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Combination of LNT and SCR for NOx reduction in passenger car applications

Maunula T.

Combustion Engines

2014

R. 53, nr 2

60--67

The removal of NOx and particulate emissions in light-duty diesel vehicles will require the use of aftertreatment methods like Diesel Particulate Filters (DPF) and Selective Catalytic Reduction (SCR) with urea and Lean NOx Trap (LNT) (Euro 6 and beyond). A new concept is the combination of LNT + SCR, which enables on-board synthesis of ammonia (NH3), which reacts with NOx on the SCR catalyst. The main application for this kind system will be lighter passenger cars, where LNTs may be used instead of full urea-SCR system. That particular combinatory system was investigated by developing platinum (Pt) and rhodium (Rh) containing LNTs and SCR catalysts in this study. In the use conditions, the maximum temperature may reach temperatures up to 800°C and NOx reduction reactions should proceed without NO2 assistance in the SCR position after LNT and DPF. PtRh/LNT with the total loadings of 85 g/cft (2.8 g/L) and higher resulted in a high NOx efficiency above 80–90% with a broad operation window in the laboratory simulations. In the experimental conditions, a higher NH3 concentration after LNT was essential to simulate well the operation of SCR catalysts. The developed Cu-SCR catalyst showed a high hydrothermal durability up to the ageing temperature of 800°C and a wide operation window without the NO2 assistance (NO only in feed). Fe-SCR and V-SCR catalysts were more dependent on NO2. A studied concept had an air injection after LNT to keep SCR condition always in lean side, where the SCR reaction was promoted by oxygen resulting in high reduction selectivity to nitrogen (N2) without NH3 emissions. The simulations in reaction conditions and system design resulted in the proposals for the optimal design and main reaction mechanism in DOC + DPF + LNT + SCR systems.

Safety of nuclear power

Strupczewski A.

Nukleonika

2005

Vol. 50,suppl.3

59-66

The main questions related to nuclear power development concern effects of small radiation doses typical for the operation of nuclear power plants (NPPs) and hazards of NPP accidents. The last decade has brought many results of large scale epidemiological studies indicating that there are no detrimental effects of low radiation doses. On the contrary, many results indicate that among the people receiving increased radiation doses the frequency of cancer mortality is reduced. The review shows that such results are obtained in the studies of people living in high background radiation areas, of workers exposed to ionizing radiation and of patients exposed to radiation for diagnostic purposes. The latest studies in molecular biology suggest an explanation for possible beneficial effects of low radiation doses. This is reflected in the statements of several scientific bodies and international organizations, although the official regulations remain unchanged. The other important issue is the safety of NPPs in case of accidents. Reasons for the Chernobyl accident are shown not to be applicable to the reactors planned for Poland and the effects of Chernobyl are shown to be much smaller than feared in original estimates after the accident. Polish NPPs will satisfy the requirements of EU utilities and will provide safety for the population even in case of hypothetical severe accidents. Nevertheless, discussion with antinuclear organizations must be expected, although the recent examples of changing attitudes of leading ecological authorities show that nuclear power is gaining recognition as a clean and environmentally friendly source of energy.