The heart of ammonia manufacture, the Haber process where nitrogen and hydrogen are reacted together under high pressure and temperature, goes back to before World War I. Hydrogen is usually produced by the steam reforming of hydrocarbons, with natural gas the dominant feedstock. It can also be produced by the partial oxidation of naphtha or residual oil using air or oxygen and from coal gasification. Nitrogen can be obtained by the liquefaction of air or from producer gas.
The purified hydrogen-nitrogen mixture is compressed to 150-350 bar, mixed with recycle feed and fed into a tubular or multi-bed reactor. The reaction takes place at 450-600 C over a catalyst. The ammonia is condensed out by refrigeration and unreacted gases are compressed and recycled.
Most process improvements have been made through better catalyst systems, improved reformer and converter designs, and integration of energy needs and heat recovery. New ammonia synthesis catalysts include a ruthenium-based system which has an activity 20 times higher than the traditional iron-based catalyst. There is a trend towards larger single train plants, for example, Krupp Uhde, in association with Synetix, has developed a flowsheet for a plant that produces over 1m tonne/year.
Designs have been developed integrating ammonia and methanol production, and the first grassroots plant to coproduce methanol with ammonia using Haldor Topsoe technology was started up in 1999 for Petronas Fertilizer in Malaysia. A number of existing units have also been converted to coproduce methanol including for BASF and Terra.
Ammonia
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Ammonia
Uses and Outlook
Ammonia is the basic building block of the world nitrogen industry and is the intermediate product from which a wide variety of nitrogen-based fertilizers and industrial products are produced. Fertilizer use accounts for around 85% of ammonia demand.
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