Impingement plates

Impingement baffles are generally made of rectangular plate, although circular plates are more desirable. Rods and other devices are sometimes used to protect the tubes from impingement. In order to maintain a maximum tube count the impingement plate is often placed in a conical nozzle opening or in a dome cap above the shell. 

When tubes are omitted from the tube layout to provide entrance area about an impingement plate, the need for sealing strips or other devices to cause proper bundle penetration by the shell-side fluid is increased. 

These scrubbers have had limited use as part of flue gas desulfurization (FGD) systems, but the scrubbing solution flow rate must be carefully controlled to avoid flooding. When absorption is used for VOC control, packed towers are usually more cost effective than impingement plate towers (discussed later). 

However, in certain cases, the impingement plate design is preferred over packed-tower columns when either internal cooling is desired, or where low liquid flow rates would inadequately wet the packing. 

PM Impingement-plate tower collection efficiencies range from 50 to 99 percent, depending upon the application. This type of scrubber relies almost exclusively on inertial impaction for PM collection. Therefore, collection efficiency decreases as particle size decreases. Short residence times will also lower scrubber efficiency for small particles. Collection efficiencies for small particles (< 1 fim in aerodynamic diameter) are low for these scrubbers hence, they are not recommended for fine PM control. 

PM Control - An impingement-plate scrubber is a vertical chamber with plates mounted horizontally inside a hollow shell. Impingement-plate scrubbers operate as eountercurrent PM collection devices. The scrubbing liquid flows down the tower while the gas stream flows upward. Contact between the liquid and the particle-laden gas occurs on the plates. The plates are equipped with openings that allow the gas to pass through. Some plates are perforated or slotted, while more complex plates have valve-like openings. 

The simplest impingement-plate scrubber is the sieve plate, which has round... 

ShefI Flange—Stationary Head End 29. Impingement Plate... 

Figure 10-11. Condensate in the steam—the result of too few steam traps-knocked off the impingement plate and damaged the calandria tubes.

An impingement plate was fitted to the reboiler to protect the tubes, but it fell off, probably as a result of repeated blows by slugs of condensate. The condensate then impinged on the tubes and squashed or broke 30 of them. 

The impingement plate had fallen off several times before and was merely put back with stronger attachments. When something comes apart, we should ask why, not just make it stronger (see Section 1.5.5). 

One of the common impingement plate assemblies is of the Chevron zig-zag style of Figures 4-17A and 4-30. This style of impact separation device will tolerate higher gas velocides, high liquid loading, viscous liquids, reasonable solids, relatively low pressure drops. The collected... 

Besides preventing a destruction of the tubes, impingement plates serve to spread out and distribute the incoming fluid into the tube bundle. If they are used in proper relation to the bundle cross-flow baffles, the fluid can be effectively spread across the bundle near the inlet end. If this is not accomplished, part of the tube area will be stagnant, and its heat transfer will be less than the other parts of the... 

Omit Tubes as Required for Tie Rods and Impingement Plates. 

The suitability of gas absorption as a pollution control method is generally dependent on the following factors (1) availability of suitable solvent (2) required removal efficiency (3) pollutant concentration in the inlet vapor (4) capacity required for handling waste gas and (5) recovery value of the pollutant(s) or the disposal cost of the unrecoverable solvent. Impingement plate scrubbers are typically used in the food and agriculture industry, and at gray iron foundries. 

Typical gas flow rates for a single impingement-plate scrubber unit are 0.47 to 35 sm3/sec (1,000 to 75,000 scfm). 

Impingement-plate scrubbers are easy to clean and maintain and are not subject to fouling as packed-bed wet scrubbers are, hence they are more suited to PM control and there are no practical limits to inlet PM concentrations. 

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