Comparative Analysis of Explosion Vent Areas for Milk Spray Dryers According to the EN-14491 (2006) and NFPA-68 (2007) Standards

Venting systems are commonly employed to minimize damage and/or losses caused by dust explosions in spray dryers. At present, the two most commonly used vent-sizing standards are the American standard NFPA-68 (2007) and the European standard EN-14491 (2006). The work described in this paper has two main aims. The first aim is to compare the results of the venting area as required by the two aforementioned standards for conventional milk drying when dealing with three products commonly treated in the dairy industry: buttermilk, powdered milk, and full-fat milk. The vent area was calculated by taking into account the reduced pressure (Pred) and the geometry of the spray dryer (aspect ratio of the vessel length/diameter). In addition, the results obtained as per NFPA-68 were also corrected on the basis of turbulence intensity and partial volume. The second aim is to apply the two standards to the real case of a spray dryer in a dairy processing plant located in the south of the province of Lugo (NW Spain). The results showed significant differences between the two standards in that the vent areas obtained following the criteria of EN-14491 were always higher than those obtained with the American standard (except for the cases in which L/D = 1).