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[en] Korea Atomic Energy Research Institute (KAERI) has launched a decommissioning program of the uranium conversion plant in 2001. The treatment of the sludge waste, which was generated during the operation of the plant and stored in the lagoon, is one of the most important tasks in the decommissioning program of the plant. The major compounds of the lagoon sludge are ammonium nitrate, sodium nitrate, calcium nitrate, calcium carbonate, and uranium compounds. The minor compounds are iron, magnesium, aluminum, silicon and phosphorus. A treatment process of the sludge was developed as figure 1 based on the results of the sludge characteristics and the developed treatment technologies. A treatment of off-gas evolved from the nitrate salts thermal decomposition is one of the important process. Off-gas treatment by using a selective catalytic reduction (SCR) method was investigated in this study
[en] Nitrogen oxides (NOx) are one of the most hazardous air pollutants arising from the combustion processes. Because of the implementation of strict emission limits many NOx removal technologies have been developed. In the present work post combustion NOx removal technique that is Selective Non-Catalytic Reduction (SNCR) has been investigated in a pilot scale 150 kW combustion rig facility. Investigation has been performed using some novel NOx reducing reagents like urea, ammonium carbonate and mixture of their 50%-50% aqueous solution within the temperature range of 700 to 1200 deg. C., at 1.1% excess oxygen and background NOx level of 500 ppm. The effects of these reagents were determined in term of their temperature characteristics and molar ratio. Among the reducing reagents used urea solution gave the highest NOx removal efficiency (81%) and was attractive due to its superior high temperature (1000 to 1150 deg. C) performance, ammonium carbonate was more effective at lower temperature range (850 to 950 deg. C) though its efficiency (32%) was lower than urea, while 50-50% solution of urea and ammonium carbonate gave higher efficiency than ammonium carbonate but slightly lesser than urea within a wide temperature range (875 to 1125 deg. C). It was also observed that the NOx removal efficiency was increased with increasing the molar ratio. (author)
[en] Highlights: • An absorption based laser sensor for the investigation of dynamically changing liquid film thicknesses is proposed. • The used laser wavelength was optimized to prevent dependence to the temperature. • The sensor can be used in two configurations, which leads to a higher flexibility regarding different boundary conditions. • The laser based sensor could successfully be validated in both configurations against a commercially available chromatic confocal resonance (CHR) sensor. - Abstract: In this work, an absorption based laser sensor for the investigation of dynamically changing liquid film thicknesses is developed and validated. For the wavelength selection of the single-ended, fibre-coupled, diode-laser sensor, near-infrared spectra of liquid water are measured at various thicknesses and temperatures. To reduce the influence of the film temperature, the evaluation is supported by a calibration procedure. Unknown film thicknesses of up to 440 µm could then be measured. To adapt the sensor to particular boundary conditions of different systems, the single-ended setup can be changed to a transmissive configuration. The sensor is validated in both configurations against a commercially available chromatic confocal resonance (CHR) sensor. A comparison with respect to the CHR sensor leads to an accuracy of 2.8 µm and a precision of 3.9% of the new laser based sensor.
