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Chapter 33.4.7 Combined NO x and N 2 O abatement in tail gasesDescriptionThe process comprises a combined N 2 O and NO x abatement reactor which is installed betweenthe final tail gas heater and the tail gas turbine and operates at tail gas temperatures ofapproximately 420 – 480 °C. The combined N 2 O and NO x abatement reactor consists of twocatalyst layers (Fe zeolite) and an intermediate injection of NH 3 . Within the first catalyst layer(De-N 2 O step) the decomposition of N 2 O into N 2 and O 2 is carried out at full NO x load, becausethe NO x additionally promotes the decomposition of N 2 O (co-catalysis). Within the secondcatalyst layer (De-N 2 O/De-NO x step) NO x is reduced by injection of NH 3 . Furtherdecomposition of N 2 O also takes place.Hot processgasTail gas fromabsorption:•NO x•N 2OTail gas heaterProcess gasto coolercondenser>420 ºCSCR (back-up)Emissionto airExpanderturbineCombinedreactorDe-N 2ODe-N 2ODe-NO xNH 3Figure 3.10: Combined NO x and N 2 O abatement[82, Uhde/AMI, 2004]Achieved environmental benefits• simultaneous abatement of N 2 O and NO x• N 2 O removal efficiency of 98 – 99 %• achievable emission levels of 0.12 – 0.25 kg N 2 O per tonne 100 % HNO 3 or 20 – 40 ppm• NO x removal efficiency of 99 %• NO x emission levels