Agriculture Reference
In-Depth Information
2NO + O 2 2NO 2
(4)
3NO 2 + H 2 O 2HNO 3 + NO
(5)
the conversion of ammonia to nitric acid is exothermic (heat releasing) and contributes to a
considerable release of steam. Two types of processes are currently used: single pressure and
dual pressure. In single pressure, the oxidation and absorption stages are conducted at the
same pressure (medium between 1.7 and 6.5 bar or high between 6.5 and 13 bar). In the dual
pressure process the absorption occurs at a higher pressure than the oxidation.
Nitrous oxide (N 2 O) is the most significant GHG associated with the production of nitric
acid. The N 2 O global warming potential is 298 times greater than that of CO 2 (IPCC, 2007).
The amount of N 2 O emitted is dependent upon combustion conditions (pressure,
temperature), catalyst composition, burner design (EFMA, 2000b) and emission abatement
technologies. In Table 7, N 2 O emissions of nitric acid plants in different global regions are
listed.
Most plants in Europe synthesize nitric acid by the medium pressure technique with
average emissions of 6 to 8 kg N 2 O per ton HNO 3 . Using modern technology, N 2 O emissions
can be highly reduced. The Best Available Techniques (BAT) produces emissions of only 1.8
kg N 2 O per ton HNO 3 (Kongshaug, 1998) or 1.85 kg N 2 O per ton HNO 3 (Haas & Van Dijk,
2010).
Table 7. The dinitrogen oxide emissions of nitric acid production
Region
kg N 2 O /ton HNO 3
Reference
Sources Min max
World, low pressure 5.0 4.5 5.5 a
World, medium pressure 7.0 5.6 8.4 a
World, high pressure 9.0 5.4 12.6 a
Developing countries 8.9 4.0 19.0 b
Europe (EFMA) 4.6 c
7.0 6.0 8.0 d
7.0 0.01 21.6 e
6.7 1.8 f
North America, USA 9.0 g
References: a = IPCC, 2006; b = EPA, 2010; c = Haas & van Dijk, 2010; d = Zwiers et al., 2009; e =
European Commission, 2006; f = Kongshaug, 1998; g = IEA, 2007.
The greenhouse gas emissions per ton nitric acid varies between 2.8 ton CO 2 eq./ton
nitric acid for Europe, North America and rest of the world to 3.6 for China and India
(calculated by combining the figures of N 2 O emissions, energy use/export and ammonia
production) (Kool et al., 2012).
Urea and Urea Ammonium Nitrate (UAN)
Urea has become the most widely used fertilizer in the world. Asia is today the biggest
consumer mainly due of its use in flooded rice fields.
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