Published July 2009
While the overall process layout of some well-proven ammonia processes has remained unchanged for the last decade, their performance has improved due to improvements in areas such as the synthesis gas generation and purification, the energy efficiency and reliability of carbon dioxide removal systems, synthesis loop equipment designs and the switch from electrically driven compression to the use of waste heat generated steam-driven centrifugal compressors. In addition, new plants tend to be larger, with improved economies of scale.
The KBR Purifier Process features a firing reduction in the primary reforming furnace and a cryogenic system that removes inert components from the raw ammonia synthesis gas. The cryogenic purifier removes excess nitrogen introduced by the excess of air fed to the secondary reformer, all methane and most of the argon. The technology has been in operation in more than 15 commercial ammonia plants.
This review evaluates an SRIC design based on the KBR Purifier Ammonia Process incorporating design features reflecting the above-mentioned process improvements. The front-end synthesis gas preparation is through natural gas reforming with excess air, CO shift, aMDEA carbon dioxide removal, methanation, drying and cryogenic purification. The ammonia synthesis loop features a horizontal cross-flow magnetite converter, steam-driven compressors and a unitized chiller.
Our work suggests that at a base case capacity of 1,448 million lb/yr (2,000 metric tons per day), the total fixed capital is $595.4 million. The overall natural gas energy consumption (for feed and fuel) is 13,332 Btu/lb NH3 on an LHV basis. The base case product value (net production cost plus 25%/yr return on investment) is 31.4¢/lb when natural gas is priced at 889¢/MMBTU.
