Biomass combustion

This experiment was conducted on fixed bed combustion in a one-dimensional bench. The effects of ash and moisture content on the combustion characteristics of corn straw were determined. The two parameters directly relate to the burning rate and affect combustion efficiency and the release of gas. The bed temperature distribution, mass loss rate and gas composition were measured in the bed. The results show that the optimum char combustion efficiency was achieved at 10% moisture content of corn combustion. A slight increasing the moisture content to 10% can obtain a higher bed temperature and accelerate the ignition rate in the char oxidation stage, while there is also a slight decrease in the conversion ratio of C to CO. The conversion rate of S to SO 2 for 10% moisture content was higher with the temperature zone above 1000 C. With the increased ash content, there was a slight increase in the average ignition rate; the bottom bed temperature increased with a serious ash slagging. C was converted to CO and presented a slightly increasing trend for higher ash content and the conversion of N to HCN. This work provides an overall understanding of corn combustion for large boiler system.

Rice husk lean-combustion in a bubbling and atmospheric fluidized bed reactor (FBR) of 0.3 m diameter with expansion to 0.4 m in the freeboard zone and 3 m height was investigated. Experiment design – response surface methodology (RSM) – is used to evaluate both excess air and normal fluidizing velocity influence (independent and controllable variables), in the combustion efficiency (carbon transformation), bed and freeboard temperature and silica content in the ashes. Hot gases emissions (CO2, CO and NOx), crystallographic structure and morphology of the ash are also shown. A cold fluidization study is also presented. The values implemented in the equipment operation, excess air in the range of 40–125% and normal fluidization velocities (0.13–0.15 Nm/s) show that the values near the lower limit, encourage bed temperatures around 750 °C with higher carbon transformation efficiencies around 98%. However, this condition deteriorated the amorphous potential of silica present in the ash...

Biomass co-firing with lignite represents an attractive solution for operating lignite-fired thermal power plants (TPP) with the dual advantage of using local renewable resources and  imultaneously reducing emissions. The subject of this study is technical and environmental investigation of the feasibility of the cofiring of Soma lignite with some dried agricultural residues in the Soma thermal power plant from the exergy analysis perspective, using THERMOFLEX simulation software. The use of biomass cofiring with poor quality coal could allow Turkey to comply with Kyoto commitments while benefiting from using indigenous fuel resources and reducing biomass waste disposal problems. Two technologies are considered; (1) direct cofiring, in which biomass is mixed with lignite in the same mill and fed into the boiler furnace and (2) parallel cofiring method, in which biomass is fired in a separate circulating fluidized bed boiler and produced steam is supplemented into the steam network of the power plant. The investigations reveal that both direct and parallel co-firing of the biomass could result in a significant decrease in fuel consumption, emissions and exergy destruction and a slight increase in the exergy efficiency of the Soma TPP. Olive waste, in particular, has a positive effect on general performance and emissions of the TPP, with fuel consumption, CO2 , SO2
and dust emissions, in direct co-firing dropping by approximately 20, 4, 19 and 18 percent, respectively, and in parallel co-firing by 26, 3, 20 and 25 percent, respectively.

