Single-pressure nitric acid plant

FIGURE 4.1 Process flow diagram for a single-pressure nitric acid plant. 

Fortunately the single-pressure nitric acid plant is a remarkably clean plant. It has no liquid waste streams in normal operation and... 

Fig. 22.17. Single pressure nitric acid plant, (Reproduced by permission of Monsanto Enviro-Chem Systems, Inc.)...

Figure 6.4.23 Single-pressure nitric acid plant (high pressure) using selective catalytic reduction (SCR) for NO f abatement (BFW boiler feed water). Adapted from Moulijn, Makkee, and Van Diepen (2004).

Figure 4.4. Simplified flow sheet for typical single pressure, high-pressure nitric acid plant. Reprinted from Catalyst Handbook, 2 ed., by kind permission of M. Twigg.

The process chosen for the nitric acid plant is the single pressure process based on the technology developed by C I Girdler. 

All nitric acid plants are based on the same basic chemical operations 1) Oxidation of ammonia with air to give nitric oxide, 2) Oxidation of the nitric oxide to nitrogen dioxide and 3) Absorption in water to give a solution of nitric acid. The efficiency of the first step is favored by low pressure whereas that of the second step is favored by high pressure. These considerations, combined with economic reasons give rise to two types of nitric acid plants - single pressure and dual pressure97. 

The absorber consists usually of a single stainless-steel tower, although two or more may be necessary for low-pressure plants. Another kind of absorber used is a drum absorber. In general, the cool gases along with additional air are fed to the bottom of the tower, and demineralized water is fed to the top of the tower. Instead of demineralized water, clean condensed steam can be used. Nitric acid is taken out from the bottom, whereas tail gases leave at the top of the tower. The absorption towers can be packed with sieve plates, bubble cap plates, or turbo-grids. 

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