Out-of-furnace ammonia desulphurization ammonia dosing system

The invention relates to an out-of-furnace ammonia desulphurization ammonia dosing system which is characterized in that an ammonia dosing spot is arranged on a pipeline between a desulfurizing tower and an inlet of a circulating pump, and ammonia dosage is automatically adjusted with the content of sulfur dioxide in untreated flue gas after improvement. It proves through tests that the improved system operates stably and reliably, content of SO2 in purified flue gas is controlled steadily and can completely meet the new environmental protection requirement (being less than or equal to 200 mg/Nm ). By the system, automatic adjustment of ammonia dosing is realized, ammonia escape is reduced, tailing phenomena at the outlet of a chimney is greatly minimized, and utilization rate of liquid ammonia is increased by 10%.