This work concentrates on automatic procedures for simplifying chemical models for realistic fuels using skeletal mechanism construction and Quasi Steady-State Approximation (QSSA) applied to detailed reaction mechanisms. To automate the selection of species for removal or approximation, different indices for species ranking have thus been proposed. Reaction flow rates are combined with sensitivity information for targeting a certain quantity, and used to determine a level of redundancy for automatic skeletal mechanism construction by exclusion of redundant species. For QSSA reduction, a measure of species lifetime can be used for species ranking as-is, weighted by concentrations or molecular transport timescales, and/or combined with species sensitivity. Maximum values of the indices are accumulated over ranges of parameters, (e.g. fuel-air ratio and octane number), and species with low accumulated index values are selected for removal or steady-state approximation. In the case of QSSA, a model with a certain degree of reduction is automatically implemented as FORTRAN code by setting a certain index limit. The code calculates source terms of explicitly handled species from reaction rates and the steady-state concentrations by internal iteration. Homogeneous-reactor and one-dimensional laminar-flame models were used as test cases. A staged combustor fuelled by ethylene with monomethylamine addition is modelled by two homogeneous reactors in sequence, i.e. a PSR (Perfectly Stirred Reactor) followed by a PFR (Plug Flow Reactor). A modified PFR model was applied for simulation of a Homogeneous Charge Compression Ignition (HCCI) engine fuelled with four-component natural gas, whereas a two-zone model was required for a knocking Spark Ignition (SI) engine powered by Primary Reference Fuel (PRF). Finally, a laminar one-dimensional model was used to simulate premixed flames burning methane and an aeroturbine kerosene surrogate consisting of n-decane and toluene. In general, detailed calculations of temperature, pressure, concentration and flame velocity show excellent agreement with measurements. Skeletal mechanisms for PRF were constructed for the SI engine case, reproducing autoignition well on removal of reactions pertaining to 15% of the species. QSSA reduction was tested on the staged combustor and the engines, using pure and weighted lifetime indices. Monitoring NO concentrations in the staged combustor and ignition timing in the engines, good reproduction is possible while approximating about 70% of the species. However, some species have to be manually retained for accuracy and numerical stability. For improved ranking, sensitivity was added to the index applied to the premixed flames, in addition to necessary molecular transport information. The maximum atomic mass fraction occupied by a certain molecular species was also constrained to limit the mass and energy deficiency caused by QSSA. For methane, the laminar flame velocities as well as concentration profiles are well predicted by the most strongly reduced mechanism with five global reaction steps. For the kerosene surrogate mechanism, QSSA involving 50% of the species was successfully attempted.

This paper presents a transient model for the simulation of biomass combustion in a fixed bed boiler fed through particle drop. The method combines classical CFD techniques, which are used to simulate the gas phase, with a set of Eulerian variables defined to model the solid phase and Lagrangian trajectories that model the particle drop. Several submodels are implemented to simulate the numerous processes that occur during the combustion of the solid phase. These submodels include the thermal conversion of biomass, heat and mass transfer, particle shrinkage and bed compaction as well as the interaction of the DPM (Discrete Phase Model) trajectories and the bed variables. The predictions are contrasted with various experimental tests, which provide reasonably good results and demonstrate the overall good behavior of the models. The simulation facilitates an understanding of the heat transfer inside the boiler and the instability of the emission measurements.

The future outlook for biomass combustion is quite promising, despite the fact that petroleum and coal prices should remain low for the foreseeable future. The political and environmental benefits will continue to provide impetus to the use of biomass in combustion processes (indigenous supply, low sulfur, no net CO2, biodegradable, etc.). In view of the anticipated rapid development of biomass combustion processes, and because of the tremendous diversity of biomass feedstocks, a great need exists for a robust, comprehensive model that could be utilized to predict yields, composition and properties of pyrolysis products. Such a model would constitute a valuable tool in process development and process simulations. It could also be used to improve simulations of fires involving wood and related materials (paper, cardboard, etc.). No such model is currently available. The specific problem addressed in this study was related to the inability to predict a priori gas, liquid, and solid products on the basis of known feedstock characteristics and process conditions (temperature, pressure, heating rate, residence time, etc.).

Rice husk lean-combustion in a bubbling and atmospheric fluidized bed reactor (FBR) of 0.3 m diameter with expansion to 0.4 m in the freeboard zone and 3 m height was investigated. Experiment design – response surface methodology (RSM) – is used to evaluate both excess air and normal fluidizing velocity influence (independent and controllable variables), in the combustion efficiency (carbon transformation), bed and freeboard temperature and silica content in the ashes. Hot gases emissions (CO2, CO and NOx), crystallographic structure and morphology of the ash are also shown. A cold fluidization study is also presented. The values implemented in the equipment operation, excess air in the range of 40–125% and normal fluidization velocities (0.13–0.15 Nm/s) show that the values near the lower limit, encourage bed temperatures around 750 °C with higher carbon transformation efficiencies around 98%. However, this condition deteriorated the amorphous potential of silica present in the ash. An opposite behavior was evidenced at the upper limit of the excess air. This thermochemical process in this type of reactor shows the technical feasibility to valorize RH producing hot gases and an amorphous siliceous raw material.

