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

Chapter 77.2.7 Conversion of Ca(NO 3 ) 2. 4 H2 O into AN and limeThe production of NPK fertilisers by digestion of phosphate rock with HNO 3 in the ODDAprocess produces calcium nitrate tetra hydrate (CNTH, Ca(NO 3 ) 2 . 4 H 2 O) as a by-product. Theconversion of CNTH with NH 3 and CO 2 results in the production of ammonium nitrate andlime, which can both be used for the production of CAN (see also Section 9.2.1).For the conversion, NH 3 and CO 2 are dissolved in an NH 4 NO 3 solution, which is circulated in acarbonising column, and forms ammonium carbonate according to:2 NH 3 + CO 2 + H 2 O (NH 4 ) 2 CO 3The reaction is exothermic and the heat is removed by cooling. Also CNTH is dissolved in aNH 4 NO 3 solution and both solutions react according to:Ca(NO 3 ) 2 + (NH 4 ) 2 CO 3 2 NH 4 NO 3 + CaCO 3On completion, excess (NH 4 ) 2 CO 3 is neutralised with HNO 3 and the approx. 65 % NH 4 NO 3(AN) solution is separated (belt filter) from the CaCO 3 (lime) and concentrated in a two stageevaporator (e.g. falling film type) using steam.Alternatively, the CNTH may be converted into commercial calcium nitrate fertiliser.7.2.8 Ammonium phosphates productionAmmonium phosphates, DAP/MAP, are a special case within the mixed acid route (ammoniumphosphates can not be produced by the nitrophosphate route). Production is usually carried outin a big, dedicated unit. Large quantities of diluted phosphoric acid are neutralised withammonia in a pre-neutraliser, or a pipe reactor, or a combination of both. The resulting slurry islater granulated, dried and conditioned in a conventional granulation loop. Exhaust gastreatment is made by a combination of high performance cyclones and intensive wet scrubbingwith phosphoric acid liquors and acidic water.7.2.9 Emission sources into air and exhaust gas treatmentExhaust gases arise from various sources. The main pollutants are:NO x (mainly NO and NO 2 ) with some nitric acid. The main source of NO x is the dissolution ofphosphate rock in nitric acid. The amount of NO x formed during particulate formation dependson the grade produced (reaction temperature, drying rate, etc.) and the production process(amount of HNO 3 used). The nature of the rock, for example organic matter and iron contentsand the reaction temperature, also affect the amount of NO x .NH 3 originating from the neutralisation process (pipe reactor, pre-neutralisation tank,granulation drum ammoniation or ammoniation tanks). The amount depends basically on thegrade produced (amount of ammonia to be reacted, pH, temperature and slurry viscosity, dryingrate) and the production process (again the amount of ammonia to be reacted, availability ofacidic scrubbing liquors, etc.). Some ammonia also evaporates in the spherodiser (when used) orin the drying drum, because of the applied temperatures.In the nitrophosphate route, there are also ammonia emissions originating from the CNTHconversion section and the AN evaporation section.288 Large Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers