Fuel-oil ve toz kömür yakılan kazanlarda ağır metal emisyonlarının incelenmesi
Başlık çevirisi mevcut değil.
- Tez No: 55522
- Danışmanlar: PROF.DR. HASANCAN OKUTAN
- Tez Türü: Yüksek Lisans
- Konular: Kimya Mühendisliği, Chemical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1996
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 95
Özet
ÖZET Yüzyılımızın önemli sorunlarından olan hava kirliliği, doğal ve antropojenik kaynaklar sonucu ortaya çıkmakta ve bilim adamlarını daha çevreci teknolojiler geliştirmeye mecbur bırakmaktadır. Özellikle kükürt oksitler, azot oksitler ve partikül kirliliği ile kendini gösteren bu sorun, insan sağlığı, akarsular, göller, ormanlar ve tüm çevre açısından son derece büyük tehlike arz etmekte ve bu konuda tedbir almayı gerekli kılmaktadır. Hava kirliliği kaynakları, orman yangını, volkan vb. doğal veya evsel ısınma araçları, sanayi kuruluşları, taşıma araçları gibi yapay olabilir. Ayrıca çöplerin yanması, kirli su kütleleri ve bina yıkma, kum-çimento gibi toz madde boşaltma faaliyetleri de hava kirliliğine neden olan kaynaklardır. Tozluluk ister doğal İster yapay nedenlerden kaynaklansın görüş mesafesini kısaltan, güneş ışınlarının absorblandığı bantı değiştiren, insan, hayvan ve bitki sağlığına olumsuz etki yapan bir kirlilik türüdür. Hava kirliliğine büyük ölçüde katkıda bulunan ancak genellikle gözardı edilen diğer bir unsur da ağır metallerdir. Özellikle taşıt egzozlarından, dökümhanelerden, evsel ve endüstriyel amaçla kullanılan kömür ve fuel-oil yakan kazanların baca gazından yayılan ağır metallerin toksik ve kanserojen etkisi bilinmek tedir. Bu çalışmada, üzerinde yok denecek kadar az çalışma yapılmış olan ağır metallerin, toz kömür ve özellikle fuel-oil yakılan kazanların gaz - toz emis yonları ile taban külündeki (cüruf) dağılım, derişim ve kütlesel debileri tesblt edilerek Hava Kalitesinin Korunması Yönetmeliği'ndeki sınır değerlerle ve diğer araştırma sonuçlarıyla karşılaştırılın ıştır. ix
Özet (Çeviri)
INVESTIGATION OF HEAVY METAL EMISSIONS FROM FUEL-OIL AND PULVERIZED COAL BOILERS SUMMARY One of the important problems of 21th century, air pollution, has recently started to attract attention in our country Although Important air pollutants that come to our mind at first are sulphur dioxide, nitrogen oxides, carbon monoxide and polycyclic aromatic hydrocarbons (PAHs), there is another important pollutant as hazardous as the others: trace elements which consist of heavy metals. These elements result from the combustion of coal and fuel-oil. Coals are known to contain most of the naturally occuring elements with widely varying concentrations depending on the rank and geological origin of the coal. The enormous quantities of coal used for electrical power generation haste given rise to a growing concern to the release of certain elements into the atmosphere, particularly those elements known to be toxic or have associated health hazards. Coal combustion has been estimated to be the main source of Hg, Ni, Sn and V emissions and the second largest source of Cd Sn, Se and Tl. A knowledge of öle concentration level of the trace elements and their mode of occurrence in the coal Is therefore of importance in order to be able to be assess the potential environmental impact of coal utilization processes. The majority of trace elements in coal are associated with the inorganic mineral matter present In all coals. This mineral matter consists primarily of clays (alüminosilicates), quartz (SiOj). carbonates, sulphides, sulphates and oxides. The trace elements may also be associated with the coal macerate, having been present In the original vegetation from which the coal was formed. While many trace elements have primarily either organic or inorganic associations, some trace elements show an affinity for both fractions. During combustion or gasification the mineral matter undergoes both decomposition and transformation reactions which may result In the release of the more volatile elements. The ultimate fate of the trace elements will largely depend on content and initial concentration of the trace elements in the coal fed, chemical form of the trace elements in the coal, combustion temperature of the facilities, particle size of the ashes, operation temperature of the control systemsPower generation by combustion of coal produces waste ( solid, liquid and gas ) which may cause damage and problems. Solid (particulate ) emission makes an interesting contrast to SO2 and NOx in respect of control methods. Firstly, the impacts of solid emissions occur almost entirely in the short range -within a few km of the source. Secondly, methods for limiting dust emission at source have long been fully developed, are provided as a matter of course and do not add more than %1 or so to the total cost of building and operating a power station. Thirdly, the scale can uncontrolled emission would be such that dispersion alone could not possibly cope with the resulting problem. In recent years, attention has been directed rather more to the elemental composition of the dust, rattier than to its nuisance value, with some stress on ihe trace elements likely to be present - particularly the heavy metals. Whereas the coal before combustion has an elemental composition broadly similar to soils and crustal rocks - and hence similar to Hie natural dust content of the atmosphere - the combustion process acts to concentrate a number of elements into the ash and dust by a concentration factor of five or six. Beyond this, a number of the more volatile elements re-condense after combustion preferentially on to the finer particles - because of their greater spesific surface area - enhancing the concentration of these elements by an even greater factor. Trace elemente in coal behaviour like that after combustion:. Readly incorporated into slag : Al, Ba, Ca, Co, Ce, Eu, Fe, Hf, K, La. Mg, Mn. Nb, Rb. Si, Sm, Sr, Ta, Th. Ti, Y, Zr Intermediate : Co, Cu, Na, Ni, U, V. More readly incorporated into : As, Cd, Ga, Mo. Pb, Sb. Sn, Zn