Research Article Computer Simulation of the Mass and Energy Balance … · 2019. 7. 31. · Research Article Computer Simulation of the Mass and Energy Balance during Gasification

Research ArticleComputer Simulation of the Mass and Energy Balance duringGasification of Sugarcane Bagasse

Anthony Anukam12 Sampson Mamphweli1 Edson Meyer1 and Omobola Okoh2

1 Fort Hare Institute of Technology University of Fort Hare Private bag X1314 Alice 5700 South Africa2Department of Chemistry University of Fort Hare Private bag X1314 Alice 5700 South Africa

Correspondence should be addressed to Anthony Anukam aanukamufhacza

Received 28 August 2013 Revised 13 January 2014 Accepted 27 January 2014 Published 16 March 2014

Academic Editor Ching Yuan Chang

Copyright copy 2014 Anthony Anukam et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

This paper investigated the mass and energy balance of the gasification of sugarcane bagasse using computer simulation The keyparameters and gasifier operating conditions were investigated in order to establish their impact on gas volume and conversionefficiency of the gasification process The heating value of sugarcane bagasse was measured and found to be 178MJkg which wasused during calculation of the conversion efficiency of the gasification process Fuel properties and gasifier design parameterswere found to have an impact on conversion efficiency of the gasification process of sugarcane bagasse The moisture content ofsugarcane bagasse was varied by 114 15 and 25 respectively Optimum conversion efficiency was achieved at low moisturecontent (114) after computer simulation of the gasification process The volume of carbon monoxide increased at low moisturecontent It was also found that maximum conversion efficiency was achieved at reduced particle diameter (6 cm) and at reducedthroat diameter (10 cm) and throat angle (25∘) respectively after these parameters were varied Temperature of input air was alsofound to have an impact on the conversion efficiency of the gasification process as conversion efficiency increased slightly withincreasing temperature of input air

1 Introduction

Sugarcane bagasse is the residue that results from the crush-ing of sugarcane It is generated in large quantities duringthe processing of sugarcane in the sugar industry Sugarcanebagasse is mainly burnt inefficiently in boilers that providethe heating for the sugar industry thus the renewed interestin its efficient utilization through an efficient means ofconversion such as gasification

The gasification technology remains an old technologythat has today reached an advanced stage and hence there is ahuge expectation from user industries for its application [1]Commercial fuels and chemicals have been produced in thepast fromgasification technologies and current developmentsshow that the use of gasification technologies to producesyngas and other chemicals will continue to be on the rise[2] For a country like South Africa with its vast agricultural

residues such as sugarcane bagasse it is imperative to have anefficient power generation system Gasification of sugarcanebagasse is a carbon dioxide emission neutral source of energyand also has the advantage of syngas production Anotheradvantage of gasification of sugarcane bagasse is the potentialto reduce storage and transport cost since the sugarcanebagasse can be used in the same place where is it generatedGasification is an alternative energy conversion technologythat converts biomass materials into energy This processis achieved by reacting the material at high temperaturesusually above 1000∘C in the presence of a limited amountof oxygen andor steam The resulting gas mixture is calledproducer gas most commonly referred to as syngas witha heating value of 4ndash6MJkg The syngas when clean canbe used in stationary gas turbines and electricity generationor as a building block for a variety of chemicals and fuelAbout 70ndash85 of the carbon in the feedstock is converted

Hindawi Publishing CorporationJournal of EnergyVolume 2014 Article ID 713054 9 pageshttpdxdoiorg1011552014713054

2 Journal of Energy

into the syngas and the ratio of carbonmonoxide to hydrogenproduced depends on the hydrogen and carbon contentof the feedstock and the type of gasifier used The syngasproduced differs from natural gas in terms of heating valuecomposition and flammability characteristics

In the gasifier the biomass material undergoes severaldifferent reaction processes including drying distillationoxidation and reduction reaction processes These reactionsare as follows [3]

2C +O2997888rarr 2CO (partial oxidation) (1)

C +O2997888rarr CO

2(complete oxidation) (2)

C + 2H2997888rarr CH

4(hydrogasification reaction) (3)

CO +H2O 997888rarr CO

2+H2(water-gas shift reaction)

(4)

CH4+H2O 997888rarr CO + 3H

2(steam reforming reaction)

(5)

C +H2O 997888rarr CO +H

2(water-gas reaction) (6)

C + CO2997888rarr 2CO (Boudourd reaction) (7)

Equations (6) and (7) are the main reduction reactions andbeing endothermic have the capability to reduce the tempera-ture of the syngasThe selection of gasification systems designand performance are influenced by the thermochemicalcharacteristics of the biomass to be converted [4] Howeverit is necessary to use fast and quick simulation techniquesin order to efficiently utilize the energy resources The keyparameters that affect the performance of the gasifier aremoisture content throat angle and throat diameter as wellas diameter of the material under study and temperature ofinput air [5] Little is known about these parameters and theirimpact on conversion efficiency of the gasification processThese parameters are the most critical operating parametersthat affect gasifier performance and are useful empirical toolsfor scale-up designs of gasifiers [5 6]

11 Principle of Operation of the DowndraftGasifier There aremany types of gasifiers used in the gasification of biomassmaterials However the choice of gasifier type depends onthe type of material to be gasified and end use of the gasproduced Fixed-bed downdraft or cocurrent gasifiers arerelatively simpler to use they are reliable and amenable togasifier different kinds of feedstock andoffer lower particulateconcentration in product gases and can achieve higherefficiencies than other gasifiers The downdraft gasifiers alsohave the advantage of the production of a gas with low tarcontent Because of uneven heat distribution in the downdraftgasifier it is only limited to small scale applications [7]However scale-up of the downdraft gasifier is possible ifheat could be evenly distributed and cold spots avoided inthe combustion zone of the gasifier since the generation ofheat and the oxidation of condensable products from thedistillation zone take place in the combustion zone Figure 1presents the main features of the downdraft gasifier

