Afşin Elbistan linyit kömürü ve pirinanın optimum oksi yakma koşullarının belirlenmesi
Determining optimum oxyfuel conditions of Afsin Elbistan lignite coal and pirina
Yazar: ONUR TORU
Danışman: PROF. DR. HANZADE AÇMA
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Kimya Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2015
Konu: Kimya Mühendisliği = Chemical Engineering

Özet:
Günümüzde ülkemiz, kullanmakta olduğu enerjinin çok büyük bir miktarını ithal etmektedir. Giderek artan enerji talebi nedeniyle, enerjide dışarı bağımlılığı her geçen gün giderek artmaktadır. Ülkemizde ana enerji kaynağı olarak fosil yakıtlar kullanılmaktadır. Kömür yataklarımız yaygın olmasına rağmen büyük bir kısmını ısıl değeri düşük, mineral maddesi çok yüksek linyit yatakları oluşturmaktadır.
Hali hazırda bulunan linyit yataklarımızın verimli ve çevreye minimum zararlı olacak şekilde değerlendirilmesi büyük önem arz etmektedir. Bu süreçte kullanılan yakma yönteminin doğru seçilmesi büyük bir rol oynamaktadır. Elimizdeki kömür yataklarının en verimli değerlendirilmesi için hava fazlası ile yakma gibi geleneksel yakma yöntemleri yetersizdir. Geleneksel yakma yöntemleri yerine oksi yakma yönteminin kullanımı giderek artmaktadır. Oksi yakma yönteminde hava ile birlikte saf oksijen kullanıldığı için, azotun seyreltici etkisi engellenmekte ve böylece külde kalan yanmamış karbon miktarı minimum değerlere indirilebilmektedir. Ayrıca oxyfuel yöntemi sonucu, geleneksel yöntemlere göre baca gazında daha derişik bir karbondioksit oranı elde edilir. Elde edilen bu karbondioksit gazı sıkıştırma ve sıvılaştırma gibi yöntemler kullanılarak değerlendirilebilir. Oksi yakma yöntemi, kömür yakma ile enerji üretiminden kaynaklanan karbondioksit emisyonlarının kontrolü için en son geliştirilen yöntem olarak karşımıza çıkmaktadır.
Ülkemiz biyokütle enerji kaynakları bakımından da oldukça zengin bir ülkedir. Biyokütle, temel bileşenleri karbon, hidrojen ve oksijen olan, yenilenebilir nitelikteki her türlü organik madde olarak nitelendirilmektedir. Biyokütle tarımsal, endüstriyel, kentsel katı atıklar ile orman atıkları, hayvansal atıklar ve su biyokütlesinden oluşmaktadır. Biyokütle enerji kaynakları, karbondioksit açısından nötr yakıtlar olarak adlandırılır. Fosil yakıtlara göre çevreye daha az olumsuz etkileri vardır ve atmosferdeki karbondioksit emisyonlarının artışı üzerindeki etkileri yok sayılabilir.
Bu çalışmada biyokütle ve kömür karışımı birlikte yakılarak zararlı emisyon çıkışının azaltılması ve yanmayan karbonun tamamına yakın bir kısmının yakılabileceği optimum oksi yakma koşullarının belirlenmesi hedeflenmiştir. Bu çalışmada zeytinyağı üretiminden geriye kalan pirinanın kömüre ilave edilerek yakılması ile değerlendirilmesi amaçlanmaktadır. Çalışmanın sonucunda kömür ve biyokütle karışımının optimum oksi yakma koşulları belirlenmiştir. Bu çalışma kapsamında Afşin Elbistan linyit kömürü ve Pirina numunesinin içerdiği karbonun tamamının yandığı, oksi yakma koşullarını belirlemek amacıyla her iki numunede farklı sıcaklık ve farklı oksi yakma koşullarında yakılmış ve optimum koşullar belirlenmiştir. Birlikte yakabilme amacıyla %5,10,25,50 oranlarında Afşin Elbistan kömürüne Pirina ilave edilerek, hazırlanan karışımların karbon içeriğinin tamamı ile yandığı oksi yakma koşulları belirlenmiştir. Ana numunelere ve yakma sonrası geriye kalan numunelere ısıl değer, kısa analiz, termal analiz ve elementel analiz uygulanmıştır.

