Biyokütle yarıkoku- kömür karışımlarının yanma davranımlarının incelenmesi
Investigation of the combustion behaviour of biomass char-coal blends
Yazar: EDA YILMAZER
Danışman: PROF. DR. AYŞEGÜL MERİÇBOYU
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Kimya Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2012
Konu: Enerji = Energy
Dizin: Bitümlü kömürler = Bituminous coals ; Biyokütle = Biomass ; Yakma = Burning ; Yakıtlar = Fuels

Özet:
Ülkemizde enerji arzı ve tüketimi arasındaki fark her yıl artmakta ve buna bağlı olarak enerji kaynakları açısından dışa bağımlılığımız da artmaktadır. Türkiye'nin gelişmesini sürdürebilmesi için ihtiyacı olan enerjiyi zamanında, yeterli miktarda, ekonomik koşullarda ve çevreye zarar vermeden sağlayıp, kullanması gerekmektedir.Türkiye'nin en önemli enerji kaynağı olan kömürlerin çoğu kül, kükürt ve nem içeriği yüksek, ısıl değeri ise az olan düşük kaliteli linyitlerdir. Ayrıca, bir tarım ülkesi olan Türkiye, biyokütle kaynakları bakımından da büyük bir potansiyele sahiptir. Biyokütle kaynakları çevre ile dost sürdürülebilir enerji üretimi için önemli bir alternatif olarak karşımıza çıkmaktadır.Kömür ve bazı biyokütle kaynaklarının doğrudan yakılması yoluyla enerji üretimi, bilinen en eski yöntemdir. Son yıllarda biyokütle-kömür veya biyokütle yarıkoku-kömür karışımlarının birlikte yakıldığı yakma sistemleri geliştirilmektedir. Bu karışımların yakılması yoluyla enerji üretimi; sera gazlarının yayınımında azalma, kükürt dioksit ve azot oksit yayınımlarının da daha düşük seviyelerde olmasını sağlamaktadır.Biyokütle-kömür veya biyokütle yarıkoku-kömür karışımlarının yakılacağı sistemlerin tasarımı için bu karışımların yanma davranımlarının ve kinetiklerinin bilinmesi gerekmektedir.Bu çalışmada, Tekirdağ Malkara ve Çorum Bayat kömürleri ile vişne ve şeftali çekirdeği numunelerinden düşük sıcaklık karbonizasyonu elde edilen yarıkokları kullanılarak hazırlanan karışımların, yanma davranımları ve kinetikleri incelenmiştir. Termogravimetrik analiz cihazında gerçekleştirilen yanma deneylerinde, biyokütle yarıkoku ve biyokütle yarıkoku-kömür karışımlarının yanmasının tek basamakta gerçekleştiği gözlenmiştir. Biyokütle yarıkokları ve Tekirdağ Malkara kömürü ile hazırlanan karışımlarda, yanma davranımının karışıma ilave edilen biyokütle yarıkokun miktarından belirgin olarak etkilendiği görülmüştür. Çorum Bayat kömüründen hazırlanan karışımlarda ise bu etki görülememiş, biyokütle yarıkoklarının Çorum Bayat kömürünün yanma davranımına çok benzer davranım gösterdiği belirlenmiştir. Bu sonuç; aynı biyokütle yarıkoklarının farklı kömürler üzerinde değişik etkilerinin olabileceğini göstermektedir.Deneysel yanma eğrilerinden elde edilen veriler kullanılarak, BASIC dilinde yazılmış bir bilgisayar programı yardımıyla yanma tepkimesine ait kinetik parametreler hesaplanmıştır. Kinetik paremetrelerin numune cinsine ve hesaplama yöntemine göre değiştiği belirlenmiştir.

