风机调速系统在静电除尘器中的应用

采用可编程逻辑控制器和变频器构成的风机调速系统可以使风机平稳起动,减小了起动时大电流对电网的冲击,延长了设备的使用寿命;同时能更精确地控制除尘器运行时电场内部的压力,有效避免压力波动剧烈,为除尘器的安全高效运行提供了保证。以某铝业公司沥青烟气净化静电除尘器风机调速系统为例具体介绍了系统设计、硬件选型、电路设计等,并对节能效益进行了评价。     

Fuzzy-logic-based power control system for multifield electrostatic precipitators

The power consumption of large precipitators can be in the range of 1 MW and above. Depending on the dust load properties, the electrical power may be reduced by up to 50% by applying fuzzy logic, without significantly increasing the dust emissions. The new approach uses fuzzy logic for optimization of existing electrostatic precipitators. The software runs on a standard personal computer platform under the Windows NT operating system. The controllers of the electrostatic precipitator power supplies are linked to the personal computer via an industrial network (e.g., PROFIBUS). The system determines online the differentials of emission versus electrical power of each field. This measurement is difficult because of overlaid events in the other zones, and process changes. The long response, time of the resultant dust emission due to electrical power changes in the precipitator is an additional complication. Rules were defined for a coarse, but fast-response power adaptation of all zones. Fine tuning the running system after the coarse optimization increased the accuracy and reliability. When installed on a 4/spl times/5 zone precipitator in a power station, significant results were obtained. The power savings over three months of operation were in the range of 40%-60% depending on the load and fuel characteristics. Data were recorded over the test period of three months. The results are presented.     

燃煤电厂静电除尘器改造方案

随着我国环保标准日益严格，很多燃煤电厂静电除尘器已不能满足排放标准的要求，需进行改造。该文首先分析了造成静电除尘器除尘效率低下的主要原因；提出3种改造方案：增加电场；改造为袋式除尘器；改造为静电袋式复合除尘器。并从技术性能和经济性2个方面对3种改造方案进行了比较．以郑州热电厂200MW机组静电除尘器改造为例对3种方案进行了对比分析．结果表明：改造为静电袋式复合降尘器的方案是静电除虫器改造的最佳方案，并认为静电袋式复合除尘是我国除尘技术来来的发展方向之一。     

Numerical simulation of three-dimensional electrohydrodynamics of spiked-electrode electrostatic precipitators

The three-dimensional flow interaction between the primary flow and the secondary flow (often called an electric wind or ionic wind) for tuft/point corona in the wire-duct type electrostatic precipitators (ESPs) has been investigated in the past. This study was further extended to incorporate the alternately oriented point corona on the wire-plate type electrodes, which are commonly used for the industrial ESPs. The secondary flow distribution without gas flow consists of a pair of long-elliptic and circulatory cells between spikes points along the wire. However, the flow rotation between spiked points is the same direction, which is opposite to that of the point corona electrode. The flow interaction is described using dimension-less number, N/sub EHD/, which is the ratio of the ionic wind velocity to the primary flow velocity. When the primary flow exists, a pair of long-elliptic spiral flows is formed in the direction of the gas flow between ground plates. When the relative distance between the spike point spacing and the wire-to-plate spacing (or the ratio of S/sub z//d) is greater than 0.17, the organized long-elliptic spiral flow is formed. When S/sub z//d is less than 0.1, the organized spiral flow is diminished, resulting in turbulence.     

Enhanced precipitation efficiency of electrostatic precipitators bymeans of impulse energization

To assess the benefits of impulse energization with different coals, experimental industrial research was performed at a 70 MWe thermal power plant. Two technologies for impulse power supplies were tested over 10000 h of operation. The results of the tests, performed according to ASME standards, demonstrated that impulse energization has great advantages over conventional energization and ensures a collection efficiency from 99.6 to 99.9%, corresponding to emission levels below 50 mg/Nm³, with a reduction in absorbed power from about 0.5 to about 0.1 Wh/Nm³. Tests showed that with impulse energization there was a considerable decrease both in solid particulate emissions (about 90%) and in energy consumption (about 80%), as compared with conventional (AC rectified voltage) energization. Almost the same improvement was obtained when the flow rate in the experimental channel was increased to 1.8 times the nominal value, thus indicating low sensitivity to gas velocity variations. Thus, the suitability of the technology for complying with the targets set by environmental regulations, even in the presence of difficult solid particulate, was proved     

Application of different types of high-voltage supplies on industrial electrostatic precipitators

