DE1085640B - Removal of nitrogen oxide from gas mixtures containing it - Google Patents

Description

GERMAN

Nitric oxide and dienes (e.g. cyclopentadiene) form polymerizable nitrosates and nitrosite. The latter, often called gumming agents, are the cause of problems in town gas in gas meters, valves and pipelines or, as self-igniting resins, are the cause of explosions when the coke oven gas is broken down by freezing. Nitrogen oxide in the flue gas prevents the extraction of carbon dioxide from flue gas by deep-freeze washing by causing the trichlorethylene detergent to decompose. Nitrogen oxide in the obtained carbonic acid makes it unusable for use for blowing steel in the converter, because it remains in the steel as nitrogen. Nitrogen oxide, which enters the water cycle of a pressurized water wash from the contaminated air or which arises from the activity of bacteria in the water cycle of the pressurized water wash, is in the wash on the washed gas, e.g. B. a NO-free converted gas (CO-1-H ₂ OH ₂ -I-CO ₂ ), transmitted and endangered the subsequent cryogenic gas decomposition.

In order to avoid the difficulties mentioned, a wide variety of methods have been developed been. So one has z. B. proposed to wash out NO aqueous solutions of salts lower To use oxides of sulfur or of chromate or bichromate. However, they only work imperfectly and have therefore not found any application in technology.

Attempts have also been made to remove NO from the exhaust gases of internal combustion engines by reduction with urea solutions, but the gas must first be freed from soot and dust by means of an alkali carbonate solution mixed with a wetting agent. Another known way of removing NO is by accelerating the oxidation of NO to NO ₂ . It is part of the state of the art to add volatile compounds of elements of group VIII of the periodic table, in particular carbonyl compounds, to the gas as a catalyst for the reaction of NO with O _2. The proposal to oxidize the NO with ozone serves the same purpose. Finally, removal of NO with O _{2 has} also been achieved by subjecting the reactants to certain conditions with regard to concentration, temperature and pressure during defined residence times.

Other processes deal with NO removal in the course of gas desulphurization using gas cleaning compounds. According to a prior art method, e.g. B. H ₂ S- and NO-containing gases passed over trays, on each of which a layer of fresh metal oxide mixed with humic substances and a layer of regenerated, but removal of nitrogen oxide
from gas mixtures containing such

Applicant:

Society for Linde's ice machines

Corporation,

ίο branch office Höllriegelskreuth,
Höllriegelskreuth near Munich

Dr.-Ing. Ernst Karwat, Pullach near Munich,
has been named as the inventor

ao still NO containing mass are applied. The gas is first passed through the fresh massage layer, until most of it is converted to metal sulfide, and then reversing the direction of flow first through the regenerated massage layer, with the last amounts of NO from the expelled regenerated mass and in the subsequent new, activated by metal sulfide formation Mass to be intercepted.

In a further cleaning process of this type, which works with detergent boxes switched backwards, the cleaner that is switched as the last detergent box is used for the NO bond and an amount of H ₂ S which is just sufficient to form the amount of iron sulfide required for the NO bond is introduced into it.

The invention takes a completely new approach to the method described, the NO from Gases containing small concentrations of NO, such as coke oven gas, generator gas, flue gas, and from water can be removed completely and economically. The method according to the invention is characterized in that that the gas mixtures to be cleaned or the water to be cleaned are supplied with chlorine-oxygen compounds in which the chlorine is present in positive electrochemical valence levels.

The first of the effective chlorine-oxygen compounds mentioned is the hypochlorous acid HClO, which is used as a washing liquid in the form of its aqueous solution. The NO goes into higher oxidation levels, such as NO ₂ , HNO ₂ , HNO ₃ . The latter remain partly in the solution and partly in the gas and can easily be removed from this by an alkaline wash. A disadvantage of this solution is that it contains elemental chlorine in the dissociation

009 567/277

3 4

contains equilibrium, which may be used according to the invention as a chlorine oxygen compound

other gas components, such as acetylene, undesirable dung the gaseous ClO ₂ to remove the nitrogen

