I. Introduction

In order to protect the environment, improve air quality, and prevent pollution caused by air pollutant emissions, the Ministry of Environmental Protection revised the "Air Pollutant Emission Standards for Thermal Power Plants" on July 29, 2011, and adjusted the limits of atmospheric pollutant discharge concentrations. The time limit for the current thermal power boiler to reach a more stringent emission concentration limit is stipulated, and the special emission limit for atmospheric pollutants is added. The standard will be implemented as of January 1, 2012. On September 27, 2012, the State Council approved the “Twelfth Five-Year Plan for Air Pollution Prevention and Control in Key Areas” jointly prepared by the Ministry of Environmental Protection, the Development and Reform Commission, and the Ministry of Finance, and divided the planning areas into key control areas and general control areas. For key control areas, implement special emission limits for key industries and adopt more effective pollution control measures. There are 47 cities in the key control area, and the four cities of Shijiazhuang, Baoding, Tangshan and Langfang in Hebei Province are listed as key areas. The dust emission standard in key areas is 20mg/Nm3, and the dust emission standard in general areas is 30mg/Nm3. The dust emission standard stipulated by the original national standard is 50mg/Nm3, and the existing dust removal facilities cannot meet the latest emission requirements, and must be modified to meet the requirements. This paper proposes some modifications through the introduction and comparison of several new dust collector technologies combined with the company's existing dust removal equipment .

Second, several new technologies for dust collectors

The new technologies of the dust collector are: waste heat utilization, WESP, electromechanical multi-complex dual-zone, high-frequency power supply, zero wind speed shut-off, flue gas quenching and tempering. More four kinds of dust collector technologies will be used to analyze and explain the working principle, dust removal effect and working condition applicability.

1. Low-temperature and low-temperature dust collector technology: 1. Temperature-adjusting principle: the heat exchange and cooling of the condensate and hot flue gas of the steam turbine are adopted. The temperature of the dust-removing smoke is reduced from the normal 120-160 °C to the low-low temperature state of 90-110 °C. 2. Principle of efficiency of electric precipitator: the temperature of smoke is reduced, the specific resistance of soot is reduced to 108~1010Ω ̇cm; the smoke temperature is reduced, the electric field wind speed is reduced, the smoke temperature is lowered, the electric field breakdown voltage is increased; The temperature is lowered and the gas viscosity is lowered. Main features: use of waste heat, reduction in power generation coal consumption 1.0 to 3.5 g / kWh, the specific resistance reducing smoke, reducing the electric field wind speed, high efficiency electric dust; + membrane surface using a heat exchanger finned / pin tube row patents, The temperature regulation of flue gas and the utilization of waste heat are good; the removal rate of sulfur trioxide is high, and it is trapped by high-quality concentration dust particles and then collected by electric dust removal, effectively solving the problem of sulfur trioxide corrosion.

2. Rotating plate dust collector technology, the electric field original fixed plate is changed to the rotating plate, and the rotating plate is generally set at the last stage electric field of the electrostatic precipitator. The plates are arranged in parallel with the flue gas, the chain drive, and the plate cleaning is not dependent on the rapping, but on the lower part of the plate. When the plate rotates to the lower end of the electric field, the cleaning brush removes the sticky ash from the plate at a position away from the air flow. Function: 1. Rotating the plate can eliminate the secondary dust; 2. Rotating the plate can avoid the back corona, the anti-corona phenomenon will often cause the loss of the final electric field function, because the rotating plate can clean the surface thoroughly, the surface of the plate is clean In the interval of two ash ashing of the same plate, the surface of the plate does not form a thick continuous dust layer, which completely eliminates the back corona caused by the air gap breakdown, which improves the dust removal efficiency. Decisive role; 3. Rotating plate can obtain a better electric field environment, because the rotating plate adopts a large flat structure, compared with the corrugated plate of the conventional electrostatic precipitator, it can create a more uniform electric field environment and reduce the influence of turbulence. Such an electric field and airflow environment can accelerate the dust drive and improve the dust collection efficiency.

Working condition adaptability: Rotary plate dust collector is a technical extension of conventional electrostatic precipitator, which retains many advantages of traditional electric precipitator such as high temperature resistance, high humidity resistance, corrosion resistance and low operating cost.

3. Electric bag composite dust removal technology: Firstly, more than 80% of the smoke in the flue gas is collected by the pre-stage electric dust removal, and a small amount of soot is filtered and collected through the dust removal area of ​​the post-stage bag, thereby stably achieving the flue gas purification discharged below 30mg/Nm3. Scientifically and reasonably play the high efficiency of front-end electric dust removal, the ease and stability of fine dust such as high-specific resistance of dust collection in the latter stage, and organically combine the advantages of two kinds of dust removal, so that the dust collector can achieve high efficiency, low resistance and energy saving performance. Fully exerting the dust removal and charging effect of electric dust removal is an important mechanism for composite dust removal of electric bags.

Main performance characteristics: 1. Dust removal performance is long-term efficient and stable, and the export emission is not affected by coal type, flue gas condition, soot composition and specific resistance value, and can reach 30mg/Nm3 or less in a long-term stable state. Set PM2.5 grade fine particle efficiency; 2. Low running resistance, practice shows that under different inlet concentration values, electric bag composite dust removal reduces bagging dust by 300-1000Pa; 3. Energy saving: under the same conditions, electricity The bag is more energy efficient than other dust removal; 4. Extend the service life of the filter bag from physical characteristics. The concentration of soot entering the bag area is only less than 20% of the inlet of the precipitator, and the running resistance of the filter bag is small, delaying the fatigue damage of the filter bag. Extend the filter bag cleaning cycle, reduce the filter bag cleaning frequency, and delay the filter bag stress alternation and damage. Applicable to the requirements of discharge requirements below 10-50mg/Nm3.

