exergetic analysis of a biodiesel production process from jatropha curcas

Applied Energy 101 (2013) 218–225

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Applied Energy

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Exergetic analysis of a biodiesel production process from Jatropha curcas

A.M. Blanco-Marigorta ⇑, J. Suárez-Medina, A. Vera-CastellanoDepartment of Process Engineering, Universidad de Las Palmas de Gran Canaria, Edificio de Ingenierıas, Tafira Baja s/n, Las Palmas de G.C. 35017, Spain

h i g h l i g h t s

" Exergetic analysis of a biodiesel production process from Jatropha curcas." A 95% of the inefficiencies are located in the transesterification reactor." Exergetic efficiency of the steam generator amounts 37.6%." Chemical reactions cause most of the irreversibilities of the process." Exergetic efficiency of the overall process is over 63%.

a r t i c l e i n f o

Article history:Received 21 December 2011Received in revised form 9 May 2012Accepted 10 May 2012Available online 20 July 2012

Keywords:Exergy analysisBiodieselJatropha CurcasExergy destructionExergetic efficiencyThermodynamic properties estimation

0306-2619/$ - see front matter � 2012 Elsevier Ltd. Ahttp://dx.doi.org/10.1016/j.apenergy.2012.05.037

⇑ Corresponding author. Tel.: +34 928 451934; fax:E-mail addresses: [email protected] (A.M. Bla

[email protected] (J. Suárez-Medina), [email protected]

a b s t r a c t

As fossil fuels are depleting day by day, it is necessary to find an alternative fuel to fulfill the energydemand of the world. Biodiesel is considered as an environmentally friendly renewable diesel fuel alter-native. The interest in using Jatropha curcas as a feedstock for the production of biodiesel is rapidly grow-ing. On the one hand, J. curcas’ oil does not compete with the food sector due to its toxic nature and to thefact that it must be cultivated in marginal/poor soil. On the other, its price is low and stable.

In the last decade, the investigation on biodiesel production was centered on the choice of the suitableraw material and on the optimization of the process operation conditions. Nowadays, research is focusedon the improvement of the energetic performance and on diminishing the inefficiencies in the differentprocess components. The method of exergy analysis is well suited for furthering this goal, for it is a pow-erful tool for developing, evaluating and improving an energy conversion system.

In this work, we identify the location, magnitude and sources of thermodynamic inefficiencies in a bio-diesel production process from J. curcas by means of an exergy analysis. The thermodynamic propertieswere calculated from existing databases or estimated when necessary. The higher exergy destructiontakes places in the transesterification reactor due to chemical reactions. Almost 95% of the exergy ofthe fuel is destroyed in this reactor. The exergetic efficiency of the overall process is 63%.

� 2012 Elsevier Ltd. All rights reserved.

1. Introduction

The increasing consumption and demand for petroleumproducts, the global warming and the environmental pollution leadto search for alternative fuels to fulfill the energy demand. Biodieselis one of the most currently available renewable fuels. Due to thesimilarity between biodiesel and diesel fuel properties, biodieselcan be blended with diesel fuel or can be used directly in most die-sel engines without extensive engine modifications requirements.Another advantage, when compared to the fossil fuel dieselobtained from non-renewable sources, is that biodiesel do havelower sulfur content, with an upper limit of 10 mg/kg of biodiesel,according to the biodiesel European Standard EN 14214.

ll rights reserved.

+34 928 458975.nco-Marigorta), jasmina.suarc.es (A. Vera-Castellano).

The EU directive on the promotion of the use of biofuels or otherrenewable fuels for transport (2003/30/EC) [1], demands from themember states a minimum proportion of liquid biofuels and otherrenewable fuels on their markets. This percentage must reach thevalue of 6.1% in 2013. Spain is far from achieving this objectivein a sustainable way: 59% of the biodiesel consumed in Spain dur-ing 2010 was imported. In the Canary Islands, some measures havebeen applied in order to achieve a sustainable production-consumesystem. Since 2007, the feasibility of Jatropha curcas cultivation inthe region has been studied. J. curcas’ oil has high triolein contain.Due to its toxicity and to the fact that it must be cultivated in mar-ginal/poor soil, its production does not compete against food farm-ing and its price is low and stable. Out of various non-edible oilresources, J. curcas oil is considered as future feedstock for biodieselproduction [2–6].

