Pyrolisis and Gasification of Food Waste-syngas Characteristics and Char Gasification Kinects

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Pyrolysis and gasication of food waste: Syngas characteristicsand char gasication kinetics

I.I. Ahmed * , A.K. GuptaThe Combustion Laboratory, University of Maryland, Department of Mechanical Engineering, College Park, MD 20742, United States

a r t i c l e i n f o

Article history:Received 4 May 2009Received in revised form 12 August 2009Accepted 14 August 2009Available online 13 September 2009

Keywords:Food waste gasicationChar gasication kineticsCatalytic effect of ashCompensation effect

a b s t r a c t

Characteristics of syngas from the pyrolysis and gasication of food waste has been investigated. Charac-teristic differences in syngas properties and overall yields from pyrolysis and gasication were deter-mined at two distinct high temperatures of 800 and 900 C. Pyrolysis and gasication behavior wereevaluated in terms of syngas ow rate, hydrogen ow rate, output power, total syngas yield, total hydro-gen yield, total energy yield, and apparent thermal efciency. Gasication was more benecial than pyro-lysis based on investigated criteria, but longer time was needed to nish the gasication process. Longertime of gasication is attributed to slow reactions between the residual char and gasifying agent. Conse-quently, the char gasication kinetics was investigated. Inorganic constituents of food char were found tohave a catalytic effect. Char reactivity increased with increased degree of conversion. In the conversionrange from 0.1 to 0.9 the increase in reactivity was accompanied by an increase in pre-exponential factor,which suggested an increase in gasifying agent adsorption rate to char surface. However, in the conver-sion range from 0.93 to 0.98 the increase in reactivity was accompanied by a decrease in activationenergy. A compensation effect was observed in this range of conversion of 0.930.98.

2009 Elsevier Ltd. All rights reserved.

1. Introduction

Dumping food waste in a landll causes environmental prob-lems. By volume, the dumped landll waste causes the largest con-tribution to methane gas production [1]. It causes odor as itdecomposes to cause public annoyance in addition to forminggerms, and attracting ies and vermin. Another serious problemof food wastes is the generation of landll leachate. Landll leach-ate is liquid that leaks from the landll and enters the environ-ment. Once it enters the environment the leachate is at risk formixing groundwater near the site which then transports to somedistances. Furthermore it has the potential to add biological oxy-gen demand (BOD) to the groundwater. BOD measures the rateof oxygen uptake by micro-organisms in a sample of water at atemperature of 20 C and over an elapsed period of ve days inthe dark.

Food wastes have high energy content. Consequently, it offers agood potential for feed stock for gasication in power plants. Foodwaste gasication helps to solve two major problems at the sametime. Gasication of food waste reduces landll problems andhelps to recover energy at the same time. Characteristics of foodwaste gasication and pyrolysis have been investigated in termsof syngas yield, hydrogen yield, energy yield and apparent thermal

efciency. The results show that food wastes offers a good poten-tial for thermal treatment of the waste with the specic aim of power generation.

The average proximate analysis of food wastes is 80% volatilematter, 15% xed carbon, and 5% ash. The volatile matter can beeasily destructed in a relatively short period of time, extendingfrom 8 to 12 min at reactor temperatures from 700 to 1000 C. En-ergy recovery from volatile components in food wastes can berecovered using a simple pyrolysis process. However, in order toconsume the residual xed carbon after the pyrolysis, the samplemust undergo a gasication process. Gasication of a food wastesample includes a pyrolysis part and a char gasication part. Chargasication reactions are slower than that of pyrolysis and conse-quently, is the rate limiting step in the overall gasication process.The ash present in the sample does not react with the gasifyingagent. The ash can be collected after cooling and cleaning the syn-gas, and then recycled for its further use in industrial processes.

