Method for removing ammonia from non-condensable gases of a pulp mill

A method for removing ammonia (NH3) from a gas produced in a pulp mill, the method comprising:

• producing raw non-condensable gas comprising ammonia (NH3) in the pulp mill,
• transferring at least some of the raw non-condensable gas to a scrubber containing aqueous scrubbing solution,
• in the scrubber, contacting the raw non-condensable gas with the scrubbing solution, to react the ammonia (NH3) of the raw non-condensable gas with the scrubbing solution to produce clean non-condensable gas and foul condensate comprising ammonium (NH4+),
• adding a compound capable of decreasing a pH of the scrubbing solution to the scrubbing solution,
• measuring a pH of the scrubbing solution,
• controlling a pH of the scrubbing solution based on the measured pH value by controlling a flow of the compound capable of decreasing a pH of the scrubbing solution to the scrubber,
• in the scrubber, spraying the scrubbing solution to form droplets of the scrubbing solution,
• contacting the non-condensable gas comprising ammonia with the droplets of the scrubbing solution,
• conveying the foul condensate from the scrubber to a stripper,
• stripping the foul condensate to produce clean condensate,
• conveying the clean condensate to a pulp bleaching area,
• bleaching pulp in the pulp bleaching area using the clean condensate to produce bleached pulp and bleaching effluent,
• conveying the bleaching effluent to a wastewater treatment area, and
• purifying water in the wastewater treatment area using the bleaching effluent,
• wherein:
• the bleaching effluent comprises ammonium (NH4+),
• the compound capable of decreasing a pH of the scrubbing solution comprises sulfuric acid (H2SO4) and
• a pH of the scrubbing solution is from 4.5 to 5.5.