Abstract:
A method of producing anhydrous calcium nitrate, anhydrous magnesium nitrate or mixture thereof involves removing water from a solution of calcium nitrate, magnesium nitrate or mixture thereof in a pulse combustion drier. The invention also provides a mixture of anhydrous calcium nitrate, anhydrous magnesium nitrate and the individual anhydrous nitrate salts in a sealed container.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to nitrates. 
         [0002]    Calcium and magnesium nitrates are used extensively in industry and agriculture. The commercially available products both contain water of crystallization. Calcium nitrate contains about 30 percent water of crystallization and magnesium nitrate about 39 percent water of crystallization The presence of this water leads to problems in storage of the product and causes problems when used in blends with each other and with other materials. 
         [0003]    At present calcium nitrate crystals are made commercially with the addition of about 6 percent ammonium nitrate to form a double salt which contains 15 percent water of crystallization. The double salt crystals are formed on a cooling belt and crushed or formed into a prill in a prilling tower. 
         [0004]    The formation of magnesium nitrate heptahydrate crystals or prills is a lesser problem because of the higher melting point of magnesium nitrate. 
         [0005]    A blend of calcium and magnesium nitrates is a useful product in agriculture, but is difficult to manufacture because of the difficulty in crystallizing the mixture. To date there is no known commercial method of making such a blend or mixture. 
       SUMMARY OF THE INVENTION 
       [0006]    According to the present invention, a method of producing anhydrous calcium nitrate, anhydrous magnesium nitrate or a mixture thereof, includes the steps of providing a solution of calcium nitrate, magnesium nitrate or a mixture thereof, and removing water therefrom in a pulse combustion drier. The solution will typically contain at least 40%, and generally at least 75%, by mass of dissolved calcium nitrate, magnesium nitrate or mixture thereof. 
         [0007]    Further according to the invention, a product useful in industry or agriculture comprises at least one kilogram of anhydrous calcium nitrate, anhydrous magnesium nitrate or a mixture thereof in a container such as a bag. 
         [0008]    Still further according to the invention, there is provided a mixture of anhydrous calcium nitrate and anhydrous magnesium nitrate. The components of the mixture will typically be present in a mass ratio of calcium nitrate to magnesium nitrate in the range 6:1 to 2:1. Particularly useful mixtures are ones containing a calcium nitrate:magnesium nitrate mass ratio of 4:1 or 2:1. The mixture is preferably homogeneous, i.e. in any milligram sample of the mixture the mass ratio calcium nitrate to magnesium nitrate will be essentially the same. A further preferred feature of the mixture is that it has a solution rate in water faster than commercially available calcium nitrate which contains ammonium nitrate and water of crystallization and generally comes in the form of a prill. The mixture will preferably be substantially ammonia free and free flowing. 
     
    
     DESCRIPTION OF EMBODIMENTS 
       [0009]    The product produced by the method of the invention is anhydrous calcium nitrate, anhydrous magnesium salt or a mixture thereof. This means that the nitrate salt or mixture will contain as low a water of crystallization content as possible and preferably be substantially free of water of crystallization. Generally, the water of crystallization content of the nitrate salt or mixture of nitrate salts will be less than 10% by mass, preferably less than 5% by mass and more preferably less than 2% by mass. 
         [0010]    The mixture of nitrate salts will preferably be homogenous, as defined above, substantially free of ammonia and free flowing. 
         [0011]    The invention has particular application to a mixture or blend of anhydrous magnesium and calcium nitrates. The water of crystallisation content of such a mixture will be less than 10% by mass and preferably less than 5% by mass and more preferably less than 2% by mass. The mixture can readily be produced in powder form and packaged in a container such as a bag. If the container is essentially air-tight, then the mixture can be kept for long periods of time without caking or solidification occurring. The water content of prior art calcium and magnesium nitrate s gives rise to caking and solidification problems both in pure products, mixtures and in blends of other salts such as hydroponic blends containing potassium nitrate, phosphate salts, ammonium nitrate or urea. 
         [0012]    The anhydrous nitrates or mixture thereof are produced in a pulse combustion drier. Examples of pulse combustion driers are described In U.S. Pat. Nos. 3,618,655, 4,226,668. 4,708,159, 4,819,873, 4,838,784, 4,941,820 and 4,992,039. Pulse combustion driers are used for drying materials such a fishmeal where rapid heat is required to avoid denaturing of proteins in the material and in drying high value products such as those produced in the pharmaceutical industry. To the best of the applicants knowledge, pulse combustion driers have never been used to dry bulk chemicals, particularly those in the agricultural industry. 
         [0013]    In the present invention, sound pressures and heat are generated in a combustion chamber or zone in a pulse combustion drier and used to dry the nitrate solution. The sound pressures and heat generated in the combustion chamber are generally passed into a drying chamber or zone where the solution to be treated is sprayed into the path of the sound pressures and heat Sound pressures as high as 180 dBA and temperatures of about 110 to 130° C. are produced in the drying chamber. Typical nitrate solutions that are introduced into the drying chamber are those having a nitrate salt concentration of at least 40%, for example a nitrate salt concentration of about 50%. The contact time of the solution to be dried in the drying chamber is measured in microseconds, as sound pressures disperse the solution into droplets which are dried by the heat and air. The fine anhydrous nitrate powder produced collects on a surface of the drying chamber, which is preferably a cooled surface, and may be recovered therefrom. The energy efficiency of this method is very good and approaches the theoretical maximum for an exit temperature of 100° C. (about 80%). 
         [0014]    The fine powder may be packed directly into essentially air-tight bags or steam agglomerated, or agglomerated in a standard pan agglomerates or and then packed. 
         [0015]    Thus, the method of the present invention provides a way of producing anhydrous magnesium nitrate or anhydrous calcium nitrate, and more particularly a mixture thereof, that is commercially viable, labour free and provides a product that does not easily cake and form solid masses in a container such as a bag over time. 
         [0016]    An example of the invention will now be given. A pulse combustion drier was used to remove water from a solution of calcium nitrate and magnesium nitrate which contained 40 mass percent of dissolved solids, i.e. nitrates. The unit size of the drier was 0.1 gJ/hr and the operating conditions were: 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 Operating heat production 
                 0.05 gJ/hr 
               
               
                   
                 Product feed rate 
                 25 kg/hr 
               
               
                   
                 Feed concentration 
                 40% solids 
               
               
                   
                 Product rate 
                 10 kg/hr 
               
               
                   
                 Product analysis 
                 Ca 19.5% Mg - 4.8%: N - 16.5%: 
               
               
                   
                   
                 Moisture-0.6% 
               
               
                   
                 Pulse rate 
                 11/sec 
               
               
                   
                 Contact temperature 
                 563 deg C. 
               
               
                   
                 Exit temperature 
                 105 deg C. 
               
               
                   
                   
               
             
          
         
       
     
         [0017]    A fine powder was collected on the lower surfaces of the drying chamber. This powder was a homogeneous mixture of anhydrous calcium nitrate and anhydrous magnesium nitrate. Each nitrate particle contained less than 2 mass % water of crystallization. The mass ratio of anhydrous calcium nitrate to anhydrous magnesium nitrate was 4:1. The mixture had an excellent solution rate in water and much faster than commercially available calcium nitrate prills. The mixture was substantially ammonia free and free flowing and was stored in a water and air-tight container and remained anhydrous, substantially ammonia free and free flowing for many months.