Low Temperature Selective Catalytic Reduction of Nitrogen Oxides in Production of Nitric Acid by the Use of Liquid Ammonia

U radu je prikazana primjena niskotemperaturne selektivne katalitičke redukcije dušikovih oksida u otpadnom plinu od proizvodnje dušične kiseline. Selektivna katalitička redukcija provodi se heterogenim katalizatorom TiO2/WO3 nanesenim na nosač od Al2O3 velike aktivne površine po obujmu, oblika pčelinjeg saća. Prikazana je učinkovitost selektivne katalitičke redukcije u temperaturnom području otpadnog plina od 180 do 230 °C uz izravnu primjenu tekućeg amonijaka, bez prethodnog isparavanja u plinovito stanje. Posebnom izvedbom sustava za izravno doziranje tekućeg amonijaka te omogućavanjem učinkovite homogenizacije s otpadnim plinom postignute su emisije dušikovih oksida od 100,0 do 185,0 mg m-3 izrađenih kao NO2 u otpadnom plinu. Pokazano je da niskotemperaturna selektivna katalitička redukcija uz izravnu primjenu tekućeg amonijaka otvara novu mogućnost za smanjenje emisije dušikovih oksida u proizvodnji dušične kiseline. Istodobno se izbjegava svaka mogućnost pojave dušikovih oksida nakon heterogenog katalizatora u procesu naknadnog iskorištenja energije otpadnog plina u plinskoj turbini. Izravnom primjenom tekućeg amonijaka omogućen je jednostavniji sustav selektivne katalitičke redukcije dušikovih oksida u otpadnom plinu, bez dodatne operacije isparavanja i predgrijavanja te se ostvaruje ekonomski i energetski učinkovitije smanjenje emisije dušikovih oksida uz poštovanje zakonskih odredbi o graničnim emisijama.This paper presents the application of low-temperature selective catalytic reduction of nitrous oxides in the tail gas of the dual-pressure process of nitric acid production. The process of selective catalytic reduction is carried out using the TiO2/WO3 heterogeneous catalyst applied on a ceramic honeycomb structure with a high geometric surface area per volume. The process design parameters for nitric acid production by the dual-pressure procedure in a capacity range from 75 to 100 % in comparison with designed capacity for one production line is shown in the Table 1. Shown is the effectiveness of selective catalytic reduction in the temperature range of the tail gas from 180 to 230 °C with direct application of liquid ammonia, without prior evaporation to gaseous state. The results of inlet and outlet concentrations of nitrous oxides in the tail gas of the nitric acid production process are shown in Figures 1 and 2. Figure 3 shows the temperature dependence of the selective catalytic reduction of nitrous oxides expressed as NO2in the tail gas of nitric acid production with the application of a constant mass flow of liquid ammonia of 13,0 kg h-1 and average inlet mass concentration of the nitrous oxides expressed as NO2 of 800,0 mgm-3 during 100 % production capacity. The specially designed liquid-ammonia direct-dosing system along with the effective homogenization of the tail gas resulted in emission levels of nitrous oxides expressed as NO2 in tail gas ranging from 100,0 to 185,0 mg m-3. The applied low-temperature selective catalytic reduction of the nitrous oxides in the tail gases by direct use of liquid ammonia is shown in Figure 4. It is shown that low-temperature selective catalytic reduction with direct application of liquid ammonia opens a new opportunity in the reduction of nitrous oxide emissions during nitric acid production without the risk of dangerous ammonium nitrate occurring in the process of subsequent energy utilization of tail gas through a gas turbine. With the direct application of liquid ammonia it is possible to create the simpler system of selective catalytic reduction of tail-gas nitrous oxides, thus avoiding the additional processes of vaporization and preheating, and thereby achieving an economic and energetic-efficient procedure for their reduction down to legally prescribed limits

Femtosecond laser pulse train effect on Doppler profile of cesium resonance lines

