Urea is industrially produced from liquid ammonia and gaseous carbon dioxide. From this point it can be understood that, out of several major nitrogen fertilizer production processes, only urea production has the potential for reducing greenhouse gas (GHG) emission by utilizing carbon dioxide as the feedstock; i.e. stoichiometrically the production of one tonne of urea requires 0.733 tonnes of carbon dioxide.
In addition, over the past half century, continuous efforts have been made to improve urea production processes, particularly to improve their energy-efficiency in the last few decades. The latest urea process consumes only half of the energy consumed by traditional urea processes developed in the 1950s and 1960s.
Because of the these features of urea production, the following cases may contribute to GHG emission reductions:
(1) Installing new urea plants using the latest energy-saving process to replace inefficient plants of equivalent capacities.
(2) Revamping/retrofitting conventional plants with the latest energy-saving technology
(3) Utilizing carbon dioxide currently emitted to atmosphere as the feedstock for urea; i.e. carbon dioxide in flue gas, off gases from chemical plants, blast furnaces, etc.
(4) Switching feedstock of existing ammonia plants from heavy hydrocarbon such as naphtha, heavy oil, etc to light hydrocarbons such as natural gas, methane, etc., supplementing the resulting shortage of carbon dioxide for urea production by the above (3)
(5) Combinations of the above.
The above aspects suggest that urea production and its project planning should be re­ evaluated as the leverage for GHG emission reductions. This paper foretells potential advantages of urea production for GHG emission reductions.