Termik santral atık uçucu küllerinin karo üretiminde değerlendirmesi

Abstract

Seyitömer ve Tunçbilek Termik Santrali atık uçucu küllerinin seramik karo üretiminde değerlendirilmesi amacıyla yapılan çalışma iki aşamada gerçekleştirilmiştir. İlk aşamada, çalışmada kullanılan hammaddelerin ve uçucu küllerin karakterizasyonları yapılmıştır. Kimyasal analiz sonuçlan uçucu küllerin yüksek oranlarda alümina, silis, alkali ve toprak alkaliler ile demir içerdiğini göstermiştir. % 10.27 oranında tespit edilen Na2O kullanılan feldispatın albit (sodyum feldispat) olduğunu göstermiştir. X-Işınlan Difraksiyon yöntemiyle yapılan mineralojik analizlerde, uçucu küllerin çoğunlukla camsı amorf fazlar içerdiği tespit edilmiştir. Kristal faz olarak a- kuvars, dolamit, karbon ve demir bileşikleri görülmüştür. Demir bileşikleri maghemit ve hematit şeklindedir. Kilin çok kompleks olan yapısının çoğunluğunu muskovit, diğer kısmını ise a- kuvars, illit ve montmorillonit oluşturmaktadır. Özgül ağırlık ölçümleri Seyitömer ve Tunçbilek uçucu külleri için 2.33 ve 2.41 gr/m3 olarak bulunmuştur. Kil, kuvars ve feldispat hammaddeleri için bu değerler 2.64, 2.63, 2.66x103 kg/m3 'tür. Uçucu küllerin tane boyutlarının 2-70 um arasında değiştiği ve Seyitömer külünün bu aralıkta daha iri tane dağılımına sahip olduğu görülmüştür. Kil, kuvars ve feldispat için tane boyut dağılımı sırasıyla 0.5-50 um, 0.6- 65 um ve 0.5-65 um 'dur. Çalışmanın ikinci aşamasında, karakterizasyonları yapılan malzemeler değişik oranlarda azaltılıp çoğaltılmak suretiyle değişik bileşimlerde harmanlanmışlardır. Bu karışımlardan yan kuru presleme yöntemiyle 41x8x5 mm. boyutlarında çubuk ve el presiyle 100x60x6 mm boyutlarında dikdörtgen numuneler üretilmiştir. Her iki numune grubun da 110°C 'de kurutulmuşlardır. Dikdörtgen numuneler sırlanarak 1180°C 'de pişirilerek sır ile etkileşim incelenmiştir. Çubuk numuneler ise 1 100°C 'de sinterlenerek çeşitli testlere tabi tutulmuşlardır. Tunçbilek ve Seyitömer uçucu küllerinin %25 oranında kullanıldığı dikdörtgen numunelerin, pişme neticesinde sır ile etkileşimleri olumlu sonuçlar vermiş ancak sır yüzeylerinde iğne deliklerine rastlanmıştır. Sırlanan numuneler kırıldığında göbeklenme (black core) problemiyle karşılaşılmıştır. Çubuk numunelerde uçucu kül ilavesi 1, 2 ve 3 nolu gruplarda toplu küçülmede artışa, 4. grupta ise kil yüzdesinin azalmasına bağlı olarak düşüşe sebep olmuştur. Herbir grupta kül yüzdesi artarken kil, kuvars ve feldispat yüzdesinin yine gruplara göre azaltılması su emme miktarında artışa, yoğunlukta ise düşüşe sebep olmuştur. Üç noktada eğme mukavemetinin 1, 2 ve 3 nolu gruplarda kül yüzdesiyle arttığı ve en yüksek mukavemet değerlerine %25 uçucu kül içeren numunelerin sahip olduğu görülmüştür. 4 nolu grupta azalan kil miktarının mukavemeti olumsuz yönde etkilendiği saptanmıştır. Sonuçta, tüm değerler karşılaştırılarak karo üretiminde kullanılacak uçucu kül ilaveli optimum bileşimin gerek Tunçbilek gerekse Seyitömer uçucu külü içeren numuneler için %50 kil, %25 feldispat, %10 kuvars ve %15 kül bileşimi olduğu tespit edilmiştir. Bu sonuca göre, atık uçucu küllerin, karo üretiminde değerlerdirilebileceği belirlenmiştir.