We present direct observation of the velocity-selective optical pumping of the Cs ground state hyperfine levels induced by the femtosecond (fs) laser oscillator centered at either D2 (6 2S1/2↦6 2P3/2, 852 nm) or D1 (6 2S1/2↦6 2P1/2, 894 nm) cesium line. We utilized previously developed modified direct frequency comb spectroscopy (DFCS) which uses a fixed frequency comb for the excitation and a weak cw scanning probe laser centered at the 133Cs 6 2S1/2↦6 2P3/2 transition (D2 line) for ground levels population monitoring. The frequency comb excitation changes the usual Doppler absorption profile into a specific periodic, comblike structure. The mechanism of the velocity selective population transfer between the Cs ground state hyperfine levels induced by fs pulse train excitation is verified in a theoretical treatment of the multilevel atomic system subjected to a pulse train resonant field interaction

The influence of Fe-oxides and organic matter on surface properties of nanostructured microaggregates of the Terra rossa and Calcocambisol

This study investigates the influence of Fe-oxides and organic matter on surface properties of nanostructured mineral microaggregates obtained from the terra rossa and calcocambisol developed on hard limestone and dolomite in Istria, Croatia. The mineral composition and the morphology of samples were investigated using X-ray diffraction and field emission scanning electron microscope (FE-SEM), respectively. In order to determine the influence of Fe-oxides and organic matter coatings on surface properties of soils, samples were selectively dissolved. Particle size distribution, specific surface area (SSA) and electrophoretic mobility (EPM) were measured on the following soil subsamples: original samples, samples treated with H2O2, samples treated with H2O2+NH4-oxalate and samples treated with H2O2+NH4-oxalate+Na-dithionite-citrate-bicarbonate. The obtained results showed that kaolinites (kaolinites which form intercalation compounds with DMSO-KlD and kaolinites which do not intercalate with DMSO-Kl) (RANGE et al., 1969), illitic material (ŚRODOŃ, 1984 ; ŚRODOŃ & EBERL, 1984) and Fe-oxides are the main mineral components in the clay fraction of the terra rossa. Calcocambisol enriched in organic matter contains kaolinites, chlorite and vermiculite as main mineral phases. The main differences in surface properties between the terra rossa and calcocambisol was a consequence of diverse particle-size distribution, mineral composition and the share of organic matter. FE-SEM analysis of the terra rossa and calcocambisol samples after removal of amorphous Fe-oxides and organic matter shows disintegration. This disintegration is evident in reducing particle size from 2 µm to 50 nm for the terra rossa and from 1.8 µm to 50 nm for calcocambisol, respectively. Kaolinite with particle size about 50 nm shows pseudohexagonal form in analysed soils. The SSA increased proportionally to the amount of the removed organic matter in both soils. After the removal of well-crystallized Fe-oxides the SSA slightly decreased in calcocambisol and significantly increased in the terra rossa due to major soil microaggregate decomposition. EPM measurements of investigated samples were diverse

Low Temperature Selective Catalytic Reduction of Nitrogen Oxides in Production of Nitric Acid by the Use of Liquid

