Ammonia synthesis
First Claim
1. In the production and recovery of ammonia synthesis gas, the method which comprises:
- providing a hydrocarbon vapor stream rich in methane and substantially free of sulfur compounds;
(b) dividing said stream into a minor portion comprising less than 45% by volume of said stream and a major portion;
(c) subjecting said minor portion to catalytic steam reforming at elevated temperature and pressure, thereby producing a primary reformate;
(d) subjecting said major portion to oxidative reforming in admixture with the obtained primary reformate by catalytic reactionwith an oxygen-enriched air stream containing 30-35% oxygen by volume, thereby producing a secondary reformate comprised principally of hydrogen, nitrogen and carbon oxides and containing a minor amount of contaminants including methane and argon;
the hydrogen content of said secondary reformate being less than that providing a 3;
1 mol ratio of hydrogen to nitrogen in said secondary reformate;
(e) subjecting said secondary reformate to a water gas shift reaction whereby contained carbon monoxide is converted to carbon dioxide and thereby also producing a further quantity of hydrogen, such that the H2 /N2 mol ratio in the shift reaction product is approximately 3;
1;
(f) removing carbon dioxide from the shift reacted secondary reformate by passing the same at superatmospheric pressure through a first bed of solid particulate adsorbent selective in retention of carbon dioxide, thereby producing a hydrogen-rich product effluent freed of carbonddioxide;
(g) passing said hydrogen-rich effluent into and through a second bed of solid particulate adsorbent selective in retention of carbon monoxide and methane as opposed to hydrogen and nitrogen and recovering from said second bed a mixture of hydrogen and nitrogen in approximately 3;
1 molar ratio and containing less than 25% of impurities on a dry basis.
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Accused Products
Abstract
An ammonia synthesis gas mixture comprised of substantially pure hydrogen and nitrogen in approximately 3/1 molar ratio is obtained form two stage reforming of a methane-rich hydrocarbon charge such as natural gas. About 40% of the fresh natural gas is charged to primary steam reforming and the obtained primary reformate product, containing about 17 volume percent of unreacted methane, is mixed with the other 60% of the fresh natural gas and the mixture is subjected to oxidative reforming with enriched air containing 30 to 35 of O2, said enriched air being supplied in an amount to produce a secondary reformate containing principally hydrogen and nitrogen, accompanied by a minor amount of oxides of carbon (CO and CO2). The secondary reformate subjected to shift reaction with steam results in conversion of contained CO to CO2, thereby releasing hydrogen in an amount which together with the hydrogen previously present in said reformate obtains a H2 /N2 molar ratio of about 3/1. Carbon dioxide is removed and recovered from the shift reaction product by pressure swing adsorption in a first adsorbent bed. The other contaminants remaining are largely removed by further adsorption in second adsorbent bed in flow-communication with the first bed, the unadsorbed effluent being a syngas mixture consisting essentially of hydrogen and nitrogen in stoichiometric ratio for production of NH3.
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Citations
14 Claims
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1. In the production and recovery of ammonia synthesis gas, the method which comprises:
- providing a hydrocarbon vapor stream rich in methane and substantially free of sulfur compounds;
(b) dividing said stream into a minor portion comprising less than 45% by volume of said stream and a major portion; (c) subjecting said minor portion to catalytic steam reforming at elevated temperature and pressure, thereby producing a primary reformate; (d) subjecting said major portion to oxidative reforming in admixture with the obtained primary reformate by catalytic reaction with an oxygen-enriched air stream containing 30-35% oxygen by volume, thereby producing a secondary reformate comprised principally of hydrogen, nitrogen and carbon oxides and containing a minor amount of contaminants including methane and argon;
the hydrogen content of said secondary reformate being less than that providing a 3;
1 mol ratio of hydrogen to nitrogen in said secondary reformate;(e) subjecting said secondary reformate to a water gas shift reaction whereby contained carbon monoxide is converted to carbon dioxide and thereby also producing a further quantity of hydrogen, such that the H2 /N2 mol ratio in the shift reaction product is approximately 3;
1;(f) removing carbon dioxide from the shift reacted secondary reformate by passing the same at superatmospheric pressure through a first bed of solid particulate adsorbent selective in retention of carbon dioxide, thereby producing a hydrogen-rich product effluent freed of carbonddioxide; (g) passing said hydrogen-rich effluent into and through a second bed of solid particulate adsorbent selective in retention of carbon monoxide and methane as opposed to hydrogen and nitrogen and recovering from said second bed a mixture of hydrogen and nitrogen in approximately 3;
1 molar ratio and containing less than 25% of impurities on a dry basis. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
- providing a hydrocarbon vapor stream rich in methane and substantially free of sulfur compounds;
Specification