In this study, the effect of corn ratio on pine chip and corn straw (high alkali metals and chlorine) co-combustion in a fixed bed were investigated. The combustion efficiency, gas emissions, and problems of corrosion and deposits were analyzed by detecting bed temperatures, gas compositions (CO2, CO, O2, CH4, C2H6, NOx, HCN, NH3, SO2, and HCl), and alkali metal emissions. The appropriate increase in the corn ratio improved flame propagation speed and shortened ignition time. Pure pine combustion caused some amount of thermal NO emissions, and the high content of N resulted to a relatively high emission of NH3 and HCN, whereas its relationship with the release of NO in the main burning stage was slight. A 30% corn ratio aided in the reduction of NO emission, and the amount of alkali metals in the corn fixed the effect of SO2. The release of KCl and HCl can be considered as the prevalent emission formation of Cl in the blended biomass co-combustion process; the additional corn straw increased the release ratio of metal chloride. The optimum corn ratio (30–50%) provide a certain reference value for the selection of fuel mixture ratio in the operation of real large-scale systems.

Combustion of wheat straw for heat and power production is often challenging due to ash related problems such as fouling deposition and high temperature corrosion. Release and transformation of ash forming elements K, Cl and S directly respond to these problems. In this work, sewage sludge was tested as an additive to reduce potassium release during the wheat straw combustion. The wheat straw with and without sewage sludge addition (5 %, wt/wt) were combusted in a temperature range 700 °C to 1000 °C. The ash residues from each combustion test were analyzed with a combination of an inductively coupled plasma optical emission spectroscopy (ICP-OES), scanning electron microscopy equipped with energy dispersive X-Ray analysis (SEM-EDX) and X-Ray diffractonmetry (XRD). It was found that that release of potassium from the wheat straw started already at 700 °C. About 80 % of the potassium released from after the wheat straw combusted at 1,000 °C for 1 h. Most of the potassium evaporated as potassium chloride in the temperature range 700-900 °C as indicated by SEM-EDX and XRD analyses. Addition of sewage sludge considerably reduced potassium release from the wheat straw as temperature was over 800 °C. At 1000 °C, less than 60 % potassium released from the wheat straw and the rest retained in ash residues after combustion tests. The SEM-EDX and XRD analysis results revealed that aluminum silicates, phosphorus and calcium in the sewage sludge played critical roles in capturing potassium from the wheat straw, through forming different potassium aluminum silicates and phosphates. The results from current study indicate that addition of sewage sludge may be beneficial to reduce potassium release and thereby fouling deposits in wheat straw combustion applications.

Bitkilerin ve canlı organizmaların kökeni olarak ortaya çıkan biyokütle, genelde güneş enerjisini fotosentez yardımıyla depolayan bitkisel organizmalar olarak adlandırılır. Biyokütleyi aynı zamanda bir organik karbon olarak da kabul etmek olanaklıdır. Biyokütle, tarım veya ormancılık ürünü olan ve tamamı veya bir kısmı içindeki enerjiyi geri kazanmak amacı ile yakıt olarak kullanılabilen bitkisel maddelerin tamamı veya bir kısmından oluşan ürünler ile çeşitli organik atıkları kapsar. Biyokütle enerjisi, yetiştiriciliğe dayalı olduğu için yenilenebilir, çevre dostu, yerli ve yerel bir kaynak olarak önem kazanmaktadır. Organik madde içeren artıkların değerlendirilmesi, çevre kirliliği ve temiz enerji üretimi bakımından önem taşımaktadır. Bu amaçla özellikte gelişmekte olan ülkelerde kullanımı en yaygın olan kaynak biyokütledir. Biyokütle, her yerde yetiştirebilmesi, çevre korunmasına katkısı, elektrik üretimi, kimyasal madde ve özellikle taşıtlar için yakıt olabilmesi nedeni ile stratejik bir enerji kaynağı olarak kabul edilmektedir.

Biyolojik kökenli yakıtlardan enerji üretimi için en etkin yöntemlerden birisi, kombine ısı ve güç üretimidir. Endüstriyel uygulamalarda, sadece ısı ve güç üretimi yerine, işlem ısısı ve buhar üretimi amacıyla da yararlanılabilir. Endüstri sektöründe kurutma gibi birçok işlem için ısı üretimine gereksinim vardır. Bu gereksinim, bölgesel ısıtma sistemi olmaksızın kombine ısı ve güç üretimi ile birlikte de karşılanabilir. Ayrıca küçük ölçekli kombine ısı ve güç tesislerinden elde edilen ısı enerjisi, kamusal ve endüstriyel binaların ısıtılmasında kullanılabilir. Ayrıca gazlaştırma ile de ısı ve güç elde edilebilir.