Feed

Drying zone

Distillation zone

Hearth zone

Air

Reduction zone

Ash grate

Ash zone

Air

Gas out

Figure 1 Fixed-bed downdraft gasifier or cocurrent gasifier [Adopt-ed from FAO Corporate Document Repository 1986] [30]

The biomass material is fed into the gasifier from thetop of the gasifier and dried in the drying zone Pyrolysis ofthe biomass takes place in the distillation zone where charand pyrolysis gases are formed The drying zone and thedistillation zone are mainly heated by radiation heat from thehearth (combustion) zone In this zone carbon dioxide andwater vapour are formed A part of the char formed in thedistillation zone is also burnt in the hearth zone Pyrolysisgases also pass through this zone and are burnt as well Theextent to which the pyrolysis gases are actually burnt dependson gasifier design the biomass feedstock and the skills ofthe operator After oxidation of the feedstock in the hearthzone the char left in the distillation zone and the combustionproducts (carbon dioxide and water vapour) in the hearthzone pass to the reduction zonewhereCOandH

2are formed

Traces of methane and other noncombustible gases are alsoformed in this zone

2 Materials and Method

21 Proximate and Ultimate Analysis The main by-productof the sugar industry in South Africa is sugarcane bagasseIt was chosen for this study because of its availability inexcess of its usage However it is necessary to understandthe composition of biomass before its application in energyconversion systems [1] Proximate and ultimate analysis ofbiomass are usually used to describe the composition ofbiomass and different indicators are often used to quantifythese components

Samples of sugarcane bagasse were obtained from theSugar Milling Research Institute in Durban South Africa Itwas received with over 50 moisture content The sugarcanebagasse was air dried for 48 hours before analysisThe reasonfor predrying before analysis was to lower the moisturecontent of sugarcane bagasse so as to make it suitable forgasification operations because high moisture content willrequiremore energy for gasification andwill reduce the insidetemperature of the gasifier as well as the heating value ofthe product gas The dried sugarcane bagasse was milled to

Journal of Energy 3

Table 1 Proximate and ultimate analysis of sugarcane bagasse

Components () CompositionMoisture content 114Volatile matter content 6999Fixed carbon 1639Ash 142N 020C 441H 57S 23Olowast 477lowastObtained by difference

size using a cryogenic grinder The results of the proximateand ultimate analysis of sugarcane bagasse are presented inTable 1

22 Energy Content of Sugarcane Bagasse The standardmea-sure of the energy content of a fuel is its heating value alsoknown as the calorific value It indicates the energy availablefor conversion to useful energy Fuel with high energy contentis always better for gasification and most biomass materialshave heating value in the range 10ndash20MJkg [8] The energycontent of a fuel type can vary significantly depending on theclimate and soil in which the fuel was grown as well as otherconditions [9] Biomass materials usually have low energycontent because of high amount of oxygen in the biomass

The heating value of sugarcane bagasse was determinedby an oxygen bomb calorimeter (CAL2K model) The calo-rimeter was calibrated with 05 g of benzoic acid beforemeas-urements were taken This was done under a pressurizedoxygen environment of 3 000 kpa

23 Downdraft Gasifier Modeling A DOS based downdraftgasifier modeling program developed by Jayah et al 2003was used to undertake computer simulation of the gasifica-tion process of sugarcane bagasseThis software is specificallydesigned for the simulation of the fixed-bed downdraft gasi-fiers Table 2 presents the parameters used during gasificationsimulation

Gas profiles were obtained from the simulation softwareprogram and these gas profiles were used to calculate thegas heating value from the percentage composition of thecombustible gases in the syngas as follows [10]

HVgas

= ((COvol times HVCO) + (H

2vol times HVH2) + (CH

4vol times HVCH4)

100)

(8)

where HVgas is the gas heating value in MJkg COvol is thevolume concentration of carbonmonoxide gas in percentageHVCO is the heating value of carbon monoxide gas (usually1264MJkg by standard) [11] H

2vol is the volume concen-tration of hydrogen gas in percentage HVH

2is the heating

value of hydrogen gas (101MJkg by standard) [12] CH4vol

is the volume concentration of methane gas in percentageand HVCH

4is the heating value of methane gas (38MJkg

by standard measurement) [11] The heating value of thecombustible gases was obtained from the standard gas table

The conversion efficiency of the gasification processwas determined after computer simulation by the followingequation [10]

120578 = [(

HVgas times 2

HVfuel) times 100] (9)

where 120578 is the efficiency of the gasifier HVgas the gas heatingvalue and HVfuel the heating value of the fuel

The computer software was basically a model developedfor the downdraftwood gasifiers to study the effects of operat-ing and design parameters on the performance of the gasifier[13] It consists of two submodels namely flaming pyrolysisand gasification zone submodels Flaming pyrolysis zone sub-model is used to determine the product concentration andtemperature of gas leaving the flaming pyrolysis zone Thegasification zone submodel is used to predict the output ofthe product gas and the length of the gasification zone at anygiven time [14]The principle of mass and energy balance wasalso used

231 Flaming Pyrolysis Zone Submodel In the flaming pyrol-ysis zone the general equation of reaction of the material canbe expressed by

CH119886O119887+ 119908H

2O + 119898 (021O

2+ 079N

2)

997888rarr 119909char Char + 119909tarTar + 1199091CO + 1199092H2

+ 1199093CO2+ 1199095CH4+ 1199096N2

(10)

where char was taken as carbon and ultimate analysis oftar as CH

103O003

[15] From (11) and (12) we can obtainthe equilibrium equation and the corresponding equilibriumconstant respectively as follows

CO +H2Olarrrarr CO

2+H2

(11)

1198703=1199093times 1199092

1199091times 1199094

(12)

The correlation between the temperature and equilibriumconstants for the above is given by [16]

log (1198703) = minus3672508 +

3994704

119879minus 446241

times 10minus3

119879 + 671814 times 10minus7

1198792

+ 122228 log (119879) (13)

where T is the temperature (K)By mass balance the following equation can be obtained