In the last decade, biodiesel production research has beenfocused on the optimization of operation conditions [7–13] as well

Nomenclature

_E exergy flow rate (kW)_m mass flow rate (kg/s)

p pressure (bar)T temperature (�C)_W electric power (MW)

y exergy destruction ratio (%)h enthalpy (kJ/kg)s entropy (kJ/(kg K))Z compressibility factorR gas constant, 8314 (kJ/kmol K)V molar volume (cm3/mol)nA number of atoms in a molecule

Greek letterse exergetic efficiencyx Pitzer acentric factor

SubscriptsD destructionF fueli ith streamk kth componentP productL loss0 environmentc critical stateb normal boiling point

r reduced propertiesvp vapor pressure

SuperscriptsCH chemicalPH physicalTOT total� reference state or an ideal-gas state(0) simple fluid function(1) deviation function

AbbreviationsJC Jatropha curcasFFAs free fatty acidsMIXER mixer unitTRANS-REACTOR transesterification reactor unitHX heaterDISTILL distillate unitWASHER washer unitNEUTR neutralizer unitPUMP pump unitRECTIF rectification column unitCONDENS

condenser unitSTEAM-GEN steam generator unit

A.M. Blanco-Marigorta et al. / Applied Energy 101 (2013) 218–225 219

as on the election of the more appropriate raw material [14–20].Currently, the improvement of the energetic efficiency of the pro-cess and the decrease of the energetic inefficiencies of the differentcomponents, capture the interest of the researchers [21–26].

Exergy analysis combines the First and the Second Law of Ther-modynamics in order to quantify the thermodynamic inefficiencieswithin an energy process. By means of an exergy analysis, thelosses and destructions of useful work taking place during a pro-cess can be determined at a component level [27,28]. The exergyanalysis reveals two aspects: the destruction of exergy within asystem component, and the exergetic efficiency, which in turnshows how effectively the exergetic resources supplied to a com-ponent have been used. In this way, the location and magnitudeof the inefficiencies are obtained. Therefore, these inefficienciescan be decreased and the performance of the process can beimproved.

Several previous studies have evaluated the performance ofbiodiesel production plants by means of exergetic analysis.Talens-Peiro et al. [29,30] applied an exergy analysis to biodieselproduction from used cooking oil. Hou and Zheng [31] proposeda new design concept using a solar utility to supply steam and elec-tricity for biodiesel production. They compared different alterna-tives using exergy methods. Jaimes et al. [32] performed anexergy analysis of palm oil biodiesel production. The exergeticanalysis of microalgal and Jatropha biodiesel production plants,carried out by Ofori-Boateng et al. [21], was based on three ther-modynamic performance parameters, namely exergy destruction,exergy efficiency and thermodynamic improvement potentials.Their results showed that 44% of the total exergy content of the in-put resources were destroyed for 1 ton of biodiesel produced.

In this work, an exergetic analysis of a biodiesel production pro-cess from J. curcas is carried out. The location, magnitude andsources of thermodynamic inefficiencies are identified. Processparameters are taken from a former design project [33] which

evaluates the feasibility of a biodiesel plant from J. curcas in the Can-ary Islands.

2. Description of the process

The raw material for this biodiesel production process is vege-table oil from Jatropha curcas (JC), which is a non-food feedstock.It is a drought-resistant perennial, growing well in marginal/poorsoil. Its oil has low acidity, so it does not require a pre-esterificationbefore the usual transesterification process. JC’s oil consists basi-cally of Free Fatty Acids (FFAs) and triolein, which is an unsatu-rated fat. The reaction between triolein and short chain alcohols,such as methanol, yields glycerol, and fatty acid methyl esters (bio-diesel). The process can be divided in four stages: (a) transesterifi-cation, (b) glycerol post-treatment, (c) biodiesel post-treatment,and (d) methanol reforming.

Fig. 1 represents a schematic of the biodiesel productionprocess. Input data and process parameters are taken from the de-sign performed by Espino [33]. The first stage is focused in thetransesterification reaction where JC’s oil reacts with methanolproducing biodiesel, as main product, and glycerol. This reactionneeds the presence of an alkaline catalyst. Methanol (stream 21)and the catalyst (sodium hydroxide – stream 31) are previouslymixed (MIXER) to produce an alkoxide (stream 23) which later re-acts with the triglyceride (stream 12) on the transesterificationreactor (TRANS-REACTOR). The mixing process of methanol and so-dium hydroxide is exothermic; to avoid temperatures higher than40 �C in the mixture cold water (20 �C) is used (stream 74). Thetransesterification reactor works at a constant temperature of60 �C. A steam stream (76) is used for that propose. The productsof the transesterification reaction (stream13) are centrifugally sep-arated in two streams. One of the streams (14) contains biodiesel,methanol and the remaining unreacted triolein, which is separated(stream 15) and recirculated into the reactor. The second stream

NaOH

Triolein + FFA

NaCl

HCl

HCl

85 84

75 74

7273

31

22

15

76

7714

41

61

78

32

47

4544

4611 12

13

7971

34

35

33

51

52

53

62

56

82

83

57

64

65

66

6768

69

63

91 90

8887 86

METHANOLMIXER

HX-1

HX-2

NEUTR-2NEUTR-1

FFA

PUMP-1

PUMP-3

WATER

DISTILL-1

DISTILL-2

WASHER

BIODIESEL

METHANOL81 80

21

PUMP-2

GLYCEROL

CONDENS

89

RECTIF

BOTTOMS

23TRANS -REACTOR

Fig. 1. Schematic of the Biodiesel production process.

220 A.M. Blanco-Marigorta et al. / Applied Energy 101 (2013) 218–225

(51) contains glycerol, water, methanol, and sodium oleate. Theformation of sodium oleate and water is due to the reaction be-tween the free fatty acid molecules and the catalyst, in a simpleacid–base reaction. The free fatty acids are, in turn, produced bythe hydrolysis of the esters formed on the transesterificationreaction.

In the second stage, glycerol effluent is treated (NEUTR-2). First,the mixture (stream 51) is fed into an acidulation tank with hydro-chloric acid (stream 33) to avoid the formation of soaps (sodiumoleate) resulting in the production of sodium chloride and FFA.After acidulation, effluent is cooled with a water stream (80) toavoid the precipitation of salts. Then, sodium chloride (stream35) and FFA (stream 34) are separated from the mixture with athree-phase centrifuge device. The remaining mixture (stream53) is flash distilled (DISTILL-2) to recuperate glycerol (stream56) and methanol (stream 62).

The third stage covers the post-treatment of the ester phasecontaining mainly biodiesel and methanol (stream 41). Methanol(stream 61) is recovered in a flash distillation unit (DISTILL-1)and biodiesel (stream 44) is neutralized in an acidulation tank(NEUTR-1) with HCl (stream 32). Following, biodiesel (stream 46)is recuperated in a washing unit (WASHER) using hot water at 60�C (stream 71). In the last stage, recuperated methanol from thedifferent streams (streams 61 + 62) is condensed (CONDENS) andpurified with a rectification column (RECTIF).

