Chemoprojekt, a. s. is experienced and authorized company to design the modern Nitric acid plants based on the technology provided by French company GPN (member of TOTAL Corporation). GPN (earlier Grande Paroisse s.a.), is one of the world leaders in the branch of technology for nitrogen fertilizer production based on nitric acid and one of the greatest nitrogen fertilizer producer in Europe. In last 5 years nitric acid belongs to the most succesful products of Chemoprjekt.
1) Nitric acid for fertilizer industry
The base material for nitrogen fertilizers as well as for other chemical products is nitric acid, which is usually produced in 60-68% concentration.
For production of fertilizers is mainly utilized the nitric acid with 60% concentration. Production of weak nitric acid (60-68%) is based on two technological processes ¨C mono pressure and dual pressure process:
Mono pressure process ¨C has lower investment cost, but operating costs (specific consumption of amonium and loss on catalyst) are slightly worse than in case of dual pressure process. Mono pressure process is usually used for capacity of the unit lower than 1000 tonnes/day (calculated for pure nitric acid).
Dual pressure process is operationly more suitable and more sophisticated. The operation parametres are more convenient, but the investment costs are higher than by units using mono pressure process. Currently dual pressure process is realized in BAT (Best Available Technology) and is highly reccommended.
Technology preference depends on economic indicators, but can be also influenced by other parametres and local conditions.
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.
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)
The raw material for production of nitric acid air and liquid ammonia. Filtered atmospheric air is compressed to one of above mentioned pressure levels. Liquid ammonia fed to the Nitric acid plant is vaporized and mixed with compressed air. The mixed air/ammonia gas is directed to the catalytic oxidizing reactor, which is connected with boiler for waste heat . 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.. The tail gas (reduced nitrous gas) leaves to the absorption tower in temperature from 25 to 35¡ãC with concentration NOx approximately 1000 ppmv. Tail gas is heated by hot hot nitrous gas on the output from the boiler. Residual content of NOx in tail gas is dissolved by selective catalytic reduction. The energy of hot tail gas is recovered by passing the expander, where it expands from operation pressure to pressure close atmospheric pressure and is then passed by the stack to the atmosphere.
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 0,4 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 N20 content. Nitric acid from absorber is stripped by hot air and cooled before dispatch to the store.
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 usually 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 100 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 ¨C 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.