Carbon 1 = 119909char + 119909tar + 1199091 + 1199093 + 1199095

Hydrogen 119886 + 2119908 = 103119909tar + 21199092 + 1199091 + 21199094 + 41199095

Oxygen 119887 + 119908 + 042119898 = 003119909tar + 1199091 + 21199093 + 1199094

Nitrogen 079119898 = 1199096

(14)

4 Journal of Energy

Table 2 Parameters used during gasification simulation

Fuel properties Value Gasifier operating conditions ValueCarbon () 441 Throat diameter (cm) 255Hydrogen () 57 Throat angle (∘) 30Oxygen () 477 Insulation thickness (cm) 175Nitrogen () 020 Thermal conductivity (WcmK) 28Fixed carbon () 1819 Temperature of input air (K) 300Bulk density (gcm3) 0178 Air input (kghr) 445Diameter of SB particle (cm) 143 Heat loss () 128Moisture content 117 ()

The energy balance in flaming pyrolysis zone is given by

HC Wood = HC Char +HCTar +HCGas

+HS Char +HSTar +HSGas +Heatloss(15)

The number of moles of water (119908) including fuel moistureair moisture and water or steam addition can be calculatedby the following equation [17]

Moisture in fuel = dry matter in fuel times moisture contenton dry basis

119908 = (12 times 1 + 1 times 119886 + 16 times 119887) timesmcdb kg (16)

The values of 119886 and 119887 have been given Heat loss and 119898(number of moles of oxygen input) are obtained from theexperiment 119909

5 119909char and 119909tar are assumed and 119909

1 1199092 1199093 1199094

1199096 and 119879 are solved by using the successive approximation

method with a Fortran program The higher heating values(MJkg) of bagasse char and tar are calculated from theequation as follows [18]

HCWood = 03491119891C + 01783119891H minus 01034119891O

(N2 and ash content are neglected)

HC Char = 03491times119891Cchar

HCTar = 03491 times 119891Ctar + 01783119891Htar minus 01034119891Otar

(17)

The chemical energy content of output gas and sensibleenergy of char tar and output gases are calculated as follows

HCGas = 2410001199091 + 2830001199092 minus 8023001199095

HS Char = 1215119909 Char times (119879 minus 300)

HSTar = 2195119909tar times (119879 minus 300)

HSGas = 1199091HCO + 1199092HH2

+ 1199093HCO

2

+ 1199094HCO

2

+ 1199094HH2O + 1199095HCH

4

+ 1199096HN2

(18)

232 Submodel of Gasification Zone The gasification zoneis modelled by following a particle along the axis of thereactor The computer program has been formulated usingFortran language to calculate the characteristic profiles alongthe reactor axis The profile includes temperature concen-trations efficiency and distance the particle travelled The

Table 3 Measure of the energy content of sugarcane bagasse fromthis study and from previous authors

Fuel (sugarcane bagasse) Energy content (MJkg)Present study 178Stanmore 2010 [20] 19Aboyade et al 2013 [21] 166Jenkins et al 1998 [22] 173ndash194Jorapur and Rajvanshi 1997 [23] 181Demirel 2012 [24] 17-18

length coordinate is coupled with a time variable through thesolid phase velocity A small time increment approach is usedin calculating the product composition of the zone It involvesthe use of a step procedure starting from the gasification zoneand marches axially through the reactor in appropriate timeincrements The output values of the flaming pyrolysis zoneare used as inputs for modelling the gasification zone [14]

3 Results and Discussion

31 Heating Value of Sugarcane Bagasse Table 3 presents themeasure of the energy content of sugarcane bagasse fromthis study and from previous authorsThis was obtained aftercomplete combustion of sugarcane bagasse to carbon dioxideand water vapour in an oxygen bomb calorimeter

The heating value of sugarcane bagasse was measuredand found to be 178MJkg and the value is comparable towhat is found in the literature as evident from Table 3 Con-version efficiency of the gasification process is based purelyon this value This value was used during calculation of theconversion efficiency of the gasifier after computer simulationof the gasification process

32 Gasifier Simulation A downdraft biomass gasificationsimulation software program developed by Jayah et al 2003described in Section 23 was used to undertake computersimulation of the gasification process of sugarcane bagasseThe initial parameters used for the gasification simulationprocess are presented in Table 2 in Section 23 Howeverthese parameters were later varied in order to investigate theirimpact on conversion efficiency of the gasification processMoisture content was also varied in order to investigateits impact as well not only on conversion efficiency of the

Journal of Energy 5

Table 4 Parameters varied during gasification simulation

Parameter RangeMoisture content () 114 15 25Diameter of SB particle (cm) 6 20 30Temperature of input air (∘C) 27 627 1227Throat diameter (cm) 10 30 50Throat angle (∘) 25 40 90

gasification process but also on gas volume The parametersvaried are presented in Table 4

The parameters varied were particle diameter throatdiameter and throat angle as well as temperature of inputair and moisture content as evident in Table 4 Figureswere played around with before finally establishing thosefigures that resulted in optimum conversion efficiency aswell as those that lead to reduced conversion efficiency ofthe gasification process Moisture content of 114 (from theproximate analysis in Table 1) is as measured from the samplewhile 15 and 25moisture contents were assumed based onthe maximum allowable moisture content [19]

321 Impact of Fuel Properties and Gasifier Operating Con-ditions on Conversion Efficiency The ratio of the productsformed during gasification of biomass is influenced notonly by the composition of the biomass but also by theoperating conditions of the gasifier [8] The heating value ofsugarcane bagasse described in Section 21 was measured andfound to be 178MJkg and was used during calculation ofthe conversion efficiency of the gasification process Time-consuming gasification simulation was conducted to inves-tigate the impact of fuel properties such as moisture contentand particle diameter and gasifier operating conditions suchas throat angle and throat diameter as well as temperatureof input air on the conversion efficiency of the gasificationprocess of sugarcane bagasse The impact of these fuelproperties and gasifier operating conditions is described inthis section

