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Chapter 8Various strategies have been developed to realise “total recycling processes”, these include:• conventional processes without stripping (older plants, provided by various suppliers, seeSection 8.4.1)• CO 2 stripping processes, e.g. by Stamicarbon or Toyo’s ACES process (see Section 8.4.2)• NH 3 stripping processes, e.g. by Snamprogetti (see Section 8.4.3)• the Isobaric Double Recycling process (IDR), applying stripping with NH 3 and CO 2 , byMontedison (see Section 8.4.4).Finally, the urea solution from the synthesis/recycling stages of the process is concentrated viaevaporation or crystallisation to a urea melt for conversion to a solid prilled or granular productfor use as a fertiliser or technical grade. In some cases, urea is produced solely for melamineproduction.Emissionto airCO 2NH 3Synthesis(high pressure)Stripping(optional)Exhaust gastreatmentRecovery ofcarbamate,NH 3 and CO 2Emissionto airExhaust gastreatmentCarbamatedecomposition(lower pressures)Urea solutionCondensationand condensatetreatmentEvaporation orcrystallisationand meltingUrea meltWastewaterPrilling orgranulationUreaFigure 8.1: Overview of the production of urea by total recycling processesFigure based on [52, infoMil, 2001]Large Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers 325