Ammonia synthesis process

Claim 1

A process for the production of ammonia comprising (i) forming ammonia synthesis gas by (a) reacting a volatile hydrocarbon feedstock with steam and a gas containing oxygen and nitrogen at a pressure in the range 25 to 50 bar abs. using process conditions and reactant proportions so as to produce a crude gas containing hydrogen, unreacted steam, and medium boiling gas containing carbon monoxide, and nitrogen in an excess of that required in the ammonia synthesis gas, and in which the molar ratio of hydrogen plus carbon monoxide to nitrogen and other medium boiling gas, if any, is in the range 1.25 to 2.50, and the content of carbon monoxide plus carbon dioxide, if any, is in the range 10 to 25% v/v on a dry basis; (b) converting carbon monoxide to carbon dioxide by subjecting the crude gas to a single stage of catalytic shift reaction to produce a raw gas having a carbon monoxide content of less than 0.5% v/v on a dry basis and in which at least 90% of the total medium boiling gas is nitrogen, said shift reaction being controlled at 230° to 280° C. and operated in indirect heat exchange with a coolant, thereby producing a stream of heated coolant, and at least some of the steam employed in the step (a) being introduced by contacting the feedstock with a stream of heated water, comprising hot water or a mixture of hot water and steam, said stream of heated water comprising said heated coolant, where the coolant is water, or being obtained by indirect heat exchange with the stream of heated coolant; (c) removing carbon dioxide and medium boiling gas, including the excess of nitrogen, from the raw gas by a pressure swing adsorption process, to give a product gas; and (d) methanating the product gas to convert residual carbon oxides therein to methane; and (ii) passing the ammonia synthesis gas over an ammonia synthesis catalyst to produce a reacted gas stream containing synthesised ammonia, and separating synthesised ammonia from said reacted gas stream.