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

Chapter 55.4.3 Hemi-dihydrate recrystallisation process, single-stage filtrationDescriptionFigure 5.5 gives an overview of the hemihydrate recrystallisation process (HRC or HDH-1).The dissolution reactor operates under hemihydrate conditions. The reactors that follow operateunder conditions favouring rehydration of the hemihydrate to gypsum. Dihydrate seed crystalsin the recycled slurry from the filter feed initiate this rehydration. The product acid is a similarconcentration as that from the dihydrate process but the gypsum is much purer.Phosphate rockH 2OHemihydrateconditionsT = 100 °CReaction andcrystallisationDihydrate conditionsT = 80 °CRecrystallisationH 2OH 2SO 4H 3PO 4FiltrationGypsumCaSO 4 . 2 H 2OWeak acid30 – 32 % P 2O 5Figure 5.5: Overview of the hemihydrate recrystallisation process[29, RIZA, 2000]Achieved environmental benefits• produces relatively pure dihydrate• high P 2 O 5 efficiency: 97 %• lower sulphuric acid consumption.Cross-media effects• requires a fine rock grind• requires sulphuric acid dilution• may dissolve more partially soluble impurities• requires acid evaporation.Operational dataSee description.230 Large Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers