The method of cleaning gas containing nitrogen oxides

 

(57) Abstract:

Use: for cleaning a gas containing nitric oxide, from toxic impurities. The inventive method of cleaning gas containing nitric oxide, including the processing gas connection alkali metal, and use the amount of oxygen in the gas is equal to the stoichiometric amount required for oxidation of nitric oxide to nitrogen dioxide, and as a compound of an alkali metal is used, the alkali metal pyrosulfite in the amount sufficient for the formation of alkali metal nitrite, nitrate of an alkali metal and sulfur dioxide by the reaction of nitric oxide with oxygen. 7 C.p. f-crystals, 2 Il.

The invention relates to a cleaning gas containing nitrogen oxides, toxic impurities, particularly to the purification of the fumes from thermal plants, prior to their release to the atmosphere. More specifically to a method for gas purification from nitrogen oxides and preferably from nitric monoxide (NO).

Smoke generated due to the combustion of gaseous, liquid or solid combustible materials, usually contaminated with oxides of nitrogen derived from nitrogen in the atmosphere and, in the case of nitrogen-containing compounds present in the fuel.

2).

Most toxicity of nitric oxide and nitrogen dioxide makes it necessary to remove them from the fumes before the release of the last in the atmosphere

Offers a way to clear the smoke from nitrogen oxides according to which the sulfate of an alkali metal and ammonia gas is introduced into the smoke to restore the oxides of nitrogen to nitrous oxide (N2O), which is then reduced to nitrogen using ammonia.

In the case of smoke, containing both nitrogen oxides and sulfur dioxide, sulfite of an alkali metal is formed in situ in smoke due to the introduction of carbonate or bicarbonate of an alkali metal.

This known method has the disadvantage of having to use multiple reagents, of which the gaseous reagent (ammonia) with toxic nature, necessitates the adoption of a significant security measures.

The invention avoids this disadvantage by the fact that a new method, which allows for fast and efficient cleaning gas from the oxide (co) nitrogen without the use of hazardous gaseous reagent and which can be implemented at moderate temperatures, giving excellent results.

Lichnogo metal, according to which the use amount of oxygen in the gas at least equal to the stoichiometric amount required for oxidation of nitric oxide to nitrogen dioxide, and as a compound of an alkali metal chosen the alkali metal pyrosulfite, which is used in a quantity sufficient for the conversion of nitric oxide from the gas in the nitrite and nitrate of an alkali metal.

When the treated gas contains oxide and nitrogen dioxide, preferably use the amount of alkali metal pyrosulfite, at least sufficient for the conversion of carbon oxide and dioxide nitrogen to nitrite and nitrate of an alkali metal.

The invention is applicable to all gases containing nitric oxide (NO). It is especially applicable for gases generated by combustion of combustible materials in the presence of air or oxygen.

Subsequently, the gas generated by the combustion of combustible material, will be called "smoke". When the invention is applicable to smoke, combustible material is not critical and may be gas, liquid or solid.

Combustible material may include fossil fuel (such as oil and oil products, the angle of the waste or municipal waste.

The origin of the smoke is not critical, and it may happen, for example, from thermal power plants, centralized installation of urban heating or incineration of domestic or municipal waste.

Gas processed by the method of the invention necessarily contains the nitric oxide (NO). It may contain other nitrogen oxides, addition of nitrogen monoxide, for example, nitrous oxide (N2O), nitrogen trioxide (N2O3), nitrogen pentoxide and nitrogen dioxide (NO2).

In a further nitrogen oxide gas will be designated in their entirety as NOx. In General, the volume fraction of nitric oxide (NO) among the set of all oxides of nitrogen (NOxin Gaza is at least 50% and usually above 75%; it can reach 100%.

Alternatively, the gas may contain other compounds, especially oxides of sulfur. Sulfur oxides, particularly sulfur dioxide, are usually present in the fumes generated by the combustion of sulfur-containing combustible fossil (oil and oil products, coal, coke).

According to the invention in a gas using the oxygen amount at least equal to the stoichiometric quantity corresponding to that which is necessary for oxidation OK the SNO invention, the oxygen does not essentially a function of the oxidation of nitric oxide to nitrogen dioxide, and since the introduction of it coexists with the nitric oxide gas in a quantity at least equal to the stoichiometric amount theoretically required for this oxidation.

According to the invention the molar ratio of O2/NO in Gaza since there must be at least equal to 0.5. In practice, it appears desirable to implement gas molar ratio of O2/NO higher than 1 and preferably at least equal to 8, and the recommended values above 10.

Although the method according to the invention does not cause the high limit of the oxygen content in the gas is not of interest exceeding the molar ratio of O2/NO equal to 100, in order not to exaggerate useless volume of gas.

Usually suitable value higher than 15, preferably higher than 25. Oxygen can be used in pure form or, more simply, as the surrounding air.

When the processed gas is a smoke, oxygen can be injected due to an excess of air supplied to the furnace, where combustion of fuel; you can also enter the air in the smoke from the lower part of the furnace.

The alkali metal pyrosulfite performs the function of turning the ACS is UB>2S2O5+2NO2_ MHSO3+CO2,

2MHSO3_ M2S2O5+H2O.

In the preferred embodiment, the method of introducing a bicarbonate of an alkali metal in the gas where it is converted to the alkali metal pyrosulfite according to the above reactions.

In this embodiment of the invention uses the presence of sulfur dioxide gas in a quantity sufficient to obtain the number of alkali metal pyrosulfite at least equal to the stoichiometric quantity necessary for interaction with all nitrogen oxides in the gas.

This option has the advantage that it does not need to use harmful reactive gas to remove, on the one hand, sulfur dioxide and oxides of nitrogen NOxin Gaza and, on the other hand, sulfur dioxide, which is generated by the reaction of alkali metal pyrosulfite with oxides of nitrogen.

This method is used preferably when processing fumes released due to the combustion of combustible materials of fossil origin, which contain derivatives of nitrogen and sulfur derivatives.

The method according to the invention leads to oala.

This residue can be easily removed by treating the gas in the device is an adequate device for dedusting, which may include, for example, an electrostatic filter.

In the case of processing a dry way, according to the above definition, you can use the filter from the filter fabrics (fabric filter), the efficiency of which is optimal.

The method according to the invention is used to clean any gas containing nitrogen oxides NOx. It finds use in the purification of the fumes originating from the incineration of domestic or municipal waste, as well as during cleaning of the fumes resulting from the combustion of combustible materials of fossil origin, such as natural gas, coal and oil.

It is mostly used for clearing the fumes from power plants.

In Fig. 1 and 2 show two diagrams representing the composition of the gas containing the nitrogen oxides NOx.

Example 1 (reference example). Get artificial gas consisting essentially of argon and nitrogen oxide [400 ál of nitric oxide (NO) on l gas], but devoid of oxygen.

In addition, the layer is prepared from 1 g of particles of sodium pyrosulfite in layer 5 g of silicon dioxide, smeshannoj">

The gas is subjected to movement in the upward flow through the layers (with a certain speed) for liquefaction layer of sodium pyrosulfite.

During the experiment the temperature in the layer increases gradually from 300 to 800 K. the Results are shown in two diagrams of Fig.1.

On each chart, Fig.1 on the x-axis is the temperature of the gas at the entrance to the layer (expressed in degrees Kelvin). The upper diagram of Fig.1 y-axis plotted the volume concentration of each of the components NO, NO2and N2O gas at the outlet of the layer (these concentrations are expressed in M. D. ál or component on l gas and must be divided by 50 in the case of N2O).

In the bottom diagram of Fig.1 on the y-axis of deferred volumetric concentration of sulfur dioxide in the gas (expressed in ál of SO2/l gas). From the diagram of Fig.1 shows that in each of the carried out experiments the gas at the outlet of each layer has approximately the same structure as the input layer.

At a temperature of 425 - 430 in gas content increases up to about 3 ml/l of sulphur dioxide, corresponding to the decomposition of sodium pyrosulfite.

Example 2 (according to the invention) Repeat the experience of example 1 with artificial gas, formed by the mixture of argon, oxide asousi volumetric composition of

NO = 410 ál/l;

O2= 22587 ál/L.

Proceed as in example 1. The results of the experiment are shown in the diagram of Fig. 2, the abscissa axis which caused the temperature of the gas at the entrance to the layer (expressed in degrees Kelvin) the y-axis on the left represents the volumetric concentration of each of the components NO, NO2and N2O in the gas at the outlet of the layer (these concentrations are expressed in meters etc. or ál component per 1 liter of gas in the case of N2O must be divided by 20), and the ordinate axis on the right caused the volumetric oxygen concentration in the gas at the outlet of the layer (expressed in M. D. ál or oxygen at l gas).

It is seen that the gas undergoes an optimal cleaning at temperatures of 450 - 500 K. At a temperature of about 480 To the gas at the outlet of the layer has the following composition

NO = 73 μl/l;

NO2= 73 μl/l;

N2O = 7 ál/l;

O2= 20000 ál/L.

Comparing the results of examples 1 and 2 directly shows the progress made in the removal of nitric oxide, when according to the invention combine the introduction of oxygen in the gas to be cleaned and then processing it with the help of sodium pyrosulfite.

1. The method of cleaning gas containing nitric oxide, according to which the gas is treated sedimentational number, required for oxidation of nitric oxide to nitrogen dioxide and a compound of an alkali metal is an alkali metal pyrosulfite, which is used in a quantity sufficient for the formation of a nitride of alkaline metal nitrate of an alkali metal and sulfur dioxide by the reaction of nitric oxide with oxygen gas.

2. The method according to p. 1, characterized in that when the gas contains nitrogen dioxide, use a sufficient amount of alkali metal pyrosulfite for the conversion of nitric oxide and nitrogen dioxide in the nitrite and nitrate of an alkali metal.

3. The method according to p. 1 or 2, characterized in that use more than 0.25 mol of alkali metal pyrosulfite per mole of nitric oxide and nitrogen dioxide in the gas.

4. The method according to p. 3, characterized in that the use of 0.4 to 2.5 mol of alkali metal pyrosulfite per mole of nitric oxide in the gas.

5. The method according to any of paragraphs.1 to 4, characterized in that the processing gas by using an alkali metal pyrosulfite carry out dry by.

6. The method according to any of paragraphs.1 to 5, characterized in that use a molar ratio of ABOUT2/NO more than 1.

7. The method according to p. 6, characterized in that use a molar ratio of ABOUT2/NO, brainwise 25.

 

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