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Suzhou Boiler discusses boiler ultra-low emission control methods

Suzhou Boiler discusses boiler ultra-low emission control methods

As thermal power plants are currently facing severe environmental pressures, the implementation of ultra-low emission retrofits is a necessary step. However, coal-fired power stations burn a large amount of coal and emit a large amount of flue gas with low concentrations of complex pollutants such as sulfur dioxide, nitrogen oxides, and soot. The realization of ultra-low emissions has high requirements for the prevention and control of air pollution. This paper analyzes the emission characteristics of air pollutants from coal-fired power plants and proposes ultra-low emission control technologies for coal-fired power plant boilers, with a view to providing a reference for the design of ultra-low emission control measures for coal-fired power stations. introduction


Coal-fired power plant boilers emit a large amount of flue gas with complex components and high pollutant concentrations. Therefore, the implementation of ultra-low emission control has high technical requirements. The research on ultra-low emission control of coal-fired power plant boilers mainly lies in:


① Technology for enhancing performance of wet desulfurization equipment, such as double circulation, spin-coupling coupling, double tray, and high-efficiency demister;


② Research on the technical route with low-temperature electrostatic precipitators, wet electrostatic precipitators, electric bag precipitators, mobile electrodes, high-frequency power supply and other dedusting equipment as the core;


③ Temperature adjustment and energy saving of economizer, flue gas cooler, GGH and other heat exchange equipment;


④ Optimization of denitration technologies such as low nitrogen combustion, SCR efficiency enhancement, and wide-load denitration;


⑤ Ultra-low emission technology of fluidized bed. This paper intends to clarify the ultra-low emission control method for coal-fired power plants by combining air pollutants emitted by coal-fired power plants and control system technology, and provide a reference for the realization of ultra-low emissions.


1 Analysis of air pollutants in coal-fired power stations


The quality of coal-fired coal-fired power stations is complex, and the emission concentrations of soot, sulfur dioxide and nitrogen oxides are relatively high. The characteristics of soot depend on the type of boiler. The pulverized coal furnace has the characteristics of rapid burning, complete, large capacity and high efficiency. However, a small part of coarse ash formed by the combustion of pulverized coal forms ash and falls into the cold ash bucket. Finally, it is cooled to solid ash. Most of the finer particles of ash are taken away by the flue gas, which is usually called ash fly. The ash fly produced by the pulverized coal furnace is as high as 80 ~ 90%. Fluidized bed combustion is regarded as clean combustion. The desulfurization rate can reach 80 to 95%, the NOx emission can be reduced by 50%, and the combustion efficiency is high, as high as 95 to 99%. The nitrogen oxides produced by coal-fired power stations are mainly NO and NO2, collectively referred to as NOx. The main hazards are damage to the ozone layer, damage to animals and human bodies, and photochemical smog and acid rain.


2 Analysis of ultra-low emission control methods for coal-fired electric boiler stations


2.1 Smoke and dust ultra-low emission control technology


According to the working principle of the ultra-low emission control technology of smoke and dust, there are mainly these types: electrostatic type, rotary electrode type and wet electrostatic type. The advantages of electrostatic dedusting technology are that it is not easy to be affected by the external temperature during work, and has high working efficiency, can remove most of the dust, and the electrostatic dedusting can continue high-intensity operation without causing much loss to the equipment, saving Activity cost. The disadvantage of electrostatic dedusting is that it is almost impossible to remove fine dust. The advantages of rotating electrode dedusting are that the probability of occurrence of back corona is reduced, and the equipment used is smaller. It does not require much use area, and the shortcomings of rotary electrode type dust removal are that it has a small scope of application, requires high professional skills of equipment operators, and has a complicated installation process. The advantage of wet electrostatic dust removal is that it can keep the residue on the dust plate The removal of fine dust can also reduce the impact of resistance and enhance the ability of the dust collecting plate to adsorb the charged fine dust. In addition, the dust removal method can also effectively suppress the content of composite pollutants such as fine dust and acidic pollutants. However, wet electrostatic dust removal is likely to bring secondary pollution to the environment due to the use of water for dust removal. Proposed sustainable development concept.


