Process for removing oxides of sulfur, dust and mist from combustion waste gas

A process for removing oxides of sulfur, sodium sulfite, sodium sulfate, dust and mist from combustion waste gas evolved from a glass melting furnace which comprises the steps of:

• pre-scrubbing said combustion waste gas with an absorbing solution discharged from an absorption zone, whereby chiefly dust and mist particles are removed from said waste gas;
• contacting said pre-scrubbed waste gas with an absorbing solution continuously supplied with at least one alkali absorbent selected from the group consisting of sodium hydroxide, sodium carbonate and sodium sulfite such that the concentration of absorbent in said solution is 0.1-3 weight % which solution cools said waste gas to a temperature of 50.degree.-90.degree.C and humidifies said waste gas by at least saturating said gas with moisture;
• adjusting the pH of said absorbing solution discharged from said pre-scrubbing zone and the pH of said absorbing solution discharged from said contacting step to 5-7 and 6-9, respectively, in order to prevent the formation of sodium carbonate;
• passing said contacted waste gas through a glass fiber filter of a density of 150-250 kg/m.sup.3 which is maintained in a moistened condition to promote the effective filtration of dust and mist from said contacted waste gas;
• oxidizing said pH adjusted absorbing solution discharged from said pre-scrubbing zone and said pH adjusted absorbing solution discharged from said contacting step with oxygen or an oxygen-containing gas whereby sodium sulfite in said pH adjusted absorbing solutions is converted to sodium sulfate;
• purifying the oxidized absorbing solutions by adding a solution of sodium hydroxide thereby precipitating from said oxidized absorbing solution hydroxides of metal salts contained therein;
• neutralizing the oxidized absorbing solution having hydroxides of metal salts precipitated therefrom thereby precipitating crystalline sodium sulfate;
• and
• recovering said precipitated crystalline sodium sulfate.