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Fluid Journal : Winter 2013
13 The Fluid Journal Winter 2013 Specific Gravity and pH Variability Affect UAN Blending Prudence needed to produce viable end product. The Fluid Journal • Official Journal of the Fluid Fertilizer Foundation • Winter 2013 • Vol. 21, No. 1, Issue # 79 Most nitrogen (N) fertilizer production begins with the reformation of natural gas to produce hydrogen, which is then used for ammonia production. As a result, natural gas constitutes about 70 percent of the cost of ammonia production. Ammonia is then used to produce various N-containing fertilizer products and intermediates such as: • Urea • Ammonium nitrate • Ammonium sulfate • Ammonium phosphate • Urea-ammonium nitrate solution. This makes natural gas one of the raw, precursor molecules for all N materials, including both liquid and dry N fertilizers. This discussion will address the liquid urea-ammonium nitrate (UAN) combinations that have seen substantial increases in demand. Since 1980s What has occurred since the 1980s is that UAN has continued to increase in total U.S . market share (Figure 1) while domestic natural gas prices have increased in cyclical swings, which at times significantly increased the cost of all N-related materials, including UAN (Figure 2). These cyclical increases in price volatility were further compounded by extremely low-cost natural gas in many other parts of the global economy. As a result, over the past 30 years many of the major N producers acquired smaller companies and, owing to higher natural gas costs, then closed or moth-balled the smaller, less efficient production facilities. This significantly decreased North American N production. Because of this, imported N materials have continued to increase and today are well over 50 percent of U.S . N consumption. With major natural gas reserves being identified across the northern U.S . in recent years, natural gas prices have fallen low enough to start discussions on the building of new N facilities in North America. Ratio variations With the loss of production and production personnel due to retirement and an increased volume of solutions being imported from the international market, we are seeing observable variations in the ratios of urea to ammonium nitrate. It is fairly common for imported UAN to be of higher analysis than 32 percent and sometimes lower. It is sometimes being cut with water, but this may not always be a refined process and, as a result, there are often observable variations in pH and specific gravity by the time the product reaches the dealer. In some cases, the addition of anhydrous ammonia is used to meet grade or possibly as a corrosion inhibitor. The problem that is created by the addition of free ammonia to meet total N grade or for corrosion inhibition is that there are observable broad ranges of UAN pH in the market. These variations in free ammonia and pH can significantly affect UAN compatibility with common-mix partners. Blending One major fluid fertilizer product mixed with UAN is ammonium polyphosphate (APP) as either 10-34-0 or 11-37-0. The blending of these two components tends to be done in the early to mid-part of the growing season. It has been observed over the last decade that there are sometimes causes of precipitate formation when these two materials are co-mingled in several typical fertilizer blends. In many cases where the individual components of UAN and APP could be individually tested, it has been found that the pH of UAN is higher than typical MSDS data sheets indicate. During this time, the UAN that has been tested has been found to have a pH in the 6.8 to 9.2 range. Figure 3 presents the relationship of the free ammonia content to the pH of UAN products. In addition, there is a relatively broad range of specific urea to ammonium nitrate formulations that can be used in making UAN solution--and variations do occur, depending upon the specific producer and the time of year. While the production of a specific analysis of UAN may include a range of specific urea:ammonium nitrate ratios (Figure 4), the products that UAN may be blended with often do not allow for such significant ranges in the proportion of urea to ammonium nitrate or pH. This is not only true of mixing with ammonium polyphosphates but with other secondary and micronutrients as well. Two tests It is recommended that when receiving UAN, two tests should be used to determine potential formulation issues with UAN, Michael Orr and Dr. Dale Leikam Summary: In the past, UAN composition was fairly uniform and unanticipated blending issues were relatively infrequent. That has changed however. Variations from load to load and supplier to supplier are more common. Variations in pH and specific gravity (density) can wreak havoc on your UAN blending processes. There are different reasons for the variations in UAN composition, so it is prudent to be aware of what you are dealing with if your goal is a viable end product.
Early Spring 2013