Securing raw material supplies is becoming more and more important because high- grade raw materials in large quantities are less and less frequently available. This means that the use of raw materials of lesser quality must be resorted to more and more heavily and that the preparation of these raw materials is gaining an even greater significance. A second new direction of development is the recycling of waste materials from a company's own production or such materials from other industry branches as secondary raw materials. Fly ash, produced as waste material in coal- fired thermal power plants, present an environmental problem due to the large quantities. In our society, it is required that waste should be disposed of and got out of sight inexpensively and effectively. However, the matter cannot any longer be settled merely by storing the waste; new treatment methods must be found in which harmful environmental effects can be minimized. Utilization of fly ash has been tried for decades in many areas such as concrete, lightweight aggregate, brick, highway pavements, and so on. However, the utilization rate is still below 20% because of the difficulty in controlling the quantity of fly ash. Fly ash originates from power plants that use coal for fuel. This fly ash is collected by the cyclones and precipitator as known arrestors and stored in bunkers. The physical and chemical properties of fly ash depends on the fuel used and the combustion condition. The fly ash has different particle size and shape. In generally, fly ash has particle size distribution between 1-100 um. Some of the particles are spherical shaped, agglomerate and cornered shaped. No matter what type, fly ash is mainly composed of magnetic particles, unburned carbon and clean ash. If these components can be utilized for wider applications. The fly ash comprises chemically a mixture of the following oxides, SİO2, A1203, Fe203, CaO and MgO. The use of waste materials, especially fly ash, in the ceramic body lighter than the traditional materials, because the organic material that the waste contains burns away during the firing. This study has been investigated the possibility of using fly ash in ceramic tile production as a raw material source. For this purpose, Tunçbilek and Seyitömer power plants waste fly ashes were used. VI The investigation has been carried out in two stages. In the first step of this study, the characterization of different fly ash samples which collected from Tunçbilek and Seyitömer power plants and clay, quartz and feldispar raw materials were obtained by the following analytical techniques and tests. - Chemical Analysis - Differential Thermal Analysis (DTA) and X-Ray Diffraction - Specific gravity and particle size measurements The chemical compositions of the fly ashes of Seyitömer and Tunçbilek, clay, quartz and feldspar raw materials are in Table 1., respectively. Table 1. Chemical Analysis for used materials in the study. In the second step of the study, four groups of samples whit different proportion of fly ash and other raw material (clay, quartz, feldspar) were prepared. These groups are as Table 2. The Seyitömer and Tunçbilek power plants waste fly ashes were added to the clay, quartz and feldspar mixture separately in the range of 5-15-25 wg-% in 3 steps. Rectangle shaped (100 x 60 x 6 mm.) and bar shaped samples (41x8x5 mm.) were prepared from each group, using semi- dry pressing method. After drying the samples at 110°C, the samples were sintered at 1100°C with 10 °C/min. heating rate. The rectangle samples which have %25 ratio of both Seyitömer and Tunçbilek fly ash were glazed. After glazing, the samples were sintered at 1 180 °C. vu Table 2. Mixture percentage of used materials in the study. The following tests were carried out to evaluate the properties of the sintered samples; - Drying, firing and total shrinkage tests, - The water absorption testing, - Bulk density testing, - The three point bend strength tests. The results of the first step of this study are summarized as follows; - Chemical analysis results indicate that Seyitömer and Tunçbilek fly ashes contain high alumina, silica and iron, i.e. 16.42 wt-%, %54.87 wt-%, 11.53 wt-%; 17.91 wt-%, 53.96 