Large Volume Inorganic Chemicals - Ammonia ... - ammk-rks.net

Chapter 88.4.11 Treatment of exhaust gas from prilling/granulationDescriptionIn modern urea plants, the main pollution to the environment originates from the finishingsection, prilling or granulation. In both cases, the load of pollutants (0.4 – 0.6 % of the total feedto the plant) outweighs the load from the wet section of the plant by at least one order ofmagnitude (about 0.005 – 0.05 % of the total feed). In finishing (be it prilling or granulation) ahuge amount of air comes into contact with hot urea solution and solid urea, hence the exhaustgases are loaded with NH 3 and dust. With respect to exhaust gas treatment, a comparison ofgranulation and prilling yields the following results:• for particular industrial downstream applications, urea prills might be preferred• expensive treatment outweighs the main prilling advantage: low cost• granulation requires less air• dust from granulation is coarser, making dust removal easier.The efficiencies for NH 3 removal depend mainly on the applied scrubbing medium (acidic orwater scrubbing) and the number of absorption stages. The scrubbing liquor containing NH 3 andurea dust can be recycled to the urea process in the case of water scrubbing.SourceTreatmentAchievable levels in mg/Nm 3ReferenceDust NH 3(no treatment) 60 – 130 70 – 140 bAcidic scrubbing, up to 350000Nm 3 /hour15 – 23 3 – 9 bPrillingScrubbing, 1 kWh/1000 Nm 3 25 – 30 x a15 20 xx fWater scrubbing 55 30 ePacked bed scrubber 30 d30 30 xx cGranulationPacked bed scrubber 30 dWater scrubber, slightly acidic up to 30 10 – 20 g15 20 xx fx lower levels are achievable, but connected with a rapid rise in pressure drop and power consumptionxx including acidic scrubbinga [129, Stamicarbon, 2006]b [9, Austrian UBA, 2002], average levels, the permit level for both is 30 mg/Nm 3 , acidic scrubberc [130, Uhde, 2004], process specificationsd [127, Toyo, 2006]e [121, German UBA, 2001]f [126, Snamprogetti, 1999]g SKW PiesteritzTable 8.18: Overview of the treatment of exhaust gases from urea finishingLarge Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers 355