Impact of Fuel Moisture Content on Gas Volume The fuelproperties and gasifier operating conditions presented inTable 1 were used to undertake computer simulation withonly moisture content varied from 114 to 15 and 25respectively Figure 2 presents the impact of moisture contenton gas volumes obtained after computer simulation of thegasification process of sugarcane bagasse using the gasifieroperating parameters presented in Tables 2 and 4 respec-tively

Themajor part of the syngas is formed through reductionreactions in the reduction zone of the gasifier most of whichare endothermic reactions The impact of moisture contenton gas volumes is evident in Figure 2 The volume of carbonmonoxide (CO) was found to be higher when the moisturecontent of sugarcane bagasse was low (114) comparedto when it was higher (15 and 25 resp) This can beattributed to the fact that heat was not consumed duringthe drying of the feedstock it was rather available for thereduction reactions to take place The hydrogen (H

2) content

0

5

10

15

20

25

30

35

40

45

50

CO

Gas

vol

ume (

)

114 MC15 MC25 MC

H2 N2CH4CO2

Figure 2 Gas volumes obtained through computer simulation

0

10

20

30

40

50

60

70

0 500 1000 1500 2000 2500 3000 3500 4000 4500Time (mins)

Effici

ency

()

114 MC15 MC

25 MCDifference () (114MC25MC)

Figure 3 Simulated impact of moisture content on conversion effi-ciency

of the syngas was found to be higher when the moisturecontent of sugarcane bagasse was assumed to be higher (15and 25 resp) This is because of the availability of moisturefor the water-gas reaction to take place

Impact of Fuel Moisture Content on Conversion EfficiencyMoisture content is one important fuel property that gov-erns gasifier design and also has an impact on conversionefficiency of the gasification process [1] Figure 3 shows theimpact of fuel moisture content on conversion efficiencyThis was obtained after computer simulation of the gasi-fication process using the parameters presented in Table 1The moisture content was varied from 114 15 and 25respectively as evident in Tables 2 and 4 respectively

As moisture content increases conversion efficiencydecreases considerably as evident from Figure 3 Optimumconversion efficiency was achieved at low moisture content

6 Journal of Energy

of 114 This observation can be explained by the reactionkinetics As explained earlier in Section 1 the major part ofthe syngas is formed through reduction reactions A highquantity of energy is consumed during the drying of thematerial in the drying zone of the gasifier and the energy isno longer available for the reduction reactions to take placeAt higher moisture contents (15 and 25 resp) the lowoxidation temperature inhibiting the rate of the reactions iscompensated by a high water (H

2O) concentration which

accelerates the water-gas shift reaction (4) in Section 1 Thepercentage difference between 114 moisture content and25 moisture content is approximately 20 in terms ofefficiency This value is significantly higher when comparedto the percentage difference between 15 and 25 moisturecontents

The Impact of Particle Diameter on Conversion Efficiency Par-ticle diameter has an impact on the burning characteristicsof the fuel because it affects the rate of heating and dryingduring gasification [9] Figure 4 shows the impact of particlediameter on conversion efficiency of the gasification processof sugarcane bagasse obtained after computer simulationusing the same parameters presented in Tables 2 and 4respectively Only the particle diameter was varied between6 cm 20 cm and 30 cm respectively while other parametersremained constant

Conversion efficiency increases with decreasing particlediameter as evident in Figure 4 This is due to the fact thatsmaller particle diameters have larger surface area per unitmass and larger pore sizes which facilitates faster rates ofheat transfer and gasification Longer gasifier length is neededfor large particle diameters to achieve optimum conversionefficiency [27]

The Impact of Temperature of Input Air on Conversion Effi-ciency Gasifiers are generally operated at ambient air tem-perature of 27∘C (300K)The gasification reactions explainedin Section 1 occur simultaneously and the content and ratiosof CO H

2 and CH

4in the product gas are affected by tem-

perature of the reactants [3 28] Figure 5 presents the impactof temperature of input air on conversion efficiency Thiswas obtained after computer simulation of the gasificationprocess using the parameters presented in Tables 2 and 4 withonly temperature of input air varied between 27∘C 627∘Cand 1227∘C respectively while other parameters remainedconstant

An experiment was conducted by Mathieu and Dubuis-son 2002 to investigate the impact of temperature of inputair on gasifier conversion efficiencyThey found that reactiontemperature increased when the temperature of input air wasincreased As noticed from Figure 5 conversion efficiencyincreases slightly as temperature of input air increases Thisobservation is due to heat brought into the reactants whichinduces an increase in reaction temperature The produc-tion of CH

4in the reactions explained earlier decreases

when reaction temperature and hence temperature of inputair increases The production of carbon monoxide (CO)increases at the expense of carbon and carbon dioxide whentemperature increases [25 29]

52

54

56

58

60

62

64

66

0 1000 2000 3000 4000 5000

Effici

ency

()

6 cm20 cm30 cm

Time (mins)

Figure 4 Impact of particle diameter on conversion efficiency

0

10

20

30

40

50

60

70

80

0 1000 2000 3000 4000 5000

Effici

ency

()

Time (mins)

27∘C

627∘C

1227∘C

Figure 5 Impact of temperature of input air on conversion efficien-cy

The Impact of Throat Diameter on Conversion EfficiencyThe main purpose of the throat in a downdraft gasifier isto distribute heat evenly around the combustion zone andconsequently along the gasification axis This heat distribu-tion is important for optimum conversion efficiency [19]Figure 6 shows the impact of throat diameter on conversionefficiencyThis was obtained after computer simulation of thegasification process using the parameters presented in Tables2 and 4 with only the throat diameter varied between 10 cm30 cm and 50 cm respectively Other parameters remainedconstant

The smaller the throat diameter the more efficient thegasification process as evident in Figure 6 Whereas largerthroat diameters (30 cm and 50 cm resp) result in lower con-version efficiency smaller throat diameters (10 cm) increaseconversion efficiency This is because larger throat diameters

