Ammonia production plants

The previous sections mainly considered the individual process steps involved in the production of ammonia and the progress made in recent years. The way in which these process components are combined with respect to mass and energy flow has a major influence on efficiency and reliability. Apart from the feedstock, many of the differences between various commercial ammonia processes lie in the way in which the process elements are integrated. Formerly the term ammonia technology referred mostly to ammonia synthesis technology (catalyst, converters, and synthesis loop), whereas today it is interpreted as the complete series of industrial operations leading from the primary feedstock to the final product ammonia. 

With the exception of the Koppers-Totzek coal gasification process, which operates at near atmospheric pressure, all modern gasification processes operate at elevated pressure. Steam reforming of light hydrocarbons at 30-40 bar and partial oxidation of heavy hydrocarbons at 40-90 bar are generally used. 

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Generally, configuration I is desired for such applications as hydrogen plants in petroleum refineries and for hydrocracking and hydrotreating. Configuration II would be the choice for applications where moderate conversions are necessary to keep some hydrocarbons in the product stream for further processing such as ammonia production plants. 

All ammonia production plants in the world operate according to the same basic principles i.e. reaction of nitrogen and hydrogen in a catalyst-filled pressure reactor at temperatures between 400 and 500°C, pressures between 100 and 1000 bar (depending upon the plant) and removal of the ammonia formed from the reaction gas. The plants differ in their design, catalyst composition and production and purification of the synthesis gas. 

Membrane technology is employed in the separation of gases, e.g., H2 from N2, CO, and CH4 CO2 and water vapor from natural gas. It finds use in H2 recovery from ammonia production plants. The... 

The main line of the Gulf Central Rpeline originates at anhydrous ammonia production plants near New Orleans, Louisiana. This main line parallels the Mississippi River north to Iowa. The main line then turns west across the state of Iowa and terminates in Aurora, Nebraska. 

As shown in the previous section, the conventional ammonia production plant requires several gas separation units. The attempt to minimise the use of those units contributes to the idea of catalytic membrane reactor. The catalytic membrane is a combination of catalyst bed and gas separation membrane. The membrane reactor improves the ammonia formation rate by product removal or the control of reactant concentration. However, only a few catalytic membrane reactors for ammonia production are reported. Itoh, Machida, and Adachi (2000) and Itoh, Saito, Tajima, and Machida (2007) reported ammonia production in a catalytic membrane reactor consisting of Ru catalysts loaded on a Ag-Pd hydrogen permeable membrane. It was found that the presence of high-reactivity atomic hydrogen from the Ag—Pd membrane enhances the ammonia formation rates. 

Another possibility is to site ammonia production plants in regions where cheap hydroelectric power is available. This has already happened, long ago, in Norway, Canada and Egypt (Aswan Dam.) Other remote areas with untapped hydropower include Alaska, Iceland and Brazil. As one moves to more remote sites of hydropower, it may be advantageous to pipe the hydrogen to a more convenient location to build a chemical plant rather than to process it in-situ. 

In the ammonia synthesis process like most other processes the main processing unit and one that attracts most attention from a control point of view is the rector. In ammonia production plant there exists two reactors, the mathanation and the synthesis. The methanation reactor is of much less importance as little amount of reaction takes place in it, while the synthesis reactor is of outmost importance. In this paper initially a four-bed ammonia synthesis catalytic reactor is simulated in a dynamic environment. The simulation is then used to analyze the effect of sudden change on feed pressure and variation of feed distribution on different beds on process parameters such as temperature, pressure, flow rate and concentration through the process. 

Initially, this process was used for removing CO traces from H2-rich streams in ammonia production plants (Kopyscinski et al., 2010). However, nowadays it is considered as an interesting alternative for producing substitute natural gas (SNG), since it is free from contaminants like H2S and its production from biomass has a neutral carbon footprint (Kopyscinski et al., 2010). 

Figure 2.6 Billingham on Teeside, the site of the first ammonia production plant in the UK.

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