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环保钢结构的设计与制造【优秀含10张CAD图纸+全套机械毕业设计】

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毕业设计（论文）任务书

题目环保钢结构的设计与制造——袋式除尘器

1、本论文的目的、意义随着工业的高速发展，环境污染日益严重，在人们生活水平不断提高的同时，对生活环境的质量要求也越来越高。特别在环境保护工作日益突出的今天，伴随着我国钢铁需求量的不断增加，针对冶金工业设计除尘器。对烟气进行综合治理，改善周边环境。加强对环境的保护，同时又能将从烟尘中带走的各种金属进行回收利用，特别是一些贵重的金属和稀有金属。起到了节约资源的作用。此题目的选择具的重要的意义。

2、学生应完成的任务

1）完成A0当量图纸大于3张，

2）设计说明书1份

3）英文翻译大于10000字符

4）论文日志

5）设计论文光盘一个

内容包括：1.文献综述

2.结构计算与校核

3.方案的选择与制定

4.计算结果

5.成本核算

3、论文各部分内容及时间分配：（共 15 周）

第一部分查阅文献及调研 (2周)

第二部分设计方案制定，并进行相关的计算校核 (8周)

第三部分绘制设备结构与相关制造大样图 (2周)

第四部分论文书写 (1周)

第五部分(1周)

评阅及答辩(1周)

摘要

在冶金过程中，产生大量的废气，这些废气的含尘浓度高，烟尘的危害性大，对环境造成严重的污染。同时，这些烟尘又有一定的回收和利用价值。因此，治理这些烟尘具有显著的经济效益和社会效益。

本设计针对冶炼的生产及场地等的具体情况，来设计布袋除尘器，并且使其排污情况达到国家相关的排放标准要求。而且，又要尽量满足投资少、运转费用低、操作方便、维护简单的要求。

目前，国内外除尘设备的种类和型号较多，通过对它们的原理的分析以及性能的比较等，根据实际情况，选出了对冶金炉废气控制的最佳方案。选用袋式除尘器并进行了设计计算确定了布袋的型号、尺寸、根数，对除尘器外部箱体、支架和灰斗等钢结构部件也进行了设计，并计算了其重量和面积和列出材料的数量表。然后对除尘系统进行长效防腐设计，根据现场，合理对各个部件进行了布局。

本设计选用的负压吸灰的袋式除尘器在原有除尘器的基础上，进行了一系列的改进。该除尘器节约成本，扩大了除尘的效率，同时，冷却塔的设计，降低了含尘气体的温度，保证了除尘器内布袋使用寿命，并合理地利用了空间，对除尘和清灰达到了全自动化控制。

在本设计中，不但完成了对除尘系统总体的设计，而且强化细节，做到了所设计的除尘系统可以直接进行加工、安装、调试并投入使用。并对成本进行了投资预算.对所要的材料都进行了全部的统计。

关键词：大气污染；袋式除尘器；钢结构；长效防腐

Abstract

In the process of metallurgy, a large amount of exhaust gas will be produced, which contains a high concentration of ash or dust. This kind of ash is very harmful and will pollute the environment. At the same time, the ash also has a value in reclamation and reuse. Therefore, it has a significant economic and social benefit to treat with it.

In this dpaper, according to the idiographic case of the producing and place etc. of smelting, it designs hop-pocket dust catcher and makes waste-excreting up to the relevant national standard criterion. What’s more, it should meet the requests of less investment, low running cost, conveniency for operation and easiness for maintenance as necessary as possible.

At present, there are relatively too many sorts and models of dust catcher at home and abroad, through the analyse of their theories and comparison of capability, according to the practical condition, we select the best scheme in calcium carbide furnace exhaust gas controlling. Having the hop-pocket dust catcher selected and the design calculation worked out, we fixed the model, size and root-number of the bag, and we have also designed the steel structure of the dust catcher’s several parts such as the exterior box, bracket and the ash- funnel etc. moreover, with its weight and area calculated. Then, towards the dust-removing system, we carried out the long-effective antisepticising design. According to the locale, we made a proper overall arrangement of each part, and checked on the economic and running cost at last.

This devise has a series of improvement. Compared with the original one，this hop-pocket dust catcher using a minus- pressure ash- absorbing technology. It will not only save the cost and enhance the dust-removing efficiency, because the design of cooling tower, it will also lower the temperature of the gas containing dust, in order to have the??? effective longevity of the bag guaranteed. Besides, the room can be used properly; the removing of dust and cleaning of ash are entirely automatically controlled.

