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This article describes the influence of various design modifications of the ammonia oxidation reactor operating in nitric acid plant TKIV in Kędzierzyn-Koźle on flow distribution of an air-ammonia mixture. The CFD (Computational Fluid Dynamics) simulations of turbulent flow were carried out with SST k-ω turbulence model to close the system of RANS (Reynolds Averaged Navier-Stokes) equations. The simulation results show that the properly selected perforated plate screen and the conical diffuser ensure uniform flow of gas on the ammonia oxidation catalysts and on the catalysts for nitrous oxide decomposition. It was proved experimentally achieving uniform temperature of nitrous gases in different locations under the catalytic gauzes and high efficiency of ammonia oxidation and nitrous oxide decomposition

The article describes the technology of NOx emission abatement by SNCR method. The scope of research included CDF simulations as well as design and construction of the pilot plant and tests of NOx reduction by urea in the plant located in industrial pulverized-coal fired boiler. The key step of research was to determine the appropriate temperature window for the SNCR process. The proposed solution of the location of injection lances in the combustion chamber enabled to achieve over a 30% reduction of NOx. It is possible to achieve higher effectiveness of the proposed SNCR technology and meet the required emission standards via providing prior reduction of NOx to the level of 350 mg/um3 using the primary methods.

The tightening standards of nitrogen oxides emission from industrial plants encourage nitric acid producers to search for new efficient solutions to meet the stringent emission limits. Industrial practice and the patent literature show that the effectiveness of deNOx (SCR) and deN2O technology is affected not only by the type and shape of the catalyst, but also by the method of its installation in a heterogenous catalytic reactor. The article presents the background of the problem, related to the emission of nitrogen oxides from nitric acid plants, and describes the technology of the tail gases purified from NOx and N2O. It shows various aspects that should be considered in designing reactors for deNOx and deN2O processes in nitric acid plants. The advantages and disadvantages of different catalytic basket designs, their industrial application and the direction of their design development were also indicated. [ABSTRACT FROM AUTHOR]

In modern dual-pressure nitric acid plants, the tail gas temperature usually exceeds 300 °C. The NH3-SCR catalyst used in this temperature range must be resistant to thermal deactivation, so commercial vanadium-based systems, such as V2O5-WO3 (MoO3)-TiO2, are most commonly used. However, selectivity of this material significantly decreases above 350 °C due to the increase in the rate of side reactions, such as oxidation of ammonia to NO and formation of N2O. Moreover, vanadium compounds are toxic for the environment. Thus, management of the used catalyst is complicated. One of the alternatives to commercial V2O5-TiO2 catalysts are natural zeolites. These materials are abundant in the environment and are thus relatively cheap and easily accessible. Therefore, the aim of the study was to design a novel iron-modified zeolite catalyst for the reduction of NOx emission from dual-pressure nitric acid plants via NH3-SCR. The aim of the study was to determine the influence of iron loading in the natural zeolite-supported catalyst on its catalytic performance in NOx conversion. The investigated support was firstly formed into pellets and then impregnated with various contents of Fe precursor. Physicochemical characteristics of the catalyst were determined by XRF, XRD, low-temperature N2 sorption, FT-IR, and UV–Vis. The catalytic performance of the catalyst formed into pellets was tested on a laboratory scale within the range of 250–450 °C using tail gases from a pilot nitric acid plant. The results of this study indicated that the presence of various iron species, including natural isolated Fe3+ and the introduced FexOy oligomers, contributed to efficient NOx reduction, especially in the high-temperature range, where the NOx conversion rate exceeded 90%. [ABSTRACT FROM AUTHOR]

The supported double-promoted cobalt spinel catalyst has been tested for N2O decomposition in the model and real gas streams (tail gas) from nitric acid plant. Activity tests carried out in the model gas stream showed a high activity of the developed supported catalyst. However, during catalytic investigations performed under real industrial conditions it was found that this catalyst is very sensitive to NOx poisoning. The negative influence of these oxides is visible even at their low concentration. However, the stability tests performed in real nitric acid plant gas streams showed that the developed catalyst preserves its initial activity for at least 40 days. Therefore, the authors propose to apply it in a dual-bed catalytic system consisting of deNOx and deN2O catalyst beds. At the first stage, tail gas is purified from NOx in the NH3-SCR process in the presence of commercial catalyst and at the second stage, catalytic decomposition of N2O into N2 and O2 takes place over the developed supported cobalt spinel catalyst. The deNOx catalyst bed applied in the proposed dual-bed catalytic system allowed for the complete conversion of NOx from the tail gases. After installation of the supported cobalt spinel catalyst downstream of the deNOx catalyst bed, a significant increase in deN2O catalyst activity in the real tail gas stream was observed. Under optimal conditions, this system (F = 150 L/h; T = 425–450 °C) allowed for the complete reduction of N2O emission. It is shown that the proposed catalytic system is robust and allows to obtain high conversions of both NOx and N2O. [ABSTRACT FROM AUTHOR]

