Biyokütlenin piroliz reaktivitesinin farklı yöntemler kullanılarak incelenmesi
Determination of biomass pyrolysis reactivity by using different methods
Yazar: MERVE ÖZFİDAN
Danışman: PROF. DR. HANZADE AÇMA
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Kimya Mühendisliği Ana Bilim Dalı / Kimya Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: Kimya Mühendisliği = Chemical Engineering
Dizin: Biyoenerji = Bioenergy ; Yenilenebilir enerji = Renewable energy

Özet:
Dünya nüfusunun artması ve her geçen gün gelişen teknolojinin beraberinde getirdiği sonuçlardan biri artan enerji ihtiyacıdır. Artan enerji ihtyacının karşılanmasında akla ilk gelen birincil enerji kaynakları olan kömür, petrol ve doğalgaz gibi fosil yakıtların kullanımı birçok sorunu da beraberinde getirmektedir. Bu yakıtların kullanımının artmasıyla mevcut rezervler azalırken iklim değişikliğine neden olan sera gazlarının salınımı artmaktadır.  Fosil yakıt kullanımının dezavantajlarından dolayı artan enerji talbeini karşılamak için yenilenebilir enerji kaynakları arayışı her geçen gün önem kazanmaktadır.
Güneş enerjisi, rüzgâr enerjisi, hidrolik enerji, jeotermal enerji ve biyokütle enerjisi temel yenilenebilir enerji kaynaklarıdır. Artana enerji talebini çevreye zarar vermeden ve sürdürülebilir bir şekilde sağlayabilecek enerji kaynakları arasında biyokütleden üretilen biyoenerji önemli bir paya sahiptir. Biyoenerji temelde ışık enerjisinin biyokütle yapısında fotosentez yolu ile depolanmasına ve bu enerjinin kimyasal enerjiye dönüşmesine dayanmaktadır. Bitkisel kaynakları, hayvansal atıkları, deniz biyokütlesini, orman ve kentsel atıkları içeren fosil olmayan, yapısında lignoselüloz olarak bilinen selüloz, hemiselüloz ve lignin organik maddelerdir. Biyokütle en çok ormansal ürünlerden olmak üzere, tarımsal ürünlerden ve atıklardan temin edilmektedir. 
Eski zamanlardan itibaren ısınma ve pişirme amacı ile doğrudan yakılarak kullanılan biyokütle günümüzde elektrik enerjisi, ulaşım sektörü için yakıt üretimi ve kimyasal madde üretimi için de kullanılmaktadır. Biyokütle katı, sıvı ve gaz halindeki yakıtlara dönüştürülebilmektedir ve oluşan bu yakıtların düşük enerji içeriği, düşük enerji verimi, düşük yoğunluk ve fazla hacminden kaynaklı taşıma zorlukları gibi dezavantajlarını engellemek için dönüşüm prosesleri uygulanmaktadır. Termokimyasal dönüşüm proseslerinden biri olan piroliz işleminin amacı biyokütleden katı, sıvı ya da gaz yakıt elde etmektir. Bu süreçte biyokütle azot atmosferi altında belli bir ısıtma hızı ile belli son sıcaklığa çıkarılıp bu sıcaklıkta belli bir süre bekletilmektedir. Piroliz işlemi sonucunda elde edilecek olan ürünler, son sıcaklık, ısıtma hızı, bekleme süresi gibi işlem koşulları ile değişiklik göstermektedir.
Yakıt yakma sistemlerinin gelişitilmesi için kullanılan yakıtların reaktivitelerinin incelenmesi oldukça önemlidir. Biyokütle pirolizi sonucu oluşan yakıtların reaktivitelerinin incelenmesi de günden güne önem kazanmaktadır.
Bu çalışmada, numunelerin her biri için piroliz işlemi gerçekleştirilmiş ve farklı ısıtma hızının, son sıcaklığın ve biyokütle çeşidinin piroliz reaktivitesi üzerine etkileri incelenmiştir. Bu incelemeler esnasında termal analiz eğrilerinden ve literatürde uygun bulunan çalışmalardan faydalanılmıştır. Nem içeriği giderilmiş farklı numunelerin 125°C'deki ilk başlangıç ağırlığının %5'ini kaybettiği T%5 sıcaklıkları, piroliz reaktivitesi değerleri, birim zamandaki ağırlık kayıp hızlarını gösteren, DTG eğrilerinden belirlenen Rmax değerleri ve bu maksimum ağırlık kayıp hızının gerçekleştiği Tmax sıcaklık değerleri, DSC eğrisinden okunan en yüksek ısı akışı değeri olan Hmax ve gerçekleştiği T(H-max) sıcaklık değerleri, DTA eğrilerinden okunan maksimum sıcaklık farkı olan  ΔTmax ve gerçekleştiği T(ΔT-max) sıcaklık değerleri ile numunelerin nemini kaybettikleri süre ihmal edilerek nem çıkışı olduktan sonraki başlangıç kütlerinin %50'sini kaybetmeleri için geçen süre olan t50 değerleri incelenmiştir. Bunlara ek olarak literatürden bulunan ortalama reaktivite, Rm, ve reaktivite indeksi, Rc, formülleri kullanılarak çalışmada kullanılan numunelerin reaktivite incelemeleri yapılmıştır.

