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

Chapter 22.4 Techniques to consider in the determination of BATConventional steam reforming is described in Section 2.2.3.Partial oxidation is described in Section 2.2.4.2.4.1 Advanced conventional processesDescriptionThe different process steps for the conventional steam reforming process are integrated withrespect to mass and energy flow. During the years of development, a considerable reduction inenergy consumption has been achieved by improving the existing components in the process. Inaddition, today’s equipment and machinery can achieve a considerable thermodynamicefficiency and a high degree of reliability. Online availability exceeding 93 % is not uncommonin such plants. Advanced conventional process plants are usually characterised by the followingfeatures:• high duty primary reformer using high pressures of up to 40 bar• equipped with low NO x burners• stoichiometric air in secondary reforming (stoichiometric H/N ratio)• low energy CO 2 removal system.Differences in the configurations offered by the various engineering contractors generally resultfrom the optimised arrangements that they utilise and from using different well developedequipment designs. Specific examples of some applied techniques are:• increasing the temperatures of the mixed feed and process air in line with the current limitsfor metallurgical standards for construction. This, in turn, allows for a reduced reformerfiring and an increase in the reformer operating pressure, which also saves in the energyneeded for compression of the synthesis gas• utilising the recovered heat after the secondary reformer to raise and superheat steam• applying improved designs of high temperature shift reactors for lower steam to carbon ratio• utilising ammonia converter designs which use small size catalysts for higher conversions• ensuring the efficient recovery of a large proportion of reaction heat energy from theammonia synthesis. This is achieved by extracting the heat from the ammonia synthesisloop and using it to raise high pressure steam• applying a highly efficient ammonia condensation and refrigeration system.The high levels of NO x emissions of the conventional process are mainly due to the particularfiring conditions in the primary reformer. The use of low NO x burner techniques minimises thelevel, but relatively high NO x emissions still remain.Achieved environmental benefitsIn comparison with conventional processes, the following environmental benefits are achieved:• reduced reformer firing, lower NO x emissions• energy savings.For achievable emission and consumption levels, see:• Table 2.6 for energy consumption• Table 2.7 for NO x emissions• and Table 2.8 and Table 2.9 for other levels.58 Large Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers