Yanma koşullarının kömürdeki eser elementlerin davranışlarına etkisi
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Date
2003
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Marmara Üniversitesi, Fen Bilimleri Enstitüsü
Abstract
Türkiye’nin fosil eneği kaynaklan arasında en önemli birincil eneği kaynağı toplam rezervi, 8 milyar tonu aşan linyit kömürüdür. Türkiye’de halen elektrik enerjisinin % 18’i termik santrallerden, kömürün yakılması sonucu elde edilmektedir. Kömürün yakılarak enerji elde edilmesi, SOa, NOx ve katı partikül emisyonları gibi çeşitli çevre problemlerini beraberinde getirmektedir. CO2 emisyonları da günümüzde iklim değişikliği açısından önem kazanmıştır.
Kömürün içerisindeki minerallerin kalitatif ve kantitatif olarak bilinmesi, çevresel etkiler, geri kazanım, korozyon, ısı transferi gibi konular açısından gereklidir. Eser elementler, hem çevresel etki hem de geri kazanım açısından önemlidirler. Gerek kömür özelliklerinin, gerekse yanma koşullarının (hava fazlası, yakma sıcaklığı), eser element emisyonlan/dağılımları üzerine etkisi vardır. Çeşitli veri tabanlarında yapılan kaynak araştırmaları, ülkemizde bulunan kömürlerde eser elementlerle yapılmış çalışma sayısının azlığına işaret etmektedir. Diğer yandan, özellikle son on yılda, kömür ve küllerde eser elementlerin davranışlarının araştırılmasına yönelik çalışmalar, gelişmiş ülkelerde büyük bir hız kazanmıştır.
Bu çalışmada, Afşin-Elbistan, Yatağan, Tunçbilek linyit numuneleri çalışma kapsamına alınmıştır. Linyit numuneleri, rezerv miktarları, termik santrallerde kullanılıyor olmaları, daha önce bu linyitlerle ilgili herhangi bir veri olmaması ve kül içeriklerinin farklılıklar göstermesinden dolayı, seçilmişlerdir. Temsili linyit numuneleri, ASTM ve DB olmak üzere iki farklı yanma ortamında, sırasıyla (750, 830, 950 °C) ve (750, 800, 820, 830, 840, 860, 900, 950 °C) olmak üzere 8 farklı sıcaklıklarda yakılmışlardır.
Temsili linyit numunelerinde ve bu linyit numunelerin değişik yanma ortamında ve koşullarında yakılarak elde edilen elde edilen kül numenelerinde majör (Ca, Si, Al), minör elementler (Fe, Na, K, Mg, Ti), eser elementler (Cu, Ni, Co, Zn, Mn, Pb, Cd, Cr), Atomik Absorpsiyon Spektrofotometresiyle ölçülmüştür. AAS ile ölçülen major, minör ve eser element konsantrasyonları, WDXRF, ICP-AES, EDXRF teknikleri ile elde edilen sonuçlarla da karşılaştırılmış ve sonuçların uyum içinde oldukları gözlenmiştir.
Sonuçlar, yanma ortamına, yanma koşullarına, (% kül) ve özellikle sıcaklığına bağlı olarak eser majör, minör ve eser element konsantrasyonlarının külde değiştiğine işaret etmiştir.
Temsili linyit kömür numunelerinin ve bu linyit kömürlerinin (ASTM ve DB) yanma ortamlarında ve yanma koşullarında elde edilen kül numunelerinin FT-ir spektrumlarında, Ca bileşiklerinin nasıl bir davranış gösterdikleri konusunda ipuçları elde edilmiştir. Yakma koşullarının ve özellikle sıcaklığın külün bileşimi üzerine etkisinin olduğu saptanmıştır. Elde edilen sonuçlar, aynı numunelerin XRD spektrumları sonuçlan ile karşılaştırılmış ve sonuçları kendi içerisinde uyumlu olduğu gözlenmiştir. Temsili kömür numunelerinde, 5 farklı yöntemle ölçülen major, minör ve eser element konsantrasyonları kullanılarak, teorik olarak kül’de ve yanma sonucu gaz fazına geçen element konsantrasyonları, kütle eşitlikleri kullanılarak teorik kullanarak hesaplanmıştır.