In the paper, it has finished contriving the dust-removing system not only on the whole, furthermore, it has intensified the details of the device, so that it is able to carry out processing, installing, adjusting and been put in to effect directly. Moreover, the budget of investment and listed all the materials needed have worked out statistically.

keywords：air pollution, hop-pocket dust catcher, steel structure, long-effective antisepticising

第一章绪论1

1.1环境保护与可持续发展1

1.1.1环境与环境问题1

1.1.2 可持续发展2

1.2对大气的结构及组成的认识3

1.2.1大气圈及其及结构3

1.2.2 大气污染物4

1.2.3 锅炉大气污染物排放标准6

1.2.4 污染与健康7

1.2.5 大气污染的综合防治8

1.3 任务的提出与意义10

1.3.1 设计要求以及基本参数10

1.3.2 设计内容包括10

1.3.3 选题的意义10

第二章除尘设备的分类及其型号的选择11

2.1除尘设备的概述11

2.1.1 除尘器的概念11

2.1.2 除尘器的分类11

2.2 各种除尘器原理12

2.2.1 机械式除尘器12

2.2.2 静电除尘器19

2.2.3 湿式除尘器20

2.2.4袋式除尘器20

2.2.5 复合式除尘器26

2.2.6各种除尘器的性能比较及其型号的选择26

2.3 确定方案27

2.3.1滤袋速度的选择28

2.3.2 清灰方式的确定28

2.3.3 滤袋形式的确定31

2.3.4 过滤方向的确定31

2.3.5 进风口位置的选择31

2.3.7滤料的选择33

第三章除尘器的设计与计算37

3.1参数的计算37

3.1.1 计算需要的过滤面积和袋室数目37

3.2 风机的选择43

3.2.1 风机性能的比较43

3.3 冷却塔的设计45

3.3.1 冷却方式的选择45

3.3.2 冷却塔主要参数的计算48

3.4 除尘器卸灰系统设计49

3.4.1 除尘器卸灰阀的设计49

3.5 除尘器的基础的设计50

3.6钢结构部分的设计50

3.7 屋架的设计51

3.8 房子主体结构设计51

第四章.施工及其焊接要求53

4.1施工要求53

4.2 环保钢结构手工电弧焊焊接施工53

4.2.1对焊接有关人员的要求53

4.2.2开坡口53

4.2.3质量要求53

4.2.4施工准备53

4.2.5 材料的关键要求55

4.2.6 作业条件55

4.2.7 质量关键要求55

4.3 工艺流程56

4.3.1工艺流程图56

4.4 安全保护措施56

4.5 环境保护措施57

4.6 质量记录58

第五章除尘器的防腐与维护59

5.1防腐工艺的实施59

5.1.1高压空气的制备59

5.1.2工件喷砂处理59

第六章成本核算及投资63

6.1工程建设投资核算63

6.1.1 除尘器本体部分建造投资63

6.2养护、维修投资核算65

6.2.1 电耗费用65

6.2.2 维修费用65

第七章经济效益的评估66

结论67

致谢68

参考文献69

参考文献

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[5] 何争光主编.大气污染控制工程及应用实例.北京：化学工业出版社,2004.

[6] 蒋文举,宁平主编.大气污染控制工程.成都：四川大学出版社,2001.

[7] 李坚等主编.环境工程设计基础.北京：化学工业出版社,2002.

[8] 孙熙主编.袋式除尘技术与应用.北京：机械工业出版社,2004.

[9] 祝燮权主编.实用五金手册.上海：上海科学技术出版社,2001.

[10] 陈胜颐主编.钢结构设计手册.北京：轻业出版社,1990.

[11] 严兴忠主编.工业防尘手册.北京：劳动人事出版社出版,1989.

[12] 罗邦富,沈祖炎主编.钢结构设计手册.北京：中国建筑工业出版社,1989.

[13] 黄呈伟主编.钢结构设计.北京:科学出版社,2005.

[14] 张建勋编著.现代焊接生产与管理.北京：机械工业出版社,2006.

[15] 何铭新,钱可强主编. 机械制图.第四版. 北京.高等教育出版社,1997.

[16] 吴忠标主编.大气污染控制工程.北京：科学出版社,2002.

[17] 肖亚明主编. 建筑钢结构设计.合肥：合肥工业大学出版社,2006

[18] 王丽萍主编. 大气污染控制工程.北京.高等教育出版社,2002

[19] 李连山主编. 大气污染控制工程.北京.高等教育出版社.2003

[20] 徐世明,胡月华, 李卉, 张改芳. 反吹风布袋除尘器的应用.磷肥与复肥.

