1、英文翻译原文The effects of particle concentration and charge exchange on fly ash beneficiation with pneumatic triboelectrostatic separationFederico Cangialosi a, Michele Notarnicola a, Lorenzo Liberti a, John M. Stencel bAbstract:Pneumatic transport, triboelectrostatic separation is a well-known technique
2、 for separating unburned carbon from coal combustion fly ashes to create ash products useful as pozzolanic additives in cement. Although considerable fundamental insight has been gained about particle interactions and charging during carbon-ash beneficiation, little work has been done to examine how
3、 particle concentration in the ash transport charging line, and how tribocharged particles colliding with electrodes and causing particle charge reversal, relate to carbon-ash separation performance. We show ash-carbon separation performance diminishes with increasing particle concentrations, especi
4、ally for carbon-rich fly ashes, and exhibits a maximum related to the electric field strength. On the basis of this investigation, an improved separator geometry was established that helps to overcome the limits imposed by charge reversal.1.IntroductionThe production of coal combustion fly ash from
5、Italian and US thermoelectric power plants has risen to 0.9 Mtons/y and 110 Mtons/y, respectively. Because fly ash is pozzolanic and classified as a “non-hazardous” waste by European and US regulations 1, potentially large markets exist for its use as an inexpensivereplacement for cement in concrete
6、. However, the application of low-NOx burners in coal-fired utilities has diminished fly ash qualities, increasing the loss-on-ignition (LOI) content and preventing its use as an admixture in cement. As average LOI contents in fly ash from power plants equipped with low-NOx burners can be near 15%,
7、a three-fold reduction in LOI would be required to meet requirements for ash re-use in concrete, as defined by EN-450 European (LOI 5%) 2. Dry separation of unburned carbon from ashes using triboelectrostatic processing is known to reduce the carbon content with acceptable ash product recoveries 36.
8、 Using pneumatic transport technology to produce saleable ash products complements operations and addresses issues already considered important in power plants: first, pneumatic ash transport is already used in most ash handling plants 7; second, although pneumatic transport of ash causes wear on pi
9、ping, the potential locations of the most severe erosion are well understood within coal power and ash handling plants. Furthermore, because pneumatic transport triboelectrostatic beneficiation technology contains no mechanical moving parts, the extent of wear is much less than that experienced by o
10、ther beneficiation technologies. Independent of the triboelectrostatic beneficiation technology selected for carbon-ash separation, particle charging properties and interactions of charged and uncharged particles with high voltage electrodes may influence carbon-ash separation. For example, research
11、 on charge acquired by glass beads and fly ashes, measured by the use of a Faraday cage, suggested significant reduction in the charge-to-mass ratio, q/m, as the particle concentration or feed rates were increased 811. Li, et al.12 discovered that substantial particle charge reversal occurred when t
12、ribocharged particles collided with electrode surfaces, but the combined roles of increasing feed rates and charge reversal on triboelectrostatic beneficiation performance were not examined. Furthermore, the importance of these factors on system design and scale-up, and the possible increasing influ
13、ence of space charge within the electric field as the feed rate is increased, has also not been assessed.Hence, this work elucidates the effect of feed rate on ash triboelectrostatic beneficiation and how it relates to secondary charge reversal caused by particles colliding with high voltage electro
14、des. Presented are data and a theoretical derivation that illuminate the extent to which feed rates and particle-electrode impacts influence separation efficiency. These results are used to provide insight into a modified separator geometry with improved s eparation performance2. Experimental2.1. Ma
15、terialsTwo fly ashes, FA1 (LOIF = 7.1%) and FA2 (LOIF = 27.5%),generated from pulverized coal combustion in two large Italian power stations, were examined. Ashes were sampled from the storage bins of the electrostatic precipitators. Materials were dry sieved using British Standard screens to produc
16、e five narrow size fractions plus a sixth fraction that included all material having particle sizes 150_m. Each size fraction was heated at 950 Cfor1 h to remove unburned carbon and to determine LOIs. The LOIs and size distributions of unburned carbon along with ash masses are presented in Fig. 1.2.2. Apparatus A schematic of the bench-scale triboelectrostatic beneficiation system is shown in Fig. 2. It was used to characterize
