Fuel and Combustion Properties of Bio-Wastes

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Fuel and Combustion Properties of Bio-wastesAyhan Demrbaşa

a Department of Chemical Engineering Selcuk University Konya, Turkey

To cite this Article Demrbaş, Ayhan(2005) 'Fuel and Combustion Properties of Bio-wastes', Energy Sources, Part A:Recovery, Utilization, and Environmental Effects, 27: 5, 451 — 462To link to this Article: DOI: 10.1080/00908310490441863URL: http://dx.doi.org/10.1080/00908310490441863

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Energy Sources, 27:451–462, 2005Copyright © Taylor & Francis Inc.ISSN: 0090-8312 print/1521-0510 onlineDOI: 10.1080/00908310490441863

Fuel and Combustion Properties of Bio-wastes

AYHAN DEMIRBAS

Department of Chemical EngineeringSelcuk UniversityKonya, Turkey

All human and industrial processes produce wastes, that is, normally unused andundesirable products of a specific process. Biomass absorbs carbon dioxide duringgrowth, and emits it during combustion. Utilization of biomass as fuel for powerproduction offers the advantage of a renewable and CO2-neutral fuel. Although thestructural, proximate and ultimate analyses results of bio-wastes differ considerably,some properties of the biomass samples such as the hydrogen content, the sulfurcontent and the ignition temperatures changed in a narrow interval. The burningvelocity of pulverized biomass fuels is considerably higher than that of coals. The useof biomass fuels provides substantial benefits as far as the environment is concerned.

Keywords bio-waste, cofiring, combustion, fuel analysis, fuel properties

Bio-waste fuels potential include wood, short-rotation woody crops, agricultural wastes,short-rotation herbaceous crops, animal wastes, and a host of other materials. Animalwastes are another significant potential biomass resource for electricity generation, and,like crop residues, have many applications, especially in developing countries. Biomassis the only organic petroleum substitute that is renewable.

Biomass can be converted into liquid, solid and gaseous fuels with the help ofsome physical, chemical and biological conversion processes. The conversion of biomassmaterials has a precise objective to transform a carbonaceous solid material, which isoriginally difficult to handle, bulky and of low energy concentration, into fuels havingphysico-chemical characteristics that permit economic storage and transferability throughpumping systems.

The use of bio-waste fuels provides substantial benefits as far as the environment isconcerned. Biomass absorbs carbon dioxide during growth, and emits it during combus-tion. Therefore, biomass helps the atmospheric carbon dioxide recycling and does notcontribute to the greenhouse effect. Biomass consumes the same amount of CO2 fromthe atmosphere during growth as is released during combustion. In addition, overall CO2emissions can be reduced because biomass is a CO2-neutral fuel.

Some processes such as pyrolysis, gasification, anaerobic digestion and alcohol pro-duction have widely been applied to biomass in order to obtain its energy content. Bio-waste can be directly fired in dedicated boilers. However, cofiring bio-waste and coalhas technical, economical, and environmental advantages over the other options. Cofir-ing bio-waste with coal, in comparison with single coal firing, helps reduce the totalemissions per unit energy produced.

Received 12 June 2003; accepted 21 July 2003.Address correspondence to Professor Ayhan Demirbas, Department of Chemical Engineering,

Selcuk University, Campus, 42031, Konya, Turkey. E-mail: [email protected]

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452 A. Demirbas

Fuel Properties of Bio-wastes

The limitations were primarily due to relying on bio-waste as the sole source of fuel,despite the highly variable properties of bio-waste. The high moisture and ash contentsin bio-wste fuels can cause ignition and combustion problems. The melting point ofthe dissolved ash is also low, which causes fouling and slagging problems, because ofthe lower heating values of bio-waste accompanied by flame stability problems. It isanticipated that blending biomass with higher quality coal will reduce flame stabilityproblems, as well as minimize corrosion effects.

