New Technique for Measuring Fluid Flow Patterns on a Multiple Downcomer Tray

Abstract

Fluid flow patterns on a distillation tray played an important role in the tray efficiency. A new technique for measuring fluid flow patterns on a distillation tray was introduced. The new technique involved observing a step input of a liquid tracer of higher temperature while keeping a record with a thermal infrared camera, and the principle for measurement was also deduced. Experiments were carried out in a 1200-mm-diameter simulation column using two types of trays with one and two hanging downcomers. With the new technique, the detailed picture of the residence time distribution on a multiple downcomer tray was obtained. The results showed that the new technique was convenient, accurate, and not contaminated to measure the residence time distribution of the tray. A stagnant region existed in the multiple downcomer tray. The size of the stagnant region decreased with a decrease of the liquid rate and bubbling of air. The initial velocity of liquid entering the tray determined the flow pattern of the tray.

Development of a Refined RTD-Based Efficiency Prediction Model for Cross-Flow Trays

“…Liquid flow patterns on trays are complex and far from uniform because of the agitation caused by rising vapor, dispersion, and expanding and contracting flow paths owing to the circular cross-section of the column . Several experimental investigations have revealed the existence of liquid maldistribution on the trays. − The stimulus-response method has been largely preferred for determining flow and mixing patterns of liquid. In this method, the liquid residence time distribution (RTD) is obtained through dispersion of a tracer (e.g., dye or salt solution), which is injected in the inflowing liquid stream prior to inlet weir as an instantaneous pulse or step .…”

Computational Fluid Dynamics Modeling of Hydrodynamics of a New Type of Fixed Valve Tray

“…Mass transfer tray column is an important type of gas–liquid contact equipment widely used in the oil refining and chemical industries, as it has features of easy maintainability, low cost, convenient feed, and side withdrawing. − Fixed valve tray, one of the major research and industrial interests recently, draws more attention as a hybrid of floating valve tray and sieve tray. In industrial practice, however, the performance of the trays always suffers from a loss of separation ability due to maldistributed or abnormal flow regime, for example, liquid phase circulation, which occurs frequently on a tray. − It has been long established that the prediction of distillation tray hydrodynamics is necessary for the separation efficiency and overall performance. ,,− Besides, the understanding of these two-phase hydrodynamic phenomena on trays is helpful for the fine-tuning and optimization of modern tray design. − The hydrodynamics of fixed valve tray is significantly influenced by the configuration and type of the valves, and the operating conditions, which, in turn, affect the product properties. − …”