Urea storage tank (SCR retrofit)

A urea storage tank is the dosing-reagent tank added when a ship is retrofitted with selective catalytic reduction (SCR) to meet the IMO NOx Tier III limit of MARPOL Annex VI Regulation 13 in emission control areas. SCR injects a urea solution (typically 40% aqueous urea, marine grade) upstream of a catalyst, where ammonia from the urea reduces NOx to nitrogen and water, cutting NOx by up to 80%. The retrofit sizes the tank for voyage time inside ECAs, adds heated and insulated stainless or coated steel construction to keep the solution above its 9 C crystallization point, plus dosing pumps, mixing, and a soot-blowing reactor. Tank location and structure need class approval.