Concentrated Urea solution comes from the Evaporator and is sprayed downwards from the top of the Prilling Tower. The inlet air draft rising inside the Prilling Tower cools the falling, sprayed solution, which then forms into solid ‘prills’. The prills then continue to fall, to the bottom of the tower for collection.
At the top of the tower, around the sprayer heads, the Urea microprills (100 microns ) and average 1 micron diameter mist are entrained by the air going on up to the roof fans and thus out to atmosphere.
Mist loads can vary greatly according to the design and age of the tower, from 100 mg/m3 to more than 1,000 mg/m3.
PROBLEMS TO SOLVE
Product loss (collected liquid can be recycled within the plant)
1st stage irrigated ‘Becoil’ Demister / ‘Becone’ Coalescer in 304 Stainless Steel or special alloy + co-knitted glass fibre
1st stage BlueFil® meshpad in PP with irrigation sprays (horizontal or vertical vessel on ground or vertical housing on top of Prilling Tower)
Then one of the following :
2nd stage ‘Becoil’ Demister in 304 Stainless Steel or special alloy (this 2 stage mesh pad arrangement is commonly used in Russian technology plants where housings are placed around the top of the Prilling Tower, often in a ‘horseshoe’ arrangement)
2nd stage BlueFil® meshpad in PP with irrigation sprays, and final BlueFil® meshpad in PP as demister. (horizontal or vertical vessel on ground)
Medium Velocity ‘Becofil’ Candle Filters, standing type F, with B12 Glass Fibre elements and 304 Stainless Steel structure.
High Efficiency, Brownian Diffusion ‘Becofil’ Candle Filters, hanging type HT or standing type F, with TGW15, B14W or B14 Glass Fibre elements and 304 Stainless Steel structure.
Note: demineralised water spraying of any filter medium is required to dissolve formed crystals and so prevent blockage.