1 coal-fired power plant flue gas pollution prevention necessity
As the power industry is the basic industry of the national economy, with the rapid economic development, the demand for electricity in our country is constantly increasing and the basic structure of coal-fired units will be maintained in the power structure for a long time to come. While coal-fired power plants continue to deliver clean energy, coal-fired fumes, sulfur dioxide, nitrogen oxides, heavy metal mercury and other pollutants will also continue to grow, potential environmental problems continue to emerge, increasing the degree of acid rain pollution, Aggravating the influence of water eutrophication and directly endangering the living environment of human beings. This poses a severe test for the protection of atmospheric environment in our country, especially for the prevention and control of acid rain pollution. Therefore, coal-fired power plants must complement and improve environmental protection facilities such as dust removal, desulfurization and denitration, and effectively control pollutants such as soot, sulfur dioxide, nitrogen oxides and heavy metal mercury from the source.
2 coal-fired power plant flue gas pollutants prevention and control technology
The "Emission Standard of Air Pollutants for Thermal Power Plants" (GB13223-2011) was officially implemented on January 1, 2012. The standard strictly controls the emission standards of soot, SO2 and NOx pollutants. The three pollutants, namely, soot, SO2 and NOx The emission limits are reduced from 50 ~ 200mg / m3, 400 ~ 1200mg / m3, 450 ~ 1100mg / m3 to 30mg / m3, 100 ~ 200mg / m3 and 100 ~ 200mg / m3, respectively. At the same time, for the first time, the emission limit of atmospheric mercury pollutants in thermal power plants (0.03mg / m3) was added. Now on the coal-fired power plant flue gas pollutants prevention and control, especially heavy metal mercury removal methods are analyzed and discussed.
2.1 smoke and dust control
There are two main types of dust removal technologies in coal-fired power plants: ESP and bag filter. At present, electric dust removal is still the mainstream of China's power dust removal process. Dust particles in the flue gas through the high-voltage electrostatic field, with the positive and negative ions and electrons collide with the charge and charge (or ion diffusion movement in the charge), with ions and ions in the dust under the action of the electric field To the opposite electrode movement and attached to the opposite electrode, by means of rapping so that the dust on the electrode fall into the collection hopper, the flue gas through the electrostatic precipitator to be purified, to protect the atmosphere, the purpose of protecting the environment.
At present, most of the coal-fired power plants have complicated coal types, prominently co-firing low quality coal, and harsh conditions of smoke and dust conditions. However, electrostatic precipitators are more sensitive to soot characteristics and coal dust removal and other factors reduce dust removal efficiency. For the problems in the application of electrostatic precipitators, the relevant manufacturers or units of domestic electrostatic precipitators begin to reform the conventional electrostatic precipitators. Among them, the most representative is the high-frequency power technology. By adopting the new high-power and high-frequency high-voltage power supply technology , Can greatly improve the dust removal efficiency.
After the high-efficiency coal-fired power plant dust emissions were basically aerodynamic diameter of less than 10 microns of fly ash, and most belong to PM2.5, and bag dust removal technology is the biggest advantage of high dust removal efficiency, electrostatic precipitator and bag dust On the fine particle capture efficiency can reach more than 95%. Therefore, with the improvement of environmental protection requirements and the increasingly stringent emission standards in our country, the dust control has gradually shifted to bag-type dust removal and electric bag dust removal technologies. Especially in recent years, the electric bag filter has started to be used on a large scale in coal-fired power plants.
2.2 sulfur dioxide treatment
Flue gas desulfurization is the most widely used and most effective SO2 control technology in the world, which can be applied to various units and coal combustion conditions. Wet desulfurization absorption tower set dust, desulfurization, oxidation and many other functions in one, the use of cheap limestone or lime for desulfurization absorbent, with a wet ball mill will not exceed 20mm limestone grinding into absorbent slurry. As the absorption of slurry recycling, desulfurization absorbent utilization is high.
In the absorption tower, the absorption slurry is mixed with the flue gas, the SO2 in the flue gas is chemically removed from the calcium carbonate in the slurry and the air of bubbling, and the final reaction product is gypsum (calcium sulfate dihydrate). Desulfurized flue gas through the mist eliminator to remove small droplets entrained flue gas, net smoke through the smoke into the chimney. Desulfurized gypsum slurry dehydration after dehydration device recovery.
2.3 Nitrogen oxides governance
Selective catalytic reduction (SCR) denitration process is the most widely used and the most efficient denitrification, the most mature denitration technology. The SCR method is a post-combustion NOx control process. Under the action of the catalyst, NH3 (gas) reacts with NOx to convert NOx in the flue gas to H2O and N2. The denitration efficiency is not less than 90%. Selective catalytic reduction (SCR) denitrification wide range of applications, high rate of denitrification, ammonia escape is too low, the impact of downstream equipment is small. However, high investment, the use of catalysts, the reaction temperature in the lower range (280 ~ 420 ℃).
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