2.2 SO2 ultra-low emission control technology


Common treatment methods for desulfurization of flue gas from coal-fired power plants are dry, semi-dry and wet. Among them, there are two methods used in traditional dry desulfurization, namely oxidation method and solid phase adsorption method. The desulfurization method is more effective when the sulfur content in the flue gas is low. However, the desulfurization method cannot scientifically use desulfurization. The products used in the semi-dry desulfurization method are many. Common methods include spray semi-dry method, post-calcium furnace activation method, ash slag external circulation semi-dry method and fluidized bed desulfurization method. The desulfurization method Although the effect is obvious, the ash cycle efficiency of the desulfurized product will be reduced. As for the wet desulfurization method, this method has many advantages:


① The desulfurization effect is remarkable;


② Competent for large displacement flue gas desulfurization tasks;


③ Desulfurization treatment cost is not high;


④ The product after desulfurization can be used scientifically.


However, the wet desulfurization treatment system is relatively complicated and requires high technical staff. In recent years, many scholars have studied this and proposed some advanced desulfurization technologies. For example, the urea solution is used as an absorbent for desulfurization treatment in a high gravity environment. This method has the advantages of small equipment footprint and low cost.


2.3 HgO ultra-low emission control technology


2.3.1 Mercury distribution in coal-fired flue gas


Under normal circumstances, the proportion of mercury in the flue gas emitted from coal-fired boilers is 1-20 μg / m3. Most of them consist of elemental Hg0, oxidation state Hg2 + (mainly HgCl2) and particulate mercury HgP. Among them, Hg2 + can Dissolved in water, therefore, a small amount of Hg2 + can be removed by means of flue gas wet desulfurization or denitrification processes, and particulate mercury HgP can be removed by using dust in a dust removal device. However, the other 20 to 50% of elemental mercury exists in the gas phase. Due to the very stable thermodynamic properties of elemental mercury, it can hardly be oxidized in a low temperature environment and will not be dissolved by water. Therefore, it is not easy to use conventional methods at low temperatures. Oxidation has stable thermodynamic properties, is insoluble in water, and is difficult to remove the element Hg0 in the flue gas. At present, the commonly used method is to change the element Hg0 in the flue gas to a form and then remove it by conventional means.


2.3.2 Mercury removal technology in coal-fired power plants


Aiming at the problem of mercury removal from coal-fired power plants, the American Electric Power Research Institute (EPRI) has also done research. The results of the research show that elemental mercury in the flue gas can be converted into mercury oxide when the coal-fired power plants use catalysts to remove nitrate In order to be able to remove mercury in subsequent processes. During the study and analysis of the working principle of this process, it was found that elemental mercury was first adsorbed by the catalyst, and then combined with oxygen in the air to form mercury oxide through a series of chemical reactions. After the reaction, mercury oxide was detached from the catalyst. However, this chemical process is affected by many factors, such as the speed of smoke emission, ammonia concentration, and the combined effect of the two. Low flow rates are beneficial for the oxygen oxidation process, but at the same time increase the ammonia reduction process. Therefore, the optimal residence time should be found to improve the synergistic removal efficiency of SCR denitration system for mercury.


2.4 Multi-pollutant control technology


The multi-pollutant control technology is mainly aimed at the emission control of two kinds of pollutants, NOx and SOx. Common methods include solid-phase adsorption / regeneration, gas-phase oxidation, electron beam radiation, and wet washing. Among them, the solid-phase adsorption / regeneration method and the gas-phase oxidation method have a wide application range, and this article will elaborate in detail.


2.4.1 Solid-phase adsorption / regeneration technology


The solid-phase adsorption / regeneration technology refers to the use of the solid adsorbent's own properties to absorb or cause chemical reactions with pollutants in the exhaust gas, and then convert it into easily removable pollutants. This technology can make solid adsorbents Used repeatedly. Common processes used for solid-phase adsorption / regeneration technology are activated carbon / activated carbon adsorption / regeneration process, CuO adsorption / regeneration process, NOxSO adsorption and regeneration process, and SNAP adsorption / regeneration process. Among them, activated carbon activated coke adsorption / regeneration process is widely used. Do focus analysis.

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