PATENT ABSTRACT
A process for the preparation of granular fertilizer grade DAP (a product composed of ammonium phosphates, principally diammonium phosphate, resulting from the ammoniation of phosphoric acid, as defined in Official Publication No. 52 of the Association of American Plant Food Officials, dated 1999) comprising partially preneutralizing orthophosphoric acid with ammonia, completing the ammoniation of the orthophosphoric acid with ammonia in a rotary ammoniator-granulator to provide granular DAP, sizing the granular DAP to provide the granular DAP product, reducing the particle size of the oversized granular DAP, and recycling the undersized granular DAP and the sized-reduced oversized granular DAP to the ammoniator-granulator. The ammoniacal nitrogen concentration of the granular DAP recycle, hence the granular DAP product, is enhanced by subjecting the finely-divided recycled granular DAP to anhydrous gaseous ammonia which is at a super atmospheric pressure and which is at a temperature sufficient to maintain said anhydrous ammonia in the gaseous state. The increase in the ammoniacal nitrogen concentration is a function of the absolute ammonia pressure, the initial moisture content of the granular DAP recycle, and the contact time of the ammonium with the granular DAP recycle.

PATENT DESCRIPTION
This application is related to the application entitled “Method for Producing Fertilizer Grade DAP Having an Increased Nitrogen Concentration In a Spray Column”, filed concurrently herewith. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a method of enhancing the nitrogen concentration of fertilizer grade DAP. Fertilizer grade DAP is defined in Official Publication No. 52 (1999) of the Association of American Plant Food Control Officials as a product composed of ammonium phosphates, principally diammonium phosphate, resulting from the ammoniation of phosphoric acid. It may contain up to 2 percent non-ammoniacal nitrogen. The guaranteed percentage of nitrogen and available phosphate shall be stated as part of the name. 
     2. Background of the Invention 
     Phosphorus as well as nitrogen are essential plant nutrients. Phosphorus and nitrogen ensure cell multiplication and thus growth since both are structural components of nucleic acids. Plants use the phosphorus and nitrogen to grow. Since fertilizers are generally formed by the reaction of phosphoric acid and ammonia, they are used to provide a rich source of nitrogen and phosphorus to the plants. Such fertilizers are generally applied to the soil and are readily assimilable by plants. 
     The phosphoric acid used in fertilizers is usually manufactured from rock phosphate typically in one of two ways. Phosphate rock is composed chiefly of calcium phosphates and calcite. 
     In the first prior art method, commonly known as the furnace acid process, the phosphoric acid is made by heating phosphate rock to a form of relatively pure elemental phosphorus which is then converted into the phosphoric acid. More particularly, this prior art process uses an electric furnace heated to about 1500° K. The phosphate rock is reduced by coke in the presence of sand or silicon dioxide according to the following reaction: 
     
       
         Ca 3 (PO 4 ) 2 +3SiO 2 +5C═3CaSiO 3 +5CO+P 2    
       
     
     Gaseous P 2  condenses to form a solid P 4 . In the air, the P 4  converts to phosphorus pentoxide. Water is then added to the phosphorus pentoxide to form the phosphoric acid. The process usually yields 85 percent phosphoric acid which is colorless and has a density of about 1.69 kg/L. The phosphoric acid formed by this prior art process generally yields a purer phosphoric acid as compared to the phosphoric acid formed by the second prior art process, which is described below. However, this first process is also much more costly than the second prior art process. 
     The second prior art method used to produce phosphoric acid is known as the wet process. Most of the phosphoric acid produced in the United States is produced by this process. In this wet process, finely ground phosphate rock is slurried with sulfuric acid. Sometimes, recycled dilute phosphoric acid is included in the slurry. The reaction that occurs in this wet process is set forth below: 
     
       
         Ca 3 (PO 4 ) 2 +3H 2 SO 4 =3CaSO 4 +2H 3 PO 4    
       
     
     In addition to the orthophosphoric acid, the reaction yields gypsum and numerous other suspended and dissolved impurities. The slurry is generally filtered to remove the solid impurities, mainly, gypsum. The resultant filtrate contains between 25 and 35 percent P 2 O 5  and between 1 and 8 percent by weight of suspended solids or impurities that are not removed by the filtration process. Examples of wet process methods are disclosed in U.S. Pat. Nos. 4,487,750, 4,485,078, 4,657,559, 4,665,790 and 4,655,789, which are incorporated herein in their entirety. U.S. Pat. No. 4,710,366 discloses methods of removing further impurities from the filtrate; such patent is incorporated herein in its entirety. 
     As used herein, the terms phosphoric acid and wet process phosphoric acid mean orthophosphoric acid. 
     Phosphoric acid is reacted with anhydrous ammonia to form ammonium phosphates, which constitute a large class of phosphorus fertilizers. See Examples 7 and 9 of U.S. Pat. No. 4,485,078. The common ammonium phosphates include monoammonium phosphate and diammonium phosphate, which are the primary components of the fertilizers commonly known as MAP and DAP, respectively. DAP (fertilizer grade) is a product composed of ammonium phosphates, principally diammonium phosphate, resulting from the ammoniation of phosphoric acid. The phosphoric acid is preferably reacted with the proper proportion of anhydrous ammonia which primarily provides diammonium phosphate, which is a source of nitrogen and phosphorus readily assimilable by food crops. 
     The TVA (Tennessee Valley Authority) in the early 1960s developed a process for the preparation of granular DAP from ammonia and phosphoric acid. The conventional TVA process for preparing granular DAP is described on pages 248 to 251 of  Manual of Fertilizer Processing , edited by Francis T. Nielsson, Marcel Dekker, Inc., (1987). The conventional TVA type of process has a preneutralizer for partial ammoniation of the phosphoric acid and completion of ammoniation is done in a rotary ammoniator-granulator. Granulation is controlled by recycling product fines to the drum. The basic TVA process involves partial preneutralization of the acid in a preneutralizer (reaction tank) followed by completion of ammoniation to DAP in the rotary ammoniator-granulator. Excess ammonia, which must be fed to the ammoniator-granulator to produce DAP, is recovered by scrubbing the off gases with the acid to be used in the process. The granular product is normally dried, cooled, and screened, having the undersized and crushed oversized granular DAP recycled to the granulator to control granulation. 
     Pure diammonium phosphate [(NH 4 ) 2 HPO 4 ] is also termed dibasic ammonium phosphate. Page 561 of  The Merck Index,    10 th Ed., (1983), states that diammonium phosphate gradually loses about 8 percent NH 3  on exposure to air. 
     Triammonium phosphate is (NH 4 ) 3 PO 4 . 
     BROAD DESCRIPTION OF THE INVENTION 
     An object of the invention is to provide a process for enhancing the ammoniacal nitrogen concentration of DAP. Another object of the invention is to provide a process for producing DAP fertilizer with the nitrogen and phosphate concentrations required for international trade, using the lower quality orthophosphoric acid currently being produced, without using expensive nitrogen supplements. A further object of the invention is to provide a process for the production of fertilizer grade diammonium phosphate. Other objects and advantages of the invention are set forth herein or are obvious herefrom to one skilled in the art. 
     The objects and advantages of the invention are achieved by the process of the invention. 
     There currently exists a need for a process to produce ammonium phosphate from orthophosphoric acid having a high concentration of impurities. Furthermore, a need exists for increasing the nitrogen content of DAP used for fertilizers. The invention provides a solution to such needs. 
     It has been found that reacting finely divided DAP with high pressure, anhydrous, gaseous ammonia will enhance or increase the ammoniacal nitrogen concentration of the DAP, but such treated DAP has the disadvantages that, as it ages, it tends to lose significant amounts of the added nitrogen and to gain excessive moisture. 
     The invention involves a process for enhancing the ammoniacal nitrogen concentration of DAP. The DAP, which is in finely divided form, is subjected to anhydrous gaseous ammonia, which is at a super atmospheric pressure and which is at a temperature sufficient to maintain the ammonia in the gaseous state. The increase in the ammoniacal nitrogen concentration is a function of the absolute ammonia pressure, the initial moisture content of the DAP and the contact time of the ammonia with the DAP. The enhancement of the ammoniacal nitrogen content of the DAP is also a function of the particle size of the DAP. 
     The DAP should be de-aerated before it is treated with the gaseous ammonia. The ammonia may have converted some of the DAP to triammonium phosphate and/or been adsorbed by the DAP. 
     A preferred embodiment of the invention process involves modification or improvement of the conventional TVA process, or such type of process, for the preparation of granular DAP from ammonia and orthophosphoric acid. 
     The conventional TVA type of process has a preneutralizer for partial ammoniation of the phosphoric acid and a rotary ammoniator-granulator for completion of the ammoniation. Granulation is controlled by recycling product fines to the drum. The TVA process involves partial preneutralization of the acid in a preneutralizer (reaction tank) followed by completion of ammoniation to DAP in the rotary ammoniator-granulator. Excess ammonia, which must be fed to the ammoniator-granulator to produce DAP, is recovered by scrubbing the off gases with the acid to be used in the process. The granular product is normally dried, cooled, and screened, with the undersized and crushed oversized granular DAP being recycled to the granulator to control granulation. 
     Such preferred embodiment, as already stated, involves improving the conventional TVA type of process for the preparation of granular DAP product. The conventional TVA type of process involves partially preneutralizing orthophosphoric acid with ammonia, completing the ammoniation of the orthophosphoric acid in a rotary ammoniator-granulator to provide granular DAP, sizing the granular DAP to provide the granular DAP product, reducing the particle size of the oversized granular DAP, and recycling the undersized granular DAP and the sized-reduced oversized granular DAP to the ammoniator-granulator. The invention involves the improvement of enhancing the ammoniacal nitrogen concentration of the granulated DAP recycle, hence the granular DAP product, by subjecting the finely-divided granular DAP recycle to anhydrous gaseous ammonia which is at a super atmospheric pressure and which is at a temperature sufficient to maintain the anhydrous ammonia in the gaseous state. The increase in the ammoniacal nitrogen concentration is a function of the absolute ammonia pressure, the initial moisture content of the granular DAP recycle, and the contact time of the ammonia with the granular DAP recycle. The enhancement of the ammoniacal nitrogen content of the DAP is also a function of the particle size of the granular DAP recycle. 
     Recycle in the invention process can include dust from the granulator. 
     The independent functions (variables) which provide increase in ammoniacal nitrogen concentration in the invention process can be represented with more particularity by the following regression equation: 
     
       
         % Nitrogen Increase=0.355×nitial % Moisture+0.027×Contact Time (min.)+0.009×NH 3  Pressure (psia)−0.240  
       