The process requires the input of steam at different stages: pre-heating of JC’s oil (with stream 72); heating in the transesterifica-tion reactor (with stream 76), in the flash distillation units (withstream 78 and 82) and in the recuperation of methanol (withstreams 86 and 90). In Fig. 2 the schematic of the steam generationprocess is represented. It consists of a closed circuit: generatedsteam (stream 103) is first used in the process and then recirculat-ed into the steam generator (stream 104). Before entering thesteam generator, part of stream 104 is used to increase the temper-ature of the biodiesel washing water stream (70) and, afterwards,

pre-heated with the refrigeration water (stream 89) from themethanol condenser unit (CONDENS).

2.1. Assumptions

The former flow diagram [33] has been simplified as it is shownin Fig. 1. Biodiesel process is divided in 14 operation units whichare studied as isolated systems from an exergy analysis viewpoint.The overall process occurs at atmospheric pressure and within atemperature range of 20–94 �C. JC’s oil is simulated as triolein,99.95% and FFA, 0.05%. The conversion assumed in the transesteri-fication reaction is 96%.

The process is modeled by assuming that all components areadiabatic, except the steam generator system, and operating atsteady state. Heat loss in the steam generator is estimated as 2%of the heat reaction. Changes in potential and kinetic energy offluid streams are assumed negligible. Pressure losses were set tozero because these losses are negligible when compared to theother sources of exergy destruction. Recirculation pumps are omit-ted due to their negligible energy contribution.

Production of biodiesel is considered as 50,000 ton/year. Withthis production 5% of the Canary biodiesel consumption is pro-vided. Biodiesel production supplies the fuel requirements of thesteam generator. The process consumes 706 kg of steam/ton of bio-diesel. In the process, a high amount for water is also needed forrefrigeration purposes: 4614 kg/ton of biodiesel.

3. Thermodynamic evaluation

3.1. Exergy analysis

A conventional exergetic evaluation of the kth component of asystem is performed using following variables [34]:

� exergy destruction rate:

Fig. 2. Schematic of the steam generation process.


_ED;k ¼ T0_Sgen;k ¼ T0 _mksgen;k ð1Þ

The exergy destruction rate is obtained in this study from an exergybalance:

_ED;k ¼ _EF;k � _EP;k ð2Þ

� exergetic efficiency:

ek ¼_EP;k

_EF;k

¼ 1�_ED;k

_EF;k

ð3Þ

� exergy destruction ratios:

yD;k ¼_ED;k

_EF;tot

ð4Þ

y�D;k ¼_ED;k

_ED;tot

ð5Þ

For the calculation of the exergy of the fuel and the product ofthe components, some devices have been put into groups, takinginto account their particular characteristics. The following formu-las have been then applied:

TRANS-REACTOR (mixer of NaOH and Methanol + transesterifi-cation reactor + centrifugal separators):

_EF;TRANS�REACTOR ¼ _E31 þ _E21 þ _E12 þ ð _E76 � _E77Þ ð6Þ_EP;TRANS�REACTOR ¼ _E41 þ _E51 þ ð _E75 � _E74Þ ð7Þ

DISTILL-1 (Methanol flash distillation unit + PUMP-1)ð _WPUMP�1 ¼ 40;051 WÞ:_EF;DISTILL�1 ¼ _m61 eCH

41 � eCH61

� �þ _m78ðe78 � e79Þ þ _WPUMP�1 ð8Þ

_EP;DISTILL�1 ¼ _m61 ePH61 � ePH

41

� �þ _m45ðe45 � e41Þ ð9Þ

NEUTR-1:

_EF;NEUTR�1 ¼ _m45ðe45 � e46Þ ð10Þ_EP;NEUTR�1 ¼ _m32ðe46 � e32Þ ð11Þ

WASHER:

_EF;WASHER ¼ _E46 � _E47 ð12Þ_EP;WASHER ¼ _E63 � _E71 ð13Þ

NEUTR-2 (glycerol effluent acidulation tank + three-phasecentrifuge device):_EF;NEUTR�2 ¼ _E51 � _E53 ð14Þ_EP;NEUTR�2 ¼ ð _E81 � _E80Þ þ ½ð _E34 þ _E35Þ � _E33� ð15Þ

