Method for producing ammonia with reduced emissions and system thereof

A process for synthesis of ammonia from natural gas, wherein the natural gas is converted into a gas comprising hydrogen and nitrogen, which is subsequently converted into ammonia in an ammonia synthesis unit, the process comprising:

• (i) conversion of a charge of desulphurized natural gas and steam, with air, oxygen-enriched air or with oxygen, in a conversion section into a first synthesis gas, the first synthesis gas containing hydrogen, CO and CO2, and the conversion section comprising at least one furnace;
• (iiia) separation of H2 from CO and CO2 in at least part of the first synthesis gas through permeation over a first membrane, thus obtaining a first hydrogen-rich gaseous stream and a first hydrogen-depleted gaseous flow;
• (ii) subjecting the first hydrogen-depleted gaseous flow and the part of the first synthesis gas not processed in step iiia) to a shift reaction of the carbon monoxide into CO2, in a shift conversion unit, thereby obtaining a second synthesis gas, and subsequent separation of CO2 from the second synthesis gas in a CO2 removal unit, thus obtaining a CO2-depleted synthesis gas and a CO2-rich gaseous flow containing the CO2 separated from the gas;
• and
• wherein the first hydrogen-rich gaseous flow is fed as fuel to at least one furnace in the conversion section;
• and
• wherein a purge gas of the ammonia synthesis unit, containing hydrogen and methane, is treated so as to recover the hydrogen contained in the purge gas, thereby obtaining a hydrogen-rich gas and a tail gas containing methane;
• and wherein at least part of the tail gas is recycled and subjected to the step (i) of conversion of the natural gas into synthesis gas.

An ammonia production plant comprising:

• a conversion section for converting of a charge of desulphurized natural gas and steam, with oxygen-enriched air or with oxygen, into a first synthesis gas, the first synthesis gas containing hydrogen, CO and CO2, wherein the conversion section comprises at least one furnace;
• a first membrane for separating hydrogen from at least part of the first synthesis gas, thus obtaining a first hydrogen-rich gaseous stream and a first hydrogen-depleted gaseous flow,
• a treatment section for treating the first synthesis gas and including at least
• a shift conversion unit for reacting the carbon monoxide present in the first hydrogen-depleted gaseous flow and the part of the first synthesis gas not processed in the first membrane into CO2, thereby obtaining a second synthesis gas;
• and
• a carbon dioxide removal unit, downstream of the shift conversion unit, for separating the CO2 from the second synthesis gas, thereby obtaining a CO2-depleted synthesis gas;
• an ammonia synthesis unit, for converting a gas comprising hydrogen and nitrogen, into ammonia;
• a fluid communication between the first hydrogen-rich gaseous flow and at least one furnace in the conversion section;
• and wherein the plant is further configured to treat a purge gas of the ammonia synthesis unit, containing hydrogen and methane, so as to recover the hydrogen contained in the purge gas, thereby obtaining a hydrogen-rich gas and a tail gas containing methane;
• and to recycle at least part of the tail gas to the conversion section.