     
     wherein the coefficients associated with the three independent functions (variables), i.e., the absolute ammonia pressure, the initial percent moisture and the contact time, can each vary plus or minus up to 50 percent (and still be within the scope of the regression equation). The dependent variable “% Nitrogen Increase” represents the increase of the ammoniacal nitrogen concentration. The coefficients in the above regression equation are based on the combined data from Tables 6 and 10 below. As mentioned above, the coefficients of the above regression equation can each vary plus or minus 50 percent, but note that such coefficients may vary an even greater magnitude, and still be within the scope of the above regression equation, for wet process phosphoric acid with a significantly different combination of impurities. 
     Conducting the invention process according to the above regression formula provides DAP which has enhanced ammoniacal concentration and which is stable (i.e., as to the enhanced ammoniacal concentration) upon aging. 
     The invention process provides fertilizer grade DAP, a product composed principally of diammonium phosphate, as defined in Official Publication No. 52 of the Association of American Plant Food Control Officials, dated 1999. The preferred process enhances the ammoniacal nitrogen concentration of DAP above what can normally be obtained, with a given orthophosphoric acid quality, in the standard TVA style DAP plant using a preneutralizer and granulator. The additional ammoniacal nitrogen is obtained by producing and incorporating a variable amount of triammonium phosphate into the DAP granular product and/or adsorbing a variable amount of ammonia on the surface and in the pores of the granular DAP, and incorporating this material into the DAP product. 
     The DAP recycle treated according to the invention process is finely divided. The particle size of the finely-divided DAP recycle is generally −9 mesh or less. The broad range for the particle size is smaller than 6.83 mm (3 mesh Tyler sieve size) with no theoretical lower limit. The preferred particle size range is smaller than 2.00 mm (9 mesh Tyler sieve size) and larger than about 0.01 mm (10 microns). 
     The ammonia gas pressure used is super atmospheric, with the ammonia gas pressure being preferably 15 to 100 psia (and more preferably 30 to 85 psia). There are two basic reasons that the upper limit for the preferred ammoniation pressure is 100 pounds per square inch gauge (psig) or 114.7 pounds per square inch absolute (psia). First, the codes (ASTM) regulating the fabrication of pressure vessels make a vessel rated for pressures up to 100 psig. Second, once the pressure gets significantly about 100 psig, parts of the process may require the addition of heat (during periods of extremely cold ambient temperatures) to avoid condensation of the ammonia. 
     The theoretical upper limit to the ammoniation pressure range would be the critical pressure for ammonia (11 1.5 atmospheres absolute or about 1624 pounds per square inch gauge pressure). If the ammonia temperature is less than or equal to the critical temperature for ammonia (405.5° Kelvin or 270.68° F.), ammonia cannot exist as a gas at or above the critical pressure. In functional language, this can be stated as the region in terms of pressure and temperature where ammonia exists in the gaseous state. 
     The contact time of the pressurized gaseous ammonia with the DAP recycle should be sufficient to allow the required amount of triammonium phosphate to be formed by chemical reaction and/or the required amount of ammonia to be adsorbed. The contact time is broadly between about 10 seconds and 2 hours, preferably 5 minutes to one hour. 
     The temperature of the pressurized gaseous ammonia is generally between about 450 and about 200° F. The broad temperature range for the ammonia is at least 32° F. (0° C.) and not more than 250° F. (121.1° C.) when it enters the pressure reactor. The preferred temperature range is at least 55.4° F. (13° C.) and not more than 175° F. (79.4° C.) when it enters the pressure reactor. 
     The initial moisture (H 2 O) content of the DAP recycle is generally between about 0.2 to about 4 percent, preferably about 0.5 to 3.5 percent. 
     One especially preferred method involves de-aerating the granular DAP recycle in a first sealed vessel by the application of vacuum. The de-aerated granular DAP recycle is subjected in a second sealed vessel to an atmosphere consisting of anhydrous gaseous ammonia which is at a pressure of at least 15 psia, for a time period sufficient for the required amount of triammonium phosphate to be formed and/or the required amount of ammonia to be adsorbed. The ammonia-treated granular DAP recycle is transferred to a third sealed vessel and the excess ammonia is removed by vacuum applied to the third vessel. The vacuum-treated, ammonia-treated granular DAP recycle is recycled to the ammoniator-granulator. 
     Another especially preferred method involves placing the granular DAP recycle in a sealed vessel, de-aerating the granular DAP recycle by the application of vacuum to the sealed vessel, feeding anhydrous gaseous ammonia into the sealed vessel until a pressure of at least 15 psia is obtained in the sealed vessel, and keeping the granular DAP recycle in contact with the ammonia in the sealed vessel for a time period sufficient for the required amount of triammonium phosphate to be formed and/or the required amount of ammonia to be adsorbed. At the end of the time period, the excess ammonia is removed by vacuum applied to the sealed vessel. The vacuum-treated, ammonia-treated DAP recycle is recycled to the ammoniator granulator. 
     Another method of operating the process includes introducing a portion of the DAP recycle into an entry lock vessel at atmospheric pressure (with no effort to remove the air that enters the vessel with the recycle). This vessel is then pressurized with gaseous ammonia such that the total pressure is essentially equal to the total pressure in a second reactor vessel, the gas in this second reactor vessel being a mixture containing no more than 15 percent air and no less than 85 percent ammonia. A valve connecting the entry lock vessel and reactor vessel is then opened and the DAP recycle is allowed to flow into the reactor vessel. The valve connecting the entry lock vessel and reactor vessel is then closed and the gas in the entry lock vessel is vented to another part of the process, such that the ammonia contained in the gas can be recovered in a useful manner. The primary objective of the venting step is to reduce the pressure in the entry lock vessel to atmospheric pressure, such that additional DAP recycle can be introduced into the entry lock vessel. The DAP recycle that is now in the reactor vessel is kept in the reactor vessel, in contact with the ammonia atmosphere at elevated pressure, for a period of time (i.e., the reaction time) sufficient to allow the required amount of triammonium phosphate to be formed by chemical reaction, and/or the required amount of ammonia to be adsorbed. While the DAP recycle is in the reactor vessel, an exit lock vessel is pressurized with ammonia, such that the total pressure in the exit lock vessel is essentially equal to the total pressure in the reactor vessel. At the end of the reaction time a valve connecting the reaction vessel with the exit lock vessel is opened and the ammonia enriched recycle is allowed to flow into the exit lock vessel. The valve connecting the reaction vessel with the exit lock vessel is then closed. At this time, additional DAP recycle can be introduced into the reaction vessel in the manner indicated above. After the valve connecting the reaction vessel with the exit lock vessel is closed, the gas in the exit lock vessel is vented to another part of the process, such that the ammonia contained in the gas can be recovered in a useful manner. The primary objective of the venting step is to reduce the pressure in the exit lock vessel to atmospheric pressure. A second valve on the exit lock vessel is then opened and the ammonia enriched recycle is removed from the exit lock vessel and transferred to the ammoniator granulator where it is incorporated into the DAP product. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a schematic of a conventional TVA process for the production of granular DAP; 
     FIG. 2 is a graph of contact time versus percent nitrogen increase for DAP dust and recycle; 
     FIG. 3 is a graph of weight changes of a DAP aging test; 
     FIG. 4 is a graph of percent nitrogen increase versus DAP particle size; 
     FIG. 5 is a schematic of the pilot plant used in Example J for the production of DAP; 
     FIG. 6 is a schematic of the DAP pilot plant of FIG. 5 showing the location of the pressure reactor module; and 
     FIG. 7 is a schematic showing the details of how the pressure reactor module is integrated into the DAP pilot plant of FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention provides a process for increasing the amount of nitrogen in a diammonium phosphate composition. The result is fertilizer grade DAP, as defined in Official Publication No. 52 of the Association of American Plant Food Control Officials, dated 1999. 
     The invention provides a method for producing DAP fertilizer with the lower quality phosphoric acid currently being produced, without using expensive nitrogen supplements. The invention process can also produce a higher analysis fertilizer with, for example, a phosphate concentration (expressed as percent P 2 O 5 ) of about 48 percent and an ammonia concentration (expressed as percent N) of about 20 percent. 
     The purpose of enhancing such nitrogen concentration of the DAP is so that it can be used as nitrogen rich fertilizer without having to use expensive nitrogen supplements. The reacting of finely divided DAP with high pressure, anhydrous, gaseous ammonia enhances or increases the ammoniacal nitrogen concentration of the DAP. Such ammonia-treated DAP is not suitable as a nitrogen rich fertilizer because it lacks the necessary stability since as it ages it tends to lose significant amounts of the added nitrogen and to gain excessive moisture. These disadvantages are present even after aging for only two weeks. 
     The flow path of a conventional TVA (Tennessee Valley Authority) process for the production of granular DAP is shown in FIG.  1 . Phosphoric acid (30 to 54 percent P 2 O 5 ) is fed into the top of the preneutralizer (reaction tank)  100  via lines  102  and  104 . Water is fed into the top of the preneutralizer  100  via line  106 . Ammonia is fed into the preneutralizer  100  via lines  108  and  110 , and is normally conveyed to a point below the liquid level in the tank. The phosphoric acid is partially preneutralized by the ammonia in preneutralizer  100 . The heat of reaction of ammonia and phosphoric acid is used to evaporate water in preneutralizer  100 . Preneutralizer  100  is vented to the atmosphere via top lines  122  and  124  with water vapor coming off via line  126 . Further phosphoric acid is fed into the upper portion of scrubber  112  via lines  102  and  114 . Water is fed into line  114  via line  116 . The solution of the partially preneutralized phosphoric acid is fed from preneutralizer  100  via line  130  to rotary ammoniator-granulator  132 . Further ammonia is fed via lines  108  and  134  into ammoniator-granulator  132 , wherein the ammoniation is completed. Excess ammonia is required in ammoniator-granulator  132  to produce DAP. The granular product from ammoniator-granulator  132  is fed via line  136  into dryer  138 . Exhaust containing ammonia and water vapor from ammoniator-granulator  132  is fed into the bottom of scrubber  112  via line  120 . Water vapor comes off of scrubber  112  via line  1   18 . The ammonia is scrubbed out of the off gases from ammoniator-granulator  132  and the phosphoric acid is fed from scrubber  112  via line  128  into the top of preneutralizer  100 . (As an alternative, the granular material from dryer  138  can go directly to screen  146 , with only the product size DAP going through cooler  142 .) The dried granular DAP is fed via line  140  into cooler  142 . The granular DAP is fed via line  144  into screen  146 . The sized granular DAP product is removed via line  156  from screen  146 . The undersized granular DAP exits screen  146  via line  152 . The oversized granular DAP is removed from screen  146  and fed via line  148  into crusher  150 . The crushed DAP exits from crusher  150  via line  154  and is mixed with the undersized granular DAP from line  152 , to form a mixture of fines. The fines mixture is recycled via line  158  into the front end of ammoniator-granulator  132 . Product size DAP can also be included in the recycle stream to aid in ammoniator-granulator operation. 
     Advantages can be taken of the maximum solubility of the ammonia/phosphoric acid mole ratio of about 1.45; therefore, the preneutralizer  100  is preferably operated at as near this point as is practical to obtain the most concentrated slurry having satisfactory fluidity. This slurry can either flow by gravity into a sawtooth weir pipe (not shown) for distribution in ammoniator-granulator  132 , or be pumped into a sparged spray system (not shown) located over the moving bed (not shown) of dry recycle inside of ammoniator-granulator  132 . The later procedure provides more consistent control and better slurry distribution. Ammoniation of the slurry in the ammoniator-granulator drum (not shown) to a mole ratio of about 2.0 lowers the solubility and causes crystallization of DAP. The heat of reaction between the monoammonium phosphate in the slurry and the ammonia causes the majority of the water present to vaporize and exit with the granulator off gases. 
     Broadly speaking, a preferred embodiment of the invention process involves treating solid DAP recycle (in a TVA type operation) with gaseous ammonia at elevated pressure to increase the ammoniacal nitrogen concentration. This recycle is then returned to the DAP granulator and incorporated into the final DAP product. 
     Preferably, one method of producing the triammonium phosphate or adsorbing the ammonia involves, first, introducing a portion of the DAP recycle material, normally present from the TVA process, into a vessel under vacuum, such that any air introduced with the recycle is removed. The DAP recycle material is then transferred to a second vessel in which there is an essentially 100 percent ammonia atmosphere at a pressure at or above 15 psia and a temperature sufficiently high to insure that the ammonia exists in the gaseous state. The DAP recycle material is kept in this second vessel, in contact with the ammonia atmosphere, for a period of time sufficient to allow the required amount of triammonium phosphate to be formed by chemical reaction, and/or the required amount of ammonia to be adsorbed. The DAP recycle material is then transferred to a third vessel where the excess ammonia is removed by vacuum, or vented to another part of the process, such as, the preneutralizer or scrubber. The ammonia-enriched DAP recycle is then transferred to the granulator where it is incorporated into the DAP product. 
     Preferably, another method for the production of triammonium phosphate and/or adsorption of ammonia is carried out in a single vessel as a batch process. In this case, the DAP recycle is placed in the vessel and the vessel is sealed. A vacuum is then applied to the vessel to remove the air. Anhydrous gaseous ammonia is then fed to the vessel until a pressure at or above 15 psia is obtained. The DAP recycle is then allowed to remain in the vessel, in contact with the ammonia, until the required amount of triammonium phosphate is formed and/or the required amount of ammonia is adsorbed. A vacuum is then applied to the vessel to remove the excess ammonia. The vessel is then opened and the ammonia-enriched DAP recycle is removed and transferred to the granulator where it is incorporated into the DAP product. 
     The particle size of the finely-divided DAP recycle is generally −9 mesh or less. 
     The ammonia gas pressure used is super atmospheric, with the ammonia gas pressure preferably being at least 15 psia and more preferably 30 to 95 psia. 
     The contact time of the pressurized gaseous ammonia with the DAP recycle should be sufficient to allow the required amount of triammonium phosphate to be formed by chemical reaction and/or the required amount of ammonia to be adsorbed. The contact time is generally between about 0.25 and about 90 minutes, preferably 5 to 60 minutes. 
     The initial moisture (H 2 O) content of the DAP recycle is generally between about 0.2 to about 4 percent, preferably about 0.5 to 3.5 percent. 
     The temperature of the pressurized gaseous ammonia can be as low as 33° F., but is generally between about 45° and about 200° F. 
     The independent functions (variables) which provide increase in ammoniacal nitrogen concentration in the invention process can be represented with more particularity by the following regression equation: 
     
       
         % Nitrogen Increase=0.355×Initial % Moisture+0.0027×Contact Time (min.)+0.009×NH 3  Pressure (psia)−0.240  
       
     
     wherein the coefficients associated with the three independent functions (variables), i.e., the absolute ammonia pressure, the initial percent moisture and the contact time, can each vary plus or minus up to 50 percent (and still be within the scope of the regression equation). The dependent variable “% Nitrogen Increase” represents the increase of the ammoniacal nitrogen concentration. The coefficients in the above regression equation are based upon the combined data from Tables 6 and 10 below. As mentioned above, the coefficients of the above regression equation can each vary plus or minus 50 percent, but note that such coefficients may vary an even greater magnitude, and still be within the scope of the above regression equation, for wet process phosphoric acid with a significantly different combination of impurities. 
     Conducting the invention process according to the above regression formula provides DAP which has enhanced ammoniacal concentration and which is stable (i.e., as to the enhanced ammoniacal concentration), when recycled to the granulator and incorporated into the DAP product, upon aging. 
     The increase in the ammoniacal nitrogen concentration is also a function of the particle size of the granular DAP (recycle). Specifically, the smaller the particle size, the larger the increase in the percent nitrogen increase. The effect of the particle size is usually of small practical effect because the treated DAP (recycle) usually contains a relatively low amount of very small particles. The invention process includes treating recycle from a conventional TVA process which is composed of DAP dust, DAP undersized recycle material and crushed DAP oversize recycle material. 
     As used herein, all percentages are on a weight basis unless otherwise stated herein or obvious herefrom to one skilled in the art. 
     DAP is a product composed of ammonium phosphate, principally diammonium phosphate, resulting from the ammoniation of phosphoric acid. Diammonium phosphate is a chemical compound having the formula (NH 4 ) 2 HPO 4 . 
     The following examples serve to further illustrate the invention in greater detail. 
     In the following examples, the pressure ammoniation procedure of the (recycle) DAP was as follows: 
     (a) The weighed quantity of (recycle) DAP was placed in a pressure vessel, which was then sealed. 
     (b) A vacuum of 24 to 25″ Hg was then applied to the sealed vessel to remove the air. 
     (c) Gaseous ammonia was added to the sealed vessel until the desired pressure was obtained. 
     (d) The (recycle) DAP was held in the sealed vessel for the required time, with additional ammonia being added to maintain the desired pressure (that is, to replace the ammonia consumed in the reaction). 
     (e) A vacuum of 24 to 25″ Hg was again applied to the sealed vessel to remove the unreacted ammonia. 
     (f) Air was bled into the vessel to relieve the vacuum. 
     (g) A vacuum of 24 to 25″ Hg was applied to the vessel again to help remove the last traces of ammonia. 
     (h) Air was bled into the vessel to relieve the vacuum. 
     (i) The vessel was opened and the ammoniated (recycle) DAP was removed and weighed. 
     EXAMPLE A 
     Small particles of (granular) DAP (produced by a conventional TVA process), comprising 17.82 percent nitrogen and 46.70 percent phosphate, having a N/P mole rate of 1.93:1 and having a particle size between −4 mesh and +14 mesh, were exposed to ammonia pressure of 15, 30 or45 psia for 30, 45 or 60 minutes as set forth in Table 1 below. There were nine test samples. The above-described ammoniation procedure was used. Each of the nine DAP samples was separately placed in the pressure reactor and the pressure reactor was sealed. A vacuum was pulled on the sealed reactor to remove the air. The reactor was then filled with ammonia and pressurized to the desired test pressure. As necessary, additional ammonia was bled into the reactor to maintain the pressure. At the end of the specified contact time a vacuum was again applied to the reactor to remove the unreacted ammonia. Air was then bled into the reactor, the reactor was opened and the ammoniated DAP sample was removed. The results of these tests (high pressure ammonia treatment of DAP product) are set forth in Table 1 below. The results showed increases in the ammoniacal nitrogen concentration from 0.48 to 1.0 percent, that were generally proportional to the ammonia pressure and contact time. 
     
       
         
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Test 
                 Contact 
                 Ammonia 
                   
                   
                   
                   
               
               
                 Sample 
                 Time, 
                 Pressure, 
                 N, 
                 P 2 O 5 , 
                 Molar 
                 % N 
               
               
                 No. 
                 min. 
                 psia 
                 % 
                 % 
                 Ratio 
                 Increase 
               
               
                   
               
             
             
               
                 A-1 
                 30 
                 15 
                 18.30 
                 46.40 
                 2.00 
                 0.48 
               
               
                 A-2 
                 45 
                 15 
                 18.30 
                 46.51 
                 1.99 
                 0.48 
               
               
                 A-3 
                 60 
                 15 
                 18.20 
                 46.44 
                 1.99 
                 0.38 
               
               
                 A-4 
                 30 
                 30 
                 18.36 
                 46.41 
                 2.00 
                 0.54 
               
               
                 A-5 
                 45 
                 30 
                 18.60 
                 46.20 
                 2.04 
                 0.78 
               
               
                 A-6 
                 60 
                 30 
                 18.47 
                 46.09 
                 2.03 
                 0.65 
               
               
                 A-7 
                 30 
                 45 
                 18.68 
                 46.29 
                 2.04 
                 0.86 
               
               
                 A-8 
                 45 
                 45 
                 18.82 
                 46.09 
                 2.07 
                 1.00 
               
               
                 A-9 
                 60 
                 45 
                 18.82 
                 46.04 
                 2.07 
                 1.00 
               
               
                   
               
             
          
         
       
     
     Test Sample Nos. A-2, A-5 and A-8, as well as a control, were aged for two weeks to determine if the nitrogen gains were stable. [The control was small particles of (granular) DAP which had not been ammoniated.] A portion of each of the samples and the control was aged in a sealed container; and a portion of each of the samples and the control was aged in an open pan. The results from these tests are set forth in Table 2: 
     
       
         
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 Sealed Container 
                 Open Pan 
                   
               
             
          
           
               
                 Test 
                 Ammonia 
                   
                   
                 Vac. 
                 Dry 
                   
                   
                   
                 Vac. 
                 Dry 
                   
                 Relative 
               
               
                 Sample 
                 Pressure, 
                 N, 
                 P 2 O 5 , 
                 Oven 
                 Basis 
                 Mole 
                 N, 
                 P 2 O 5 , 
                 Oven 
                 Basis 
                 Mole 
                 N Loss, 
               
               
                 No. 
                 psia 
                 % 
                 % 
                 Moist. 
                 % N 
                 Ratio 
                 % 
                 % 
                 Moist. 
                 % N 
                 Ratio 
                 % 
               
               
                   
               
             
          
           
               
                 Control 
                   
                 17.95 
                 47.03 
                 0.83 
                 18.10 
                 1.93 
                 17.23 
                 47.44 
                 1.96 
                 17.57 
                 1.84 
                 2.90 
               
               
                 (Duplicate 
                   
                   
                   
                   
                   
                   
                 17.68 
                 47.34 
                   
                 18.03 
                 1.89 
                 0.37 
               
               
                 Analy.) 
               
               
                 A-2 
                 15 
                 18.32 
                 46.6  
                 0.45 
                 18.40 
                 1.99 
                 16.98 
                 44.83 
                 6.80 
                 18.22 
                 1.92 
                 1.00 
               
               
                 A-5 
                 30 
                 18.53 
                 46.34 
                 0.68 
                 18.66 
                 2.03 
                 16.19 
                 42.66 
                 9.57 
                 17.90 
                 1.92 
                 4.04 
               
               
                 (Duplicate 
                   
                 18.43 
                 46.28 
                   
                 18.56 
                 2.02 
                   
                   
                   
                   
                   
                 3.52 
               
               
                 Analy.) 
               
               
                 A-8 
                 45 
                 19.02 
                 46.02 
                 1.43 
                 19.30 
                 2.09 
                 16.27 
                 42.09 
                 10.78 
                 18.24 
                 1.96 
                 5.49 
               
               
                 (Duplicate 
                   
                   
                   
                   
                   
                   
                 15.87 
                 41.03 
                   
                 17.79 
                 1.96 
                 7.82 
               
               
                 Analy.) 
               
