A pilot study of mercury liberation and capture from coal-fired power plant fly ash

The coal-fired electric utility generation industry has been identified as the largest anthropogenic source of mercury (Hg) emissions in the United States. One of the promising techniques for Hg removal from flue gas is activated carbon injection (ACI). The aim of this project was to liberate Hg bound to fly ash and activated carbon after ACI and provide high-quality coal combustion products for use in construction materials. Both bench- and pilot-scale tests were conducted to liberate Hg using a thermal desorption process. The results indicated that up to 90% of the Hg could be liberated from the fly ash or fly-ash-and-activated-carbon mixture using a pilot-scale apparatus (air slide) at 538 degrees C with a very short retention time (less than 1 min). Scanning electron microscope (SEM) evaluation indicated no significant change in fly ash carbon particle morphology following the thermal treatment. Fly ash particles collected in the baghouse of the pilot-scale apparatus were smaller in size than those collected at the exit of the air slide. A similar trend was observed in carbon particles separated from the fly ash using froth flotation. The results of this study suggest a means for power plants to reduce the level of Hg in coal-combustion products and potentially recycle activated carbon while maintaining the resale value of fly ash. This technology is in the process of being patented.     

火力发电厂飞灰对抗生素磺胺的吸附性能

研究了吸附时间、飞灰用量、初始溶液pH和振荡频率等因素对飞灰吸附去除水溶液中磺胺的影响,并对其吸附机理进行了初步探讨。研究结果表明,飞灰用量增大有利于提高其对磺胺的吸附去除率。在25℃、振荡频率150 r/min、飞灰用量50 g/L、磺胺浓度4 mg/L条件下吸附10 min,磺胺的吸附去除率可达到92.8%。电厂飞灰对磺胺的吸附符合二级动力学模型,属于单分子层吸附。     

The accumulation by plants of emissions from a coal-fired power plant

Foliar concentrations of Ca, Cl, F, Mg, Mn, P, S and Zn were measured in Eucalyptus crebra and E. moluccana growing at distances up to 28 km from a 2000 MW coal-fired power plant. The results showed that concentrations of F, Mn and Zn in leaves of E. moluccana were negatively correlated with distance from the emission source (P < 0.01), the foliar concentration of Zn was positively correlated with F and Mn concentrations (P < 0.01) and that S concentration was positively correlated with P and Cl concentrations (P < 0.01). In contrast, no elements in E. crebra leaves were correlated with distance from the power plant but significant positive correlations were found between Mg and F and between S and Ca concentrations. Concentrations of Mn in both species and F in E. crebra exceeded those measured in Eucalyptus species growing in areas of Australia remote from industrial emissions, but no symptoms of air pollution-induced injury were found. All other foliar element concentrations were comparable with background concentrations in Eucalyptus species in Australia.     

Nucleation properties of fly ash in a coal-fired power-plant plume

Airborne aerosol samples were collected on Nuclepore filters in the plume of a coal-fired power plant. Transmission and scanning electron microscopes were used to determine the concentration and size distribution of aerosols and an X-ray energy spectrometer was used to determine the elemental composition of individual particles. It was found that on a mass basis, only about 2% of the fly ash aerosol is water soluble. However, due to surface coating of insoluble fly ash particles with water soluble materials, the number of cloud condensation nuclei in a plume can be enhanced multifold over the background concentration. The passivation of the ice nucleation capability of fly ash can be alleviated by the evaporation of surface-deposited compounds.     

淄博某热电厂粉煤灰双免砖的研制

研究了粉煤灰的用量、成型水分、粘结剂的种类及用量、外加剂的种类及用量、养护时间等因素对粉煤灰双免砖的影响,探讨了粘结剂的作用机理.     

XPS investigation of air pollution ejected by a coal-fired power plant

A method for sampling and investigating the aerosol participates and gaseous pollutants of the air is described. The pollutants were collected on silver (Ag), copper (Cu) and graphite surfaces placed in the neighbourhood of a coal-fired power plant. The study of the composition of the aerosol and gaseous pollutants was carried out by means of XPS (X-ray photoelectron spectroscopic) method, as a function of the distance from the power plant.     

