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

Chapter 99.4 Techniques to consider in the determination of BAT• for product cooling, see Section 7.4.5• for recycling of warm air, see Sections 7.4.6• concerning granulation recycle, see Sections 7.4.7.9.4.1 Optimisation of the neutralisation sectionDescriptionThe neutralisation section has a significant effect on the environmental performance of thesystem. Various neutralisation processes are used and several parameters can affect theneutralisation section environmental performance. Table 9.7 gives an overview.ParameterPreheatingpH controlWatercontentTemperaturePressureImpuritiesDescriptionAN formation is an exothermic reaction. The heat produced is frequently used topreheat the HNO 3 or to concentrate the ANSA two-stage neutraliser operates with a low pH in the first stage and a neutral pH in thesecond. Due to this change in pH value, most of the steam is produced in the first stageand most of the NH 3 emission in the second. A two-stage neutraliser reduces theoverall NH 3 emission compared to a single-stage neutraliser, but it is more expensiveThe decomposition of AN proceeds slower at higher water contentsHigher temperatures lead to the decomposition of AN. The higher the temperature inthe neutraliser, the more important it is to control the pH value and the level ofimpuritiesNeutralisation at an increased pressure increases the steam temperature and theconcentration of AN in the solution. Although energy is needed to pressurise theneutraliser, most modern processes at elevated pressures are net producers of energy(excluding product finishing). Most older plants working at atmospheric pressure needto import steam. Atmospheric neutralisers have relatively low capital costs and arerelatively simple to operate, so atmospheric neutralisers are often preferred whensufficient steam is readily available from the by-product or from other low costsources. Building pressure might cause physical explosions, however in all cases itshould be possible to relieve pressureMany substances have a significant catalytic effect on AN decomposition. Allcontaminations are potentially hazardous, but especially organic materials (