               
                   
               
             
          
         
       
     
     Note: The relative nitrogen loss (percent) is based upon the dry basis percent nitrogen of the portion of the sample aged in the sealed container. 
     The results in Table 2 of the aging test showed significant moisture gains and nitrogen losses for all of the treated samples. Thus, simply reacting the DAP product with high pressure ammonia would not be practical since such treated product tended to lose the added nitrogen and to gain excessive moisture. 
     A particle size analysis for the starting DAP in this experiment was not run, however, since the starting DAP was obtained from a DAP production plant, a “typical” particle size distribution could be inferred. An example of a typical (30 day rolling average) particle size distribution is shown below: 
     
       
         
               
               
               
               
               
               
               
               
             
           
               
                   
               
             
             
               
                 Tyler 
                 4 
                 5 
                 6 
                 8 
                 9 
                 10 
                 14 
               
               
                 Sieve Size 
               
               
                 Cumulative Percent 
                 1.2 
                 4.5 
                 10.7 
                 56.8 
                 77.1 
                 89.4 
                 98.8 
               
               
                 Retained 
               
               
                 Standard Deviation 
                 0.80 
                 1.8 
                 3.7 
                 11.9 
                 10.3 
                 7.2 
                 1.7 
               
               
                   
               
             
          
         
       
     
     Also, it should be noted that this material was product size DAP, not recycle. The recycle consists of undersize material and crushed oversize with typically about 97 percent being smaller than 9 mesh. 
     EXAMPLE B 
     DAP dust, from the dryer in a conventional TVA process, was exposed to a 100 percent ammonia atmosphere at pressures from 15 psia to 90 psia. The DAP dust used in these tests was not mixed with any other DAP material. The size distribution of the DAP dust is shown below: 
     
       
         
               
               
               
               
               
               
             
           
               
                   
               
             
             
               
                 Tyler 
                 24 
                 42 
                 60 
                 100 
                 200 
               
               
                 Sieve Size 
               
               
                 Micron Size 
                 707 
                 354 
                 250 
                 149 
                 74 
               
               
                 Cumulative Percent 
                 1.56 
                 37.31 
                 53.40 
                 60.72 
                 74.96 
               
               
                 Retained 
               
               
                   
               
             
          
         
       
     
     The remaining portion of the dust (25.04 percent) passed through the 200 mesh sieve and was, thus, smaller than 74 microns. Contact times between the dust and the ammonia was 1 hour 40 minutes for test sample number B-1 and was 45 minutes for sample numbers B-2 to B-7. The results of these tests (DAP dust) are set forth in Table 3. The reasoning behind these tests was that the nitrogen enriched dust could be coated with slurry in the granulator and incorporated into the DAP product. The slurry was partially neutralized phosphoric acid, at a temperature of about 240° F., with an N/P mole ratio of about 1.4:1 to 1.6:1 and the following typical analysis: 43.4 percent P 2 O 5 , 13.5 percent N, 13.5 percent H 2 O. The results of these tests showed nitrogen increases of 2.34 to 3.54 percent and nitrogen concentrations in the treated dust of 20.55 to 21.75 percent. 
     
       
         
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
             
             
               
                 Test 
                   
                   
                 Starting 
                 NH 3   
                   
                 Final 
                   
                   
               
               
                 Sample 
                 Starting 
                 Starting 
                 Moisture, 
                 Pressure, 
                 Residence 
                 % 
                 Final 
                 % N 
               
               
                 No. 
                 % P 2 O 5   
                 % N 
                 % 
                 psia 
                 Time, min. 
                 P 2 O 5   
                 % N 
                 Increase 
               
               
                   
               
               
                 B-2 
                 46.20 
                 18.21 
                 1.51 
                 15 
                 45 
                 44.68 
                 20.55 
                 2.34 
               
               
                 B-3 
                 46.20 
                 18.21 
                 1.51 
                 30 
                 45 
                 44.21 
                 21.18 
                 2.97 
               
               
                 B-1 
                 46.20 
                 18.21 
                 1.51 
                 45 
                 100  
                 43.56 
                 21.74 
                 3.53 
               
               
                 B-7 
                 46.20 
                 18.21 
                 1.51 
                 45 
                 45 
                 44.04 
                 20.96 
                 2.75 
               
               
                 B-4 
                 46.20 
                 18.21 
                 1.51 
                 60 
                 45 
                 43.66 
                 21.37 
                 3.16 
               
               
                 B-5 
                 46.20 
                 18.21 
                 1.51 
                 75 
                 45 
                 42.76 
                 21.08 
                 2.87 
               
               
                 B-6 
                 46.20 
                 18.21 
                 1.51 
                 90 
                 45 
                 42.60 
                 21.75 
                 3.54 
               
               
                   
               
             
          
           
               
                   
                   
                   
                   
                   
                   
                   
                   
                 % N 
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 Loss 
               
               
                   
                   
                   
                   
                   
                   
                 Final 
                   
                 Based 
               
               
                 Test 
                 Initial 
                 Initial 
                 Final 
                 Weight 
                 Calculated 
                 Grams 
                 N 
                 On 
               
               
                 Sample 
                 Weight, 
                 Grams 
                 Weight, 
                 Gain, 
                 Grams 
                 N by 
                 Loss, 
                 Weight 
               
               
                 No. 
                 grams 
                 N 
                 grams 
                 grams 
                 N (1)   
                 Analysis 
                 grams 
                 Gain 
               
               
                   
               
               
                 B-2 
                 20.58 
                 3.75 
                 21.42 
                 0.84 
                 4.44 
                 4.40 
                 0.04 
                 4.97 
               
               
                 B-3 
                 20.20 
                 3.68 
                 21.11 
                 0.91 
                 4.43 
                 4.47 
                 −0.04 
               
               
                 B-1 
                 20.01 
                 3.64 
                 20.42 
                 0.41 
                 3.98 
                 4.44 
                 −0.46 
               
               
                 B-7 
                 20.14 
                 3.67 
                 21.17 
                 1.03 
                 4.52 
                 4.44 
                 0.08 
                 7.60 
               
               
                 B-4 
                 20.30 
                 3.70 
                 21.49 
                 1.19 
                 4.68 
                 4.59 
                 0.09 
                 7.56 
               
               
                 B-5 
                 20.05 
                 3.65 
                 21.26 
                 1.21 
                 4.65 
                 4.48 
                 0.17 
                 13.76 
               
               
                 B-6 
                 20.19 
                 3.68 
                 21.52 
                 1.33 
                 4.78 
                 4.68 
                 0.10 
                 7.16 
               
               
                   
               
               
                 Note:  
               
               
                   (1) Initial Grams N plus Weight Gain × 14/17.  
               
             
          
         
       
     
     EXAMPLE C 
     A number of pressure ammoniation tests were run with DAP dust, which was from the dryer in a conventional TVA process, to determine the effect of contact time on nitrogen adsorption. Contact times from 0.25 to 30 minutes were investigated at ammonia pressures from 15 to 45 psia. The DAP dust in these tests were not mixed with any other DAP material. The dust had a particle size of −80 mesh. As with all of the tests in these examples, the air in the reactor was evacuated before pressurizing with ammonia. Moisture analyses were also run on all of the samples prior to the ammonia treatment. The results of this test series (DAP) are set forth in Table 4. 
     
       
         
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
               
                 Test 
                 Contact 
                 NH 3   
                   
                   
                   
                   
                   
                   
               
               
                 Sample 
                 Time, 
                 Pressure, 
                 Initial % 
                 Starting 
                 Starting 
                 Final 
                 Final 
                 % N 
               
               
                 No. 
                 min. 
                 psia 
                 Moisture 
                 % P 2 O 5   
                 % N 
                 % P 2 O 5   
                 % N 
                 Increase 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 C-1  
                 30 
                 45 
                 2.16 
                 45.76 
                 17.07 
                 42.62 
                 21.23 
                 4.16 
               
               
                 C-2  
                 30 
                 30 
                 2.16 
                 45.76 
                 17.07 
                 43.23 
                 20.57 
                 3.50 
               
               
                 C-3  
                 20 
                 45 
                 2.16 
                 45.76 
                 17.07 
                 43.37 
                 20.41 
                 3.34 
               
               
                 C-4  
                 15 
                 45 
                 2.16 
                 45.62 
                 17.07 
                 43.14 
                 20.10 
                 3.04 
               
               
                 C-5  
                 45 
                 45 
                 1.98 (2)   
                 45.54 
                 17.59 
                 43.99 
                 20.54 
                 2.95 
               
               
                 C-6  
                 30 
                 30 
                 1.70 (1)   
                 46.19 
                 18.07 
                 44.08 
                 20.75 
                 2.68 
               
               
                 C-7  
                 20 
                 30 
                 2.16 
                 45.62 
                 16.99 
                 43.67 
                 19.66 
                 2.68 
               
               
                 C-8  
                 10 
                 45 
                 2.16 
                 45.76 
                 17.07 
                 43.64 
                 19.71 
                 2.64 
               
               
                 C-9  
                 20 
                 30 
                 1.70 (1)   
                 46.19 
                 18.07 
                 44.31 
                 20.40 
                 2.33 
               
               
                 C-10 
                 5 
                 45 
                 2.16 
                 45.76 
                 17.07 
                 44.15 
                 19.31 
                 2.24 
               
               
                 C-11 
                 30 
                 15 
                 2.16 
                 45.76 
                 17.07 
                 44.00 
                 19.24 
                 2.17 
               
               
                 C-12 
                 20 
                 15 
                 2.16 
                 45.95 
                 16.98 
                 44.41 
                 19.13 
                 2.15 
               
               
                 C-13 
                 10 
                 30 
                 2.16 
                 45.76 
                 17.07 
                 44.26 
                 19.22 
                 2.15 
               
               
                 C-14 
                 15 
                 15 
                 2.16 
                 45.62 
                 17.07 
                 43.95 
                 19.11 
                 2.05 
               
               
                 C-15 
                 10 
                 30 
                 1.70 (1)   
                 46.19 
                 18.07 
                 44.77 
                 20.08 
                 2.01 
               
               
                 C-16 
                 10 
                 30 
                 2.16 
                 45.62 
                 16.99 
                 44.42 
                 18.91 
                 1.92 
               
               
                 C-17 
                 10 
                 15 
                 2.16 
                 45.95 
                 16.98 
                 44.65 
                 18.64 
                 1.66 
               
               
                 C-18 
                 5 
                 30 
                 2.16 
                 45.62 
                 16.99 
                 44.70 
                 16.58 
                 1.60 
               
               
                 C-19 
                 1 
                 30 
                 2.16 
                 46.33 
                 17.17 
                 45.04 
                 18.75 
                 1.58 
               
               
                 C-20 
                 2 
                 45 
                 2.16 
                 45.76 
                 17.07 
                 44.77 
                 18.63 
                 1.56 
               
               
                 C-21 
                 1 
                 45 
                 2.16 
                 46.26 
                 17.35 
                 44.73 
                 18.89 
                 1.54 
               
               
                 C-22 
                 2 
                 30 
                 2.16 
                 45.26 
                 16.99 
                 44.66 
                 18.51 
                 1.53 
               
               
                 C-23 
                 0.75 
                 30 
                 2.16 
                 46.33 
                 17.17 
                 45.43 
                 18.67 
                 1.50 
               
               
                 C-24 
                 10 
                 15 
                 2.16 
                 45.62 
                 16.99 
                 44.71 
                 18.46 
                 1.48 
               
               
                 C-25 
                 5 
                 30 
                 1.70 (1)   
                 46.19 
                 18.07 
                 45.27 
                 19.48 
                 1.41 
               
               
                 C-26 
                 0.75 
                 45 
                 2.16 
                 46.33 
                 17.17 
                 45.37 
                 18.54 
                 1.37 
               
               
                 C-27 
                 20 
                 30 
                 0.70 
                 45.92 
                 17.98 
                 45.05 
                 19.30 
                 1.32 
               
               
                 C-28 
                 0.25 
                 30 
                 2.16 
                 46.33 
                 17.17 
                 45.55 
                 18.48 
                 1.31 
               
               
                 C-29 
                 1 
                 45 
                 2.16 
                 46.33 
                 17.17 
                 45.40 
                 18.42 
                 1.25 
               
               
                 C-30 
                 0.5 
                 30 
                 2.16 
                 46.33 
                 17.17 
                 45.37 
                 18.39 
                 1.22 
               
               
                 C-31 
                 0.5 
                 45 
                 2.16 
                 46.33 
                 17.17 
                 45.54 
                 18.38 
                 1.21 
               
               
                 C-32 
                 0.25 
                 45 
                 2.16 
                 46.33 
                 17.17 
                 45.74 
                 18.32 
                 1.15 
               
               
                 C-33 
                 1 
                 45 
                 2.16 
                 46.26 
                 17.35 
                 45.88 
                 18.41 
                 1.06 
               
               
                 C-34 
                 20 
                 30 
                 0.78 
                 46.52 
                 18.21 
                 46.01 
                 19.26 
                 1.05 
               
               
                 C-35 
                 5 
                 15 
                 2.16 
                 45.95 
                 16.98 
                 45.27 
                 18.01 
                 1.03 
               
               
                 C-36 
                 30 
                 30 
                 0.73 
                 46.47 
                 18.29 
                 45.77 
                 19.27 
                 0.98 
               
               
                 C-37 
                 20 
                 30 
                 0.87 
                 46.88 
                 18.43 
                 45.93 
                 19.40 
                 0.97 
               
               
                 C-38 
                 15 
                 30 
                 0.70 
                 45.92 
                 17.98 
                 44.74 
                 18.94 
                 0.95 
               
               
                 C-39 
                 2 
                 30 
                 2.16 
                 45.76 
                 17.07 
                 44.98 
                 17.95 
                 0.88 
               
               
                 C-40 
                 15 
                 30 
                 0.78 
                 46.52 
                 18.21 
                 46.11 
                 19.07 
                 0.86 
               
               
                 C-41 
                 10 
                 30 
                 0.78 
                 46.52 
                 18.21 
                 45.97 
                 19.00 
                 0.79 
               
               
                 C-42 
                 20 
                 30 
                 0.70 
                 46.01 
                 18.04 
                 45.15 
                 18.76 
                 0.73 
               
               
                 C-43 
                 10 
                 30 
                 0.73 
                 46.47 
                 18.29 
                 46.08 
                 19.00 
                 0.72 
               
               
                 C-44 
                 15 
                 30 
                 0.87 
                 46.88 
                 18.43 
                 45.82 
                 19.14 
                 0.71 
               
               
                 C-45 
                 20 
                 30 
                 0.73 
                 46.47 
                 18.29 
                 45.85 
                 19.98 
                 0.69 
               
               
                 C-46 
                 15 
                 30 
                 0.70 
                 46.01 
                 18.04 
                 45.43 
                 18.72 
                 0.68 
               
               
                 C-47 
                 5 
                 30 
                 0.78 
                 46.52 
                 18.21 
                 46.40 
                 18.85 
                 0.64 
               
               
                 C-48 
                 2 
                 15 
                 2.16 
                 45.95 
                 16.98 
                 45.63 
                 17.62 
                 0.64 
               
               
                 C-49 
                 5 
                 30 
                 0.73 
                 46.47 
                 18.29 
                 46.23 
                 18.92 
                 0.64 
               
               
                 C-50 
                 10 
                 30 
                 0.87 
                 46.88 
                 18.43 
                 46.16 
                 19.06 
                 0.63 
               
               
                 C-51 
                 10 
                 30 
                 0.70 
                 46.01 
                 18.04 
                 45.66 
                 18.63 
                 0.59 
               
               
                 C-52 
                 0.75 
                 15 
                 2.16 
                 46.33 
                 17.17 
                 45.25 
                 17.76 
                 0.59 
               
               
                 C-53 
                 5 
                 30 
                 0.87 
                 46.88 
                 18.43 
                 46.58 
                 19.01 
                 0.58 
               
               
                 C-54 
                 0.25 
                 15 
                 2.16 
                 46.33 
                 17.17 
                 45.40 
                 17.74 
                 0.57 
               
               
                 C-55 
                 5 
                 30 
                 0.70 
                 46.01 
                 18.04 
                 45.91 
                 18.60 
                 0.57 
               
               
                 C-56 
                 0.5 
                 15 
                 2.16 
                 46.33 
                 17.17 
                 45.44 
                 17.66 
                 0.49 
               
               
                 C-57 
                 1 
                 15 
                 2.16 
                 46.33 
                 17.17 
                 45.27 
                 17.63 
                 0.46 
               
               
                   
               
             
          
         
       
     
     Notes: 
     (1) Sample Nos. C-6, C-9, C-15 and C-25 each had sufficient water added to reach the initial percent moisture indicated. 
     (2) Sample No. C-5 was a mixture of dust samples and was humidified to reach the initial percent moisture indicated. 
     The results from these tests indicate that nitrogen adsorption is a function of ammonia pressure, contact time and initial moisture. [This conclusion was based upon statistical analysis which provided a regression equation that the percent nitrogen increase for the DAP was a function of the (absolute) ammonia pressure, the ammonia contact time and the initial dust moisture.] 
     EXAMPLE D 
     This example illustrated the results of pressure ammoniation tests run with DAP recycle material from a conventional TVA process. The DAP recycle material comprises a combination of dust, undersize particles (−9 mesh) and crushed oversize particles. Where samples of actual recycle going to the granulator could not be collected, separate samples (D-I and D-II) of the three-size fractions were collected and blended. The blending ratio in these samples (D-I and D-II) was one part of dust, three parts of crushed oversize particles and parts of undersize particles. For sample D-III, the actual recycle going to the granulator was used. However, for all experiments, the actual recycle or simulated recycle was screened on a 9 mesh screen; and any oversize particles which did not pass through the screen were ground (to pass the 9 mesh screen) and combined with the original sample. The recycle screen analysis for samples D-I, D-II and D-III are set forth in Table 5. 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 5 
               
               
                   
               
               
                 Sieve 
                   
                 D-I 
                 D-II 
                 D-III 
               
               
                 (Tyler) 
                 Micron 
                 % Retained 
                 % Retained 
                 % Retained 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                  7 
                 2830  
                 0 
                 0 
                 0 
               
               
                  9 
                 2000  
                 2.43 
                 2.13 
                 1.58 
               
               
                 12 
                 1410  
                 31.20 
                 27.32 
                 20.30 
               
               
                 16 
                 1000  
                 13.30 
                 11.65 
                 8.65 
               
               
                 24 
                 707 
                 21.50 
                 18.83 
                 13.99 
               
               
                 35 
                 420 
                 11.00 
                 9.63 
                 7.16 
               
               
                 48 
                 297 
                 4.90 
                 4.29 
                 3.19 
               
               
                 60 
                 250 
                 3.00 
                 2.63 
                 1.95 
               
               
                 80 
                 177 
                 0.10 
                 0.09 
                 0.07 
               
               
                 100  
                 149 
                 1.80 
                 1.58 
                 1.17 
               
               
                 170  
                  88 
                 6.00 
                 5.25 
                 3.90 
               
               
                 250  
                  63 
                 2.36 
                 2.07 
                 1.54 
               
               
                 325  
                  44 
                 1.60 
                 1.40 
                 1.04 
               
               
                 Pan 
                 −44 
                 1.00 1   
                 0.88 1   
                 0.65 1   
               
               
                   
               
             
          
         
       
     
     Note: 1. Percent passing through 325 mesh sieve. 
     Samples D-I, D-II and D-III were subject to ammonia pressures from 30 psia to 85 psia for a time period of 5 minutes to 90 minutes. The results of the recycle ammoniation tests are set forth in Table 6. 
     