Journal of Energy 7

Table 5 A comparison of the simulated results from this study with experimental data from the literature

Parameter Range Conversion efficiency ()

This study

Moisture content114 6615 5825 50

Particle diameter6 cm 6520 cm 5830 cm 51

Temperature of input air27∘C 57627∘C 591227∘C 61

Throat diameter10 cm 6530 cm 6250 cm 58

Throat angle25∘ 6540∘ 6290∘ 57

Mamphweli 2010 [19] Moisture content 15 73Basu et al 2009 [25] Particle diameter 250ndash1500 120583m 72ndash85Basu et al 2009 [25] Temperature of input air 400ndash680∘C 60ndash70

Gunarathne et al 2013 [26] Throat diameter125mm 7166150mm 7279175mm 7266

decrease temperature due to divergent effect and hence therate of the gasification reaction Even though smaller throatdiameters increase conversion efficiency longer gasificationperiod is required to achieve that efficiency [1]

The Impact of Throat Angle on Conversion Efficiency Throatangle is a special unique feature of the downdraft gasifier andits impact on conversion efficiency is important [1] Figure 7presents the impact of throat angle on conversion efficiencyat 25 40 and 90 degrees respectively also obtained throughcomputer simulation of the gasification process using theparameters presented in Tables 2 and 4 Only the throat anglewas varied while other parameters remained constant

Smaller throat angles (25∘) tend to result in higherconversion efficiency as evident in Figure 6 whereas largerthroat angles (40∘ and 90∘) decrease conversion efficiencybecause the latter decrease the temperature of the gasificationreaction due to divergent effect Although smaller throatangle increases efficiency it also requires longer gasificationperiod to achieve maximum conversion efficiency [1]

33 Comparison with Experimental Data Based on Litera-ture The study though did not look at experimental datahowever a comparison between the simulated process stud-ied and experimental data based on literature has beenundertaken Table 5 presents a comparison of the parame-ters considered for optimum gasification efficiency betweensimulated data from this study and experimental data fromprevious authors

The simulation results agree well with the experimentaldata found in the literature as evident in Table 5 and are useful

52

54

56

58

60

62

64

66

0 1000 2000 3000 4000 5000

Effici

ency

()

Time (mins)

10 (cm) TD30 (cm) TD50 (cm) TD

Figure 6 The impact of throat diameter on conversion efficiency

to understand the processes reproducing the experimentaldata

4 Conclusion

Computer simulation of a downdraft biomass gasifier wasperformed on sugarcane bagasse and results showed thatseveral characteristics affect the gasification process and per-formance of sugarcane bagasse including moisture contentand particle diameter as well as gasifier operating parameters

8 Journal of Energy

52

54

56

58

60

62

64

66

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Efci

ency

()

Time (mins)

25∘TA

40∘TA

90∘TA

Figure 7 The impact of throat angle on conversion efficiency

such as throat angle throat diameter and temperature ofinput air Results also showed that these parameters arequite interrelated Gasification rate process efficiency andgas heating value are affected by each of these parametersGas volume increased at reduced moisture content and thegas heating value is largely influenced by the volume ofcombustible gases in the syngas which in turn influences theconversion efficiency of the gasification process It was alsofound that conversion efficiency is enhanced at low moisturecontent Conversion efficiency also increased slightly withincreasing temperature of input air due to additional enthalpyneeded for reaction to occur Reduced throat angle andthroat diameter also enhanced the conversion efficiency ofthe gasification process The study finally established that alaboratory scale as well as a large scale gasifier with enhancedconversion efficiency can be designed using simulationresults

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This research was supported by the Fort Hare Institute ofTechnology University of Fort Hare and Eskom as well as theNational Research Foundation and Govan Mbeki Researchand Development Centre in form of funding provided andtheir support is gratefully acknowledged

References

[1] S S Kumar K Pitchandi and E Natarajan ldquoModeling and sim-ulation of down draft wood gasifierrdquo Journal of Applied Sciencesvol 8 no 2 pp 271ndash279 2008

[2] S Sadaka Book chapter on Gasification Associate Scien-tist Center for Sustainable Environmental Technologies andAdjunct Assistant Professor Department of Agricultural andBiosystems Engineering Iowa State University 2002

[3] A Kumar D D Jones and M A Hanna ldquoThermochemicalbiomass gasification a review of the current status of thetechnologyrdquo Energies vol 2 no 3 pp 556ndash581 2009

[4] P Iyer T Rao P Groover and N Singh Biomass-Thermo-chemical Characterization Chemical Engineering DepartmentIndian Institute of Technology Delhi India 2002

[5] T Reed and A Das Handbook of Biomass Downdraft GasifierEngine System SERI Golden Colo USA 1988

[6] J Perez O Diaz R Obando and A Molina ldquoDesign method-ology of a pilot-scale downdraft fixed bed biomass gasifierrdquo RevTechnologicas no 22 pp 121ndash140 2009

[7] Solar Energy Research Institute Handbook of Biomass Down-draft Gasifier Engine Systems 1988

[8] T Chandrakant Biomass GasificationmdashTechnology and Utiliza-tion Humanity Development Library Artes Institute Glucks-burg Germany 2002 httpwwwpssurvivalcom

[9] DCiolkoszCharacteristics of Biomass as aHeating Fuel Renew-able and Alternative Energy Fact Sheet Penn State College ofAgricultural Sciences Agricultural Research and CoorporativeExtension 2010 httpwwwenergyextensionpsuedu

[10] S Mamphweli Implementation of a 150 KVA biomass gasifiersystem for community economic empowerment in South Africa[PhD thesis] University of Fort Hare 2009

[11] D Bjerketvedt J R Bakke and K Van Wingerden ldquoGasexplosion handbookrdquo Journal of Hazardous Materials vol 52no 1 pp 1ndash150 1997

[12] M Fossum and R BeyerCo-Combustion Biomass Fuel Gas andNatural Gas SINTEF Energy Research Trondheim Norway1998

