SU1736582A1 - Method of cleaning waste gases of organic matter - Google Patents

Abstract

The invention relates to methods for purifying waste gases from organic matter. Usage: mainly chemical and metallurgical industry. SUMMARY OF THE INVENTION: The waste gases of a heat treatment furnace of smolodolite refractories are burned at 850–950 ° C, then the gases are enriched with oxygen to 10–12% by volume and processed at 500–550 ° C. 0.8–1 s — oxidation polycyclic aromatic hydrocarbons (PAHs), then catalytic gas cleaning is performed at the same temperature. The degree of purification from PAHs and benzo (a) pyrene is 99.895-99.91%. 1 tab., 1 sludge

Description

The invention relates to a technique for the purification of waste gases from organic substances and can be used in the chemical, metallurgical and other industries.

A known method for purification of gas emissions containing a mixture of high- and low-boiling hydrocarbons, according to which the source gas stream is cooled, the condensate formed is burned in a flare, and non-condensed emissions are divided into two streams, one of which is used as an oxidant during flaring, and the other is mixed with the products of flare combustion and is fed to catalytic oxidation.

At the same time, the ratio of uncondensed emissions to the flaring and catalytic oxidation is set to 0.6-1.0: 1.0.

In addition, the number of flare products supplied for mixing with uncondensed emissions supplied for catalytic oxidation is maintained at 0.10-0.20 of the total yield of combustion products.

The disadvantage of this method is due to the limited scope, in particular, the impossibility of cleaning gas emissions with an oxygen content of less than 1%. due to the fact that in this purification method one of the uncondensed emissions streams is used as an oxidizer during flare combustion.

The closest to the proposed technical essence and the achieved result is a method of purification of exhaust gases from organic impurities including catalytic purification and thermochemical combustion, while prior to catalytic purification, the mixture of exhaust gases with combustion products is maintained at 600-700 ° С for 0.2- 0 5 s and then

cl

with

subjected to thermomechanical combustion at 1000-1100 ° C.

The disadvantage of this method is the high degree of purification of multi-core polycyclic aromatic hydrocarbons (PAHs) due to the absence of their stepwise thermal oxidation.

The purpose of the invention is to increase the degree of purification of waste gases from PAHs, mainly from benzo (a) pyrene,

The method includes thermal combustion of gases at 850–950 ° C, subsequent enrichment with air of oxygen up to 10–12 vol%, heat treatment at 500–550 ° C for 0.8–1 s, and then catalytic purification at the same temperature.

The need to enrich the exhaust gases with air oxygen and their oxidation after heat treatment before catalytic purification is due to the following.

The enrichment of exhaust gases with air oxygen and their oxidation are carried out in a mixer in the temperature range of 500- 550 ° C.

In this temperature range, the main reaction is dehydrogenation, which leads to the formation of polymerization and polycondensation products. Thermal effects on heavy PAHs contained in the gas to be cleaned in the presence of atmospheric oxygen result in the elimination of hydrogen and methyl groups with the formation of radicals, which recombine into larger molecules. The action of atmospheric oxygen is reduced to the intensification of the dehydrogenation process. During thermal exposure in the presence of air oxygen in a gas mixer for 0.8–1 s, decomposition of larger molecules into simple hydrocarbon compounds occurs.

As a result, oxidation products (PAHs), which are peroxides containing the -0-0- group, in which half of the oxygen is in the weakly bound state, fall on the active catalyst layer, are highly oxidized to CO2 and H2O. Oxidation of heavy multi-nuclear PAHs on the catalyst without their prior thermal decomposition in the presence of air oxygen in a gas mixer leads to the formation of pyrocarbon compounds (soot) on the catalyst bed, which reduce the activity of the catalyst.

When the ratio of the mixture of pyrolysis gases and air is less than 1: 1, the oxidation process of PAH, including benzo (a) pyrene, is not efficient enough due to the low oxygen content. At a ratio of

five

0

five

0

five

0

five

0

gas-air more than 1: 1.5, the temperature of the reaction mixture decreases significantly, which leads to a decrease in the rate of oxidation of PAH, including benzo (a) pyrene.

When PAH oxidation duration in the mixer is less than 0.8 with complete thermal destruction of heavy multicore hydrocarbons, it does not occur due to the lack of time to carry out sequential stepwise oxidation of heavy PAHs. An increase in the thermal oxidation time in the mixer for more than 1 s leads to a significant increase in size. equipment with the same degree of oxidation.