Abstract:
As a natural result of the constant increase in world population, and new technologies evolving every day, a gradual increase is shown in energy need of the world. In addition, many problems have emerged with the use of fossil fuels, which have a large share in the existing energy sources such as petroleum, coal, natural gas, to meet the increasing energy requirement due to the increasing urbanization and industrialization processes. The use of fossil fuels leads to a decrease in the existing reserves, while it also causes emission of greenhouse gases which cause climate change and deterioration of the natural life balance.
Due to the negative outcomes that come along with the use of fossil fuels, the need for alternative and renewable energy sources to meet the increasing energy demand has come forward. Solar energy, wind energy, hydraulic energy, geothermal energy and biomass energy are the main renewable energy sources. In terms of environmental friendliness, and sustainability, bioenergy produced from biomass comes into prominence, to meet the demand for energy as a result of the increase in industrialization, when compared to fossil fuels. Bioenergy is produced from organic materials known as biomass, in other words, from all biological structures that are not fossilized.
Bioenergy is basically based on the storage of light energy in the biomass structure by photosynthesis and the transformation of this energy into chemical energy. Compared to the fossil fuel, which is known to be depleted in the future, the energy produced by the carbon neutral biomass results in less CO2 emission, which causes global warming. Therefore, biomass energy, which is one of the largest renewable energy sources, is sustainable. Biomass is defined as all non-fossil organic materials including plant sources, animal waste, marine biomass, forest and urban waste that can be renewed in less than 100 years. Biomass is regarded as a strategic source of energy not only because it is renewable, but also because it can be grown in many regions on the world, to provide socio-economic development, to contribute to the protection of the environment and to have great potential.
Biomass, a versatile energy source, is mostly used for heating and cooking needs worldwide. While this process has been implemented from ancient times up to now, today, electricity is used for fuel production and chemicals production for the transportation sector. Unlike other energy sources, biomass can be converted into solid, liquid and gaseous fuels. Biomass is procured from agricultural products, and waste, and the forestry sector is the sector that makes the greatest contribution to biomass supply.
The importance given to the cycle technologies and conversion processes to obtain high quality fuel and energy from biomass, which is one of the first energy sources used by humanity, is increasing day by day. Disadvantages of biomass such as low energy content, and efficiency, low density and handling difficulties caused by excess volume can be prevented by the transformation processes applied. Solid, liquid and gaseous fuels can be obtained from biomass, which is more directly used by thermochemical, biochemical and physical methods.
Pyrolysis, one of the thermochemical conversion processes, is the process of heating biomass to a certain temperature with a certain heating rate in the oxygen-free environment to obtain solid, liquid and gas biofuels, and chemical breaking down of the long-chain organic substances into small amounts of chemical substances. In other words, pyrolysis is the process of degrading hydrocarbon-containing structures in an inert atmosphere to give a liquid-rich product. Pyrolysis method is used for commercial production of various fuels and chemicals from biomass raw material. The products to be obtained as a result of pyrolysis; based on various factors such as particle size, last reached temperature, dwell time and heating rate.
As scientific studies progress, a new approach to reactivity calculations is being added to the literature every day. The calculations of the reactivity, which must be taken into account in combustion systems, vary. Investigation of the reactivity of the fuels used has been a significant issue for the development of systems using these fuels. Investigation of the reactivity of tar resulted by pyrolysis, that is one of the transformation processes to obtained better quality fuels by using biomass, has been an important issue. 
In this study, pyrolysis process was performed for each of the samples and the results of the thermogravimetric analysis (TGA), differential thermogravimetric analysis (DTG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC) curves were used. During the analysis, these results were used to obtain reactivity values. The effect of heating rate, final temperature and biomass type on the reactivity of different biomass samples used during the study were examined. Thermal analysis curves and studies which were found suitable in the literature were used during these investigations.