       
         
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 6 
               
               
                   
               
               
                 Test 
                 Initial 
                   
                 Initial 
                 Contact 
                 Ammonia 
                 Final 
                   
                   
                   
               
               
                 Sample 
                 % 
                 Initial 
                 % 
                 Time, 
                 Pressure, 
                 % 
                 Final 
                 Ammonia 
                 % N 
               
               
                 No. 
                 P 2 O 5   
                 % N 
                 Moisture 
                 min. 
                 psia 
                 P 2 O 5   
                 % N 
                 Circulation 
                 Increase 
               
               
                   
               
             
             
               
                 D-I 
                 45.46 
                 17.87 
                 1.67 
                  5 
                 30 
                 45.38 
                 18.27 
                 No 
                 0.41 
               
               
                 D-I 
                 45.46 
                 17.87 
                 1.67 
                 10 
                 30 
                 45.24 
                 18.43 
                 No 
                 0.57 
               
               
                 D-I 
                 45.46 
                 17.87 
                 1.67 
                 15 
                 30 
                 45.28 
                 18.59 
                 No 
                 0.73 
               
               
                 D-I 
                 45.46 
                 17.87 
                 1.67 
                 20 
                 30 
                 45.00 
                 18.57 
                 No 
                 0.71 
               
               
                 D-I 
                 45.40 
                 17.83 
                 1.67 
                 10 
                 45 
                 45.04 
                 18.97 
                 No 
                 1.14 
               
               
                 D-I 
                 45.40 
                 17.83 
                 1.67 
                 15 
                 45 
                 45.07 
                 18.82 
                 No 
                 0.99 
               
               
                 D-I 
                 45.40 
                 17.83 
                 1.67 
                 20 
                 45 
                 44.76 
                 18.64 
                 No 
                 0.81 
               
               
                 D-I 
                 45.40 
                 17.83 
                 1.67 
                 30 
                 45 
                 44.20 
                 19.37 
                 No 
                 1.54 
               
               
                 D-I 
                 45.92 
                 18.03 
                 1.73 
                 45 
                 75 
                 45.13 
                 19.38 
                 ? 
                 1.35 
               
               
                 D-I 
                 45.92 
                 18.03 
                 1.73 
                 45 
                 75 
                 44.85 
                 19.93 
                 Partial 
                 1.90 
               
               
                 D-I 
                 45.92 
                 18.03 
                 1.73 
                 45 
                 60 
                 44.83 
                 19.91 
                 No 
                 1.88 
               
               
                 D-I 
                 46.01 
                 17.98 
                 1.73 
                 45 
                 60 
                 44.84 
                 20.36 
                 Yes 
                 2.38 
               
               
                 D-I 
                 45.62 
                 17.47 
                 1.94 
                 45 
                 60 
                 44.26 
                 20.29 
                 Yes 
                 2.82 
               
               
                 D-II 
                 45.62 
                 17.47 
                 1.94 
                 90 
                 60 
                 43.32 
                 20.78 
                 Yes 
                 3.31 
               
               
                 D-II 
                 45.62 
                 17.47 
                 1.94 
                 90 
                 75 
                 43.86 
                 20.55 
                 No 
                 3.08 
               
               
                 D-II 
                 45.62 
                 17.47 
                 1.94 
                 45 
                 75 
                 43.87 
                 20.41 
                 No 
                 2.94 
               
               
                 D-III 
                 46.22 
                 17.62 
                 2.13 
                 60 
                 75 
                 44.24 
                 20.48 
                 No 
                 2.86 
               
               
                 D-III 
                 46.22 
                 17.62 
                 2.13 
                 60 
                 60 
                 44.47 
                 20.47 
                 No 
                 2.85 
               
               
                 D-III 
                 46.22 
                 17.62 
                 2.13 
                 30 
                 75 
                 44.58 
                 20.10 
                 No 
                 2.48 
               
               
                 D-III 
                 46.22 
                 17.62 
                 2.13 
                 30 
                 60 
                 44.98 
                 19.78 
                 Yes 
                 2.16 
               
               
                 D-III 
                 46.22 
                 17.62 
                 2.13 
                 90 
                 45 
                 44.40 
                 20.65 
                 Yes 
                 3.03 
               
               
                 D-III 
                 46.22 
                 17.62 
                 2.13 
                 60 
                 45 
                 44.53 
                 20.40 
                 Yes 
                 2.78 
               
               
                 D-III 
                 46.22 
                 17.62 
                 2.13 
                 45 
                 45 
                 44.87 
                 19.87 
                 Yes 
                 2.25 
               
               
                 D-III 
                 46.22 
                 17.62 
                 2.13 
                 30 
                 45 
                 44.93 
                 20.02 
                 Yes 
                 2.40 
               
               
                 D-III 
                 46.22 
                 17.62 
                 2.13 
                 60 
                 75 
                 44.61 
                 20.33 
                 No 
                 2.71 
               
               
                   
               
             
          
         
       
     
     Using the results of the recycle ammoniation tests, a linear regression equation can be developed to predict the percent ammoniacal nitrogen increase as a function of the (absolute) ammonia pressure, the contact time and the starting recycle moisture. The predictions of the linear regression equation can then be incorporated into a mathematical mass balance model of the reactor and granulator portions of a conventional TVA DAP plant to calculate the conditions necessary to produce 1846-0 DAP using the starting recycle ammoniacal nitrogen and P 2 O 5  concentrations. 
     [The mass balance model is designed to calculate equilibrium conditions (mainly product weight, product P 2 O 5  concentration and product ammoniacal nitrogen concentration) in a DAP plant when a change is made in one or more of the process variables (i.e., starting conditions) and consists of a series of mathematical equations in a Microsoft® Excel® spreadsheet. The starting conditions are entered by the user in a group of cells at the top of the spreadsheet. These include initial recycle weight, the percent recycle ammoniated (in the pressure reactor), the recycle to product ratio, the slurry mole ratio, the granulator/slurry mole ratio (i.e., the moles of ammoniacal nitrogen fed to the reactor plus the moles of ammoniacal nitrogen fed to the granulator divided by the moles of phosphorus in the phosphoric acid), the ammonia pressure in the pressure reactor, the residence (contact) time of the pressure reactor, the pressure reactor efficiency (normally 100 percent), the percent moisture in the product leaving the dryer, the regression equation coefficients for the pressure reactor (i.e., contact time, ammonia pressure and moisture) and the phosphoric acid feed rate (weight/unit time) and P 2 O 5  concentration fed to the plant. Below the starting conditions are a series of rows where masses (weights) and concentrations are calculated for various parts of the plant. Each row terminates with values for the product weight, the P 2 O 5  concentration of the DAP product and the nitrogen concentration of the product. The first row uses only the starting conditions for the product calculations. The second row then uses the values calculated in the first row to calculate a new value for the product weight, the P 2 O 5  concentration of the DAP product and the nitrogen concentration of the product. The third row uses the values from the second row and so on down the spreadsheet. Each row represents one pass of the recycle material through the plant and can be related to the time required for the recycle to go through the plant (i.e., the recycle residence time). Eventually (typically between rows 20 to 30), the calculated values for the product become essentially constant, indicating that the plant has reached equilibrium. If the product composition is acceptable at this point, the model run is finished. Otherwise one or more of the starting conditions can be adjusted and the model run again. Thus, the model can be used to predict the effect of treating a portion of the recycle with high pressure ammonia.] 
     Treating DAP recycle with high pressure ammonia is a practical method of producing DAP without the use of nitrogen supplements. 
     The results from Table 6 indicate that, in general, the recycle DAP did not absorb as much ammonia as did dust at similar conditions of ammonia pressure, contact time and initial moisture. FIG. 2 shows a comparison of the nitrogen adsorption for the DAP recycle and the DAP dust (Example C). 
     An attempt was also made to determine the effect of circulating the ammonia during the test. In this case, due to equipment limitations, the results were inconclusive. Since the initial moisture appeared to have a strong effect on the quantity of nitrogen adsorbed, several tests were run at the end of this series in which additional moisture was added to starting recycle. These tests showed fairly high increases in the nitrogen concentration at contact times of 5 to 7 minutes, with the temperatures inside of the reactor in the range of 217° to 218° F. Since condensate was also observed in the vacuum line used to evacuate the ammonia from the reactor after the test, this suggests that some of the added water was vaporized during the reaction and did not remain with the DAP recycle. Unfortunately, since the available moisture determination methods cannot distinguish between moisture loss and ammonia loss, accurate moisture analyses of the ammoniated recycle samples could not be obtained. 
     EXAMPLE E 
     To determine how the ammonia-fortified DAP recycle behaves when incorporated into granular DAP product, a series of small scale batch granulation tests were conducted. Since it was impractical to spray preneutralizer slurry onto the recycle granular DAP in the ammoniator granulator, as would be done in the conventional TVA process, preneutralizer slurry obtained from a commercial scale DAP plant using the conventional TVA process was blended with granular DAP recycle in a dough mixed and then rapidly transferred to a bench scale ammoniator granulator. The bench scale ammoniator granulator had a cylinder (14 inches diameter×8 inches long) mounted on its side and attached to a motor with a chain drive such that it could be rotated. A variable speed motor was provided to adjust the rotation speed. A removable hatch was provided on the circumference of the cylinder through which material could be added or removed. A pipe (the ammonia sparger) entered the drum at one end through a seal and was routed to and across the bottom of the cylinder (offset ˜15° in the direction of rotation). The pipe was fixed in the cylinder and did not rotate with the cylinder. The portion of the pipe extending across the bottom of the cylinder was perforated to provide even distribution of the ammonia. The opposite end of the drum contained two ports. One port was used for a thermocouple and the other port was used as an exhaust port. In these tests weighted portions of DAP recycle and hot (˜240° F.) partially ammoniated phosphoric acid slurry were blended in the dough mixer and then placed in the rotating drum where ammonia was sparged into the blend. After removal from the drum (granulator) the product was dried in a laboratory oven at 225° F. for (typically) 30 minutes. To provide a basis for comparison, some of the tests were run with normal (untreated) DAP recycle, while other tests were run with ammonia-fortified DAP recycle. 
     Tests E-3, E-4, E-8 and E-9 were run with untreated, normal, (plant) DAP recycle as controls and to provide a basis for comparison with granulation tests conducted with ammonia-treated DAP recycle. Tests E-5, E-6 and E-7 were conducted with DAP recycle which had been treated with 60 psia ammonia for 45 minutes (using the pressure ammoniation procedure described above). Test E-10 was conducted with DAP recycle which had been treated with 60 psia ammonia for 90 minutes (using the pressure ammoniation procedure described above). Test E-11 was conducted with DAP recycle (using the pressure ammoniation procedure described above) that had been treated with 75 psia ammonia for 30 minutes. The results of granulation tests E-3 to E-1 1 are set forth in Table 7. 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 7 
               
               
                   
               
             
             
               
                 Test 
                 E-3 
                 E-4 
                 E-5 
                 E-6 
                 E-7 
               
               
                 Recycle Type 
                 Plant 
                 Plant 
                 Treated 
                 Treated 
                 Treated 
               
               
                   
               
               
                 Recycle Analysis 
               
               
                 % P 2 O 5   
                 46.28 
                 45.63 
                 45.13 
                 45.13 
                 44.85 
               
               
                 % N 
                 18.02 
                 18.02 
                 19.38 
                 19.38 
                 19.93 
               
               
                 % H 2 O 
                 2.12 
                 2.22 
                 1.44 
                 .44 
                 1.44 
               
               
                 Slurry Analysis 
               
               
                 % P 2 O 5   
                 42.36 
                 43.70 
                 43.53 
                 43.53 
                 43.93 
               
               
                 % N 
                 12.99 
                 13.28 
                 13.29 
                 13.27 
                 13.24 
               
               
                 % H 2 O 
                 13.24 
                 10.38 
                 11.70 
                 11.70 
                 11.54 
               
               
                 Dried Product Analysis 
               
               
                 % P 2 O 5   
                 46.98 
                 46.89 
                 47.48 
                 46.02 
                 45.13 
               
               
                 % N 
                 18.41 
                 17.86 
                 18.48 
                 18.61 
                 18.40 
               
               
                 % H 2 O 
                 0.39 
                 0.75 
                 0.23 (1)   
                 1.80 
                 2.90 
               
               
                 Overall Mass Balance, 
               
               
                 % 
               
               
                 P 2 O 5   
                 102.89 
                 N/A 
                 101.77 
                 99.44 
                 100.08 
               
               
                 N 
                 97.50 
                 N/A 
                 96.75 
                 103.23 
                 98.60 
               
               
                 % N Loss-Granulator 
                 1.44 
                 N/A 
                 −2.27 
                 −3.04 
                 0.36 
               
               
                 % N Loss Dryer 
                 1.07 
                 2.97 
                 5.40 
                 −0.18 
                 1.04 
               
               
                   
               
             
          
           
               
                 Test 
                 E-8 
                 E-9 
                 E-10 
                 E-11 
               
               
                 Recycle Type 
                 Plant 
                 Plant 
                 Treated 
                 Treated 
               
               
                   
               
               
                 Recycle Analysis 
               
               
                 % P 2 O 5   
                 45.62 
                 45.53 
                 43.32 
                 45.11 
               
               
                 % N 
                 17.47 
                 17.27 
                 20.78 
                 20.06 
               
               
                 % H 2 O 
                 1.29 
                 1.48 
                 1.94 
                 2.59 
               
               
                 Slurry Analysis 
                   
                 
                   (2) 
                 
                   
                 
                   (4) 
                 
               
               
                 % P 2 O 5   
                 44.38 
                 50.61 
                 45.13 
                 49.49 
               
               
                 % N 
                 14.08 
                 7.31 
                 14.08 
                 11.94 
               
               
                 % H 2 O 
                 7.04 
                 N/A 
                 8.43 
                 0.99 
               
               
                 Dried Product Analysis 
                   
                   
                 
                   (3) 
                 
               
               
                 % P 2 O 5   
                 45.74 
                 47.04 
                 46.79 
                 47.27 
               
               
                 % N 
                 17.71 
                 17.81 
                 17.33 
                 19.17 
               
               
                 % H 2 O 
                 1.05 
                 1.16 
                 2.46 
                 0.99 
               
               
                 Overall Mass Balance, % 
               
               
                 P 2 O 5   
                 100.98 
                 107.48 
                 101.73 
                 101.12 
               
               
                 N 
                 98.12 
                 94.84 
                 96.13 
                 99.76 
               
               
                 % N Loss-Granulator 
                 1.60 
                 6.57 
                 2.69 
                 −0.11 
               
               
                 % N Loss Dryer 
                 0.29 
                 −1.51 
                 1.21 
                 0.35 
               
               
                   
               
             
          
         
       
     