Since the char gasication process is the rate limiting step, it isimportant to quantify the kinetic parameters of char gasication.Char gasication has been investigated by a large number of researchers. Some of the important parameters investigated in-clude the origin of the char sample, gasifying agent, total pressure,variation of partial pressure of gasifying agents, geometric changesof the sample during gasication, and catalyzed char gasication.One of the most important parameters which have been investi-gated is the catalytic effect of ash content on char gasication.

0306-2619/$ - see front matter 2009 Elsevier Ltd. All rights reserved.doi: 10.1016/j.apenergy.2009.08.032

* Corresponding author. Tel.: +1 301 405 5311.E-mail address: [email protected] (I.I. Ahmed).

Applied Energy 87 (2010) 101108

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Applied Energy

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Catalytic effect of ash on char gasication has been investigated forseveral biomass samples. Kinetics of food waste char gasicationdid not draw the attention of researchers in this eld. Since foodwaste has considerable ash content, its catalytic effect must beinvestigated. Results show that ash has a positive effect on charreactivity. Kinetic parameters have been calculated for differentdegrees of conversion. Values of kinetic parameters were found

to be affected by the degree of conversion. Quantitative analysisof kinetic parameters dependency on sample conversion has beenexamined here. Quantifying the catalytic effect of ash on charkinetics will help assist improving gasiers design with better con-trolled parameters for input and operational conditions, such as,operating temperature, gasication condition, gasifying supportmedia, rate of feedstock to the gasier. In conjunction with uiddynamic simulations, improved expressions for reaction rates willhelp provide better estimate on char particles residence time in thereactor by providing an accurate conversion-time relationship.Consequently, for a desired feed rate of feedstock into the reactorand for known gasier operational conditions an accurate reactiv-ity expression will lead to a close estimate of the gasier size andconguration. If a constant reactivity value is used in reacting owsimulations for feedstock having time dependant reactivity, mis-leading information on char particles residence time will be ob-tained. This will consequently result in a departure gasier sizefrom the true design size and conguration. For example, if a con-stant reactivity value is used for chars having ash catalytic effect,such as the case examined here, the designed gasier size will beover estimated since the reactivity of char was fond to increasewith the degree of conversion.

2. Background

Tancredi et al. [2] investigated the catalytic effect of ash on chargasication for eucalyptus wood chars. The ash content in char wasof the order of 1.45% on mass basis. The reactivity of the char in-creases monotonically with conversion. At low and intermediateconversion, it can be attributed to the increase in surface area asgasication proceeds. At high conversion levels a steeper increasein reactivity has been observed, which cannot be explained bythe development of surface area. This region of the reactivity-conversion curves can be better explained as the result of an in-crease in catalytic effect of the metallic constituents (mainly Naand K) present as inorganic matter in the chars. Here CO 2 was usedas the gasifying agent. Activation energies determined were foundto vary within a narrow range of 230257 kJ/mol. Arrhenius plotsshowed parallel lines for different degrees of conversion. Parallelline of Arrhenius plot indicates similar activation energies. The in-crease in reactivity was mainly due to an increase in pre-exponen-tial factor. In a similar study by Montesinos et al. [3], steamgasication and CO 2 gasication of grape fruit skin char were

investigated. They also observed an increase in reactivity at highvalues of conversion. However, a different trend of activation ener-gies values was observed; in the case of CO 2 gasication, as theconversion increased, a decrease in activation energy was ob-served. On the other hand an increase in activation energy was ob-served in case of steam gasication. This increase in activationenergy was also, observed by Marsh et al. [4] . The decrease in acti-vation energy values in the case of CO 2 gasication was accompa-nied by a decrease in pre-exponential factor as well. This behavioris called the compensation effect [5] . Montesinos et al. obtained avalue of isokinetic temperature of 1150 K. The isokinetic tempera-ture is the temperature at which all reactivities are equal for differ-ent conversions. An isokinetic temperature of 1449 K was obtainedby Dhupe et al. [6] for CO2 gasication using catalyzed sodium lig-

nosulfonate. Feistel et al. [7] found this temperature to be 1425 K,obtained using potassium-catalyzed steam gasication.