Investigations of the requirements for high-voltage (HV) power supplies for zones within an electrostatic precipitator (ESP) were conducted with regard to the properties of different technologies for HV generation. The zones of an ESP show different electrical behavior and efficiency. This is a result of: 1) the different dust loads of the zones; 2) the particle size and properties; and 3) the possibility of charging the particles in the entire zone using suitable technology. An overview of common and new topologies of HV supplies and their typical properties is given. It is shown how these properties can be used to match the requirements of the different zones of an ESP regarding the actual operating conditions. Large particles and high dust loads can be addressed effectively using high-frequency dc power supplies. Fine particles, however, can be separated even more efficiently by pulsed power supplies. Additionally, the power consumption of different HV sources has been investigated in relation to the separation efficiency. Experimental results were obtained on an industrial ESP containing 3 zones in a sinter plant and on a large scale precipitator in a fossil power plant, containing 30 zones. It was shown that a high frequency IGBT inverter combined with a microsecond-pulsed power supply significantly improved the overall performance of the precipitator.     

A new approach to calculation of flue gas scrubbing efficiency in electrostatic precipitators

The majority of existing approaches to computation of electrostatic precipitator (ESP) efficiency do not take into account particle reentrainment from collecting electrodes. The first attempts to take into consideration particle reentrainment were made only recently. However, the existing reentrainment models for ESP are not sufficiently substantiated. A general model, which takes into account precipitation of particles, entering the ESP inlet (direct precipitation), as well as precipitation of reentrained particles (secondary precipitation), is presented in the paper. The model describes physical processes in an ESP using three integral parameters. These parameters are direct precipitation coefficient, secondary precipitation coefficient, and reentrainment coefficient, which is the ratio of reentrained particle flux to precipitation flux. An improved technique for computation of direct precipitation that takes into account particle charge distribution function is proposed. The influence of gas flow turbulence on charge distribution function parameters, as well as on other parameters of precipitation phenomena, is taken into account. The method has low computational costs. The secondary precipitation coefficient is also computed using this method. The most difficult task is calculation of the reentrainment coefficient. We suggest using data of periodical ESP testing to determine the reentrainment coefficient. The analysis of experimental data indicates that a fly ash layer on collecting electrodes is of paramount importance. It has been shown that the flux per unit length of particles falling into hoppers is proportional to weight (thickness) per unit length of the fly ash layer. Distributions of precipitation flux, flux into hoppers, reentrained particle flux along the ESP duct, and particle penetration through the ESP are computed using experimental data. A novel model that is based on a flux balance equation for each length element of an ESP duct is presented. The model has the form of a connection between physical phenomena that take place on two successive length elements of the collecting electrode. The model qualitatively agrees with experimental data. However, correction of the secondary precipitation coefficient and the reentrainment coefficient is required for quantitative agreement. In this regard, a model of layer growth and determination of functional relations between layer weight, hopper flux, and particle penetration play a key role.     

Ozone production in electrostatic air cleaners with contaminatedelectrodes

Runaway ozone generation due to contamination of electrode surfaces is a limiting factor in the long-term effectiveness of electrostatic air cleaners. Modification of the form of the corona discharge, accompanied by a significant rise in current, is the cause of increased ozone levels. After one week of operation in filtered air containing Arizona Road Dust, ozone concentration in a laboratory air cleaner increases by 460%. In this case, there is slight contamination on the discharge wires, but the ozone increase is attributed exclusively to back corona on the collection plates. On the other hand, oxidized discharge wires are believed to contribute to an order of magnitude increase in ozone concentration in a commercial air cleaner, operated in room air for 7 weeks. Wire contamination alone can increase ozone generation. An insulating tape adhesive applied to a 0.254 mm diameter stainless steel wire causes a 10-fold increase in ozone concentration     

新型高效静电除尘器在火力发电厂输煤系统中的应用

通过对火力发电厂输煤系统3种除尘方式在设备初投资、长期运行费用以及维护管理的繁简程度方面进行比较,认为在火力发电厂输煤系统中采用新型高效静电除尘器除尘不仅能大大地提高除尘效率．节省劳动力,并且设备运行的可靠性、稳定性和自动化程度也较高。     

Ozone generation in dry air using pulsed discharges with andwithout a solid dielectric layer

