Storage of 28-0-0 UAN solution is the preferred solution to over winter. Due to the higher salt out temperature, 32-0-0 may crystallize a significant amount of urea and /or nitrate in the bottom of the tanks.
When the temperature drops below -18° C, some “salt out” of urea and/or nitrate can occur. When the temperature rises above -10° C, re-circulation of the tank is required to re-dissolve the crystallized product in 28-0-0 solution.
Suggestions for storing solution over the winter:
In situations where UAN solution has resulted in “salt out” occurring due to cold temperatures, it is possible to re-dissolve the crystals back into solution once the outside temperature has gone significantly above the “salt out” temperature.
The situation is similar to putting salt in water. If you add a given amount of salt into a glass of water, in theory all of the salt should dissolve into solution. The problem that arises is that without mixing you do not have the “ideal” solution. The salt does not dissolve completely and you may end up with a layer of solution just above the salt which is saturated with dissolved salt, but above that the solution may not be saturated. The only way to dissolve all of the salt is through good mixing. The same goes for UAN solution.
When recirculating tanks ensure hose fittings are tight and secured to prevent inadvertent loosening do to vibrations.
Do not let tanks recirculate unattended. In the event of a possible rupture, someone needs to be around to shut down the system
Empty tank with UAN crystallized in the bottom of the tank.
With salt out, the product could be predominantly ammonium nitrate. If you are planning to store
product over winter, do not let any oils, gas, greases come in contact with the solution. There have been stories of customers using gear oil to color the UAN solution; this could be a dangerous situation if ammonium nitrate happened to crystallize out of the UAN solution. The result could be an explosive mixture.
When using liquid UAN fertilizers, it is recommended that machinery be cleaned daily with water to prevent corrosion from the UAN fertilizer. Spray lines and tanks should also be flushed out daily to prevent salting out (crystallization) of the liquid UAN fertilizer, as this may result in handling and application problems.
Source Information gathered over the years from Yara, Koch, Nutrien & Simplot along with personal experiences.