Biyokütle yakıtlar yeniden üretilebilen organik maddelerdir. Kullanılan biyokütle yakıtların büyük çoğunluğu, odunsu yakıtlar, enerji bitkileri ve hayvansal atıklardan  elde edilir. Kentsel belediye katı atıkları da bir biyokütle yakıt kaynağıdır. Biyokütle yakıtlardan elde edilen enerjiye biyokütle enerjisi denmektedir. Biyokütle yakıtının yanma emisyonları azdır. Fosil yakıtlara göre çok az asit yağmuru ve duman üretir. Uygun teknolojiler ve uygun yöntemler kullanılarak doğru bir şekilde enerjiye dönüştürüldüğünde,  çevre üzerinde etkisi az, hızlı bir şekilde yeniden üretilebilen, uzun süreli ve güvenli bir enerji kaynağıdır. Biyokütlenin enerji üretimi açısından göz önünde tutulması gereken en önemli özelliği bünyesinde bulunan nemdir. Nem miktarı yanma verimini düşürür. Gazlaştırma ya da pelet yapımı gibi bazı yakıt üretme teknolojilerinde ise biyokütlenin belirli oranda bir nem içermesi istenir. Bununla birlikte ne kadar kuru olursa olsun biyokütle, her zaman petrol ve doğal gaz gibi fosil yakıtlardan daha az ama yerli kömür ve linyitlere benzer enerji yoğunluğuna sahiptir.  Diğer bir deyişle, aynı miktarda ısı elde edebilmek için petrol ve doğal gaz gibi fosil yakıtlara göre daha fazla, yerli kömür ve linyitlere yakın biyokütle kullanmak gerekir.

Diğer taraftan orman ve tarım atıkları gün geçtikçe çevresel olarak problem yaratmaktadır. Sürdürülebilir kalkınmanın ve sürdürülebilir çevresel yaşamın önemli bir parçası olan orman ve tarım faaliyetlerinden arta kalan atıklar maalesef önemli çevresel sorunlar olarak karşımıza çıkmaktadır. Bu çevresel sorunları çözerken sahip oldukları enerji potansiyelinden de faydalanmak gerekir. Böylece hem bu atıkların yaratmış olduğu problemler çözülmüş, hem de bu problemler faydalı enerji haline dönüştürülmüş olur.

Hızlı bir artış gösteren nüfus ve sanayileşme enerji ihtiyacını da beraberinde getirmiştir. Enerjinin çevresel kirliliğe yol açmadan sürdürülebilir olarak sağlanabilmesi için kullanılacak kaynakların başında ise biyokütle enerjisi gelmektedir. Biyokütle enerjisi tükenmez bir kaynak olması, her yerde elde edilebilmesi, özellikle kırsal alanlar için sosyo-ekonomik gelişmelere yardımcı olması nedeniyle uygun ve önemli bir enerji kaynağı olarak görülmektedir.

Biyokütle için mısır, buğday gibi özel olarak yetiştirilen bitkiler, otlar, yosunlar, denizdeki algleri, hayvan dışkıları, gübre ve sanayi atıkları, evlerden atılan tüm organik çöpler (meyve ve sebze artıkları) kaynak oluşturmaktadır. Petrol, kömür, doğal gaz gibi tükenmekte olan enerji kaynaklarının kısıtlı olması, ayrıca bunların çevre kirliliği oluşturması nedeni ile, biyokütle kullanımı enerji sorununu çözmek için giderek önem kazanmaktadır. Bitkilerin ve canlı organizmaların kökeni olarak ortaya çıkan biyokütle, genelde güneş enerjisinin fotosentez yardımıyla depolayan bitkisel organizmalar olarak adlandırılır. Biyokütle, bir türe veya çeşitli türlerden oluşan bir topluma ait yaşayan organizmaların belirli bir zamanda sahip olduğu toplam kütle olarak da tanımlanabilir.     
                                                       
Fotosentez yoluyla enerji kaynağı olan organik maddeler sentezleşirken tüm canlıların solunumu için gerekli olan oksijeni de atmosfere verir. Üretilen organik maddelerin yakılması sonucu ortaya çıkan karbondioksit ise, daha önce bu maddelerin oluşması sırasında atmosferden alınmış olduğundan, biyokütleden enerji elde edilmesi sırasında çevre, CO2 salımı açısından korunmuş olacaktır. Bitkiler yalnız besin kaynağı değil, aynı zamanda çevre dostu tükenmez enerji kaynaklarıdır.                                                   
Bitkilerin toprak altında milyonlarca yıl kalmasıyla oluşan fosil yakıtlar, aslında yukarıda tanımlanan biyokütle ile aynı özellikleri taşımalarına karşın yer altındaki sıcaklık ve basınçla değişime uğradıklarından, yakıldıklarında havaya birçok zararlı madde atarlar.
   
Ayrıca, milyonlarca yılda oluşan bu birikimin kısa süre içinde yakılması havada ki karbondioksit dengesinin bozulmasına yol açar ve bu da küresel ısınmaya neden olur.

Türkiye’nin enerji tüketim hızı, enerji üretim hızından daha fazladır. Bu da, Türkiye’yi bir enerji ithalatçısı yapmaktadır. Enerji, ekonomik ve sosyal gelişim için gerekli olup, Türkiye’deki yaşam kalitesinin arttırılması için şarttır. Türkiye’deki başlıca enerji kaynakları linyit, su, jeotermal, rüzgar, güneş ve biyokütle enerjisidir. Biyokütle doğrudan yakılarak veya çeşitli süreçlerle yakıt kalitesi arttırılıp, mevcut yakıtlara eşdeğer özelliklerde alternatif biyoyakıtlar (kolay taşınabilir, depolanabilir ve kullanılabilir yakıtlar) elde edilerek enerji teknolojisinde değerlendirilebilir. Atık biyokütle (tahıl kalıntıları, orman ve orman endüstrisi atıkları, hayvan dışkıları, vs.) geleneksel olarak dünyanın birçok yerinde yemek pişirmede ya da ısınmada doğrudan kullanılmaktadır. Dünya enerji tüketiminin yaklaşık % 15’i, gelişmekte olan ülkelerde ise enerji tüketiminin yaklaşık % 43’ü biyokütleden sağlanmaktadır. Hayvan atıkları, zirai kalıntılar ve meyve çekirdekleri gibi biyokütle kaynakları yakıt olarak doğrudan kullanılabilecekleri gibi biyogaz, biyokarbon ve biyodizel üretimi için de oldukça elverişli ve yüksek potansiyele sahip ürünlerdir.

Biyokütle kaynakları, çevrim teknikleri ve elde edilen ürünler özetlenmiştir. Bu makalede ülkemizin bitkisel-orman atıkları ve enerji bitkileri kaynaklı biyokütle potansiyeli
irdelenecektir.

A model for NO and N2O emissions from biomass-fired circulating fluidized bed (CFB) combustors has been developed and evaluated in this study. All the model parameters were chosen for a typical woody biomass–pinewood chips. Both drying and devolatilization of biomass particles were modelled with limited rates, which were selected from the literature based on woody biomass fuels. The partition of fuel-nitrogen between volatiles and char was also specifically chosen for pinewood based on available experimental data from the literature. Volatile nitrogen was assumed to consist of NH3, HCN and N2 with the distribution between three species as input parameters to the model. Twenty-five homogenous and heterogeneous global chemical reactions were included in the model, of which 20 reactions represents the global fuel-nitrogen reactions. Both gaseous and solid phase were assumed to be in plug flow. The model has been applied to the modelling of a 12 MWth CFB boiler. The predicted N2O emissions were always less than 5 ppmv for pinewood combustion, which was consistent with the experimental results. The predicted NO emissions increased with the total excess air of the riser and the fuel-N content while the predicted percentage conversion of fuel-N to NO decreased with increasing fuel-N content. The NO emissions were also predicted to decrease with increasing primary zone stoichiometry. These predictions agree with the experimental results. The predicted NO emissions decreased slightly with increasing bed temperature, whereas experiments showed that NO emissions slightly increased with bed temperature for birch chips combustion and did not change with bed temperature for fir chips combustion. Sensitivity analyses reveal that the reaction between NO and char is the key reaction to determine the NO emissions.

