Fractionator efficiency

Eig. 6. Penetration and fractional efficiency for fine particles. Erom ref. 152,... 

The grade efficiency T of most collectors can be expressed as a function of the aerodynamic particle size in the form of an exponential equation. It is simpler to write the equation in terms of the particle penetration Pf (those particles not collected), where the fractional penetration = 1 — T, when T is the fractional efficiency. The typical collection equation is... 

Each is discussed in Sec. 17 of this handbook under Gas-Sohds Separations. The effectiveness of conventional air-poUution-control equipment for particulate removal is compared in Fig. 25-23. These fractional efficiency cui ves indicate that the equipment is least efficient in removing particulates in the 0.1- to 1.0- Im range. For wet... 

FIG. 25-23 Fractional efficiency curves for conventional air-pollution-control devices. [Chem. Eng., 87(13), 83 (June 30, 1980).]... 

Engineering factors include (a) contaminant characteristics such as physical and chemical properties - concentration, particulate shape, size distribution, chemical reactivity, corrosivity, abrasiveness, and toxicity (b) gas stream characteristics such as volume flow rate, dust loading, temperature, pressure, humidity, composition, viscosity, density, reactivity, combustibility, corrosivity, and toxicity and (c) design and performance characteristics of the control system such as pressure drop, reliability, dependability, compliance with utility and maintenance requirements, and temperature limitations, as well as size, weight, and fractional efficiency curves for particulates and mass transfer or contaminant destruction capability for gases or vapors. 

Modern measuring techniques, an increased requirement for the indoor environment, and the efficiency of filters in separating particles led to EUROVENT 4/9 1992 Method of Testing Air Filters Used In General Ventilation for the Determination of Fractional Efficiency. This method also provides the basis for the next revision or upgrade of European Standard EN 779 1999. 

Fractional efficiency The efficiency of a device expressed for different fractions, e.g., the efficiency of a filter for particles of different sizes. 

American Institute of Chemical Engineers, Bubble Tray Design Manual, Prediction of Fractionation Efficiency, Amer. Inst. Chem. Engrs. (1958). 

Increasing the gas plant pressure. A 10 psi increase in absorber pressure increases C3 recovery by 2% (Figure 9-10). However, this can reduce the wet gas compressor capacity. Fractionation efficiency decreases as the column pressure increases. 

Power for pumping liquids HP = (gpm)(psi difference)/(1714) (fractional efficiency). 

Fractionation by GPC was sessed by changing injected concentrations and by GPC analysis of polymer before and after fractionation. Efficiency of fractionation of polymer from monomer did not appear to be a source of error. In fact, an advantage of this method over others is that the separation of monomer from the polymer can be clearly monitored and controlled,... 

If the areas under the curves are denoted by A, then (based on equal dose) All/Al is the fraction absorbed by oral route. Alll/All is the fraction efficiency of the solid dosage form. The reason for this latter is, of course, that the solid dosage form has to dissolve before the drug contained in it is available for absorption. It is the latter ratio that is important to the investigating pharmaceuticist, and therefore the outcome of the parenteral form is actually not a consideration from a formulation point of view. It is critical overall and if it is low, it may, at the point of parenteral data acquisition, be advisable to stop the program and evaluate the possibility of derivatives that would give better availability. 

Figure 16-3 The fractional efficiency of various devices for removing various size particles from air.

The broad spectrum of derived fractional efficiency curves in Fig. 2 simply reflects the effects of cyclone designs deviating from consistence with the basic premises and from ill defined particle characteristics. 

Figure 9.15 Fractionation of two trace elements il and i2 during fractional crystallization according to equation (9.5.2). AD is the difference Dn — Di2. Incompatible elements are not fractionated efficiently even for large extents of solid removal.

AIChE, Bubble tray design manual, Prediction of fractionation efficiency, AIChE, New-York (1958). 

Let us assume that both the reflux rate and the overhead propane product rate are constant. This means that the total heat flow into the tower is constant. Or, the sum of the reboiler duty, plus the feed preheater duty, is constant. If the steam flow to the feed preheater is increased, then it follows that the reboiler duty will fall. How does this increase in feed preheat affect the flow of vapor through the trays and the fractionation efficiency of the trays ... 

As the flow of vapor through the absorption section trays is unaffected by feed preheat, the fractionation efficiency of the trays in the upper part of the tower will not change as feed preheat is increased. On the other hand, the reduced vapor flow through the stripping section may increase or decrease fractionation efficiency—but why ... 

Varying the enthalpy, or heat content, of the feed is an additional independent variable that an operator, or process design engineer, can use to optimize fractionation efficiency. An additional benefit of feed preheat is that a lower-level temperature heat source can be used. If valuable 100-psig steam is required for the reboiler, then low-value 20-psig steam might be adequate for the feed preheat exchanger. 

Meanwhile, all the liquid flow must drain through that portion of the tray that is lower. The net result, as can be seen in Fig. 7.2, is dry packing in one portion of the tower, and overrefluxing in the adjacent portion. This is called vapor-liquid channeling, and this is the root cause of poor fractionation efficiency in any tower. 

The problem we have just discussed—poor fractionation efficiency due to inadequate vapor and liquid initial distribution—is rather similar to tray deck dumping in trayed fractionators. And, just like trays, packed towers are also subject to flooding. 

If the liquid holdup is too low, fractionation efficiency will be bad. We say that the height equivalent to a theoretical plate (HETP) will be high. If the liquid holdup is too high, fractionation efficiency will also be poor. We again say that the HETP will be high. This idea is expressed in Fig. 7.6. When the holdup rises above the point that corresponds to the minimum HETP, we can say that the packing is beginning to flood. The minimum HETP point on Fig. 7.6 corresponds to the point of incipient flood, discussed in Chap. 1. 

For structured-type packing, a liquid holdup of 4 to 5 percent corresponds to this optimum packing fractionation efficiency. For 1-in Raschig rings, this optimum holdup would be roughly 10 to 12 percent. 

The way we increase the fractionation efficiency of trays is to make the trays work harder. The correct engineering way to say this is To improve the separation efficiency between a light and heavy product, the vapor flow rate through the trays is increased, and the internal reflux flowing across the trays is increased. ... 

Reducing the pumparound duty increases the tray loadings on trays 1 through 7. But in so doing, the trays operate closer to their incipient flood point. This is fine. The incipient flood point corresponds to the optimum tray performance. But if we cross over the incipient flood point, and trays 5, 6, and 7 actually start to flood, their fractionation efficiency will be adversely affected. Then, as we decrease the pumparound heat-removal duty, the mutual contamination of diesel and gas oil will increase. 

The assembly shown in Fig. 2.104 illustrates a set-up for simple fractionation using a Vigreux column which has moderate fractionating efficiency and is probably one of the most widely used columns. The column consists of a glass tube with a series of indentations such that alternate sets of indentations point downwards at an angle of 45° in order to promote the redistribution of liquid from the walls to the centre of the column. The mixture to be fractionated is placed in a flask of convenient size (it should be one-third to one-half full), a few fragments of porous porcelain added and a water condenser attached to the side-arm. The distillate is collected in small flasks or in test tubes. The bulb of the thermometer... 

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