Gokarn and Muhlen [8] investigated the gasication of charusing two types of catalysts and a mixture of both the catalysts.The investigated catalysts were calcium lignosulfonate and sodiumlignosulfonate. The carbon matrix was saturated by calcium ligno-sulfonate at 10% by weight. However, this saturation did not affectthe catalytic effect of sodium lignosulfonate in the mixed catalyticsystem.

Li and Cheng [9] investigated the catalytic gasication of coalchar using Na 2CO3 and K2CO3 as catalysts. Effect of catalyst loadingwas investigated. Increase in catalysts loading was found to beeffective until 25% by weight of K 2CO3 loading and 20% by weightof Na 2CO3 loading. Further increase in catalysts loading resulted ina decrease in char reactivity. The results of reactivity versus con-version plots showed an increase in char reactivity initially. Fur-ther increase in conversion showed a decrease in char reactivity.They attributed this decrease to the char pores blocking the cata-lyst at high degrees of conversion. A compensation effect was ob-served and an isokinetic temperature of 1289 C for Na2CO3 and1466 C for K2CO3 were obtained.

Food wastes, especially which have high percentage of vegeta-ble oil and animal fat, provide a good potential for production of liquid fuels though transesterication. Transesterication is theprocess of exchanging the organic group R 00of an ester with the or-ganic group R 0 of an alcohol. The process is widely used to producebiodiesel fuels from vegetable oils and animal fats. The process isoften catalyzed by an acid or a base.

Other than acid or base catalysts, enzyme or heterogeneous cat-alysts might be used as well. Among the mentioned catalysts, alkalicatalysts are more effective. However, if the oil has high free fattyacid (FFA) content, higher than 3% (approximately), acid catalyzedtransesterication is used rather than a base catalyst [10,11] .

Drawbacks of alkaline or acid catalysis process include: (a) it re-quires considerable amounts of energy; (b) separation of glycerol isdifcult; (c) the alkaline catalyst has to be removed from the prod-uct, free fatty acid and water interfere with the reaction. On theother hand, enzymatic catalysts have the advantage of effectivelyacting as catalyst in the transesterication of triglycerides in eitheraqueous or non-aqueous systems. Besides, free fatty acids con-tained in waste oils and fats can be completely converted to alkylesters. However, production cost of enzymatic catalysts is signi-cantly higher than that of an alkaline catalyst [10] .

It is to be noted that the conversion rate increases with reactiontime and temperature. At xed reaction time the increase in tem-perature provides the same effect of increased conversion [10] .

Al-Widyan and Al-Shyoukh [11] conducted an experimentalinvestigation of the transesterication of waste palm oil into bio-diesel fuel. Acidic catalyst has been used due to the high free fattyacid content of 1015%. Effect of catalyst concentration and alcohollevels, amongst other parameters, has been investigated.

The results show that at any given catalyst concentration and

reactor temperature, specic gravity decreases exponentially withtime and ends up with an asymptotic value. However, higher cat-alyst concentrations, results in obtaining the terminal value of spe-cic gravity in much shorter times. Higher the excess alcohol levelsconsistently led to desirable lower values of specic gravitythroughout the reaction time.

He et al. [12] investigated the continuous production of biodie-sel fuel from vegetable oil using supercritical methanol process.Reactor temperature, pressure, alcohol to oil ratio and residencetime was varied in order to determine conditions for maximumproduction rate. The optimal reaction condition under constantreaction temperature process was found to be 40:1 molar ratio of alcohol to oil, 25 min of residence time, 35 MPa and 310 C. Atthese conditions, the maximum production yield was 77% for a

constant reaction temperature. Side reactions of unsaturated fattyacid methyl esters (FAME) were observed when reaction tempera-

102 I.I. Ahmed, A.K. Gupta/ Applied Energy 87 (2010) 101108


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ture exceeded 300 C, which led to a loss in unsaturated fatty acidmethyl esters (FAME). They proposed a new methodology to avoidthe loss of FAME at high temperatures, through gradual heating of the reactants along the reactor to a high temperature. With thenew reaction technology, the methyl esters yield reached morethan 96%.

3. Experimental

Fig. 1 shows a photograph of the laboratory scale experimentalfacility used to examine the pyrolysis and gasication of foodwastes. Steam is generated from the stoichiometric combustionof hydrogen and oxygen. Steam generated is then introduced intothe superheater section to form the gasifying agent at the desiredcondition. The temperature of the gasifying agent heater is keptat the same temperature as that of the main reactor in which sam-ple material was allowed to undergo gasication. Steam is thenintroduced into the main reaction chamber that contained thehydrocarbon sample. The syngas owing out from the main reac-tion chamber is sub-divided into two paths; one passes to the sam-pling line while the other is passed through the exhaust system.

The bypass line has a non-return valve and a ow meter to assurethe desired unidirectional ow out from the reactor. The syngassample is then introduced to a condenser followed by a low pres-sure lter and a moister absorber (anhydrous calcium sulfate). Thisprocedure assured that the sample is dry prior to its introductioninto a gas analyzer. The ltered and dried syngas is then analyzedusing a GC or a mass spectrometer.

3.1. Syngas characteristics experiments

The syngas characteristics were determined using a Micro gaschromatograph (GC). The syngas ow is introduced to a threeway valve that allowed for either lling sampling bottles or intro-ducing the syngas directly to the micro GC for detailed analysis of

the gas. The sampling bottles are used only when short samplingintervals are needed (0.51 min). Direct sampling and analysiswere carried out by the GC when longer sampling time intervalswere required.

A constant ow rate of inert gas (nitrogen) is introduced withthe oxygen ow, in case of gasication. However, only nitrogen isused for all experiments carried out during pyrolysis. The nitrogen

is detected by the GC and used to determine the ow rate of differ-ent syngas species by comparing the species mole fraction to thatof the nitrogen mole fraction.

3.1.1. Experimental conditions for syngas characteristics

Sample: 35 g of food waste.

Reactor temperature: 800 and 900 C. Inert gas: 2.6 LPM of nitrogen. Gasifying agent: 8 g/min of steam.

3.2. Char kinetics experiments

Char-steam reactions are slower than that of pyrolysis reac-tions; consequently it is the rate determining step in the overallgasication process.

3.2.1. Char preparationFor char preparation, both the main and gasication condition-

ing reactors were heated up to 900 C. A continuous ow of argonwas introduced to both reactors during and after heating. Then a

sample was introduced to the main reactor through a fast connec-tion located at the reactor exit. The sample was kept at this tem-perature of 900 C for an hour. In order to insure that thepyrolysis process has been completed with the sample, a sampleof the exit gases was analyzed. The charring process is consideredcomplete when the analyzed exhaust contained only Argon in thestream ow.

3.2.2. Reactivity determination proceduresIn order to examine the catalytic effect of ash the char gasica-

tion a mass spectrometer was used. Data from the mass spectrom-eter was used to calculate the reactivity of carbon in the samplechar. Carbon in the sample will evolve in the form of carbon-mon-oxide through the water gas reaction (C + H 2O => CO + H2) and in

the form of carbon dioxide through the water gas shift reactionCO H2 O () CO2 H2 . Consequently, monitoring the evolutionof CO and CO2 ow rate helps to calculate the carbon consumptionrate from the sample. Helium was used as an inert gas in the reac-tivity experiments to avoid the confusion between CO and N 2 inthe mass spectrometer. The mass spectrometer was used to mea-sure the ow rate of CO and CO 2 obtained by relating the partial

Fig. 1. A photograph of the experimental facility.

I.I. Ahmed, A.K. Gupta / Applied Energy 87 (2010) 101108 103


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pressure of CO and CO 2 with the partial pressure of Helium. For thispurpose the ow rate of Helium was kept constant at a known owrate. From the carbon ow rate-time, relationship one can calculatethe total yield of carbon and instantaneous sample mass inside thereactor at time ( t ).

3.2.3. Experimental conditions for kinetics experiments

Sample: 35 g of food waste. Inert gas for charring: 6.4 g/min of argon. Charring temperature: 900 C. Charring period: 1 h. Reactor temperature: 750, 800, 850 and 900 C. Gasifying agent: 8 g/min of steam. Trace gas: 1.1 g/min of helium.

4. Results and discussion

The characteristic of syngas from food waste pyrolysis and gas-ication have been investigated. Food waste is a char-based sam-ple. Results from char-based samples (samples containingvolatile matter and char, such as paper [13] , cardboard [14,15] ,woodchips and food waste) follow, qualitatively similar trend. Syn-gas is characterized by a high ow rate initially, due to pyrolysis,and then followed by a small ow rate which lasts for longer per-iod, which is due to char gasication. The progress of the foodwaste sample through pyrolysis and gasication processes isshown in Fig. 2. Syngas characteristics may differ from a quantita-tive point of view. The differences and similarities between foodwaste and previously investigated samples is presented in the rst

section of the discussion. The second part is concerned about thekinetics of char gasication from food waste with specic focuson the catalytic effect of ash.

4.1. Syngas characteristics

Fig. 3 shows the evolution of syngas ow rate with time at two

distinctly different high temperatures of 800 and 900

C. Syngasow rate starts with a high value which is attributed to the rapiddevolatilization of volatile components from the sample. This isthen followed by sudden decrease in ow rate, and nally followedby a long period of low ow rate. The low ow rate period is attrib-uted to the char gasication. Syngas ow rate due to char gasica-tion decreases monotonically until char is consumed and only ashis left over. The area conned between the pyrolysis curve and gas-ication curve represents the syngas yield from the char gasica-tion. The increase in reactor temperature increased syngas owrate and decreased the gasication period. The syngas ow ratefrom paper at the same temperatures was higher in terms of max-imum value of ow rate. The maximum ow rate from paper gas-ication [13] was 5.5 g/min and 10 g/min at temperatures of 800and 900 C, respectively. However the maximum ow rate fromfood waste gasication was found to be 4 and 7.6 g/min at temper-ature of 800 and 900 C, respectively. The gasication period forpaper was 50 and 18 min at 800 and 900 C. However, gasicationperiod for the food waste was 105 and 38 min at same temperatureof 800 and 900 C, respectively. The experimental conditions forthe paper and food waste gasication were kept the same.

Fig. 4 shows the evolutionary of hydrogen ow rate from foodwaste gasication and pyrolysis at two different temperatures of

Pyrolysis(~15 min @ 900 oC)

Char gasification(~35 min @ 900 oC)

Gasification(~38 min @ 900 oC)

Char + Ash(~20.75%)

Ash (~5.75%)Food waste(Simulated as dog food)

(~35 grams)

Fig. 2. Progress of food waste sample through pyrolysis and gasication.

0

1

2

3

4

5

6

7

8

0 15 30 45 60 75 90 105Time (min)

g / m i n

Gasification at 800C

Pyrolysis at 800C

0

1

2

3

4

5

6

7

8

0 10 20 30 40 50Time (min)

g / m i n


Pyrolysis at 900C

Fig. 3. Syngas ow rate from gasication and pyrolysis at 800 C (left) and 900 C (right).



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800 and 900 C. Gasication yields more ow rate of hydrogenthan pyrolysis. This is a direct result of using steam as the gasifyingagent. Reactions resulting in this increase include water gas reac-tion, water gas shift reaction and steam tar reforming. The increasein temperature accelerates hydrogen evolution for both pyrolysisand gasication; however the total yield remains the same, seeFig. 7. Peak values of hydrogen ow rate from paper gasication[13] were 0.077 and 0.175 g/min at 800 and 900 C, respectively,which are almost double the values obtained from the gasicationof food waste.