DISTILL-2 (distillation unit + PUMP-2) ð _WPUMP�2 ¼ 4166 WÞ:_EF;DISTILL�2 ¼ _m57 eCH

53 � eCH57

� �þ _m82ðe82 � e83Þ þ _WPUMP�2 ð16Þ

_EP;DISTILL�2 ¼ _m57 ePH57 � ePH

53

� �þ _m62ðe62 � e53Þ ð17Þ

CONDENS:_EF;CONDENS ¼ _m64ðe64 � e65Þ ð18Þ_EP;CONDENS ¼ _m88ðe89 � e88Þ ð19Þ

RECTIF:

_EF;RECTIF ¼ _E86 � _E87 ð20Þ_EP;RECTIF ¼ ð _E85 � _E84Þ þ ½ð _E68 þ _E69Þ � ð _E67 þ _E63Þ� ð21Þ

STEAM-GEN:

_EF;STEAM�GEN ¼ ð _E38 þ _E37Þ � _E39 ð22Þ_EP;STEAM�GEN ¼ _E103 � ð _E101 þ _E102Þ ð23Þ

HX (�1, �2, �3, and �4):

_EF;HX ¼ _Ehot;in � _Ehot;out ð24Þ_EP;HX ¼ _Ecold;out � _Ecold;in ð25Þ

PUMP-3 ð _WPUMP�3 ¼ 4473 WÞ:

_EF;PUMP�3 ¼ _WPUMP�3 ð26Þ_EP;PUMP�3 ¼ _E66 � _E65 ð27Þ

For the overall system the exergy balance is

_EF;tot ¼ _EP;tot þX

k

_ED;k þ _EL;tot ð28Þ

The exergy of the product, EP,tot, of the overall process is equal tothe exergy of the biodiesel stream that leaves the system (stream47) minus the biodiesel used in the steam generator (stream 37).


The exergy losses of the overall biodiesel production system isequal to the sum of the exergy of exhausted gases and the exergydifference between outlet and inlet streams of the cooling waterused in some of the devices of the process:

_EL;tot ¼ _E39 þ ð _E75 þ _E81 þ _E92 þ _E85 � _E74 � _E80 � _E84 � _E88Þ ð29Þ

The exergetic efficiency of the overall system is

e ¼_EP;tot

_EF;tot

ð30Þ

The exergy of the flow streams was calculated taken intoaccount both physical and chemical exergies. The values of thestandard chemical exergy of chemical components were taken from[35]. Diedrichsen calculated standard chemical exergies for an exer-gy-reference environment consisting of 17 chemical elements. Thestandard molar chemical exergy of any substance consisting ofthese elements can be determined using the change in the specificGibbs function, Dgo, for the formation of this substance from thereaction of chemical elements present in the environment:

eCHðT0;p0Þ ¼ DgoðT0; p0Þ þXn

i¼1

mi eCHi ðT0;p0Þ � Dgo

i ðT0;p0Þ� �

ð31Þ

where mi; Dgoi and eCH

i , denote, for the ith chemical element, thestoichiometric coefficient in the reaction, the Gibbs function at T0

and p0, and the standard chemical exergy, respectively.The values of the specific physical exergy where calculated by:

ePH ¼ ðh� h0Þ � T0ðs� s0Þ ð32Þ

Thermodynamic properties, h, s and g, were calculated from EESdatabases [36] when possible. Unfortunately, only methanol, so-dium hydroxide, sodium chloride, hydrochloric acid and waterare present in EES databases. Alternatively, Aspen Plus software[37] was used for triolein, methyloleate, oleic acid and glycerol. So-dium oleate properties where estimated by other means, becausethis compound does not appear in ASPEN or EES databases. Envi-ronmental values are taken from ISO conditions: T0 = 288 K andp0 = 101.3 kPa.

