Adana Tufanbeyli Linyit Kömürünün Tanecik Boyutunun Yanma Özelliklerine Etkisi

Abstract

Dünya nüfusuna ve sanayileşmeye paralel olarak artan enerji ihtiyacının büyük bir kısmı fosil yakıtlardan karşılanmakta ve fosil enerji kaynaklarının rezervleri, artan ihtiyaç ile birlikte giderek azalmaktadır. Fosil enerji kaynaklarından biri olan kömür dünya enerji üretiminde önemli bir rol oynamaktadır. Kömür, kaynaklarının çok çeşitli ve büyük olmasının yanında, diğer yakıtlara oranla daha ucuz olması nedeniyle de uzun vadede önemli üstünlüklere sahiptir. Ülkemiz fosil yakıt rezervleri içerisinde kömür en büyük paya sahiptir ve ülkemizde kül, kükürt ve nem içeriği yüksek, ısıl değeri düşük olan linyitlerden, kaliteli linyitlere kadar çok çeşitli kömürler bulunmaktadır. Kömürlerin verimli yakılması, günümüz enerji teknolojisinin en önemli sorunlarından birini oluşturmaktadır. Yanma, kömürün temel yanıcı elemanları C, H, S ile havanın yakıcı elemanı O2 arasında, yüksek sıcaklıkta ısı ve emisyon oluşumlu, karmaşık bir oksitlenme sürecidir. Kömürün yanması temel olarak üç aşamada gerçekleşmektedir. Birinci aşamada kömürden yarıkok oluşumu ve uçucu madde çıkışı meydana gelirken, ikinci aşamada uçucu maddenin yanması ve üçüncü aşamada yarıkokun yanması olayları gerçekleşmektedir. Bu çalışmada kömür numunesinin farklı tane boyutları sabit sıcaklıkta ve farklı sürelerde yatay boru fırında tutulmasıyla, yanma süresinin sabit yataklı yakma sistemlerinde yanma davranımına etkisi incelenmiştir. Çalışmada yeni bulunan yüksek rezervli düşük kaliteli Adana Tufanbeyli linyit kömürü kullanılmıştır. İlk olarak 5 farklı tanecik boyutuna ayrılan kömür, daha sonra farklı sürelerde yatay boru fırında 900 ºC’de yakılmıştır. 0.5, 1, 2, 4, 8, 16 ve 32 dakika boyunca yakılan farklı tanecik boyutlu kömürlerin daha sonra kısa analizleri, elementel analizleri, ısıl değerleri ve termal analizleri incelenmiştir.

