Application of Low-low Temperature Electrostatic Precipitator Technology in Thermal Power Plant

Transcription

1 2017 2nd International Conference on Environmental Science and Engineering (ESE 2017) ISBN: Application of Low-low Temperature Electrostatic Precipitator Technology in Thermal Power Plant Jun-jie ZHANG 1, *, Jian-xing REN 1, Kai-kai ZHU 1 and Hai-wen WANG 1 College of Energy and Mechanical Engineering, Shanghai University of Electric Power, Shanghai , China Keywords: Electrostatic precipitation, Low-low temperature electrostatic precipitator, Energy conservation. Abstract. Electrostatic precipitation technology has been widely used in various industrial fields, very nice collection of large size particles, but for the smaller particle size of particles to achieve flue gas pollutant emission standards. Electrostatic precipitation technologies are introduced low-low temperature electrostatic precipitator technology (LLT-ESP). Through the principle of low-low temperature electrostatic precipitation technology, work processes, technical features and other aspects of the study, we can see that Low-low temperature electrostatic precipitator technology can effectively reduce SO 3 and PM 2.5 emissions, on the other hand to recycle the residual heat from flue gas. Low-low temperature electrostatic precipitation technology is effective technologies to achieve energy conservation and emission reduction in coal-fired power plant. Introduction With the development of the power industry, emissions increased sharply, causing serious environmental pollution in the atmosphere. Among them, burning coal is one of the main causes of serious air pollution, which is coal-consuming countries, with coal as the main energy consumption structure is difficult to change in a very long time, this makes the environmental pollution is very serious in China [1]. Among them, caused by coal smoke generated, especially PM 2.5 is smog, atmospheric visibility factors; NO and SO 2 cause acid rain and photochemical pollution is killer; Hg accumulation will aggravate pollution; plaster rained down will cause destruction of the surrounding environment; SO 3 in coal-fired flue gas acid fog is also difficult to remove for subsequent equipment corrosion, atmospheric environment pollution. Environmental pollution causes inconvenience to people's lives and serious threats to people's health. Traditional ESP is the mainstream of air pollution control equipment in thermal power plants, but it is more sensitive to dust ratio resistance and coal in our country under the conditions of changeable, for high resistivity dust conditions, prone to back Corona, the dust removal efficiency decreases, This is a major drawback of traditional electrostatic precipitator in the traditional ESP [2]. Low-low temperature electrostatic precipitator technology, from ESP inlet gas temperature, to take waste heat utilization technology to achieve gas temperature, to adapt it to ESP to work efficiently, but also provides the implementation of energy-saving operation. In addition, the flue gas waste heat recovery device in conjunction with ESP, reducing flue gas temperature, improves dust absorption efficiency; achieve the goal of energy conservation and emission reduction. Low-low 19

2 temperature electrostatic precipitator technology energy conservation effect obvious, for protection of the environment and energy is of great significance. Low-low Temperature Electrostatic Precipitator Technology Summaries Brief Introduction of Low-low Temperature Electrostatic Precipitator Technology Low-low temperature electrostatic precipitation technology from ESP and wet method flue gas desulfurization technology of single dust removal and desulfurization technology evolved. Low-low temperature electrostatic precipitation technology ESP inlet gas temperature dropped below the acid dew point temperature and significantly improving efficiency can efficiently capture SO 3. Ensure that coal-fired power plants to meet low emission requirements, and effectively reduce PM 2.5 emissions are low at low temperature electric dust collection systems when the use of low temperature economizer, recycling heat can also be used with good energy-saving effect [3]. ESP with high efficiency, low energy consumption, simple to use, low maintenance cost and no secondary pollution advantages for most domestic coal has good adaptability. Low-low temperature electrostatic precipitator by means of low temperature economizer or hot medium gas heat exchanger (MGGH) ESP inlet gas temperature dropped below the acid dew point temperature, minimum temperature meet the temperature requirements of wet flue gas desulfurization system ESP. Low-low Temperature Electrostatic Precipitator Technology Principle of Operation Low-low temperature electric dust removal system in electric precipitator to increase flue gas heat exchange system will enter the electric dust collector is reduced to below the acid dew point, generally 85~90 degrees, the technology includes two kinds of equipment: no leakage pipe type water heater and low-low temperature electrostatic precipitator. Most of the SO 3 in the flue gas in the heat exchanger in the system of condensed sulfuric acid mist and dust is reduced due to temperature, adsorption, neutralization, dust is significantly lower than the resistance, anti-corona has been effectively avoided, improve cleaning efficiency, enlarge the adaptability of ESP for coal, and remove most of the SO 3 [4]. Low-low temperature electric dust removing system and the traditional route layout is different upstream power filter the layout of the GGH heat exchanger. Figure 1. Schematic diagram of low temperature ESP system. Heat recovery of flue gas cooler, before transferred to the chimney flue gas heaters, increased emissions from the flue gas temperature, making the smoke increased. Heat 20