3.2. Estimation of the thermodynamic properties

To perform an energy and exergy analysis of a chemical process,physical and thermodynamic properties of the substances involvedin the process are required. Although there are many experimentaldata collected in various publications, the growth experienced bythe Chemical Industry, with the emergence of many new sub-stances, has made this tabulated experimental data insufficient.Therefore, it is necessary to use methods based on structural con-siderations, together with some experimental determined proper-ties, to estimate them. In this work, physical and thermodynamicproperties of sodium oleate are estimated. Properties of other sub-stances like triolein, methyloleate, glycerol and oleic acid were alsocalculated just for validation of the corresponding estimationmethod.

Critical properties. To obtain the critical properties, Tc, pc, and vc,the group contribution methods of Ambrose, Lydersen, Eduljee andJoback [38,39] have been applied. Results of Joback’s method fortriolein, methyloleate, glycerol and oleic acid are the closest onesto values present in ASPEN database, therefore, critical propertiesfor sodium oleate were estimated by Joback’s method [39]:

Tc ¼ Tb½0;584þ 0;965 � RDT � ðRDTÞ2��1 ð33Þpc ¼ ð0;113þ 0;0032 � nA � RDpÞ�2 ð34Þvc ¼ 17;5þ RDv ð35ÞTb ¼ 198þ RDTb

ð36Þ

where Tb, is the boiling temperature in K, nA is the number of atomsin the molecule and RDTb

, RDT, RDp, and RDv are the sums of thegroup contribution values [38,39].

Acentric factor. According to Pitzer [39], the acentric factor is de-fined as:

x ¼ � log pvprðat Tr ¼ 0:7Þ � 1000 ð37Þ

To get the value of the acentric factor, reduced vapor pressure,Pr, determined at Tr = 0.7, is needed. Clausius–Clapeyron equation[39] offers a two-parameter corresponding states method to esti-mate the vapor pressure:

ln pvpr¼ b 1� 1

Tr

� �ð38Þ

with b ¼ Tbr

ln pc1:01325

� �1� Tbr

ð39Þ

where Tbr is the reduced boiling temperature expressed in K.Variation of thermodynamic properties. The variation of any ther-

modynamic property between two states is independent of thepath chosen to pass from one state to the other. Rarely are heatcapacities available at high pressures, therefore, the usual pathfor determining (h2 � h1) is

Dh ¼Z p�

p1

@h@p

� �T1

dpþZ T2

T1

copdT þ

Z p2

p�

@h@p

� �T2

dp ð40Þ

Dh ¼ ðh� � hp1ÞT1þZ T2

T1

copdT þ ðh� � hp2

ÞT2ð41Þ

The terms ðh� � hp1ÞT1

and ðh� � hp2ÞT2

are called departure func-tions. They relate a thermodynamic property at some p, T to a ref-erence state at the same temperature. They can be calculated froman equation of state. The term

R T2T1

copdT is evaluated in the ideal-gas

state and values of cop are estimated according to Joback’s method

[39], based on group contribution techniques. Departure functionsare calculated though the corresponding states correlations sug-gested by Lee-Kesler [39,40], which expresses the compressibilityfactor, Z, as a linear function of the acentric factor, x:

Z ¼ Zð0Þ þx � Zð1Þ ð42Þ

Similarly, linear expressions are used to obtain residualproperties:

ho � hRTc

¼ ho � hRTc

� �ð0Þþx

ho � hRTc

� �ð1Þð43Þ

For entropy, analogous equations can be found:

so � sR¼ so � s

R

� �ð0Þþx

so � sR

� �ð1Þð44Þ

Gibbs function is, then, obtained by:

Dg ¼ Dh� TDs ð45Þ

In this work, all these calculations were performed with a sub-routine implemented using EES software [36].

4. Results and discussion

The results of the thermodynamic analysis are shown in Tables1 and 2. Table 1 shows thermodynamic and exergetic data of thestreams for the biodiesel production process and Table 2 showscorresponding values of the parameters for the streams involvedin the steam generation process.

