Ammonia production is been done mostly from natural gas and naphtha as feed stock. This high molecular weight feed stock is reformed to produce hydrogen element which is required in the Stiochiometry ratio of 3 moles for 1 mole of nitrogen. After vaporization and purification of the feed stock which is mixed with steam is reformed in reforming section which is the heart of the process for the production of synthesis gas, which consists of nitrogen, hydrogen, carbon dioxide, and traces of carbon monoxide. Totally three steps of chemical reactions occur in the sequences which are as
CnHm+H2O à Cn-1Hm-2+CO+2H2 - heat
CH4+H2O ß---àCO+3H2 - heat
CO+H2Oß---àCO2+H2 + heat
For the above reaction to occur equipments like prereformer, primary reformer and secondary reform are used which are explained by the diagrams from KBR Technologies. First reaction is handled in a prereformer where a packed bed of catalyst is used to convert higher weight hydrocarbons to methane. Methane is converted to hydrogen and carbon monoxide in the tubular reactor which is induced draught box heater because of the endothermic reaction, which occur approximately at temperatures 490 to 600 deg C based on the catalyst and the design. Outlet of the primary reformer contains about 12 mole % of methane and this is reduced to 0.6 mole % in secondary reformer due to combustion process where CO and methane are combusted in presence of pressurized air which ultimately yield the ratio of nitrogen and hydrogen. Unconverted carbon monoxide by a third reaction given above know as shit reaction which is exothermic in nature takes place in to section of high temperature and low temperature shift reactors.
Carbon dioxide and carbon monoxide are removed in the purification section with absorption of GV solution and remaining traces are converted to methane in methanator. Synthesis gas which has the perfect ratio of hydrogen and nitrogen is fed to the horizontal ammonia synthesis reactor designed by KBR to produce ammonia by catalytic reaction.
Block Diagram of Ammonia Process Plant