Maximum vapor load

Pressure. Within limits, pressure may have Htfle effect in air-sparged LPO reactors. Consider the case where the pressure is high enough to supply oxygen to the Hquid at a reasonable rate and to maintain the gas holdup relatively low. If pressure is doubled, the concentration of oxygen in the bubbles is approximately doubled and the rate of oxygen deHvery from each bubble is also approximately doubled in the mass-transfer rate-limited zone. The total number of bubbles, however, is approximately halved. The overall effect, therefore, can be small. The optimum pressure is likely to be determined by the permissible maximum gas holdup and/or the desirable maximum vapor load in the vent gas. 

The maximum vapor load on the drum is based on the largest release from safety valves discharging as a result of a single contingency. Vapor velocities in the drum are based on 100% of critical velocity (refer back to Equation 1). However, a velocity of 175% of critical is permitted when one is applying the 1.5... 

Maximum Vapor load 210,000 Ib/hr = (347 ftVsec) System Non-foaming, non-corrosive, non-fouling... 

The maximum efficiency is frequently found at approximately 60% of the maximum vapor load. At higher loads, vapor contact time is decreased and entrainment may significantly reduce tray efficiency. 

The maximum vapor loading of a tray column has to be adapted to the liquid loading, so that no liquid is carried by the vapor to the next upper tray. With minimum vapor loading, reflux should not drain through the floor drilling and the column should not become empty. 

Another design aspect of reactive distillation that is different from conventional is tray holdup. Holdup has no effect on the steady-state design of a conventional column. It certainly affects dynamics but not steady-state design. Column diameter is determined from maximum vapor-loading correlations after vapor rates have been determined that achieve the desired separation. Typical design specifications are the concentration of the heavy key component in the distillate and the concentration of the light key component in the bottoms. However, holdup is very important in reactive distillation because reaction rates directly depend on holdup (or the amount of catalyst) on each tray. This means that the... 

Also, the vapor load at the time of relief may be reduced below the normal design rate, due to the higher pressure, which may suppress vaporization at the time of the overpressure. Pinchout of a reboiler is such a situation. In such a case, steam pressure design conditions may be used, rather than the maximum steam pressure which could exist under pressure relieving conditions of the steam system. These changes can be taken into account, where appropriate, both for the equipment involved and for downstream equipment. 

The single contingency which results in the largest vapor load regardless of any associated liquid load, is used to determine the maximum required vapor space C-F, and a high level alarm is placed at point C. 

Example The maximum flare load of a system is 1,000,000 Ibs/hr of vapor. The pressure at the base of the flare stack is 2 psig, the average molecular weight of the vapor is 50, at a temperature of 200°F at the combined header to the flare stack. The distance from the drum to the stack is 500 ft. The line consists of two 90° welding elbows and an orifice for a flow controller. The total pressure drop at the knock-out drum is 0.5 psi. Determine the pressure at the inlet of the knock-out drum. 

VAPOR LOAD, % MAXIMUM FOR FULLY LOADED SLOTS... 

Vapor load corrected for density, ft/sec Maximum allowable vapor load per tray, ft /sec Superficial vapor velocity in tower, ft/sec (based on tower cross ection)... 

Calculate required column area and diameter using the maximum superficial vapor velocity, Un,axl> ttd the actual vapor load. 

Displacement-Purge Cycle This cycle, which is somewhat similar to the previous one, differs from it in that a gas or vapor which adsorbs about as strongly as the adsorbate is used to remove the adsorbate (see Figure 1) Removal is thus facilitated both by adsorbate partial-pressure reduction in the fluid around the particles and by competitive adsorption of the displacement medium. As with the inert-purge cycle, the maximum delta loading is the equilibrium loading ... 

Equations (3.89) and (3.90) equate the tray active area vapor loading VN to the maximum VM for determining the gas in liquid entrainment flooding of the tray. The early work of Souders and Brown [12], based on a force balance on an average suspended droplet of liquid, led to the definition of a capacity parameter VM- Both VN and Where refer to the active area of the tray. This active area is simply the net tower cross-section internal area less the downcomer areas. The downcomer areas include both the downcomer inlets and outlets. 

Wu and Chen (167) recommend pilot testing over the entire range between the expected minimum and maximum operating rates, and taking the highest measured HETP as the basis for scaleup. The author concurs. With structured packings, the loed effect may be due to liqnid rather than vapor loads, and the pilot tests should cover the range of liquid loads (i.e., gpm per square foot of column cross section) that is expected in the prototype. 

Tray supports must prevent trays from being lifted by upflowing vapor. Trays are usually designed to withstand an uplift pressure of about three times the tray pressure drop at maximum vapor and liquid loads (49) or 0.25 psi (107) (normally, whichever is larger). 

Pharmaceuticals Methanol dehydrator sieve trays Column flooded prranaturefy in the upper part of the bottom section due to insufficamit fi acdonal hole area on the sieve tray. This was presumably caused by the trays being sized to accommodate the vfgxir loads at the tower base. Since water has a hi er latent heat than methanol, the vapor load near the feed was hi er. Ensure that trays are sized for the maximum vapor and liquid loads anticipated in the tower. 

The diameter d of the separator can then be calculated using Eq. (2-7). The required minimum height Zq of the free vapor space can be found using Eq. (2-9), in which is the maximum vapor space loading chosen such that... 

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