SU959812A1 - Method of cleaning exhaust gases from nitrogen oxides - Google Patents

Description

This invention relates to methods for removing nitrogen oxides in the production of nitric acid by catalytic decomposition. The known method of purification of exhaust gases from nitrogen oxides by absorption by alkali before the gas leaves the apparatus in 1/20 - 1/3 of the reaction volume 1. The main disadvantages of this method are the high percentage of nitrogen oxides in the purified gas and the low degree of purification. The closest to the invention in technical essence and the achieved result is a method of cleaning tail gas from nitrogen oxides in the production of nitric acid by displacing them in the combustion chamber with natural and oxygen-containing gases and further catalytic reduction of nitrogen oxides in the presence of natural gas 2. Ratio of natural gas to oxygen in the gas mixture at the inlet to the reactor, it is 0.52-0.60. Of the total amount of natural gas supplied to the catalytic refining, 60% is sent to the combustion chamber and 40% directly to the reactor. The disadvantage of this method is the high content of flammable substances, carbon monoxide and nitrogen oxides in the purified gas (up to 0.3; 0.13 and 0.005%, respectively), which leads to increased natural gas consumption. The purpose of the invention is to reduce the consumption of natural gas and increase the degree of purification. The goal is achieved by the fact that according to the method of purifying exhaust gases from nitrogen oxides by displacing them in the combustion chamber with natural and oxygen-containing gases and further catalytic reduction of nitrogen oxides in the presence of natural gas, the volume ratio of natural gas to oxygen in the gas mixture is maintained in the range of 0 35-0.48. Moreover, at the stage of catalytic reduction, natural gas is introduced in the amount of 40-50% of its amount fed to the combustion chamber. A distinctive feature of the proposed method is that the volume ratio of natural gas to oxygen in the gas mixture is maintained in the range

0.35-0.48, and also the fact that natural gas is introduced into the catalytic reduction stage in the amount indicated above.

A decrease in the CH ratio of less than 0.35 leads to an increase in the content of nitrogen oxides in waste gas, and their increase in more than 0.48 leads to an increase in combustible components in gases to 0.3-0.4 due to incomplete combustion of natural gas and CO in the reactor.

Reducing the consumption of natural gas in the reactor below 40% of its flow into the combustion chamber also leads to an increase in the content of nitrogen oxides in the waste gases, and an increase in the consumption of natural gas above 50% leads to an increase in the concentration of combustible components in the gases.

Example 1. "Tail nitrous gases after absorption columns in the amount of 35,000 with a nitrogen oxide content of 0.15% and a temperature of 30 ° C enter the combustion chamber of the reactor, where they are heated to a temperature of 450-470 ° C by mixing 640 natural gas and 5300 air. The ratio of SND: Ye 0.35.

The temperature of the gas above the combustion chamber is controlled by changing the amount of natural gas supplied to the combustion chamber, the consumption of natural gas is 640.

After the combustion chamber "tail gas mixed with natural gas is sent to the reactor. The amount of natural gas in this case is 320, i.e. 50% of its flow into the combustion chamber.

In the reactor on a two-layer catalyst, where the top layer is palladium alumina, at a temperature of 650-730 ° C, the carbon-containing components are burned and the nitrogen oxides are reduced to elemental nitrogen.

The purified tail gas after the reactor enters the catalyst, and then, after passing through economizers, is released into the atmosphere.

The content of nitrogen oxides in the purified gas is 0.0041%, combustible - 0.1%, CO - 0.0%.

Example 2. The process is carried out analogously to example 1. The amount of "tail nitrous gases supplied to the combustion chamber is 35,000 natural gas - 580, air - 4900.

The ratio of 0.45. The amount of natural gas fed to the reactor 245, which is 42% of its flow into the combustion chamber.

The table shows the results of the cleaning process for this and the known methods.

Tail gas flow, 4127041270

The temperature in the combustion chamber, C

Temperature in the reactor, C

The percentage of nitrogen oxides in the initial mixture,%

The percentage of nitrogen oxides in the purified gas,%

The percentage of flammable in the purified gas,%

CO content in purified ha. 38,%

450-470450-470

650-750650-750

0,12-0,200,12-0,20

0,0030,005

0.1

0.3

0.05

0.13

As follows from the table, the proposed method allows to reduce the percentage of combustible in the purified gas by three times, the CO content in the purified gas more than doubled, and the content of nitrogen oxides by 1.5 times.

Claims (2)

1. A method of purifying waste gases from nitrogen oxides by mixing them in a combustion chamber with natural and oxygen-containing gases and further catalytic reduction of nitrogen oxides in the presence of natural gas, characterized in that, in order to reduce the consumption of natural gas gas and increasing the degree of purification, the volume ratio of natural gas to oxygen in the gas mixture is maintained in the range of 0.35-0.48%, 2. A method according to claim 1, characterized in that at the stage of catalytic reduction of nitrogen oxides natural gas is introduced in an amount of 40-50% of its quantity fed into the combustion chamber. Sources of information taken into account in the examination 1. USSR Author's Certificate No. 392958, cl. B 01 D 53/14, 1971. 2. Nitrogen industry. Collection of abstract information. 1973, No. 3, p. 71