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

Chapter 99.4.3 Energy considerations and steam exportDescriptionThe formation of AN is strongly exothermic. The produced heat is often used to generate steam,which is often used to preheat the nitric acid or to concentrate the obtained AN solution. Theconcentration of the HNO 3 used represents an important factor, since it influences the amount ofwater that has to be removed. Product finishing requires energy, but due to the amount ofenergy introduced to the finishing section by the warm ANS, additional energy requirement fordrying is zero or very low (see also Section 9.4.5).Average energy consumption in Europe is 0.7 GJ/tonne AN produced, but modern AN plantsrequire only 0.09 – 0.22 GJ/tonne AN. The energy consumption of a CAN production plant issomewhat higher, due to the fact that the grinding of raw materials (e.g. dolomite) also requiresenergy. The process requires 150 – 200 kg steam/tonne CAN and 10 – 50 kWh/tonne CAN(about 36 – 180 MJ/tonne CAN) [52, infoMil, 2001].Steam is needed to evaporate the ANS but the amount needed will depend on the HNO 3concentration and the product concentration needs. The evaporation process may, in someplants, use steam from the neutralisers but this may not be a practicable proposition as a retrofitto an existing process. Energy is needed to evaporate liquid ammonia in some plants. This isnormally supplied from the process, for example, by using the steam from the neutraliser. Steamrequirements can be variable from zero to 50 kg/tonne of product. If the plant only makes ANS,steam can be exported at a rate of up to 170 kg/tonne of AN and some plants can export hotwater. The production of an ANS with approximately 95 % AN is achievable without anadditional energy demand for evaporation by carrying out a pressure neutralisation. Plants thatmake solid CAN also need around 150 – 200 kg steam per tonne of product, together withelectrical power of 10 – 50 kWh/tonne of product [148, EFMA, 2000]. Table 9.8 shows acomparison of expected consumption levels for new plants.VacuumneutralisationAt 2 bar with directheat recoveryPressure neutralisationAt 4 bar with cleansteam productionSteam import, kg/tonne AN 130 (10 bar) 10 52 (10 bar)Steam export, kg/tonne AN None None 240 (5 bar)Cooling water, m 3 /tonne AN 31.0 22.5 3.8Electricity, kWh/tonne AN 2.0 3.8 4.8Ammonia, kg/tonne AN 213 213 213Nitric acid, kg/tonne AN 789 789 789Figures for 60 % w/w HNO 3 and 96 % w/w AN product, a cooling water jT of 10 ºCTable 9.8: Comparison of expected consumptions for new plants[101, Uhde, 2003]Achieved environmental benefitsIf the plant only makes ANS, steam can be exported at a rate of up to 170 kg/tonne of AN andsome plants can export hot water. The production of an ANS with approximately 95 % AN isachievable without an additional energy demand for evaporation by carrying out a pressureneutralisation.378 Large Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers