NOVELTY - Catalytic production of ammonia from nitrogen-hydrogen gas mixture involves forming synthesis gas from natural gas and oxygen-rich gas in an autothermal reactor, catalytic conversion of CO into H2, removal of CO, CO2 and methane and supplying the obtained nN2-H2 mixture to catalytic synthesis of NH3.    USE - Specifically the ammonia produced is at least partially converted into urea by reaction with carbon dioxide, especially using CO2 recovered from the gas purification stage of the process (all claimed).    ADVANTAGE - A pure N2-H2 mixture is obtained. NH3 and urea are obtained with low energy consumption. The amount of natural gas used is ca. 27.3 GJ per tonne of ammonia and ca. 19 GJ per tonne of urea, i.e. markedly lower than in conventional processes. Use of an (expensive) steam reforming stage is avoided. The N2 in the N2-H2 mixture can be added as liquid nitrogen in the scrubbing stage. Methane can be separated in the scrubbing stage and recycled to the autothermal reformer, allowing the reformer to be operated at relatively low temperature (ca. 950 degrees C). A CO-rich stream obtained in the scrubbing stage can be recycled to the CO conversion, allowing use of robust, inexpensive iron conversion catalysts rather than copper catalysts. The plant can have a modular construction and occupies a relatively low surface area.    DETAILED DESCRIPTION - Catalytic production of ammonia from a nitrogen-hydrogen gas mixture involves:    (a) supplying natural gas and oxygen-rich gas to an autothermal reformer at 900-1200 degrees C and 40-100 bars in presence of a cracking catalyst, to give crude synthesis gas (I) containing (by volume, on a dry basis) 55-75% H2, 15-30% carbon monoxide and 15-30% carbon dioxide, the H2 to CO volume ratio being 1.6-4;    (b) withdrawing (I) from the reformer, cooling and subjecting (I) to catalytic conversion of CO into H2, giving converted synthesis gas (II) containing (by volume, on a dry basis) at least 55% H2 and at most 8% CO;    (c) subjecting (II) to multi-stage purification to remove CO2, CO and methane; and    (d) supplying the obtained nN2-H2 mixture to the catalytic synthesis of NH3.    DESCRIPTION OF DRAWING(S) - The figure shows a flow diagram of an embodiment of the process.    Natural gas supply (1)    Steam supply (1a)    Natural gas pretreatment (e.g. desulfurization) stage (40)    Burner (2)    Autothermal reformer (3)    Oxygen-rich gas supply (4)    Fluidized bed of cracking catalyst (3a)    Crude synthesis gas outlet (7)    Heat exchanger (8)    Catalytic converter (10)    Converted synthesis gas outlet (11)    Indirect cooler (12)    Gas scrubber, using methanol at -20 degrees C (14)    Carbon dioxide outlet (20)    Urea synthesis (21)    Second gas scrubber, using liquid nitrogen (23)    Carbon monoxide-rich gas outlet (41)    Methane-rich gas outlet (42)    Synthesis gas (hydrogen-nitrogen molar ratio 1:3) outlet (24)    Indirect heat exchanger (45)    Compressor(25) Indirectly cooled ammonia synthesis reactor (46)    Adiabatic ammonia synthesis reactor (26)