Bleaching tower and method for nitric acid production

Patent metadata

Field	Value
Publication number	US-12252399-B2
Application number	US-202017422682-A
Country	US
Kind code	B2
Filing date	Feb 14, 2020
Priority date	Feb 22, 2019
Publication date	Mar 18, 2025
Grant date	Mar 18, 2025

Abstract

A vertical bleaching tower for removing dissolved nitrogen oxides from an aqueous nitric acid solution using a stripping gas such as air, nitrogen, oxygen or combinations thereof in a process for producing nitric acid, comprising a structured packing; a liquid distributor comprising a feed box having a serrated weir for distribution of the aqueous nitric acid solution comprising the dissolved nitrogen oxides through upward-pointing serrations of the serrated weir into perforated trays of the liquid distributor and located above the structured packing for distributing the aqueous nitric acid solution comprising the dissolved nitrogen oxides to the structured packing; an inlet and outlet, both suitable for aqueous nitric acid solution; and an inlet and outlet, both suitable for the stripping gas. The present invention further comprises a bleaching method for removing dissolved nitrogen oxides from an aqueous nitric acid solution in a vertical bleaching tower.

First claim

The invention claimed is:

1. A vertical bleaching tower for removing dissolved nitrogen oxides from an aqueous nitric acid solution comprising said nitrogen oxides, using a stripping gas substantially devoid of nitrogen oxide gases, selected from air, nitrogen, oxygen or combinations thereof, in a process for producing nitric acid, the vertical bleaching tower comprising:
a structured packing;
a liquid distributor comprising a feed box having a serrated weir for distribution of the aqueous nitric acid solution comprising the dissolved nitrogen oxides through upward-pointing serrations of the serrated weir into perforated trays of the liquid distributor and located above the structured packing for distributing the aqueous nitric acid solution comprising the dissolved nitrogen oxides to the structured packing;
an aqueous nitric acid solution inlet;
an aqueous nitric acid solution outlet;
a stripping gas inlet; and
a stripping gas outlet.

2. A vertical bleaching tower for removing dissolved nitrogen oxides from an aqueous nitric acid solution comprising said nitrogen oxides, using a stripping gas substantially devoid of nitrogen oxide gases, selected from air, nitrogen, oxygen or combinations thereof, in a process for producing nitric acid, the vertical bleaching tower comprising:
a structured packing;
a liquid distributor comprising a feed box having a serrated weir for distribution of the aqueous nitric acid solution comprising the dissolved nitrogen oxides through upward-pointing serrations of the serrated weir into perforated trays of the liquid distributor and located above the structured packing for distributing the aqueous nitric acid solution comprising the dissolved nitrogen oxides to the structured packing;
an aqueous nitric acid solution inlet;
an aqueous nitric acid solution outlet;
a stripping gas inlet; and

a stripping gas outlet, wherein the structured packing has a surface area of at least 250 m 2 /m 3 .

3. The vertical bleaching tower according to claim 1 , wherein the liquid distributor has a drip-point density of at least 30 dripping points per m 2 .

4. The vertical bleaching tower of claim 1 , wherein the ratio between the height of the structured packing and the vertical bleaching tower diameter is at least 1.

5. A bleaching method for removing dissolved nitrogen oxides from an aqueous nitric acid solution comprising said nitrogen oxides in a vertical bleaching tower according to claim 1 , using a stripping gas substantially devoid of nitrogen oxide gases, selected from air, nitrogen, oxygen or combinations thereof, to remove dissolved nitrogen oxides from the aqueous nitric acid solution, comprising the steps of
introducing the aqueous nitric acid solution comprising the dissolved nitrogen oxides in the top of the vertical bleaching tower through the liquid distributor;
allowing the aqueous nitric acid solution to travel downwards into the vertical bleaching tower through the structured packing;
contacting the aqueous nitric acid solution with the stripping gas moving in a counter-current direction to the aqueous nitric acid solution through the structured packing; and
exiting the stripping gas comprising the removed nitrogen oxides.

6. The method according to claim 5 , further comprising the step of returning the removed nitrogen oxides to a compressor for nitrogen oxide gases, located upstream an absorption tower, or directly to an absorption tower for subsequent conversion of the removed nitrogen oxides to nitric acid.

7. The method according to claim 5 , wherein the nitrogen oxides are nitrogen dioxide (NO 2 ) and dinitrogen tetroxide (N 2 O 4 ).

8. The method according to claim 5 , wherein the stripping gas is air moving in a counter-current direction to the aqueous nitric acid solution and is in an air/acid solution ratio of lower than 75 m 3 air/m 3 acid solution.

9. The method according to claim 5 , wherein the pressure drop over the vertical bleaching tower is between 25 mbar and 65 mbar.

10. The vertical bleaching tower according to claim 2 wherein the structured packing surface area is 450 to 750 m 2 /m 3 .

11. The vertical bleaching tower according to claim 3 wherein the liquid distributor drip-point density is from 60-200 dripping points per m 2 .

12. The vertical bleaching tower according to claim 4 wherein the ratio between the height of the structured packing and the vertical bleaching tower diameter is at least 1.5.

13. The vertical bleaching tower according to claim 12 wherein the ratio between the height of the structured packing and the vertical bleaching tower diameter is at least 2.

14. The method according to claim 8 wherein the air/acid solution ratio is lower than 45 m 3 air/m 3 acid solution.

15. The method according to claim 14 wherein the air/acid solution ratio is lower than 30 m 3 air/m 3 acid solution.

16. The method according to claim 15 wherein the air/acid solution ratio is lower than 20 m 3 air/m 3 acid solution.

Assignees

• Yara Int Asa

Inventors

• Oien Halvor
• Melgard Arnulf Idar

Classifications

• B01D2257/40

  Nitrogen compounds · CPC title

• B01D53/185

  Liquid distributors · CPC title

• B01D53/1418

  Recovery of products · CPC title

• C01B21/40 Primary

  Preparation by absorption of oxides of nitrogen {(C01B21/26 takes precedence)} · CPC title

• C01B21/46 Primary

  Purification; Separation {; Stabilisation (C01B21/40 takes precedence)} · CPC title