wt-%, %1 1.13 wt-%. Owing to this high Si02 content, the fly ashes can also be used as a substitute for determining the superior properties of fly ash additive products as well as improving the ability to withstand high temperature firing. The chemical analysis result indicate that feldspar contain 10.27 wt-% of Na20. This result illustrated that feldspar was albit (sodium feldspar). - X-ray diffraction study showed that the fly ash samples mainly consisted of glassy phase and the remaining crystalline phases. The Seyitömer fly ash consists of a- quartz, dolomite, anorthite, albite, biotite, carbon and iron compounds. The Tunçbilek fly ash consists of a- quartz, silimanite, dolomite, clinoenstatite, gismondine, carbon and iron compounds. Both fly ash's compounds are maghemite and hematite forms. vm After fly ashes were sintered at 1 100°C, a-quartz changed in to crystabolite. Clay raw material mainly consists of muscovite and a-quartz, illite and montmorillonit. X-ray diffraction of quartz raw material showed that it's structure completely constitutes a- quartz. Feldspar mainly consists of sodium feldspar and a-quartz. - The result of the wet sieve analyses showed that particle size of Tunçbilek and Seyitömer fly ashes were greater than 45 um. (i.e. 40.88 wt-% and 86.15 wt-%), respectively. Result of clay's particle size distribution showed that only 8.5 wt-% was greater than 45 urn. This fineness means that, in preparation clay bodies require less grinding. The particle size distribution of quartz and feldspar (i.e. 86.11 wt-% and 82.95 wt-%, respectively.) were greater than 45 um. In the second step of particle size analysis, particle size distribution of fine particles (under the 45 um.) carried out in the Shimadzu Centrifugal Particle Size Analyzer. Results of fly ashes analysis revealed size distribution between 2-70 um. Particle size of clay, quartz and feldspar were the range of 0.5-50 um., 0.6-65 um. and 0.5-65 um., respectively. - The specific gravity results showed that of Seyitömer and Tunçbilek fly ashes, clay, quartz and feldspar are 2.33, 2.41, 2.64, 2.63 and 2.66x103 kg/m3, respectively. The specific gravity for fly ashes is higher than the average specific gravity value (2.15x103 kg/m3). This is due to the higher percentage iron oxide content. Tests carried out on samples sintered at 1100°C have given the following results. - In glazed samples, the interaction between masse and glaze was good but pin holes were seen on the glazed surfaces. When the sintered samples were broken, black core problem was seen. Black core problem came out when the organic materials in the tile body did not have enough combustion and oxidation. - Changing fly ash, quartz and feldspar constituents were no changed drying shrinkage. Therefore, the total shrinkage quantity was investigated. The total shrinkage was found to be increased with 15 wt-% fly ash and 10 wt-% feldspar addition in group 1. Then, 25 wt-% fly ash and 0 wt-% feldspar addition was decreased the total shrinkage. In group 2, decreasing in quartz percentage but increasing in fly ash percentage, resulted to an increase in the total shrinkage the samples. In group 3, decreasing in both quartz and feldspar percentage, resulted to an increase, then to a decrease in the total shrinkage the samples. The total shrinkage in group 4 samples, decreasing in clay percentage, resulted to a decrease. These results were thought that, this is due to the loss of carbon in fly ash, partly decomposition of CaS04 and the loss of crystal water in clay. IX - Increasing the addition of both Tunçbilek and Seyitömer fly ashes causes increase in water absorption. Therefore, each of group's bulk density value decreased with the increasing fly ash percentage. - The results of three point bend strength tests showed that the strength increases with the increase in groups 1,2 and 3 whit fly ash percentage. In group 4, strength decreases with the increase clay. This due to the formation of glassy phase. The overall results showed that, optimum mixture for tile application was 50 wt- % clay, 25 wt-% feldspar, 10 wt-% quartz and 15 wt-% fly ash. This will head to cheaper raw materials as well as minimize to pollution of the environmental.