Abstract:
Turkey is a country which imports the most part of its energy need, so the present foreign dependency on energy is gradually increasing. The fossil energy sources provide the significant portion of our energy need. On the other hand, a great deal of coal reserves in Turkey is comprised of lignites which have low calorific value and high mineral matter.
One of the most important indicators of the country's level of development is energy production. Energy production depends on availability of resources and utilization of these resources at an optimum level. With inceasing population and as a result of this increasing energy needs and pollution, biomass energy is becoming popular day by day. This energy is the sustainable source for the growing energy problem. Biomass can be defined as the total mass of living organisms belonging to a community which consists of various types in a certain time. In general, biomass is herbal organism that stores solar energy by the help of photosynthesis. Solar energy is stored as chemically cellulosic and later used in different ways. As a result of being converted CO2 into other organic compounds, solar energy is stored as fixed carbon in biomass. In photosynthesis, O2, necessary compund of human respiration, is released to atmosphere and CO2 is used for generation of organic materials. This shows biomass energy can be an environmental friendly enegry source. Biomass is the oldest renewable energy sources. Biomass sources are trees, tree wastes, agriculturel products and wates, domestic solid waste, animal waste, processed food waste, aquatic plants and algs. This energy is mostly produced from trees and tree wastes. Biomass is a inexhaustible energy source as long as the solar energy exists. Biomass contains stored energy. That's because plants absorb energy from the sun through the process of photosynthesis. When biomass is burned, this stored energy is released as heat. As a result of increasing population and life standards, development in industry, energy resources are running out of fastly. Fossil fuels such as coal, oil and gas are also derived from biological material, however material that absorbed CO2 from the atmosphere many millions of years ago. Coal has different and big amount of sources and also cheaper than the other fuels so it is more preferable than the other chocies. Coal is a kind of sedimentary rock which is one of 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. Coal includes organic and inorganic compounds in different amounts. Basic component of coal is C. This sedimentary rock is formed through biochemical and physical changes of plant residuals in marshes. Minerals materials in coal are important because they are used for classification, testing and usage of coals.
Biomass is one of the most plentiful and well-utilised sources of renewable energy in the world. Our country has very rich biomass reserves. It is defined as any organic substance which is mainly consisted of carbon, hydrogen, and oxygen, and it is generally formed from agricultural, industrial, and municipal solid wastes, forestry remnants, animal wastes, and aquatic flora. This organic substance is carbon based and is composed of a mixture of organic molecules containing hydrogen, usually including atoms of oxygen, often nitrogen and also small quantities of other atoms, including alkali and heavy metals. These metals are often found in functional molecules such as chlorophyll. Most of biomass species are regarded as carbon dioxide neutral. They show lower environmental impact compared to fossil fuels, and their contribution to the increase in atmospheric carbondioxide concentration is negligible. As an energy source, biomass can either be used directly by combustion to produce heat, or indirectly after converting it to various forms of biofuel.
In order to control carbondioxide emissions, co-combustion of 'carbon neutral' biomass with coal is being carried out nowadays. Carbon neutrel means, carbondioxide that is produced after burning of biomass is equilevent of carbondioxide that has been used in photosynthesis in biomass growth. Co-combustion method is a good way to convert low economic value agricultural, industrial and forest waste into energy.
Different than coal, many biomass species have different physical and chemical characteristics. Having high oxygen and volatile material content, low calorific value, low density and low fixed carbon is the most significant differences between biomass and coal. Wooden biomasses builng blocks cellulose, hemi cellulose and lignin have rather weak ether bonds than coal. With termal effects they would have high reactivity and their burning process can occur at low temperatures. Released heat and maximum temperatures are much more lower than coal.