Trace element concentrations in lichens near a coal-fired power plant

Samples of two different species of lichens (Parmelia caperata and Parmelia rudecta) were analyzed by instrumental neutron activation analysis (INAA) to determine the concentrations of trace elements. The relation between atmospheric concentrations of elements borne by particles and composition patterns in lichens are examined by calculating enrichment factors (EF). The lichens collect material from the atmosphere to which they have been exposed. However, they collect preferentially larger particles, which are probably deposited by impaction and/or dry deposition, but not rain or filtration. No significant differences in concentrations were observed among lichens collected at various distances ranging from 1.6 to 20 km from the plant, suggesting that the effects of plume touchdown are small compared with normal ambient concentrations of particles.     

Leaching characteristics of stabilized/solidified fly ash generated from ash-melting plant

This study was designed to elucidate the leaching characteristics of stabilized/solidified (S/S) fly ash generated by ash-melting. For this study, pH-dependent leaching tests, sequential extraction procedures, and column leaching tests were carried out. The pH-dependent leaching test results for Pb, Cu, and Zn showed that the heavy metal concentrations in the high-pH range were lower than the predicted values for hydroxide and carbonate. During sequential extraction, Cu and Pb were principally distributed in the S/S ashes' organic matter fraction in the chelating agent, suggesting that metals bind to the chelating agent. The percentage of the water-soluble fraction for Pb and Cu was low (<0.2 %). The fly ashes treated with a chelating agent and cement had low leachability potential for metals in the high-pH range. Column tests for S/S fly ashes showed that two leaching stages were distinguishable: one for short time, corresponding to faster metal leaching, and another for the leaching rate. Kinetic speciation was then applied to data obtained from column leaching tests. The first-order reaction/diffusion model showed a better fit for Ca, Pb, and Cu, suggesting that the initial dissolution of soluble compounds, such as metal chloride, was controlled by the first-order reaction (surface wash off). Subsequently, insoluble compounds such as hydroxide or carbonate might penetrate into the porous matrix by diffusion.     

火力发电厂粉煤灰干燥特性研究

介绍了利用实验台对粉煤灰的干燥特性进行试验研究的情况 ,给出了粉煤灰的干燥曲线、干燥速率曲线和粉煤灰平衡湿含量计算式 ,分析了在干燥过程中粉煤灰的阻力特性 ,为粉煤灰干燥装置的工业化设计提供了理论依据     

Investigation of aerosol and gas emissions from a coal-fired power plant under various operating conditions

The concentrations of fine particles and selected gas pollutants in the flue gas entering the stack were measured under several common operation modes in an operating coal power plant producing electricity. Particle size distributions in a diameter range from 10 nm to 20 μm were measured by a scanning mobility particle sizer (SMPS), and the flue gas temperature and concentrations of CO₂ and SO₂ were monitored by a continuous emission monitoring system (CEMS). During the test campaign, five plant operating modes were studied: soot blowing, bypass of flue-gas desulfurization (FGD), reheat burner operating at 0% (turned off), 27%, and 42% (normal condition) of its full capacity. For wet and dry aerosols, the measured mode sizes were both around 40 nm, but remarkable differences were observed in the number concentrations (#/cm³, count per square centimeter). A prototype photoionizer enhanced electrostatic precipitator (ESP) showed improved removal efficiency of wet particles at voltages above +11.0 kV. Soot blowing and FGD bypass both increased the total particle number concentration in the flue gas. The temperature was slightly increased by the FGD bypass mode and varied significantly as the rating of reheat burner changed. The variations of CO₂ and SO₂ emissions showed correlations with the trend of total particle number concentration possibly due to the transitions between gas and particle phases. The results are useful in developing coal-fired power plant operation strategies to control fine particle emissions and developing amine-based CO₂ capture technologies without operating and environmental concerns associated with volatile amine emissions.

Implications: The measurement of the fine particle size distributions in the exhaust gas under several common operating conditions of a coal-fired power plant revealed different response relations between aerosol number concentration and the operating condition. A photo-ionizer enhanced ESP was demonstrated to capture fine particles with higher efficiency compared to conventional ESPs, and the removal efficiency increased with the applied voltage. The characteristic information of aerosols and main gaseous pollutants in the exhaust gas is extremely important for developing and deploying CO₂ scrubbers, whose amine emissions and operating effectiveness depends greatly on the upstream concentrations of fine particles, SO₂, from the power plant.     

