nfcl, mangalore dap/npk plant feasibility study - Environmental ...

10ANNEXURE-IVTo prevent absorption of moisture by final product during the cooling processair have to be conditioned (chilled and dehumidified), mainly when ambient airis too wet, thus downstream Cooler Air Chiller is installed the Air Heater forreducing the air relative humidity above the product CRH. This is especiallyimportant when producing NPK/NP with high Urea content since they are veryhygroscopic compounds.DAP has a critical relative humidity CRH of about 75-85% at 30°C (lower athigher temperature) but Urea based NPK/NP has lower CRH, of around 45-50% , and they could retain moisture if the air feed to cooler has higher relativemoisture.The Cooler Air Chiller (and also the Quench Air Chiller) reduces the ambientair temperature by vaporizing the incoming liquid ammonia that is then fedPreneutralizer from ammonia separator. The chillers are followed by ademisters to prevent any condensed water may reach the Cooler (orCombustion Chamber in case of Quench air chiller).Dust coming out with the air leaving the Cooler is recovered in a battery ofcyclones and collected in their respective hoppers, from where it is fed back tothe recycle conveyor.About 55-65 % of the air leaving Cooler cyclones will be sent to the Cooler &Dedusting Scrubber for its washing, through the Cooler & Dedusting Exhaustfan, whereas the rest of this semi-clean warm air (35 - 45%) will be recycled tothe dryer as dilution air, through Air Cooler Recirculation Fan, improvingenergy efficiency and reducing at the same time the size of scrubbingequipment.Rotary Cooler discharges cooled product directly to Final Product Elevatorwhich lift it to the single desk Polishing Screen. Fines under 1 mm areseparated and returned back to recycle, whereas commercial size product