In this study, a mathematical model was introduced to calculate the collection efficiency of dust particles in a wire-pipe single-stage electrostatic precipitator (ESP). The aerodynamic diameters of these particles are less than 10 mu m (PM10). The mathematical model, using combined Deutsch-Anderson Equation, considers coupling effects among gas flow field, electric field and particle field. A simplified 2-D ESP model was established using GAMBIT and a software application (FLUENT) was used to investigate the effects of the diffusion charging on PM10 collection efficiency. Furthermore, the effects of different variables such as applied potential, gas velocity and particle distribution on diffusion charging and collection efficiency were also studied. The numerical results indicate that grade efficiency of ESP satisfies U-shape distribution. It was further demonstrated that, for particles with a diameter of less than 10 micrometers, the influence of diffusion charging on PM10 collection efficiency is significant with either decreasing applied potential or increasing gas velocity of the inlet. Moreover, the reduction of size distribution parameter and mean diameter of particles results in the phenomenon that diffusion charging has a more significant effect on PM10 overall efficiency, but there is no guarantee for improving overall collection in the case.

The PM10 collection efficiency of a wire-cylinder electrostatic precipitator (ESP) was studied by means of a developed mathematical model, including the multi-field coupling between the gas flow field, the particle dynamic field and the electric field, and applying the Deutsch–Anderson Equation. The diffusion charging mechanism was considered due to the diameter range of PM10. The investigated variables were the applied potential, the gas velocity and the particle distribution. Numerical results indicate that the diffusion charging has significant influence on PM10 removal performance and the effect is more obvious with the decreasing diameter, and that the PM10 collection efficiency increases with the increasing applied potential and the increment of collection efficiency is more significant at lower voltage. Moreover, as the gas velocity at inlet decreases, collection efficiency of PM10 will increase. Finally, the overall efficiency increases with increasing the mean diameter of particle distribution. The research results can provide theoretical and technical references for the design of novel ESP aiming at economy and environment protection.

To study the PM10 collection in a wire-plate ESP, a numerical model was built and performed by FLUENT software. Deutsch-Anderson Equation was subsequently applied to collection efficiency calculation. The numerical results under different gas velocities at inlet and particle distributions indicate that the collection efficiency of PM10 increases with a decrease in gas velocity, and that the increment of grade efficiency will become bigger if particle diameter gets smaller. By comparing with a decrease in gas velocity, diffusion charging mechanism is found to be valuable for PM10 in aspect of collection. As two parameters of Rosin-Rammler distribution decrease, grade efficiency will increase, especially for fine particles, and a larger positive effect the diffusion charging mechanism will have on collection efficiency, but overall efficiency will decrease. Finally, the effect of particle distributions on grade efficiency is much smaller than that of diffusion charging mechanism or the gas velocity at inlet.

In this paper, a numerical simulation was carried out to analyze the effect of diffusion charging on collection efficiency of a wire-plate electrostatic precipitator (ESP). The gas flow field, the electric field, and the particle field with diffusion charging considered were included in the numerical model, which was implemented by using the commercial FLUENT software. Collection efficiency was calculated by using the Deutsch-Anderson equation, in which the parameters were provided from the numerical solutions. The simulated results indicate that the effect of diffusion charging on the wire-plate ESP particle collection increases with the decreasing particle diameter, as well as applied potential, particularly for PM10. Moreover, with the increasing applied potential, collection efficiency of PM10 is obviously improved, and the effect extent first increases and then decreases with particle size increasing, but also, the size range of particle, which is significantly affected by the diffusion charging, becomes smaller. As gas velocity becomes higher, the effect of diffusion charging on grade efficiency also becomes more obvious, and the affected range of particle size gets much larger, however, at the price of grade efficiency decreasing. Using collection efficiency as reference variable of judgment, instead of particle charge, may lead to a more accurate estimation of the aforementioned size range, which can provide a great help in the further analysis of fine particle collection.

In order to study the flow characteristics and trapping process of the dust particles in a wire-duct electrostatic precipitator,the mathematic model of the flow field,electric field and particle dynamic field was built,and the numerical simulation was achieved by FLUENT software.The results indicate that the average diameter of escaping particle is nonlinearly decreasing with the increase of operating voltage,but linearly increasing with the increase of inlet velocity.Furthermore,the movement trend towards the dust collection plate can be obviously strengthened by the increase of the voltage,but weakened by the increase of the inlet velocity.

A typical coal used widely in the power stations in Shanghai area is adopted as the experimental coal type. A pilot-scale coal-combustion furnace was designed and constructed to study the mercury speciation and transformations in the flue gas under different conditions. The results showed that gaseous mercury in the tested coal products accounted for two thirds of total mercury and solid-state mercury accounted for one third of total mercury. It indicates that gaseous mercury is the main form of mercury emission from the tested coal-fired flue gas. The bivalent mercury accounted for about three fifth of the total gaseous mercury and the elementary mercury accounted for about two fifth of the total gaseous mercury. Of the solid-state mercury, mercury in the fly ash was around thirty one percent and mercury in the slag was about three percent of the total mercury. It shows that bivalent mercury is the main form of gaseous mercury, the mercury content in the fly ash compared to the end of the mercury is higher. The addition of chloride additive makes the percentage of both gaseous bivalent and gaseous elemental mercury in the total mercury decline at some degree, and percentage of particle mercury increase correspondingly. However, with the increasing of additive, the increasing trend of particle mercury became flat gradually and the decreasing of elemental mercury becomes gentle gradually.

