Port Shrouding or Nozzle Sizing

Shrouds are generally placed around grid holes to reduce the velocity at the gas-solids interface and reduce particle attrition. Shrouds simply consist of short pipes centered over the smaller grid holes which have been selected in size and number to operate at a hole velocity defined by Eq. (9). 

To be effective, shrouds must be long enough to contain the expanding (11 -degree included angle) gas j et leaving the grid orifice. 

As can be seen from the Fig. 6, the minimum shroud length should be  

In practice, it is prudent to increase Lmin by a factor of 50 to 100%. A shroud length less than Lmin causes significantly more erosion and attrition than no shroud at all. Significant attrition can also occur if the shroud is not centered over the smaller hole. 

The nozzle or shroud details inside a sparger pipe grid are illustrated in Fig. 7. 

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