Bio-waste offers important advantages as a combustion feedstock due to the highvolatility of the fuel and the high reactivity of both the fuel and the resulting char. How-ever, it should be noticed that in comparison with solid fossil fuels, bio-waste containsmuch less carbon and more oxygen and has a low heating value. Also, chlorine con-tents of certain bio-wastes, like straw, can exceed the level of coal. In the combustionapplications, bio-waste has been fired directly either alone or along with a primary fuel.Chlorine, which is found in certain bio-waste types, such as straw, may affect operationby corrosion. The high chlorine and alkali content of some bio-waste fuels raise con-cerns regarding corrosion. The greatest concern focuses on high-temperature corrosionof super-heater tubes induced by chlorine on the surface.

Bio-waste differs from coal in many important ways, including the organic, inorganic,energy content, and physical properties. Table 1 shows the physical, chemical and fuelproperties of bio-waste and coal fuels. Relative to coal, bio-waste generally has lesscarbon, more oxygen, more silica and potassium, less aluminum and iron, lower heatingvalue, higher moisture content, and lower density and friability (Table 1). The point onthe burning profile at which the rate of weight loss due to combustion is maximumcalled as “peak temperature.” The burning profile peak temperature is usually taken asa measure of the reactivity of the sample. The peak temperatures for biomass samplesgenerally vary from 560 K to 575 K.

Table 1Physical, chemical and fuel properties of

bio-waste and coal fuels

Property Biomass Coal

Fuel density (kg/m3) ∼500 ∼1300Particle size ∼3 mm ∼100 µmC content (wt% of dry fuel) 42–54 65–85O content (wt% of dry fuel) 35–45 2–15S content (wt% of dry fuel) max 0.5 0.5–7.5SiO2 content (wt% of dry ash) 23–49 40–60K2O content (wt% of dry ash) 4–48 2–6Al2O3 content (wt% of dry ash) 2.4–9.5 15–25Fe2O3 content (wt% of dry ash) 1.5–8.5 8–18Ignation temperature (K) 418–426 490–595Peak temperature (K) 560–575 —Friability Low HighDry heating value (MJ/kg) 14–21 23–28

Source: Demirbas (2003).


Properties of Bio-wastes 453

Table 2Ultimate analyses of typical fuel samples given in the literature

(wt% of dry fuel with ash)

Fuel sample C H N S O Reference

Hazelnut shell 52.8 5.6 1.4 0.04 42.6 Demirbas (1997)Sawdust 46.9 5.2 0.1 0.04 37.8 Abbas et al. (1994)Corn stover 42.5 5.0 0.8 0.20 42.6 Paul and Buchele (1980)Poplar 48.4 5.9 0.4 0.01 39.6 Ebeling and Jenkins (1985)Rice husk 47.8 5.1 0.1 — 38.9 Hartiniati and Youvial (1989)Cotton gin 42.8 5.4 1.4 0.50 35.0 LePori (1980)Sugarcane bagasse 44.8 5.4 0.4 0.01 39.6 Ebeling and Jenkins (1985)Peach pit 53.0 5.9 0.3 0.05 39.1 Ebeling and Jenkins (1985)Alfafa stalk 45.4 5.8 2.1 0.09 36.5 Tillman (2000)Switchgrass 46.7 5.9 0.8 0.19 37.4 Tillman (2000)

Table 3Ultimate analyses of typical fuel samples (wt% of dry fuel with ash)

Fuel sample C H N S Cl O (diff.)

Coal type 1 81.5 4.0 1.2 3.00 — 3.3Red oak wood 50.0 6.0 0.3 — — 42.4Wheat straw 41.8 5.5 0.7 — 1.5 35.5Olive husk 49.9 6.2 1.6 0.05 0.2 42.0Beech wood 49.5 6.2 0.4 — — 41.2Spruce wood 51.9 6.1 0.3 — — 40.9Corncob 49.0 5.4 0.5 0.20 — 44.5Tea waste 48.0 5.5 0.5 0.06 0.1 44.0Walnut shell 53.5 6.6 1.5 0.1 0.1 45.4Almond shell 47.8 6.0 1.1 0.06 0.1 41.5Sunflower shell 47.4 5.8 1.4 0.05 0.1 41.3

Sources: Demirbas (1997); Demirbas (1998b).

The ultimate analyses of typical fuel samples given in the literature and determinedare shown in Tables 2 and 3, respectively. It is difficult to establish a representative bio-waste due to large property variations, but two examples are included here for comparison.The composition variations among bio-waste fuels are larger than among coals, but as aclass, bio-waste has substantially more oxygen and less carbon than coal. Less obviously,nitrogen, chlorine, and ash vary significantly among bio-waste fuels. These componentsare directly related to NOx emissions, corrosion, and ash deposition. Bio-waste generallyhas relatively low sulfur compared to coal.

The proximate analyses of selected bio-waste samples given in the literature anddetermined as defined by ASTM are shown in Tables 4 and 5, respectively. The inorganicproperties of selected fuel samples are given in Table 10. Inorganic components in coalvary by rank and geographic region. As a class, coal has more aluminum, iron, and


454 A. Demirbas

Table 4Proximate analyses of selected bio-waste samples given in the literature

(wt% of dry fuel)

Volatile FixedFuel sample Ash matter carbon Reference

Hazelnut shell 1.5 76.3 21.2 Demirbas (1997)Sawdust 2.8 82.2 15.0 Abbas et al. (1994)Corn stover 5.1 84.0 10.9 Paul and Buchele (1980)Poplar 1.3 — 16.4 Ebeling and Jenkins (1985)Sugarcane bagasse 11.3 — 15.0 Ebeling and Jenkins (1985)Peach pit 1.0 — 19.9 Ebeling and Jenkins (1985)Rice husk 22.6 61.0 16.7 Hartiniati and Youvial (1989)Alfafa stalk 6.5 76.1 17.4 Tillman (2000)Switchgrass 8.9 76.7 14.4 Tillman (2000)

Table 5Proximate analyses of selected bio-waste samples

(wt% of dry fuel)

Fuel sample Ash Volatile matter Fixed carbon

Beech wood bark 5.7 65.0 29.3Oak wood 0.5 77.6 21.9Wheat straw 13.7 66.3 21.4Olive husk 4.1 77.5 18.4Beech wood 0.5 82.5 17.0Spruce wood 1.7 80.2 18.1Corncob 1.1 87.4 11.5Tea waste 1.5 85.5 13.0Walnut shell 2.8 59.3 37.9Almond shell 3.3 74.0 22.7Sunflower shell 4.0 76.2 19.8Colza seed 6.5 78.1 15.4Pine one 1.0 77.3 21.7Cotton refuse 6.6 81.0 12.4Olive refuse 9.2 66.1 24.7

Sources: Demirbas (1997); Demirbas (1998b); Haykırı-Açma (2003).

titanium than biomass. Bio-waste has more silica, potassium, and some times calciumthan coal. The wood and woody materials tend to be low in nitrogen and ash content,while the agricultural materials can have high nitrogen (Tables 2 and 3) and ash contents(Tables 4 and 5).

Straw may have a high content of chlorine and potassium, elements which are veryundesirable in power plant fuels. Levels of K2O and Cl were found as 20.0% and 3.6% inash, respectively, in wheat straws (Table 6). A pretreatment process to remove potassium



Table 6Inorganic properties of typical fuel samples (wt% of ash)