2000年第15卷第5期:P17

[21] 吴英浩. 升压风机在电厂烟气脱硫中的应用及选择. 云南电力技术.2004年11月第35期.

[22] 石增斌. 布袋除尘器技术及其应用. 煤炭技术.Vol 25(1),2006年:123-

[24] 李国厚,赵明富. 除尘器通用控制仪的设计. 金属矿山,2006年第3期:77

[24] 张瑞平,赵士骐,吴利勤. 布袋除尘器的应用及前景.煤气与电力.2004年7月第7期.

[25] 李志华. 袋式除尘器设计参数的确定.综述与专论.2004年.30卷P29

[26] 朱健，马从生，陈永仕. JLDC立窑袋式除尘器的设计与应用. 水泥CNMENT

2004.NO.2:49

[27] 王升,杨彦香. 环保设备用焊管的生产. 焊管,Vol25(4) 2002:33

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内容简介：: 11concentrations of heavy metal are at their lowest in the first collector chamber and highest in the last chamber. The concentration ofcadmium in fly ash used as fertiliser can be reduced by as much as 70% by applying electrostatic precipitation fractionation. The removalof other heavy metals is not as ecient as that of cadmium. The results show that electrostatic precipitation is an adequate method in theas increasing amounts of biofuels are used. Wood and peatash can be spread onto forest lands or arable land as fertil-ably lower, being about 6% in 1997.materials increase the ash-contained Cd concentrations,and then screen out the cadmium containing materials.ents in ash, on the solubility of nutrients in the ash and thesoil, and on soil properties, e.g. acidity and nutrient con-centrations (Orava et al., 2004; Silfverberg, 1996). Table2 shows the heavy metal concentrations of four ash types.Many substances contained in ash are in extremelypoorly soluble forms. As the heavy metals (e.g. cadmium,*Corresponding author.E-mail addresses: hanne.oravamikkeliamk.fi (O. Hanne), timo.nord-manoulu.fi (N. Timo), hannu.kuopanporttimikkeliamk.fi (K. Hannu).Minerals Engineering 19 (2006)iser or as soil improvement material, and with the purposeof adding calcium to the soil. The use of ash has been con-strained by factors such as its dust content and heavy metalconcentrations; the latter having in many cases exceededthe maximum permitted levels imposed in Finland on soilimprovement 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-Small amounts of fly ash are used as a fertiliser both inagriculture and in forestry. Generally, various ash types aremore suitable as a soil improvement material than fertilis-ers in agriculture because the amounts of soluble plantnutrients in ash are fairly low. Peat ash is used mainly asa phosphate fertiliser and wood ash in liming of mineralsoils and as a basic and support fertiliser in the growingof cereal crops. The liming and fertiliser eects of ash inthe soil depend on the concentrations of calcium and nutri-fractionating of fly ash to be used as a fertiliser or soil amendment.C211 2006 Elsevier Ltd. All rights reserved.Keywords: Electrostatic 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 peryear. The amounts of such ash will increase in the futureThe extraction of heavy metals from fly ash could enableits more ecient utilisation. Currently, it appears thatmanipulating the power plant fuel quality is the onlymethod available for this purpose. This means that we mustknow the combustible fuels exact consistency, and whichIncrease the utilisation of fly ashOrava Hannea,*, Nordman TimoaYTI Research Centre, Mikkeli Polytechnic,bUniversity of Oulu, P.O. Box 4300,Received 28 April 2006;Available onlineAbstractThe basic idea in this study is to look into the possibilities of reducingtrostatic precipitation. The utilisation of fly ash as fertiliser is hamperedvariable. Fly ash fractionation experiments were done using electrostatic0892-6875/$ - see front matter C211 2006 Elsevier Ltd. All rights reserved.doi:10.1016/j.mineng.2006.07.002with electrostatic precipitationb, Kuopanportti HannuaP.O. Box 181, FI-50101 Mikkeli, FinlandFI-90014 Oulun yliopisto, Finlandaccepted 7 July 2006September 2006the heavy metal concentrations of fly ash by means of elec-by its high concentrations of heavy metals, which are highlyprecipitators at four power plants. Based on the results, theThis article is also available online at:/locate/mineng15961602ntslead, nickel) in ash are in very poorly soluble forms, it canTable 2Heavy metal concentrations of various ash types (Palola, 1998)Heavy metals (mg/kg) Coal ash Peat ash Wood ash Bark ashArsenic (As) 2.3200 2200 0.260 728Cadmium (Cd) 0.01250 0.058 0.440 420Chrome (Cr) 3.67400 15250 15250 4081Copper (Cu) 303000 20400 15300 57144Mercury (Hg) 0.0180 0.0011 0.021 0.0120.4Nickel (Ni) 1.8800 15200 20250 3652Lead (Pb) 3.11800 5150 151000 53140Zinc (Zn) 1413,000 10600 1510,000 11005100Table 1Maximum permitted concentrations of heavy metals in soil improvementmaterials