外文翻譯--利用靜電增加對灰塵的沉積英文版

1、Increase the utilisation of fly ash with electrostatic precipitationOrava Hanne a,*, Nordman Timo b, Kuopanportti Hannu aa YTI Research Centre, Mikkeli Polytechnic, P.O. Box 181, FI-50101 Mikkeli, Finland b University of

2、 Oulu, P.O. Box 4300, FI-90014 Oulun yliopisto, FinlandReceived 28 April 2006; accepted 7 July 2006 Available online 11 September 2006AbstractThe basic idea in this study is to look into the possibilities of reducing the

3、 heavy metal concentrations of fly ash by means of elec- trostatic precipitation. The utilisation of fly ash as fertiliser is hampered by its high concentrations of heavy metals, which are highly variable. Fly ash fracti

4、onation experiments were done using electrostatic precipitators at four power plants. Based on the results, the concentrations of heavy metal are at their lowest in the first collector chamber and highest in the last cha

5、mber. The concentration of cadmium in fly ash used as fertiliser can be reduced by as much as 70% by applying electrostatic precipitation fractionation. The removal of other heavy metals is not as efficient as that of ca

6、dmium. The results show that electrostatic precipitation is an adequate method in the fractionating of fly ash to be used as a fertiliser or soil amendment. ? 2006 Elsevier Ltd. All rights reserved.Keywords: Electrostati

7、c separation; Sizing; Classification; Flue dusts; Recycling1. IntroductionHeating-energy plants and power plants in Finland gen- erate approx. 400,000 tonnes of ash of biofuel origin per year. The amounts of such ash wil

8、l increase in the future as increasing amounts of biofuels are used. Wood and peat ash can be spread onto forest lands or arable land as fertil- iser or as soil improvement material, and with the purpose of adding calciu

9、m to the soil. The use of ash has been con- strained by factors such as its dust content and heavy metal concentrations; the latter having in many cases exceeded the maximum permitted levels imposed in Finland on soil im

10、provement substances (Table 1). In 2001, the utilisation rate of coal ash (84%) was con- siderably higher than that of peat and mixed fuel ash (43%). Wood fly ash utilisation rates have been consider- ably lower, being a

11、bout 6% in 1997.The extraction of heavy metals from fly ash could enable its more efficient utilisation. Currently, it appears that manipulating the power plant fuel quality is the only method available for this purpose.

12、 This means that we must know the combustible fuel’s exact consistency, and which materials increase the ash-contained Cd concentrations, and then screen out the cadmium containing materials. Small amounts of fly ash are

13、 used as a fertiliser both in agriculture and in forestry. Generally, various ash types are more suitable as a soil improvement material than fertilis- ers in agriculture because the amounts of soluble plant nutrients in

14、 ash are fairly low. Peat ash is used mainly as a phosphate fertiliser and wood ash in liming of mineral soils and as a basic and support fertiliser in the growing of cereal crops. The liming and fertiliser effects of as

15、h in the soil depend on the concentrations of calcium and nutri- ents in ash, on the solubility of nutrients in the ash and the soil, and on soil properties, e.g. acidity and nutrient con- centrations (Orava et al., 2004

16、; Silfverberg, 1996). Table 2 shows the heavy metal concentrations of four ash types. Many substances contained in ash are in extremely poorly soluble forms. As the heavy metals (e.g. cadmium,0892-6875/$ - see front matt

17、er ? 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2006.07.002* Corresponding author. E-mail addresses: hanne.orava@mikkeliamk.fi (O. Hanne), timo.nord- man@oulu.fi (N. Timo), hannu.kuopanportti@mikkeliamk

18、.fi (K. Hannu).This article is also available online at: www.elsevier.com/locate/minengMinerals Engineering 19 (2006) 1596–1602it may be stated, for example, that electrostatic precipitator fly ash has a higher Cd conten

19、t than cyclone ash, which is partly due to the fact that, compared to cyclones, electro- static precipitators separate smaller particles that contain the majority of heavy metals. In this case, the portion of the fly ash

20、 that is suitable for use as a fertiliser, in terms of its consistency, remains at the cyclone (Obernberger and Biedermann, 1997). The electrostatic precipitator can more effectively frac- tionate fly ash than the tradit

21、ional methods when a mechanical classifier (cyclone) is connected before the ash reaches the precipitator. Fig. 3 shows a basic layout draw- ing of a power plant fired by using biofuels and which is provided with a multi

22、-cyclone before the electrostatic pre- cipitator. As much as 75–90% of the heavy metals (Cd and Zn) contained in fly ash are bound to the fine fly ash fraction separated by the electrostatic precipitator (Dahl et al., 20

23、02). Properly designed and adjusted electrostatic precipita- tion is in principle, capable of separating that fraction of the flue gases, which contains the greatest amount of heavy metals but only a fraction of the over

24、all amount of ash. The heavy metal concentrations in the main part of theash can thus be reduced to below the maximum permitted concentrations.2. Materials and methodsThe fractionating trials with fly ash were performed

25、at four power plants (A, B, C and D). The electrostatic pre- cipitators were operated at the power plants at different voltage levels and samples were taken from the ESP’s var- ious fields. All the samples taken from the

26、 electrostatic pre- cipitators were taken from the ash feeders located under the electrostatic precipitators before the ash was fed into the silo. The samples were analysed for the presence of Pb, Cu, Zn, Ni, As and Cd u

27、sing the graphite method and particle size determination was done using a Malvern device. Power plant A uses peat, forest chip and oil and the by- products of the mechanical wood processing industry as its fuels. The boi

28、ler capacity available to the power plant is 150 MW. The fractionating trials were performed with the power plant’s current 3-field electrostatic precipitator. Power plant B uses two boilers, one a Pyroflow circulat- ing

29、 fluidized-bed boiler (capacity 55 MW) and the other a fluidized-bed boiler (capacity 42 MW). The trials were car- ried out using the fluidized-bed boiler. The power plant’s principal fuel is milled peat with wood fuels,

30、 soot and alu- minium oxide mixed in with it. The fly ash from both boil- ers is conveyed via 2-field electrostatic precipitators to a common ash silo. Power plant C is equipped with two power plant boilers. Boiler 1 is

31、a fluidized-bed boiler with a fuel capacity of 267 MW. Boiler 2 is a Pyroflow circulating fluidized-bed boiler with a fuel capacity of 315 MW. The tests were per- formed using the Pyroflow circulating fluidized-bed boile

32、r. The fuels used at the power plant were mainly milled peat and various wood fuels. Both boilers are equipped with 3- field electrostatic precipitators from which the boilers’ fly ash is blown pneumatically to a common

33、ash silo. The electrical power generated by power plant D’s fluid- ized-bed boiler plant is 77 MW and its heating capacity is 246 MW. The fuels used in the fluidized-bed boiler areFig. 2. Heavy metal concentrations and t

34、heir division as bulk percentage figures in bottom ash, cyclone fly ash and filter fly ash (Agarwal and Agarwal).Fig. 3. The ash fractions produced by a biofuel-fired power plant (Agarwal and Agarwal).1598 O. Hanne et al