Fate of polychlorinated dibenzo-p-dioxins and dibenzofurans in a fly ash treatment plant

To understand the fate of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in a fly ash treatment plant that used the Waelz rotary kiln process (hereafter the Waelz process), the samples of input and output media were collected and analyzed. The most important PCDD/F source in input mass was electric arc furnace (EAF) fly ash, which had a mean PCDD/F content of 18.51 ng/g and contributed more than 99% of PCDD/F input mass, whereas the PCDD/F input mass fractions contributed by the coke, sand, and ambient air were only 0.04%, 0.02%, and 0.000002%, respectively. For the PCDD/F output mass in the Waelz process, the major total PCDD/F contents of 43.73 and 10.78 ng/g were in bag-filter and cyclone ashes, which accounted for approximately 69% and 17%, respectively, whereas those of stack flue gas and slag were 14% and 0.423%, respectively. The Waelz process has a dechlorination mechanism for higher chlorinated congeners, but it is difficult to decompose the aromatic rings of PCDD/Fs. Therefore, this resulted in the accumulation of lower chlorinated congeners. The output/input ratio of total PCDD/F mass and total PCDD/F international toxicity equivalence (I-TEQ) was 0.62 and 1.19, respectively. Thus, the Waelz process for the depletion effect of total PCDD/F mass was positive but minor, whereas the effect for total PCDD/F I-TEQ was adverse overall.     

粉煤灰对焦化废水总铬去除的影响

以1 mg/L模拟焦化废水为研究对象,采用高锰酸钾氧化-二苯基碳酰二肼分光光度法测定焦化废水中总铬,研究不同条件下粉煤灰对总铬去除率的影响.结果表明:(1)粉煤灰粒径、粉煤灰用量、搅拌时间、pH对总铬去除率都有一定的影响.最佳条件:粉煤灰粒径为150μm,粉煤灰用量为4.00 g/L,搅拌时间为40 min,pH为3.在最佳条件下,总铬去除率可达98.82%.(2)在粉煤灰处理模拟焦化废水的最佳条件下,粉煤灰处理实际焦化废水的总铬去除率达90.00%.(3)粉煤灰处理焦化废水,可以以废治废,而且处理效果好、处理费用低、原料获取方便,在实践中具有可操作性.     

Characterization of individual fly ash particles emitted from coal- and oil-fired power plants

Individual particles from coal- and oil-fired power plants were analyzed by scanning electron microscope equipped with an energy dispersive X-ray spectrometer to investigate size, morphology, and composition. Samples were collected on filters by dichotomous sampler in the fine ( <2.5 μm aerodynamic diameter) and coarse (2.5 to 5–10 μm) fractions. In both fractions coal fly ash particles were predominantly ( > 95%) smooth, mineral spheres. No cenospheres (perforated hollow spheres) were detected, and almost 90% of the mass concentrations occurred in the coarse fraction. Sulfur as lared as a surface layer on the mineral core; the abundances of Fe and S were highly variable. The Al/Si ratio was fairly constant for most of the spheres but not for the relatively few Fe-rich or non-spherical coal fly ash particles. Over 90% of the mass of oil fly ash occurred in the fine fraction. The size distribution of chemical and morphological properties of individual oil fly ash particles was found to be trimodal. Oil fly ash particles smaller than 0.7 μ (geometric diameter) were non-spherical and relatively pure in sulfate, and 90% of such particles were smaller than 0.5 μm; V or Ni could be detected in 50% to 60% of such particles larger than 0.3 μm. Those particles in the 0.7–3 μm range of geometric diameters were predominantly spherical and of mineral composition, highly variable in Al, Si, P, Ca, Ti and Fe; 50–60% of them contained detectable amounts of V or Ni. Larger oil fly ash particles had a lacy morphology and consisted of carbonaceous material and sulfur.     

The internal microstructure and fibrous mineralogy of fly ash from coal-burning power stations

Coal fly ash (CFA) is a significant environmental pollutant that presents a respiratory hazard when airborne. Although previous studies have identified the mineral components of CFA, there is a paucity of information on the structural habits of these minerals. Samples from UK, Polish and Chinese power stations were studied to further our understanding of the factors that affect CFA geochemistry and mineralogy. ICP-MS, FE-SEM/EDX, XRD, and laser diffraction were used to study physicochemical characteristics. Analysis revealed important differences in the elemental compositions and particle size distributions of samples between sites. Microscopy of HF acid-etched CFA revealed the mullite present possesses a fibrous habit; fibres ranged in length between 1 and 10 μm. Respirable particles (<10 μm) were frequently observed to contain fibrous mullite. We propose that the biopersistence of these refractory fibres in the lung environment could be contributing towards chronic lung diseases seen in communities and individuals continually exposed to high levels of CFA.     