and in fly ash from power plant A (Orava, 2003)Element Power plant A: fly ash (mg/kg) Maximumpermittedconcentration(mg/kg)Year 2002 Year 2001 Year 1999Mercury (Hg) 2.5 0.31 2.0Cadmium (Cd) 2.69 5.05 6.3 3.0Arsenic (As) 18.34 19.73 35 50Nickel (Ni) 100Lead (Pb) 56.59 106.5 52.7 150Copper (Cu) 86.7 290.1 178 600Zinc (Zn) 189.7 376.9 706 1500O. Hanne et al. / Minerals Engineerinbe assumed that ash fertilisation will not result in signifi-cant heavy-metal impacts, e.g. in water systems, within ashort period of time following fertilisation. In the longrun, harmful heavy metals may, however, be released fromash in soluble forms and be thereby translocated into thevegetation (Nieminen, 2003). The liming eect of ash low-ers the solubility of heavy metals in the soil. Ash may atfirst raise the cadmium concentration in tree stands, butonce tree growth has improved the concentrations of traceelements and heavy metals may fall even below the initiallevel. The rise in the Cd concentration in some plant speciescan last for a long time (Moilanen, 2003). Cadmium is con-sidered to be the most harmful of all heavy metals becauseit remains in the soil, it becomes enriched in food chains,and it is toxic to organisms.Electrostatic precipitation (Fig. 1) is currently the mostcommon method used in separating the solid matter frompower plant flue gases. The advantages of electrostatic pre-cipitation include high collection eciency (as high as99.9%) and its suitability for dealing with particles of dier-ent sizes (even particle sizes below 1 lm) and variable fluegas volumes. Its further advantages are long service life,good operational reliability, and low operating and mainte-nance costs (Walsh, 1997; Immonen, 1987).The functioning of the electrostatic precipitator is signif-icantly dependent on the properties of the fly ash to be col-lected. The amount and size distribution of the particles tobe removed have a significant impact on the functioning ofthe electrostatic precipitator. Although the collection e-ciency of electrostatic precipitator is more or less constantirrespective of the particle mass, the eective migrationvelocity is lower in the case of small particles. Due to thedierent charging properties of the particles, the collectioneciency of the particles varies as a function of particlesize. The most dicult particle size from the point of viewof separation is 0.20.5 lm(Nykanen, 1993; Kouvo, 2003).The concentrations of heavy metal in ash can be reducedby fractionation of the finest ash particles from flue gasesby means of multi-chamber electrostatic precipitators.The fractionating properties of the precipitator can beinfluenced by actions such as restricting and pulsating thecurrent. Our research results have shown that heavy metalsFig. 1. Alstom Finland Oys electrostatic precipitator (Jalovaara et al.,2003).g 19 (2006) 15961602 1597are concentrated in fine ash particles (Orava et al., 2004;Orava, 2003). According to the results of Thun and Korho-nen (1999), the 3-field electrostatic precipitator wasstopped, depending on the operating conditions, 8495%of the overall amount of ash in the first field, 415% inthe second field, and approx. 1% in the last field. The cad-mium concentration of ash can be reduced at least by 1525% by means of fractionating the ash using electrostaticprecipitators (Orava et al., 2004; Thun and Korhonen,1999).Depending on the boiler in question, ashes from barkfuelled and wood chip fuelled power plants (grate boilers)are divided into weight percentage categories as follows:bottom ash 7090%, cyclone fly ash 1030%, electrostaticprecipitator fly ash 28% and dust emissions 0.13.0%(Agarwal and Agarwal, 1999). In dust combustion and flu-idized-bed combustion, the share of fly ash generation is80100%. As much as 7590% of the heavy metals (Cdand Zn) are contained in the fine particle fraction of thefly ash, which is separated by electrostatic precipitators(Dahl et al.). Fig. 2 sets out the zinc, lead and cadmiumcontents (mg/kg and m-%) in bottom ash, cyclone ashand electrostatic precipitator fly ash. Based on the figure,ntsash can thus be reduced to below the maximum permittedconcentrations.2. Materials and methodsThe fractionating trials with fly ash were performed atfour power plants (A, B, C and D). The electrostatic pre-cipitators were operated at the power plants at dierentvoltage levels and samples were taken from the ESPs var-ious fields. All the samples taken from the electrostatic pre-cipitators were taken from the