Operation method of urea production plant including multiple systems

An operation method of a urea production plant including multiple systems, at a time of producing urea by using a urea synthesis plant that includes:

• an ammonia synthesis facility including a reforming device having a reforming furnace that reforms natural gas to hydrogen (H2) and carbon monoxide (CO) by using water vapor, a CO-shift converter that converts carbon monoxide (CO) in reformed gas to carbon dioxide, a carbon-dioxide removal device that removes obtained carbon dioxide (CO2) in the reformed gas, a synthesis gas compressor that compresses synthesis material gas containing hydrogen and nitrogen, from which carbon dioxide has been removed by the carbon-dioxide removal device, and an ammonia synthesis reactor that synthesizes ammonia from compressed synthesis material gas;
• a liquefied ammonia storage facility that branches ammonia obtained by the ammonia synthesis reactor from an ammonia supply line for supplying ammonia to a urea synthesis unit and stores a part of synthesized ammonia in a liquefied state;
• a carbon-dioxide recovery facility that recovers carbon dioxide in fuel flue gas from the reforming furnace;
• and a carbon-dioxide supply line for supplying the removed carbon dioxide (removed CO2) and the recovered carbon dioxide (recovered CO2) to a urea synthesis unit, comprising:
• providing at least two systems of the urea synthesis plants;
• storing a predetermined amount of obtained ammonia in a liquefied state in the liquefied ammonia storage facility;
• when a trouble occurs in the ammonia synthesis facility of one of the systems and production of ammonia is stopped,
• temporarily supplying carbon dioxide (recovered CO2) recovered by the other system to a CO2 supply line of the shut down system via an emergency CO2 supply line in order to supply the temporarily supplied CO2 to the urea synthesis unit;
• supplying a predetermined amount of liquefied ammonium stored in the shut down system from an ammonia supply line to the urea synthesis unit;
• producing urea by using the temporarily supplied CO2 and stored liquefied ammonia even in the shut down system, thereby enabling to perform a continuous operation when the ammonia synthesis facility is shut down.