Method for belt conditioning in pelletizing plants, method for pelletizing urea and pelletizing plant

Abstract

Method for belt conditioning in pelletizing plants, method for pelletizing urea and pelletizing plant. The invention relates to a method for belt conditioning in pelletizing plants with a rotating steel belt to which is applied in drop-like manner a melt of a product to be pelletized which is then solidified on the steel belt. According to the invention there are steps of washing off product residues left on the steel belt after removing the solidified pellets using a washing liquid containing at least the dissolved product and drying the washing liquid adhering to the steel belt for forming a dry product film thereon prior to the renewed application of a melt of a product to be pelletized. Use e.g. for pelletizing urea.

1 . Method for belt conditioning in pelletizing plants with a rotating steel belt to which is applied in drop-like manner a melt of a product to be pelletized and which is then solidified on the steel belt, characterized by the following steps: 
 washing away product residues present on the steel belt after removing the solidified pellets using a washing liquid containing at least the dissolved product and    drying the washing liquid adhering to the steel belt for forming a dry product film on said steel belt prior to the renewed application of a melt of a product to be pelletized.    
   
   
       2 . Method according to  claim 1 , further characterized by drawing off of the steel belt following washing off for forming a washing liquid film adhering to said steel belt.  
   
   
       3 . Method according to  claim 1 , wherein the dry product film has a thickness of less than 5 μm.  
   
   
       4 . Method according to  claim 1 , wherein the washing liquid exclusively comprises a solution of the product with a solvent.  
   
   
       5 . Method according to  claim 4 , wherein water is used as the solvent.  
   
   
       6 . Method according to  claim 1 , wherein the washing liquid contains an unsaturated product solution.  
   
   
       7 . Method according to at  claim 1 , further characterized by heating the steel belt and/or the air surrounding the steel belt for drying a detergent film adhering to the belt.  
   
   
       8 . Method according to  claim 1 , wherein the product to be pelletized forms a hygroscopic melt.  
   
   
       9 . Method according to  claim 8 , wherein the product to be pelletized forms a salt melt or basic melt.  
   
   
       10 . Method according to  claim 1 , wherein the product to be pelletized is urea.  
   
   
       11 . Method according to  claim 1 , wherein the washing liquid contains between 40% and 80% solvent, and between 60% and 20%, of the product to be pelletized.  
   
   
       12 . Method according to  claim 1 , wherein the washing liquid contains an agent for preventing caking of the pelletized product.  
   
   
       13 . Method according to  claim 12 , wherein the agent is a urea-formaldehyde reaction product.  
   
   
       14 . Method according to  claim 11  wherein the washing liquid contains 2% to 8% of the anti-caking agent.  
   
   
       15 . Method for pelletizing urea, characterized by a belt conditioning according to  claim 1 .  
   
   
       16 . Pelletizing plant with a rotating steel belt to which is applied in drop-like manner a melt of a product to be pelletized which is then solidified on the steel belt, characterized by means for washing off product residues present on the steel belt after removing the solidified pellets using a washing liquid containing at least the dissolved product, and for forming a dry product film on the steel belt prior to the renewed application of a melt of a product to be pelletized.  
   
   
       17 . Pelletizing plant according to  claim 16 , wherein the means has a washing device downstream of a point for removing solidified product pellets from the steel belt, the washing device has a roller for applying the washing liquid extending over the width of and engaging on the steel belt.  
   
   
       18 . Pelletizing plant according to  claim 17 , wherein the roller engages on and is driven by the steel belt.  
   
   
       19 . Pelletizing plant according to  claim 17 , wherein the roller has a smooth surface and engages substantially linearly on the steel belt.  
   
   
       20 . Pelletizing plant according to  claim 17 , in wherein the roller has a plastic surface.  
   
   
       21 . Pelletizing plant according to  claim 17 , wherein the roller is sectionally immersed in a tank fillable with washing liquid.  
   
   
       22 . Pelletizing plant according to  claim 16 , wherein the means has at least one elastic draw-off lip engaging on the steel belt positioned downstream of washing device considered in the running direction of the belt.  
   
   
       23 . Pelletizing plant according to  claim 22 , wherein there are two substantially parallel draw-off lips, which can be individually replaced.  
   
   
       24 . Pelletizing plant according to  claim 16 , wherein the means have heating coils beneath the return strand of the steel belt and/or at least one heating drum engaging on a return strand of the steel belt.  
   
   
       25 . Method according to  claim 3 , wherein the thickness is less than 1 μm.  
   
   
       26 . Method according to  claim 11 , wherein the washing liquid contains 50% of the product to be pelletized.  
   
   
       27 . Method according to  claim 11 , wherein the solvent is water.  
   
   
       28 . Method according to  claim 11 , wherein the product to be pelletized is urea.  
   
   
       29 . Method according to  claim 14 , wherein the washing liquid contains 5% of the anti-caking agent.