Plerospheres and their role in reduction of emitted fine fly ash particles

Particles, less than PM10 in size, emitted from the stack of pulverized coal-fired power plants are of environmental concern since they can easily enter the human respiratory track. These fine particles are examined by Scanning Electron Microscope/Electron Dispersive Spectrometry （SEM/EDX）. Plerospheres are found in fly ash and are particles containing smaller particles formed during combustion of coal. The large plerospheres 〉50 μm mostly are present in ESP fly ash, indicating that they are effectively capturing fine particles and reducing their stack emission.     

Study on the distribution of PAHs in fly ash from coal and residual char combustion in a pressurized fluidized bed

Direct coal combustion not only has a low utilizing efficiency, but also produces a large amount of pollutants such as particulate, CO2, SO2, NOx, polycyclic aromatic hydrocarbons （PAHs）, PCDD/PCDFs, and so on. Coal gasification is a clean coal technology that presents good prospects for coal use, mainly for producing electricity with a high coal conversion efficiency and low environmental impact. However, there is a problem about the minimization of PAHs in coal gasification or direct coal combustion. PAHs are harmful to the environment and human health due to their high degree of mutagenicity and carcinogenicity when they enter human bodies through breathing, eating, and drinking. It is said that about 75%-90% cancers of human beings are mainly caused by PAHs. So the US EPA has prioritized 16 PAH compounds as hazardous air pollutants; these compounds are naphthalene （NAP）, acenaphthylene （AcPy）, acenaphthene （AcP）, fluorene （Flu）, phenanthrene （PhA）, anthracene （ANT）, fluoranthene （FluA）, pyrene （Pyr）, benzo （a） anthracene （BaA）, chrysene （Chr）, benzo （b） fluoranthene （BbF）, benzo （k） fluoranthene （BkF）, benzo （a） pyrene （BaP）, indeno（1,2,3,-cd） pyrene [In（1,2,3-cd） P], dibenzo （a,h） anthracene （DbA）, and benzo （ghi） perylene （BghiP）. The residual char is one of the main products during coal gasification, and then it is brought into the combustion chamber to combust. To investigate the distribution of PAHs in fly ash, the combustion of coal and residual char was tested in a pressurized spouted fluidized bed. After Soxhlet extraction and K-D concentration, the contents of 16 PAHs recommended by US EPA in coal, residual char, and fly ash, were analyzed by a HPLC coupled with fluorescence and diode-array detection.     

Leaching Behavior of Fly Ashes from Power Plants

The Yanzhou mine district, located in southwestern Shandong Province, is about 1300 km2 with more than 8×109tons of proved coal reserves and there are 10 big power plants in this area. A large amount of coal ashes, which are regarded as waste materials, have been stockpiled in the area and have influenced the environment of the mine district. In this paper, analysis of fly ash samples from three power plants is carried out, the enrichment and concentration of trace elements, Pb, Zn, Cu and As, in coal ashes are analyzed, and petrological and mineralogical characteristics and chemical compositions of coal ashes are studied. The aim of this work is to provide basic scientific data for utilization of ashes and reduction of environmental pollutions.     

Synthesis of Mullite from High-alumina Fly Ash: a Case from the Jungar Power Plant in Inner Mongolia, Northern China

In this paper, an experimental study was conducted in order to test the feasibility of sintering mullite directly from the high-alumina fly ash, without adding any extra material. The results show that the mullite contents in most sintered samples are over 70%. The samples sintered from the beneficiated fly ash have a higher content of mullite than those from the as-received fly ash under the same synthetic conditions. To obtain an equal amount of mullite, a higher sintering temperature is needed for the beneficiated fly ash than for the as-received fly ash. Considering the physical properties of sintered mullite, the favorable sintering temperature is 1400℃ for the as-received fly ash and 1500℃ for the beneficiated fly ash. A higher sintering temperature and a shorter holding time are profitable to sintering mullite. The orthogonal test confirmed that the dominant factor affecting mullite synthesis is sintering temperature, and that the most profitable matching conditions are 200 MPa-1500℃-3 h for the as-received fly ash and 200 MPa-1500 ℃-4 h for the beneficiated fly ash.     

Concentrations of heavy metals in fly ash from CAN coal combustion thermal power plant （Canakkale-Turkey）-II

Coal combustion can mobilize trace elements by introducing them to terrestrial, aquatic and atmospheric environments, and if leached, these elements may cause the contamination of soils, surface waters and groundwater. Therefore, these elements may become a hazard to the environment because of their contribution to the formation of toxic compounds, if the ash is not utilized or disposed of properly. This possible contamination could lead to health, environmental and land-use problems. A fluid coal-t-fred thermal power plant （320 MWel） has been in operation since 2005 in Can （Canakkale-Turkey） and currently produces almost half a million tones of fly ash per year. Fly ash is classified based on the nature of constituents present. Fly ashes of Class C contain less than 70% but greater than 50% of silica, alumina, and iron oxide which are typical for the western part of Turkey. When the ash concentrations of these three constituents exceed 70%, fly is classified as F, which is representative of those, produced from Can. Fly ash is enriched in many trace elements particularly metals in this thermal power plant ash. These metals are part of the pyrite structure in the coal and become concentrated in the fly ash during the combustion process. These elements may be surface adsorbed on the glassy spherical fly ash particles. Elements that are surface adsorbed can be quite mobile.     

Removal of fluoride from aqueous solution by modified fly ash

Removal of fluoride from aqueous solution by modified fly ash was studied in batch model. The influences of the contact time, the initial F^- concentration, the dosage of fly ash, and the temperature on removal of F have been studied, respectively. It was found that fly ash modified with dilute HCl has the maximum adsorption of fluoride from aqueous solutions, and that the retention of fluoride ions by material was 85% or higher with initial 10 mg F^-/L. First-order kinetics was observed for the adsorption process, which follows the Langrnuir and Freundlich isotherms. The thermodynamic parameters such as ΔG0, ΔH0, ΔS0 were calculated from Langmuir constants. The positive value of ΔH0 （1.273 J/mol） confirms the endothermic nature of adsorption.