Vapor-handling capacity

An increase in steam pressure over design will not increase vapor handling capacity for the usual fixed capacity ejector. The increased pressure usually decreases capacity due to the extra steam in the diffuser. The best ejector steam economy is attained when the steam nozzle and diffuser are proportioned for a specified performance [8]. This is the reason it is difficult to keep so-called standard ejectors in stock and expect to have the equivalent of a custom designed unit. The throttling type ejector has a family of performance curves depending upon the motive steam pressure. This type has a lower compression ratio across the ejector than the fixed-type. The fixed-type unit is of the most concern in this presentation. 

Increases vapor density and therefore vapor-handling capacity. This leads to major reductions in column diameter and capital costs under vacuum, and to smaller reductions up to pressures of 50 to 150 psia (6). 

Swept-back weirs increase the weir length and decrease the active area of the tray (Fig. 7). They are often the lowest-cost method to decrease weir load as long as sufficient vapor handling capacity is available. 

Vapor-handling capacity Liquid-handling capacity Mass transfer efficiency... 

The downcomer seal plate shown in Fig. 4.6 is an example of a dynamic downcomer seal. The Koch-Glitsch "Nye" tray also uses a dynamic downcomer seal to increase vapor-handling capacity. All trays with a dynamic downcomer seal suffer from two disadvantages ... 

API RP 521, Section 3.18.5, indicates that, where the low-pressure side is in the vapor phase, full credit can be taken for the vapor handling capacity of the outlet and inlet lines, provided that the inlet lines do not contain check valves or other equipment that could prevent back flow. The same approach would apply in cases in which the low-pressure side is liquid full, provided that the released material also remains in the liquid state. However, when the low-pressure side contains liquid and vapor is released or generated through a rupture tube, the effective relieving capacity with which the piping system can be credited should be based solely on an equivalent vapor flow. 

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