Termodinamik denge esasına dayalı bir bilgisayar kodu (Solgasmix-PV), AE temsili linyit kömürün’de 5 farklı analiz metoduyla ölçülen major, minör ve eser element konsantrasyonları kullanarak, (C-O-H-N-X), (C-0-H-N-S-X),
(C-O-H-N-Cl-X), (C-0-H-N-C1-S-X), 4 farklı sistem’de, sabit basınçta (P=1 atm), deneysel sıcaklıklar’da, (750-950 °C) çalıştırılmıştır. Ayrıca, 1103-1773 K arasındaki teorik sıcaklıklarda da major, minör ve eser elementlerin davranışları incelenmiştir. Elementlerin, gaz fazı ve kül’de dağılımlarına hava fazlalık katsayısının etkiside (HF= teorik, 1.1, 1.2) detaylı olarak incelenmiştir. Denge durumunda, gaz fazında ve külde bulunan bütün element/bileşiklerinin konsantrasyonları hesaplanmış ve bunlar teorik ve deneysel olarak elde edilen sonuçlarla karşılaştırılmıştır. Teorik hesaplamalar’dan elde edilen sonuçların, programdan elde edilen sonuçlarla karşılaştırıldığında, bazı elementlerin yanma ortamına ve yanma koşullarına bağlı olarak gaz fazında veya külde, bazılarının da her iki yanma ortamında teorik sonuçlarla uyumlu oldukları (% hata oranlan göz önüne alınarak) bulunmuştur.
Radyoaktif elementler ise, sadece 3 adet temsili kömür numunelerinde (238U, 232Th, 40K, 226Ra) düşük sayım sistemi ile ölçülmüştür. 238U aktivitesinin sadece, Afşin-Elbistan kömür numunelerinde, Dünya ortalamalarının üzerinde olduğu bulunmuştur. Diğer radyonüklit aktivitelerinin, dünya ortalamasının altında kaldığı bulunmuştur.
With its total reserve of over 8 billion tons, lignite constitutes the most important indigenous primary fossil energy source for Turkey. Currently, 18 % of Turkish electricity production is provided by coal fired power plants. Energy production via coal combustion is associated with environmental problems resulting from SO2, NOx and particulate emissions. CO2 emissions have also become an issue due to the global warming problem. Knowledge of qualitative and quantitative constituents of coal minerals, their elements and compositions is required for assessing their environmental impact, along with the problems associated with during utilization and post-utilization. Detailed information on trace elements is useful for defining their environmental impacts and potentials for their recovery. Combustion is a widely applied way of coal utilization. Both coal properties and combustion conditions such excess air coefficient, combustion temperature affect trace element distributions in the solid and gaseous phases. Literature survey conducted utilizing various data bases indicated that studies related to trace elements of Turkish coals are rather scarce. On the other hand, studies related to trace element distribution in coals and ashes have gained a momentum in developed countries especially during the last ten years. In this study, representative samples from Afşin-Elbistan, Yatağan, and Tunçbilek power plants were used. These sites were selected due to the fact that: 1) they have large reserves, 2) their lignite is used in coal fired plants, 3) they have not been studied previously in terms of trace elements and 4) they have large differences among themselves in terms of percent ash produced as a result of combustion. Representative samples were combusted according to two different standards (ASTM and DB) at temperatures between 750-950 0 C with 8 different final temperatures. Representative samples were combusted according to two different standards (ASTM and DB) at temperatures between 750-950 ° C with 8 different final temperatures. Concentrations of major elements (Ca, Si, Al), minor elements (Fe, Na, K, Mg, TO and trace elements (Cu, Ni, Co, Pb, Zn, Mn, Cr and Cd) in lignite samples and their ashes from combustion tests were measured by AAS technique. Results obtained by AAS technique and, WDEXRF, ICP-AES and EDXRF techniques were compared with each other. It was found that they were in a good agreement. Results show that major, minor and trace element concentrations in ashes vary depending on combustion environment, ash content and combustion conditions, particularly combustion temperature. The FT-ir spectrums of lignite samples and their ashes obtained after firing at various temperatures and combustion medium were examined. Results provided important clues about the behavior of Ca components. It was also found that combustion environment and conditions affect the composition of ashes. Chemical analysis data was compared to the respective XRD spectrum. It was found that both data compares well. Using the major, minor and trace element concentrations of original samples determined by 5 different methods as a basis, theoretical concentrations in ash and gas phases were calculated by applying mass balance equations to available data. A computer program (Solgasmix-PV) based on thermodynamic equilibrium was used for investigating the behavior of major, minor and trace elements in coal. Major, minor and trace element concentrations of Afşin Elbistan lignite sample, which were determined by five different chemical analysis methods, were combined with coal element data, and used as the input for this computer program. Equilibrium concentrations of elements and/or compositions of gas and solid phases were calculated by the computer program for different systems, including (C-H-O-N-X), (C-H-O-N-S- X), (C-H-O-Cl-N-X) and (C-H-O-N-S-Cl-X), at constant pressure (latm), a number of , experimental (750-900 °C) and high temperatures (1023-1773 °C) and various excess air constant conditions. Effects of excess air constant (1.1 and 1.2) on the distribution of elements in gas phase and ash were thoroughly investigated. Steady state concentrations of all elements/compositions in gas phase and ash were calculated and compared to theoretical and experimental results. The other coal samples, namely TB and Y were investigated in a similiar manner. Results generated by the Solgasmix-pv computer program were compared to experimental and theoretical data. It was found that predicted base element concentrations in gas phase and/or ash were within the relative error limits in most cases depending on combustion environment and conditions. The radioactivity (U238, Th232, K40, Ra226) of the lignite samples from the three thermal power stations was analyzed by Low Level Counting Technique. It was found that only Afşin-Elbistan lignite contained a U238 activity higher than world average,