The design of experiments (DoEs) with response surface methodology (RSM) were used to investigate the effect of operating parameters on the ammonia oxidation process. In this paper, the influence of reactor's load and temperature of reaction as independent variables was investigated. The efficiency of NH3 oxidation to NO and N2O concentration in nitrous gases gas was identified as response variables. As a result of these studies, statistically significant models for two responses variables were developed. [ABSTRACT FROM AUTHOR]

Thecatalytic activity of a doubly promoted K/Zn–Co3O4spinel catalyst in the deN2O reactionwas tested for 10 weeks in a nitric acid pilot plant. A charge of15 kg of the catalyst was synthesized via precipitation method, dried,calcined, and formed into 5 × 5 mm tablets. The catalytic testswere carried out in the wide range of process parameters: 320 < T< 425 °C; 80 < VRG< 180 N m3·h–1, 3 < p< 9.5 bar(a). During the operation the chemical compositionof tail gases from ammonia oxidation reactor outlet varied withinthe following range: 300 < CN2O<1500 ppm(v); 30 < CNOx< 3000 ppm(v);10000 < CO2< 50000 ppm(v); 1000< CH2O< 18000 ppm(v); N2– rest. In these conditions, the N2O conversionwas above 70% at 400 °C and was stable in time. Fresh and usedcatalysts were compared through detailed structural and morphologicalcharacterization (XRD, Raman, BET, SEM, XPS, H2-TPR), andtheir deN2O performance was verified in laboratory conditions.Long-term catalytic tests proved persistent stability of the catalystwith respect to its high activity, composition, structure, and morphology. [ABSTRACT FROM AUTHOR]

Background N2O is a powerful greenhouse gas emitted in nitric acid plants, and emission control technologies are required. Results A 0.25%Rh/50%Ce0. 9Pr0. 1O2/γ- Al2O3 catalyst has been prepared and tested for N2O decomposition in a real nitric acid plant gas stream. The catalyst is active enough to achieve 100% N2O removal, maintaining a constant catalytic activity after 40 h operation without deactivating. Characterization of the fresh and used catalyst, using different techniques, revealed no changes during the N2O decomposition experiments: (i) XRD and Raman spectroscopy show the fluorite structure of the Ce-Pr mixed oxide before and after the catalytic tests, (ii) the crystal size of the Ce-Pr mixed oxide particles and the BET surface area of the catalyst is maintained, evidencing no sintering of ceria particles, (iii) H2-TPR indicates that the reducibility of the catalyst is similar before and after the catalytic tests, revealing chemical stability, and (iv) TEM and XPS analysis indicated the high stability of the rhodium particle size and oxidation state. Conclusion An active and stable catalyst with formulation 0.25%Rh/50%Ce0. 9Pr0. 1O2/γ- Al2O3 has been prepared and successfully tested for N2O decomposition in a real nitric acid plant gas stream. © 2013 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: Synthesis of a multicomponent (K, Zn-doped) cobalt spinel deN2O catalyst developed in a laboratory was extended to a pilot scale. The optimal composition and morphology of the prototype catalyst elucidated in the laboratory conditions were successfully reproduced upon large scale synthesis and shaping. Tuning of the catalyst properties was guided by in situ work function measurements in conjunction with the TPRS tests of N2O decomposition including the effect of water and oxygen inhibitors. In the pilot tests the engineered catalyst exhibited high performance (conversion >95% below 350°C) in N2O removal from the real tail gases of the nitric plant for at least 20 days. [Copyright &y& Elsevier]