[en] TPD / TPR techniques are used to titrate the active species of a catalyst for determining its activity towards a specific reaction. After discussing the basic features of the different techniques, the paper shows some significant example of application to acid catalysts, metallic copper, metals supported on alumina
[en] Kinetics of catalytic reduction of uranyl species, U(VI) to U(IV) with hydrazine nitrate was studied over Pt/SiO2 catalyst in nitric acid medium. Experiments were carried out in a stainless-steel autoclave as a function of mixing intensity, temperature, catalyst loading and concentration of nitric acid, hydrazine and uranium. Langmuir-Hinshelwood approach was considered to derive various model equations and each of them was evaluated. Results of the present study indicated that catalytic reduction of U(VI) can be described by surface reaction between adsorbed molecules. The activation energy of the reaction was calculated to be 74.5 kJ/mol, suggesting a chemical reaction controlled process. (author)
[en] It is presented a revision and discussion about the characteristics and factors that relate activity and selectivity in the catalytic and not catalytic partial oxidation of methane and the effect of variables as the temperature, pressure and others in the methane conversion to methanol. It thinks about the zeolites use modified for the catalytic oxidation of natural gas
[en] Uranium-plutonium separation is an essential step in the PUREX process employed in spent nuclear fuel reprocessing. This partitioning in the PUREX process is achieved by selective reduction of Pu(IV) to Pu(III) using uranous nitrate as reductant and hydrazine as stabilizer. Currently in our Indian reprocessing plants, the requirement of uranous nitrate is met by electrolytic reduction of uranyl nitrate. This process, however, suffers from a major drawback of incomplete reduction with a maximum conversion of ~ 60%. Catalytic reduction of U(VI) to U(IV) is being considered as one of the promising alternatives to the electro-reduction process due to fast kinetics and near total conversion. Various catalysts involving noble metals like platinum (Adams catalyst, Pt/Al_2O_3, Pt/SiO_2 etc.) have been reported for the reduction. Sustained activity and stability of the catalyst under harsh reaction conditions are still the issues that need to be resolved. We present here the results on zirconia supported noble metal catalyst that is developed in BARC for reduction of uranyl nitrate to uranous nitrate. Supported noble metal catalysts with varying metal loadings (0.5 - 2 wt%) were prepared via support precipitation and noble metal impregnation. The green catalysts were reduced either by chemical reduction using hydrazine hydrate or by heating in hydrogen flow or combination of both the steps. These catalysts were characterized by various techniques such as, XRD, SEM, TEM, N_2 adsorption and H_2 chemisorption. Performance of these catalysts was evaluated for U(VI) to U(IV) reduction with uranyl nitrate feed using hydrazine as reductant. The results with the most active catalyst are named as 'BARC-CAT', which was developed in our lab. (author)
[en] A new material for neutralization of nitrogen oxides is presented. Two or three metals containing catalysts with a good activity and selectivity towards NOx have been obtained. Preparation of carbon catalysts by deposition of the active phase precursor on the initial carbon material prior to activation is considered as the most promising method. An active carbon-based catalyst (AC/Co) has been synthesized Apricot shells preliminary impregnated with a water-alcohol solution of Co nitrate have been used as initial carbon material. after drying they have been subjected to one-phase steam pyrolysis using a fix-bed reactor. The catalyst thus obtained has a specific surface area (BET) of 53 m2g-1, a favorable mesopore volume/total volume ratio (about 0.85) determined by nitrogen adsorption, a suitable mesopore distribution, about 70% of the mesopores being characterized by rp larger than 25 A and a high dispersion of the Co oxide phase. In addition the catalyst possesses the necessary mechanical resistance. The catalyst has exhibited a high activity with respect to NOx reduction with CO at low temperatures (at 150-250oC which are the temperatures of industrial flue gases, nO conversion up to 60-95% occurs) and a high selectivity. No presence of H2O has been established over the whole temperature range (100-300oC). An additional advantage of the catalyst is the fact that the amount of CO above 150oC is lower than the stoichiometric which indicates parallel participation in the process of both the active phase and the support (active carbon) It is also important that the presented catalyst has a low price due to the use of waste products from agriculture and the elimination of special thermal treatment of the supported Co nitrate. There are possibilities of using of other organic wastes from agriculture as well as wastes obtained during flotation of coal. (author)
[en] Highlights: • Removal of NOx by plasma-catalyst system at different temperatures were studied. • Catalyst addition dramatically improved NOx removal efficiency with plasma. • 12Mn-12Cu/ZSM5 exhibited the best performance in NOx removal with plasma. • Temperature affected the discharge and catalytic activity for NOx removal. - Abstract: Manganese-copper catalysts are well-known catalysts for selective catalytic reduction (SCR) of NOx. To evaluate the NOx removal in the combination system of catalysts and plasma, a series of Cu-Mn/ZSM-5 catalysts with varying amounts of manganese doping were synthesized by an incipient wetness impregnation method and used for SCR of NOx assisted by plasma at different temperatures. The results showed that the combination of catalyst and plasma promoted NO removal efficiency, the introduction of Mn on Cu/ZSM5 enhanced the catalyst activity, and 12Mn-12Cu/ZSM5 exhibited the best NO removal performance with about 90% NO removal efficiency at 25 °C. With a rise in temperature, the reduced electric field (E/N) increased, intensifying the discharge and generating more active radicals. In the absence of catalyst, an increase in the temperature had a negative effect on NO removal due to the reduction of the predominant oxidant O3. However, when the temperature increased in the combination system, NO removal efficiency decreased below 100 °C, while increased above 100 °C, which increased dramatically at low discharge power above 150 °C.