With its total reserve of over 8 billion tons, lignite constitutes the most important indigenous primary fossil energy source for Turkey. Currently, 18 % of Turkish electricity production is provided by coal fired power plants. Energy production via coal combustion is associated with environmental problems resulting from SO2, NOx and particulate emissions. CO2 emissions have also become an issue due to the global warming problem. Knowledge of qualitative and quantitative constituents of coal minerals, their elements and compositions is required for assessing their environmental impact, along with the problems associated with during utilization and post-utilization. Detailed information on trace elements is useful for defining their environmental impacts and potentials for their recovery. Combustion is a widely applied way of coal utilization. Both coal properties and combustion conditions such excess air coefficient, combustion temperature affect trace element distributions in the solid and gaseous phases. Literature survey conducted utilizing various data bases indicated that studies related to trace elements of Turkish coals are rather scarce. On the other hand, studies related to trace element distribution in coals and ashes have gained a momentum in developed countries especially during the last ten years. In this study, representative samples from Afşin-Elbistan, Yatağan, and Tunçbilek power plants were used. These sites were selected due to the fact that: 1) they have large reserves, 2) their lignite is used in coal fired plants, 3) they have not been studied previously in terms of trace elements and 4) they have large differences among themselves in terms of percent ash produced as a result of combustion. Representative samples were combusted according to two different standards (ASTM and DB) at temperatures between 750-950 0 C with 8 different final temperatures. Representative samples were combusted according to two different standards (ASTM and DB) at temperatures between 750-950 ° C with 8 different final temperatures. Concentrations of major elements (Ca, Si, Al), minor elements (Fe, Na, K, Mg, TO and trace elements (Cu, Ni, Co, Pb, Zn, Mn, Cr and Cd) in lignite samples and their ashes from combustion tests were measured by AAS technique. Results obtained by AAS technique and, WDEXRF, ICP-AES and EDXRF techniques were compared with each other. It was found that they were in a good agreement. Results show that major, minor and trace element concentrations in ashes vary depending on combustion environment, ash content and combustion conditions, particularly combustion temperature. The FT-ir spectrums of lignite samples and their ashes obtained after firing at various temperatures and combustion medium were examined. Results provided important clues about the behavior of Ca components. It was also found that combustion environment and conditions affect the composition of ashes. Chemical analysis data was compared to the respective XRD spectrum. It was found that both data compares well. Using the major, minor and trace element concentrations of original samples determined by 5 different methods as a basis, theoretical concentrations in ash and gas phases were calculated by applying mass balance equations to available data. A computer program (Solgasmix-PV) based on thermodynamic equilibrium was used for investigating the behavior of major, minor and trace elements in coal. Major, minor and trace element concentrations of Afşin Elbistan lignite sample, which were determined by five different chemical analysis methods, were combined with coal element data, and used as the input for this computer program. Equilibrium concentrations of elements and/or compositions of gas and solid phases were calculated by the computer program for different systems, including (C-H-O-N-X), (C-H-O-N-S- X), (C-H-O-Cl-N-X) and (C-H-O-N-S-Cl-X), at constant pressure (latm), a number of , experimental (750-900 °C) and high temperatures (1023-1773 °C) and various excess air constant conditions. Effects of excess air constant (1.1 and 1.2) on the distribution of elements in gas phase and ash were thoroughly investigated. Steady state concentrations of all elements/compositions in gas phase and ash were calculated and compared to theoretical and experimental results. The other coal samples, namely TB and Y were investigated in a similiar manner. Results generated by the Solgasmix-pv computer program were compared to experimental and theoretical data. It was found that predicted base element concentrations in gas phase and/or ash were within the relative error limits in most cases depending on combustion environment and conditions. The radioactivity (U238, Th232, K40, Ra226) of the lignite samples from the three thermal power stations was analyzed by Low Level Counting Technique. It was found that only Afşin-Elbistan lignite contained a U238 activity higher than world average,
Description
Keywords
Coal, Kömür, Combustion conditions, Yanma koşulları, Trace elements, Eser elementler
Citation
Öztürk, N. (2003). Yanma koşullarının kömürdeki eser elementlerin davranışlarına etkisi. (Yayımlanmamış doktora tezi). İstanbul : Marmara Üniversitesi, Fen Bilimleri Enstitüsü.