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SAFINA
CHEMOPROJEKT
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Nitric acid for fertilizer industry
The fertilizer industry uses weak nitric acid in the range of 50 to 70% strength. Operating range is 70-110% of nominal plant capacity.
The typical plants for production of 60% nitric acid are designed as a single pressure or dual pressure units. For production rates up to 1000 MTPD single pressure process is preferred due to economic and operating conditions, for units with higher capacity is dual pressure process preferred due to reduction of capital costs.
Chemoprojekt, a. s.
is experienced and authorized company to design the modern Nitric acid plants based on the technology provided by French company Grande Paroisse s.a., the world leader in the branch of nitrogen chemistry and one of the greatest nitrogen fertilizer producer in Europe.
1) Mono pressure process
Simplified process description:
In the single pressure plants, the oxidation and absorption steps take place at essentially the same pressure. The oxidation and absorption steps can be classified as:
- Low pressure (pressure below 0,1 MPa)
- Medium pressure (pressure between 0,1 and 0,6 MPa)
- High pressure (pressure between 0,6 and 1,3 MPa)
When ammonia oxidation is carried out at higher pressure (close to absorption pressure of the nitrous gases and process of an acid formation), nitrous gas compressor is not required.
Liquid ammonia fed to the Nitric acid plant is vaporized and mixed with compressed air. The mixed air/ammonia gas is directed to the ammonia burner where the ammonia is catalytically oxidized to NO and water (at approx. pressure 0,7 MPa). Nitrous gases from the burner are cooled down and the energy is recovered with steam production, tail gas and process air heating.
During final cooling down weak acid is condensed, nitrous gases are recycled to the absorption tower at 0,7 MPa where they react with water to form nitric acid. The product is bleached with secondary air and cooled down before sending to battery limit. Nitrogen oxides of the waste gas selectively react in a catalyst reactor with ammonia provided as a reducing agent. The tail gas from the absorber is passed through the heat recovery and the expander section for energy recovery and is then passed to the stack.
Advantages:
- Proven reliability
- Low investment costs
- Low NOx tail gas content (up to 100 ppm after SCR)
2) Dual pressure process
Simplified process description:
Ammonia oxidation occurs at low pressure while high pressure improve absorption of the nitrous gases and process of an acid formation. Liquid ammonia imported to the Nitric acid plant is evaporated and mixed with air before oxidation in the burner at low pressure about 0,5 MPa. Maximum energy is recovered by steam generation and cooling of nitrous gases via cross exchange with tail gas. After further cooling of the low pressure nitrous gases with simultaneous weak acid condensation gases are compressed to above 1,1 MPa in the NOx compressor. The high pressure nitrous gases are then cooled by cross exchange with tail gas and further weak acid condensation before entering the absorption tower where they react with water to form nitric acid. The product acid is bleached with secondary air and cooled down before sending to battery limit. The tail gas from the absorption tower is heated in the tail gas heater and than mixed with ammonia and introduced to the selective catalytic reactor (SCR) for reduction of NOx content and than expanded in the power recovery turbine.
Advantages:
- Proven reliability
- Low investment costs
- High ammonia conversion efficiency
- High heat recovery
- Low NOx tail gas content (up to 50 ppm after SCR)
3) Nitric acid for explosives and organic chemistry
High concentrated nitric acid (98% to 99% concentration) can be obtained by concentrating the weak nitric acid (30% to 70% concentration) using extractive distillation. The distillation must be carried out in the presence of a dehydrating agent.
Advantages:
- Proven reliability
- High heat recovery
- NOx content up to 50 ppm
4) N2O Emission Reduction
Kyoto Protocol - the international treaty on climate change has come into force after it has been ratified by Russia at the end of 2004.
Until ratification of Kyoto Protocol very little concern has been paid to N2O comparing to NOx. N2O arises as an unwanted by-product of ammonia catalytic oxidation during HNO3 production in quantities ranging typically from 350 to 3500ppmv.
Considering one ton of N2O accounts for 310 tons of CO2 equivalent in terms of emissions trading, N2O reduction in tail gas has become high importance issue for HNO3 producers as well as for the entire governments.
N2O contrary to NOx cannot be absorbed from tail gas and therefore new catalytic processes shall be applied.
Nowadays, two feasible processes of N2O destruction exist and both can be provided by Chemoprojekt a.s.
- High temperature (880-930C) catalytic reduction just under platinum gauzes
- Middle temperature (380-450C) catalytic reduction – so called end of technology process
Both processes reduce N2O content in tail gas exceeding overall N2O conversion of 90% thus preparing HNO3 production units for new more stringent regulations on N2O emissions which shall yet to come.
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