Waste gas de-nitrification by scrubbing with dithionite soln. - and electrochemical regeneration, useful for small or medium scale operations

摘要

Denitrification of waste gases is carried out by scrubbing with a dithionite soln. (I) and electrochemical regeneration of spent (I) contg. H sulphite. Pref. spent (I) is regenerated in the cathode compartment of an electrolytic cell, pref. a diaphragm cell. Before or after scrubbving with (I), the gas is scrubbed with a soln. (II) of a transition metal salt, pref. an aq. acidic Fe++ salt soln. (IIA), which gives a (Fe(H2O)5NO)++ soln., from which a nitrate/nitrite mixt., NaNO3 or NHO3 is recovered by alkaline oxidn. (using Ca(OH)2 or aq. NaOH soln.). Scrubbing with (I) and (IIA) is carried out in a single 2-stage scrubber. The Fe+++ (Fe(OH)3 sludge) produced by alkaline oxidn. is reduced to Fe++ with dithionite, which is regenerated electrochemically. Part of the spent (I) can be sepd. and worked up to SO2, H2SO4 and/or S and the rest of (I) regenerated. USE/ADVANTAGE - The process avoids rapid consumption of expensive chemicals and is suitable for small and medium scale plants not justifying the use of the denitrification plants used at large power stations. It adapts rapidly and easily to changes in the waste gas. It is very economical, requires little equipment and gives by-prods. which are not harmful to the environment or which can be sold.