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

Chapter 55.4 Techniques to consider in the determination of BAT5.4.1 Dihydrate process (DH)DescriptionThe dihydrate process consists of four stages, namely grinding, reaction, filtration andconcentration. Figure 5.3 gives an overview. The dihydrate process offers a wide range ofoptions and the advantages of dihydrate systems are:• there is no phosphate rock quality limitation• online time is high• operating temperatures are low• startup and shutdown are easy• wet rock can be used thereby saving drying costs.The optimum operating conditions for dihydrate precipitation are 26 – 32 % P 2 O 5 and 70 –80 °C. The slurry temperature is controlled by the use of a flash cooler. This also de-gases theslurry making pumping easier. The temperature may also be controlled, for instance, by usingan air circulation cooler.Waste gasPhosphate rockExhaust gastreatmentFlashcoolerCondenserVacuumH 2OGrindingAttack tanksAgingtankH 2ODihydratefiltrationH 2SO 4Weak acidH 3PO 426 – 32 % P 2O 5GypsumCaSO 4 . 2H 2OFigure 5.3: Overview of the dihydrate process[31, EFMA, 2000]EvaporationAchieved environmental benefits• low operating temperatures• saving of energy for rock drying.226 Large Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers