Ammonia purge

Membrane modules have found extensive commercial appHcation in areas where medium purity hydrogen is required, as in ammonia purge streams (191). The first polymer membrane system was developed by Du Pont in the early 1970s. The membranes are typically made of aromatic polyaramide, polyimide, polysulfone, and cellulose acetate supported as spiral-wound hoUow-ftber modules (see Hollow-FIBERMEMBRANEs). 

Table 4 summarizes commercial and precommercial gas separation appHcations (86,87). The first large-scale commercial appHcation of gas separation was the separation of hydrogen from nitrogen ia ammonia purge gas streams. This process, launched ia 1980 by Monsanto, was followed by a number of similar appHcations, such as hydrogen—methane separation ia refinery off-gases and hydrogen—carbon monoxide adjustment ia oxo-chemical synthetic plants. 

Hydrogen Hydrogen recovery was the first large commercial membrane gas separation. Polysulfone fiber membranes became available in 1980 at a time when H9 needs were rising, and these novel membranes qiiickly came to dominate the market. Applications include recovery of H9 from ammonia purge gas, and extraction of H9 from petroleum crackiug streams. Hydrogen once diverted to low-quahty fuel use is now recovered to become ammonia, or is used to desulfurize fuel, etc. H9 is the fast gas. 

Metal Hydride Process for Ammonia Purge Gas, The metal hydride process will be illustrated using the case of hydrogen recovery from an ammonia purge gas stream generated during ammonia manufacture. 

Figure 15. Applications map for hydrogen recovery process A, ammonia purge gas B, refinery stream C, coal conversion recycle gas D, ethylene plant cracked gas E, FCC minus gas...

Hydrogen h2/n2 Ammonia purge gas Successful Condensables must be removed... 

Ammonia TPD experiments were carried out by heating the sample in a stream of dry nitrogen up to 600 C at a heating rate of 10 C/min. The effluent gas was passed through a washing flask, and evolved ammonia purged into the flask was automatically titrated with 0.1 N HCl, sustaining a pH value of about 5. 

Between 1979 and 1985, forty-five PRISM separator recovery systems have been successfully implemented on ammonia purges around the world. As a result of hydrogen recovery, an incremental ammonia production of 3 to 5% can be achieved. Alternatively, at constant ammonia production energy savings amount to 0.6 to 0.9M BTU/ton ammonia. For a typical 1,150 ton/day plant, these improvements translate into 3M/year energy savings. 

H /N, Ammonia purge gas PSA Polysulfone Pd-based Plant installed (Prism by Permea) Lab scale... 

Hydrogen recovery from ammonia purge streams... 

E. Perry, Process for Hydrogen Recovery from Ammonia Purge Gases. US Patent 4172885, Assigned to Monsanto Co.,... 

As previously mentioned, the first widespread commercial application of membranes in GS was the separation of hydrogen in the ammonia purge stream, by using Permea Prism T systems. Hydrogen recovery is applicable to several processes, divided into three main categories ... 

Fig. 6.2 A shows a loop with both recirculator and make-up gas addition point after the ammonia separator. This layout is from several points of view the most advantageous layout. Ammonia condensation and separation are done before the converter exit gas is diluted with fresh make-up gas, and consequently at the highest possible partial pressure of ammonia. Purge gas may be taken from the point in the synthesis loop where the ammonia concentration is lowest and the concentration of inert components is highest. The recycle gas from the separator is diluted with the fresh make-up gas, so that the lowest possible ammonia concentration is obtained at converter inlet. Also the volume of gas which must be recompressed in the recirculator is the lowest possible, since product ammonia has already been separated.

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