The influence of Zn and K promoters on N2O decomposition over Co3O4 was investigated by work function measurement and temperature-programmed surface reaction. The beneficial effect of the promoters resulting in spectacular decrease in the temperature of 50% conversion by 200 °C was found to be essentially of electronic origin. The strong correlation between the catalyst work function and deN2O activity allowed for the optimization of the doping level of both additives. The pilot plant tests in real nitric acid tail gases revealed that the optimized double promoted (Zn, K) cobalt spinel catalyst maintained its remarkable activity in N2O decomposition (conversion >95% at the target temperature of 350 °C) for more than 60 h. [ABSTRACT FROM AUTHOR]

Catalytic high temperature decomposition (secondary abatement) of nitrous oxide over calcium aluminate 12CaO · 7Al2O3 (mayenite) was studied in the model laboratory tests (TPSR) and pilot units (steady-state) using the real feed. X-ray diffraction (XRD), scanning electron microscopy (SEM), N2-sorption (BET), electron paramagnetic resonance (EPR) and Raman spectroscopies were used to characterize the synthesized material. The catalyst exhibited high efficiency and selectivity in N2O removal, reaching practically 100% conversion at 1150 K without appreciable total losses of NO x . Owing to its high thermal stability and resistivity to sintering and low cost of production raw materials, mayenite was found to be a promising catalyst for economically appealing secondary abatement of nitrous oxide in nitric acid plants. [ABSTRACT FROM AUTHOR]

Natural zeolite of the heulandite-type framework was modified with iron and tested as a catalyst for the selective catalytic reduction of nitrogen oxides with ammonia (NH3-SCR) in the temperature range of 150–450 °C. The catalyst was prepared at a laboratory scale in a powder form and then the series of experiments of its shaping into tablets was conducted. Physicochemical studies of the catalyst (N2 sorption at −196 °C, FT-IR, XRD, UV-vis) were performed to determine the textural and structural properties and identify the surface functional groups, the crystalline structure of the catalysts and the form and aggregation of the active phase. The activity tests over the shaped catalyst were performed industry-reflecting conditions, using tail gases from the pilot nitric acid plant. The influence of a temperature, catalyst load, and the amount of reducing agent (ammonia) on the NOx reduction process were investigated. The results of catalytic tests that were performed on model gas mixture showed that non-modified clinoptilolite exhibited around 58% conversion of NO at 450 °C. The temperature window of the shaped catalyst shifted to a higher temperature range in comparison to the powder sample. The catalytic performance of the shaped Fe-clinoptilolite in the industry-reflecting conditions was satisfactory, especially at 450 °C. Additionally, it was observed that the ratio of N2O concentration downstream and upstream of the catalytic bed was below 1, which indicated that the catalyst exhibited activity in both DeNOx and DeN2O process. [ABSTRACT FROM AUTHOR]

Different variants for abatement of N2O emission from nitric acid plants with the use of catalysts developed at Łukasiewicz-INS were analyzed. Activity tests on a pilot scale confirmed the high activity of the studied catalysts. A two-stage catalytic abatement of N2O emission in nitric acid plants was proposed: by high-temperature decomposition in the nitrous gases stream (HT-deN2O) and low-temperature decomposition in the tail gas stream (LT-deN2O). The selection of the optimal variant for abatement of N2O emission depends on the individual characteristics of the nitric acid plant: ammonia oxidation parameters, construction of ammonia oxidation reactor and temperature of the tail gas upstream of the expansion turbine. It was shown that the combination of both deN2O technologies, taking into account their technological constraints (dimensions of the catalyst bed), allows for a greater abatement of N2O emission, than the use of only one technology. This solution may be economically advantageous regarding the high prices of CO2 emission allowances. [ABSTRACT FROM AUTHOR]

In this paper, the design of experiments and response surface methodology were proposed to study ammonia oxidation process. The following independent variables were selected: the reactor's load, the temperature of reaction and the number of catalytic gauzes, whereas ammonia oxidation efficiency and N2O concentration in nitrous gases were assumed as dependent variables (response). Based on the achieved results, statistically significant mathematical models were developed which describe the effect of independent variables on the analysed responses. In case of ammonia oxidation efficiency, its achieved value depends on the reactor's load and the number of catalytic gauzes, whereas the temperature in the studied range (870–910 °C) has no effect on this dependent variable. The concentration of nitrous oxide in nitrous gases depends on all three parameters. The developed models were used for the multi-criteria optimization with the application of desirability function. Sets of parameters were achieved for which optimization assumptions were met: maximization of ammonia oxidation efficiency and minimization of the N2O amount being formed in the reaction. [ABSTRACT FROM AUTHOR]