Connections. Oxyds from the gas mixture used. To clean-

The gas stream according to the invention is free from this disadvantage, the chlorine dioxide is _{fed in with a carrier gas which is inert to solutions of the chlorous acid H Cl O 2} 5 chlorine dioxide to be used. Carrier gas in water. Such a solution is expediently a component of the gas mixture to be cleaned that is passed through it, the nitrogen oxide in full gas mixture, e.g. B. nitrogen. Chlorine is added to a carrier gas, as is more common than any other for NO-Ent nitrogen, the chlorine-containing removal agent that has become known up to now. The green carrier gas is passed through an aqueous solution of NaClO.
when a lying 7-12 _pH value _, _{T "n} _ _Λ". _, _n
which can easily be increased to the desired value by Ul ₂ -h ζ IN a Ul U ₂ - Z i \ a Ui -f- ^ Ul U ₂
Addition of O Η ions to the solution of technical from 1 mole of chlorine 2 moles of Cl O, can be formed, which can be set in sodium chlorite, especially since the transfer of the carrier gas, which is then supplied to the commercial form of the salt already a low content of 15 gas mixture to be purified will. Despite the presence of caustic soda. In order to maintain this alkalinity - only trace presence of NO in the coke, in the case of cleaning coke oven gas, the NO is again practically completely oven gas or converted gas, which is oxidized to NO by deep-freezing and this and residues of chlorine decomposition are to be broken down. the sodium chlorite scrubbing compounds are removed by a subsequent, alkaline scrubbing after the work stages to remove the carbon-reducing scrubbing from the gas dioxide to be cleaned: pressurized water scrubbing and caustic scrubbing, mixed, even if the volume of the demineralises. For example, 10,000 Nm ^s / h of chlorine dioxide fed in on gas is only V2 to 4 times 12 atmospheres compressed, de-carbonated coke is the volume of the nitrogen oxide to be converted. furnace gas, which still contains 1 pM NO, in a washing tower completely filled with Raschig rings with 25 digits of Cl O ₂ formation every hour. The additional 20 to 50 ^msec of 1 to 10 percent by weight of Na Cl O ₂ gaseous chlorine is washed in the size-containing aqueous solution of p _H = 9. Order of the amount of NO present and is therefore no longer detectable in the scrubbed gas. practically very small, size 0.5 to 3 cm ³ The detergent is in the washing tower by a chlorine per m ³ coke oven gas.
Circulation pump circulated. A second 3 ° R "'1
Washing tower of the same type serves to maintain the purity of the e 1 s ρ 1 e

to ensure scrubbed gas when the scrubbing 50 ^ms nitrogen with 0.01 ° / »= 5 1 chlorine solution of the first tower approaches exhaustion under 12 atmospheric pressure through a saturation vessel. If the washing capacity of the first washing tower, in which 50 l of an aqueous solution is exhausted, the second washing tower will be the first 35 of 10 weight percent Na Cl O ₂ at room temperature and the previous first one after changing the washing. The nitrogen leaves loaded with 10 1 by means of a counter, fresh solution as a second switch. Chlorine dioxide the vessel and becomes a stream of

Should high-carbon gas mixtures such as smoke 10000 Nm ³ coke oven gas with 2% CO ₂ and IpM NO

gas containing e.g. 50 pM NO is added for the purpose of extraction at a pressure of 12 atmospheres. After 2 to 6 seconds

of the carbon dioxide are freed from nitrogen oxide, so 4 ° the mixing and reaction time is the gas mixture

it is subjected to an acidified Na Cl O ₂ solution, the CO ₂ removal and finally with

the _pH value is 6-3, preferably washed thiosulfate solution. In the scrubbed gas

= 4.5 is, washed, with the result that these are only harmless small traces of NO,

the scrubbed gas no longer contains NO. With the same mostly no NO at all to be found.

