A method of reducing an amount of ammonia in a CO2 lean flue gas stream resulting from an ammonia-based CO 2 capture system, the method comprising: introducing a cooled flue gas stream having a temperature below ambient temperature to an absorbing system comprising at least a first absorber, wherein the absorbing system operates at a temperature between 0° and 20° Celsius; contacting the flue gas stream with an ammoniated slurry or solution within the first absorber, wherein the ammoniated slurry or solution removes carbon dioxide (CO 2) from the flue gas stream thereby forming an ammonia-containing flue gas stream; and introducing at least a portion of the ammonia-containing flue gas stream from the first absorber to a wash vessel, the wash vessel having first and second absorption stages (181a, 181b) to absorb ammonia from the ammonia-containing flue gas stream thereby reducing an amount of ammonia in a flue gas stream exiting the wash vessel, each of the first and second absorption stages (181 a, 181 b) including a spray head system, a mass transfer device located beneath the spray head system and a liquid delivery path for transporting liquid to the spray head system; introducing a first liquid at the top of the first absorption stage (181 a) to the liquid delivery path of the first absorption stage such that the first liquid flows in a direction countercurrent to the ammonia-containing flue gas stream to contact the ammonia-containing flue gas stream and the mass transfer devices of the first and second absorption stages (181a, 181b); introducing a second liquid at the top of the second absorption stage to the liquid delivery path of the second absorption stage such that the second liquid flows in a direction countercurrent to the ammonia-containing flue gas stream to contact the ammonia-containing flue gas stream and the mass transfer device of the second absorption stage, whereby the first and second liquids (187a, 187b) absorb ammonia from the ammonia-containing flue gas stream to form an ammonia-rich liquid; collecting and removing the ammonia-rich liquid from the bottom of the wash vessel; cooling a first portion of the ammonia-rich liquid in a heat exchanger and recycling the first portion to the second absorption stage as liquid; sending a second portion of the ammonia-rich liquid to a stripping column and regenerating the second portion of the ammonia-rich liquid in the stripping column and introducing the regenerated second portion as liquid in the first absorption stage. introducing a cooled flue gas stream having a temperature below ambient temperature to an absorbing system comprising at least a first absorber, wherein the absorbing system operates at a temperature between 0° and 20° Celsius; contacting the flue gas stream with an ammoniated slurry or solution within the first absorber, wherein the ammoniated slurry or solution removes carbon dioxide (CO 2) from the flue gas stream thereby forming an ammonia-containing flue gas stream; and introducing at least a portion of the ammonia-containing flue gas stream from the first absorber to a wash vessel, the wash vessel having first and second absorption stages (181a, 181b) to absorb ammonia from the ammonia-containing flue gas stream thereby reducing an amount of ammonia in a flue gas stream exiting the wash vessel, each of the first and second absorption stages (181 a, 181 b) including a spray head system, a mass transfer device located beneath the spray head system and a liquid delivery path for transporting liquid to the spray head system; introducing a first liquid at the top of the first absorption stage (181 a) to the liquid delivery path of the first absorption stage such that the first liquid flows in a direction countercurrent to the ammonia-containing flue gas stream to contact the ammonia-containing flue gas stream and the mass transfer devices of the first and second absorption stages (181a, 181b); introducing a second liquid at the top of the second absorption stage to the liquid delivery path of the second absorption stage such that the second liquid flows in a direction countercurrent to the ammonia-containing flue gas stream to contact the ammonia-containing flue gas stream and the mass transfer device of the second absorption stage, whereby the first and second liquids (187a, 187b) absorb ammonia from the ammonia-containing flue gas stream to form an ammonia-rich liquid; collecting and removing the ammonia-rich liquid from the bottom of the wash vessel; cooling a first portion of the ammonia-rich liquid in a heat exchanger and recycling the first portion to the second absorption stage as liquid; sending a second portion of the ammonia-rich liquid to a stripping column and regenerating the second portion of the ammonia-rich liquid in the stripping column and introducing the regenerated second portion as liquid in the first absorption stage.