Fuel sample Si2O Al2O2 TiO2 Fe2O3 CaO MgO Na2O K2O SO3 P2O5 Cl

Coal type 1 42.0 20.0 1.2 17.0 5.5 2.1 1.4 5.8 5.0 — —Coal type 2 59.7 19.8 2.1 8.3 2.1 1.8 0.8 2.1 2.0 0.2 —Coal type 3 51.5 22.6 2.0 14.9 3.3 0.9 1.0 2.0 3.5 0.2 —Red oak wood 49.0 9.5 — 8.5 17.5 1.1 0.5 9.5 2.6 1.8 0.8Wheat straw 48.0 3.5 — 0.5 3.7 1.8 14.5 20.0 1.9 3.5 3.6Walnut shell 23.1 2.4 0.1 1.5 16.6 13.4 1.0 32.8 2.2 6.2 0.1Almond shell 23.5 2.7 0.1 2.8 10.5 5.2 1.6 48.5 0.8 4.5 0.2Sunflower shell 29.3 2.9 0.1 2.1 15.8 6.1 1.5 35.6 1.3 4.8 0.2Olive husk 32.7 8.4 0.3 6.3 14.5 4.2 26.2 4.3 0.6 2.5 0.2Hazelnut shell 33.7 3.1 0.1 3.8 15.4 7.9 1.3 30.4 1.1 3.2 0.1

Source: Demirbas (1998b); Demirbas (2003).

from straw fuel may be based on pyrolysis followed by char wash. The straw is pyrolyzedat moderate temperatures at which the potassium is retained in the char. Potassium andresidual chlorine is extracted from the residual char by water (Jensen et al., 2001). Charand pyrolysis gases may then be used in a conventional boiler without problems due tothe high straw potassium content. To evaluate this pretreatment process, knowledge aboutthe char wash process is needed. Alkalis, when reacted with sulfates and chlorine, mayharm thermochemical conversion systems, fouling heat exchange surfaces, gas-turbineblades, and other power system components (Richard et al., 1998).

Combustion Properties of Bio-wastes

In general, combustion models of bio-waste can be classified as macroscopic or micro-scopic. The macroscopic properties of bio-wastes are given for macroscopic analysis,such as ultimate analysis, heating value, moisture content, particle size, bulk density, andash fusion temperature. Properties for microscopic analysis include thermal, chemicalkinetic, and mineral data. Fuel characteristics such as ultimate analysis, heating value,moisture content, particle size, bulk density, and ash fusion temperature of bio-wasteshave been reviewed (Bushnell et al., 1989). Fuel properties for the combustion analysisof bio-wastes can be conveniently grouped into physical, chemical, thermal, and mineralproperties.

Physical property values vary greatly and properties such as density, porosity, andinternal surface area are related to bio-waste fuels, whereas bulk density, particle size,and shape distribution are related to fuel preparation methods.

Important chemical properties for combustion are the ultimate analysis, proximateanalysis, analysis of pyrolysis products, higher heating value, heat of pyrolysis, heatingvalue of the volatiles, and heating value of the char.

Thermal property values such as specific heat, thermal conductivity, and emissivityvary with moisture content, temperature, and degree of thermal degradation by one orderof magnitude. Thermal degradation products of biomass consist of moisture, volatiles,char and ash. Volatiles are further subdivided into gases such as light hydrocarbons,carbon monoxide, carbon dioxide, hydrogen and moisture, and tars. The yields dependon the temperature and heating rate of pyrolysis. Some properties vary with species,location within the bio-waste, and growth conditions. Other properties depend on the


456 A. Demirbas

Figure 1. Burning profile of sunflower shell. Source: Haykırı-Açma (2003).

combustion environment. Where the properties are highly variable, the likely range ofthe property is given (Ragland et al., 1991).

Some Combustion Properties of Selected Biomass Samples

Non-isothermal and isothermal thermogravimetric techniques have commonly been usedto investigate the reactivities of carbonaceous materials (Küçükbayrak, 1993; Sentorunand Küçükbayrak, 1996; Yaman and Küçükbayrak, 1997). A plot of the rate of weightloss against temperature while burning a sample under oxidizing atmosphere is referredto as burning profile (Wagoner and Duzy, 1967). The burning profiles of sunflower shelland pine cone samples are shown in Figures 1 and 2. The first peak, observed on theburning profiles of the biomass samples, corresponds to their moisture release. After

Figure 2. Burning profile of pine cone. Source: Haykırı-Açma (2003).



releasing the moisture, some small losses in the mass of the sample occurred due todesorption of the adsorbed gases. A sudden loss in the mass of the samples started at thetemperatures between 450–500 K, representing the release of some volatiles and theirignition. In the rapid burning region, the rate of mass loss proceeded so rapidly thatit reached to its maximum value. Rapid loss of mass immediately slowed down at thetemperatures between 600 K and 700 K. After then, burning rate apparently decreasedand consequently some small losses in the mass of the sample continuously went on aslong as temperature was increased up to 1273 K, indicating the slow burning of the partlycarbonized residue. At the end of hold time at 1273 K, samples reached to the constantweight after given periods (Haykırı-Açma, 2003).

