Temperature Ammonia-Hydrogen Exchange Process

The dual-temperature principle for providing reflux for the ammonia-hydrogen deuterium exchange process was proposed by the British firm Constructors John Brown [C12], has been tested in pilot-plant experiments conducted by Friedrich Uhde Gmbh at the plant of Farbwerke Hoechst in Germany [W2], and is to be used in a commercial plant at Talcher, India (item 19, Table 132), being constructed by Uhde. 

Supplementary feed to plate number n = Ratio, supplementary feed to feed, F lF Ratio, production/ feed, P/F Percent production increase 

Elimination of the net heat input needed to dissociate ammonia at 740°C 

Elimination of the need to synthesize ammonia for reflux and the costs associated with this step 

Even though flow conditions for the dual-temperature system. Fig. 13.37, were chosen to give a minimum number of stages, the increase from 5.7 stages for the monothermal system to 

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Figure 13.37 Material flow sheet for dual-temperature ammonia-hydrogen exchange process. Flow units, kg-mol/h.

Availability of this catalyst has led to interest in its possible use in dual-temperature water-hydrogen exchange processes. With liquid-water feed and recirculated hydrogen gas, this catalyst could be used in a dual-temperature process similar in principal to the GS process, with a schematic flow sheet like Fig. 1325. With ammonia synthesis-gas feed and recirculated water, this catalyst could be used in a dual-temperature process similar to the ammonia-hydrogen process flow scheme of Fig. 13.37, provided that impurities in synthesis-gas feed that would poison the catalyst can be recovered sufficiently completely. 

The dual-temperature, methylamine-hydrogen exchange process described in Sec. 13 could also be used to concentrate deuterium from ammonia synthesis gas produced from natural gas and steam containing the normal abundance of deuterium instead of the enriched steam used in the Sulzer flow sheet. Fig. 13.40. Figure 13.42 is a flow sheet for such a process giving the deuterium content of each stream in the first stage of the plant. 

A variant of the H2/NH2 chemical exchange process uses alkyl amines in place of ammonia. Hydrogen exchange catalyzed by NH2 is generaHy faster using alkyl amines than ammonia, and a dual-temperature flow sheet for a H2/CH2NH2 process has been developed (69). 

Table 13.26 Comparison of hydrogen exchange processes monothermal and dual-temperature ammonia-...

All of the previously mentioned plants except those employing distillation of water were parasitic to a synthetic anunonia plant. Their deuterium-production rate is limited by the amount of deuterium in ammonia synthesis gas. To produce heavy water at a sufficient rate, a growing industry of heavy-water reactors requires a deuterium-containing feed available in even greater quantity than ammonia synthesis gas. Of the possible candidates, water, natural gas, and petroleum hydrocarbons, water is the only one for which an economic process has been devised, and the dual-temperature hydrogen sulfide-water exchange process is the most economic of the processes that have been developed. 

Dual-temperature exchange processes using ammonia and hydrogen, methylamine and hydrogen, and water and hydrogen are described in Secs. 12, 13, and 14, respectively, and are compared with the GS process in Sec. 14. 

AECL did extensive development of a variant of the ammonia-hydrogen process based on aminomethane (CH3NH2) rather than ammonia. This has better kinetics and a wider envelope of operating temperatures but can only be configured bithermally. This process was superseded by development of processes based on water-hydrogen exchange. 

Chemical recuperation of high-temperature heat is an alternative to raising steam [427]. In ammonia plants the steam is used to drive the S5mgas compressor (refer to Section 2.5), but as discussed for hydrogen plants (refer to Section 2.2) and GTL plants at remote locations (refer to Section 2.6.5) there may be no need for the steam, and recuperation of the heat of the hot process gas in a heat exchange reformer may be an option (as illustrated in Figure 2.35 and Figure 2.36). 

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