Hydrogen for ammonia production

Interaction of methane with steam on a nickel surface is the basis of the natural gas reforming process. The process is used as a source of hydrogen for ammonia production and methanol synthesis and, therefore, finds a large-scale industrial application. 

Hydrogen for Ammonia Production and the Economics of Alternate Feedstocks... 

This paper analyzes the sources of hydrogen for ammonia production, presents the feed and fuel requirements of the natural gas steam reforming process, estimates the relative economics of alternate feedstocks and briefly discusses the outlook for the ammonia industry. 

The importance of such a source of hydrogen for ammonia production lies in the value of phosphoric acid, a plant food, as an ammonia carrier. A plant for the production of phosphorus according to this process is in operation at the cyanamide plant at Piesteritz, Germany. The phosphorus produced is shipped to the Badlsche Anilin und Soda Fabrik at Merseburg, where it is oxidized with steam to phosphoric acid and hydrogen. 

Hydrogen for ammonia production may also be produced by hydrolysis [370-374] or it may be obtained from refinery off gas [375]. Plants have been constructed from such feedstocks in the past [376, 377] and it may still be economical in special circumstances. In modern times plants have been constructed on the basis of off gases from petrochemical plants such as ethylene plants and methanol plants [378, 379], but such cases will most likely remain rare and be economical only in special circumstances. Production of ammonia from gases produced in steel plants is suggested in [380-383]. 

This excess hydrogen is normally carried forward to be compressed into the synthesis loop, from which it is ultimately purged as fuel. Addition of by-product CO2 where available may be advantageous in that it serves to adjust the reformed gas to a more stoichiometric composition gas for methanol production, which results in a decrease in natural gas consumption (8). Carbon-rich off-gases from other sources, such as acetylene units, can also be used to provide supplemental synthesis gas. Alternatively, the hydrogen-rich purge gas can be an attractive feedstock for ammonia production (9). 

Synthesis Gas Preparation Processes. Synthesis gas for ammonia production consists of hydrogen and nitrogen in about a three to one mole ratio, residual methane, argon introduced with the process air, and traces of carbon oxides. There are several processes available for synthesis gas generation and each is characterized by the specific feedstock used. A typical synthesis gas composition by volume is hydrogen, 73.65% nitrogen, 24.55% methane, <1 ppm-0.8% argon, 100 ppm—0.34% carbon oxides, 2—10 ppm and water vapor, 0.1 ppm. 

The use of air alone leads to a relatively low calorific value product gas, of the order of 4-6 MJ/mi (LHV basis), which is not attractive for H2 production in view of the large bulk of N2 to be separated from it compared to a preseparation from the air. Only the application of hydrogen in ammonia production would need N2 as cofeedstock. Therefore, in this context only steam- or oxygen-blown gasification concepts are dealt with. The raw product gas can, thus, be produced by an oxygen-blown or indirectly heated steam-blown processes. 

P. C. Hallenbeck (1983) Immobilized microorganisms for hydrogen and ammonia production. Enzyme Microb. Technol., S 171-180... 

Thus methanol and ammonia plants are sometimes combined since carbon dioxide, which must be removed from hydrogen to use it for ammonia production, can in turn be used as feed to adjust the COrHj ratio to 1 2 for efficient methanol synthesis. The methanol can be condensed and purified by distillation, bp 65 °C. Unreacted synthesis gas is recycled. Other products include higher boiling alcohols and dimethyl ether. 

Therefore, it is not surprising that currently about 70% of the world ammonia capacity is based on obtaining hydrogen from natural gas reforming. Of course, the economic analysis of various raw materials used for ammonia production is not complete without considering their relative price and availability which could ultimately dictate the choice for a particular feed. 

Process Feed Requirement. The theoratical hydrogen required for ammonia production can be calculated from the synthesis reaction ... 

Some 60% of the hydrogen use in industry is for ammonia production. The process is... 

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