3 recovery of flue gas cooler, used to heat the boiler steam for the steam turbine, energy-saving effect is obvious. The Characteristics of low-low Temperature Electrostatic Precipitator Technology High Dust Removal Efficiency There are many factors affecting dust removal performance, including fly ash from flue gas properties, characteristics, structures and operating conditions, such as electrostatic precipitators, which effect is more prominent than the resistance. Electrostatic precipitation technology at low temperature by reducing the ESP inlet gas temperature decreased to below acid dew point (generally around 90 degrees), so most of the flue gas SO 3 is condensed into sulfuric acid mist in the heat recovery and adhesion on the surface of dust, dust has changed a lot, specific resistance fell sharply, the dust removal efficiency can be greatly improved. Conventional electrostatic precipitators operating temperature between 130~150 degrees, highest resistivity of fly ash, and improved low temperature operating temperature is only about 85 of the electrostatic precipitator, greatly reduced fly ash specific resistance, electrostatic precipitators can achieve the best effect [5]. Reduce SO 3 and PM 2.5 Emissions ESP entrance flue gas temperature to reduce acid dew point, the SO 3 in the flue gas and steam combined to form sulfuric acid vapor. The smoke contains large amounts of dust, sulfuric acid vapor in fly ash particles on the surface of condensed sulfuric acid vapor adsorption of particles by the electrostatic precipitator capture, so SO 3 will be removed to another. Hand, sulfuric acid vapor and dust particles suspended in the flue gas to form an aerosol particle size increases, can reduce the PM 2.5 [6]. Low-low temperature electrostatic precipitator technology not only improves the efficiency of dust removal, reduces the PM 2.5 emissions, but also removes most of the SO 3,on the other hand, it can effectively reduce the pollutants in the atmosphere and protect the environment. Energy-saving Effect is Obvious Low-low temperature electrostatic precipitator technology to reduce the electric precipitator entrance flue gas temperature, heat recovery can be used to improve the heating boiler make-up water or steam turbine condensate to the boiler efficiency, coal saving. On the other hand to reduce the temperature of flue gas, flue gas to reduce the amount of wet flue gas desulfurization system of water consumption will be reduced, with the decrease in water saving. The amount of flue gas, and can reduce the power consumption downstream of the fan, so that the energy saving effect is remarkable. Comparison of Performance and Economy Kinds of Single/Combined Dust Removal Technology Compared with the conventional electrostatic precipitator, low-low temperature electrostatic precipitator, wet electrostatic precipitator and electric bag composite dust remover, the specific performance and economic performance are shown in Table 1. 21

4 Table 1. The specific performance and economic performance. Number Electric bag composite dust remover Coal, electrical resistivity changes do not affect the efficiency of dust removal, dust emission concentration is less than10mg/m 3 ; Combined with desulfurization dust removal effect can be less than 5mg/m 3 The removal rate of PM 2.5 was high and the removal efficiency of heavy metal particles was 60 ~70% Suitable for combustion of low-quality coal, the use of coal ash is not limited The best flue gas temperature range is from 130~150 degrees,the best flue gas temperature range is from 130 to 150 DEGC, and the bag filter has high cost performance ratio Daily maintenance, replacement filter is more complex Conventional electrostatic precipitator The coal ash composition, resistivity, changes of dust removal efficiency, can not guarantee long-term dust emission concentration is less than 10mg/m 3 The removal efficiency of fine particles PM2.5 in general, the removal efficiency of heavy metal particles 40 ~ 50% Affected by the change of coal Flue gas temperature range Less daily maintenance Low-low temperature electrostatic precipitator Wet electrostatic precipitator The coal ash composition, After resistivity, changes of dust desulfurization removal efficiency, can ensure, the smoke long-term dust emission emission concentration is less than 10mg/m 3 concentration ;Combined with can be as low desulfurization dust removal effect can be less than 5mg/m 3 as 1mg/m 3 The removal efficiency of PM2.5 is higher, and the removal efficiency of heavy metal particles 40~50% The change of coal type has a great influence, but the low temperature and low temperature dust removal system has the function of self adjustment Flue gas temperature range Less daily maintenance The removal efficiency of PM2.5 and heavy metal particles was the highest The corrosion of equipment should be considered, and the change of coal type is less affected Flue gas temperature range Less daily maintenance circulating water system, water pump repair The Problems and Solutions of low-low Temperature Electrostatic Precipitator Technology The Second Dust Problem Low-low temperature electrostatic precipitator technology to reduce the electric precipitator entrance flue gas temperature in flue gas, the dust resistance decreased. Because the dust will weaken the adhesion to the electrostatic dust collecting anode 22

