In recent years, with the frequent human activities, air pollution has become more and more serious. Studies have shown that industrial waste gas contains organic compounds, sulfides, fluorides and other chemicals, which seriously harm human health and greatly increase the incidence of respiratory-related cancers.
Polycyclic aromatic hydrocarbons have strong carcinogenicity. Sulfide-containing gases enter the human body, which mainly damage the respiratory system and stimulate the mucous membranes. Long-term intake of fluoride-containing gases can cause brain damage and affect cell metabolism and protein synthesis.
With the continuous development of society and economy, people's awareness of environmental protection has gradually strengthened, and the requirements for environmental quality have become higher. In the future, the control and degradation of atmospheric pollutants is bound to be one of the main research directions of future environmental science.
Next, I organized ten kinds of waste gas treatment processes for everyone.
Method for treating exhaust gas
There are many types of exhaust gas pollutants with different characteristics. For different types of exhaust gas, choose an appropriate treatment method. Commonly used treatment methods are: condensation method, absorption method, combustion method, catalytic method, adsorption method and so on.
1.Condensation recovery method
The condensation recovery method is a method of directly introducing exhaust gas into the condenser or firstly adsorbing and absorbing the concentrated exhaust gas after analysis, and then the condensate is separated to recover valuable organic matter.
Advantages: The condensation method is mainly used for the recovery of high-boiling-point and high-concentration VOC polluted gases. The applicable concentration range is> 5% (volume), and the process is simple and the recovery rate is high.
Disadvantages: This method requires additional refrigeration equipment, which requires large investment, high energy consumption, and high operating costs. At the same time, the exhaust gas after condensation still contains a certain concentration of organic matter and serious secondary pollution, so this method is rarely used for the treatment of low concentration exhaust gas.
2. Absorption method
Absorption methods can be divided into chemical absorption and physical absorption. Because organic waste gas contains a large amount of "triphenyl" gas and has low chemical activity, chemical absorption cannot generally be used.
Physical absorption is that one or more components in the exhaust gas are dissolved in the selected liquid absorbent. This absorbent should have high affinity with the absorbing components, low volatility, and should also have less volatility. After being saturated, the absorption liquid is desorbed by heating and then cooled and reused.
Advantages: suitable for low temperature, medium and high concentration waste gas, can selectively absorb waste gas such as hydrogen sulfide, the process is simple, and no additional steam and other heat sources are required.
Disadvantages: It needs to be equipped with recovery devices such as heating analysis and condensation. The installation volume is large, the investment is large, and there is also secondary pollution, and the purification effect is not ideal.
3.Direct combustion method
The direct combustion method uses the heat released by the combustion of auxiliary fuels such as gas or fuel to heat the mixed gas to a certain temperature (700-800 ° C) and stay for a certain time (0.3-0.5 seconds) to cause high-temperature decomposition of combustible harmful substances A method for harmless substances.
Advantages: The direct combustion method has simple process and small equipment investment, and is suitable for high-concentration, small-air-volume exhaust gas treatment.
Disadvantages: large energy consumption and high operating costs; high technical requirements for operation, difficult to control and master, and basically not promoted in China.
4. Thermal combustion method
Thermal combustion refers to the process of increasing the temperature of the exhaust gas to the temperature of the combustible gaseous pollutants to cause them to undergo oxidative decomposition.
The process flow diagram is as follows:
Advantages: It is suitable for the purification treatment of exhaust gas with a low content of combustible organic substances. The combustion purification treatment technology has high thermal efficiency, long equipment life, anti-aging, and corrosion resistance.
Disadvantages: large equipment, inconvenient transportation; high equipment prices and high operating costs; poor treatment of sulfur and halogen organic waste gas.
5, catalytic combustion method
Catalytic combustion is the process of completely oxidizing harmful combustible components in exhaust gas into carbon dioxide and water under the action of a catalyst.
Advantages: The catalytic burner has high purification rate, low operating temperature, low energy consumption, less restrictions on the concentration of combustible components and heat value, simple operation and good safety.
Disadvantages: Some gas combustion conditions are harsh, requiring high temperature, high altitude and high water vapor partial pressure, so the catalyst must have high activity, high thermal stability, high hydrothermal stability, and a certain ability to resist poisoning.
6. Activated carbon adsorption method
Activated carbon adsorption is to send the organic waste gas to the adsorption bed by the exhaust fan. The organic waste gas is adsorbed on the adsorption bed by the activated carbon adsorbent to purify the gas. The purified gas is discharged to the atmosphere to complete the purification process.
Advantages: high adsorption rate, low operating energy consumption, low cost and cost, safety and reliability, suitable for hazardous places with explosion, adsorbent can be recycled, energy saving and environmental protection.
Disadvantages: not resistant to high temperature, can not maintain a good adsorption capacity under wet conditions; flammable, quickly reach saturated adsorption and lose its effectiveness; produce secondary solid or liquid pollutants.
7. Biological law
Biological method is a method in which microorganisms use organic components as a carbon source and energy source and decompose them into CO2 and H2O.
Advantages: simple equipment, low investment, low operating costs, no secondary pollution, ideal treatment of VOCs exhaust gas.
Disadvantages: The reaction device has a large floor area and a long reaction time.
8. Plasma decomposition method
Plasma decomposition is an exhaust gas treatment method in which a large number of energetic electrons generated by dielectric discharge bombard pollutant molecules under the action of an external electric field, which triggers a series of complex physical and chemical reactions, thereby enabling the pollutants to be degraded and removed.
Advantages: simple process, low energy consumption, equipment materials with strong oxidation resistance, corrosion resistance, long service life, and can efficiently remove waste gas containing volatile organic, inorganic, hydrogen sulfide, ammonia and other major pollutants.
Disadvantages: The required vacuum environment of the plasma technology in the process of waste treatment has brought certain technical difficulties. It is still in the research stage. At present, many studies only focus on a single pollutant.
The UV method is a method of irradiating exhaust gas with a special high-energy high-ozone UV ultraviolet beam to change the molecular structure of the exhaust gas, so that the molecular chain of the organic or inorganic high-molecular exhaust gas compound is degraded and converted into low-molecular compounds under the irradiation of high-energy ultraviolet beam.
Advantages: small footprint, lower operating costs, and lower equipment investment.
Disadvantages: low removal efficiency and fewer types of gases that can be processed.
10.Biological filtration method
The biological trickling method is that the exhaust gas is passed through pretreatment processes such as dust removal, humidification or temperature reduction, and then passes from the bottom of the filter bed to the bottom through the filter bed composed of the filter material. The exhaust gas is transferred from the gas phase to the water-microbial mixed phase and is fixed by A method used to break down microbial metabolism on filter media.
Advantages: low processing cost, simple process, ecological and environmental protection.
Disadvantages: large area, fillers need to be replaced regularly, the process is not easy to control, problems are easy to occur after a period of operation, and the treatment of hydrophobic and difficult biodegradable substances is still difficult.