Energy integration and cogeneration are commonly used in large mineral fertilizer production complexes for many years. Production of nitrogen fertilizers is an energy intensive industry branch consuming about 5200 PJ of fossil fuels, mainly natural gas. Urea is the major straight nitrogen fertilizer with 46% nitrogen content, and the total production of 155 MM metric tons yearly. About 600–900 kg MP or HP steam and 50–120 kWh electricity per ton urea are consumed in modern low energy urea plants.
In this work the exergy method is used to analyze the dependence of the primary energy consumption and GHG emissions in the ammonia and urea production complexes on basic parameters of the subsystems (ammonia and urea production units and CHP plant) and on the allocation of the additional fuel (natural gas) burning and steam generation.
The results show that the most effective allocation scheme depends mainly on the relative efficiencies of the subsystems and mashinery (compressors and steam turbines).