The executive meeting of the State Council on December 2, 2015 decided that full implementation of ultra-low emissions and energy-saving retrofits to coal-fired units by 2020 will reduce the average coal consumption per MWh of all active power plants to less than 310 grams and lower the average coal consumption of new power plants In 300 grams, the outdated production capacity and does not meet the relevant mandatory standards required to resolutely phase out the shutdown, the eastern and central regions to advance to 2017 and 2018 compliance. To ultra-low emissions and energy-saving reform to increase policy incentives, transformation of input-based enterprises.
Low emission concept
For ultra-low emissions, at present, the more common concept in China is that the pollutant discharge standards of coal-fired power plants basically meet the emission limits of gas turbines in the GB13223-2011 standard (that is, soot, sulfur dioxide and nitrogen Oxide concentrations are not higher than 10,35,50 mg / m3), but in this standard, the oxygen content of flue gas corresponding to the emission limits of natural gas turbine and coal-fired boiler is 15% and 6%, respectively. If converted To the same oxygen content conditions, natural gas turbine emission limits are actually 2.5 times the limit of coal-fired units, we can see that after the completion of ultra-low emission modification, coal-fired units emission standards lower than the gas.
Transform the technical route
Denitration technology route
At present, the denitrification technology widely used in coal-fired power plants is mainly "low-nitrogen combustor + selective catalytic reduction method". Low-nitrogen combustion technology mainly increases the proportion of burnt-out wind by adjusting the ratio of the secondary air to the exhaust air So as to reduce the NOX generated in the burnout wind area. At present, the latest low-nitrogen combustion technology can control the nitrogen oxides concentration in the flue gas at the boiler outlet to about 200mg / m3. The nitrogen oxides in the flue gas after the flue gas enters the denitration reactor Further react with the ammonia to reduce the concentration of nitrogen oxides in the flue gas to less than 100 mg / m3.
To achieve ultra-low emission standards, mainly through two ways to achieve, one is to increase the area of ​​the catalyst in the denitrification reactor, increase ammonia injection to improve the efficiency of denitration to reduce the concentration of nitrogen oxides emissions; the other is the boiler combustion Low nitrogen combustion engine transformation (the boiler has been modified boiler can only take the former one). At present, in the transformation of ultra-low-emission of major power plants, the two approaches are basically implemented by combining low-nitrogen burners first and then increasing the area of ​​denitrification catalysts appropriately, especially in the case of tangentially fired boilers . For hedging boiler swirl burner, the general use of only increasing the area of ​​denitrification catalyst, increase the amount of ammonia injection to reduce the concentration of nitrogen oxides.
Desulfurization technology route
Active coal-fired units on July 1, 2014 began to implement the "thermal power plant emission standards for air pollutants" (GB13223-2011) standards in the standardization of sulfur dioxide transformation, the general by increasing the height of the absorption tower, increase absorption tower limestone slurry spray Shower layer technology to achieve. In the transformation of ultra-low emissions, desulphurization system mainly uses the following methods:
First, desulfurization dust integration technology. The single-tower integrated desulfurization and dust removal depth purification technology can simultaneously achieve the desulfurization efficiency of more than 99% and the dedusting efficiency of more than 90% in an absorption tower to meet the ultra-clean emission requirements of sulfur dioxide emission 35mg / m3 and soot 5mg / m3. The integrated desulfurization and dust removal device is an integrated device optimized with three systems of rotating exchange coupling device, high efficiency and energy saving sprinkler device and tube bundle dedusting device, and is applied to sulfur dioxide removal in wet desulfurization tower. As shown in Figure 1.
Second, single-tower dual-zone high-efficiency desulfurization dust removal technology. Using an absorption tower, the slurry is designed as a two-zone slurry tank, which separates the slurry tank into two upper and lower levels (upper low-pH zone and lower high-pH zone). The upper zone is primarily responsible for oxidation while the lower zone is responsible for absorption and installation efficiency Ring, spray layer plus layer, porous distributor and other measures to significantly improve the desulfurization effect, and set the original flue spray dust removal system can effectively improve the dust removal effect.
Third, double tray technology. Double-tray desulfurization system adds a layer of alloy tray on the basis of the original single-layer tray. The double tray has one layer of liquid film than the single tray, and the gas-liquid exchange is more sufficient, thereby performing desulfurization and synergistic effect. This technology is more advantageous when the desulfurization efficiency is higher than 98% or the coal with high sulfur content.
Fourth, double-loop double-loop technology. In fact, the double-column double-circulation technology upgrades the auxiliary tank to an absorption tower. The double-circulation technology and the spray layer and mist eliminator are provided at the same time to further enhance the double-circulation desulfurization and dust removal effects. However, it occupies a large area and is not suitable for the layout of a relatively compact power plant with more auxiliary machines and high operating costs.
Dust removal technology route
Active coal-fired units to meet the "thermal power plant emission standards for air pollutants" (GB13223-2011) standard dust emissions standards for dust remover more use of high-frequency power transformation, installation of low-temperature economizer, increase the ESP electric field, Last electric field sub-district power supply is widely used. In the transformation of ultra-low emissions, dust removal system mainly uses the following methods:
First, wet electrostatic precipitator. Wet electrostatic precipitator dust collection principle and dry electrostatic precipitator the same, the main deal with high moisture content and even saturated wet gas. Can effectively remove the flue gas dust, acid mist, water droplets, PM2.5 and other harmful substances, dust removal efficiency, more reliable operation.
Second, the electric bag composite dust. Electric bag composite dust collector is a combination of electrostatic precipitator and bag dust removal features, through the pre-electric field pre-dust collection, charging and post-filter bag filter dust an efficient dust collector with high efficiency and stability Strong advantage. However, there is a short life of the bag, high maintenance costs shortcomings.
In the recent two years of ultra-low-emission reform, it is often the combination of the above technical routes for the reorganization of existing units, mainly in the following categories:
Desulfurization dust integration + denitrification catalyst plus layer + high-frequency power. Single investment 50 million -100 million, while low operating and maintenance costs, downtime can be controlled within a minimum of 40 days, belonging to the last two years of new technology, operational reliability to be tested;
Integration of desulfurization and dust removal + denitration catalyst plus layer + high frequency power transformation + MGGH. Reliable performance, investment and operation and maintenance costs are relatively low. A single machine about 1-1.5 billion investment, downtime 40 days, at the same time be able to solve the "white smoke" and the corrosion of the chimney;
Desulfurization dust integration + denitrification catalyst plus layer + high frequency power transformation + wet dust removal. About 1-1.3 billion single-machine investment, downtime 50 days, the terminal dust removal effect will be more obvious, but can not eliminate the "white smoke" and solve the problem of corrosion of the chimney;
Single tower dual zone desulfurization and dedusting technology + denitrification catalyst plus layer + high frequency power transformation + MGGH. Investment and Route and (1) Close to 50 days of downtime, this technology not only meets the ultra-low emission requirements but also eliminates "white smoke" and solves the problem of chimney corrosion, but the dust removal effect is relatively poor.
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