TruTec™ Scanning Services (North America, Mexico, Venezuela, Peru and Caribbean)

Tru-Grid™ Scan
Packed Column Application

• Verify placement of packed beds, distributors and collectors
• Evaluate the quality of liquid phase distribution
• Detect problems such as fouled or crushed packing, flooding, foaming or overflowing distributors and collector trays

A packed column Tru-Grid™ Scan is one of the most common and cost effective methods of identifying liquid maldistribution and other problems attending packed column performance. A Tru-Grid™ Scan is a series of four different scans performed in sequence. A Tru-Grid™ Scan of a bed that has uniform distribution throughout will show little variation (implying little density difference) from one scan to another with all four scanlines overlaying one another.

Non-uniformity among the scans implies density differences which can normally be attributed to an imbalance in liquid and vapor traffic. A scan that registers higher counts (higher levels of radiation detected through the bed) is associated with liquid deficiency. Conversely, lower counts (less radiation detected through the packed bed) is normally attributed to more liquid - which implies liquid channeling.

A Tru-Grid™ Scan can measure the liquid level on liquid distributors and collectors designed to hold liquid; such as trough-type distributors, orifice plate distributors, chimney trays, etc. These liquid levels are useful for determining if liquid levels are uniform across devices or if liquid may be overflowing vapor risers. Tru-Grid™ Scans can also detect evidence of problems such as fouling and crushed or corroded packing which often result in distribution problems. Collapsed beds, displaced packing, flooding, foaming, and fouling are other anomalies readily detected by using the Tru-Grid™ Scan technique.

Interpretation Guide for Gamma Scan Plots
As applied to distillation columns, gamma scanning uses a small, sealed radiation source and a sensitive detector aligned on opposite sides of the column. The scanning apparatus is kept on the outside surface of the process equipment, so the procedure is completely non-invasive and non-interactive to the normal operation of the process.

Typically, trayed columns are scanned with the radiation beam passing across the tray active area, or through the downcomers. For a packed column, the usual scanning procedure uses four scanlines in a 2x2 grid with equal chord lengths. It is critically important to have equal scan chord lengths so that the radiation passes through an equal thickness of “material” on all sides of the column. The basis is that uniform or good liquid distribution also has uniform or equal bulk density through the packing. Therefore when the data plots of all four scanlines coincide, or overlay on top of each other; this indicates uniform liquid distribution through the packing.

Liquid maldistribution is the most common cause of unexpected poor separation in packed columns. A perfect liquid distributor puts down the liquid uniformly over the entire cross section of the column at the top of the packed bed. Perfect distribution is not achievable, and not necessary in practice. But, if the initial distribution is inadequate, the efficiency of the packing will suffer.

Tracerco has an extensive database of projects undertaken and reference lists of companies that have used Tru-Grid™ Scan technology can be supplied on request. If you would like to learn more about our Tru-Grid™ Scan technology please contact a Technical Advisor in your area.

Brochure A PDF version of the Tru-Grid™ Scan Packed Column Application Brochure is available, to download it click here