Ammonia synthesis system and ammonia production method

An ammonia synthesis system, comprising:

• an ammonia synthesis reaction unit including one or two or more ammonia synthesis reactor(s) that synthesize ammonia from nitrogen and hydrogen using an ammonia synthesis catalyst under a condition of a reaction pressure of 10 MPa or less;
• an ammonia cooler that cools an ammonia-containing gas which is discharged from the ammonia synthesis reaction unit and which contains ammonia gas synthesized by the ammonia synthesis reaction unit;
• a gas-liquid separator that separates liquefied ammonia produced from the ammonia-containing gas cooled by the ammonia cooler from a circulated gas which contains unreacted nitrogen gas, unreacted hydrogen gas, and ammonia gas;
• and
• an ammonia synthesizing gas supplying unit that supplies nitrogen gas and hydrogen gas to be added to at least one of the ammonia-containing gas and the circulated gas,
• the circulated gas having added thereto the nitrogen gas and hydrogen gas supplied by the ammonia synthesizing gas supplying unit being supplied to the ammonia synthesis reaction unit,
• the circulated gas supplied to the ammonia synthesis reaction unit having an ammonia gas concentration of 6% by volume or more.