With the increasing concern for the environment, stringency of legislation and industry's awareness of its own environmental responsibility, the demand for the reduction of emission levels of nitrogen oxides is becoming increasingly urgent.
Shell has developed a low temperature catalytic deNOx system for deep removal of nitrogen oxides, which includes a low-pressure-drop reactor, This process is able to achieve over 90% removal of process is able to achieve over 90% removal of nitrogen oxides and therefore can be expected to meet legislation requirements for the coming years.
The development of a low-temperature catalyst makes it possible to operate at temperatures as low as 120 degrees C, compared to 300–400 degrees C for the conventional honeycomb and plate-type catalysts. This allows an add-on construction, which is most often a more economical solution than the retrofits in the hot section required with conventional deNOx catalysts.
The Lateral Flow Reactor (LFR), which is used for dust-free flue gas applications, and the Parallel Passage Reactor (PPR) for dust-containing flue gas Passage Reactor (PPR) for dust-containing flue gas applications, have been developed to work with pressure drops below 10 mbar. pressure drops below 10 mbar
Introduction
More and more, industry will be faced with stronger emission legislations, due to the growing concern for the environment. Among the components subject to restriction are nitrogen oxides.
The main nitrogen oxides (NOx) are nitric oxide (NO), nitrogen dioxide (NO2) and nitrous oxide (N2O). Nitrogen oxides contribute to acid precipitation (NO and NO2), to smog formation (NO precipitation (NO and NO2), to smog formation (NO and NO2), to global warming (N2O) and to the depletion of the ozone layer (N2O).
Due to the effects of nitrogen oxides on the environment and the increasing awareness on the part of both government and industry of the need to protect the environment, industrial engineers to an protect the environment, industrial engineers to an ever-increasing extent will have to concern themselves with nitrogen oxide abatement measures.
Sources of man-made nitrogen oxides can be divided into mobile sources (automotive) and stationary sources: burning of biomass, industrial (furnaces, turbines) and power generation, An approximate distribution of the various sources of NOx emission is presented in Figure 1. Typical emission levels from industrial sources are 50 to 1 000 cm/m NOx, with special cases within the chemical industry containing up to 10 000 cm/m NOx, mainly as NO2.
The legislation on existing and future NOx emissions from stationary sources varies considerably per country. Figure 2 shows the Dutch emission limits currently operative for the combustion of gaseous and liquid fuels in process furnaces. The limit imposed for gaseous fuel is 30 cm/m, which is very low. in a few areas, like Southern California, even more strict limits are foreseen: as low as 10 cm/m.
NITROGEN OXIDES CONTROL MEASURES
In combustion processes, nitrogen oxides can be formed from nitrogen compounds in the fuel (fuel NOx) or from nitrogen present in the air in the combustion zone (thermal NOx).
The emission of nitrogen oxides can be reduced using primary measures, These are mainly aimed at primary measures, These are mainly aimed at prevention of (thermal) NOx formation by lowering prevention of (thermal) NOx formation by lowering the flame temperature or use of lower local oxygen content.
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