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

Chapter 55.4.6 RepulpingDescriptionFigure 5.8 gives an overview of the repulping process. This further optimisation of thehemihydrate recrystallisation process (HRC or HDH-1) can be made by re-slurrying andwashing the gypsum, followed by a second filtration step in the “repulping process”. Most ofthe free acid which is not removed in the first filtration step can be removed in this process andthe efficiency can be improved by up to 1 % (depending on the amount of free acid).The gypsum from the first filter is re-slurried in a tank and then pumped to a second filter wherethe gypsum is dewatered. The gypsum is then washed with the fresh water coming into theplant. The liquid obtained from the second filter is used on the first filter to wash the gypsum.The repulping process is actually an additional step in the countercurrent washing of thegypsum, using the water that enters the plant.FiltrationGypsumAcidRepulpingtankRepulpfilterH 2Ofeed intoplantCleangypsumFiltratetankFigure 5.8: Overview of the repulping process[29, RIZA, 2000, 31, EFMA, 2000]Achieved environmental benefits• purer gypsum• higher efficiency.Cross-media effectsNone believed to be likely.Operational dataNo information provided.236 Large Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers