Bypass Recovery

Bypass recovery is still the most widely used form of vacuum control today for LRVPs. In this process, an already pumped gas is released from the pressure side to the suction side via a valve. If the process vacuum is lower than desired, the valve is opened until the setpoint value is reached. 

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AH three parameters, the cut size, sharpness index, and apparent bypass, are used to evaluate a size separation device because these are assumed to be independent of the feed size distribution. Other measures, usually termed efficiencies, are also used to evaluate the separation achieved by a size separation device. Because these measures are dependent on the feed size distribution, they are only usefiil when making comparisons for similar feeds. AH measures reduce to either recovery efficiency, classification efficiency, or quantitative efficiency. Recovery efficiency is the ratio of the amount of material less than the cut size in the fine stream to the amount of material less than the cut size in the feed stream. Classification efficiency is defined as a corrected recovery efficiency, ie, the recovery efficiency minus the ratio of the amount of material greater than the cut size in the fine stream to the amount of material greater than the cut size in the feed stream. Quantitative efficiency is the ratio of the sum of the amount of material less than the cut size in the fine stream plus the amount of material greater than the cut size in the coarse stream, to the sum of the amount of material less than the cut size in the feed stream plus the amount of material greater than the cut size in the feed stream. Thus, if the feed stream analyzes 50% less than the cut size and the fine stream analyzes 95% less than the cut size and the fine stream flow rate is one-half the feed stream flow rate, then the recovery efficiency is 95%, the classification efficiency is 90%, and the quantitative efficiency is 95%. 

There are relationships between the independent size separation device parameters and the dependent size separation efficiencies. For example, the apparent bypass value does not affect the size distribution of the fine stream but does affect the circulation ratio, ie, the ratio of the coarse stream flow rate to the fine stream flow rate. The circulation ratio increases as the apparent bypass increases and the sharpness index decreases. Consequendy, the yield, the inverse of the circulating load (the ratio of the feed stream flow rate to the fine stream flow rate or the circulation ratio plus one), decreases hence the efficiencies decrease. For a device having a sharpness index of 1, the recovery efficiency is equal to (1 — a). 

The same procedure maybe used at other pump flows to permit plotting the series of balance-point curves as has been done in Fig. 29-61. From such curves, one can establish the maximum lean pump at any total tower outflow, and combining this with the semilean-pump performance curve results in Fig. 29-55. Bypass flow plotted in Fig. 29-55 is obtained by adding simultaneous lean- and semilean-pump flows and subtracting the recovery pump-turbine flow required to make the balance point at that lean-pump flow. 

FIG. 29-59 Head-horsepower-capacity characteristics of a power-recovery turbine operating as the sole driver of a lean pump. If the total capacity of lean and semilean pumps exceeds the values indicated by available head limit, bypass must be used. Net recovery-pump head at 8.71 mVmin (2300 gal/min) is figured as follows ... 

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...

Power recovery trains recover energy from the flue gas. The FCC starts to resemble a large jet engine air is compressed into a combustion zone and expanded across a turbine. Power recovery increases the efficiency of the unit but adds one more mechanical device to an already long list. Since they are too big to bypass, power trains need to be as reliable as the rest of the unit. 

Carbon dioxide flooding is the most promising enhanced oil-recovery method. To overcome the tendency of CO2 to bypass the smaller pores containing residual oil, one approach is to plug the larger pores by chemical precipitation. Several relatively inexpensive water-soluble salts of the earth alkali group react with CO2 to form a precipitate. 

Recovery — Recovery control (RC) solutions were prepared in 10/90 v/v ACN/water. Recovery evaluation (RE) samples were prepared in human plasma. Aliquot of RC solutions into assay plates followed sample preparation procedure steps 1 and 2. Instead of adding 50 pL of diluent, wells containing RC solutions were dried down under a steady stream of room temperature N2. The dried wells were then reconstituted with 250 pL of diluent. Reconstituted RC solutions were directly injected onto an HPLC analytical column, bypassing the extraction column. RE samples were aliquoted into an assay plate following normal sample preparation. RE samples were analyzed using the full extraction procedure (with extraction column). The analyte was tested at three concentration levels and the internal standard was tested at one. Mean extraction recovery for fenofibric acid varied from 93.2 to 111.1%, and mean extraction recovery for the Pestanal internal standard was 105.2%. 

There are several methods of reheating the vapor, including hot gas exchange, in-line burners, hot gas bypass, or indirect steam reheat. Each has advantages and disadvantages generally indirect steam reheat is most expensive but yields higher recoveries. 

Kilgore, K.S., Shwartz, C.F., Gallagher, M.A., Steffen, R.P., Mosca, R.S., and Bolling, S.F. RSR13, a synthetic allosteric modifier of hemoglobin, improves myocardial recovery following hypothermic cardiopulmonary bypass. Circulation 1999, 100, 11351-11356. 

For patients with chronic CAD, nuclear imaging is essential for addressing the following major clinical issues (i) detection of ischemic myocardium, (ii) differentiation between viable hibernating or stunned myocardium and scar tissue in mechanically dysfunctional regions, and (ill) risk stratification for future major adverse events. Such information provides the basis for percutaneous coronary intervention (PCI) or coronary artery bypass (CAB) surgery and assessing their outcomes based on detection of residual ischemia and recovery of contractile function. 

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