Method for the preparation of ammonia synthesis gas
Method for the preparation of ammonia synthesis gas based on a combination of autothermal reforming and electrolysis of water.
1. Method for the preparation of ammonia synthesis gas comprising the steps of:
(a) providing a hydrocarbon feed stock;
(b) preparing a separate hydrogen stream and a separate oxygen stream by electrolysis of water;
(c) providing process air for use in autothermal reforming by enriching atmospheric air with the oxygen stream from step (b);
(d) autothermal reforming at least a part of the hydrocarbon feed stock with the oxygen enriched process air to a process gas stream comprising hydrogen, nitrogen, carbon monoxide and carbon dioxide;
(e) treating the process gas stream obtained in the autothermal reforming step (d) in one or more water gas shift reactions;
(f) removing the carbon dioxide from the water gas shift treated process gas stream;
(g) purifying the process gas stream from step (f); and
(h) obtaining the ammonia synthesis gas, wherein at least a part of the hydrogen stream obtained from the electrolysis of water in step (b) is added to the process gas stream after step (g) in an amount to provide a molar ratio of the hydrogen to the nitrogen of 2.7-3.3 in the ammonia synthesis gas, and wherein the electrolysis of water in step (b) is performed at an increased pressure relative to the pressure of the process gas stream.
2. The method of claim 1 , comprising the further step of steam reforming a part of the hydrocarbon feed stock in indirect heat transfer relationship with the process stream leaving the autothermal reforming step (d) to obtain a heat exchange steam reformed gas stream, and mixing the heat exchange steam reformed process gas stream with autothermal reformed process gas stream upstream step (e).
3. The method of claim 1 , comprising the further step of heat exchange steam reforming the hydrocarbon feed stock in indirect heat transfer relationship with the process stream leaving the autothermal reforming step (d) and passing the heat exchanged steam reformed hydrocarbon feed stock to step (d).
4. The method of claim 1 , wherein the process air contains between 22 and 45 mole% oxygen.
5. The method according to claim 1 , wherein the purifying of the process gas stream in step (f) is performed by methanation.
6. The method according to claim 1 , wherein the purifying of the process gas stream in step (f) is performed cryogenic.
7. The method according to claim 1 , wherein the electrolysis of water is powered by renewable energy.