Production of ammonia from natural gas, LNG, LPG or naphtha. The process uses conventional steam reforming synthesis gas generation in the front-end, while the synthesis section comprises a once-through section followed by a synthesis loop. It is thus optimized with respect to enable ammonia plants to produce very large capacities with proven equipment. The first plant based on this process will be the SAFCO IV ammonia plant in Al-Jubail, Saudi Arabia, which is currently under construction. This concept provides the basis for even larger plants (4,000 – 5,000 metric tpd).
The feedstock (e.g. natural gas) is desulfurized, mixed with steam and converted into synthesis gas over nickel catalyst at approximately 42 bar and 800 – 850°C in the primary reformer. The Uhde steam reformer is a top-fired reformer with tubes made of centrifugal micro-alloy steel and a proprietary “cold outlet manifold,” which enhances reliability.
In the secondary reformer, process air is admitted to the syngas via a special nozzle system arranged at the circumference of the secondary reformer head that provides a perfect mixture of air and gas. Subsequent high-pressure (HP) steam generation and superheating guarantee maximum process heat recovery to achieve an optimized energy efficient process.
CO conversion is achieved in the HT and LT shift over standard catalyst, while CO2 is removed either in the BASF-aMDEA, the UOP-Benfield or the UOP-Amine Guard process. Remaining carbonoxides are reconverted to methane in catalytic methanation to trace ppm levels.
The ammonia synthesis loop consists of two stages. Makeup gas is compressed in a two-stage inter-cooled compressor, which is the lowpressure casing of the syngas compressor. Discharge pressure of this compressor is about 110 bar. An indirectly cooled once-through converter at this location produces one third of the total ammonia. Effluent from this converter is cooled and the major part of the ammonia produced is separated from the gas.
In the second step, the remaining syngas is compressed to the operating pressure of the ammonia synthesis loop (approx. 210 bar) in the HP casing of the syngas compressor. This HP casing operates at a much lower than usual temperature. The high synthesis loop pressure is achieved by combination of the chilled second casing of the syngas compressor and a slightly elevated front-end pressure.
Liquid ammonia is separated by condensation from the once through section, and the synthesis loop and is either subcooled and routed to storage, or conveyed at moderate temperature to subsequent consumers.
Ammonia flash and purge gases are treated in a scrubbing system and a hydrogen recovery unit (not shown), the remaining gases being used as fuel.
Licensor: Uhde GmbH