Ammonium Nitrate Solution Synthesis and Concentration
CEAMAG and SYNTHESIS process
- Probably the safest available technology,
- Very high production yield,
- Very Low OPEX, with low maintenance cost,
- Optimal environmental compatibility with highest requirements,
- Auto-thermal and self controlled process,
- Nitric Acid concentration as low as 55%.
More and more Ammonium Nitrate based fertilizers are nowadays produced as granules, leading to products having better mechanical properties, bigger granulometry and better aspect than the prilled products.
The majority of granulation processes are using Ammonium Nitrate solution with a concentration between 95 and 97.5% weight.
It is worth to point out that proposed process is perfectly complementary to any granulation process, in particular the Spherodizer process, offered by CEAMAG for production of several types of AN based fertilizers, like AN 33.5, CAN upwards from 20% N, several types of ASN.
Highlights of the technology
The process is based on a liquid loop which includes the main reactor R121 and the final AN concentration system with exchangers E131 and E132. The heat evolved in the reactor is removed in the AN concentration system. The loop is operating under basic pH conditions.
The reactor operates under a slight excess of ammonia and under pressure, in such a way that no process vapour can be produced.
The ratio of feed reactants is adjusted so as to maintain a controlled amount of free ammonia in the circulating loop.
The free ammonia in the production off-take is neutralized in a trim post reactor R122 by a small injection of nitric acid.
After the trim post reactor R122, the AN solution off-take is flashed and concentrated in the pre-concentration E121.
The concentration of AN solutions in the reaction loop and after the pre-concentration is directly related to the concentration of the nitric acid feed to reactor R121.
After pre-concentration, the solution is sent to the final AN concentration system where the solution is concentrated to 97.5%.
Completeness of reaction at the reactor outlet
A specific reactor design, combined with optimized circulation flow rate under controlled pressure conditions, achieves high mass transfer rates at the interface of numerous small bubbles of injected ammonia gas. The reaction of nitric acid is therefore complete at the outlet of reactor R121.
The production rate is set by the NH3 feed stream with an ammonia / nitric acid ratio control which adjusts the nitric acid supply.
As the concentration of nitric acid feed can be subject to variations, a very accurate mass flow control of the acid supply insures the stability of the ammonia / acid ratio, leading to a very stable operation of the plant.
One of the essential features of the process is the pH control, insuring a control of the ammonia excess in the loop.
As full reaction is completed at the outlet of reactor R121, sampling points for pH controls are located close to the top outlet of the reactor. Optimization of the accuracy of measurements and of the answering time of pH meters are achieved by specific design of sampling systems and pH sensors position. pH meters and sampling systems cabinets are part of mandatory supplies by CEAMAG.
Plant stability and flexibility
This auto-thermal process demonstrates a remarkable stability within the extended flexibility of production range (30 to 100%).
Start-up from cold to full capacity:
- Loading: 2h
- Full capacity: 2h
Stable auto-thermal operation with Nitric Acid concentration from 55%.
Effluent control and process yield
The process does not generate gaseous effluents, with the exception of a very small amount of non condensable at the top point of the circulating loop.
In separators S121 and S132 vapours are washed with acidic solutions leading to very pure condensates after condensation. The pool of condensates leaving the plant remains below the EFMA-BAT requirement with reported average value as low as 15 ppm weight of ammonium nitrate equivalent.
Depending upon the site, the use of the AN process condensates may be optimized with the Customers in terms of flow rate and AN content. Accordingly, the condensates quality, the operating conditions of separators and process condensate network can be adapted to local specification requirements, for optimization of OPEX and CAPEX.
As the sole loss of AN production may occur in the process condensate, the production yield exceeds 99.99%.
Safe design approach
The process control is designed in such a way that safe operation will, at all times, be achieved without any supervision.
The most obvious risks in any AN unit relate to the conjunction of high temperature and high concentration solutions which may become acidic and where a significant decrease of density resulting from the presence of bubbles may lead to a run-away situation.
In the proposed process, such risky situation cannot exist: the highest temperature that can be reached is at the outlet of the reactor R121 where a low concentration solution is maintained under an operating pressure which prevents all possibility of vaporisation, while pH is basic.
Due to basic conditions of pH in the circulating flow, there is no special steel requirement on items in the loop except for the reactor itself.
Typical Lay-out for 2800 mtpd Plant and 52% Nitric Acid
Typical Flow Diagram for Nitric Acid Concentration higher that 58%