Bypass vapor

The bypassed vapor heats up the liquid there, thereby causing the pressure to rise. WTien the bypass is closed, the pressure falls. Sufficient heat transfer surface is provided to subcool the condensate, (f) Vapor bypass between the condenser and the accumulator, with the condenser near ground level for the ease of maintenance When the pressure in the tower falls, the bypass valve opens, and the subcooled liquid in the drum heats up and is forced by its vapor pressure back into the condenser. Because of the smaller surface now exposed to the vapor, the rate of condensation is decreased and consequently the tower pressure increases to the preset value. With normal subcooling, obtained with some excess surface, a difference of 10-15 ft in levels of drum and condenser is sufficient for good control, (g) Cascade control The same system as case (a), but with addition of a TC (or composition controller) that resets the reflux flow rate, (h) Reflux rate on a differential temperature controller. Ensures constant internal reflux rate even when the performance of the condenser fluctuates, (i) Reflux is provided by a separate partial condenser on TC. It may be mounted on top of the column as shown or inside the column or installed with its own accumulator and reflux pump in the usual way. The overhead product is handled by an alter condenser which can be operated with refrigerant if required to handle low boiling components. 

Bypass vapor must enter the vapor space of the reflux dmm. 

Correct piping is mandatory for the success of the hot vapor bypass control method. Bypass vapor must enter the vapor space of the reflux drum (Fig. 17.5d). The bypass should be free of pockets where liquid can accumulate any horizontal runs should drain into the reflux drum. If noncondensables are likely, vents are required on the condenser and drum. The condenser vent can be directed to the vapor space of the drum. Most important, liquid from the condenser must enter the reflux drum well below the liquid surface. The bottom of the drum (Fig. 17.5d) is the most suitable location. In one case (164) subcooled liquid entered the drum vapor space (presumably due to unflooding of the liquid inlet). The vapor space was 100°F hotter rapid condensation sucked the liquid leg between the drum and condenser into the drum in seconds. 

The calculation of the surface energy of metals has been along two rather different lines. The first has been that of Skapski, outlined in Section III-IB. In its simplest form, the procedure involves simply prorating the surface energy to the energy of vaporization on the basis of the ratio of the number of nearest neighbors for a surface atom to that for an interior atom. The effect is to bypass the theoretical question of the exact calculation of the cohesional forces of a metal and, of course, to ignore the matter of surface distortion. 

MnO.F, is obtained as a green vapor when KMnO reacts with anhydrous HF. The highly unstable gaseous green-violet permanganyl chloride [15605-27-3], MnO Cl, is prepared bypassing dry HCl gas through a solution of KMnO in concentrated sulfuric acid at —50°C (104). 

The thermocycle system can be operated only when condensing water is available at a temperature lower than the required chilled-water-supply temperature. Modifications for a centrifugal refrigeration unit include the installation of a small liqmd-refrigerant pump, cooler spray header nozzles, and a vapor bypass line between the cooler and the condenser. Without the compressor operating, a thermocycle capacity up to 35 percent of the refrigeration-unit rating can be produced. 

Bypassing. Baffles should prevent bypass of inlet vapor into the vent. This is very important. 

The fix for the erratic reflux drum pressure problem was to provide for separate pressure control of the fractionator column and the reflux drum. A new pressure control valve was installed upstream of the condenser and the old condenser outlet control valve was removed. A hot gas bypass, designed for 20% vapor flow, was installed around the pressure control valve and condenser. A control valve was installed in the hot gas bypass line. The column pressure was then maintained by throttling the new control valve upstream of the condenser. The reflux drum pressure w as controlled by the hot gas bypass control valve and the psv saver working in split range. The new system is shown in the figure below. 

If a bypass or PR valve is provided, it must also have sufficient capacity to relieve the vapor generated from the cold fluid by heat input from the hot side under design flow conditions, if vaporization could also cause the cold side to be overpressurized. 

Usually, the closed liquid drain header is run as a separate line to the drum and provided with a high level cut-off valve with local manual reset. In some cases the closed drain system is segregated into a number of subheaders, as described earlier. Hydrocarbon liquids may be bypassed around the drum through a connection from the closed drain header directly to the pumpout pump suction, provided that the liquid can be routed to a safe disposal location, considering its vapor pressure and temperature. Emergency liquid pulldown connections, if provided, are routed to the blowdown drum via the closed drain header. 

Pressnre taps are often specified on each side of an in-line flame arrester for checking the pressnre differential across the arrester while in service. The taps and instmment installation mnst not provide a flame bypass aronnd the flame arrester. By monitoring pressnre drop, fonling or plngging may be detected early, if there is a snfficient vapor flow rate. 

On June 1, 1974, a cyclohexane vapor cloud was released after the rupture of a pipe bypassing a reactor. In total, approximately 30,000 kg of cyclohexane was released. The cyclohexane formed a cloud which ignited after a period of approximately 30 to 90 seconds. As a result, a very strong explosion occurred which caused the death of 28 people and injured 36 people. The plant was totally destroyed and 1821 houses and 167 stores and factories in the vicinity of the plant were damaged. 

A bubble tray cones when the liquid seal over the slot is low and the vapor rate is so high as to force the liquid completely away from the cap, thus bypassing the liquid entirely. Obviously, efficiency is unsatisfactory. The dynamic slot seals recommended in Table 8-18 normally will prevent such action. 

In some instances the baffle spacing must be rearranged to allow for a nozzle or coupling connection, ft is important that changes in baffle location be reviewed, as performance or pressure drop can be seriously affected. This is of extreme importance in vacuum units. Baffle orientation is sometimes misinterpreted by the fabricator, and this can cause serious problems where liquid drainage is concerned, or the revised vapor flow path can allow for bypassing the tube surface. 

Properties of some halides useful in CVD are listed in Table 3.3. As can be seen, some of these halides are gaseous or liquid at room temperature and, as such, are easily transported in the reaction chamber. The solid halides, however, must be heated to produce sufficient vapor. This sometimes presents a problem which can be bypassed by generating the halide in situ (see Ch. 5). Most halides are available commercially. 

The feed pipes connecting the reactors were 28 inches in diameter. Because only 20-inch pipe stock was available at the plant, the connections to reactor 4 and reactor 6 were made using flexible bellows-type piping, as shown in Figure 1-10. It is hypothesized that the bypass pipe section ruptured because of inadequate support and overflexing of the pipe section as a result of internal reactor pressures. Upon rupture of the bypass, an estimated 30 tons of cyclohexane volatilized and formed a large vapor cloud. The cloud was ignited by an unknown source an estimated 45 seconds after the release. 

In critical evaluation of the effect of a gas, vapor, or aerosol inhaled in to the respiratory tract of an animal, the dosimetric method has been recommended (Oberst, 1961). However, due to the complexity of measuring the various parameters simultaneously, only a few studies on gaseous drugs or chemicals have employed the dosimetric method (Weston and Karel, 1946 Adams et al., 1952 Leong and MacFarland, 1965 Landy et al., 1983 Stott and McKenna, 1984 Dallas et al., 1986, 1989). For studies on liquid or powdery aerosols, modified techniques such as intratracheal instillation (Brain et al., 1976) or endotracheal nebulization (Leong et al., 1988) were used to deliver an exact dose of the test material into the lower respiratory tract (LRT) while bypassing the URT and ignoring the ventilatory parameters. 

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. 

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