Fig. 5 shows the output power form food waste gasication andpyrolysis at 800 and 900 C. One can see form Fig. 5 that initiallyoutput power is totally attributed to pyrolysis. The area connedbetween the pyrolysis and gasication curves represents the extra

energy gained from the gasication of char.Figs. 6 and 7 show the total syngas and hydrogen yield, respec-

tively, from food waste during pyrolysis and gasication at 800 and900 C. Hydrogen yield from food waste was 1.6 g at both thetemperatures. The total hydrogen yield from paper gasication[13] was about the same value (1.5 and 1.6 g) at reactor tempera-ture 800 and 900 C.

Figs. 8 and 9 show the energy yield and apparent thermal ef-ciency, respectively. The apparent thermal efciency was calcu-lated based on a heating value of 6528 Btu/lb [16] . The increasein temperature increased energy yield and apparent thermal ef-ciency for both pyrolysis and gasication. These results are similarto that found from gasication and pyrolysis of paper [13] . How-ever, food waste yields more energy and better apparent thermal

efciency as compared to paper. Energy yield and apparent ther-mal efciency from paper gasication were 345 and 0.68 at

800 C and 405 and 0.84 at 900 C. On the other hand, energy yieldand apparent thermal efciency from food waste gasication were425 and 0.8 at 800 C and 468 and 0.9 at 900 C.

4.2. Char gasication kinetics

The char gasication reaction is slowest in the overall gasica-tion process. So, it is important to quantify how fast this process is.The main constituent of char is carbon and main reaction in the

char gasication process is the water gas reaction C H2 O >CO H2 . The carbon-monoxide may undergo a water gas shift

0

0.02

0.04

0.06

0.08

0 15 30 45 60 75 90 105

Time (min)

g / m i n


Pyrolysis at 800C

0

0.02

0.04

0.06

0.08

0 10 20 30 40 50

Time (min)

g / m i n


Pyrolysis at 900C

Fig. 4. Hydrogen ow rate with time from gasication and pyrolysis at 800 C (left) and 900 C (right).

0

20

40

60

80

100

120

140

0 15 30 45 60 75 90 105

Time (min)

O u

t p u

t p o w e r (

k J / m i n )


pyrolysis at 800C

0

20

40

60

80

100

120

140

0 10 20 30 40 50

Time (min)

O u

t p u

t p o w e r

( k J / m i n )


Pyrolysis at 900C

Fig. 5. Output power from gasication and pyrolysis at 800 C (left) and 900 C (right).

Syngas yield (g)

0

5

10

15

20

25

30

35

800 900

Temperature (o

C)

GasificationPyrolysis

Fig. 6. Syngas yield from gasication and pyrolysis of food waste.

I.I. Ahmed, A.K. Gupta / Applied Energy 87 (2010) 101108 105


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reaction CO H2 O () CO2 H2 . Therefore, the carbon reactivityin the char can be inferred from the molar ow rate of carbon-monoxide and carbon dioxide. A mass spectrometer has been usedto calculate the CO 2 and CO ow rate. From the CO and CO 2 owrate, the total carbon yield and carbon conversion history can bedetermined. Fig. 10 shows the carbon conversion versus time attemperatures of 750, 800, 850 and 900 C. The plots are character-

ized by an initial constant slop. The results show that lower is thetemperature longer is the conversion time.

Carbon reactivity was dened as r 1m dmdt , where m is the massat time ( t ). History of carbon mass inside the reactor was calculatedfrom the carbon ow rate history. While, dmdt is the carbon mass owrate measured by the mass spectrometer. Fig. 11 shows the changeof carbon reactivity with conversion. Carbon reactivity increasesmonotonically with conversion until conversion value of 0.7 fol-lowed by a steeper increase in reactivity. The steepness at lowertemperature plots may not be observed because of the r valuesscale. The food waste char contains 27.7% ash, most of which issalt. The inorganic components in char are the main reason of reac-

H2 yield (g)

0

0.2

0.40.6

0.8

1

1.2

1.4

1.6

1.8

800 900

Temperature ( oC)


Fig. 7. Hydrogen yield from gasication and pyrolysis of food waste.

