- Classification of production plants
- Technology and engineering suppliers
Classification of production plants
Industrial plants are classified according to the pressure used:
- Mono-pressure plants. These plants operate at the same pressure in the ammonia oxidation and absorption sections of the plant. Mono-pressure plants are classified as low pressure (0.3-0.5 MPa; 3-5 bar) and high pressure (0.8-1. 3 MPa; 8-13 bar).
- Dual-pressure plants. These plants operate under lower pressure in the ammonia oxidation section than in the absorption section.
In general, high-pressure operation permits smaller plant units to be used for a given output and helps to reduce capital costs. High pressures also favour NO2 absorption; however, high-pressure ammonia oxidation induces greater catalyst losses and also increases power requirements unless additional equipment is installed for power recovery.
Because of the emphasis on pollution control, the ability of high-pressure processes to attain acceptably low NOx levels in the tail-gas has favoured their adoption. Therefore, most new plants use either mono-high-pressure or dual-pressure (medium pressure combustion, high-pressure absorption) processes although some mono-medium-pressure processes are used.
High-pressure processes generally will have the lowest capital cost and highest operating cost because of higher platinum losses, less efficient NH3 conversion, and lower steam recovery. Medium-pressure processes have the highest capital cost and lowest operating cost (assuming the NOx content of the tail-gas is acceptable). The dual-pressure process represents a compromise. The choice may be influenced by local site conditions.
The very first nitric acid plants used near-atmospheric pressure throughout. However, practically all modern plants use elevated pressures. The choice of the process always depends on local conditions; however, a general principle may be that lower capacity plants favour the high mono-pressure alternative. The-dual-pressure choice seems to be a compromise between the higher investment costs of mono-medium pressure and higher operating costs of mono-high pressure alternative. Overall capital costs estimates and typical process requirements for the various plants are available.
Technology and engineering suppliers
The Fertilizer Manual describes the state-of-the-art technology, as in the late 1990s, of processes offered by UHDE (Thyssenkrupp UHDE), Grand Paroisse (CASALE), GIAP, and Weatherly (KBR). In addition, other suppliers, such as Stamicarbon, are available.
Each of the organisations offers several processes to meet various client needs. In addition, several other companies offer nitric acid processes, and there is no intention to imply that processes offered by certain companies mentioned by name are necessarily superior to those offered by other companies. Such a reference does not imply any kind of endorsement by the International Fertiliser Society.
References
Fertilizer Manual, edited by the United Nations Industrial Development Organization (UNIDO) and the International Fertilizer Development Center (IFDC), Kluwer Academic Publishers, 1998.
Links to related IFS Proceedings and recordings
106, (1969), Nitric Acid Manufacture – A Comparison between High and Medium Pressure Processes, J M Lerolle
818, (2018), Dual pressure nitric acid technology with high energy recovery, P Muñoz
Links to external resources
The nitrogen industry – properties, G. D. Honti, Akademia Kiado, Budapest, Hungary, 1976, pages 409-413.
Various processes for the production of commercial-grade nitric acid, G. D. Honti, 1985, Fertilizer science and technology series, USA, pages 61-98.
Various processes for the production of concentrated nitric acid, G. D. Honti, Nitric acid and fertilizer nitrates, Marcel Dekker, New York – Basel, 1985, pages 99-130.
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