The most important characteristic temperatures of a burning profile are ignitiontemperature and peak temperature (Haykırı-Açma et al., 2001). The ignition temperaturecorresponds to the point at which the burning profile underwent a sudden rise. Theignition temperatures of samples were determined from their burning profiles. Table 7shows some combustion properties of selected bio-waste samples. As seen in Table 7, thetemperatures were determined as 475 K for sunflower shell, 463 K for colza seed, 475 Kfor pine cone, 467 K for cotton refuse and 473 K for olive refuses (Haykırı-Açma, 2003).In combustion, the point on the burning profile at which the rate of weight loss due to ismaximum known as peak temperature. The burning profile peak temperature is usuallytaken as a measure of the reactivity of the sample. These temperatures were found as573 K for sunflower shell, as 535 K for colza seed, as 565 K for pine cone, as 598 Kfor cotton refuses and as 537 K for olive refuse (Table 7). The rate of weight loss at theburning profile peak temperature is called the maximum combustion rate. The maximumcombustion rates of the sunflower shell, colza seed, pinecone, cotton refuse and oliverefuse was calculated as 5.5, 2.8, 5.2, 3.7, and 3.4 mg/min, respectively (Haykırı-Açma,2003).

The weight loss percentages of five different biomass samples versus temperatureare illustrated in Figure 3. From Figure 3, the weight losses of the samples increasedsharply above 500 K. The weight loss differences between olive refuse and other samplesstarted to increase above 620 K. Olive refuse has the lowest volatile matter content andthe highest ash content; in other words, olive refuse has the lowest combustible part.The weight loss percentages of the sunflower shell, colza seed, pinecone, cotton refuseand olive refuse at 1273 K were % 95.07, 91.05, 84.80, 86.74, and 78.69, respectively(Haykırı-Açma, 2003).

Table 7Some combustion properties of selected bio-waste samples

Ignition Maximum Peaktemperature combustion rate temperature

Sample (K) (mg/min) (K)

Sunflower shell 417 5.50 573Colza seed 423 2.80 535Pine cone 463 5.20 565Cotton refuse 423 3.70 598Olive refuse 438 3.40 537

Source: Haykırı-Açma (2003).


458 A. Demirbas

Figure 3. Weight loss percentages of different biomass samples versus temperature. Symbols forthe biomass samples: �: Sunflower shell, �: Colza seed, �: Pine cone, �: Cotton refuse, �: Oliverefuse. Source: Haykırı-Açma (2003).

Cofiring of Bio-waste and Coal Blends

Cofiring refers to the combustion of bio-waste and coal for power production. Cofiringbio-waste with coal, in comparison with single coal firing, helps reduce the total emissionsper unit energy produced. Coal and bio-waste fuels are quite different in composition.Cofiring bio-waste with coal has the capability to reduce both NOx and SOx levels fromexisting pulverized-coal fired power plants. Cofiring may also reduce fuel costs, minimizewaste and reduce soil and water pollution depending upon the chemical composition ofthe biomass used. The oldest of all fuels, bio-wastes, and the old original fuel of theindustrial revolution, coal, are key to this move to a new mission. Technical issues thatcan lead to doubt about of bio-waste cofiring with coal are being resolved through testingand experience (Hughes, 2000).

As such, the air pollution emissions accompanying the coal combustion are signif-icant. Among these pollutants are oxides of sulfur (SOx) and nitrogen (NOx), whichlead to acid rain and ozone depletion. In addition, greenhouse gas emissions (CO2, CH4,etc.) have become a global concern. Numerous methods have been proposed for reducinggaseous emissions of SO2, NOx and CO2 from fossil fuel combustion and for reducingcosts associated with these mitigation techniques.

