Patent ID: 7897130

Claim:
A process for obtaining a synthesis gas at a predetermined high pressure corresponding to an ammonia synthesis pressure, in which there are hydrogen and nitrogen in a 3/1 molar ratio, comprising the steps of: feeding a continuous flow of natural gas to a primary reforming step with steam and to a subsequent secondary reforming step with excess air obtaining a gaseous flow to be purified comprising hydrogen, excess nitrogen with respect to said molar ratio, undesired substances such as impurities and inerts; purifying said gaseous flow in a purification step comprising cryogenic rectification in a separator unit obtaining a continuous flow of synthesis gas comprising hydrogen and nitrogen in a 3/1 molar ratio; compressing said flow of synthesis gas in a subsequent compression step up to a pressure value required for ammonia synthesis; continuously separating a portion of said synthesis gas leaving said compression step, which is compressed up to the pressure value required for ammonia synthesis, and expanding said portion of compressed synthesis gas to obtain a cooled portion; and placing said cooled portion in heat exchange relationship with said gaseous flow to be purified.