In this paper, both a numerical model and an experimental study were developed to determine the important parameters of corn length for combustion behavior in a fixed-bed reactor. As an important factor impacting thermal conversion, changes in the burning rate follow variations in corn length, which then affect gas emissions. As a result of insufficient knowledge concerning the mechanisms of complex combustion, the development of a combustion system has been restricted. Modeling of this combustion system will complement experimental data; however, improving such a model is challenging as a result of the unique characteristics of corn, such as its moisture content and porosity. The results show that corn straw with a shorter length has a shorter ignition time, increased bed temperature, and reduced amounts of unburned carbon in the ash residues. Furthermore, the burning of shorter corn straw causes high emission concentrations from pyrolysis products, such as CH4 , CO, and most prevalently NO, near the grate, which indicates the beginning of the char oxidation stage. Corn straw with longer lengths increases the difficulty of accurately modeling the irregular shape of corn straw particles for theoretical calculations. In addition, in an actual bed, local bed structures that have not been uniformly mixed result in uncertainties in the flame propagation as well as the time at which the fuel is ignited. The application of numerical modeling allows for a more detailed description of the corn combustion process and can be used as a reference to develop biomass combustion in a large system.

This study aimed to investigate the effect of biomass-sulfur interaction on ash composition and agglomeration for the co-combustion of high-sulfur lignite coals and olive cake in a circulating fluidized bed combustor. The tests included co-combustion of 50-50% by wt. mixtures of Bursa-Orhaneli lignite+olive cake and Denizli-Kale lignite+olive cake, with and without limestone addition. Ash samples were subjected to XRF, XRD and SEM/EDS analyses. While MgO was high in the bottom ash for Bursa-Orhaneli lignite and olive cake mixture, Al2O3 was high for Denizli-Kale lignite and olive cake mixture. Due to high Al2O3 content, Muscovite was the dominant phase in the bottom ash of Denizli Kale. CaO in the bottom ash has increased for both fuel mixtures due to limestone addition. K was in Arcanite phase in the co-combustion test of Bursa/Orhaneli lignite and olive cake, however, it mostly appeared in Potassium Calcium Sulfate phase with limestone addition.

In the present paper NOx emissions from biomass combustion was studied, with the objective to demonstrate the applicability of stationary computational fluid dynamics simulations, including a detailed representation of the gas phase chemistry, to a multi-fuel lab-scale grate fired reactor using biomass as fuel. In biomass combustion applications, the most significant route for NOx formation is the fuel NOx mechanism. The formation of fuel NOx is very complex and sensitive to fuel composition and combustion conditions. And hence, accurate predictions of fuel NOx formation from biomass combustion rely heavily on the use of chemical kinetics with sufficient level of details. In the present work we use computational fluid dynamics together with three gas phase reaction mechanisms; one detailed mechanism consisting of 81 species and 1401 reactions, and two skeletal mechanisms with 49 and 36 species respectively. Using the detailed mechanism (81 species), the results show a high NOx reduction at a primary excess air ratio of 0.8, comparable to the NOx emission reduction level achieved in the corresponding experiment, demonstrating both the validity of the model and the potential of NOx reduction by staged air combustion.

Emission formation during thermal conversion of biomass fuels at different conditions has been the scope of this study. The experiments were conducted in a quartz glass reactor where the temperature and atmosphere can be adjusted. The fuels were selected accurately in order to cover a wide range of biomass/waste compositions. They are torrefied softwood, spruce bark, waste wood, miscanthus, and wheat straw. The fuels were first grinded and then pressed into pellets of the same size and weight with a pellet maker. Each pellet was about 200 mg. The experiments were performed under combustion and pyrolysis condition, with atmosphere of 3 % O2 and 100 % N2, respectively. Each fuel was combusted under temperatures of 800, 900, and 1,050 °C. O2 and the formed SO2, NO, CO and CO2 were monitored by three analysers. The fuel pellet was kept under combustion and pyrolysis at four residence times. The residue weight was measured after each process and the comparison with the ash content of the original fuel is made. Time dependent formation of NO and SO2 and other emissions is presented and discussed in this paper. Effect of temperature and combustion condition is also considered for the conclusion.