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

8.4 Techniques to consider in the determination of BAT• for product cooling, see Section 7.4.5• concerning granulation recycle, see Sections 7.4.7.Chapter 88.4.1 Conventional total recycling processDescriptionTable 8.13 gives an overview of a conventional total recycling process. A key feature of thisprocess is the separation of NH 3 and CO 2 from the reaction solution by stepwise pressurereduction (decomposers) and recycling into the reactor (as carbamate or NH 3 ).In order to minimise effluent volumes, aqueous NH 3 solutions of various origins are recycledinto the reactor. This decreases the conversion to urea in the reactor due to the higher watercontent. To keep the overall yield, carbamate and NH 3 recycling are extended, requiringadditional energy.Process sequenceSteps and conditionsNH 3 /CO 2 ratio 4:1ReactorCarbamatedecomposition(heat distillation)ConversionPressureDecomposer 1Decomposer 2Decomposer 365 – 67 % of CO 2 input200 barat 16 – 20 barat 3 barat 1 barCarbamate recyclingNH 3 recyclingPurge gas treatment(from decomposition)Absorption/rectificationCondensation, NH 3 bufferScrubbing with H 2 O, the liquor (NH 3 solution) is recycled to the processVacuum crystallisation, condensate treatment (stripping)Solidification andfinishingCentrifugationDrying, (wet) cyclones, scrubbing for exhaust gas treatmentMeltingPrilling, scrubber for exhaust gas treatmentTable 8.13: Example for a conventional total recycling process[121, German UBA, 2001], BASF, LudwigshafenLarge Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers 337