Ammonia synthesis system and ammonia production method

A method for producing ammonia, the method comprising:

• an ammonia-containing gas production step of reacting nitrogen and hydrogen using an ammonia synthesis catalyst under a condition of a reaction pressure of 10 MPa or less to produce an ammonia-containing gas which contains ammonia gas;
• an ammonia-containing gas cooling step of cooling the ammonia-containing gas produced by the ammonia-containing gas production step;
• an ammonia separation step of separating ammonia liquefied by cooling of the ammonia-containing gas by the ammonia-containing gas cooling step from a circulated gas which contains unreacted nitrogen gas, unreacted hydrogen gas, and ammonia gas, to obtain liquefied ammonia;
• and
• an ammonia synthesizing gas supply step of supplying nitrogen gas and hydrogen gas to be added to at least one of the ammonia-containing gas and the circulated gas,
• the ammonia-containing gas production step being a step of reacting nitrogen and hydrogen using the circulated gas added thereto the nitrogen gas and hydrogen gas supplied by the ammonia synthesizing gas supply step,
• the circulated gas used in the ammonia-containing gas production step having an ammonia gas concentration of 6% by volume or more.