ash feeders located underthe electrostatic precipitators before the ash was fed intothe silo. The samples were analysed for the presence ofPb, Cu, Zn, Ni, As and Cd using the graphite method1598 O. Hanne et al. / Minerals Engineering 19 (2006) 15961602it may be stated, for example, that electrostatic precipitatorfly ash has a higher Cd content than cyclone ash, which ispartly due to the fact that, compared to cyclones, electro-static precipitators separate smaller particles that containthe majority of heavy metals. In this case, the portion ofthe fly ash that is suitable for use as a fertiliser, in termsof its consistency, remains at the cyclone (Obernbergerand Biedermann, 1997).The electrostatic precipitator can more eectively frac-tionate fly ash than the traditional methods when amechanical classifier (cyclone) is connected before the ashreaches the precipitator. Fig. 3 shows a basic layout draw-ing of a power plant fired by using biofuels and which isprovided with a multi-cyclone before the electrostatic pre-cipitator. As much as 7590% of the heavy metals (Cdand Zn) contained in fly ash are bound to the fine fly ashfraction separated by the electrostatic precipitator (Dahlet al., 2002).Properly designed and adjusted electrostatic precipita-Fig. 2. Heavy metal concentrations and their division as bulk percentagefigures in bottom ash, cyclone fly ash and filter fly ash (Agarwal andAgarwal).tion is in principle, capable of separating that fraction ofthe flue gases, which contains the greatest amount of heavymetals but only a fraction of the overall amount of ash.The heavy metal concentrations in the main part of theFig. 3. The ash fractions produced by a biofuel-firedand particle size determination was done using a Malverndevice.Power plant A uses peat, forest chip and oil and the by-products of the mechanical wood processing industry as itsfuels. The boiler capacity available to the power plant is150 MW. The fractionating trials were performed withthe power plants current 3-field electrostatic precipitator.Power plant B uses two boilers, one a Pyroflow circulat-ing fluidized-bed boiler (capacity 55 MW) and the other afluidized-bed boiler (capacity 42 MW). The trials were car-ried out using the fluidized-bed boiler. The power plantsprincipal fuel is milled peat with wood fuels, soot and alu-minium oxide mixed in with it. The fly ash from both boil-ers is conveyed via 2-field electrostatic precipitators to acommon ash silo.Power plant C is equipped with two power plant boilers.Boiler 1 is a fluidized-bed boiler with a fuel capacity of267 MW. Boiler 2 is a Pyroflow circulating fluidized-bedboiler with a fuel capacity of 315 MW. The tests were per-formed using the Pyroflow circulating fluidized-bed boiler.The fuels used at the power plant were mainly milled peatand various wood fuels. Both boilers are equipped with 3-field electrostatic precipitators from which the boilers flyash is blown pneumatically to a common ash silo.The electrical power generated by power plant Ds fluid-ized-bed boiler plant is 77 MW and its heating capacity is246 MW. The fuels used in the fluidized-bed boiler arepower plant (Agarwal and Agarwal).ntsmainly milled peat and wood waste. The fly ash is sepa-rated from the flue gases by means of a 3-field electrostaticprecipitator.3. ResultsDuring trials with power plant As electrostatic precipi-tator (trials 17) the fuel used was composed 49% peat and51% wood fuels. The ash funnels of fields 13 of the elec-trostatic precipitator were sampled and analysed (Fig. 4).On the basis of the results, the Cd concentration was atits lowest in field 1 of the electrostatic precipitator and at itshighest in field 3. This is due to the bigger fly ash particlesaccumulating in field 1 and field 3 containing ash with theparticles in the first field of the electrostatic precipitator.2.833.23.4024681012CBO-ratioCd mg/kgFig. 5. The eect of the CBO ratio from electrostatic precipitator field 1on fly ash Cd concentrations (mg/kg) during trial runs with peat fuel.2.83.8425 30 35 40 45 50Voltage kVCd mg/kgFig. 