초록

The synthesis gas for an ammonia synthesis process is refined by treating same in an adsorption-desorption unit to remove nitrogen either during the carbon oxide removal step or in the ammonia synthesis loop.

대표청구항 ▼

In a process for refining an ammonia synthesis gas comprising the steps of: (a) subjecting a hydrocarbon raw material to a primary steam reforming reaction under pressure; (b) subjecting the resulting gas from the step (a) to a secondary steam reforming reaction by feeding air into said resulting ga

In a process for refining an ammonia synthesis gas comprising the steps of: (a) subjecting a hydrocarbon raw material to a primary steam reforming reaction under pressure; (b) subjecting the resulting gas from the step (a) to a secondary steam reforming reaction by feeding air into said resulting gas; (c) subjecting carbon monoxide in the resulting gas from the step (b) to a catalytic carbon monoxide shift conversion reaction; (d) removing carbon oxides from the gas obtained by the step (c) to produce an ammonia synthesis gas containing nitrogen and hydrogen: (e) subjecting said ammonia synthesis gas to an ammonia synthesis reaction to produce ammonia and feeding the ammonia synthesis gas that contains produced ammonia to an ammonia separator unit to separate ammonia from the remaining ammonia synthesis gas; and (f) circulating said remaining ammonia synthesis gas separated from ammonia to the step (e), the improvement which comprises: (A) in step (b), feeding said air in excess of the amount of air equivalent to the nitrogen stoichiometrically required for the synthesis of ammonia; (B) in either step (d) or step (e), treating the ammonia synthesis gas in an adsorption-desorption unit to remove excess nitrogen as well as non-ammonia-producing gaseous components and, in the case of the synthesis gas of step (e), ammonia, from the ammonia synthesis gas, the amount of nitrogen that is removed being so regulated that the hydrogen-to-nitrogen ratio in the ammonia synthesis gas is the stoichiometric ratio required for the synthesis of ammonia and wherein the treatment in said adsorption-desorption unit comprises: (i) feeding said ammonia synthesis gas to a first adsorption bed which is saturated with adsorbed nitrogen, thereby causing said first bed to adsorb water vapor, carbon dioxide, carbon monoxide, methane and argon contained in said ammonia synthesis gas and to desorb the nitrogen previously adsorbed on said first bed while allowing gases of hydrogen and nitrogen to flow out of said first bed; (ii) feeding a portion of the gas flowing out of said first bed into a succeeding downstream second adsorption bed which has undergone desorption and repressurization steps, thereby to adsorb nitrogen contained in said portion of said gas fed therein and flowing substantially pure hydrogen from said second bed; and (iii) when said succeeding downstream second adsorption bed becomes saturated with adsorbed nitrogen, switching said first bed undergoing the step (i) to undergo a subsequent desorption step, switching said succeeding downstream second bed to simultaneously undergo the step (i), and simultaneously switching a further succeeding adsorbent bed which has undergone desorption and repressurization to undergo the step (ii), thereby cyclically continuing adsorption; (iv) combining the gas discharged from said further succeeding downstream bed undergoing the step (ii) with the portion of the gas which has been discharged from said bed undergoing the step (i) but has not been sent to said further succeeding downstream bed undergoing the step (ii) whereby to form an ammonia synthesis gas, while controlling the flow rates of both said gases so that the hydrogen-to-nitrogen ratio in the ammonia synthesis gas can be adjusted to a predetermined value nearest to the stoichiometric ratio required for the synthesis of ammonia.