Ammonium polyphosphate solution (APP, 10-34-0, 11-37-0) is the most common liquid P fertilizer material in the U.S. today. While 10-34-0 is the most common grade of APP solution, 11-37-0 is also found in some markets. While the following comments reference 10-34-0, most comments are applicable to 11-37-0 as well. The only real differences will be density, salt-out temperature and water content. While APP solution can commonly be found throughout the fertilizer industry, proper storage and handling techniques are not always followed at the retail level. As a result, it is far too common to hear of storage problems associated with APP solution. Grayish-brown and white precipitates at the bottom of the tank, cottage cheese-like particles floating in the product and slimy, stringy masses throughout the product are all evidence of storage problems associated with APP solution and/or other grades made with APP solution.
Most of the APP solution produced today is made by the pipe reactor process. In this process, wet-process superphosphoric acid and anhydrous ammonia are reacted in a “pipe” to produce a melt that has a temperature of 600° F to 700° F and a polyphosphate content of 70% to 75%. After the initial reaction in the pipe, the melt must be rapidly cooled, diluted with water, and further neutralized with ammonia to maintain the high polyphosphate content and resultant high quality. At the time of manufacturing, the APP solution should have the following properties (approximate, may vary): …….. (continued, view and download below)