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

Chapter 5Cross-media effects• relatively weak product acid (26 – 32 % P 2 O 5 ), hence high energy consumption in the acidconcentration stage• low P 2 O 5 efficiency: 94 – 96 %. Losses occur mostly as co-crystallisation with the calciumsulphate• produces impure dihydrate containing 0.75 % P 2 O 5• may require rock grinding.Operational dataSee Description.ApplicabilityGenerally applicable.[33, VITO, 2005] reports a modified DH process with higher yield. The modifications include:• double attack system (1 st step 70 % of the rock, 2 nd step 30 % with fresh H 2 SO 4 )• prolonged reaction time• recovery of P 2 O 5 washed out of the phosphogypsum during pumping to the stack and fromrain water.The modified DH process achieves an average P 2 O 5 efficiency of >97.5 %. The relateddihydrate contains 0.58 % P 2 O 5 . Where waste heat is available on-site that cannot be usedelsewhere, the concentration of H 3 PO 4 from the DH is not seen as a cross-media issue. For themodification, a significant investment was necessary to increase the residence time. Therecycling of water from the stack is common practice in industry.EconomicsNo specific information provided.Driving force for implementationNo phosphate rock limitation, online time is high, wet rock can be used, easy startup andshutdown.References to literature and example plants[29, RIZA, 2000, 31, EFMA, 2000, 33, VITO, 2005], Nilefos ChemieLarge Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers 227