Process for producing ammonia synthesis gas

A process for producing ammonia synthesis gas, comprising the steps of:

• feeding a gas flow comprising hydrocarbons and a gas flow comprising steam to a primary reformer equipped with a plurality of externally heated catalytic tubes,
• reacting said hydrocarbons with said steam in the catalytic tubes of said primary reformer at an operating pressure of more than 35 bar in the catalytic tubes, obtaining a product gas,
• feeding said product gas and a flow of air to a secondary reformer in the absence of added hydrocarbons, said air being added in excess over the nitrogen amount required for ammonia synthesis for reforming all the hydrocarbons content of said product gas exiting the primary reformer,
• subjecting said product gas to reaction with said air and then to secondary reforming, obtaining a reformed gas comprising nitrogen in excess over the amount required for ammonia synthesis, hydrogen, carbon oxides and unreacted steam, and
• removing carbon oxides and excess nitrogen from said reformed gas to obtain said synthesis gas,
• wherein the outlet temperature of said gas product from the tubes of the primary reformer does not exceed 750° C. so as to increase the lifetime of said tubes;
• wherein said step of removing carbon oxides and excess nitrogen from said reformed gas comprises the following operative stages:
• removing carbon monoxide from said reformed gas by catalytic conversion with unreacted steam into carbon dioxide and hydrogen,
• removing carbon dioxide by scrubbing said reformed gas with a solution or solvent after said step of carbon monoxide removal, so obtaining a reformed gas still including carbon oxides, and
• one of:
• removing said carbon oxides from said reformed gas containing them by catalytic conversion to methane, obtaining a reformed gas deprived of carbon oxides, and removing excess nitrogen from said reformed gas deprived of carbon oxides by cryogenic separation;
• and
• removing said carbon oxides and said excess nitrogen by passing said reformed gas still including carbon oxides through a PSA or TSA molecular sieve.