     Notes: 
     (1) Dried 2 hours at 232° F. 
     (2) Slurry augmented with 54 percent phosphoric acid. 
     (3) Ammonia supply to granulator exhausted before required quantity added. 
     (4) Laboratory produced slurry using clarified phosphoric acid. 
     EXAMPLE F 
     Product size (−4, +14 mesh) DAP samples from three of the granulation tests of Example E, were subjected to a six-week aging test. Two of the granulation samples, i.e., E-5 and E-7 N-fortified recycle, were made with ammonia-fortified ammonium phosphate recycle. The third granulation sample, i.e., E-8 plant recycle, was made from the unfortified plant DAP recycle. The aging test involved placing a known weight of each sample in a pan and placing the pans in a non-climate controlled area (i.e., covered to exclude rain, but otherwise subject to normal outside variations of temperature and humidity). The sample weights were then determined periodically and samples collected for analysis after 2 weeks, 4 weeks and 6 weeks. A portion of each sample was also aged in a closed container and sampled at the same time as the pan samples for comparison. All three samples (open pans) tended to gain and lose weight as a function of prevailing weather conditions (i.e., they gained weight after heavy rains and lost weight during dry periods). However, test sample number F-5 showed the greatest weight variation. FIG. 3 shows the weight changes for the three samples. Both of the samples in the closed containers and the samples in the open pans lost ammonia during the six weeks. No pattern to the ammonia losses, however, was observed. At the end of the tests, the greatest ammonia loss was from the open pan containing one of the samples made with the ammonia fortified recycle material. However, the open pan containing the other sample made with ammonia fortified recycle had the lowest ammonia loss of the exposed samples. The open pan containing the sample made with plant recycle showed an ammonia loss between the other two test samples. Thus, the DAP made with ammonia fortified recycle did not show any significant difference in aging behavior from the DAP made with normal recycle. Table 8 shows the ammonia analyses (expressed as dry basis to account for changes in moisture) from the aging test. The results indicate that treating DAP recycle with high pressure ammonia is a practical method of producing DAP having an enhanced ammoniacal nitrogen concentration. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 8 
               
               
                   
                   
               
               
                   
                 Granulation Test 
                 Granulation Test 
                   
               
               
                   
                 Sample F-5 
                 Sample F-7 
                 Granulation Test F-8 
               
               
                   
                 N Fortified Recycle 
                 N Fortified Recycle 
                 Plant Recycle 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Initial % N 
                 18.85 
                 18.92 
                 17.90 
               
               
                 2 Weeks - Aging 
               
               
                 % N Sealed Sample 
                 18.61 
                 18.67 
                 17.34 
               
               
                 % N Pile Sample 
                 18.56 
                 18.36 
                 17.62 
               
               
                 % N Loss Sealed Sample 
                 0.24 
                 0.25 
                 0.56 
               
               
                 % N Loss Pile Sample 
                 0.29 
                 0.56 
                 0.28 
               
               
                 4 Weeks - Aging 
               
               
                 % N Sealed Sample 
                 18.43 
                 18.79 
                 17.64 
               
               
                 % N Pile Sample 
                 18.46 
                 18.72 
                 17.79 
               
               
                 % N Loss Sealed Sample 
                 0.42 
                 0.13 
                 0.26 
               
               
                 % N Loss Pile Sample 
                 0.39 
                 0.20 
                 0.11 
               
               
                 6 Weeks - Aging 
               
               
                 % N Sealed Sample 
                 18.41 
                 18.52 
                 17.21 
               
               
                 % N Pile Sample 
                 18.10 
                 18.45 
                 17.27 
               
               
                 % N Loss Sealed Sample 
                 0.44 
                 0.40 
                 0.69 
               
               
                 % N Loss Pile Sample 
                 0.75 
                 0.47 
                 0.63 
               
               
                   
               
             
          
         
       
     
     EXAMPLE G 
     The effect of particle size on ammonia adsorption into DAP recycle was determined by separating samples of DAP into four discrete size fractions, that is, −10, +20 mesh, −20, +48 mesh, −48, +80 mesh and −80 mesh. Each size fraction of each test sample was then treated with ammonia at elevated pressure (using the pressure ammoniation procedure described above). The weighted quantity of recycle was placed in a pressure vessel and sealed. A vacuum of 24 to 25 inches mercury was then applied to the vessel to remove the air. Gaseous ammonia was added to the vessel until the desired pressure was obtained. The recycle was kept in the vessel for the required time with additional ammonia added as needed to maintain the desired pressure. After the set time, a vacuum of 24 to 25 inches mercury was again applied to the vessel to remove any unreacted ammonia. Air was bled into the reactor. Once again, a vacuum was applied to remove any residual trace of ammonia. Air was then bled into the vessel. The vessel was opened and the recycle is removed and weighed. 
     In this experiment, all of the samples were collected from operating (commercial scale) DAP plants. The sample labeled “DAP1 Recycle Batch 2” was collected from a chute feeding the bottom of the recycle elevator (that feeds the ammoniator-granulator) at a first DAP plant and contains undersize material and crushed oversize material from the plant screening circuit (at whatever proportions they happened to be running in the plant that day). The sample labeled “DAP1 Recycle” was collected at the same location (as the “DAP1 Recycle Batch 2” sample). The sample labeled “DAP 2W Recycle” was collected from a chute feeding the bottom of the recycle elevator on the west side of a second DAP plant (this plant has two mirror image DAP trains; East and West) and contains a similar mixture of undersize and crushed oversize material from the plant screening circuit. The sample labeled “DAP1 Gran Feed (Recycle)” was collected from the chute at the top of the recycle elevator that goes directly to the ammoniator-granulator in the first DAP plant and contains the same mixture of undersize and crushed oversize. The screen size distributions of the various samples when they were collected are shown below: 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
               
               
                 Screen 
                 DAP1 Recycle 
                 DAP1 
                 DAP2W 
                 DAP1 Gran 
               
               
                 Size 
                 Batch 2 
                 Recycle 
                 Recycle 
                 Feed (Recycle) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 −10, +20 
                 61.38% 
                 65.36% 
                 91.46% 
                 66.31% 
               
               
                 −20, +48 
                 27.70% 
                 24.02% 
                 7.87% 
                 19.08% 
               
               
                 −48, +80 
                 5.48% 
                 7.17% 
                 0.32% 
                 6.46% 
               
               
                 −80 
                 5.44% 
                 3.44% 
                 0.35% 
                 8.15% 
               
               
                   
               
             
          
         
       
     
     The results from this experiment are set forth in Table 9. As seen from the data, the largest size fraction (−10, +20 mesh) shows a significantly lower nitrogen increase than the other size particles. For −20 mesh size fractions and small size fractions, the percent nitrogen increase generally increased with decreasing particle size. In these samples, the moisture concentrations of the samples were similar and the ammonia pressures were not vastly different. Therefore, the only statistically significant variables were particle size and contact time. FIG. 4 shows a plot of the percent nitrogen increase as a function of particle size for a contact time of ten minutes. 
     
       
         
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 9 
               
               
                   
               
               
                   
                   
                 Average 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                   
                 Sieve Size 
                 Particle 
                 NH 3   
                 Contact 
               
               
                   
                 (U.S. Std. 
                 Size 
                 Pressure 
                 Time 
                 Initial 
                 Initial 
                 Initial 
                 Final 
                 Final 
                 % N 
               
               
                 Initial Sample Source 
                 Mesh) 
                 (microns) 
                 (PSIA) 
                 (min.) 
                 % P 2 O 5   
                 % N 
                 % H 2 O 
                 % P 2 O 5   
                 % N 
                 Increase 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 DAP1 Recycle Batch 2 
                 −10:+20 
                 1420.5 
                 60 
                 10 
                 46.06 
                 17.32 
                 1.65 
                 45.75 
                 17.97 
                 0.65 
               
               
                 DAP1 Recycle Batch 2 
                 −20:+48 
                 569 
                 60 
                 10 
                 45.70 
                 17.47 
                 2.22 
                 43.96 
                 20.37 
                 2.90 
               
               
                 DAP1 Recycle Batch 2 
                 −48:+80 
                 237 
                 60 
                 10 
                 45.72 
                 17.43 
                 2.40 
                 43.70 
                 20.76 
                 3.33 
               
               
                 DAP1 Recycle Batch 2 
                 −80 
                 88.5 
                 60 
                 10 
                 46.09 
                 17.39 
                 2.21 
                 43.75 
                 20.60 
                 3.22 
               
               
                 DAP1 Recycle Batch 2 
                 −10:+20 
                 1420.5 
                 60 
                  5 
                 46.05 
                 17.36 
                 1.65 
                 45.80 
                 17.56 
                 0.20 
               
               
                 DAP1 Recycle Batch 2 
                 −20:+48 
                 569 
                 60 
                  5 
                 46.07 
                 17.40 
                 2.22 
                 45.23 
                 18.36 
                 0.96 
               
               
                 DAP1 Recycle Batch 2 
                 −48:+80 
                 237 
                 60 
                  5 
                 45.70 
                 17.36 
                 2.40 
                 44.22 
                 19.80 
                 2.44 
               
               
                 DAP1 Recycle Batch 2 
                 −80 
                 88.5 
                 60 
                  5 
                 45.82 
                 17.30 
                 2.21 
                 44.12 
                 19.95 
                 2.65 
               
               
                 DAP1 Recycle Batch 2 
                 −10:+20 
                 1420.5 
                 60 
                 20 
                 46.61 
                 17.25 
                 1.65 
                 45.94 
                 18.13 
                 0.88 
               
               
                 DAP1 Recycle Batch 2 
                 −20:+48 
                 569 
                 60 
                 20 
                 46.37 
                 17.41 
                 2.22 
                 43.92 
                 21.07 
                 3.66 
               
               
                 DAP1 Recycle Batch 2 
                 −48:+80 
                 237 
                 60 
                 20 
                 46.27 
                 17.41 
                 2.40 
                 43.08 
                 21.93 
                 4.52 
               
               
                 DAP1 Recycle Batch 2 
                 −80 
                 88.5 
                 60 
                 20 
                 46.53 
                 17.47 
                 2.21 
                 43.88 
                 21.13 
                 3.66 
               
               
                 DAP1 Recycle 
                 −10:+20 
                 1420.5 
                 60 
                 10 
                 46.95 
                 17.25 
                 1.97 
                 46.70 
                 17.49 
                 0.24 
               
               
                 DAP1 Recycle 
                 −20:+48 
                 569 
                 60 
                 10 
                 46.62 
                 17.25 
                 2.16 
                 45.83 
                 18.57 
                 1.32 
               
               
                 DAP1 Recycle 
                 −48:+80 
                 237 
                 60 
                 10 
                 46.94 
                 17.23 
                 2.25 
                 44.18 
                 20.62 
                 3.39 
               
               
                 DAP1 Recycle 
                 −80 
                 88.5 
                 60 
                 10 
                 47.09 
                 17.30 
                 2.12 
                 44.52 
                 20.56 
                 3.26 
               
               
                 DAP1 Recycle 
                 −10:+20 
                 1420.5 
                 60 
                 20 
                 46.95 
                 17.25 
                 1.97 
                 46.19 
                 18.07 
                 0.82 
               
               
                 DAP1 Recycle 
                 −20:+48 
                 569 
                 60 
                 20 
                 46.62 
                 17.25 
                 2.16 
                 44.07 
                 20.75 
                 3.50 
               
               
                 DAP1 Recycle 
                 −48:+80 
                 237 
                 60 
                 20 
                 46.94 
                 17.23 
                 2.25 
                 43.06 
                 22.27 
                 5.04 
               
               
                 DAP1 Recycle 
                 −80 
                 88.5 
                 60 
                 20 
                 47.09 
                 17.30 
                 2.12 
                 43.94 
                 21.12 
                 3.82 
               
               
                 DAP 2W Recycle 
                 −10:+20 
                 1420.5 
                 60 
                 10 
                 46.30 
                 17.69 
                 2.27 
                 45.86 
                 18.22 
                 0.53 
               
               
                 DAP 2W Recycle 
                 −20:+48 
                 569 
                 60 
                 10 
                 46.38 
                 17.60 
                 2.54 
                 44.76 
                 19.52 
                 1.92 
               
               
                 DAP 2W Recycle 
                 −48:+80 
                 237 
                 60 
                 10 
                 46.00 
                 17.68 
                 2.64 
                 44.16 
                 20.89 
                 3.21 
               
               
                 DAP 2W Recycle 
                 −80 
                 88.5 
                 60 
                 10 
                 46.34 
                 17.61 
                 2.64 
                 43.88 
                 20.79 
                 3.18 
               
               
                 DAP 2W Recycle 
                 −10:+20 
                 1420.5 
                 60 
                 20 
                 46.30 
                 17.69 
                 2.27 
                 45.15 
                 18.89 
                 1.20 
               
               
                 DAP 2W Recycle 
                 −20:+48 
                 569 
                 60 
                 20 
                 46.38 
                 17.60 
                 2.54 
                 43.64 
                 21.30 
                 3.70 
               
               
                 DAP 2W Recycle 
                 −48:+80 
                 237 
                 60 
                 20 
                 43.21 
                 17.68 
                 2.64 
                 46.00 
                 21.92 
                 4.24 
               
               
                 DAP 2W Recycle 
                 −80 
                 88.5 
                 60 
                 20 
                 43.51 
                 17.61 
                 2.64 
                 46.34 
                 21.23 
                 3.62 
               
               
                 DAP1 Gran Feed (Recycle) 
                 −10:+20 
                 1420.5 
                 85 
                  5 
                 46.8 
                 17.59 
                 2.19 
                 45.88 
                 17.93 
                 0.34 
               
               
                 DAP1 Gran Feed (Recycle) 
                 −20:+48 
                 569 
                 85 
                  5 
                 45.99 
                 17.68 
                 2.31 
                 45.04 
                 19.01 
                 1.33 
               
               
                 DAP1 Gran Feed (Recycle) 
                 −48:+80 
                 237 
                 85 
                  5 
                 46.14 
                 17.63 
                 2.41 
                 44.09 
                 20.13 
                 2.50 
               
               
                 DAP1 Gran Feed (Recycle) 
                 −80 
                 88.5 
                 85 
                  5 
                 47.01 
                 17.66 
                 2.17 
                 44.47 
                 20.34 
                 2.68 
               
               
                 DAP1 Gran Feed (Recycle) 
                 −10:+20 
                 1420.5 
                 85 
                 10 
                 46.8 
                 17.59 
                 2.19 
                 45.38 
                 18.23 
                 0.64 
               
               
                 DAP1 Gran Feed (Recycle) 
                 −20:+48 
                 569 
                 85 
                 10 
                 45.99 
                 17.68 
                 2.31 
                 44.22 
                 20.02 
                 2.34 
               
               
                 DAP1 Gran Feed (Recycle) 
                 −48:+80 
                 237 
                 85 
                 10 
                 46.14 
                 17.63 
                 2.41 
                 43.82 
                 20.90 
                 3.27 
               
               
                 DAP1 Gran Feed (Recycle) 
                 −80 
                 88.5 
                 85 
                 10 
                 47.01 
                 17.66 
                 2.17 
                 43.99 
                 20.79 
                 3.13 
               
               
                   
               
             
          
         
       
     
     Under a given set of ammonia pressure, contact time and moisture conditions, smaller DAP particles adsorb significantly more ammonia than larger particles. However, due the limited quantity of smaller DAP particles normally present in the DAP recycle, this effect may be of minimal practical use. 
     EXAMPLE H 
     The effect of temperature on ammonia adsorption was determined by heating samples of DAP recycle, placing them in a preheated reactor and then treating the samples with ammonia at elevated pressures. These results were then compared with samples of DAP recycle at room temperature that were treated with pressurized ammonia in the same manner (with the reactor at room temperature). The results of these tests are set forth in Table 10. 
     