Recent studies have shown that burning bio-waste with fossil fuels has a positiveimpact both on the environment and the economics of power generation (Sami et al.,2001; Hughes and Tillman, 1998; Harding and Adams, 2000). The emissions of SO2 andNOx were reduced in most cofiring of bio-waste and coal techniques.

Table 8 shows the physical properties and dry heating values of bio-waste and coalfuels. Bio-waste is much less dense and has significantly higher aspect ratios than coal.It is also much more difficult to reduce to small sizes. Bio-waste that is cofired withcoal can be as much as 1/4 inch, sometimes more. These physical properties give rise toseveral interesting combustion issues (Table 8).



Table 8Physical properties and dry heating values of

bio-waste and coal fuels

Property Biomass Coal

Fuel density (kg/m3) ∼500 ∼1300Particle size ∼3 mm ∼100 µmDry heating value (MJ/kg) 16 25


Table 9Ultimate analyses of typical fuel samples

C H N S Cl Ash O (diff.)

Coal 81.5 4.0 1.2 3.0 — 7.0 3.3Red oak wood 50.0 6.0 0.3 — — 1.3 42.4Wheat straw 41.8 5.5 0.7 — 1.5 15.0 35.5


Table 10Inorganic properties of typical fuel samples

Si2O Al2O2 TiO2 Fe2O3 CaO MgO Na2O K2O SO3 P2O5 Cl

Coal 42.0 20.0 1.2 17.0 5.5 2.1 1.4 5.8 5.0 — —Red oak wood 49.0 9.5 — 8.5 17.5 1.1 0.5 9.5 2.6 1.8 0.8Wheat straw 48.0 3.5 — 0.5 3.7 1.8 14.5 20.0 1.9 3.5 3.6


Table 9 shows the ultimate analysis results of typical fuel samples. The elemen-tal composition differences between coal and bio-waste are indicated by the ultimateanalyses (Table 9). Coal compositions vary with coal rank and geographic region, withtwo representative examples of a high-rank eastern coal and a low-rank western coalindicated here. It is difficult to establish a representative biomass due to large propertyvariations, but two examples are included here for comparison. The composition vari-ations among bio-waste fuels are larger than among coals, but as a class, biomass hassubstantially more oxygen and less carbon than coal. Less obviously, nitrogen, chlorine,and ash vary significantly among bio-waste fuels. These components are directly relatedto NOx emissions, corrosion, and ash deposition.

Table 10 shows the inorganic properties of typical fuel samples. The inorganic prop-erties of coal also differ significantly from bio-waste (Table 10). Inorganic componentsin coal vary by rank and geographic region. As a class, coal has more aluminum, iron,and titanium than bio-waste. Table 11 shows the proximate analysis results of typicalfuel samples. Bio-wastes have more silica, potassium, and some times calcium than coal.A proximate analysis (Table 11), as defined by ASTM, is the determination by prescribedmethods of moisture, volatile matter, fixed carbon (by difference) and ash.


460 A. Demirbas

Table 11Proximate analyses of typical fuel samples

Moisture Ash Volatile matter Fixed carbon(% of fuel) (% of dry fuel) (% of dry fuel) (% of dry fuel)

Coal 4.8 ± 2.6 8.3 ± 1.5 2.4 ± 5.9 43.6 ± 3.8Oak wood 6.5 ± 0.8 0.5 ± 0.1 78.6 ± 3.8 21.5 ± 2.1Wheat straw 7.3 ± 1. 12.7 ± 3.6 64.0 ± 5.1 23.4 ± 2.5


Pyrolysis of Bio-wastes

Pyrolysis is defined as the thermal destruction of organic materials in the absence ofoxygen. Pyrolysis is the basic thermochemical process for converting bio-waste into amore useful fuel (Demirbas, 1998a). Bio-waste is heated in the absence of oxygen,or partially combusted in a limited oxygen supply, to produce a hydrocarbon rich gasmixture, an oil-like liquid and a carbon rich solid residue.