fly-ash Intermediate : Se. Remaining as vapour throughout : Hg. CI. Br the plant The first group elements likely to be found in Hie furnace bottom ash, the second group elements are found in the fly-ash and the third group elements are emitted in vapour form. XIThe international environmental regulations are now getting increasingly tough and control of coal combustion waste Is stricter. A more in-deptli knowledge of the composition of the products of combustion and the factors which influence said composition is thus becoming a necessity. There are certain elements in trace amounts which accompany coal; which do not Intervene directly In the combustion process, even though they undergo transformations during the process. In any kind of combustion, the final destination of these elements Is to form part of the combustion products. These products may later undergo uncontrolled natural processes when deposited or emitted. The most important phenomenon of the trace element distribution is that of the vaporisation-condensation, which is present in all stages of the combustion process. That Is why the combustion temperature has the most relevant role to play In the distribution of trace elements In combustion products and the final chemical form in said products. In order to analyze distribution of the trace elements in the combustion products, the ideal situation Is to have an exact knowledge of the chemical form of the elements and the operating temperature of the boiler and of the control systems. Thus, it should be possible to determine the fate of the trace elements fairly exactly. If the combustion conditions are always maintained the same and the coals used come from the same coal basin, which mean similar properties and rank of coal, a prediction of the trace elements destination in the final products, through correlations and the mathematical models, will be possible. The emission of trace elements to the atmosphere occurs through the discharge of stack particulates which are the fine ash particles escaping from the collector ( fabric filter or electrostatic precipitator). These fine ash particles contain relatively high levels of environmentally sensitive trace elements brought about by tiie absorption of volatile species from the flue gas onto the surface of the particles (in the cooler sections of the convention path). Trace elements are also emitted in the flue gas. These elements are also of environmental concern and are generally highly volatile species. The monitoring of the emission of trace elements to the atmosphere therefore necessitates the sampling of both solids and gas in the flue gas discharge. Of particular Interest is the partitioning of trace elements between the solid and gas discharge since the volatile species present In the gas phase will ultimately be manifested as ultra-fine condensed species with probably different plume dispersion characteristics to the stack particulates. XIIA major problem in monitoring the gas discharge is the limited capacity of the chemical reagent used to trap the volatile trace element species. This arises from the sulphur dioxide in the flue gas which causes rapid degradation of the reagent and hence the sampling time. The increased combustion of oil has led in recent times to an increased in the emission of heavy metals in the environment. The most significant metals present in the residual oils used in power generation are iron, nickel and vanadium, although there is not much concern with high levels of Fe in ashes emitted from petroleum-fire facilities, as iron toxicity to plants has scarcely been reported, except for rice. Yet nickel and vanadium are well known as potentially toxic elements to plants, animals and humans. Plant " accumulators *, defined as plants that have dry-weight elemental concentrations greater than either the associated substrate or normal plants, have been widely used for assessing heavy metal pollution. In this study, mass flux and concentration of heavy metals emitted from the pulverized coal and fuel-oil boilers to atmosphere have been studied. Especially, emissions resulted from fuel-oil combustion have been focused since there is a few study about this kind of emission. Emissions have been examined as gas and dust emissions. Gas sampling was carried out by passing the flue gas, sampled by a pump, through a thimble to remove solid particles and extracting tire trace elements in a solution of 6 percent potassium permanganate in nitric acid. Sampling times were approximately 30 min. The gas emission rates of the trace elements detected were determined from a measurement of the flue gas discharge and the volume of reagent. The stack particulates were sampled isokinetically using Andersen Universal Stack Sampler and collected in a thimble using small system. From the mass of particulates collected, the solids emission rate could be determined. The samples were chemically analysed using a number of techniques including atomic absorption spectrophotometry, ultraviole spectrophotometry and X-ray diffractometer. Pb, Ni, Co, Cd, Cr, Mn, Cu, As and V have been analysed using Atomic Absorption Spectrophotometry and Fe has been analysed using Ultraviole Spectrophotometry. Datas for the fuel-oil and coal have been compared with eachother and limit values suggested by Hava Kalitesini Koruma Yönetmeliği. X1HIn addition, heavy metals in the slag have been examined and results were compared with coal fly-ash. The major inorganic phase in the fuel-oil fly-ash was found as anorthite (CaAfeSfeOs) and amorphous ash particles; major inorganic phases in the coal fly-ash were found as quartz (SİO2) and Mulllt (Ale Sİ2 O13) using Rlgaku- Rlnt trademarked X- ray dlffractometer. As a result of this study, an idea about heavy metal emission resulted from fuel-oil combustion was handled. Fuel-oil based emissions were found much more than coal based emissions, so this result may effluence ' our preference of fuel. XIV
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