       
         
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 10 
               
             
             
               
                   
                   
               
               
                   
                 Initial Recycle Analysis 
                 Ammoniation Conditions 
                   
               
             
          
           
               
                   
                 Average 
                 NH 3   
                 Contact 
                 Initial 
                 Average 
                 Product Recycle Analysis 
               
             
          
           
               
                   
                   
                   
                   
                 Size 
                 Pressure 
                 Time 
                 Recycle 
                 Reaction 
                   
                   
                 % N 
               
               
                 TEST 
                 % P 2 O 5   
                 % N (1)   
                 % H 2 O 
                 (microns 
                 (psia) 
                 (min) 
                 Temp. ° F. 
                 Temp. ° F. 
                 % P 2 O 5   
                 % N (1)   
                 Increase 
               
               
                   
               
             
          
           
               
                  1 
                 45.63 
                 17.45 
                 1.82 
                 1100 
                 85 
                 10 
                 68.4 
                 118.9 
                 44.20 
                 19.56 
                 2.12 
               
               
                  2 
                 46.26 
                 17.71 
                 1.22 
                 1098 
                 85 
                 10 
                 166.0 
                 169.0 
                 45.30 
                 19.04 
                 1.34 
               
               
                  3 
                 46.06 
                 17.75 
                 0.82 
                 1131 
                 85 
                 10 
                 162.9 
                 166.2 
                 45.59 
                 18.93 
                 1.19 
               
               
                  4 
                 45.47 
                 17.52 
                 2.63 
                 1176 
                 85 
                 10 
                 137.0 
                 166.6 
                 44.51 
                 19.68 
                 2.17 
               
               
                  5 
                 45.93 
                 17.56 
                 1.75 
                 1167 
                 85 
                 10 
                 171.8 
                 199.1 
                 45.62 
                 19.00 
                 1.44 
               
               
                  6 
                 45.68 
                 17.58 
                 2.00 
                 1139 
                 85 
                  5 
                 71.6 
                 107.5 
                 45.10 
                 18.31 
                 0.73 
               
               
                  7 
                 44.68 
                 17.33 
                 4.08 
                 1174 
                 85 
                 10 
                 133.5 
                 178.5 
                 43.43 
                 19.62 
                 2.29 
               
               
                  8 
                 45.45 
                 17.52 
                 2.33 
                 1219 
                 85 
                 10 
                 144.6 
                 173.3 
                 44.67 
                 19.07 
                 1.55 
               
               
                  9 
                 45.10 
                 17.54 
                 1.92 
                 1139 
                 85 
                 10 
                 123.0 
                 163.7 
                 44.21 
                 19.36 
                 1.82 
               
               
                 10 
                 46.23 
                 17.38 
                 0.65 
                 1350 
                 85 
                 10 
                 79.8 
                 86.3 
                 45.86 
                 17.67 
                 0.30 
               
               
                 11 
                 45.76 
                 17.13 
                 2.20 
                 1346 
                 85 
                 10 
                 78.3 
                 122.0 
                 44.83 
                 18.71 
                 1.58 
               
               
                 12 
                 45.95 
                 17.24 
                 1.78 
                 1356 
                 85 
                 10 
                 169.3 
                 183.4 
                 45.38 
                 18.50 
                 1.26 
               
               
                 13 
                 45.83 
                 17.39 
                 2.12 
                 1354 
                 85 
                 10 
                 172.6 
                 193.4 
                 45.16 
                 18.60 
                 1.21 
               
               
                 14 
                 45.67 
                 16.91 
                 2.92 
                 1398 
                 75 
                 10 
                 148.8 
                 177.9 
                 44.70 
                 18.64 
                 1.74 
               
               
                 15 
                 45.55 
                 17.09 
                 2.33 
                 1288 
                 85 
                  5 
                 163.4 
                 202.4 
                 45.39 
                 18.37 
                 1.29 
               
               
                 16 
                 45.43 
                 16.90 
                 3.56 
                 1236 
                 85 
                 10 
                 138.6 
                 186.4 
                 44.63 
                 18.99 
                 2.10 
               
               
                 17 
                 45.19 
                 16.82 
                 3.98 
                 1280 
                 85 
                 10 
                 150.1 
                 193.0 
                 44.38 
                 18.85 
                 2.03 
               
               
                 18 
                 45.39 
                 16.94 
                 3.55 
                 1235 
                 85 
                 10 
                 77.9 
                 183.8 
                 44.09 
                 19.25 
                 2.31 
               
               
                 19 
                 46.09 
                 17.29 
                 1.65 
                 1104 
                 85 
                 10 
                 81.2 
                 121.7 
                 45.24 
                 18.27 
                 0.98 
               
               
                 20 
                 46.18 
                 17.22 
                 1.90 
                 1062 
                 75 
                  5 
                 83.4 
                 115.5 
                 45.36 
                 18.15 
                 0.93 
               
               
                 21 
                 46.25 
                 17.27 
                 1.86 
                 1016 
                 65 
                 15 
                 83.9 
                 136.7 
                 45.16 
                 18.72 
                 1.46 
               
               
                 22 
                 46.18 
                 17.27 
                 2.11 
                  996 
                 85 
                 10 
                 174.0 
                 205.8 
                 45.54 
                 19.04 
                 1.77 
               
               
                 23 
                 46.18 
                 17.35 
                 1.99 
                 1075 
                 95 
                  5 
                 168.3 
                 194.1 
                 45.85 
                 18.64 
                 1.29 
               
               
                 24 
                 45.90 
                 17.40 
                 1.66 
                 1216 
                 75 
                 15 
                 176.0 
                 199.0 
                 44.98 
                 19.06 
                 1.66 
               
               
                 25 
                 46.01 
                 17.20 
                 1.85 
                 1187 
                 85 
                 15 
                 171.2 
                 198.2 
                 45.17 
                 18.64 
                 1.44 
               
               
                 26 
                 45.88 
                 17.30 
                 1.90 
                 1215 
                 75 
                  5 
                 180.4 
                 211.7 
                 45.45 
                 18.14 
                 0.84 
               
               
                 27 
                 45.86 
                 17.38 
                 1.42 
                 1242 
                 95 
                 10 
                 166.4 
                 204.9 
                 44.41 
                 19.04 
                 1.66 
               
               
                 28 
                 45.71 
                 17.24 
                 2.04 
                 1078 
                 95 
                 15 
                 174.0 
                 197.8 
                 45.10 
                 18.85 
                 1.62 
               
               
                 29 
                 46.14 
                 17.34 
                 1.68 
                 1231 
                 95 
                 10 
                 174.4 
                 199.3 
                 45.29 
                 18.69 
                 1.35 
               
               
                 30 
                 46.07 
                 17.36 
                 1.54 
                 1234 
                 45 
                 10 
                 175.3 
                 195.1 
                 45.77 
                 18.08 
                 0.72 
               
               
                 31 
                 45.85 
                 17.42 
                 1.87 
                 1154 
                 65 
                  5 
                 168.5 
                 196.3 
                 45.65 
                 18.71 
                 1.29 
               
               
                 32 
                 45.91 
                 17.15 
                 1.52 
                 1294 
                 45 
                  5 
                 181.6 
                 190.5 
                 45.75 
                 17.89 
                 0.74 
               
               
                 33 
                 46.39 
                 17.54 
                 1.16 
                 1247 
                 45 
                 15 
                 186.3 
                 185.4 
                 46.18 
                 18.26 
                 0.72 
               
               
                 34 
                 45.88 
                 17.40 
                 1.32 
                 1260 
                 35 
                 10 
                 166.7 
                 179.2 
                 45.71 
                 18.19 
                 0.79 
               
               
                 35 
                 45.87 
                 17.41 
                 1.63 
                 1298 
                 65 
                  5 
                 157.3 
                 190.4 
                 45.28 
                 18.52 
                 1.12 
               
               
                 36 
                 46.11 
                 17.53 
                 1.30 
                 1264 
                 65 
                 10 
                 179.9 
                 204.3 
                 45.33 
                 18.51 
                 0.98 
               
               
                 37 
                 45.55 
                 17.29 
                 1.69 
                 1252 
                 55 
                 15 
                 168.9 
                 183.2 
                 44.80 
                 18.89 
                 1.60 
               
               
                 38 
                 45.83 
                 17.45 
                 1.08 
                 1252 
                 55 
                 10 
                 170.4 
                 187.6 
                 45.24 
                 18.43 
                 0.98 
               
               
                 39 
                 45.82 
                 17.43 
                 1.22 
                 1184 
                 55 
                  5 
                 172.2 
                 198.1 
                 46.03 
                 18.13 
                 0.70 
               
               
                 40 
                 45.90 
                 17.26 
                 1.50 
                 1129 
                 35 
                 10 
                 171.2 
                 183.5 
                 45.66 
                 1769 
                 0.43 
               
               
                 41 
                 45.80 
                 17.32 
                 1.73 
                 1247 
                 35 
                 15 
                 163.2 
                 174.5 
                 44.95 
                 18.77 
                 1.46 
               
               
                 42 
                 45.52 
                 17.39 
                 1.30 
                 1208 
                 35 
                 10 
                 66.7 
                 83.6 
                 45.17 
                 18.05 
                 0.66 
               
               
                 43 
                 45.75 
                 17.53 
                 1.35 
                 1254 
                 35 
                 15 
                 70.0 
                 92.5 
                 45.24 
                 18.27 
                 0.74 
               
               
                 44 
                 45.61 
                 17.53 
                 1.39 
                 1043 
                 35 
                  5 
                 72.5 
                 97.1 
                 45.39 
                 18.19 
                 0.66 
               
               
                 45 
                 45.66 
                 17.48 
                 1.25 
                 1103 
                 35 
                 10 
                 173.9 
                 194.6 
                 45.07 
                 18.67 
                 1.20 
               
               
                 46 
                 46.70 
                 17.65 
                 1.14 
                  838 
                 85 
                 10 
                 157.2 
                 174.7 
                 46.15 
                 18.21 
                 0.56 
               
               
                 47 
                 46.50 
                 17.66 
                 1.05 
                  809 
                 85 
                  5 
                 209.5 
                 234.7 
                 46.47 
                 18.41 
                 0.75 
               
               
                 48 
                 46.21 
                 17.65 
                 1.03 
                  950 
                 85 
                  5 
                 73.4 
                 138.3 
                 45.34 
                 18.85 
                 1.21 
               
               
                 49 
                 46.78 
                 17.66 
                 1.06 
                  795 
                 35 
                 10 
                 74.7 
                 106.9 
                 45.29 
                 18.94 
                 1.29 
               
               
                 50 
                 46.25 
                 17.65 
                 0.93 
                  939 
                 85 
                 10 
                 74.2 
                 129.6 
                 44.78 
                 19.42 
                 1.77 
               
               
                 51 
                 46.49 
                 17.58 
                 1.06 
                 1038 
                 85 
                 15 
                 72.7 
                 138.7 
                 44.91 
                 19.45 
                 1.87 
               
               
                 52 
                 46.69 
                 17.64 
                 0.74 
                 1026 
                 85 
                 15 
                 173.3 
                 213.9 
                 45.18 
                 19.30 
                 1.66 
               
               
                 53 
                 46.75 
                 17.63 
                 0.78 
                  904 
                 35 
                 10 
                 178.4 
                 192.0 
                 45.94 
                 18.31 
                 0.68 
               
               
                 54 
                 46.56 
                 17.61 
                 1.07 
                  869 
                 35 
                 15 
                 85.9 
                 124.3 
                 45.66 
                 18.61 
                 1.00 
               
               
                 55 
                 46.52 
                 17.69 
                 1.00 
                  961 
                 35 
                  5 
                 80.2 
                 121.2 
                 45.69 
                 18.57 
                 0.88 
               
               
                 56 
                 46.55 
                 17.63 
                 1.01 
                  801 
                 35 
                 15 
                 159.4 
                 181.1 
                 45.86 
                 18.81 
                 1.18 
               
               
                 57 
                 46.45 
                 17.67 
                 1.01 
                  746 
                 35 
                  5 
                 171.3 
                 197.9 
                 46.25 
                 18.15 
                 0.48 
               
               
                   
               
               
                 Note:  
               
               
                   (1) Ammoniacal nitrogen.  
               
             
          
         
       
     
     Based on a statistical analysis of the data from these tests, the starting temperature of the DAP recycle, within the range of about 65° to about 200°, was found to be a statistically insignificant variable for the percent nitrogen increase resulting from the treatment of the recycle with high pressure ammonia. 
     The following regression equation has been calculated incorporating particle size as a fourth independent variable: 
     
       
         %N increase=0.0079×NH 3  Pressure (psia)+0.088×Contact Time (min.)+0.540×Initial % Moisture−0.333×Particle Area+0.297  
       
     
     The particle size is expressed in the above regression equation as the surface area (Particle Area) in units of millimeters squared. Assuming the particles are spheres, the surface area is a direct function of the particle size (particle diameter) according to the following equation: 
     
       
         Area (mm 2 )=4π(d/2) 2 , where d is the particle diameter in millimeters (1 mm=1000 microns) and π is the constant Pi.  
       
     
     The data shown in Tables 9 and 10 was used to derive the above regression equation. The coefficients in the above regression equation differ somewhat from the coefficients in the regression equation having only three independent variables (NH 3  Pressure, Contact Time and Initial % Moisture) because the variation in the dependent variable (%N Increase) is now spread over four independent variables, rather than three independent variables. Also, it is important to realized that the particle size (and, thus, particle area) is an average particle size. 
     EXAMPLE I 
     Since operating a commercial diammonium phosphate plant wherein the entire recycle stream is treated with high pressure ammonia might be impractical, batch granulation tests were run in which 15 percent by weight of the recycle was treated with high pressure ammonia. This recycle was then combined with “normal” recycle, and mixed with DAP plant reactor slurry, and such composition was placed in a batch granulator where additional ammonia was added. The apparatus for and the procedure described above was used. 
     This example had several objectives. One objective was to determine if the pressure-ammoniated DAP recycle could be incorporated into DAP product and retain the added ammonia when the DAP was dried. Another objective was to determine if the effectiveness of the pressure ammoniation would decrease with DAP recycle that was derived from DAP product made using pressure-treated recycle. 
     Based on actual and estimated chemical analyses, the required quantities of normal recycle, pressure treated recycle, reactor slurry (phosphoric acid ammoniated to an N/P mole ratio of about 1.5) and ammonia were calculated. The normal recycle and pressure treated recycle were then combined in a slow speed solids mixer and the hot (about 260° F.) reactor slurry was blended in. The resultant mixture was next placed in the preheated batch granulator and a measured quantity of ammonia was added to the tumbling bed of solids. Following the ammonia addition, air was passed through the granulator to purge any unreacted ammonia and trap it in the scrubber attached to the granulator exhaust. The material from the granulator was then placed in a laboratory oven and dried for 30 minutes at about 225° F. 
     Except as noted, plant reactor slurry was used in all of the tests. The normal recycle for the first test (I-12) was obtained from a DAP plant and the ammoniated recycle was obtained from a previous ammoniation test (according to the invention). For all subsequent tests (I-13 to I-18), the recycle was obtained from the previous test (i.e., the recycle for test I-13 was obtained from test I-12, the recycle for test I-14 was obtained from test I-13, etc.). A portion of the recycle (about 15 percent of the total) was ammoniated for 10 minutes at an ammonia pressure of 85 psia. During each test samples were collected at various stages in the procedure to check for ammonia loses and establish a component mass balance. 
     The test results are set forth in Table 11. 
     
       
         
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 11 
               
               
                   
               
               
                 Test 
                 I-12 
                 I-13 (1)   
                 I-14 
                 I-15 
                 I-16 
                 I-17 
                 I-18 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Standard Recycle 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Weight, gms 
                 1275.01 
                 1275.05 
                 1275.05 
                 1275.05 
                 1275.08 
                 1105.04 
                 1190.03 
               
               
                 % P 2 O 5   
                 46.54 
                 45.07 
                 45.95 
                 45.19 
                 44.64 
                 45.54 
                 45.52 
               
               
                 % N 
                 17.66 
                 17.84 
                 17.88 
                 17.98 
                 18.00 
                 18.07 
                 18.06 
               
               
                 % H 2 O (3)   
                 1.14 
                 1.59 
                 1.88 
                 3.01 
                 2.70 
                 2.53 
                 2.49 
               
               
                 Ammoniated 
               
               
                 Recycle (2)   
               
               
                 Weight, gms 
                 225.14 
                 225.28 
                 225.20 
                 226.06 
                 225.23 
                 195.25 (5)   
                 210.35 
               
               
                 % P 2 O 5   
                 44.42 
                 44.00 
                 43.92 
                 43.51 
                 42.71 
                 42.05 
                 43.12 
               
               
                 % N 
                 20.15 
                 19.98 
                 20.32 
                 20.62 
                 21.06 
                 21.64 
                 21.52 
               
               
                 % H 2 O (3)   
                 2.20 
                 3.23 
                 4.87 
                 5.69 
                 5.74 
                 6.28 
                 6.97 
               
               
                 Reactor Slurry 
               
               
                 Weight, gms 
                 466.83 
                 473.82 
                 510.25 
                 471.69 
                 470.70 
                 651.76 (6)   
                 510.08 (7)   
               
               
                 % P 2 O 5   
                 44.40 
                 43.52 
                 43.82 
                 43.47 
                 43.31 
                 48.97 
                 40.14 
               
               
                 % N 
                 13.69 
                 13.83 
                 13.80 
                 13.75 
                 13.52 
                 13.63 
                 12.28 
               
               
                 % H 2 O (4)   
                 11.80 
                 7.52 
                 8.55 
                 7.84 
                 8.88 
                 11.67 
                 16.25 
               
               
                 Dried Product 
               
               
                 Analysis 
               
               
                 % P 2 O 5   
                 45.49 
                 45.30 
                 45.14 
                 44.72 
                 44.62 
                 45.63 
                 45.71 
               
               
                 % N 
                 17.90 
                 18.13 
                 18.15 
                 18.05 
                 18.10 
                 18.18 
                 18.02 
               
               
                 % H 2 O (3)   
                 1.45 
                 1.70 
                 2.24 
                 3.01 
                 2.44 
                 2.73 
                 2.43 
               
               
                 Mole Ratio 
                 1.99 
                 2.03 
                 2.04 
                 2.05 
                 2.06 
                 2.02 
                 2.00 
               
               
                 Component Mass 
               
               
                 Balance, % 
               
               
                 P 2 O 5   
                 104.76 
                 102.36 
                 104.97 
                 104.85 
                 104.44 
                 107.86 
                 102.63 
               
               
                 N 
                 97.04 
                 97.73 
                 97.09 
                 95.29 
                 95.29 
                 90.13 
                 98.16 
               
               
                 % N Loss-Granulator 
                 1.07 
                 −0.80 
                 −1.14 
                 0.34 
                 1.03 
                 5.35 
                 −0.56 
               
               
                 % N Loss-Dryer 
                 −1.06% 
                 −0.56% 
                 0.53% 
                 0.95% 
                 0.54% 
                 0.29% 
                 −1.04% 
               
               
                 inc. Samples (8) 
               
               
                   
               
             
          
         
       
     
