During high temperature processes generating SO2-rich gases thermal or fuel-bound NOx is produced. Although the BAT document of ESA/Fertilizers Europe mentions NOx emissions above 200 mg/Nm³ effluent gas for smelter plants, information how these are handled is rare.
How are NOx eliminated from the effluent gas? Is there a catalytic/non-catalytic reduction step for the raw gas or a final treatment of the effluent gas available? Which techniques are used to avoid/reduce the contamination of the produced acid with dissolved NOx?
Absorption Towers that are fitted with candle type mist eliminators have an effective method for trapping and diverting these mist droplets containing the absorbed NOx. Standing candles can be easily converted to segregate the drips by Mani folding together the existing candle tube sheet drains and routing to outside the tower.
Many techniques are known for destroying NOx in gases. Most are inefficient and/or expensive, both in capital and operating cost. Only a few will be discussed here: −
1. Absorption in scrubbing solutions –
2. Selective non-catalytic reduction (SNCR)
3. Selective catalytic reduction (SCR)
More detail please find attached articles.
Thank you for your response! Can you mention the source of the figure you attached?
The trapping of NOx in demisters means that these are absorbed in sulphuric acid and may either end in the product acid or that these are released somewhere else. According to the Haldor Topsoe document most acid plants use a catalytic reduction for the NOx elimination. Is this the case?
Useful link and paper: https://www.topsoe.com/sites/default/files/advances_in_nox_removal_in_smelter_acid_plants.ashx__0.pdf
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