Process for producing sodium carbonate using ammonia and/or for producing refined sodium bicarbonate, wherein: - a low CO 2 content gas generated by a unit for producing sodium carbonate using ammonia and/or generated by a unit for producing refined sodium bicarbonate, - is enriched into a CO 2 enriched gas using a CO 2 concentration module, such as an amine-type or ammonia or PSA (Pressure Swing Adsorption) or TSA (Temperature Swing Adsorption) or cryogenic distillation type or membrane-type CO 2 concentration module, and said CO 2 -enriched gas has an increased CO 2 content of: +10% (at least) to +90% (at most) by volume on a dry gas basis relative to the CO 2 concentration of the low content gas, and - the CO 2 -enriched gas is subsequently recycled to the unit for producing sodium carbonate using ammonia or optionally to the unit for producing refined sodium bicarbonate, in order: • to produce at least one product selected from the following: sodium carbonate, or ammoniacal sodium bicarbonate, or refined sodium bicarbonate, • or to carbonate at least part of effluent from the unit for producing sodium carbonate using ammonia and/or generated by the unit for producing refined sodium bicarbonate, and wherein the CO 2 concentration module uses energy for the CO 2 concentration of the low CO 2 content gas, and: - at least part of the energy is steam with a pressure of less than 10 bar relative, generated by an apparatus of the unit for producing sodium carbonate using ammonia and/or of the unit for producing refined sodium bicarbonate, and the steam with a pressure of less than 10 bar relative is a high pressure steam which has been expanded after giving up part of its heat energy in at least one apparatus of the unit for producing sodium carbonate using ammonia or of the unit for producing refined sodium bicarbonate; - and/or at least part of energy is a condensate or a liquid effluent having a temperature of at least 35°C and not more than 110°C, generated by at least one apparatus of the unit for producing sodium carbonate using ammonia or optionally of the unit for producing refined sodium bicarbonate. - a low CO 2 content gas generated by a unit for producing sodium carbonate using ammonia and/or generated by a unit for producing refined sodium bicarbonate, - is enriched into a CO 2 enriched gas using a CO 2 concentration module, such as an amine-type or ammonia or PSA (Pressure Swing Adsorption) or TSA (Temperature Swing Adsorption) or cryogenic distillation type or membrane-type CO 2 concentration module, and said CO 2 -enriched gas has an increased CO 2 content of: +10% (at least) to +90% (at most) by volume on a dry gas basis relative to the CO 2 concentration of the low content gas, and - the CO 2 -enriched gas is subsequently recycled to the unit for producing sodium carbonate using ammonia or optionally to the unit for producing refined sodium bicarbonate, in order: • to produce at least one product selected from the following: sodium carbonate, or ammoniacal sodium bicarbonate, or refined sodium bicarbonate, • or to carbonate at least part of effluent from the unit for producing sodium carbonate using ammonia and/or generated by the unit for producing refined sodium bicarbonate, • to produce at least one product selected from the following: sodium carbonate, or ammoniacal sodium bicarbonate, or refined sodium bicarbonate, • or to carbonate at least part of effluent from the unit for producing sodium carbonate using ammonia and/or generated by the unit for producing refined sodium bicarbonate, - at least part of the energy is steam with a pressure of less than 10 bar relative, generated by an apparatus of the unit for producing sodium carbonate using ammonia and/or of the unit for producing refined sodium bicarbonate, and the steam with a pressure of less than 10 bar relative is a high pressure steam which has been expanded after giving up part of its heat energy in at least one apparatus of the unit for producing sodium carbonate using ammonia or of the unit for producing refined sodium bicarbonate; - and/or at least part of energy is a condensate or a liquid effluent having a temperature of at least 35°C and not more than 110°C, generated by at least one apparatus of the unit for producing sodium carbonate using ammonia or optionally of the unit for producing refined sodium bicarbonate.