     Notes: 
     (1) Starting with Test 13, recycle was a portion of the dried product from the previous test. 
     (2) Ammoniation conditions; 85 psia ammonia, contact time 10 minutes. 
     (3) Vacuum oven method. 
     (4) Karl Fisher method. 
     (5) −14 mesh recycle used in pressure ammoniation. 
     (6) Additional phosphoric acid added to slurry. 
     (7) Slurry diluted with water. 
     (8) inc. =including (i.e., the nitrogen loss due to samples collected before drying was accounted for in the calculations). 
     From the second test (I-1 3) onward, the product analyses show nitrogen concentrations above 18 percent. In fact, a problem during the series of tests was keeping the nitrogen concentration low enough to prevent excessive dilution (by the ammonia) of the P 2 O 5 . 
     Pressure ammoniating 15 percent of the total recycle was sufficient to increase the ammoniacal nitrogen concentration of the DAP product to 18 percent. In addition, repeat pressure ammoniations of DAP recycle derived from DAP product made with pressure ammoniated recycle, showed no decrease in ammonia adsorption ability. 
     EXAMPLE J 
     A series of pilot scale tests were run to determine the utility of the present invention. The objectives of the pilot test were to integrate the process of treating a portion of the recycle with ammonia at an elevated pressure into a continuous DAP production process, to determine how much of the nitrogen grade of the DAP product could be increased by treating a portion of the recycle and to produce a large quantity of DAP product that could be evaluated for physical properties and storage characteristics. 
     The pilot plant was capable of producing a maximum of about 900 pounds per hour of DAP and contained all of the major unit operations of a typical DAP plant, except the (ammonia) scrubber. FIG. 5 is a schematic of the pilot plant for the production of DAP. FIG. 6 is a schematic of the DAP pilot plant showing the location of the pressure reactor module and FIG. 7 is a schematic showing the details of how the pressure reactor module was integrated into the DAP pilot plant. 
     In FIG. 5 (also see FIG.  6 ), phosphoric acid (30 to 54 percent P 2 O 5 ) is fed into the top of the preneutralizer (reaction tank)  100  via lines  102  and  104 . Water is fed into the top of the preneutralizer  100  via line  106 . Ammonia is fed into the preneutralizer  100  via lines  108  and  110 , and is normally conveyed to a point below the liquid level in the tank. The phosphoric acid is partially preneutralized by the ammonia in preneutralizer  100 . The heat of reaction of ammonia and phosphoric acid is used to evaporate water in preneutralizer  100 . Preneutralizer  100  is vented to the atmosphere via top lines  122  and  124  with water vapor coming off via line  126 . The solution of the partially preneutralized phosphoric acid is fed from preneutralizer  100  via line  130  to rotary ammoniator-granulator  132 . Further ammonia is fed via lines  108  and  134  into ammoniator-granulator  132 , wherein the ammoniation is completed. Excess ammonia is required in ammoniator-granulator  132  to produce DAP. The granular product from ammoniator-granulator  132  is fed via line  136  into dryer  138 . The granular material from dryer  138  goes via line  160  directly to screen  146 . The sized granular DAP is removed via line  156  from screen  146  and sent via line  162  into cooler  142 . The sized granular DAP is removed from cooler  142  via line  164 . The oversized granular DAP is removed from screen  146  and fed via line  148  into crusher  150 . The crushed DAP exits from crusher  150  via line  154  and is mixed with the undersized granular DAP from line  152 , to form a mixture of fines. The fines mixture is recycled via line  158  into the front end of ammoniator-granulator  132 . Product size DAP can also be included in the recycle stream to aid in ammoniator-granulator operation. 
     Referring to FIG. 6, to accomplish the high-pressure ammonia treatment of the DAP recycle, pilot-scale pressure reactor module  168  was fabricated to be integrated into the DAP pilot plant. Pressure reactor module  168  is connected to line  152  via inlet line  166  and outlet line  170 . Ammonia is fed via lines  108  and  172  into pressure reactor module  168 . 
     Referring to FIG. 7, pressure reactor module  168  is composed of feed hopper  174 , three pressure vessels  176   a ,  176   b  and  176   c , and discharge hopper (conveyor)  180  (plus various piping, valves and controls, which are not shown). Undersize DAP exits screen  146  via line  152 . Part or all of the undersize DAP in line  152  is diverted via lines  166   a  and  166   b  (with the aid of screw feeder  172 ) into feed hopper  174 . Such undersize DAP is fed into the top of pressure reactor module  168 , specifically top pressure vessel  176   a , and passes downward through pressure vessels  176   b  and  176   c . Ammonia from line  172  is passed into middle pressure vessel  176   b . The undersized DAP is thereby enriched with ammonia. The ammonia-enriched DAP exits the bottom of pressure reactor module  168  via line  178  into discharge hopper  180 , and moves from hopper  180  via line  170   a  into screw feeder  182  and from screw feeder  182  via line  170   b  into fines recycle line  158  (or into ammoniator-granulator  132 ). 
     Pressure reactor module  168 , shown in FIG. 7, is designed to ammoniate the recycle on a batch basis, but by using feed hopper  174  and discharge hopper  180  as surge vessels, the removal of untreated recycle from the overall recycle flow and the discharge of ammonia enriched recycle back to the pilot plant ammoniator granulator  132  is essentially continuous. 
     Two types of tests were run, control tests and pressure reactor module tests. During the control tests none of the recycle was treated with ammonia in the pressure reactor module and the pilot plant was operated in a manner consistent with a conventional TVA DAP plant. The purpose of these tests was to establish a baseline, in terms of DAP product nitrogen concentration, for comparison with the pressure reactor module tests. During the pressure reactor module tests a portion of the undersize recycle was diverted to the pressure reactor module, treated with ammonia at elevated pressure for a given amount of time and then recombined with the untreated recycle going to the ammoniator granulator. 
     Table 12 shows the results of the first control test (Control Test No. 1). As used in Table 12 (and Tables 13, 14 and 15 below), the Slurry Mole Ratio is the molar concentration of nitrogen divided by the molar concentration of phosphorus in the partially neutralized phosphoric acid going from the preneutralizer ( 100 ) via line  130  (in FIG. 1) to the ammoniator granulator ( 132 ), the Recycle Ratio is the weight of recycle (line  158  in FIG. 1) divided by the weight of granular DAP product (line  156  in FIG. 1) and the Product Mole Ratio is the molar concentration of nitrogen divided by the molar concentration of phosphorus in the granular DAP product. In the Feed Acid Analysis section at the bottom of Table 12 (and Tables 13, 14 and 15 below), the KF H 2 O is the percent free water in the acid by the Karl Fischer method. The granular DAP product from this test contained an average 46.57 percent of P 2 O 5  and an average 17.99 percent of nitrogen. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 12 
               
             
             
               
                   
               
               
                 Control Test #1 
               
             
          
           
               
                   
                   
                 DAP 
                   
                   
               
               
                 Operating 
                   
                 Production 
                   
                 DAP Product Analyses 
               
             
          
           
               
                 Time 
                 Slurry 
                 Rate 
                 Recycle 
                   
                   
                   
                 Product 
               
               
                 (Hours) 
                 Mole Ratio 
                 (Lbs/Hr) 
                 Ratio 
                 % N 
                 % P 2 O 5   
                 % Moist 
                 Mole Ratio 
               
               
                   
               
               
                 0.50 
                 1.48 
                   
                   
                   
                   
                   
                   
               
               
                 1.00 
                 1.51 
               
               
                 1.50 
                 1.45 
                 796 
                 4.9 
                 17.90 
                 46.71 
                   
                 1.94 
               
               
                 2.00 
                 1.43 
                 946 
                 4.0 
               
               
                 2.50 
                 1.44 
                 781 
                 4.1 
                 18.09 
                 47.06 
                   
                 1.95 
               
               
                 3.00 
                 1.43 
                 1027  
                 3.2 
               
               
                 3.50 
                 1.43 
                 904 
                 3.9 
                 18.02 
                 46.56 
                   
                 1.96 
               
               
                 4.00 
                 1.48 
                 961 
                 3.4 
               
               
                 4.50 
                 1.43 
                 889 
                 3.5 
                 18.03 
                 46.43 
                   
                 1.97 
               
               
                 5.00 
                 1.42 
                 1023  
                 3.6 
               
               
                 5.50 
                 1.42 
                 836 
                 3.7 
                 17.93 
                 46.41 
                   
                 1.96 
               
               
                 6.00 
                 1.42 
                 777 
                 4.1 
               
               
                 6.50 
                 1.43 
                 858 
                 3.7 
                 17.98 
                 46.53 
                   
                 1.96 
               
               
                 7.00 
                 1.48 
                 871 
                 3.5 
               
               
                 7.50 
                   
                 783 
                 4.1 
                 17.97 
                 46.28 
                 0.99 
                 1.97 
               
               
                 Average 
                 1.45 
                 881 
                 3.8 
                 17.99 
                 46.57 
                 0.99 
                 1.96 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 12 
               
             
             
               
                   
               
               
                 Control Test #1 
               
             
          
           
               
                   
                   
                 DAP 
                   
                   
               
               
                 Operating 
                   
                 Production 
                   
                 DAP Product Analyses 
               
             
          
           
               
                 Time 
                 Slurry 
                 Rate 
                 Recycle 
                   
                   
                   
                 Product 
               
               
                 (Hours) 
                 Mole Ratio 
                 (Lbs/Hr) 
                 Ratio 
                 % N 
                 % P 2 O 5   
                 % Moist 
                 Mole Ratio 
               
               
                   
               
               
                 0.50 
                 1.48 
                   
                   
                   
                   
                   
                   
               
               
                 1.00 
                 1.51 
               
               
                 1.50 
                 1.45 
                 796 
                 4.9 
                 17.90 
                 46.71 
                   
                 1.94 
               
               
                 2.00 
                 1.43 
                 946 
                 4.0 
               
               
                 2.50 
                 1.44 
                 781 
                 4.1 
                 18.09 
                 47.06 
                   
                 1.95 
               
               
                 3.00 
                 1.43 
                 1027  
                 3.2 
               
               
                 3.50 
                 1.43 
                 904 
                 3.9 
                 18.02 
                 46.56 
                   
                 1.96 
               
               
                 4.00 
                 1.48 
                 961 
                 3.4 
               
               
                 4.50 
                 1.43 
                 889 
                 3.5 
                 18.03 
                 46.43 
                   
                 1.97 
               
               
                 5.00 
                 1.42 
                 1023  
                 3.6 
               
               
                 5.50 
                 1.42 
                 836 
                 3.7 
                 17.93 
                 46.41 
                   
                 1.96 
               
               
                 6.00 
                 1.42 
                 777 
                 4.1 
               
               
                 6.50 
                 1.43 
                 858 
                 3.7 
                 17.98 
                 46.53 
                   
                 1.96 
               
               
                 7.00 
                 1.48 
                 871 
                 3.5 
               
               
                 7.50 
                   
                 783 
                 4.1 
                 17.97 
                 46.28 
                 0.99 
                 1.97 
               
               
                 Average 
                 1.45 
                 881 
                 3.8 
                 17.99 
                 46.57 
                 0.99 
                 1.96 
               
               
                   
               
             
          
         
       
     
     Table 13 shows the results of the first test using the pressure reactor module (Pressure Reactor Module Test #1). During this test an average of 389 pounds per hour of undersize recycle was processed through the pressure reactor, where it was treated with gaseous anhydrous ammonia, at a pressure of 90 psia for average time of 14.75 minutes. The granular DAP product from this test contained an average 46.12 percent of P 2 O 5  and an average 18.37 percent of nitrogen. Thus, the nitrogen concentration of the product was 0.38 percent higher than Control Test No. 1 as a result of the pressure reactor module operation. 
     
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 13 
               
             
             
               
                   
               
               
                 Pressure Reactor Module Test #1 
               
             
          
           
               
                   
                   
                 DAP 
                 Reactor 
                   
                   
                   
                   
               
               
                 Operating 
                 Slurry 
                 Production 
                 Production 
                   
                 Pressure Reactor 
                   
                 Product 
               
               
                 Time 
                 Mole 
                 Rate 
                 Rate 
                 Recycle 
                 Module Analyses 
                 DAP Product Analyses 
                 Mole 
               
             
          
           
               
                 (Hours) 
                 Ratio 
                 (Lbs/Hr) 
                 (Lbs/Hr) 
                 Ratio 
                 % N 
                 % P 2 O 5   
                 % N 
                 % P 2 O 5   
                 % Moist 
                 Ratio 
               
               
                   
               
               
                  1 
                 1.43 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                  2 
                 1.39 
                 361 
                   
                 9.4 
               
               
                  3 
                 1.43 
                 779 
                   
                 4.1 
               
               
                  4 
                 1.42 
                 627 
                   
                 6.2 
                 18.84 
                 45.84 
                 18.19 
                 46.59 
                   
                 1.98 
               
               
                  4 
                 1.41 
                 673 
                 258 
                 5.9 
               
               
                  5 
                 1.41 
                 612 
                 500 
                 7.0 
                 19.13 
                 46.44 
                 18.25 
                 46.57 
                   
                 1.99 
               
               
                  6 
                 1.42 
                 697 
                 502 
                 6.1 
               
               
                  7 
                 1.43 
                 460 
                 501 
                 9.0 
                 19.11 
                 46.35 
                 18.46 
                 46.73 
                   
                 2.00 
               
               
                  8 
                 1.43 
                 737 
                 256 
                 5.7 
               
               
                  9 
                 1.45 
                 510 
                 495 
                 8.1 
                 19.19 
                 46.14 
                 18.30 
                 46.56 
                   
                 1.99 
               
               
                 10 
                 1.46 
                 1166  
                 488 
                 2.9 
               
               
                 11 
                 1.47 
                 946 
                 251 
                 3.3 
                 19.23 
                 46.07 
                 18.34 
                 46.29 
                   
                 2.01 
               
               
                 12 
                 1.46 
                 539 
                 475 
                 4.4 
               
               
                 13 
                 1.47 
                 546 
                 457 
                 4.1 
                 19.82 
                 45.56 
                 18.22 
                 45.55 
                   
                 2.03 
               
               
                 14 
                 1.47 
                 625 
                 452 
                 5.3 
               
               
                 15 
                 1.42 
                 763 
                 222 
                 3.7 
                 20.28 
                 44.97 
                 18.38 
                 45.82 
                   
                 2.03 
               
               
                 16 
                 1.43 
                 788 
                 228 
                 4.0 
               
               
                 17 
                 1.52 
                 803 
                 445 
                 3.6 
                 20.32 
                 44.93 
                 18.41 
                 45.78 
                   
                 2.04 
               
               
                 18 
                 1.46 
                 843 
                 444 
                 3.5 
               
               
                 19 
                 1.46 
                 581 
                 226 
                 5.7 
                 20.44 
                 44.79 
                 18.33 
                 45.92 
                   
                 2.02 
               
               
                 20 
                 1.44 
                 803 
                 440 
                 3.9 
               
               
                 21 
                 1.45 
                 713 
                 443 
                 4.2 
                 20.41 
                 44.71 
                 18.51 
                 45.78 
                   
                 2.05 
               
               
                 22 
                 1.46 
                 493 
                 217 
                 6.3 
               
               
                 23 
                   
                 733 
                 436 
                 4.2 
                 20.56 
                 44.64 
                 18.50 
                 45.95 
                   
                 2.04 
               
               
                 24 
                   
                 662 
                 432 
                 5.0 
                 20.54 
                 44.60 
                 18.52 
                 45.91 
                 2.54 
                 2.04 
               
               
                 Average 
                 1.44 
                 700 
                 389 
                 5.2 
                 19.82 
                 45.42 
                 18.37 
                 46.12 
                   
                 2.02 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 13 
               
             
             
               
                   
               
               
                 Pressure Reactor Module Test #1 
               
             
          
           
               
                   
                   
                 DAP 
                 Reactor 
                   
                   
                   
                   
               
               
                 Operating 
                 Slurry 
                 Production 
                 Production 
                   
                 Pressure Reactor 
                   
                 Product 
               
               
                 Time 
                 Mole 
                 Rate 
                 Rate 
                 Recycle 
                 Module Analyses 
                 DAP Product Analyses 
                 Mole 
               
             
          
           
               
                 (Hours) 
                 Ratio 
                 (Lbs/Hr) 
                 (Lbs/Hr) 
                 Ratio 
                 % N 
                 % P 2 O 5   
                 % N 
                 % P 2 O 5   
                 % Moist 
                 Ratio 
               
               
                   
               
               
                  1 
                 1.43 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                  2 
                 1.39 
                 361 
                   
                 9.4 
               
               
                  3 
                 1.43 
                 779 
                   
                 4.1 
               
               
                  4 
                 1.42 
                 627 
                   
                 6.2 
                 18.84 
                 45.84 
                 18.19 
                 46.59 
                   
                 1.98 
               
               
                  4 
                 1.41 
                 673 
                 258 
                 5.9 
               
               
                  5 
                 1.41 
                 612 
                 500 
                 7.0 
                 19.13 
                 46.44 
                 18.25 
                 46.57 
                   
                 1.99 
               
               
                  6 
                 1.42 
                 697 
                 502 
                 6.1 
               
