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

Chapter 55.4.4 Hemi-dihydrate recrystallisation process, double-stage filtrationDescriptionFigure 5.6 gives an overview of the hemi-dihydrate recrystallisation process with double-stagefiltration (HDH-2). In this process it is possible to obtain 40 – 52 % P 2 O 5 acid directly, byacidulating under hemihydrate conditions and separating the hemihydrate before recrystallising.The additional filter and the other equipment needed add to the capital cost of the plant butenable savings to be made on evaporation.Phosphate rockHemihydrateconditionsT = 100 °CReaction andcrystallisationHH 2SO 3PO 44Filtration40 – 52 % P 2O 5Weak acidDihydrate conditionsT = 80 °CRecrystallisationH 2OFiltrationGypsumCaSO 4 . 2 H 2OFigure 5.6: Overview of the hemi-dihydrate recrystallisation process with double-stage filtration[29, RIZA, 2000]Achieved environmental benefits• energy savings due to reduction or elimination of the need for evaporation equipment ifconcentrated acid is required for downstream processing• produces purer acid (low SO 4 , Al, F)• energy savings by elimination of rock grinding (may use coarse rock)• low sulphuric acid consumption• highest P 2 O 5 efficiency: 98.5 %• produces relatively pure dihydrate (0.19 % P 2 O 5 ).Cross-media effectsNone believed to be likely.Operational dataSee description.232 Large Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers