Lignoselülozik biyokütlenin inorganik bileşenlerinin uzaklaştırılmasının kül özellikleri üzerine etkisinin incelenmesi
Investigation of the effect on ash properties of removal of inorganic components from lignocellulosic biomass
Yazar: ÖVÜL HALİL ÇÖP
Danışman: PROF. DR. HANZADE AÇMA
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Kimya Mühendisliği Ana Bilim Dalı / Kimya Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2018
Konu: Enerji = Energy ; Kimya Mühendisliği = Chemical Engineering

Özet:
ÖZET
Günümüzde fosil yakıt rezervlerinin tükenmeye başlamasının endişesi yaşanırken, bu kaynaklara alternatif olabilecek yeni enerji kaynakları araştırılmaktadır. Yenilenebilir bir enerji kaynağı olan biyokütle umut verici bir potansiyele sahiptir. Giderek artan enerji ihtiyacının bir kısmının sürdürülebilir ve yerli kaynaklardan karşılanabilmesi için biyokütlenin kullanımı giderek artan bir önem kazanmaktadır. 
Biyokütle türüne göre farklı oranlarda ve türlerdede inorganik bileşen içermektedir.  Lignoselülozik biyokütlenin içerdiği inorganik bileşenler termokimyasal ve biyokimyasal dönüşüm proseslerinde farklı sorunlara neden olmaktadır. Farklı termal proseslerle biyokütleden üretilen yakıtlar doğrudan yakma proseslerinde değerlendirilmeden önce bu inorganik yapıların azaltılması önemlidir. Biyokütle dönüşüm proseslerinde kül birikimi ve cüruf oluşumu nedeniyle zaman zaman tıkanmalar meydana gelmekte ve bu durum sistemin durmasına, korozyona ve ısı transferinde kayıplara neden olmaktadır. Ayrıca bu kaynakların içerdikleri inorganik bileşenler verimi düşürmekte ve yakıtın kalitesini olumsuz yönde etkilemektedir. Biyokütlenin dönüşüm proseslerinde değerlendirimesinden önce inorganik bileşenlerin uzaklaştırılması için uygulanabilecek farklı yöntemler mevcuttur. 
Bütün dünya genelinde olduğu gibi Türkiye'de de enerji ihtiyacı giderek artmaktadır. Bu sebeple, çalışmaya başlamadan önce Türkiye'de biyokütleden enerji üretimi için hammadde kaynakları araştırılmıştır. Türkiye'de her mevsim birçok farklı tarım ürünü yetiştirilmektedir. Bu ürünler içerisinde mısır bitkisi 6-7 milyon tonluk üretimiyle önemli bir paya sahiptir. Tarlada kalan tahmini mısır bitkisi atığı 2 milyon tondur. Yapılan hesaplamalara göre tarlada kalan mısır bitkisi atığının termal dönüşüm proseslerinde değerlendirilmemesinden dolayı yaklaşık olarak 7.8 x 1015 cal/gr ısıl değere sahip biyokütlenin değerlendirilemediği belirlenmiştir. Türkiye'de ve dünya genelinde üretiminde son yıllarda %50'ye varan bir artış olan mısır bitkisinin kullanılmayan gövde ve yaprak kısımları üzerinden inorganik yapıların uzaklaştırılması ve kül ergime sıcaklıkları üzerine etkilerinin incelenmesi çalışmanın temel amacını oluşturmaktadır. 
Mısır bitkisinin mısır koçanları alındıktan sonra tarlada kalan kısımları yakıt olarak kullanılmak yerine anız olarak tarlada yakılarak bertaraf edilmektedir.  Bu durum çevre kirliliğine sebep olduğu kadar biyokütleden elde edilebilecek olan enerjinin de kaybına neden olmaktadır. Bu çalışmada Doğu Akdeniz Tarımsal Araştırma Enstitüsünden alınan mısır bitkisi atıkları kullanılmıştır. Öncelikle laboratuvar ortamında kurutulmuş daha sonra etüvde 60℃'de öğütme yapabilmek için kaba nemi uzaklaştırılmıştır. Numuneler tane boyutunun etkisini incelemek amacıyla; elek çapı 0.25 mm., 1 mm., 2 mm. ve 4 mm. tanecik boyutunun altına geçilecek şekilde  öğütülmüştür. Farklı çözeltiler kullanılarak üç farklı yöntem (bekletme, akıtma ve daldırma yöntemleri) uygulanarak yıkama işlemleri gerçekleştirilmiştir. Yıkama işlemi için kullanılan çözeltiler; su, HCl, H2SO4, HNO3, H3PO4, NaOH ve CH3COOH olarak seçilmiştir. Ağırlıkça %5'lik çözeltiler kullanılmış ve bu çözeltilerle yapılan yıkama işlemleriyle ana numuneden K, Mg, Ca, Fe ve Na bileşenlerinin uzaklaştırılması amaçlanmıştır. 
Deneysel çalışmanın ilk kısmında ana numuneden ve yıkanmış numunelerden kül üretimi gerçekleştirildikten sonra küllerin ICP-OES analizi yapılmıştır. K, Mg, Ca, Fe ve Na elementlerinin uzaklaştırılmasında en etkili çözelti H3PO4 çözeltisi, en etkin yıkama yönteminin ise bekletme yönteminin olduğu belirlenmiştir. Yıkanan ve orijinal numunenin; ilk deformasyon, yumuşama, ergime ve akma sıcaklıkları belirlenmiştir. 2 mm. tane boyutundan küçük olan H3PO4 ile bekletilerek yıkanmış numunenin ilk deformasyon, yumuşama, ergime ve akma sıcaklıkları değerlerinde artış olduğu belirlenmiştir.
2 mm. boyutundan küçük işlem görmemiş ana numuneler ile H3PO4 çözeltisiyle bekletme yöntemi ile yıkanmış numunelerin; ısıl değerleri belirlenip, kısa analiz, yanma analizi, kinetik analiz, XRD analizi, FTIR ölçümleri ve SEM görüntüleri aracılığıyla kıyaslaması yapılmıştır. Sonuç olarak H3PO4 çözeltisi ile bekletme yöntemi ile yıkama işleminin K, Mg, Ca, Fe ve Na bileşenlerinin uzaklaştırılmasında etkili bir yöntem olduğu, en fazla etkinin 2 mm. altı tanecik boyutluu mısır bitkisi atıklarında görüldüğü belirlenmiştir.

Abstract:
SUMMARY
As is known, there is a close relationship between the living standards of a country and energy consumption. In general, if energy consumption per person increases, life standard is higher. Energy has an important role in increasing the quality of life of people living in a country and the socio-economic development of countries. Biomass is the first fuel that used by mankind and also is the main source of global fuel economy until the middle of the 18th century. Later, fossil fuels with higher energy content took the place of biomass.
Nowadays fossil fuel reserves are running out. New energy sources that may be alternative to fossil resources are being investigated. Renewable energy sources are basically; solar energy, wind energy, hydraulic energy, geothermal energy and biomass energy. Biomass is a renewable energy source and has a promising potential. 
Fossil fuels have some problems such as greenhouse gases, climate change, global warming, fluctuations on fossil fuel prices. In contrast to fossil fuels, biomass can be found easily in any part of the world. It is clean, eco-friendly and cheap resource. The use of biomass is becoming increasingly important in order to supply some of its growing energy needs from sustainable and domestic sources. In areas that are not rich in fossil fuel reserves, biomass has a important potential to increase energy security, reduce dependence on fossil fuels, and reduce emissions of harmful gases in the atmosphere.
Biomass is defined as a mixture of carbon, oxygen, hydrogen, nitrogen, and small amount of sulphur. Woody materials, and forestry residues, industrial wastes, municipal solid wastes (MSW), agricultural residues, algae, biosolids, and other many types of residues can be regarded as biomass energy resources. Combustion of biomass emits an amount of CO2 which is almost equivalent to the previously captured CO2 from atmosphere during photosynthesis of the fresh biomass. Because of this reason biomass can be regarded as a carbon-neutral unlike fossil fuels. 
Biomass sources are classified in two main groups although they are very diverse. These are untreated biomass, and wastes. Untreated biomass is examined in two groups: lignocellulosic biomass (wood, biomass and leaves) and carbohydrate biomass (plants and vegetables). Wastes are secondary biomass. These are municipal solid wastes (MSW), biological solid materials, industrial wastes, animal wastes, agricultural wastes, forest wastes and tree barks.
Biomass can be transformed into biofuels by physical, thermochemical and biochemical processes. In physical processes, compression processes such as biomass crushing, heating and pressure are applied. In thermochemical processes, heat energy and chemical catalysts are used to separate biomass into high value energy products. In biochemical processes, enzymes and microorganisms are used to convert biomass to desired energy products. In most cases the type of energy required to determine the course of the process, then the types and quantities of available biomass are monitored. The thermochemical transformation processes of biomass can be carried out in five forms. These; combustion, pyrolysis, torrefaction, gasification and liquefaction.
Biomass contains inorganic components in different proportions and different species. The inorganic components that are contained in the lignocellulosic biomass cause different problems in the thermochemical and biochemical conversion processes. It is important to reduce these inorganic components before fuels produced from biomass with different thermal processes. Inorganic components such as alkali elements cause the formation of slag and foul in the combustion systems.  This leads to the failure of equipment.  They can also have adverse effects on the properties of the biofuel produced. The fouling impedes the heat transfer rate, while the slagging obstructs fuel delivery, combustion and ash removal. There are different methods that can be applied to remove inorganic components before biomass is used in thermal conversion processes.   
As all of the worlds country, energy need is also increasing in Turkey. Therefore, before starting work, the raw materials was investigated for the production of energy from biomass sources. Because of having a mild climate and appropriate soil and field characteristics,  Turkey highly important country with respect to biomass-based products and technology. Many different crops are grown each season in Turkey. Within these products, corn fruit has an important part with 6-7 million tons production in yearly. The estimated corn fruit waste remaining in the field is 2 million tons. In the production of corn fruit in Turkey and the worldwide there is an increase in the up to 50% in recent years. The removal of inorganic components from unused stem and leaf parts of corn fruits and the investigation of their effects on ash melting temperatures constitute the main objective of the study. 
After the corn cobs of the corn fruit have been taken, the remaining parts of the field are burned in the field as stubble instead of being used as fuel. This causes environmental pollution as well as loss of energy that can be obtained from the biomass. In this study, corn fruit wastes that supplied from the Eastern Mediterranean Agricultural Research Institute (Adana), were used.  
Corn fruit wastes were first dried in the laboratory. Then, these wastes were dried in a laboratory medium at 60 °C for 2 days with drying oven and the coarse moisture has been removed. In order to examine the effect of the sample size, samples was ground to a particle size of below 0.25 mm, 1 mm, 2 mm and 4 mm. 
Washing operations were carried out by applying three different methods (soaking, flushing and immersion methods) using different solutions. Solvents used for washing methods are H2O, HCl, H2SO4, HNO3, H3PO4, NaOH and CH3COOH. Solutions were prepared as 5% wt. It is aimed to remove the components K, Mg, Ca, Fe and Na from the main sample by means of these washing processes.
In the soaking method the samples at four different sizes  were stored for two hours in 5% weight solutions. At the end of two hours, the samples were filtered using gooch crucible (4P). In the flushing methods, Samples of different sizes were placed inside the gooch crucible. The prepared solutions were slowly poured onto the samples. In the immersion methods, the prepared solution is placed in a beaker. The samples were added to extraction soxhlet that was made of high quality cellulose in size 33x80 mm from Schleicher & Schuell 603. These soxhlet were expected to be filtered after being immersed in the solution. In all methods, seven different solutions were applied to the samples below 4 mm, 2 mm, 1 mm and 0.25 mm and a total of 84 washed samples were obtained. After the washing processes, the washed samples were dried for one day. For analysis of characterization, some of the samples were left dry while the rest was reserved for ash formation.
In the first part of the experimental study, ash production was carried out from the main sample and washed samples. Then ICP-OES analysis of the ashes was performed. As a result of washing the samples with seven different solutions, the removal rates of Mg, K, Na, Fe and Ca were examined. The highest element removal was found to be carried out by washing with H3PO4 solution. It has been determined that the most effective washing method is the soaking method, and the most effective grain size is also 2 mm. When the percentages of removal rates of Mg, K, Na, Fe, and Ca with H3PO4 were examined, it was observed that the change was between 55.32% and 100% removal. 
Then the higher heating values were determined for the main samples and washed samples with the saoking method. It has been found that there is no significant reduction in the higher heating values of the samples washed with the H3PO4 solution. Also initial deformation, softening, melting and flow temperatures were determined for the main samples and washed samples with the saoking method. As a result of ash analysis; it was decided that the most suitable grain size was below 2mm by looking at the removal of the elements, initial deformation, softening, melting and flow temperatures.  
According to the results obtained in the washing process, a below 2 mm particle size sample was selected for the subsequent analysis. Proximate analysis, combustion analysis, kinetic analysis, XRD analysis, FTIR measurements and SEM images were performed for the below 2mm grain size of main samples and the samples which washed with H3PO4 solutions on soaking method.
According to ICP-OES analysis results, there was no significant decrease in the higher heating values of the samples washed with the H3PO4 solution. When the H3PO4 acid solution was used again in the washing process, the removal effect on the samples were continued. This result shows that the H3PO4 solution can be used again and the potential harmful effects of the H3PO4 solutions to the environment can be reduced. 
When kinetic analysis results and combustion analysis results are examined, it was determined that MFA2 sample has low ignition temperature and low reaction temperature. According to the results of the FTIR analysis, it has been determined that the thermal value is reduced as a disadvantage due to the separation of C-H and C = C structures. Although the disadvantage of 8.67% reduction in the thermal value, soaking washing method with a 5% wt by H3PO4 solution should be preferred. 
When SEM images were examined, it was determined that after washing with H3PO4, there was a more porous structure of the corn fruit  due to  removal of the mineral matter. XRD results also support this situation. XRD results indicated that minerals containing K and Cl structures were removed.
It has been determined that by ignoring the thermal loss of 8.67%, corn fruit can be used in Turkey with washing methods with H3PO4 solutions in a combustion system.