A simultaneous test between a dry and wet based SCEM system was conducted at ESP outlet of a power station. The data by the dry and wet based methods showed a similar changing trend, and the difference between the two is within an acceptable range. According to the analysis of the relative standard difference (RSD), it was found that the dry based method could provide higher quality data than the wet based method. The practical experimental process shows that the dry based method can work well for more time than the wet based method under unattended condition. The dry based mercury SCEM is expected to be a trend of the mercury SCEM and it is more possible for the dry based SCEM than the wet based SCEM to become a compact model and enter the control room in the power station to provide mercury concentration in the flue gas. At the other hand, as a new developing technology, the dry based SCEM needs more practical tests.

Mercury speciation distribution features in flue gas were studied on an self-designed one-dimensional pulverized coal combustion test rig.And the influence of NaCl,being used as an additive into the coal combustion,on the mercury speciation distribution was analyzed.Results show that the gaseous state of mercury is of the overwhelming content in the emitted mercury for the test coal,and the bivalent mercury is of the major part in the gaseous mercury.In addition,the mercury content in fly ash is higher than that in slag.Adding NaCl causes a certain reduction of percentage of both gaseous bivalent and elemental mercury in the total content,but an increment of ratio of particle mercury.However,with increased addition of NaCl,the particle mercury increases smoothly and the elemental mercury reduces also slowly.

利用汞蒸气发生器产生的单质汞,与压缩空气组成模拟烟气,在吸附剂评价实验台上进行吸附剂脱汞实验,研究不同吸附剂对单质汞的脱除效率.实验结果表明,活性炭对汞的吸附效率在60%左右,未改性的燃煤飞灰吸附效率在10%～20%,改性后的燃煤飞灰比表面积有很大程度的提高,吸附效率可以达到25%,与活性炭吸附效率相比仍有不小的差距.

Mercury is harmful to our health and environment, so research on mercury emission from coal-fired power station, the main source of anthropogenic mercury emission, is very important. In this paper, mercury emission and speciation in the flue gas from a coal-fired power station was measured by three methods, i.e., OHM (Ontario Hydro method), Hg SCEM (semi-continuous emission monitors), and EPA Appendix K (carbon trap method). The effects of boiler load, flue gas characteristics on mercury emission and its speciation were analyzed. Mercury mass balance was calculated based on the analyses of mercury contents in coal, pyrite, bottom ash, fly ash, FGD (flue gas desulphurization) slurry, and flue gas at FGD inlet and stack. The results indicate that data by the three methods have good consistency within acceptable range. The total mercury emission increases with the increasing of mercury content in fuel and boiler load. The percentages of elemental mercury in the flue gas at FGD inlet and stack are around 26%-48% and 70%-85% respectively. Wet FGD would capture more than 80% of oxidized mercury.

Due to its adverse effects on human health and ecosystem, mercury emission from the coal-fired utility boiler has been generating more and more concern. Sorbent injection upstream of the electrostatic precipitator (ESP) or bag-house has been deemed one of the recommended mature technologies to reduce mercury emission. Before a sorbent is used in practice, its mercury capture ability needs to be evaluated, but has until recently only been demonstrated in bench-, pilot- or full-scale experiments separately. In this paper, a lab-scale multiphase flow reactor and a pilot-scale slipstream reactor were set up and conducted such evaluation on the two scales. After that, some kinds of sorbents were injected at a full-scale power station. The experimental results show that the lab- and pilot-scale reactor systems in this paper can provide accurate information of sorbent evaluation under flue gas atmosphere. There was significant difference between the mercury removal efficiency of tested sorbents, varying from 98.3% down to 23%. SO2 in the flue gas was shown to inhibit mercury oxidization and capture. The sorbents have higher mercury capturing efficiency with higher injection rate and longer residence time when other conditions were held constant. In the pilot-scale, four injection ports vertical to the flue gas flow direction could help improve mixture of sorbent and flue gas so that the mercury removal efficiency became higher. The pilot-scale data can be used to predict the full-scale results. Some of the chemical and physical mechanisms responsible for the mercury removal of the sorbents were identified.

Due to its harm to human health, more and more concern has been put on the mercury emitted from power stations burning coal. Both of the US EPA and European Commission have set regulations on the mercury emission from the electric utilities. China also pays more and more attention to the mercury emission and starts to sponsor the projects relative to the mercury emission. To reduce mercury emission, sorbent injection upstream the ESP or bag-house is one of the recommended methods. Before a sorbent is used in practice, its mercury capture ability needs to be evaluated. A lab-scale multiphase flow reactor was set up to conduct such evaluation. The experimental results show that the system can provide accurate information of sorbent evaluation under flue gas atmosphere. There was significant difference between the mercury removal efficiencies of tested sorbents, varying from 95% down to 23%. SO2 in the flue gas could inhibit the mercury oxidization and capture. The sorbents tested has higher removal efficiency on the elemental mercury than on oxidized mercury. The sorbent would have higher mercury capturing efficiency with higher injection rate and longer residence time when other conditions were held constant.