Carnit Ammonium Nitrate Process

Keywords: Ammonium nitrate, Effluent, pH control, Steam production.

The Kemira Carnit process for production of concentrated ammonium nitrate solutions requires no external heat supply.

Reaction of ammonia and nitric acid occurs in a recycle flow loop, where the pressure is higher than the vapour pressure of the solution. The recycle solution, which is slightly ammoniacal, supplies heat for the final concentration and for production of export steam. The free ammonia in the production offtake is neutralised before pressure reduction and subsequent concentration steps.

A specific feature of the Carnit is the self-regulating combination of the adiabatic flash upon pressure reduction with the first isobaric concentration step, where the flashed vapours supply the heat of evaporation. Efficient pH control achieves a liquid effluent with less than 50 ppm equivalent ammonium nitrate.

The process combines high thermal efficiency and low maintenance cost with ease of operation. The production rate can be varied between 30% and 100% of design capacity.

Energy self-sufficiency can be maintained even with 45 wt% acid. When 97.5 wt% solution is produced with 60 wt% nitric acid feed, 128 kg/t AN of clean 6 bar export steam is produced.

The contract for the Kemira Tertre 2 100 t/day AN (100% AN base) unit was awarded to UHDE in March 1989, and the plant was put on stream in December 1990.

Since start-up, production of 97.5 wt% solution has been continuous, with a total of 166 hours shutdown time over a period of 18 months, i.e. an on-stream time efficiency of 98.7%.

The Carnit ammonium nitrate production process’ is available for licensing through Kemira SA. (Belgium).

Dr J L Bovens and Dr F van Hecke, Kemira SA, Tetre, Belgium.

32 Pages, 13 Figures, 3 Tables.