froth height on a tray is measured from gamma scan data using new detector technology and software interpretation. This method is shown in Figure 1b on page 2. Dividing the total froth height by the tray space provides the percentage of tray space occupied by tray froth. This “% tray space” has been shown to correlate very well with % flood, thus is a way of using a field measurement and directly relating this to specific tray design criteria to determine the useful capacity of operating trays.

The “inspiration” for the development of FrothView™ technology was taken from a presentation given by Mike Resetarits, Technical Director of Fractionation Research Inc. (FRI) at the 2011 A.I.Ch.E. Spring Meeting titled “On Distillation Tray Entrainment” (1). Tracerco determined from the presentation that the degree of entrainment is very difficult to quantify. If it cannot be reliably quantified then it is very difficult to use entrainment in tray correlations particularly to measure tray capacity. Most, if not all, tray capacity correlations use a calculated tray froth height or level. An article written by Mark Harrison with Eastman Chemical explores using tray froth heights to measure tray capacity. (2) Mr. Harrison proposed a graphical method for measuring tray froth heights. However it is unclear to what extent Mr. Harrison was able to test and utilise this method.

During the past couple of years Tracerco has had opportunities to scan a trayed pilot plant tower under varying operating conditions, from weeping to flooding. One objective of this study was to find a method to quantify the scan results to provide a more objective diagnosis of the tray’s hydraulic condition.


View More

  • Optimise your alkylation process and take control with the Profiler™ TGA

    The Challenge. Alkylation processes present some of the more challenging applications for interface measurement and control in refinery operations. It is important for the operator to have confidence in the process to optimise alkylate production, while ensuring safe operation and environmental compliance. In ...

  • Profiler™ TGA

    The Profiler™ TGA provides extremely reliable liquid level and interface measurements for alkylation units and other harsh service environments. The Profiler™ TGA is specifically designed to measure the vertical distribution of multiple interfaces in real time and at high resolution. Key features • ...

  • Tracerco™ Level System

    Bulk level measurement. Developed to comply with the latest functional safety standards, the SIL2 certified TracercoTM level system delivers extremely reliable bulk level measurements, regardless of process conditions. Its external modular design, with no moving parts, provides measurement redundancy, ...

  • Profiler™ GPS

    Level, interface and multiphase measurement. The Profiler™ GPS provides a ‘window’ into the vessel to enable the operator to improve production throughput, reduce the number of unscheduled shutdowns and achieve significant cost savings. The Profiler™ GPS has no moving parts and is installed in ...

  • Optimus™

    Bulk level and interface measurement. Optimus™ is designed for liquid level, interface and solids monitoring in upstream and downstream vessels. Optimus™ is suitable for bulk level measurement in the most challenging oil, chemical and petrochemical industry applications, including those with the ...

  • Hyperion™

    Bulk level and density measurement. Designed using innovative scintillator-based technology, Hyperion™ is a non-contact, no moving parts measurement solution that provides accurate and extremely reliable bulk level and density measurements. This enables operators in the oil, gas, petrochemical, refining, ...

  • FCC stripper - distribution studies

    A Tracerco Diagnostics™ Distribution study can be performed to identify catalyst and vapor distribution in the stripper. Uniform distribution of catalyst and steam in the stripper is critical to achieve high stripping efficiency (less carry-down of the hydrocarbon products from reactor to regenerator). ...

  • Exchanger leak testing - chemical tracers

    Tracerco has been at the forefront of the development of online leak detection for the last 40 years. The method allows the detection of leaks as small as 0.5%. However, customer demands to measure smaller leaks affecting product quality, has prompted extensive research to develop alternative online ...

  • Tracerco Diagnostics™

    Providing real time measurement technologies to assist with critical decision making. Tracerco Scanning Services TRU-SCAN® Application. Do you have problems with the operation of your stripper/absorber or fractionation tower? Is this limiting production? Do you want to reduce your operating costs? ...

  • Tracerco Diagnostics™ FCCU Study

    The Fluidized Catalytic Cracking Unit (FCCU) is the economic heart of a modern refinery. Even small increases in its yield can bring about significant overall gains in productivity and revenue. Tracerco is a world leading industrial technology company providing unique and specialized detection, diagnostic ...

  • Responsive image ITW technologies online cleaning
  • Responsive image NAPCON games transform the way you train
  • Responsive image Axens blog
  • Responsive image Your experts for burners & combustors
  • Responsive image FCC additives and addition systems
  • Responsive image Bottom of the barrel upgrading
  • Responsive image NeXRing™ NeXt big thing in random packing
  • Responsive image Follow PTQ and DigitalRefining on LinkedIn
  • Responsive image OpX® Digital
  • Responsive image Corrosion control
  • Responsive image Optimize everything plant-wide