In this study, following parameters were observed: T%5 temperatures where samples with different dehumidified content lost 5% of initial initial weight at 125 °C, pyrolysis reactivity values, Rmax values determined from DTG curves showing weight loss velocities in unit time, Tmax temperature values at which this maximum weight loss rate occurs, Hmax the highest heat flow value read from the DSC curve, and  TH-max temperature values, the maximum temperature difference, ΔTmax its temperature TΔTmax,, and  t50 values which are the time to lose 50% of the initial mass after the moisture output are examined. In addition to these, by using Rm, mean reactivity, and reactivity index Rc, from the literature, analysis were performed.
It is seen that olive oil residue (OOR) and rhododendron dehumidified samples lost 5% of their initial weight at 125°C, and when T5% temperatures are compared, OOR is more reactive than rhododendron sample at low temperatures.
When the Rmax values determined from the DTG curves, which show the weight loss rates of OOR and rhododendron samples per unit time; it was observed that the maximum weight loss rates in unit time increased due to the increase in heating rate, and this ratio was 788% for the OOR  sample and 660% in the rhododendron sample. It has been determined that Rmax value is more affected by the increase of heating rate of OOR sample compared to rhododendron sample. The effect of the heating rate increase on Tmax values was higher in the OOR sample. However, the Tmax values of the rhododendron sample are higher than the OOR sample.
The Hmax values of the rhododendron sample with high Tmax values from the DSC curve were found to be lower compared to the OOR sample values. It is observed that the change in Tmax values and Hmax values are inversely proportional.
When DTA results for OOR and rhododendron sample are investigated, it was observed that theTΔTmax values of OOR samples are generally high at all heating rates, whereasT(ΔTmax)  values of rhododendron sample are in line with the values for OOR at a heating rate of 40°C/min and 50°C/min.
When the Rm results of OOR and rhododendron samples were examined, it was observed that these values increased in both OOR and rhododendron samples with the increase of the heating rate whereas when Rc values of reactivity index were examined, it was determined that these values increased in close rates due to the increase in heating rate.
When the pyrolysis reactivity values of OOR and ash tree samples were examined, it was observed that the increase in the heating rate of OOR sample resulted in a greater increase when compared to the ash tree sample.
When maximum weight loss rates Rmax per unit time determined from DTG curves of ash tree and ORR samples, and Tmax values were observed, it is seen that, since the maximum weight loss rate of the ORR sample is higher than the values of the ash tree sample, it has been determined that the degradation rate is more rapid and higher temperatures and more reactive.
When t50,  the time for the half of the initial mass of ash tree and ORR samples to be lost, is investigated, with the doubling of the rate of heating, it was determined that there was a 50% decrease in the t50 values of the samples of ORR and ash tree.
During the investigation of mean reactivity values of ash tree and ORR samples expressed with Rm, it is concluded that OOR sample is more reactive. 
Comparing T%5  values of RDF and sunflower seed shell samples, the final temperature values obtained on the T%5 results of the RDF sample were found to be more effective compared to the sunflower seed shell  sample.
When the pyrolysis reactivity results of RDF and sunflower seed shell samples were examined, it was determined that the increase in the final temperature was more effective on the reactivity of the RDF sample.
When the maximum determined heat flow values from the DSC curves of RDF and sunflower seed shell samples Hmax were examined, it was observed that the change in the final temperature reached no effect on these samples.
The samples used are evaluated in terms of T(Hmax) indicating the temperature of Hmax, according to the increase of the last temperature reached, the values of RDF sample increased by 226.5%, whereas the increase in sunflower seed shell sample showed a decrease of only 2.25%.
When the average reactivity values of RDF and sunflower seed shell samples, Rm,  are examined, it is seen that the samples with high volatile matter content have higher reactivity at low temperatures.
When the values of Artichoke stalk, beans stalk, buckwheat, grape seed, and cherry stalk pyrolysis reactivity results are taken into consideration, high T%5 supports high reactivity value.
When Tmax values of these samples were examined, it was determined that the grape seed sample had the highest T value of 5% and reactivity.
When the T(ΔTmax) values for artichoke stalk, beans stalk, buckwheat, grape seed, and cherry stalk are observed, it is seen that this value is affected by pyrolysis reactivity value. 
The highest and lowest reactivity results, and the relevant samples' calculated conversion results are seen to be consistent with the conversion-time and conversion-temperature graphs drawn according to the heating rate and final temperature values.
In addition to the determination of the pyrolysis reactivity results of biomass samples based on the Rmax and Tmax, Hmax and T(Hmax), ΔTmax and T(ΔTmax) parameters of the combustion rate determined by using the thermal analysis curves performed during the pyrolysis process, it was determined that the comparison of the calculated reactivity values using the methods in the current studies in the literature will give a healthier result.