Liquid level split

Figure 6.4 Split liquid-level indication caused by foam.

Break foam with hot pipes Water shots in hot oil Rapid depressurization Gamma-ray foam detectors Defoaming chemicals Split liquid levels... 

Rather, these split liquid levels are a positive indication of foam or froth in the bottom of the tower. 

Many of you may have observed this on a process vessel. We certainly cannot have layers of liquid-vapor-liquid-vapor in the vessel. Rather, these split liquid levels are a positive indication of foam or froth in the bottom of the tower. 

Split Shear Ring 39. Liquid Level Connection... 

Now we must decide how to control the liquid level in the reactor. This liquid consists of mostly the heavy- products, components G and H. The more fresh reactant components ) and are fed into the process, the more products will be produced. So we select the two fresh feed flowrates F n and F to control reactor liquid level. We ratio one to the other depending upon the desired split between components G and H in the final product. Simple flow ratios should be accurate enough to maintain the desired product distribution without any feedback of product compositions. So on-line analyzers on the product streams should not be required. 

In addition, there are four degrees of freedom that are adjustable during design and are also adjustable during operation of the column reflux flow rate (/ ), vapor boilup (V), sidestream flow rate (5), and the liquid split ratio (jSl = i-p/i-R)- The variable Lp is the liquid flow rate fed to the prefractionator side of the wall, and Lp is the total liquid leaving the bottom tray in the rectifying section. Of course, the rest of the liquid coming from the bottom of the rectification section is fed to the sidestream side of the column. Distillate and bottoms flow rates are used to maintain liquid levels in the reflux drum and column base, respectively. 

The liquid level in the base of the rectifier corresponds physically to the total liquid trap-out tray. A pump and two parallel lines with control valves in each are installed. Since the flow rate to the sidestream side of the wall is the larger of the two, the level on the trap-out tray is controlled by manipulating the control valve in the liquid line to that side of the wall. A ratio scheme then adjusts the other control valve to maintain the desired liquid split. The liquid flow rate to the sidestream section is measured, and this signal is sent to a multiplier whose other input is adjusted to give the desired liquid split. The output of the multiplier is the set point signal to a flow controller that manipulates the valve in the liquid line to the prefractionator to achieve the specified flow rate. Note that this ratio is changed by the composition controller in the prefractionator. 

This chapter presented a concept drawing of a distillation process that included flow rate sensors, liquid level sensors, temperature sensors, and process control valves. The process streams were identified and labeled. The standard definition of reflux ratio was presented, and the concepts of separation power and material balance split were introduced. 

Storage of split fatty acids Liquid level 12... 

Figure 52 also shows that the actual recovery curve does not decrease below a certain level. This indicates that a certain amount of material is always recovered to the underflow and bypasses classification. If a comparison is made between the minimum recovery level of solids to the liquid that is recovered, they are found to be equal. Therefore it is assumed that a percent of all size fractions reports directly to the underflow as bypassed solids in equal proportion to the liquid split. Then each size fraction of the actual recovery curve is adjusted by an amount equal to the liquid recovery to produce the "corrected recovery" curve shown in Figure 52. As the Djoc point changes from one application to another, the recovery curves shift, along the horizontal axis. In order to determine a single graph which represents the corrected recovery curve, the particle size of each size fraction is divided by the Dj value and a "reduced recovery" curve can be plotted, as shown in Figure 53. Studies reported by Arterburn have shown that this curve remains constant over a wide range of cyclone diameters and operating conditions when applied to a slurry...

---