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Measures and schemes for asphalt flue gas treatment
1、 The necessity of asphalt flue gas treatment.
The asphalt fume is easy to adhere and is flammable and explosive at a certain temperature. During the collection, transportation and smoke elimination of asphalt fume, it is easy to adhere to the surface of pipes and equipment and form liquid or even solid asphalt. It is difficult to remove solid asphalt, which often leads to pipeline blockage and equipment damage, which makes the system unable to operate normally.
In addition, the composition of asphalt flue gas is very complex, which varies due to the source of asphalt. Asphalt fume contains not only solid and liquid particles condensed by volatile components of asphalt, but also organic substances in vapor state. Some organic compounds are macromolecular polymers, which will cause serious pollution to the environment. The flue gas contains a variety of organic substances, including carbon-cyclic hydrocarbons, cyclic hydrocarbon derivatives and other compounds, which are harmful to human health. Asphalt smoke contains polycyclic aromatic hydrocarbons such as benzopyrene, benzoanthracene, carbazole, etc. Most of them are carcinogens and strong carcinogens, which are harmful to human health. Its main way is to attach to dust below 8um and inhale it through the respiratory tract. Therefore, it is necessary to purify the asphalt flue gas to make the emission meet the atmospheric environmental standards.
2、 Parameters of flue gas treatment system.
1. Determine the amount of flue gas.
According to the actual situation of the site, the smoke production points on the site shall be collected in a centralized manner. Each smoke production point shall be equipped with a smoking hood to determine the distribution of the system air volume.
2. Governance objectives.
The flue gas emission shall comply with the limit value of Class II standard in the Integrated Emission Standard of Air Pollutants (GB16297-1996), i.e. the concentration of asphalt smoke ≤ 40mg/NM3, and the concentration of benzo [a] pyrene ≤ 0.3X10 ^ - 3.
3、 Key points of process flow and system design.
Asphalt fume is easy to adhere and burn above a certain temperature. During the collection, transportation and smoke elimination of asphalt smoke, it is easy to stick to the surface of pipeline equipment to form liquid or even solid asphalt, which is difficult to remove and will affect the normal operation of the system. In addition, the main components of asphalt smoke are aromatics and heterocyclic compounds, which will cause serious pollution to the environment.
According to relevant data, the relevant properties of asphalt and asphalt fume are as follows: asphalt self-ignition point 610 ℃, lower explosive limit 35g/m ³， The maximum ignition energy is 40mJ, the maximum explosion pressure is 0.32MPa, the average pressure rise rate is 2.5MPa/s, and the critical oxygen content to prevent dust from being ignited by electric spark is 16%.
According to these data, the system needs to design high-pressure spray fire protection device and explosion-proof device. According to the relevant data and the characteristics of asphalt smoke, the design points are as follows:
1. The optimum temperature of the asphalt smoke trap is 60 ℃ - 80 ℃, lower than 50 ℃, the asphalt is easy to bind, and it is not easy to trap above 100 ℃, which does not meet the process requirements of the asphalt smoke trap;
2. Prevent asphalt from burning in the flue and open fire and dark fire from entering the asphalt smoke collector;
3. Try to reduce the coal dust in the flue gas and improve the fluidity of coal tar asphalt in the asphalt smoke collector;
4. The asphalt smoke collector is equipped with explosion-proof device;
5. In order to solve the problem of large diameter and airflow bias of the electric capture equipment, the equipment must be equipped with an advanced diversion gas distribution system at the bottom.