Ammonia Production from Natural Gas (Combined Reforming)

The process under analysis comprises three major sections: (1) Steam Reforming; (2) Raw Syngas Purification; and (3) Ammonia Synthesis.

Steam Reforming. After being compressed and desulfurized, the natural gas is mixed with steam for primary steam reforming reactions. In a tubular fired heater filled with a Ni-based catalyst, the methane is reacted with steam, generating a crude syngas mixture composed mainly of CO and hydrogen. The partially reformed natural gas is fed to the Autothermal Reformer (ATR), where the remaining methane is converted to CO and hydrogen. The effluent from the ATR is cooled, generating steam.

Raw Syngas Purification. The outlet from the ATR is fed to a two-stage high and low temperature reactors, where the bulk of the carbon monoxide is converted into carbon dioxide and hydrogen. The shifted gas is then cooled in two exchangers, generating steam, in such a way that water present in the gas condenses and it is removed in a knockout drum. The gas stream is sent to the CO2 Absorption, which utilizes a methyldiethanolamine wash for the removal of CO2. The gas stream free from CO2 is heated and fed to the Methanator, where residual carbon oxides are converted to methane in the presence of catalysts. After being cooled and dried in molecular sieves, the syngas is fed to the Syngas Purifier, composed of a feed/effluent exchanger, a low speed expander and a rectifying column. There, excess nitrogen, methane, most of the argon and other impurities are removed and used as fuel.

Ammonia Synthesis. The purified syngas is compressed, heated and fed to the Ammonia Reactor, an intercooled horizontal converter. The cooled down reactor outlet is then directed to a multistream heat exchanger that causes the condensation of the Ammonia. Residual gases are recycled to the Syngas Compressor.