POLLUTANTS ABATMENT, NOx AND SOx ABATEMENT
Selected catalytic reduction SCR
Involves reacting NOx with ammonia(NH3) or urea(CH4N2O) in a catalytic bed at the appropriate temperature. According with temperature windows there are several catalysts available. The most common are vanadium and titanium oxides(TiO2 and V2O5) embedded in ceramic or metallic substrate, or zeolites. The catalyst units are modular honeycomb structures. The operating temperature of the system are usually from 200°C to 500°C with the optimum between 300°C and 450°C.
Selected catalytic reduction SCR
Involves reacting NOx with ammonia(NH3) or urea(CH4N2O) in a catalytic bed at the appropriate temperature. According with temperature windows there are several catalysts available. The most common are vanadium and titanium oxides(TiO2 and V2O5) embedded in ceramic or metallic substrate, or zeolites. The catalyst units are modular honeycomb structures. The operating temperature of the system are usually from 200°C to 500°C with the optimum between 300°C and 450°C.
Selected non-catalytic reduction SNCR
Also known as thermal DeNOx, the oxides of nitrogen in the waste gases are reduced by reaction with ammonia or urea. The chemical reactions are the same of SCR system but take place at higher temperatures without the need for a catalyst. The operating temperature is in the range 900-1050°C and the optimum is around 950°C for ammonia and 1000°C for urea. For this reason in SNCR the reagent injection is closer to the furnace than SCR. 1-2 seconds are required to obtain a good efficiency from the reaction.
FILTRATION – DEDUSTING
BAG FILTERS SLEEVES
Basic principle is to select a fabric membrane which is permeable to gas but retain the dust. Initially dust is deposited both on the surface fibers and within the depth of the fabric, but as the surface layer builds up, it itself become the dominating filter medium. This “cake” of dust increase also the resistance to gas flow, so periodic cleaning of the filter are mandatory to prevent the pressure drops.
HIGH TEMPERATURE FILTER MEDIA CERAMIC CANDLES
Same principles of bag filter but the filter material is ceramic (or stone wool in some cases) that can resist to higher temperatures: this device is called candle. Further technologies combine NOx removal by the embedding of catalyst in this ceramic candles.
FILTRATION PROPOSED FILTER SIZE
According to heat exchanger models we can find 12 different filers that can be used with the same volume of the waste gasses.
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