[13] J Chen Kinetic Engineering Modeling of Co-Current MovingBed Gasification Reactors For Carbonaceous Material CornellUniversity New York NY USA 1986

[14] T Jayah Evaluation of a Downdraft Wood Gasifier for TeaManufacturing in Sri Lanka Melbourne University VictoriaAustralia 2002

[15] TN Adams ldquoA simple fuel bedmodel for predicting particulateemissions from a wood-waste boilerrdquo Combustion and Flamevol 39 no 3 pp 225ndash239 1980

[16] WGumzGas Producers and Blast FurnacesTheory andMethodof Calculation John Wiley amp Sons New York NY USA 1950

[17] J Chen Kinetic engineering modelling of co-current moving bedgasification reactors for carbonaceous material [PhD thesis]Cornell University New York NY USA 1987

[18] S Gaur and T Reed Thermal Data For Natural and SyntheticFuels Marcel Dekker New York NY USA 1998

[19] S Mamphweli ldquoPhysics 505 lecture notesrdquo University of FortHare Alice South Africa Unpublished lecture notes 2010

[20] B R Stanmore ldquoGeneration of energy from sugarcane bagasseby thermal treatmentrdquo Waste and Biomass Valorization vol 1no 1 pp 77ndash89 2010

[21] A Aboyade J Gorgens M Carrier E Meyer and J KnoetzeldquoThermogravimetric study of the pyrolysis characteristics andkinetics of coal blends with corn and sugarcane residuesrdquo FuelProcessing Technology vol 106 pp 310ndash320 2013

[22] B Jenkins L Baxter T Miles Jr and T Miles ldquoCombustionproperties of biomassrdquo Fuel Processing Technology vol 54 no1ndash3 pp 17ndash46 1998

Journal of Energy 9

[23] R Jorapur and A Rajvanshi ldquoSugarcane leaf-bagasse gasifiersfor industrial heating applicationsrdquo Biomass and Bioenergy vol13 no 3 pp 141ndash146 1997

[24] Y Demirel ldquoEnergy and Energy typesrdquo inEnergy Green Energyand Technology pp 27ndash70 Springer London UK 2012

[25] P Basu M Vichuda and M A Leon ldquoGasification of ricehusk in supercritical waterrdquo in Proceedings of the 8th WorldConference on Chemical Engineering paper 971 p 520Montreal Canada August 2009

[26] D Gunarathne S Jatunarachchi S Senanayake and B WeildquoThe effect of throat diameter on the performance of adowndraft biomass gasifierrdquo International Journal of EnergyEngineering no 3 pp 171ndash175 2013

[27] V Kirubakaran V Sivaramakrishnan R Nalini T Sekar MPremalatha and P Subramanian ldquoA review on gasification ofbiomassrdquoRenewable and Sustainable Energy Reviews vol 13 no1 pp 179ndash186 2009

[28] T H Jayah L Aye R J Fuller and D F Stewart ldquoComputersimulation of a downdraftwood gasifier for tea dryingrdquoBiomassand Bioenergy vol 25 no 4 pp 459ndash469 2003

[29] P Mathieu and R Dubuisson ldquoPerformance analysis of a bio-mass gasifierrdquo Energy Conversion and Management vol 43 no9ndash12 pp 1291ndash1299 2002

[30] FAO Corporate Document Repository ldquoWood gas and enginefuelrdquo 1986 httpwwwfaoorgdocrept0512et0512e0ahtm

TribologyAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

FuelsJournal of


Journal ofPetroleum Engineering


Industrial EngineeringJournal of


Power ElectronicsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

CombustionJournal of


Journal of


Renewable Energy

Submit your manuscripts athttpwwwhindawicom


StructuresJournal of


RotatingMachinery


EnergyJournal of


Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Nuclear InstallationsScience and Technology of


Solar EnergyJournal of


Wind EnergyJournal of


Nuclear EnergyInternational Journal of


High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

2 Journal of Energy

into the syngas and the ratio of carbonmonoxide to hydrogenproduced depends on the hydrogen and carbon contentof the feedstock and the type of gasifier used The syngasproduced differs from natural gas in terms of heating valuecomposition and flammability characteristics

In the gasifier the biomass material undergoes severaldifferent reaction processes including drying distillationoxidation and reduction reaction processes These reactionsare as follows [3]

2C +O2997888rarr 2CO (partial oxidation) (1)

C +O2997888rarr CO

2(complete oxidation) (2)

C + 2H2997888rarr CH

4(hydrogasification reaction) (3)

CO +H2O 997888rarr CO

2+H2(water-gas shift reaction)

(4)

CH4+H2O 997888rarr CO + 3H

2(steam reforming reaction)

(5)

C +H2O 997888rarr CO +H

2(water-gas reaction) (6)

C + CO2997888rarr 2CO (Boudourd reaction) (7)

Equations (6) and (7) are the main reduction reactions andbeing endothermic have the capability to reduce the tempera-ture of the syngasThe selection of gasification systems designand performance are influenced by the thermochemicalcharacteristics of the biomass to be converted [4] Howeverit is necessary to use fast and quick simulation techniquesin order to efficiently utilize the energy resources The keyparameters that affect the performance of the gasifier aremoisture content throat angle and throat diameter as wellas diameter of the material under study and temperature ofinput air [5] Little is known about these parameters and theirimpact on conversion efficiency of the gasification processThese parameters are the most critical operating parametersthat affect gasifier performance and are useful empirical toolsfor scale-up designs of gasifiers [5 6]

11 Principle of Operation of the DowndraftGasifier There aremany types of gasifiers used in the gasification of biomassmaterials However the choice of gasifier type depends onthe type of material to be gasified and end use of the gasproduced Fixed-bed downdraft or cocurrent gasifiers arerelatively simpler to use they are reliable and amenable togasifier different kinds of feedstock andoffer lower particulateconcentration in product gases and can achieve higherefficiencies than other gasifiers The downdraft gasifiers alsohave the advantage of the production of a gas with low tarcontent Because of uneven heat distribution in the downdraftgasifier it is only limited to small scale applications [7]However scale-up of the downdraft gasifier is possible ifheat could be evenly distributed and cold spots avoided inthe combustion zone of the gasifier since the generation ofheat and the oxidation of condensable products from thedistillation zone take place in the combustion zone Figure 1presents the main features of the downdraft gasifier