Success and even better economy is that 45 The consumption of sodium chlorite in the same

Feeding in gaseous chlorine dioxide in too pure time is about 40 gNaClO ₂ . As an example of the city

low carbonated gas mixtures can be used. gas cleaning to prevent gum formation in

Then advise the implementation of the chlorine dioxide, valves and pipes can do the same

with the nitrogen oxide, the gas mixture with alkali numbers becomes as in the previous example for

Lischen aqueous solutions such as caustic soda or coke gas cleaning apply. Because on the CO ₂ removal

Washed thiosulfate or sodium sulfite. Such a solution is not valued here, there is no

Solutions remove both the NO ₂ formed and washing with lye. Instead of thiosulphate, this is done with

possible traces of chlorine or the reaction ClO ₂ treated gas of a sodium sulfite scrub and

escaped oxygen compounds of the chlorine. Which is subjected to a rewash with water before it is in

However, reducing laundry has neither the task of feeding the distribution network. When applied

nor the function of removing NO from the gas of the method according to the invention is omitted in FIG

because this has already been _{oxidized to NO 2} beforehand. City gas networks are the annoying and costly one

the. Apparatus and method of reducing gum formation, and in cryogenic gas separation plants

Laundry is basically the same as for which the risk of explosion due to Nitrosite is

Sodium chlorite scrubbing described. 60 lifted.

The oxidizing effect of the Na Cl O ₂ solution at the entrance is already due to the penetration of NO, the gas mixture is almost exclusively _{directed towards the nitrogen oxide in the pressure water scrubbing for the purpose of CO 2} removal - however, the reduction of the gases that are subjected has been discussed. If such NaClOg solution is incidentally present with a disproportionate ratio, the cleaning chlorine dioxide of the NaClO _{2 is} accompanied by which constantly a 65 after the pressurized water _{wash, but before the caustic part of the NaClO 2 used} for the NO oxidation wash in fed the coke oven gas. Invention lost. according to that in the water, e.g. B. when ventilating

The further development of the inventive concept with air containing NO also penetrated nitrogen oxide

leads to an economically better exploitation of what is destroyed in the water itself. To this end,

Sodium chlorite. 70 neither the water itself sodium chlorite, NaClO ₂ ,

added until the dissolved NO disappears. The end point of the addition can be seen from the fact that water treated in this way no longer gives off any NO to the gas that has been passed through. However, gassing the N O-containing water with chlorine dioxide-containing carrier gas, which, for example, in the manner described above, was charged with ClO ₂ by gassing a sodium chlorite solution with chlorine-containing carrier gas, is more economical in terms of chlorite consumption. No more NO can be converted into the gas phase from water treated in this way.

Claims (8)

Patent claims: 1. Process for removing nitric oxide from such as a contaminant in small concentrations containing gases such as town gas, coal gas, coke oven gas, generator gas, flue gas, and from water, characterized in that the gases to be cleaned or the Water chlorine-oxygen compounds are supplied, in which chlorine in positive electrochemisehen There are valencies. 2. The method according to claim 1, characterized in that NaClO _{2 is} used as the chlorine-oxygen compound. 3. The method according to claim 1 and 2, characterized in that the gases _{are washed with an aqueous solution of NaClO 2 or NaClO 2 is} added to the water to be purified. 4. The method according to claim 1, characterized in that ClO _{2 is} used as the chlorine-oxygen compound. 5. The method according to claim 1 and 4, characterized in that a _{carrier gas containing Cl O 2} is mixed with the gas or water to be cleaned. 6. The method according to claim 1, 4 and 5, characterized in that a chlorine-containing carrier gas is passed through an aqueous solution of NaClO ₂ and then mixed as a Cl O ₂ -containing carrier gas with the gas or water to be cleaned. 7. The method according to claim 1, 4 to 6, characterized in that subsequent to the implementation the chlorine dioxide with the gas to be cleaned this with a lye, z. B. sodium hydroxide, washed will. 8. The method according to claim 1, 4 to 6, characterized in that subsequent to the implementation of the chlorine dioxide with the gas to be cleaned this with a reducing agent, e.g. B. one aqueous alkaline solution of thiosulfate or sodium sulfite, is washed. Considered publications:
German Patent Nos. 568 814, 660 734, 633, 725 697, 767 189, 851 107. © 009 567/277 7.60