ATR-Asahi Process System

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Nitric Acid Concentration Plants

Commercial acids or re-usable waste acids can be brought to the concentration required for the application in question by distillation, but the azeotropic point necessitates two different processes :

  • Rectification for preliminary concentration
  • Extractive distillation (with sulfuric acid) to high concentration of over 98%.

Rectification for Preliminary concentration

In the preconcentrating of nitric acid in the region below the azeotropic point, part of the water is vaporized and drawn off. The weak acid is pre-heated utilizing the heat of condensation of the vapour and is fed to the column as a liquid. By heat and mass transfer between the vapour rising from the evaporator and the counter-flow of liquid the mixture is separated so that water is obtained as the top product and nitric acid of virtually azeotropic composition is obtained as the bottom product. For the heating system it is common to use natural circulation evaporators made of borosilicate glass with bayonet-type heaters made of titanium, tantalum or niobium. ATR-ASAHI design principles are distinguished by :

  • Fully corrosion-resistant construction.
  • Optimization with respect to capital and operating costs by individual planning of each plant.
  • ATR-ASAHI heat exchanger which are corrosion resistant on both sides achieve the maximum heat recovery.

Extractive distillation (with sulfuric acid) to high concentration

In order to obtain virtually water-free nitric acid from the weak acid it must be distilled in the presence of an extractive agent such as sulfuric acid. This displaces the vapour liquid equilibrium of the HNO3-H2O system which reaches an azeotropic composition so that above a certain proportion of sulfuric acid the azeotrope no longer appears.

ATR-ASAHI is doing the process by indirect heating which results in distinct advantages:

  • Reduction of the amount of live steam.
  • Reduction of the consumption of sulfuric acid.
  • Possibility of using sulfuric acid of lower concentration.
  • Higher output for a given column diameter.
  • Simpler process control system.

ATR-ASAHI plant for the production of highly concentrated acid for individually designed, and optimized to suit the duly and the concentration of the weak acid, taking capital costs and operating costs into account.

The packed columns for concentrating and bleaching are constructed in borosilicate glass in the diameter range of DN80 to DN800. Tantalum is used as the material for the column heater. Glass coil heat exchangers and shell and tube heat exchangers have proved to be effective for the pre heaters, coolers and condensers of plants for the production of highly concentration acid.

The integral sulfuric acid re-concentrating unit operates as a vacuum forced-circulation evaporator of the design described in the sulfuric acid concentration plants.

Extensive process know-how add the use of the most up-to-date process controls systems make it possible to construct fully automated plants which supply 

nitric-plant

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