Synthesis processing, cryogenic processes

Braun A variation on the classic ammonia synthesis process in which the synthesis gas is purified cryogenically. Widely used since the mid 1960s. 

Purifier An ammonia synthesis process, developed C.F. Braun and now licensed by Kellog Brown and Root. An important feature is the cryogenic removal of inert gases from the system. Seventeen plants were operating in 2005. 

Hydrogen is used in a large number of chemical processes, and may be used as a fuel itself or as a reactant in the production of synthetic fuels such as in the Fischer-Tropsch hydrocarbon synthesis process, for example. In applications where hydrogen purification is required, membranes can be used for hydrogen separation. Other hydrogen purification methods include pressure swing adsorption and cryogenic separation. 

A wide range and a number of purification steps are required to make available hydrogen/synthesis gas having the desired purity that depends on use. Technology is available in many forms and combinations for specific hydrogen purification requirements. Methods include physical and chemical treatments (solvent scmbbing) low temperature (cryogenic) systems adsorption on soHds, such as active carbon, metal oxides, and molecular sieves, and various membrane systems. Composition of the raw gas and the amount of impurities that can be tolerated in the product determine the selection of the most suitable process. 

Final Purification. Oxygen containing compounds (CO, CO2, H2O) poison the ammonia synthesis catalyst and must be effectively removed or converted to inert species before entering the synthesis loop. Additionally, the presence of carbon dioxide in the synthesis gas can lead to the formation of ammonium carbamate, which can cause fouHng and stress-corrosion cracking in the compressor. Most plants use methanation to convert carbon oxides to methane. Cryogenic processes that are suitable for purification of synthesis gas have also been developed. 

The process begins with a gasification process that converts coal into carbon monoxide and hydrogen. Part of this gas is sent to a water-gas shift reactor to increase its hydrogen content. The purified syngas is then cryogenically separated into a carbon monoxide feed for the acetic anhydride plant and a hydrogen-rich stream for the synthesis of methanol. 

HARP [Hybrid argon recovery process] A process for extracting argon from the hydrogen recycle stream in ammonia synthesis. Both PSA and a cryogenic process are used. Krishnamurthy, R., Lemer, S. L., and MacLean, D. M., Gas Sep. Purif, 1987,1, 16. 

Description The key steps in the KAAP plus process are reforming using the KBR reforming exchanger system (KRES), cryogenic purification of the synthesis gas and low-pressure ammonia synthesis using KAAP catalyst. 

Description The key features of the KBR Purifier Process are mild primary reforming, secondary reforming with excess air, cryogenic purification of syngas, and synthesis of ammonia over magnetite catalyst in a horizontal converter. 

HARP [Hybrid Argon Recovery Process] A process for extracting argon from the hydrogen recycle stream in ammonia synthesis. Both PSA and a cryogenic process are used. 

---