ES2540170B1 - Procedure for the treatment of nitrogen oxides from thermal energy storage by molten salts - Google Patents

Abstract

Procedure for the treatment of nitrogen oxides from thermal energy storage by molten salts; comprising: a) the cooling of a gas stream from thermal storage by molten salts, to a temperature between 0-90 ° C; b) the treatment of the gas stream, previously cooled, by a photo-oxidation process, ** IMAGE-01 ** obtaining OH and ozone radical molecules; c) transformation of nitrogen oxides (NO and NO {sub, 2}) into nitric acid (HNO {sub, 3}) by reaction ** IMAGE-02 ** d) absorption of nitric acid (HNO {sub , 3}) in a scrubber and the neutralization of nitric acid (HNO {sub, 3}) with a chemical for its transformation into a salt and e) the crystallization of said salt for reuse.

Description

DESCRIPTION

Procedure for the treatment of nitrogen oxides from thermal energy storage by molten salts.

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Object of the invention.

The object of the present invention is a process for the treatment of nitrogen oxides from storage of thermal energy by molten salts and more specifically of the emissions of nitrogen oxides (NOx). 10

Field of application of the invention.

This invention is applicable in the treatment of gases (NOx) from thermal energy storage systems; for example, although not limited to 15 solar thermal power plants.

State of the art

Currently, molten salt technology is known to store a large amount of thermal energy and subsequently use it for electricity generation.

In the solar thermal power plants, sunlight is concentrated in a tower that contains the salts, being able to reach up to 800ºC, these molten salts being conducted by pipes to an exchanger where the thermal energy accumulated by them is used to generate electricity.

Some of the salts used in this technology are sodium nitrate or potassium nitrate and although this technology of molten salts provides important advantages of use, it presents some drawbacks such as the release during heating and decomposition in 30 nitrogen oxides (NOx ) in the form of discontinuous and variable concentration emissions.

This necessitates the use of a NOx gas treatment system.

A known technique for the treatment of these NOx gases is the selective catalytic reduction (SCR) technology that reduces nitrogen oxide (NOx) emissions through the use of a catalyst.

This technology (SCR) is normally applied in combustion processes offering a reduction of up to 95% NOx. 40

Another known technique for the treatment of nitrogen oxides is the washing of gases that is effective in the case of nitrogen dioxide (NO2) that is soluble in water, but not in the case of nitrogen monoxide (NO) which is not Water soluble and provides low performance. Four. Five

In EP 2307813, with priority of US 8318084, a method and a device for cleaning air pollution based on a photo-oxidation process consisting of accelerating the self-cleaning mechanisms of the atmosphere, ie a tight combination of atmospheric gases, water vapor, ozone and ultraviolet light. fifty

The applicant of the present invention is unaware of the existence of a background that allows the recovery of residual products from thermal storage by salts with the characteristics of the present invention.

Description of the invention 5

The process for the treatment of nitrogen oxides from storage of thermal energy by means of molten salts, object of this invention, has characteristics oriented to allow a high yield in the elimination of NOx, up to 99.999% and its transformation into a valuable product that can be reused in the form of salts in the tanks 10 of the thermal energy storage.

 This procedure includes the following phases:

 a) the cooling of the gas stream from the thermal storage tanks 15 by molten salts, from a temperature of 200-800 ° C. up to a temperature between 0 - 90 ° C. Y

 b) the treatment of the gas stream, previously cooled, by a photo-oxidation process, obtaining extremely reactive OH and ozone radical molecules towards nitrogen monoxide (NO) and nitrogen dioxide (NO2).

c) the transformation of nitrogen oxides (NO and NO2) into nitric acid (HNO3) by the reaction of OH radicals with nitrogen dioxide NO2, NO2 + OH  HNO3 ;.

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d) the absorption of nitric acid by scrubbing the gases (scrubber) and neutralization of nitric acid (HNO3) in a solution of water and a chemical, transforming it into a salt; Y

e) crystallization and reuse of said salt in the thermal energy storage system itself.

In phase b) there is a great reactivity of ozone O3 towards nitrogen oxide NO: NO + O3  NO2 + O2; and the reaction between O3 ozone is catalyzed with H2O water by UV lamps to create OH: O3 + H2O radicals  2 OH + O2. 35

In phase c) the following side reactions that may occur must also be considered:

NO + OH  HNO2 40

3NO2 + H2O  2 HNO3 + NO

O3 + NO2  O2 + NO3

However, these secondary reactions are much slower than the main reactions mentioned and are not relevant in the final process. Four. Five

In a specific embodiment, the neutralization of nitric acid (HNO3) is carried out with sodium hydroxide (NaOH), or with potassium hydroxide (KOH), respectively obtaining sodium nitrate (NaNO3), or potassium nitrate (KNO3), which are reusable salts in the thermal energy storage system itself using molten salt technology, or in other 50

Applications.

Description of the figures.

To complement the description that is being made and in order to facilitate the understanding 5 of the features of the invention, a set of figures is attached to the present specification in which, as an illustration and not limitation, the following has been represented :

- Figure 1 shows a diagram with the different phases or stages of the process for the treatment of nitrogen oxides from the gaseous emissions of the thermal energy storage tanks by molten salts.

Preferred embodiment of the invention.

The steps of the procedure described above have been schematically represented in Figure 1, including:

a) the cooling of the gas stream of the thermal storage tanks by molten salts

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b) the treatment of the gas stream by a photo-oxidation process in which the radical OH and ozone molecules are obtained;

c) the transformation of nitrogen oxides (NO and NO2) into nitric acid (HNO3) by the reaction NO2 + OH  HNO3, 25

d) the absorption of nitric acid (HNO3) in a scrubber and the neutralization of nitric acid (HNO3) with a chemical for its transformation into a salt and,

e) crystallization of said salt for reuse. 30

Once the nature of the invention has been sufficiently described, it is stated for the appropriate purposes that changes may be introduced therein, provided that this does not imply an alteration of the essential features of the invention claimed in continuation. 35

Claims (3)

1. Procedure for the treatment of nitrogen oxides from thermal energy storage by molten salts; characterized in that it comprises: a) the cooling of a gas stream containing nitrogen oxides, from thermal storage tanks by molten salts, from a temperature of 200-800 ° C. up to a temperature between 0 - 90 ° C. Y  10 b) the treatment of the gas stream, previously cooled, by a photo-oxidation process, NO + O3  NO2 + O2; O3 + H2O  2 OH + O2 obtaining extremely reactive OH and ozone radical molecules towards nitrogen monoxide (NO) and nitrogen dioxide (NO2).  fifteen c) the transformation of nitrogen oxides (NO and NO2) into nitric acid (HNO3) by reaction NO2 + OH  HNO3, d) the absorption of nitric acid (HNO3) in a scrubber and the neutralization of nitric acid (HNO3) with a chemical for its transformation into a salt and, 20 e) crystallization of said salt for reuse. 2. Method according to claim 1, characterized in that it comprises neutralizing nitric acid (HNO3) with sodium hydroxide (NaOH) and obtaining sodium nitrate (NaNO3). 3. Method according to claim 1, characterized in that it comprises neutralizing nitric acid (HNO3) with potassium hydroxide (KOH) and obtaining potassium nitrate (KNO3). 30