Large Volume Inorganic Chemicals - Ammonia ... - ammk-rks.net

Chapter 9Some examples of granulators used in AN/CAN plants include rotary pans and drums,spherodisers, pugmills and fluidised beds. The filler is normally added in the process before thegranulator if CAN is to be produced, with the AN being added to the granulator as a spray ofhot concentrated solution. No further drying of the granules will normally be required. Thegranules are screened and the oversized granules are crushed and, together with the fines,recycled to the granulator. CAN and CAN/NPK granulators include drums and pugmills, wherethe filler may be mixed with the AN solution before granulation or in the granulator itself.Granules from this process will normally require drying in a fluidised bed or rotary drier. Whendrying CAN, it might not be necessary to add any additional heat as the granules may haveretained sufficient heat to provide the necessary driving force. Such a process is known as anautothermal process. The granules are screened after drying.9.2.6 CoolingBoth granulators and prill towers normally produce a product which needs further cooling inrotary or fluidised bed coolers, with the air cleaned. Air cleaned in a dry system can generallybe re-used as secondary air to the drier, after dedusting.A bulk flow heat exchanger may be used. The product is cooled by transferring the heat to waterfrom a cooling tower in a development of a plate heat exchanger. This has minimal atmosphericeffluents.Sometimes two-stage cooling is used where the bulk flow heat exchanger normally works as thesecond stage [28, Comments on D2, 2004].9.2.7 ConditioningAN and CAN tend to cake during storage and are therefore conditioned. Anticaking agents maybe included as part of the product or applied as a coating to the outside. These additives can alsominimise dust formation and moisture absorption during storage.Large Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers 369