Vapor-line restrictions

Wet acidic vapors, 95 Wet gas compressor, 80-83, 89 fouled overhead condenser, 80-82 vapor-line restrictions, 82 rotor fouling, 82—83 Wet gas, 22, 28 Wilson-Snyder switch valve, 52... 

It has been recommended to design a forced-circulation reboiler for a high pressure drop (134). In some cases (68), a restriction is placed in the vapor line downstream of the reboiler and sized to prevent vaporization in the reboiler. This restriction is often placed at the column inlet nozzle (68), but this may generate an undesirable high-velocity jet at the column inlet (see Sec. 4.1, guideline 5). Further, a restriction downstream of the reboiler may interfere with the action of a control valve located in the liquid line to the reboiler. The author is also familiar with a case where such a restriction experienced erosion at an intolerable rate. 

Operating Pretturet The proper operating pressures within single-effect and multi-effect evaporators must be maintained to enhance thermal efficiency and capacity. The pressures can be affected by loss of vacuum and line restrictions. As frictional pressure drops or vapor pressure within each effect increases, the boiling point of the liquor is higher and additional steam at a higher pressure is needed to maintain capacity and the achievable heat transfer AT s of each effect. 

Forced-circulation reboilers are commonly horizontal as shown in Figure 4.5, but also occasionally are vertical. To minimize pressure drop, a restriction downstream of the reboiler is sized to prevent vaporization in the reboiler tubes. This restriction may be in the vapor line to the column or right at the vapor nozzle outlet. 

The inlet line consists of 50 equivalent ft of 4-in. standard pipe. The exit line consists of 50 equivalent ft of 6-in. standard pipe. No special flow restriction is in the inlet line. Preliminary calculations indicate that essentially the entire surface is in the vaporization zone. 

The amount of ethylene is limited because it is necessary to restrict the amount of unsaturated components so as to avoid the formation of deposits caused by the polymerization of the olefin(s). In addition, ethylene [boiling point —104°C (—155°F)] is more volatile than ethane [boiling point —88°C (—127°F)], and therefore a product with a substantial proportion of ethylene will have a higher vapor pressure and volatility than one that is predominantly ethane. Butadiene is also undesirable because it may also produce polymeric products that form deposits and cause blockage of lines. 

Furnace temperatures were measured by two Pt—10% Rh thermocouples. One was mounted next to the suspended substrate samples and the other next to the vapor source. The rate of flow of the dry air through the furnace was determined by measuring the air pressure upstream from a capillary restriction in the air line. The pressure was measured by an oil manometer which had been calibrated against known flow rates of air through the capillary restriction. 

Venting the channel head through the balance line shown in Fig. 8.6 will prevent an excessive accumulation of C02. This is done by continuous venting from the top of the condensate drum. For every 10,000 lb/h of steam flow, vent off 50 lb/h of vapor through a restriction orifice, placed in the condensate drum vent. This is usually cheaper than controlling reboiler steam-side corrosion, with neutralizing chemicals. 

Bottom liquid outlets. Sufficient residence time must be provided in the bottom of the column to separate any entrained gas from the leaving liquid. Gas in the bottom outlet may also result from vortexing or from forthing caused by liquid dropping from the bottom tray (a waterfall pool effect). Vortex breakers are commonly used, and liquid-drop height is often restricted. Inadequate gas separation may lead to bottom pump cavitation or vapor choking the outlet line. 

As schematically shown in Figure 7a, initial PEVD reaction and product nucleation occurs at the three-phase boundary of solid electrolyte (E), working electrode (W) and the sink vapor phase (S) which contains vapor phase reactant (B). Only here are all reactants available for the half-cell electrochemical reaction at the sink side of a PEVD system. Although the ionic and electronic species can sometimes surface diffuse at elevated temperature to other sites to react with (B) in the vapor phase, the supply of the reactants continuously along the diffusion route is less feasible and the nuclei are too small to be stabilized under normal PEVD conditions. Only along the three phase boundary line are all the reactants available for further growth to stabilize the nuclei. Consequently, initial deposition in a PEVD process is restricted to certain areas on a substrate where all reactants for the sink electrochemical reaction are available. 

Thermosiphon reboilers can suffer from flow instabilities if too high a heat flux is used. The liquid and vapor flow in the tubes is not smooth but tends to pulsate, and at high heat fluxes the pulsations can become large enough to cause vapor locking. A good practice is to install a flow restriction in the inlet line, a valve, or orifice plate so that the flow resistance can be adjusted should vapor locking occur in operation. 

Caillol, J.M. A Monte Carlo study of the dielectric constant of the restricted primitive model of electrolytes on the vapor branch of the coexistence line. J. Chem. Phys., 1995, 102, p. 5471-5479. 

The condition of the gas vaporizer is a further important consideraikMi to ethylene oxide sterilization. All cylinder supplies of ethylene oxide present the gas in liquid form under pressure, which must then be vaporized before admission to the sterilizer. Inadequate temperatures in vaporizers may lead to the introduction of liquid ethylene oxide into the sterilizer. This is undesirable because it will not fulfill its purpose and because of staining and damage to product and packaging. Overly high temperatures may lead to degradation of the ethylene oxide with resultant polymer buildup restricting gas flow in the feed lines. 

An undersized reflux line downstream of the vent, or an oversized vent line or restriction orifice can perform worse than no vent at all. At high reflux flow rates, vapor may be sucked from the vent line into the vertical leg downstream of the high point (158). At low... 

Because of the above difficulties, it is best to restrict the use of a purged system to services that can either readily tolerate the purge or to systems where transmitter lines are to be kept free from column vapors. This technique is most suitable for toxic or corrosive systems. 

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