EP0000993A1 — Ammonia production process

Claim 1

Independent Claim 185 words

An ammonia production process which comprises (a) primary catalytically reforming at superatmospheric pressure a hydrocarbon feedstock with steam to give a gas containing carbon oxides, hydrogen and methane; (b) secondary catalytically reforming the gas from step (a) by introducing air and brining the mixture towards equilibrium, whereby to produce a gas containing nitrogen, carbon oxides, hydrogen and a decreased quantity of methane; (c) converting carbon monoxide catalytically with steam to carbon dioxide and hydrogen; (d) removing carbon oxides to give a nitrogen-hydrogen ammonia synthesis gas; (e) reacting the synthesis gas to produce ammonia and recovering ammonia from the reacted gas; and (f) discaxding non-reactive gases present in the synthesis gas; and is characterised by: (i) operating step (a) in conditions of steam-to-carbon ratio, pressure and temperature to produce a gas containing at least 10% v/v methane and using in step (b) a quantity of air in excess of what would introduce 1 molecule of nitrogen per 3 molecules of hydrogen; and (ii) treating synthesis gas after reaction to synthesise ammonia to separate a stream enriched in hydrogen and returning the enriched stream to the synthesis.

Claim 2

Dependent Claim 185 words

An ammonia production process which comprises (a) primary catalytically reforming at superatmospheric pressure a hydrocarbon feedstock with steam to give a gas containing carbon oxides, hydrogen and methane; (b) secondary catalytically reforming the gas from step (a) by introducing air and brining the mixture towards equilibrium, whereby to produce a gas containing nitrogen, carbon oxides, hydrogen and a decreased quantity of methane; (c) converting carbon monoxide catalytically with steam to carbon dioxide and hydrogen; (d) removing carbon oxides to give a nitrogen-hydrogen ammonia synthesis gas; (e) reacting the synthesis gas to produce ammonia and recovering ammonia from the reacted gas; and (f) discaxding non-reactive gases present in the synthesis gas; and is characterised by: (i) operating step (a) in conditions of steam-to-carbon ratio, pressure and temperature to produce a gas containing at least 10% v/v methane and using in step (b) a quantity of air in excess of what would introduce 1 molecule of nitrogen per 3 molecules of hydrogen; and (ii) treating synthesis gas after reaction to synthesise ammonia to separate a stream enriched in hydrogen and returning the enriched stream to the synthesis.

Claim 3

Dependent Claim 42 words

A process according to claim 1 in which in step (a) the steam to carbon ratio is in the range 2.5 - 3.5, the outlet pressure is in the range 30-120 bar abs and the outlet temperature is in the range 750-850°C.

Claim 4

Dependent Claim 61 words

A process according to claim 1 or claim 2 in which in steps (b) and (i) the outlet temperature is in the range 950-1050 0 C, the outlet methane content is in the range 0.2 - 10% v/v on a dry basis and the ratio of hydrogen equivalent to nitrogen in the outlet gas is in the range 2.2 to 2.7.

Claim 5

Dependent Claim 49 words

A process according to any one of the preceding claims in which the pressure in step (a) and subsequent steps is at least 40 bar abs and step (c) includes a low temperature shift stage at a steam to dry gas molar ratio in the range 0.1 to 0.3.

Claim 6

Dependent Claim 66 words

A process according to any one of the preceding claims in which the pressure in step (a) and subsequent steps is at least 40 bar abs and step (d) includes carbon dioxide removal in two stages, in the first of which there is used as absorbent an amine regenerable without heating and in the second of which there is used an absorbent requiring heat in regeneration.

Claim 7

Dependent Claim 26 words

A process according to any one of the preceding claims in which for step (e) the synthesis gas pressure is increased by no more than 50%.

Claim 8

Dependent Claim 75 words

A process according to any one of the preceding claims in which in step (e) the ammonia synthesis catalyst contains iron, promoting compounds and cobalt, the cobalt content being 1-20% w/w calculated as 0 03 0 4 on the total oxidic composition from which the catalyst is made and in which the iron oxide is assumed to be all Fe 3 0 4 , and the synthesis catalyst outlet temperature is in the range 350-430°C.

Claim 9

Dependent Claim 26 words

A process according to any one of the preceding claims in which in step (e) ammonia is recovered from reacted synthesis gas by absorption in water.

Claim 10

Dependent Claim 87 words

A process according to any one of the preceding claims in which step (e) is carried out by pumping the synthesis gas in a loop coomprising the synthesis catalyst, an ammonia separator and a circulator and in steps (f) and (ii) a part stream of synthesis gas after reaction to synthesise ammonia and after recovery of ammonia therefrom is withdrawn from the gas leaving the circulator and treated to separate a gas enriched in hydrogen and the hydrogen-enriched gas is returned to the inlet of the circulator.

Claim 11

Dependent Claim 180 words

A process according to any one of the preceding claims in which in steps (f) and (ii) a part stream of gas is treated by: a) subjecting it in a first indirect cooling stage to heat exchange with one or more cool streams to be described; b) cooling the product of stage a) by expansion in an engine; c) subjecting the engine effluent in a second indirect cooling stage to heat exchaage with one or more cold streams to be described, whereby to decrease its temperature to below the dewpoint of nitrogen; d) separating a liquid phase containing nitrogen, methane and possibly noble elements; e) passing the hydrogen-enriched gaseous phase from stage d) into heat exchange in stage c) as one of the cold streams; f) passing the hydrogen-depleted liquid phase from stage d) into heat exchange in stage c) as one of the said cold streams; g) passing the streams thus warmed in stages e) and f) into heat excharrge in stage a) as the said cool streams; h) passing the hydrogen-enriched gaseous phase back to the synthesis loop.

Claim 12

Dependent Claim 114 words

An ammonia production plant comprising in sequence a primary steam-hydrocarbon reformer, a secondary reformer, a shift reactor, a carbon oxides removal system, an ammonia synthesis reactor and an ammonia recovery system, characterised by: (i) having primary reformer constructed to operate in conditions of steam-to-carbon ratio, pressure and temperature to produce a gas containing at least 1096 v/v of methane; (ii) having compressor means to supply to the secondary reformer air in excess of what would introduce 1 molecule of nitrogen per 3 molecules of hydrogen; and (iii) having means to treat synthesis gas after reaction to synthesise ammonia to separate a stream enriched in hydrogen and to return the enriched stream to the synthesis.

Claim 13

Dependent Claim 114 words

An ammonia production plant comprising in sequence a primary steam-hydrocarbon reformer, a secondary reformer, a shift reactor, a carbon oxides removal system, an ammonia synthesis reactor and an ammonia recovery system, characterised by: (i) having primary reformer constructed to operate in conditions of steam-to-carbon ratio, pressure and temperature to produce a gas containing at least 1096 v/v of methane; (ii) having compressor means to supply to the secondary reformer air in excess of what would introduce 1 molecule of nitrogen per 3 molecules of hydrogen; and (iii) having means to treat synthesis gas after reaction to synthesise ammonia to separate a stream enriched in hydrogen and to return the enriched stream to the synthesis.

Claim 14

Dependent Claim 22 words

A plant according to claim 11 and having means corresponding to the process features of any one of claims 2 to 10.

Ammonia production process

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