Energy yield (kJ)

0

100

200

300

400

500

800 900

Temperature ( oC)

Gasification

Pyrolysis

Fig. 8. Energy yield from food waste during gasication and pyrolysis.

Apparent thermal efficiency

0

0.2

0.4

0.6

0.8

1

800 900Temperature ( oC)


Fig. 9. Apparent thermal efciency of food waste during gasication and pyrolysis.

00.10.20.3

0.40.50.60.70.80.9

1

0 30 60 90 120 150 180 210Time (min)

C a r

b o n c o n v e r s

i o n

900C850C800C750C

Fig. 10. Conversion versus time for temperatures 750, 800, 850 and 900 C.

0.00E+00

5.00E-02

1.00E-01

1.50E-01

2.00E-01

2.50E-01

0 0.1 0 . 2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1Carbon conversion

r ( m i n - 1 )

900C

850C800C750C

Fig. 11. Char reactivity versus conversion for temperatures 750, 800, 850 and900 C.

-5

-4.5

-4

-3.5

-3

-2.5

-2

-1.5

0.00085 0.0009 0.00095 0.001

1/T (K -1)

l n ( r )

X = 0.1 X = 0.2X = 0.3 X = 0.4X = 0.5 X = 0.6X = 0.7 X = 0.8X = 0.9

Fig. 12. Arrhenius plot at different degrees of conversion from 0.1 to 0.9.



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validate the presence of correct compensation effect, the linear plotof ln(A) versus E should have a slop of 1/ RT iso, were T iso is the isoki-netic temperature and an intercept of ln(r iso), where r iso is the isoki-netic reactivity. ln ( A) versus E is shown in Fig. 15. From the slopvalue in Fig. 15, the isokinetic temperature should be 991 Cand ln(r iso) should be 0.801. T iso and ln(r iso) values obtained fromFig. 14 are 1001 C and 0.72 respectively, which is close to thevalues obtained from Fig. 15. So, in summary, compensation effectis observed by the end of conversion but was not observed beforeconversion degree of 0.9.

5. Conclusions

Gasication yielded enhanced production of syngas, hydrogenand energy as that obtained from pyrolysis. However the time re-quired for gasication is more as compared to pyrolysis. As com-pared to paper gasication at the same conditions, food wasteneeded more time to complete the gasication process. Inorganicconstituents in food char were found to have a catalytic effect. Charreactivity increased with degree of conversion. In the conversionrange from 0.1 to 0.9 the increase in reactivity was accompaniedby an increase in pre-exponential factor, suggesting an increase

in gasifying agent adsorption rate to char surface. However, inthe conversion range from 0.93 to 0.98 the increase in reactivitywas accompanied by a decrease in activation energy. A compensa-tion effect was observed in this range of conversion, from 0.93 to0.98. Isokinetic temperature obtained from Arrhenius plots for X from 0.93 to 0.98 was 1001 C.

Acknowledgment

This research was supported by the ONR and is support is grate-fully acknowledged.

References

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[12] He H, Wang T, Zhu S. Continuous production of biodiesel fuel from vegetableoil using supercritical methanol process. Fuel 2007;86:4427.

[13] Ahmed I, Gupta AK. Syngas yield during pyrolysis and steam gasication of paper. Appl Energy 2009;86:181321.

[14] Ahmed I, Gupta AK. Evolution of syngas from cardboard gasication. ApplEnergy 2009;86:173240.

[15] Ahmed I, Gupta AK. Characteristics of cardboard and paper gasication withCO2. Appl Energy 2009;86:262634.

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ln(A) = 0.000095*E - 0.801003

-2-101234

56789

101112

0 25 50 75 100 125ThousandsE (kJ/kmol)

l n ( A )

Fig. 15. ln( A) versus E for the conversion from 0.93 to 0.98.

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Pyrolisis and Gasification of Food Waste-syngas Characteristics and Char Gasification Kinects

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