Spatial and temporal variability of atmospheric mercury concentrations emitted from a coal-fired power plant in Mexico

Atmospheric mercury in the environment as a result of the consumption of fossil fuels, such as coal used in electricity generation, has gained increased attention worldwide because of its toxicity, atmospheric persistence, and bioaccumulation. Determining or predicting the concentration of this pollutant in ambient air is essential for determining sensitive areas requiring health protection. This study investigated the spatiotemporal variability of gaseous elemental mercury (GEM) concentrations and its dry deposition surrounding the Presidente Plutarco Elías Calles (CETEPEC) coal-fired power plant, located on Mexico’s Pacific coast. The CALPUFF dispersion model was applied on the basis of the daily consumption of coal during 2013 for each generating unit in the power plant and considering the local scale. The established 300-ng/m³ annual average risk factor considered by the U.S. Department of Health and Human Services (U.S. DHHS) and Integrated Risk Information System (IRIS) must not be exceeded to meet satisfactory air quality levels. An area of 65 × 60 km was evaluated, and the results show that the risk level for mercury vapor was not exceeded because the annual average concentration was 2.8 ng/m³. Although the predicted risk level was not exceeded, continuous monitoring studies of GEM and of particulates in the atmosphere, soil, and water may be necessary to identify the concentration of this pollutant, specifically that resulting from coal-fired power plants operated in environmental areas of interest in Mexico. The dry mercury deposition was low in the study area; according to the CALPUFF model, the annual average was 1.40E?2 ng/m²/sec. These results represent a starting point for Mexico’s government to implement the Minamata Convention on Mercury, which Mexico signed in 2013.

Implications: The obtained concentrations of mercury from a bigger coal-fired plant in Mexico, through the application of the CALPUFF dispersion model by the mercury emissions, are below the level recommended according to the US Department of Health and Human Services and Integrated Risk Information System. These results provide evidence of important progress in the planning and installation to the future of monitoring mercury stations in the area of interest.     

A study of production and growth of sulfate particles in plumes from a coal-fired power plant

A number of airborne plume sampling experiments designed to examine the importance of sulfate particle-generating chemical reactions within coal-burning power station plumes are described. The flights were conducted downwind of the Keystone Generating Station in western Pennsylvania, with The Penn State University research aircraft, an Aerocommander 680E. On-board aerosol sampling instrumentation included a condensation nucleus counter, an optical particle counter and an electrical aerosol analyzer. A casella cascade impactor containing electron microscope copper grids coated with carbon film was used to collect particles at varying distances from the stacks. These samples were analyzed for sulfate content and particle size distribution. Measurements of SO₂ were made with a rapid-response pulsed fluorescent analyzer. Atmospheric pressure, temperature, dewpoint, winds and aircraft position were also monitored. For each flight, a vertical spiral aircraft sounding was made upwind of the power station to determine atmospheric stability and background aerosol particle and SO₂ concentrations. Downwind, the flight pattern consisted of a series of cross wind and longitudinal plume penetrations out to distances at which SO₂ reached background levels. During the case in which cooling tower plume and stack plume merger occurred, sampling continued out to regions where the liquid plume had dissipated. It was found that when relative humidity was low, stability near-neutral and solar radiation intense, the production of new Aitken particles was the primary mechanism of SO₂ oxidation. In the case of merger between the stack plume and the cooling tower plume, the formation of sulfate on pre-existing particles predominated over the formation of new particles. During cases with intermediate meteorological conditions both processes were of equal importance.     

Impact of free calcium oxide content of fly ash on dust and sulfur dioxide emissions in a lignite-fired power plant

Emitted pollutants from the Agios Dimitrios lignite-fired power plant in northern Greece show a very strong linear correlation with the free calcium oxide content of the lignite ash. Dust (fly ash) emissions are positively correlated to free calcium oxide content, whereas sulfur dioxide (SO2) emissions are negatively correlated. As a result, at present, the Agios Dimitrios Power Plant operates very strictly within the legislative limits on atmospheric particulate emission. In the present study, the factors to be considered in assessing the impact of lignite combustion on the environment are presented and evaluated statistically. The ash appears to have a remarkable SO2 natural dry scrubbing capability when the free calcium oxide content ranges between 4 and 7%. Precipitator operating problems attributable to high ash resistivity can be overcome by injecting sulfur trioxide to reduce the ash resistivity, with, of course, a probable increase in operating costs.