[ green ammonia ]
starts with the make-up gas – a mixture of hydrogen and nitrogen – generated from the upstream electrolyzer and nitrogen generation unit . This gas is then compressed in the electricity-driven multi-service reciprocating compressor to a pressure of over 300 bar . The recycle stream containing the unconverted gas is also recompressed to the same pressure .
The ammonia converter used in the NX STAMI Green Ammonia™ process is a single-bed axialflow converter with a tubular design where the feed is pre-heated using the exothermal reaction on the catalyst side to a temperature necessary for ammonia synthesis . The start-up heater is integrated into the ammonia converter . Due to the high pressure , the reactor and catalyst volume can also be reduced .
The high pressure of the synthesis loop allows for single-stage ammonia condensation using cooling water . This eliminates the need for a refrigerating compressor , thus minimizing equipment count , leading to about 25 – 30 % CAPEX savings . Over 70 % of ammonia is recovered in separator 1 , and part of the uncondensed ammonia is condensed in separator 2 .
Ammonia can be produced at a pressurized condition ( i . e ., 16 – 18 bar ) and ambient temperature to be stored in bullets , or at ambient pressure and −33 ° C to be stored in atmospheric ammonia storage , or at any intermediate pressure level as required .
Sustainable fertilizer production
Green ammonia can be used directly in the production of urea , significantly reducing the carbon footprint associated with nitrogen-based fertilizers . However , there is an alternative pathway that may be more beneficial for specific regions or applications . Ammonium nitrate and nitric acid , key components of nitrate-based fertilizers , can offer even greater potential for reducing GHG emissions , making them a feasible and attractive option for sustainable agriculture in areas with the right conditions .
Fig . 2 . A typical 3D model of an NX STAMI Green Ammonia plant
Nearly all the industrially produced nitric acid is manufactured by the high-temperature catalytic oxidation of ammonia ( the Ostwald process ) in two main steps :
• The oxidation of ammonia ( NH 3
) to form nitric oxide ( NO ), which is further oxidized to nitrogen dioxide ( NO 2
)
• The absorption of the nitrogen dioxide ( NO 2 ) in water ( H 2 O ) to form nitric acid ( HNO 3
)
Stamicarbon offers its NX STAMI Nitrates™ portfolio , which includes its proven mono- or dualpressure designs . In the mono-pressure process ( see Figure 3 ), the oxidation and absorption sections operate at the same pressure level . Different pressure levels are used for the oxidation and absorption sections in the dual-pressure process ( see Figure 4 ). The oxidation section is operated at pressures between 4 and 6 bar , while the absorption section operates between 8 and 12 bar , combining the advantages of mediumpressure combustion with the efficiency of highpressure absorption .
The main characteristic of both processes is a specific heat exchanger network downstream of ammonia oxidation . This configuration has several advantages . On the one hand , the heat exchange network has specific process conditions selected to prevent corrosion and ensure that no expensive materials are required for equipment manufacturing .
48 Hydrogen Tech World | Issue 19 | December 2024