Vapor sparger

Low-velocity vapor-only feeds often enter via bare nozzles or V baffles (above). At higher velocities, perforated vapor spargers are used. At high velocities, vapor horns and Schoepentoeters are often preferred. Alternatively or additionally, a vapor distributor may be mounted above the feed. The vapor distributor is a chimney tray (Fig. 14-72) where liquid is collected on the deck and flows via downcom-... 

The sparger design can be based on all vapor flow, but the heat balance must include the liquid. 

The mixture acts hke a liquid and the vapor condensation is dependent on jet mixing. This will require a different type of sparger design. 

Aeration of Solution Unless specified, the solution should not be aerated. Most tests related to process equipment should be run with the natural atmosphere inherent in the process, such as the vapors of the boiling liquid. If aeration is used, the specimens should not be located in the direc t air stream from the sparger. Extraneous effects can be encountered if the air stream impinges on the specimens. 

Consequently vapor would enter the remaining orifices and condense in the cold sparger. This caused hydraulic hammering. 

The pilot-scale SBCR unit with cross-flow filtration module is schematically represented in Figure 15.5. The SBCR has a 5.08 cm diameter and 2 m height with an effective reactor volume of 3.7 L. The synthesis gas passes continuously through the reactor and is distributed by a sparger near the bottom of the reactor vessel. The product gas and slurry exit at the top of the reactor and pass through an overhead gas/liquid separator, where the slurry is disengaged from the gas phase. Vapor products and unreacted syngas exit the gas/liquid separator and enter a warm trap (373 K) followed by a cold trap (273 K). A dry flow meter downstream of the cold trap measures the exit gas flow rate. 

This situation describes an emulsion reactor in which reacting drops (such as oil drops in water or water drops in oil) flow through the CSTR with stirring to make the residence time of each drop obey the CSTR equation. A spray tower (liquid drops in vapor) or bubble column or sparger (vapor bubbles in a continuous liquid phase) are also segregated-flow situations, but these are not always mixed. We wiU consider these and other multiphase reactors in Chapter 12. 

Fluidized bed reactors typrcally are vertical cylindrical vessels equipped with a support grid and feed sparger system for adequate fluidization and feed distribution, internal cooling coils for heat removal, and either external or internal cyclones to minimize catalyst carryover. Fluidizauon of the catalyst assures intimate contact between feed and product vapors, catalyst, and heat-transfer surfaces, and results in a uniform temperature within the reactor. Reaction heat can be removed by generating steam within the cooling coils or by some oilier heat-transfer medium. 

Pilot-scale tests by Fan et al. [IChemE Symp. Ser. 142,899 (1997)] compared vapor distribution and entrainment from sparger, vapor... 

At times, with vapor feeds, it may appear attractive to orient the distributor (sparger) perforations upward. In one case, this was successful in overcoming a hammering problem (item 4 above). The author feels that this practice is troublesome and should only be used as a last resort. The following considerations apply to spargers with upward-oriented openings ... 

If a high feed pressure drop is acceptable, the use of a sparger pipe (Fig. 4.36) is recommended (289) when the vapor inlet F-factor ranges between 52.4 VAP and 81.2 VAP. The use of a sparger pipe eliminates the need for a more sophisticated vapor-distributing device. 

A vapor distributor with insufficient pressure drop may be ineffective. A case has been reported (75) where poor column efficiency resulted from specifying a vapor distributor with lower pressure drop than recommended by the manufacturer. The vapor distributor (or vapor-distributing support) pressure drop can be minimized by entering the feed via a sparger pipe with the bottom quadrant removed (rather than perforated). Although such a sparger pipe will not be an effective vapor distributor, it will serve to break the incoming vapor jet and reduce its velocity head. 

When a sparger pipe enters an intermediate feed, vapor jets must not impinge on redistributor liquid surface or other packed-column internals. Liquid surface agitation in redistributors, or mechanical damage to internals, can cause maldistribution, which can be detrimental to column efficiency. 

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