Placing a gas mixer in front of a cyclone furnace is impractical because the pyrolysis exhaust gases have a low initial temperature (200-600 ° C), which decreases further when the gases are diluted with oxygen from the air, which leads to condensation and polymerization of the pyrolysis gases. As a result, the possibility of thermal decomposition of heavy multi-nuclear PAHs is eliminated. In addition, the absence of a preliminary thermal shock in a cyclone furnace eliminates the formation of free radicals in heavy hydrocarbons and their further decomposition.

The presence of thermal aging of the mixture of exhaust gases with combustion products by a known method before thermal combustion is due to the fact that the exhaust gases are mixed with combustion products having a high temperature.

Example. The method is carried out at a pilot plant, the scheme of which is shown in the drawing, at a metallurgical plant (DMK) in Dneprodzerzhinsk.

The process parameters of thermocatalytic gas cleaning are as follows.

The amount of gases

five

0

five

entering the treatment, m / h PAH concentration

in combustible gases,

g / m3

including benzo (a) pyrene

The temperature in the furnace, ° C The temperature in the mixer, ° C The temperature in the catalyst bed, ° C Volume velocity

gas, h 1 resistance

1300

Up to 50

Do1 850-950 500-550

500-550 8000

catalyst bed, kPa4-5 Catalyst Copper-chromium Purification degree,%

from PAU99,8

from benzo (a) pyrene 99,99

The pyrolysis waste gases of the heat treatment furnace 1 of smolodolite refractory materials containing up to 50 g / m PAH, including pyrene bens (a) up to 1 g / m 3, with a temperature of 200-600 ° C along the heated duct 2 are directed to the cyclone furnace 3 at heat treatment. At the entrance to the cyclone furnace 3, the source gas is diluted with air through the nozzle 4 in a 1: 1 ratio. In the cyclone furnace 3, due to the presence of two tangentially located burners 5, there is a high turbulization of the gas flow, heating of the gases to be purified to 850–950 ° C and partial oxidation of the light PAHs. Next, the gases from the cyclone furnace 3 enrich the air through the nozzle 6 to 10-12% by volume (in the ratio 1: 1-1.5) with oxygen to complete oxidation of heavy PAHs and transfer them to a special temperature of 500-550 ° C. horizontally placed lined mixer 7. The oxidation time of heavy multi-nuclear PAHs in the mixer is 0.8-1 s.

After the gas mixer 7, the gases to be purified are directed to the catalytic reactor 8, where PAH, including benzo (a) pyrene, is exposed to deep oxidation on the active layer of the copper-chromium catalyst to harmless carbon dioxide and carbon dioxide. water, Next, the purified gases using the fan 9 through the chimney 10 are discharged into the atmosphere.

The modes for performing these operations are determined as follows. When the gas temperature in the cyclone furnace is below 850 ° C, insufficient thermal oxidation of the light PAHs occurs and soot formation begins, which ultimately leads to a decrease in the efficiency of the gas mixer and the catalytic reactor, as well as to a decrease in the service life of the catalyst. When the temperature of the gas to be purified in a cyclone furnace exceeds 950 ° C, there is a significant increase in the formation of nitrogen oxides in the exhaust gases, which, in turn, necessitates additional purification from nitrogen oxides (see table).

In addition, an increase in the gas temperature in the cyclone furnace over 950 ° C leads to a significant increase in energy consumption (natural gas) without significantly increasing the degree of gas purification, and also reduces the equipment wear resistance. According to the proposed method, thermal combustion of the mixture of gas to be purified with air is carried out in a ratio of 1: 1, while the gas-air mixture is prepared directly at the entrance to the cyclone furnace and then fed to the flare of two tangentially located gas burners.

At temperatures below 500 ° C, PAH does not completely oxidize on the active catalyst layer. including benzo (a) pyrene, to harmless carbon dioxide and water, and the formation of carbonaceous compounds on the surface of the catalyst, which leads to its rapid deterioration. At temperatures above 550 ° C, an irreversible process of destruction of the catalyst structure occurs, which also leads to its release. The averaged degree of gas purification from PAH and benzo (a) pyrene according to the proposed method is 99.895% (with a degree of purification from PAH 99.80% and benzo (a) pyrene 99.99%) and 99.91% (with a degree of purification from PAH 99.83 and benzo (a) pyrene 99.99%), which exceeds the degree of purification of exhaust gases by a known method.

Claims (1)

DETAILED DESCRIPTION OF THE INVENTION Claims A method for purifying waste gases from organic substances, including thermal combustion, heat treatment, and subsequent catalytic gas cleaning, characterized in that. that, in order to increase the degree of gas purification from polycyclic aromatic hydrocarbons, mainly benzo (a) pyrene, thermal combustion of gases is carried out at 850–950 ° C, after which the gases are enriched with air oxygen up to 10–12% by volume and heat treated them at 500-550 ° C for 0.8-1 s, followed by catalytic purification at the same temperature.