Method for producing urea fertilizer with low moisture absorption tendencies

#This application is the U.S. national phase of PCT Appln. No. PCT/EP2011/004398 filed on Aug. 31, 2011, which claims priority to EP Patent Appln. No. 10009615.5 filed on Sep. 15, 2010, the disclosures of which are incorporated in their entirety by reference herein.

#The invention relates to a urea granulation process and to the urea granule produced by the process. The invention integrates a method for recycling ammonia salts which are currently emitted to other processes, for example to UAN or NPK processes or to a conventional urea production process. Ammonia salts are homogenously mixed into the urea granulator in the current invention so that the urea fertilizer shows low moisture absorption tendencies.

#In a urea plant used air exiting a urea granulator that is equipped with a fluidized bed contains in addition to urea dust also ammonia. This ammonia contamination needs to be removed before the off-gas stream can be vented into the atmosphere.

#FIG. 1 illustrates a prior art method of producing urea granules with a low critical humidity.

#FIG. 2 illustrates one embodiment of the present invention for producing urea granules also containing ammonium compounds, and having a high critical humidity.

#Further embodiments of the current invention are related to the composition of the streams introduced into the urea granulator. Preferably, the stream introduced at the granule flow inlet side of the urea granulator consists exclusively of the urea/ammonium salt-stream and the stream introduced at the granule flow outlet side of the urea granulator consists exclusively of the urea solution without mixing both streams.

#The urea/ammonium salt-stream comprises preferably a urea:ammonium salt ratio between 7 and 16. The water content of this stream preferably is 0-5% by weight. Optionally it comprises between 0.4 to 0.8% by weight additives. The additives for the urea/ammonium salt-stream are thereby selected from the group comprising formaldehyde, aluminium sulphate, magnesium sulphate, micronutrients, and other hydrocarbon granulation additives or mixtures thereof. As preferred additive formaldehyde is used.

#The urea solution introduced at the granule flow outlet side of the urea granulator comprises a water content of 0-10% by weight, preferably a water content of 0-5% by weight and optionally up to 1.5% by weight additives, preferably between 0.4 to 0.8% by weight additives, whereby the weight additives are selected from the group comprising formaldehyde, aluminium sulphate, magnesium sulphate, micronutrients, and other hydrocarbon granulation additives or mixtures thereof. As preferred additive formaldehyde is used. Also it is possible that the urea solution comprises a minor content of impurities, as biuret.