Feed

Drying zone

Distillation zone

Hearth zone

Air

Reduction zone

Ash grate

Ash zone

Air

Gas out

Figure 1 Fixed-bed downdraft gasifier or cocurrent gasifier [Adopt-ed from FAO Corporate Document Repository 1986] [30]

The biomass material is fed into the gasifier from thetop of the gasifier and dried in the drying zone Pyrolysis ofthe biomass takes place in the distillation zone where charand pyrolysis gases are formed The drying zone and thedistillation zone are mainly heated by radiation heat from thehearth (combustion) zone In this zone carbon dioxide andwater vapour are formed A part of the char formed in thedistillation zone is also burnt in the hearth zone Pyrolysisgases also pass through this zone and are burnt as well Theextent to which the pyrolysis gases are actually burnt dependson gasifier design the biomass feedstock and the skills ofthe operator After oxidation of the feedstock in the hearthzone the char left in the distillation zone and the combustionproducts (carbon dioxide and water vapour) in the hearthzone pass to the reduction zonewhereCOandH

2are formed

Traces of methane and other noncombustible gases are alsoformed in this zone

2 Materials and Method

21 Proximate and Ultimate Analysis The main by-productof the sugar industry in South Africa is sugarcane bagasseIt was chosen for this study because of its availability inexcess of its usage However it is necessary to understandthe composition of biomass before its application in energyconversion systems [1] Proximate and ultimate analysis ofbiomass are usually used to describe the composition ofbiomass and different indicators are often used to quantifythese components

Samples of sugarcane bagasse were obtained from theSugar Milling Research Institute in Durban South Africa Itwas received with over 50 moisture content The sugarcanebagasse was air dried for 48 hours before analysisThe reasonfor predrying before analysis was to lower the moisturecontent of sugarcane bagasse so as to make it suitable forgasification operations because high moisture content willrequiremore energy for gasification andwill reduce the insidetemperature of the gasifier as well as the heating value ofthe product gas The dried sugarcane bagasse was milled to

Journal of Energy 3








HVgas



4vol times HVCH4)

100)

(8)



2is the heating






120578 = [(

HVgas times 2





CH119886O119887+ 119908H

2O + 119898 (021O

2+ 079N

2)


+ 1199093CO2+ 1199095CH4+ 1199096N2

(10)


103O003


CO +H2Olarrrarr CO

2+H2

(11)

1198703=1199093times 1199092

1199091times 1199094

(12)


log (1198703) = minus3672508 +

3994704

119879minus 446241

times 10minus3

119879 + 671814 times 10minus7

1198792

+ 122228 log (119879) (13)


Carbon 1 = 119909char + 119909tar + 1199091 + 1199093 + 1199095

Hydrogen 119886 + 2119908 = 103119909tar + 21199092 + 1199091 + 21199094 + 41199095

Oxygen 119887 + 119908 + 042119898 = 003119909tar + 1199091 + 21199093 + 1199094

Nitrogen 079119898 = 1199096

(14)

4 Journal of Energy











1 1199092 1199093 1199094



HCWood = 03491119891C + 01783119891H minus 01034119891O




(17)


HCGas = 2410001199091 + 2830001199092 minus 8023001199095



HSGas = 1199091HCO + 1199092HH2

+ 1199093HCO

2

+ 1199094HCO

2

+ 1199094HH2O + 1199095HCH

4

+ 1199096HN2

(18)









Journal of Energy 5








2) content

0

5

10

15

20

25

30

35

40

45

50

CO

Gas

vol

ume (

)

114 MC15 MC25 MC

H2 N2CH4CO2


0

10

20

30

40

50

60

70

0 500 1000 1500 2000 2500 3000 3500 4000 4500Time (mins)

Effici

ency

()

114 MC15 MC






6 Journal of Energy







2 and CH






52

54

56

58

60

62

64

66

0 1000 2000 3000 4000 5000

Effici

ency

()

6 cm20 cm30 cm

Time (mins)


0

10

20

30

40

50

60

70

80

0 1000 2000 3000 4000 5000

Effici

ency

()

Time (mins)

27∘C

627∘C

1227∘C




Journal of Energy 7



This study





Throat angle25∘ 6540∘ 6290∘ 57








52

54

56

58

60

62

64

66

0 1000 2000 3000 4000 5000

Effici

ency

()

Time (mins)




4 Conclusion


8 Journal of Energy

52

54

56

58

60

62

64

66

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Efci

ency

()

Time (mins)

25∘TA

40∘TA

90∘TA





Acknowledgments


References























Journal of Energy 9













FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

















Journal of Energy 3








HVgas



4vol times HVCH4)

100)

(8)



2is the heating






120578 = [(

HVgas times 2





CH119886O119887+ 119908H

2O + 119898 (021O

2+ 079N

2)


+ 1199093CO2+ 1199095CH4+ 1199096N2

(10)


103O003


CO +H2Olarrrarr CO

2+H2

(11)

1198703=1199093times 1199092

1199091times 1199094

(12)


log (1198703) = minus3672508 +

3994704

119879minus 446241

times 10minus3

119879 + 671814 times 10minus7

1198792

+ 122228 log (119879) (13)


Carbon 1 = 119909char + 119909tar + 1199091 + 1199093 + 1199095

Hydrogen 119886 + 2119908 = 103119909tar + 21199092 + 1199091 + 21199094 + 41199095

Oxygen 119887 + 119908 + 042119898 = 003119909tar + 1199091 + 21199093 + 1199094

Nitrogen 079119898 = 1199096

(14)

4 Journal of Energy











1 1199092 1199093 1199094



HCWood = 03491119891C + 01783119891H minus 01034119891O




(17)