In pyrolysis process, bio-waste is converted into liquid (bio-oil or bio-crude), charcoaland non-condensable gasses, acetic acid, acetone, and methanol by heating the bio-wasteto about 750 K in the absence of air. The process can be adjusted to favor charcoal,pyrolytic oil, gas, or methanol production with a 95.5% fuel-to-feed efficiency. Pyrolysiscan be used for the production of bio-oil if flash pyrolysis processes are used and arecurrently at pilot stage (EUREC Agency, 1996). Some problems in the conversion processand use of the oil need to be overcome; these include poor thermal stability and corrosivityof the oil. Upgrading by lowering the oxygen content and removing alkalis by means ofhydrogenation and catalytic cracking of the oil may be required for certain applications(Demirbas, 2000a).

As with coal, pyrolysis is a relatively slow chemical reaction occurring at low tem-peratures. The reaction mechanisms of biomass pyrolysis are complex but can be definedin five stages for wood (Demirbas, 2000b):

1. Moisture and some volatile loss.2. Breakdown of hemicellulose; emission of CO and CO2.3. Exothermic reaction causing the woody bio-waste temperature to rise from 525

to 625 K; emission of methane, hydrogen and ethane.4. External energy is now required to continue the process.5. Complete decomposition occurs.

Co-pyrolysis

Co-pyrolysis of carbonaceous material are complex functions of the experimental condi-tions under which the pyrolysis process proceeds. The most important factors that affectthe yield and composition of the volatile fraction liberated are: coal rank or biomass type,maceral composition, particle size, temperature (i.e., temperature-time history), heatingrate, atmosphere, pressure and reactor configuration. Co-pyrolysis of carbonaceous ma-terial divided into a hydrogen-rich volatile fraction, consisting of gases, vapors, andtar-components, and a carbon-rich solid residue. The pyrolysis process consists of a verycomplex set of reactions involving the formation of radicals. The radicals are very reactive



and can undergo secondary reactions like cracking and carbon deposition, both insideand outside the particle. Stabilization of a radical, primarily via hydrogen addition, leadsto a volatile component. The evolution of tar is controlled by mass transport in which thetar molecules evaporate into the light gas species and are carried out the particle at ratesproportional to their vapor pressure and the volume of light gas. High pressure reducesthe volume of light gases and hence reduces the yield of heavy molecules with lowvapor pressure. Polymerization and condensation reactions, occurring via recombinationof both volatile and non-volatile radical components, result in the formation of the solidchar particle. High pyrolysis heating rates produced chars with large macroporosites,more open pore structures, and larger macropore surface areas. Tar formation increaseswith increasing heating rate. The co-pyrolysis of the lignite sample and the bio-wastesample that resulted was the addition of lignite gave a slight synergistic effect in terms ofincreasing the oil yield from the hazelnut shell and also reduced the molecular weightsof the resultant oil considerably.

Conclusion

Biomass has a significantly lower heating value than most coal. This is in part dueto the generally higher moisture content and in part due to the high oxygen content.It was observed that the investigated bio-waste materials showed different combustioncharacteristics. The structural, proximate and ultimate analyses results of bio-wastes differconsiderably.

Pyrolysis produces energy fuels with high fuel-to-feed ratios, making it the mostefficient process for bio-waste conversion, and the method most capable of competingand eventually replacing non-renewable fossil fuel resources. The conversion of bio-wasteto crude oil can have an efficiency of up to 70% for flash pyrolysis processes. The so-called biocrude can be used in engines and turbines. Its use as feedstock for refineriesis also being considered. Some interesting trends have been obtained, especially withrespect to the effect of net heating rate and temperature on the pyrolysis time. Thereported literature results indicate a decrease in final pyrolysis time as the net heatingrate or temperature is increased (Rezzoug and Caport, 2003).

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Fuel and Combustion Properties of Bio-Wastes