This paper presents the application of low-temperature selective catalytic reduction of nitrous oxides in the tail gas of the dual-pressure process of nitric acid production. The process of selective catalytic reduction is carried out using the TiO₂/WO₃ heterogeneous catalyst applied on a ceramic honeycomb structure with a high geometric surface area per volume. The process design parameters for nitric acid production by the dual-pressure procedure in a capacity range from 75 to 100 % in comparison with designed capacity for one production line is shown in the Table 1. Shown is the effectiveness of selective catalytic reduction in the temperature range of the tail gas from 180 to 230 °C with direct application of liquid ammonia, without prior evaporation to gaseous state. The results of inlet and outlet concentrations of nitrous oxides in the tail gas of the nitric acid production process are shown in Figures 1 and 2. Figure 3 shows the temperature dependence of the selective catalytic reduction of nitrous oxides expressed as NO2in the tail gas of nitric acid production with the application of a constant mass flow of liquid ammonia of 13,0 kg h^-1 and average inlet mass concentration of the nitrous oxides expressed as NO₂of 800,0 mgm^-3 during 100 % production capacity. The specially designed liquid-ammonia direct-dosing system along with the effective homogenization of the tail gas resulted in emission levels of nitrous oxides expressed as NO₂ in tail gas ranging from 100,0 to 185,0 mg m^-3. The applied low-temperature selective catalytic reduction of the nitrous oxides in the tail gases by direct use of liquid ammonia is shown in Figure 4. It is shown that low-temperature selective catalytic reduction with direct application of liquid ammonia opens a new opportunity in the reduction of nitrous oxide emissions during nitric acid production without the risk of dangerous ammonium nitrate occurring in the process of subsequent energy utilization of tail gas through a gas turbine. With the direct application of liquid ammonia it is possible to create the simpler system of selective catalytic reduction of tail-gas nitrous oxides, thus avoiding the additional processes of vaporization and preheating, and thereby achieving an economic and energetic-efficient procedure for their reduction down to legally prescribed limits

Static and dynamic properties of low-temperature order in the one-dimensional semiconductor (NbSe₄)₃I

International audienceWe investigated static and dynamic lattice properties in a quasi-one-dimensional charge-ordered semiconductor (NbSe 4) 3 I by using Raman, femtosecond pump-probe spectroscopy and x-ray diffraction. In addition to a welldocumented pseudo-Jahn-Teller ferrodistortive structural transition at T C = 274 K, where the displacements of Nb ions lead to ferroelectric (FE) in-chain polarization with opposite direction in adjacent chains, all methods suggest an additional lowering of symmetry at T * ≈ 160 K. Although antiferroelectric (AFE) phase is partially formed at T C , our results consistently point to an enhancement of the interchain order at T * , thus leading to AFE order-disorder transition, as supported by the earlier dielectric and structural studies

The influence of Fe-oxides and organic matter on surface properties of nanostructured microaggregates of the Terra rossa and Calcocambisol

This study investigates the influence of Fe-oxides and organic matter on surface properties of nanostructured mineral microaggregates obtained from the terra rossa and calcocambisol developed on hard limestone and dolomite in Istria, Croatia. The mineral composition and the morphology of samples were investigated using X-ray diffraction and field emission scanning electron microscope (FE-SEM), respectively. In order to determine the influence of Fe-oxides and organic matter coatings on surface properties of soils, samples were selectively dissolved. Particle size distribution, specific surface area (SSA) and electrophoretic mobility (EPM) were measured on the following soil subsamples: original samples, samples treated with H2O2, samples treated with H2O2+NH4-oxalate and samples treated with H2O2+NH4-oxalate+Na-dithionite-citrate-bicarbonate. The obtained results showed that kaolinites (kaolinites which form intercalation compounds with DMSO-KlD and kaolinites which do not intercalate with DMSO-Kl) (RANGE et al., 1969), illitic material (ŚRODOŃ, 1984 ; ŚRODOŃ & EBERL, 1984) and Fe-oxides are the main mineral components in the clay fraction of the terra rossa. Calcocambisol enriched in organic matter contains kaolinites, chlorite and vermiculite as main mineral phases. The main differences in surface properties between the terra rossa and calcocambisol was a consequence of diverse particle-size distribution, mineral composition and the share of organic matter. FE-SEM analysis of the terra rossa and calcocambisol samples after removal of amorphous Fe-oxides and organic matter shows disintegration. This disintegration is evident in reducing particle size from 2 µm to 50 nm for the terra rossa and from 1.8 µm to 50 nm for calcocambisol, respectively. Kaolinite with particle size about 50 nm shows pseudohexagonal form in analysed soils. The SSA increased proportionally to the amount of the removed organic matter in both soils. After the removal of well-crystallized Fe-oxides the SSA slightly decreased in calcocambisol and significantly increased in the terra rossa due to major soil microaggregate decomposition. EPM measurements of investigated samples were diverse