               
                  7 
                 1.43 
                 460 
                 501 
                 9.0 
                 19.11 
                 46.35 
                 18.46 
                 46.73 
                   
                 2.00 
               
               
                  8 
                 1.43 
                 737 
                 256 
                 5.7 
               
               
                  9 
                 1.45 
                 510 
                 495 
                 8.1 
                 19.19 
                 46.14 
                 18.30 
                 46.56 
                   
                 1.99 
               
               
                 10 
                 1.46 
                 1166  
                 488 
                 2.9 
               
               
                 11 
                 1.47 
                 946 
                 251 
                 3.3 
                 19.23 
                 46.07 
                 18.34 
                 46.29 
                   
                 2.01 
               
               
                 12 
                 1.46 
                 539 
                 475 
                 4.4 
               
               
                 13 
                 1.47 
                 546 
                 457 
                 4.1 
                 19.82 
                 45.56 
                 18.22 
                 45.55 
                   
                 2.03 
               
               
                 14 
                 1.47 
                 625 
                 452 
                 5.3 
               
               
                 15 
                 1.42 
                 763 
                 222 
                 3.7 
                 20.28 
                 44.97 
                 18.38 
                 45.82 
                   
                 2.03 
               
               
                 16 
                 1.43 
                 788 
                 228 
                 4.0 
               
               
                 17 
                 1.52 
                 803 
                 445 
                 3.6 
                 20.32 
                 44.93 
                 18.41 
                 45.78 
                   
                 2.04 
               
               
                 18 
                 1.46 
                 843 
                 444 
                 3.5 
               
               
                 19 
                 1.46 
                 581 
                 226 
                 5.7 
                 20.44 
                 44.79 
                 18.33 
                 45.92 
                   
                 2.02 
               
               
                 20 
                 1.44 
                 803 
                 440 
                 3.9 
               
               
                 21 
                 1.45 
                 713 
                 443 
                 4.2 
                 20.41 
                 44.71 
                 18.51 
                 45.78 
                   
                 2.05 
               
               
                 22 
                 1.46 
                 493 
                 217 
                 6.3 
               
               
                 23 
                   
                 733 
                 436 
                 4.2 
                 20.56 
                 44.64 
                 18.50 
                 45.95 
                   
                 2.04 
               
               
                 24 
                   
                 662 
                 432 
                 5.0 
                 20.54 
                 44.60 
                 18.52 
                 45.91 
                 2.54 
                 2.04 
               
               
                 Average 
                 1.44 
                 700 
                 389 
                 5.2 
                 19.82 
                 45.42 
                 18.37 
                 46.12 
                   
                 2.02 
               
               
                   
               
             
          
         
       
     
     Table 14 shows the results of the second control test (Control Test No. 2). In this test the feed acid to the preneutralizer ( 100 ) contained a somewhat higher solids concentration than the feed acid used in the first test. The granular DAP product from this test contained an average 45.51 percent of P 2 O 5  and an average 17.90 percent of nitrogen. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 14 
               
             
             
               
                   
               
               
                 Control Test #2 
               
             
          
           
               
                   
                   
                 DAP 
                   
                   
               
               
                 Operating 
                   
                 Production 
                   
                 DAP Product Analyses 
               
             
          
           
               
                 Time 
                 Slurry 
                 Rate 
                 Recycle 
                   
                   
                   
                 Product 
               
               
                 (Hours) 
                 Mole Ratio 
                 (Lbs/Hr) 
                 Ratio 
                 % N 
                 % P 2 O 5   
                 % Moist 
                 Mole Ratio 
               
               
                   
               
               
                 0.50 
                 1.45 
                   
                   
                   
                   
                   
                   
               
               
                 1.00 
                 1.48 
                 779 
                 3.6 
               
               
                 1.50 
                 1.48 
                 693 
                 3.9 
               
               
                 2.00 
                 1.45 
                 700 
                 3.7 
               
               
                 2.50 
                 1.44 
                 616 
                 3.7 
               
               
                 3.00 
                 1.49 
                 623 
                 3.7 
                 17.84 
                 45.35 
                   
                 1.99 
               
               
                 3.50 
                 1.43 
                 825 
                 2.7 
               
               
                 4.00 
                 1.41 
                 642 
                 3.6 
                 18.01 
                 45.49 
                   
                 2.01 
               
               
                 4.50 
                 1.39 
                 477 
                 5.6 
               
               
                 5.00 
                 1.41 
                 524 
                 6.7 
                 17.78 
                 45.66 
                   
                 1.97 
               
               
                 5.50 
                 1.41 
                 660 
                 5.3 
               
               
                 6.00 
                   
                 620 
                 5.6 
                 17.96 
                 45.52 
                 3.02 
                 2.00 
               
               
                 Average 
                 1.44 
                 651 
                 4.4 
                 17.90 
                 45.51 
                 3.02 
                 1.99 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 14 
               
             
             
               
                   
               
               
                 Control Test #2 
               
             
          
           
               
                   
                   
                 DAP 
                   
                   
               
               
                 Operating 
                   
                 Production 
                   
                 DAP Product Analyses 
               
             
          
           
               
                 Time 
                 Slurry 
                 Rate 
                 Recycle 
                   
                   
                   
                 Product 
               
               
                 (Hours) 
                 Mole Ratio 
                 (Lbs/Hr) 
                 Ratio 
                 % N 
                 % P 2 O 5   
                 % Moist 
                 Mole Ratio 
               
               
                   
               
               
                 0.50 
                 1.45 
                   
                   
                   
                   
                   
                   
               
               
                 1.00 
                 1.48 
                 779 
                 3.6 
               
               
                 1.50 
                 1.48 
                 693 
                 3.9 
               
               
                 2.00 
                 1.45 
                 700 
                 3.7 
               
               
                 2.50 
                 1.44 
                 616 
                 3.7 
               
               
                 3.00 
                 1.49 
                 623 
                 3.7 
                 17.84 
                 45.35 
                   
                 1.99 
               
               
                 3.50 
                 1.43 
                 825 
                 2.7 
               
               
                 4.00 
                 1.41 
                 642 
                 3.6 
                 18.01 
                 45.49 
                   
                 2.01 
               
               
                 4.50 
                 1.39 
                 477 
                 5.6 
               
               
                 5.00 
                 1.41 
                 524 
                 6.7 
                 17.78 
                 45.66 
                   
                 1.97 
               
               
                 5.50 
                 1.41 
                 660 
                 5.3 
               
               
                 6.00 
                   
                 620 
                 5.6 
                 17.96 
                 45.52 
                 3.02 
                 2.00 
               
               
                 Average 
                 1.44 
                 651 
                 4.4 
                 17.90 
                 45.51 
                 3.02 
                 1.99 
               
               
                   
               
             
          
         
       
     
     Table 15 shows the results of the second test using the pressure reactor module (Pressure Reactor Module Test No. 2). During this test an average of 276 pounds per hour of undersize recycle was processed through the pressure reactor, where it was treated with gaseous anhydrous ammonia, at a pressure of 90 psia for average time of 11.9 minutes. The granular DAP product from this test contained an average 45.69 percent of P 2 O 5  and an average 18.27 percent of nitrogen. Thus, the nitrogen concentration of the product was 0.37 percent higher than Control Test No. 2 as a result of the pressure reactor module operation. 
     In addition, since the DAP product from Pressure Reactor Module Test No. 2 had an N/P mole ratio consistently greater than 2.00, some triammonium phosphate must have been produced and incorporated into the DAP product. Based on the average nitrogen and P 2 O 5  analyses for the DAP product that the amount of triammonium phosphate in the product was about 6.88 percent. 
     At the conclusion of Pressure Reactor Module Test No. 2, the DAP product was collected and transported to a DAP storage warehouse, where it was stored, as a separate pile, for 2 months. At the conclusion of the 2 month storage period, a random sample of the DAP product was collected from the pile and analyzed. The analytical results indicated the DAP product contained 45.45 percent P 2 O 5  and 18.15 percent ammoniacal nitrogen. Since the N/P mole ratio of the DAP product was still greater than 2.00, some triammonium phosphate was still present in the DAP product. 
     
       
         
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 15 
               
             
             
               
                   
               
               
                 Pressure Reactor Module Test #2 
               
             
          
           
               
                   
                   
                 DAP 
                 Reactor 
                   
                   
                   
                   
               
               
                 Operating 
                 Slurry 
                 Production 
                 Production 
                   
                 Pressure Reactor 
                   
                 Product 
               
               
                 Time 
                 Mole 
                 Rate 
                 Rate 
                 Recycle 
                 Module Analyses 
                 DAP Product Analyses 
                 Mole 
               
             
          
           
               
                 (Hours) 
                 Ratio 
                 (Lbs/Hr) 
                 (Lbs/Hr) 
                 Ratio 
                 % N 
                 % P 2 O 5   
                 % N 
                 % P 2 O 5   
                 % Moist 
                 Ratio 
               
               
                   
               
             
          
           
               
                  1 
                 1.43 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                  2 
                 1.38 
                 548 
                 267 
                 8.1 
                 20.14 
                 45.44 
                 18.44 
                 46.50 
                   
                 2.01 
               
               
                  3 
                 1.39 
                 711 
                 327 
                 4.9 
                 20.36 
                 45.10 
                 18.42 
                 46.30 
                   
                 2.02 
               
               
                  4 
                 1.43 
                 702 
                 417 
                 5.0 
                 20.17 
                 44.88 
                 18.29 
                 45.93 
                   
                 2.02 
               
               
                  5 
                 1.41 
                 659 
                 302 
                 5.2 
                   
                   
                 18.16 
                 45.67 
                   
                 2.01 
               
               
                  6 
                 1.44 
                 613 
                 126 
                 6.6 
                 19.56 
                 44.60 
                 18.21 
                 45.42 
                   
                 2.03 
               
               
                  7 
                 1.43 
                 801 
                 188 
                 4.8 
                 19.98 
                 44.33 
                 18.19 
                 45.58 
                   
                 2.02 
               
               
                  8 
                 1.40 
                 629 
                 260 
                 5.5 
                 19.78 
                 45.17 
                 18.15 
                 45.71 
                 1.56 
                 2.01 
               
               
                  9 
                 1.43 
                 734 
                 378 
                 4.6 
                 19.72 
                 45.20 
                 18.23 
                 45.56 
                   
                 2.03 
               
               
                 10 
                 1.44 
                 701 
                 183 
                 5.6 
                   
                   
                 18.34 
                 45.82 
                   
                 2.03 
               
               
                 11 
                 1.43 
                 757 
                 367 
                 4.9 
                 19.69 
                 45.14 
                 18.20 
                 45.76 
                   
                 2.02 
               
               
                 12 
                 1.43 
                 804 
                 447 
                 4.0 
                 19.97 
                 44.59 
                 18.25 
                 45.42 
                   
                 2.04 
               
               
                 13 
                 1.44 
                 806 
                 386 
                 4.7 
                 19.97 
                 44.72 
                 18.14 
                 45.66 
                   
                 2.01 
               
               
                 14 
                 1.44 
                 746 
                 383 
                 5.4 
                 20.03 
                 44.46 
                 18.34 
                 45.47 
                   
                 2.04 
               
               
                 15 
                 1.47 
                 726 
                 390 
                 5.6 
                 20.03 
                 44.52 
                 18.29 
                 45.57 
                   
                 2.03 
               
               
                 16 
                 1.46 
                 769 
                 294 
                 4.8 
                 20.16 
                 44.45 
                 18.29 
                 45.43 
                   
                 2.04 
               
               
                 17 
                 1.47 
                 690 
                 182 
                 4.9 
                 19.96 
                 44.44 
                 18.21 
                 45.69 
                   
                 2.02 
               
               
                 18 
                 1.48 
                 748 
                 277 
                 4.8 
                 20.05 
                 44.29 
                 18.12 
                 45.43 
                   
                 2.02 
               
               
                 19 
                 1.47 
                 735 
                 354 
                 4.5 
                 20.16 
                 44.23 
                 18.10 
                 45.38 
                   
                 2.02 
               
               
                 20 
                 1.47 
                 806 
                 285 
                 4.6 
                 20.18 
                 44.13 
                 18.23 
                 45.79 
                   
                 2.02 
               
               
                 21 
                 1.46 
                 789 
                 372 
                 4.7 
                 19.77 
                 44.67 
                 18.30 
                 45.58 
                 0.80 
                 2.03 
               
               
                 22 
                 1.46 
                 805 
                 277 
                 4.4 
                 20.00 
                 44.46 
                 18.20 
                 45.49 
                   
                 2.03 
               
               
                 23 
                 1.48 
                 666 
                 354 
                 5.8 
                 20.09 
                 44.63 
                 18.30 
                 45.60 
                   
                 2.03 
               
               
                 24 
                 1.48 
                 514 
                 277 
                 6.4 
                 20.16 
                 44.49 
                 18.20 
                 45.44 
                   
                 2.03 
               
               
                 25 
                 1.48 
                 587 
                 372 
                 5.2 
                 20.06 
                 44.26 
                 18.35 
                 45.40 
                   
                 2.05 
               
               
                 26 
                 1.48 
                 285 
                 275 
                 9.9 
                 20.36 
                 44.52 
                 18.52 
                 45.60 
                   
                 2.06 
               
               
                 27 
                 1.49 
                   
                 416 
               
               
                 28 
                 1.41 
                   
                 308 
               
               
                 29 
                 1.40 
                 266 
                 316 
                 10.7 
                 19.96 
                 45.34 
                 18.34 
                 45.88 
                   
                 2.03 
               
               
                 30 
                 1.42 
                 431 
                 307 
                 7.3 
                 20.26 
                 44.56 
                 18.00 
                 45.43 
                   
                 2.01 
               
               
                 31 
                 1.40 
                 597 
                 423 
                 5.7 
                 20.36 
                 44.58 
                 18.21 
                 45.23 
                   
                 2.04 
               
               
                 32 
                 1.46 
                 608 
                 226 
                 6.8 
                 20.18 
                 44.42 
                 18.30 
                 45.95 
                   
                 2.02 
               
               
                 33 
                 1.44 
                 680 
                  69 
                 7.2 
                   
                   
                 18.35 
                 46.13 
                   
                 2.02 
               
               
                 34 
                 1.44 
                 790 
                 269 
                 4.8 
                 19.85 
                 45.17 
                 18.21 
                 45.86 
                   
                 2.01 
               
               
                 35 
                 1.42 
                 748 
                 452 
                 4.2 
                 19.87 
                 45.37 
                 18.35 
                 46.01 
                   
                 2.02 
               
               
                 36 
                 1.42 
                 536 
                 333 
                 4.6 
                 20.29 
                 44.40 
                 18.07 
                 45.21 
                   
                 2.03 
               
               
                 37 
                 1.44 
                 507 
                 282 
                 5.5 
                 20.29 
                 44.64 
                 18.40 
                 45.89 
                   
                 2.03 
               
               
                 38 
                 1.44 
                 748 
                 149 
                 5.4 
                 20.20 
                 44.76 
                 18.37 
                 45.88 
                   
                 2.03 
               
               
                 39 
                 1.44 
                 718 
                 307 
                 4.2 
                 20.21 
                 44.84 
                 18.26 
                 45.67 
                   
                 2.03 
               
               
                 40 
                 1.46 
                 503 
                 307 
                 6.1 
                 20.38 
                 44.58 
                 18.40 
                 45.91 
                   
                 2.03 
               
               
                 41 
                 1.49 
                 538 
                 299 
                 6.5 
                 20.18 
                 44.93 
                 18.34 
                 45.60 
                   
                 2.04 
               
               
                 42 
                 1.51 
                 705 
                 413 
                 4.8 
                 20.38 
                 44.83 
                 18.40 
                 45.69 
                   
                 2.04 
               
               
                 43 
                 1.49 
                 586 
                 190 
                 5.9 
                 20.45 
                 44.57 
                 18.30 
                 45.63 
                   
                 2.03 
               
               
                 44 
                 1.48 
                 730 
                  99 
                 4.9 
                 20.51 
                 43.56 
                 18.28 
                 45.86 
                   
                 2.02 
               
               
                 45 
                 1.49 
                 706 
                 181 
                 4.6 
                 20.30 
                 44.56 
                 18.27 
                 46.03 
                   
                 2.01 
               
               
                 46 
                 1.48 
                 596 
                 198 
                 5.8 
                 20.51 
                 44.34 
                 18.44 
                 45.79 
                   
                 2.04 
               
               
                 Average 
                 1.45 
                 659 
                 295 
                 5.6 
                 20.11 
                 44.65 
                 18.27 
                 45.69 
                 1.18 
                 2.03 
               
               
                   
               
             
          
         
       
     
     
       
         
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 % 
                 % 
                 % 
                 % 
                   
                   
                   
                   
               
               
                 P 2 O 5   
                 Fe 2 O 3   
                 Al 2 O 3   
                 MgO 
                 % SO 4   
                 % CaO 
                 % Solids 
                 KF H 2 O 
               
               
                   
               
             
             
               
                 39.29 
                 1.81 
                 1.35 
                 0.98 
                 3.94 
                 0.42 
                 3.13 
                 35.78