Energy efficient generation of ozone is very important because ozone is being used increasingly in a wide range of industrial applications. Ozonizers usually use dielectric barrier discharges and employ alternating current (ac) with consequent heat generation, which necessitates cooling. In the present study, very short duration pulsed voltage is employed resulting in reduced heating of the gas and discharge reactor. A comparison of ozone generation in dry air using a coaxial concentric electrode system with and without a solid dielectric layer is reported. Two types of dielectric layers were employed, ceramic and polyvinylchloride (pvc). The effects of peak pulsed voltage (12.5 to 62 kV), reactor length (0.1 to 1 m), pulse repetition rate (25 to 400 pulses per second, pps), gas flow rate (1.5 to 3.0 1/min) and variation of the pitch length of the spiral wire forming the central electrode (5 to 10 mm) on the concentration and production yield of ozone (g/kWh) are reported. A comparison is made between the performance of discharge reactors with (ceramic reactor Type IIC and pvc reactor Type IIP) and without (reactor Type I) a dielectric layer, using the same electrode gap separation (15 mm) and reactor lengths (0.157 and 1 m). High production yields of ozone in dry air of ~125 52 and 60 g/kWh were obtained when using, respectively ceramic, pvc, and no dielectric layer, for a fixed pulse rate of 100 pps, 15 1/min now rate and for a relatively short length of the reactor of 157 mm     

燃煤电厂电除尘器的有效控制

燃煤电厂所使用的电除尘器常常会出现反电晕和电晕封闭现象,导致除尘效率不高。从电除尘器的微观机理上分析,这两种现象是难以根治的。因此,要对电除尘器进行科学有效的控制,采取一定的措施,抑制反电晕和电晕封闭现象,提高电除尘器的除尘效率。     

Calculation of corona onset voltage for duct-type precipitators

A pure theoretical method for calculating the onset voltage of corona in duct-type electrostatic precipitators that is independent of the arrangement of discharge wires relative to the collecting plates is described. This method is based on a criterion for self-recurring single electron avalanches in a known electric field distribution in the ionization zone surrounding the discharge wire. The results computed by this method are in reasonable agreement with those measured experimentally     

哈三电厂电除尘器存在的问题及改造

通过对哈三电厂电除尘器几年来所出现的各种问题逐一进行分析,采取了相应的解决措施,并对电除尘器进行了改造。改造后,提高了电除尘器除尘效率,降低了粉尘排放量,粉尘排放指标符合国家规定的排放标准,极大地改善了哈三电厂生产和周围生态环境。     

燃煤发电机组除尘器设计选型

介绍了静电除尘器的结构原理，以600MW临界燃煤机组的除尘器设计选型为例，对选型设计提出建议，设计选型时应根据煤种资料、燃煤的灰渣成分与特性分析、燃烧计算结果、场地布置情况等进行比较选择，既要满足环保要求，又要提高除尘效率。     

Single-stage AC electrostatic precipitation

Measurements are reported on the collection efficiency of a laboratory-scale single-stage electrostatic precipitator (3 cm plate spacing) excited by AC voltages (V_rms~8 kV, f =20→500 Hz) biased to give no time-average. With f=60 Hz, an effective migration velocity of 3.5 cm/s is observed. Previously published works on the charging and migration of particles in AC coronas and on the effects of finite turbulent diffusivity on the precipitation process are combined to predict the experimentally observed dependence of the efficiency on the magnitude and frequency of the applied voltage. When applied to the experimental situation reported here, the model reduces to one of complete mixing, with the effective particle migration velocity being predicted in terms of the velocity that is achieved with DC charging and a charging time constant that is either estimated or obtained from charging experiments     

Drop size measurements in electrostatic paint sprays

Drop-sizing experiments were performed on an electrostatic fan-spray atomizer operated in the airless mode. Tests were conducted with and without application of a high-voltage charge to the electrode tip placed downstream of the nozzle exit. A nonintrusive Malvern 2600 particle sizer, based on the forward scattering of a 5 mW He-Ne laser beam, was used to yield line-of-sight and cross-sectional drop size distributions. The atomizer was traversed across the laser beam, and drop size profiles as a function of distance from the centerline were developed. Enamel paint with a viscosity of 17 cp was sprayed over a differential pressure range of 1.38 to 6.20 MPa. Results indicate that at low injection pressures the charge application has a significant effect on the average drop size and the spatial drop distribution. However, as injection pressure is increased, the electrostatic influence on drop size and distribution decreases     

125 MW机组电除尘器的技术改造

介绍了株洲华银火力发电有限公司2台125MW机组电除尘器增效改造的方法和取得的良好效果,为在不动土建的情况下,将电厂电除尘器三电场改为四电场提供了参考经验。