HCGas = 2410001199091 + 2830001199092 minus 8023001199095



HSGas = 1199091HCO + 1199092HH2

+ 1199093HCO

2

+ 1199094HCO

2

+ 1199094HH2O + 1199095HCH

4

+ 1199096HN2

(18)









Journal of Energy 5








2) content

0

5

10

15

20

25

30

35

40

45

50

CO

Gas

vol

ume (

)

114 MC15 MC25 MC

H2 N2CH4CO2


0

10

20

30

40

50

60

70

0 500 1000 1500 2000 2500 3000 3500 4000 4500Time (mins)

Effici

ency

()

114 MC15 MC






6 Journal of Energy







2 and CH






52

54

56

58

60

62

64

66

0 1000 2000 3000 4000 5000

Effici

ency

()

6 cm20 cm30 cm

Time (mins)


0

10

20

30

40

50

60

70

80

0 1000 2000 3000 4000 5000

Effici

ency

()

Time (mins)

27∘C

627∘C

1227∘C




Journal of Energy 7



This study





Throat angle25∘ 6540∘ 6290∘ 57








52

54

56

58

60

62

64

66

0 1000 2000 3000 4000 5000

Effici

ency

()

Time (mins)




4 Conclusion


8 Journal of Energy

52

54

56

58

60

62

64

66

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Efci

ency

()

Time (mins)

25∘TA

40∘TA

90∘TA





Acknowledgments


References























Journal of Energy 9













FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

















4 Journal of Energy











1 1199092 1199093 1199094



HCWood = 03491119891C + 01783119891H minus 01034119891O




(17)


HCGas = 2410001199091 + 2830001199092 minus 8023001199095



HSGas = 1199091HCO + 1199092HH2

+ 1199093HCO

2

+ 1199094HCO

2

+ 1199094HH2O + 1199095HCH

4

+ 1199096HN2

(18)









Journal of Energy 5








2) content

0

5

10

15

20

25

30

35

40

45

50

CO

Gas

vol

ume (

)

114 MC15 MC25 MC

H2 N2CH4CO2


0

10

20

30

40

50

60

70

0 500 1000 1500 2000 2500 3000 3500 4000 4500Time (mins)

Effici

ency

()

114 MC15 MC






6 Journal of Energy







2 and CH






52

54

56

58

60

62

64

66

0 1000 2000 3000 4000 5000

Effici

ency

()

6 cm20 cm30 cm

Time (mins)


0

10

20

30

40

50

60

70

80

0 1000 2000 3000 4000 5000

Effici

ency

()

Time (mins)

27∘C

627∘C

1227∘C




Journal of Energy 7



This study





Throat angle25∘ 6540∘ 6290∘ 57








52

54

56

58

60

62

64

66

0 1000 2000 3000 4000 5000

Effici

ency

()

Time (mins)




4 Conclusion


8 Journal of Energy

52

54

56

58

60

62

64

66

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Efci

ency

()

Time (mins)

25∘TA

40∘TA

90∘TA





Acknowledgments


References























Journal of Energy 9













FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

















Journal of Energy 5








2) content

0

5

10

15

20

25

30

35

40

45

50

CO

Gas

vol

ume (

)

114 MC15 MC25 MC

H2 N2CH4CO2


0

10

20

30

40

50

60

70

0 500 1000 1500 2000 2500 3000 3500 4000 4500Time (mins)

Effici

ency

()

114 MC15 MC






6 Journal of Energy







2 and CH






52

54

56

58

60

62

64

66

0 1000 2000 3000 4000 5000

Effici

ency

()

6 cm20 cm30 cm

Time (mins)


0

10

20

30

40

50

60

70

80

0 1000 2000 3000 4000 5000

Effici

ency

()

Time (mins)

27∘C

627∘C

1227∘C




Journal of Energy 7



This study





Throat angle25∘ 6540∘ 6290∘ 57








52

54

56

58

60

62

64

66

0 1000 2000 3000 4000 5000

Effici

ency

()

Time (mins)




4 Conclusion


8 Journal of Energy

52

54

56

58

60

62

64

66

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Efci

ency

()

Time (mins)

25∘TA

40∘TA

90∘TA





Acknowledgments


References























Journal of Energy 9













FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

















6 Journal of Energy







2 and CH






52

54

56

58

60

62

64

66

0 1000 2000 3000 4000 5000

Effici

ency

()

6 cm20 cm30 cm

Time (mins)


0

10

20

30

40

50

60

70

80

0 1000 2000 3000 4000 5000

Effici

ency

()

Time (mins)

27∘C

627∘C

1227∘C




Journal of Energy 7



This study





Throat angle25∘ 6540∘ 6290∘ 57








52

54

56

58

60

62

64

66

0 1000 2000 3000 4000 5000

Effici

ency

()

Time (mins)




4 Conclusion


8 Journal of Energy

52

54

56

58

60

62

64

66

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Efci

ency

()

Time (mins)

25∘TA

40∘TA

90∘TA





Acknowledgments


References























Journal of Energy 9













FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

















Journal of Energy 7



This study





Throat angle25∘ 6540∘ 6290∘ 57








52

54

56

58

60

62

64

66

0 1000 2000 3000 4000 5000

Effici

ency

()

Time (mins)




4 Conclusion


8 Journal of Energy

52

54

56

58

60

62

64

66

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Efci

ency

()

Time (mins)

25∘TA

40∘TA

90∘TA





Acknowledgments


References























Journal of Energy 9













FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

















8 Journal of Energy

52

54

56

58

60

62

64

66

0 500 1000 1500 2000 2500 3000 3500 4000 4500

Efci

ency

()

Time (mins)

25∘TA

40∘TA

90∘TA





Acknowledgments


References























Journal of Energy 9













FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

















Journal of Energy 9













FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of





















FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

















Documents

Research Article Computer Simulation of the Mass and Energy Balance … · 2019. 7. 31. · Research Article Computer Simulation of the Mass and Energy Balance during Gasification