6. The eect of the filter voltage level (kV) from electrostaticO. Hanne et al. / Minerals Engineering 19 (2006) 15961602 1599smallest particles. The Cd concentration in field 1 varieswithin the range of 2.23.6 mg/kg and in the last fieldwithin the range of 7.212.4 mg/kg. Concentrations areaected by properties such as the ESP voltage, fuel quality,and flue gas flow rate. In almost every electrostatic precip-itators field 1 the Cd concentration is below the permittedmaximum limit (3.0 mg/kg) set down for ash intended forfertiliser use.During trial runs, the electrostatic precipitator fieldsCBO ratio (cycle block in operation) was controlled withinthe range 012. The value 0 means that all the half-cycles ofthe field in question are currently active, and for exam-ple, the value 2 means that only a third of the half-cyclesare active. Thereby the CBO value declares how manysequential half-cycles are closed, that is, how often the sep-arators supply current is pulsated. In the present research,the CBO value was controlled by the Micro-Kraft control-ler whose main task is to keep the voltage near to thebreakdown voltage.The most important thing is to be able to influence andchange the properties of field 1 in the electrostatic precipi-tator. The first field enables the production of fly ash withheavy metal concentration levels that make it suitable as afertiliser, for example.Fig. 5 shows how the electrostatic precipitators CBOratio control for field 1 aects the fly ash Cd concentrationlevels. Among other things, the increasing or decreasing024681012141234567Cd mg/kgField 1Field 2Field 3Fig. 4. Cd concentrations (mg/kg) of the fly ash in fields (13) during trialruns (17) with peat fuel when using the electrostatic precipitator.number of electrostatic precipitator field flashovers isexcluded from this control.The more field half-cycles there are deactivated, thelower the heavy metal content of the fly ash being gener-ated. Cd concentration variations are also caused by fuelquality variations, in addition to the control itself, amongother factors.Fig. 6 shows how the electrostatic precipitators filtervoltage aects the Cd concentration level of field 1. Theheavy metal concentration level increases in accordancewith the rising voltage. This is due to the fact that highervoltages can more eectively separate fine particles thatalso contain heavy metals. The filter voltage level indicatesthe fields actual status more eectively than does the CBOratio. Among other things, it also takes into account anyelectric breakdowns that occur within the field.Fig. 7 shows the particle size classes (lm) D10 and D50of fields 13 resulting from trials 5, 6 and 7. D10 is a par-ticle size with respect to which 90% of the samples particlesare larger and 10% are smaller. D50 is a halving particlesize class, or the particle size with respect to which samplesparticles are larger and smaller in the ratio of 50/50.On the basis of this figure, the smaller-sized particlestend to be concentrated in the last field and the bigger-sizedprecipitator field 1 on fly ash Cd concentrations (mg/kg) during trial runswith peat fuel.ntsThese small particles have the highest concentrations ofheavy metals (Fig. 8). The figure shows that the permissibleCd concentration level for use as a fertiliser is exceeded inparticle size category 16 lm.The cadmium concentrations were at their highest atpower plant D (Fig. 9). This was due to the bigger shareof wood fuel in the fuel when compared to the other powerplants. Following fractionation, the cadmium concentra-tion of the ash accumulated in field 3 of the electrostaticprecipitator was at best five fold compared to field 1.051015202530D10 D50 D10 D50 D10 D50mField 1Field 2Field 3Fig. 7. The particle size classes (lm) D10 and D50 of the fly ash in theelectrostatic precipitators fields 13.1600 O. Hanne et al. / Minerals Engineerin23456786 11162126Cd mg/kgThe particle size class D50 mFig. 8. Cd concentration levels (mg/kg) and particle size (lm) D50 duringtrial runs with peat fuel.0510152025BBBCCCDDDCd mg/kgField 1Field 2Field 3SiloFig. 9. Cd concentrations of the fly ash in the various fields of theelectrostatic precipitator (limit value 3 mg/kg) at power plant B, C and D.Despite this, in these tests it was not possible to eectivelyfractionate the ash at power plant D.According to the results the Pb, Cu and Ni concentra-tions are not problematic from the viewpoint of fraction-ation. With respect to these metals, fly ash can be used asa fertiliser without fractionation being necessary. Zn, Asand Cd concentrations may exceed the permitted limit val-ues and thereby cause problems for the fertiliser use of flyash. With respect to these metals, the use of the fly ash as afertiliser depends on the composition of the fuel and on theeectiveness of fractionation.Fig. 10 shows the analysed particle sizes from variousblock

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