July 31, 2023
Liquid urea ammonium nitrate (UAN) is produced by combining urea, nitric acid, and ammonia. It is used as a liquid fertilizer (liquid UAN fertilizer can be applied more uniformly than non-liquid forms of fertilizer). UAN is highly corrosive, making storing large volumes of UAN in tanks very expensive due to the corrosion protection required for steel tanks or the high number of polytanks to achieve the equivalent volume. Evaporation of the water in UAN is to be avoided as the residue may include solid urea and ammonium nitrate, which may become unstable and/or explosive when exposed to an ignition source.
Due to the volume of UAN requiring storage and with previous experience with similar applications, the client requested twin-lined and covered earth bank storages with a capacity of 50,000T (37,900,000L) to accommodate their operational requirements. The two storages were to be constructed using the “cut and fill” methodology with the internal surfaces lined with suitable geomembrane and geomembrane floating covers to eliminate potential UAN liquid contamination and to meet environmental protection requirements.
The client engaged a specialist lining contractor to design and construct the liner and cover systems. The contractor undertook an extensive material evaluation process, commencing with a desktop review and concluding with laboratory immersion and chemical resistance testing to ascertain the most appropriate material. At the completion of this assessment, Layfield’s 1.50mm thick Enviro Liner® 6060 was selected due to the geomembrane’s chemical resistance, weathering resistance, and flexibility, which was particularly important for the floating covers, to accommodate the bending and folding associated with liquid level fluctuations.
The two 9,000m2 covers were field fabricated on site using wide-width rolls. Cover appurtenances, including sampling hatches, vents, ballast tubes, walkways, and stormwater removal pump platforms, were factory fabricated using 1.00mm thick Enviro Liner® 6040 before being installed on site.
The client has been impressed with the floating covers’ performance, an innovative solution to high-volume liquid urea ammonium nitrate storage limitations.