5 plate on the specific resistance decreased, resulting in low temperature electrostatic precipitator dust phenomenon two times more than conventional electric dust removal technology has increased so, the dust removal performance declined. Therefore, low temperature electrostatic precipitator should take corresponding measures to avoid the second dust problem [7]. At present, the control caused by low-low temperature electrostatic precipitation technology of secondary dust problems and techniques used are: off rapping or rotating electrode type electrostatic precipitator technology. Off-line vibration technology is by setting at the import and export of a number of flue-gas channel of flue gas damper, needs vibration of flue gas channel bezel, vibrating isolation of power plants, and the electricity supply was cut, decreased vibration of air, reducing the voltage, so as to reduce the secondary dust. Concrete is ESP several gas flue gas baffle channels correspond to the import and export settings, bezel by turning off vibration of flue gas channel is required and the cutback of electric field within the gas channel and air flow adjustment device to prevent adjacent channel technology of flue gas flow significantly increased, as shown in Figure 3. Figure 2. Principle of off-line rapping Technology. Rotating electrode-type electrical dust separation technique in electric field with rotary electrode electric field at the end, by way of rotating anode cleaning brush and dust, avoid the anode plate vibration, secondary dust can effectively solve the problem. Usually 3 or 4 plus 1 rotary electric field in a conventional power plant, setting in the export head outlet air flow distribution Board of dust collection plate, making some too late to capture or secondary dust collecting dust again [8], as shown in Figure 4. 23

6 The Effects of High Sulfur Coal Figure 3. Principle of rotating electrode technology. Low-low temperature electrostatic precipitator technology is currently mostly used for low-sulfur coal. The higher the sulfur content in coal and flue gas SO 3 concentration in relatively higher acid corresponding to the higher the dew point temperature, increased risk of corrosion. Low-low temperature electrostatic precipitation technology on the use of high-sulfur coal also needs further study. Hopper Blocking Due to the low-low temperature electrostatic precipitation technology reduces the flue gas temperature.so 3 condenses steam attached to the sulfate particles, collected ash's relatively poor liquidity, prone to hopper blockage. In order to prevent fouling in the ash bucket, ash discharging hopper design of angles need to be larger than usual, increased hopper discharge angle, greater than 65 angles. Meanwhile, ash bucket should have good thermal insulation measures to increase hopper heating surface to prevent condensation plug. (1) Hopper discharge point increased. (2) Hopper not only heat in the lower effective heating with a steam heater or electric heaters, enhanced steam heating tubes and coated far infrared coating to ensure smooth ash. (3) Hopper wall increase the smoothness of the material [9]. Conclusions ESP high efficiency, low energy consumption, simple to use and there is no secondary pollution and so on. Development and application of low-low temperature electrostatic precipitation technology, expanding the use of ESP, has remarkable energy saving effect. The low-low temperature dust removal system can reduce the flue gas temperature, recover the waste heat of the flue gas and improve the thermal efficiency of the boiler. Most of the domestic coal-fired power plants could use low temperature electrostatic precipitation technology [10]. Low-low temperature electrostatic precipitator has been widely used in foreign countries, which shows that this technology is feasible in the use of coal-fired power plants In environmental energy shortage today, 24

7 low-low temperature electrostatic precipitation technology should be widely used in the future, become energy-saving emission reduction technology. Acknowledgement This research was financially supported by the Shanghai Municipal Science and Technology Commission ( ). References [1] Long Yuansheng, Application of Low-low Temperature Electrical Precipitation Technology of Surplus Heat Use in Coal-fired Power Plant [J].China Environmental Protection Industry (11) [2] Ye Ziyi, Liu Shengqiang, Zeng Yifu, Application of LLW Temperature ESP in Coal-fired Power Plant[J].China Environmental Protection Industry (05) [3] Liao Zengan, Research and development of low-low temperature electrostatic precipitation technology for coal fired power plant [J].Environmental Protection and Circular economy (10) [4] Guo Shiyi, Ding Chenggang, Application and Prospect of low-low temperature electrostatic precipitator [J]. Equipment machinery 2011 (1): [5] Zhao Hua, Jiang Wen, Research and application of low temperature and high efficiency flue gas treatment technology for thermal power plant [J].Applied energy technology. 2015(12) [6] Zhao Haibao, Li Jianguo, Research and application of low-low temperature electrostatic precipitator [J].China electric power (10) [7] Cui Zhanzhong, Long Hui, Characteristics of low temperature and high efficiency flue gas treatment technology and its application in China [J] Journal of power engineering. 2012(02) [8] Long Hui, Wang Dun Application of low-low temperature flue gas treatment system in 1000MW ultra supercritical unit [J].Electric power construction (02) [9] Xie Qingliang Application of low-low temperature dust removal technology in 600MW thermal power unit [J].Technology and engineering application (11) [10] He Yuzhong, He Mintao, Zhou Yuefng, Application of low-low temperature dust removal technology [J].Technology and engineering application (04)