In parallel with the increasing world population and industrialization, a large portion of energy needs are provided by fossil fuels and fossil sources of energy reserves is decreasing along with the growing need. The big part of the world energy requirement, which increases in parallel with population and industrialization, is provided from fossil fuels. Today, issues which are dealing with the environmental pollution resulting from production and consumption of fossil fuels and restricted reserves of fossil resources are the most important problems. Coal has a very important share of world energy production. The value of coal seems to be increasing in the near future due to its worldwide distributed reserves. Lignite resources existing in our country are ranging from low quality lignites, which have quite a low calorific value, high moisture and mineral matter contents, to high quality lignites. But, the amount of low quality lignites in the total lignite reserves is extremely high. Using inconvenient combustion systems causes significant reduction in the efficiency of energy production from coal and also environmental pollution. Thus, the development of appropriate technologies for the evaluation of low-quality lignite potential must be one of the most important energy policy of our country. Coal, one of the fossil energy sources, plays an important role in energy production of world. Besides having a large variety of resources, coal also has significant advantages, such as being cheaper than other fuels, in the long term. In our country, coal has the largest share of fossil fuel reserves and there are a wide range of coals from the lignite coals posessing high ash, sulfur and moisture content with a low calorific value to the high-quality lignite coals. In our country, dependency to other countries increases directly proportional with the increase in energy demand. Turkey imports 73% of its energy demand and among fossil fuel reserves, coal has the biggest share in our country. However, most of the lignites are low graded lignites having high contents of ash, sulfur and moisture, and low heating values. Coal is a kind of sedimentary rock which is the most important energy source. This fossil origin rock played an important role in the development of humanity. Although other fuels partially replace the coal, which has the most reserves, coal will be in the service of the humanity. As in many countries, large part of energy need in our country is met by coal. However, the most of the Turkish coals are low quality lignite which have high ash, sulfur and moisture contents and low calorific value. Turkish lignites are easily break up because of it has fragile character. This fragile character causes problems during storage, transportation, and handling.. Fragile lignites dragged out of the chimney in the classic grate firing systems. This causes air pollution and loss of energy. Briquetting of the dusts of lignite offers a special opportunity for more efficient usage of this energy source. Most of lignite coals can easily be converted to dust. The lignite dusts are not suitable to be burned in stoves equipped with grates or central heating furnaces, since they are carried away from chimney without burning, and owing to some difficulties take place during transportation and storage of the coals. Thus, lignite reserves in Turkey are limitedly used as domestic fuels. However, increase in the use of Turkey’s own reserves, and decrease in dependency for supplying fuel are possible by briquetting process, which is one of the most efficient process in reducing the conversion of coal to dust. Reduction of greenhouse gases causing global climate change and elusion of their negative effects are issues waiting for urgent solutions. Chronic deterioration of the environment necessitates the development of mitigation technologies of CO2 emission which is the main actor in greenhouse effect. Fossil fuel combustion greatly increases CO2 concentration of the atmosphere. Today coal has a very important share in power generation. Also, the value of coal seems to be increasing in the near future due to its worldwide distributed reserves. However, coal is disadvantageous in emitting more CO2 per energy produced than any other fossil fuels. That is why; the capture and the storage of CO2 in coal fired power plants will greatly affect the future of global warming. Coal is physically heterogeneous and chemically complex mixture of organic and inorganic species which undergoes appreciable physico-chemical changes when heat treated. The main studies of coal using thermal analysis techniques include characterisation of high pressures application to coal hydrogenation, catalytic effects due to inorganic substances, combustion, pyrolysis and kinetic analysis. In the selection of coals for combustion it is useful to have knowledge of their combustion characteristics. Ignition and combustion of coal by mechanical stokers, fluidized beds or gasifiers is accompanied by weight loss, thermal decomposition, diffusion and heat transfer. These, in turn, are influenced by the nature of the coal, particle size, density and porosity, all of which govern the thermal processes occurring in the coal. Thermal analysis methods play an important role in the investigation of useful mineral substances. Their application to the study of coals and its products has increased considerably in the last two decades. Thermogravimetry (TG), differential thermogravimetry (DTG) and the differential scanning calorimetry (DSC) are the methods widely used in characterisation of fossil fuels undergoing combustion or pyrolysis. An understanding of the oxidation rate of coals at low temperature is important for predicting self-heating and spontaneous combustion. Recent increased utilization of coal has necessitated development in technology to prevent the spontaneous combustion of coal during storage and transport. It is important to understand spontaneous combustion to prevent such occurrences. The basic process taking place is the exotherimic reaction of coal with oxygen that causes an increase in temperature, with a resultant increase in the reaction rate. If a stockpile is not to burn, then sufficient heat must be transported away to keep its temperature low. Factors significantly affecting the spontaneous combustion of a coal pile are: coal rank, the oxygen content of the coal, the flow rate of the air, particle size, the moisture content of the coal and the humidity of the air. To avoid spontaneous combustion the practice has been to control the above factors so as to reduce the heatgenerating capacity of the coal. The particle size of coal in the stock pile is an important factor in determining whether or not spontaneous combustion occurs. Low-rank coals, such as lignites, have low heating values primarily due to high moisture and oxygen contents. This results in high transportation cost per thermal unit of coal. There is considerable interest in the possibility of drying prior to use, transporting or storing in the dry state for extended periods. These coals are highly reactive towards oxygen at ambient temperatures, especially in dry state and hence are highly susceptible to oxidation, moisture re-absorption and spontaneous combustion. The coal moisture content, oxygen concentration, the distribution of oxygen containing functional groups in coals is some of the major factors affecting spontaneous combustion. Historically, investigations of the effects of coal moisture and air humidity on coal oxidation have been much concerned with the heat of adsorption and desorption of water vapour of lignites in connection with their dewatering because of the high moisture content of such low-rank coals. One of the major challenges in the present energy technologies is combustion of coals more efficiently. Combustion is a complex oxidation process that occurs between basic combustible elements of coal (i.e., C,H, and S) and burner element of air (e.g., O2) at high temperature to yield heat and emission. Coal combustion takes place primarily in three phases: (1) formation of semi-coke from coal and release of volatile substances, (2) combustion of volatile substances, and (3) combustion of semi-coke. In this study, the effect of burning time on combustion behavior at fixed bed combustion systems was examined by placing coal samples having different particle sizes in a horizontal tube furnace at constant temperature for varying periods. For this purpose, a low quality lignite coal from a newly found reserve in Adana Tufanbeyli was used. The coal was first divided into five different particle sizes and then, burned in the horizontal tube furnace at 900°C for varying periods (i.e., 0.5, 1, 2, 4, 8, 16 and 32 min). After that, the as-burned coal samples were characterized based on the results of their proximate analysis, elemental analysis, thermal analysis, calorific value analysis, FTIR analysis, SEM analysis and XRD analysis.