Autothermal ammonia cracking process

Abstract

Process for the production of a product gas containing nitrogen and hydrogen from ammonia comprising the steps of non-catalytic partial oxidation of ammonia with an oxygen containing gas to a process gas containing nitrogen, water, amounts of nitrogen oxides and residual amounts of ammonia; cracking of at least a part of the residual amounts of ammonia to hydrogen and nitrogen in the process gas by contact with a nickel containing catalyst and simultaneously reducing the amounts of nitrogen oxides to nitrogen and water by reaction with a part of the hydrogen formed during cracking of the process gas by contact of the process gas with the nickel containing catalyst; and withdrawing the hydrogen and nitrogen containing product gas.

Claims

1. Process for the production of a product gas containing nitrogen and hydrogen from ammonia, comprising the steps of: non-catalytic partial oxidation of ammonia with an oxygen containing gas to a process gas containing nitrogen, water, amounts of nitrogen oxides and residual amounts of ammonia; cracking of at least a part of the residual amounts of ammonia to hydrogen and nitrogen in the process gas by contact with a nickel containing catalyst and simultaneously reducing the amounts of nitrogen oxides to nitrogen and water by reaction with a part of the hydrogen formed during cracking of the process gas by contact of the process gas with the nickel containing catalyst; and withdrawing the hydrogen and nitrogen containing product gas.

2. The process of claim 1, wherein the amounts of nitrogen oxides generated in the non-catalytic partial oxidation step are reduced by more than 80%, and up to 100% as limited by thermodynamic equilibrium, through reaction of the nitrogen oxides with hydrogen by contact with the nickel containing catalyst.

3. The process of claim 1, wherein the non-catalytic partial oxidation of ammonia is performed by burning the ammonia in gaseous form in a burner with under-stoichiometric amounts of oxygen containing gas.

4. The process of claim 1, wherein the non-catalytic partial oxidation step and the cracking step are performed in a single reactor vessel.

5. The process of claim 4, wherein the single reactor is an autothermal cracking reactor.

6. The process of claim 1, wherein the oxygen to ammonia feed flow rate to the non-catalytic partial oxidation step is adjusted to result in an equilibrium temperature of the product gas between 700 and 1100° C. after contact with the nickel containing catalyst.

7. The process of claim 1, wherein the content of oxygen in the oxygen containing gas is varied corresponding to lambda-values between λ=0.18 and λ=0.30, where lambda is the ratio between the actual oxygen feed flow and that required for full stoichiometric combustion of the ammonia into nitrogen and water.

8. The process of claim 1, wherein the oxygen containing gas contains between 10 and 100 vol % oxygen.

9. The process of claim 1, comprising the further step of converting CO.sub.2 to methane in a methanation reactor by hydrogen obtained from the ammonia cracking step.

10. The process of claim 1, comprising the further step of separating uncracked ammonia further contained in the product gas.

11. The process of claim 8, wherein the residual ammonia is separated from the product gas by a water wash.

12. The process of claim 10, wherein the separated ammonia is recovered in an ammonia recovery step and recycled to the non-catalytic partial oxidation step.

13. The process of claim 10, comprising addition of NaOH to the ammonia recovery step.

14. The process of claim 1, comprising the further step of adjusting the hydrogen to nitrogen mole ratio of the product gas in a product gas adjustment unit.

15. The process of claim 3, comprising addition of a hydrogen source to the ammonia feed or directly to the burner.

16. The process of claim 15, wherein the hydrogen source is the ammonia cracking product gas, or product gas adjusted for ammonia content and/or hydrogen to nitrogen ratio.

17. The process of claim 15, wherein the hydrogen source is a utility supply or coming from another process.

18. The process of claim 1, comprising a CO.sub.2 removal wash of the oxygen containing gas.

Description

(1) A particular embodiment of the process according to the invention is shown in the drawings, wherein

(2) FIG. 1, is a schematic diagram of the ammonia cracking process according to a particular embodiment of the invention including an autothermal ammonia cracking reactor, an ammonia separation step, product gas adjustment and ammonia recovery.

(3) FIG. 2 shows the single reactor vessel of the present invention configured as an autothermal cracking reactor with a burner at the inlet side of the reactor vessel and a catalyst bed downstream of the burner.

EXAMPLE

(4) Process gas flows and compositions for the ammonia cracking process corresponding to a lambda value of λ=0.21 and a resulting equilibrium temperature of the product gas of 800° C. after contact with the nickel containing catalyst in the autothermal ammonia cracking reactor are shown in Table 1 below. The stream numbers refer to FIG. 1.

(5) TABLE-US-00001 TABLE 1 Stream no. 3 4 5 7 8 9 1 2 Reactor Wash Product 6 Recycle Light Stripped Description Ammonia Air outlet water gas Condensate ammonia gases condensate Flow 263200 205100 688800 68880 602700 155000 2024 145 152900 [Nm.sup.3/h] Composition H.sub.2 0.00 0.00 45.01 0.00 51.44 0.03 0.12 26.99 0.00 [mole %] N.sub.2 0.00 76.59 41.89 0.00 47.88 0.02 0.10 15.27 0.00 O.sub.2 0.00 20.60 0.00 0.00 0.00 0.00 0.00 0.00 0.00 H.sub.2O 0.00 1.85 12.50 100.00 0.35 98.61 4.00 0.02 99.96 NH.sub.3 100.00 0.00 0.31 0.00 0.02 1.31 95.78 57.48 0.00 Ar 0.00 0.92 0.27 0.00 0.31 0.00 0.00 0.23 0.00 CO.sub.2 0.00 0.03 0.01 0.00 0.00 0.04 0.00 0.00 0.04 NO.sub.x 0.00 0.00 3.3E−13 0.00 3.8E−13 0.00 0.00 0.00 0.00