Heat treatment is a basic process of metal processing, which can change the structure of the metal, thereby improving the properties of the metal and making it meet various application requirements. Common heat treatment processes include chemical heat treatment such as annealing, normalizing, quenching, tempering, aging, surface quenching and carburizing.

According to our experience, the main waste gas pollutants of heat treatment enterprises are different due to different equipment and processes, but to sum up, the main waste gas pollutants and sources of the current heat treatment industry mainly include the following aspects:

1. Oil fume mainly comes from quenching oil, tempering oil, and heating of parts;

2. Organic volatile gases such as alkane, benzene, xylene, methanol, ethanol, propranolol, acetone, triethanolamine, aniline, formamide, trichloroethylene, etc., mainly from carburizing and carbonation agents, protective atmosphere heating , organic cleaning agent, etc.;

3. Powder (smoke) dust, mainly from fuel furnace, chemical heat treatment of various solid powder methods, hot-dip galvanizing and hot-dip aluminum plating, sand blasting and shot blasting.

4. Carbon monoxide, mainly from fuel or atmosphere combustion, gas carburizing and carbonitriding, etc.;

5. Sulfur dioxide, mainly from fuel or atmosphere combustion, sulfurization and sulfur-nitrogen-carburization;

6. Nitrogen oxides, mainly from fuel or atmosphere combustion, nitrate bath, alkaline blackening;

7. Hydrogen cyanide and alkali metal hydrogenation, mainly from liquid carburizing, gas and liquid carbonitriding and carbonitriding;

8. Ammonia, mainly from ammonia permeation, ammonia carbon permeation, thiamine carbon permeation, etc.;

9. Chlorine, chloride and fluoride, mainly from high temperature and medium temperature salt bath, silicon infiltration, boron infiltration and metal infiltration, physical and chemical vapor deposition, pickling, hot-dip galvanizing and hot-dip aluminum plating flux, etc. ;

10. Hydrochloric acid, nitric acid, sulfuric acid steam, mainly from pickling;

11. Caustic alkali and nitrite steam, mainly from oxidation tank, nitrate bath, alkaline degreasing tank;

There are many difficulties in the treatment of heat treatment oil fume exhaust gas. According to our experience, the two major problems are summarized as follows:

First, exhaust gas collection is difficult. The main reason is:

· Different work pieces require different temperatures, different sizes of quenching oil tanks, and different ways of entering and exiting quenched work pieces.

· Many workshops have aerial cranes, and the collection and purification of exhaust gas cannot affect the normal operation of the aerial cranes.

· The high temperature work piece is directly placed in the medium, and the exhaust gas has strong instantaneous expansion and large impact force.

Second, waste gas treatment is difficult. The reason is:

a) The amount of heat treatment exhaust gas is large, the concentration is high, the temperature is too high, and some are accompanied by large flames, so it is necessary to consider cooling and fire resistance.

b) The heat treatment exhaust gas has high humidity, and it is necessary to consider how to deal with the water vapor.

c) The composition of exhaust gas is complex, including carbon, soot, and polyaromatic hydrocarbons such as benzopyrene, benzanthracene, and carbazole.

d) The molecular size of the exhaust gas is complex, and the adaptability of the purification equipment is relatively high. Among them, the size of the soot molecules is generally 0.8-5 microns, the particle size of the soot is 0.5-2 microns, and the particle size of the smoke is 0.07-1 microns.