The electric bag is bagged on a year-on-year basis. After the electric field is increased, the dust condition of the filter bag is improved, the dust removal efficiency of the fine particles is higher, the resistance of the filter bag is smaller, and the physical condition is more favorable for extending the life of the bag. The electric bag is the same as the filter material used for dust removal in the bag, and is affected by the chemical composition of the flue gas. The advantages of bag dust removal do not change in the dust removal of the electric bag, but the advantage of the bag dust removal is not. Therefore, in the flue gas of coal-fired boilers, bag dust can be selected, and the comprehensive performance achieved by using the electric bag dust collector is only better.

4, high-frequency high-voltage electric dust removal principle: the use of rectification equipment through the effective use of new materials and new power semiconductor devices, the comprehensive application of power electronics technology, microelectronics technology, etc., to achieve high-performance energy conversion and control, including voltage, current , frequency and waveform transformation to meet the power supply characteristics and requirements of electric dust removal.

High frequency power source of three typical applications: supporting the body 1 of the project, often a "golden combination" mode, i.e., a first high frequency power source for the electric field, the last field using a multi-electromechanical duplex dual zone electrostatic precipitator 2. Pure high-frequency power supply to improve the efficiency, replace the original first electric field power supply with high-frequency power in the case of no modification of the body. Power supply for electric bag dust collector; 3. Enriched power supply for electric field, enhance the charging effect of electric field and improve the dust removal efficiency of electric field.

The high frequency power supply can provide a higher output voltage, up to 1.3 times the power frequency power supply. The high frequency power supply can provide a larger output current, up to twice the power frequency. The high frequency power supply can effectively increase the corona power and improve the dust removal efficiency.

Third, the company's dust collector status and countermeasures

Most of the company's existing dust collectors have been completed or put into operation in recent years, and their dust removal efficiency is relatively high, reaching 27-37 mg/Nm3. After the introduction of the new standard, most of the dust collectors are not far from the new standard. We believe that from the perspective of scientific rationality, the way of reforming electrostatic precipitators must not be the same. A comprehensive analysis should be carried out from the status quo of equipment, working conditions and site conditions, and the most cost-effective and reliable reconstruction plan should be proposed for each situation of each power plant.

Most of the existing dust collectors use electrostatic precipitators. The main reasons for the failure of some electrostatic precipitators are: 1: The dust removal efficiency of the precipitator is not up to the design requirements due to its own design or installation and operation defects. 2. The original design standard is low, and the dust collector does not meet the requirements of the current standard. 3. Because the coal quality fluctuation deviates from the design value, coupled with the vicious competition in the market, the design value of the precipitator is relatively critical, which is not enough to cope with the fluctuation of coal quality, resulting in the dust removal efficiency not meeting the standard. In view of the above reasons, it is recommended that each power plant carefully analyze the reasons for the dust removal efficiency not meeting the standard, and propose the adjustment plan in a targeted manner: 1. Due to the failure of the design or installation operation, the dust removal efficiency does not meet the design requirements. It is recommended that the electrostatic precipitator should be maintained. It plays its due function. 2. Carefully analyze the combustion coal types and working conditions, and choose the most suitable dust removal method from the mechanism, whether it is electric dust removal or bag dust removal. 3. Combine the specifications, site and investment of the existing dust collector of the power plant, and choose the most scientific dust removal method.

As the new standard also greatly increases the sulfur dioxide emission standard, the regulation is 50mg/Nm3, the existing desulfurization facilities can not meet this requirement, and must be completely modified, and the calcium sulfide desulfurization in the circulating fluidized bed boiler can not meet this requirement. It is necessary to use wet desulfurization to achieve the target discharge. The wet desulfurization has a removal efficiency of 50% of the soot concentration. Therefore, the combination of the dust collector and the desulfurization reform can achieve twice the result with half the effort.

Suggestions for dust removal: According to the conditions of burning coal and working conditions, it is suitable to use the electric dust removal technology. The dust collector is caused by the lower original design standard, the design dust collection area is relatively critical, the installation and commissioning is not in place, or the fuel condition is small. The situation of emission of about 100mg/Nm3 is as follows: Firstly, special technologies such as waste heat utilization, high frequency, dual zone, and flue gas quenching and tempering are considered to meet the new standard; when the site conditions permit, the electrostatic precipitator can also be expanded by expansion. Other special technology combinations are used together to achieve ultra-low emissions; when the site conditions are not allowed and the new technology of the electrostatic precipitator is still unable to meet the new standards, the electric bag composite dust removal technology can be used for retrofitting.

If the dust collection area of ​​the original design is too small and the fuel condition is too low, the current discharge concentration of the precipitator is greater than 300mg/Nm3 and there is no site expansion. It is recommended to use bag type dust removal equipment.

Fourth, the conclusion

The above briefly introduces several of the latest dust removal technologies. Each technology has its own characteristics. In actual work, it is necessary to select a targeted solution to transform according to the actual situation of each unit to achieve new standards for soot emissions, taking into account both desulfurization and out-of-stock. The overall consideration of the renovation of the facility will result in less investment and good results.

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