The combustion method is very crucial in efficient utilization of the lignite reserves without causing any harmful effect to environment. In order to accomplish that it is very important to choose the right burning process for producing energy. It is inadequate to use general method of employing much more oxygen than the stoichiometric ratio for our lignites. Instead of using conventional burning methods, nowadays oxyfuel method is being used more commonly. In oxyfuel method, pure oxygen is used for oxidation makes it possible to reach very high combustion yields in association with the elimination of nitrogen which is present in air. Consequently, the unburned carbon content in ash reduces to very low levels. Carbon dioxide in the flue gas becomes concentrated since it is not diluted by nitrogen from air. Thus, carbon dioxide in the flue gas processed for underground storage and sequestration after some operations such as compression and liquefaction. So, the oxyfuel method has recently been the most striking method for controlling of carbondioxide emissions resulting from coal combustion.
Despite some of the disadvantages, coal and biomass cofiring have some good outcomes. Co-combustion of biomass with low grade coals such as lignite is a good way to reduce emissions. This process helps with disposing of waste biomass. Also co-combustion of biomass with coal, helps reduction of NOx and SOx levels of coal burning plants and also reduces soil and water pollution.
Co-combustion biomass with coal in different ratios will result in different outcomes that cannot be achieved by single burning of biomass or coal. This can be defined as 'synergy effect'. Synergy between different compounds will result with better result than expected results.
In this work, co-combustion of lignite / biomass blends will be carried out in order to reduce emissions and determining optimum oxyfuel burning conditions for burning unburned carbon. For this purpose, remaining waste from olive oil production process will be added to coal and used as biomass energy source. Thus, not only the disposal of industrial wastes will be performed, but also waste material will be used for energy production.
Oxy-fuel combustion is the process of burning a fuel using pure oxygen instead of air as the primary oxidant. Since the nitrogen component of air is not heated, fuel consumption is reduced, and higher flame temperatures are possible. Historically, the primary use of oxy-fuel combustion has been in welding and cutting of metals, especially steel, since oxy-fuel allows for higher flame temperatures than can be achieved with an air-fuel flame.
There is currently research being done in firing fossil-fueled power plants with an oxygen-enriched gas mix instead of air. Almost all of the nitrogen is removed from input air, yielding a stream that is approximately 95% oxygen. Firing with pure oxygen would result in too high a flame temperature, so the mixture is diluted by mixing with recycled flue gas, or staged combustion. The recycled flue gas can also be used to carry fuel into the boiler and ensure adequate convective heat transfer to all boiler areas. Oxy-fuel combustion produces approximately 75% less flue gas than air fueled combustion and produces exhaust consisting primarily of CO2 and H2O.
The justification for using oxy-fuel is to produce a CO2 rich flue gas ready for sequestration. Oxy-fuel combustion has significant advantages over traditional air-fired plants.
In the experimentel process samples first dried at laboratory then grinded under 250 μm. According to main sample results by thermal analysis, starting burning temperatures were chosen. Main idea in experiments were reducing the conventional system operating temperature by using oxyfuel combustion. First oxygen content increased by %4 from normal air conditions. With %25 Oxygen content temperatures varied from 700 to 400 for Afşin Elbistan lignite samples.
In this work optimum oxyfuel conditions coal and biomass mixture is determined. This is accomplished by burning Afşin Elbistan lignite coal and Pirina biomass seperately in different temperatures using different ratio of oxygen and nitrogen mixtures. After determining their optimum conditions seperately, lignite and biomass were mixed with different ratios to observe their behaviour as mixture. For obtaining the maximum carbon burning yield for co-combustion, biomass was added to lignite as 5,10,25,50 percent. Calorific value, termal analysis, short analysis and elementel analysis was done for main samples and post-burn samples.
As for the outcome of this work, optimum oxyfuel conditions for co-combustion of lignite / biomass blends is determined.