Abstract:
Energy is one of Turkey?s most important development priorities. The difference between energy supply and consumption in our country increases every year and accordingly, our foreign dependence on energy in terms of sources increases as well. In order to continue its development, Turkey must provide and use the required energy as economically, sufficiently and environmentally friendly.The main domestic energy resources of Turkey are lignite, hydro and biomass. Electricity is mainly produced by thermal power plants, consuming coal, lignite, natural gas, fuel oil and geothermal energy, and hydro power plants in Turkey.Coal which is a kind of sedimentary rock, is the most important energy source of Turkey and most of the Turkish coal?s are low quality lignites having high ash, sulfur, moisture content and low heating value. 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. Coal burning is a major contributor to global warming. Electricity generation using coal burning produces approximately twice the greenhouse gasses per kilowatt compared to generation using natural gas.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.Various governments worldwide are beginning to put regulations in place and to encourage development of more sustainable sources of power generation in order to protect populations worldwide from the immediate harmful effects on life and health, and to protect the environment for future generation.Biomass which is the building structure of plants and living organisms, is by solar energy storing through photosynthesis. Biomass is a inexhaustible energy source as long as the solar energy exists. Turkey as an agricultural country, has a great potential in terms of biomass resources.Biomass resources are appeared to be an important feedstock for three main reasons. First, it is a renewable resource that could be sustainably developed in the future. Second, it appears to have formidably positive environmental properties, reduced greenhouse gas (GHG) emissions, possibly reduced NOx and SOx depending on the fossil fuels displaced. However, it also has negative impacts, such as emissions of polycyclic aromatic hydrocarbons including polycyclic aromatic hydrocarbons, dioxins, furans, volatile organic compounds and heavy metals especially when combusted in traditional stoves .Energy production through the direct combustion of coal and some biomass resources is the oldest known method. In recent years, combustion systems for burning biomass-coal blends together, are being developed.Turkey?s large lignite reserves and agricultural wastes, which are important with regard to reduce our energy dependency, are widely evaluated by burning together. In this study, instead of the raw biomass, biomass char, which has a higher calorific value, and coal are burned together.Co-combustion means simultaneous combustion of two or more fuels in the same plant for energy production. Although this mode of combustion has been applied for many years, the interest has been enhanced recently.Co-combustion can be carried out in various ways for various purposes. A coarse classification could be as follows, covering new plants as well as existing ones converted for the purpose; First, a small amount (a few percent of total fuel power) of biofuel or waste is fired together with coal in a boiler, originally designed for coal. The purpose is to get rid of waste or to replace coal by biomass utilisation. Second, a small amount of fuel with a high heating value is fired together with a fuel having a low heating value that needs thermal support to attain a desired combustion temperature. Third, Spontaneous use of co-combustion with fuels in any ratio, depending on price, availability and local supply conditions.The first type is of greatest significance due to its potential ability to reduce the consumption of coal, thereby decreasing the emissions of greenhouse gases. It is of interest to assess the possibility and reliability of such utilisation of biomass and waste in a plant designed for the base fuel (normally coal). Secondly, addition of high-value fuel to a low-value one, or in general terms, combination of any fuels with different properties, may have useful secondary consequences, such as reduction of emissions or improving reliability of operation. Coal and biomass fuels are quite different in composition. Co-firing biomass with coal has the capability to reduce both NOx and SOx levels from existing pulverized coal fired power plants This could enhance the interest for combinations of fuels, because certain fuel constituents may influence each other, ?synergy effects? may take place, leading to an improvement of operation of a boiler and to avoidance of inconveniences related to some fuels.Residues from agricultural production and processing industries are readily available in large quantities and solid wastes are generated by every social activity. Combustion of these residues can reduce the volume of wastes, allowing for energy recovery and increase of economic returns to rustic communities. Co-combustion of solid residues and wastes with coal in existing power plants is a most interesting option, because apart from the environmental benefits it offers technical and economic benefits, by replacing part of conventional energy sources, while at the same time using existing infrastructures.However, practically, due to the different characteristics of biomass fuels than coal, such as their higher moisture content and much higher volatile matter content, more easily released in a combustor, modifications of the combustion systems may need to be considered along with other factors. These characteristics influence the amount of primary and secondary air required, the temperature profiles along the furnace, the flue gas emissions, the burn out time of blends and the combustion efficiency.The knowledge of the behaviour of coal and biomass fuels during combustion not only separately but also together, is essential, as interactions may occur between them that may affect the overall efficiency of the process. It is necessary to know the combustion behaviour and kinetics of biomass-coal or biomass char-coal blends for the desining of combustion systems to be used. Combustion characteristics of a fuel before it is used in energy production can be determined by using thermo-analytical techniques such as TG, DTG and DTA which cover a wide range of applications in research, development and economic assessment of fuels. They have been used in a wide variety of areas related to proximate analysis, coal reactivity, and heat effects associated with coal pyrolysis, combustion and heat of hydrogenation. Although thermogravimetric analysis technique (TGA) operates in a different condition compared to a real combustor, it provides a rapid and reliable quantitative method for thermochemical processes.In this study, combustion behaviours and kinetics of blends prepared by using Tekirdağ Malkara and Çorum Bayat lignites, and peach stone and sour cherry stone chars, obtained by low temperature carbonization, were investigated. In the combustion experiments, which are performed in a thermogravimetric analyzer, it was observed that the combustion takes place in a single step both for biomass chars and biomass char-coal blends. The combustion behaviours of blends prepared from Tekirdağ Malkara lignite and biomass chars are significantly effected by the amount of the biomass chars added to the blends. This effect was not seen for the blends prepared from Çorum Bayat lignite and biomass chars. It was determined that the combustion behaviour of biomass chars are very similar to the Çorum Bayat lignite?s combustion behaviour. This result shows that same biomass chars may have different effects on the different coals.Kinetic parameters for the combustion reaction were calculated by using with the aid the help of a computer program written in BASIC (the data obtained from the experimental combustion curves). It was determined that the kinetic parameters are varied depending on the sample type and the method of calculation.