Table 3 shows the exergy destruction, exergetic efficiency andexergy destruction ratios for each main plant component. The

Table 1Thermodynamic and exergetic data of streams for the biodiesel production process.

Stream _m (kg/s) p (bar) T (K) ePHj (kJ/kg) eCH

j (kJ/kg) eTOTj (kJ/kg) _EPH

j (kW) _ECHj (kW) _ETOT

j (kW)

11 1.8267 1.0 293 0.1 59319.3 59319.4 0.1 108359.9 108360.012 1.8267 1.0 333 6.2 59319.3 59325.5 11.4 108359.9 108371.321 0.3964 1.0 293 0.1 22171.9 22172.1 0.0 8789.7 8789.722 0.4036 1.0 327 8.8 28985.0 28993.8 3.5 11697.8 11701.323 0.4036 1.0 313 3.6 28985.0 28988.6 1.5 11697.8 11699.231 0.0071 1.0 293 0.0 2913.7 2913.7 0.0 20.8 20.832 0.000065 1.0 293 0.034 896.4 896.4 0.0 0.1 0.133 0.0065 1.0 293 0.034 896.4 896.4 0.0 5.8 5.834 0.0009 1.0 298 0.3 39405.8 39406.1 0.0 34.6 34.635 0.0103 1.0 298 4.4 219.3 223.7 0.0 2.3 2.337 0.0972 1.0 293 0.1 39856.0 39856.1 0.0 3874.9 3874.938 2.6712 1.0 293 0.045 14.9 14.9 0.1 38.2 38.439 2.6712 1.0 489 730.7 27.7 758.4 1951.8 74.0 2025.841 1.9550 1.0 329 5.4 38750.0 38755.5 10.6 75757.5 75768.144 1.8644 0.3 336 8.5 39558.8 39567.2 15.8 73755.1 73770.945 1.8644 1.0 336 7.3 39558.8 39566.1 13.7 73755.1 73768.846 1.8645 1.0 333 6.5 39557.3 39563.7 12.0 73754.9 73766.947 1.8406 1.0 333 6.4 39709.1 39715.6 11.8 73090.0 73101.951 0.2753 1.0 331 12.8 19281.9 19294.7 3.5 5307.7 5311.352 0.2817 1.0 298 0.5 18768.2 18768.7 0.1 5287.4 5287.553 0.2705 1.0 298 0.4 19416.4 19416.8 0.1 5252.1 5252.256 0.2103 0.3 336 15.2 18722.3 18737.4 3.2 3937.7 3940.957 0.2103 1.0 336 7.9 18722.3 18730.2 1.7 3937.7 3939.461 0.0906 0.3 336 87.1 22206.9 22294.0 7.9 2011.7 2019.662 0.0602 0.3 336 83.3 21922.5 22005.8 5.0 1319.1 1324.163 0.6933 1.0 333 13.1 950.5 963.7 9.1 659.0 668.164 0.1508 0.3 336 85.0 22093.3 22178.4 12.8 3330.8 3343.665 0.1508 0.3 310 1.9 22087.6 22089.4 0.3 3329.9 3330.266 0.1508 1.0 310 2.0 22087.6 22089.5 0.3 3329.9 3330.267 0.1508 1.0 336 9.7 22087.6 22097.3 1.5 3329.9 3331.468 0.1850 1.0 337 10.3 21359.1 21369.4 1.9 3952.1 3954.069 0.6590 1.0 367 38.0 67.1 105.2 25.1 44.3 69.370 0.6694 1.0 293 0.1 2.0 2.1 0.1 1.3 1.471 0.6694 1.0 333 13.3 2.0 15.3 8.9 1.3 10.374 0.2263 1.0 293 0.1 2.0 2.1 0.0 0.5 0.575 0.2263 1.0 308 2.7 2.0 4.7 0.6 0.5 1.180 0.1755 1.0 293 0.1 2.0 2.1 0.0 0.4 0.481 0.1755 1.0 323 8.1 2.0 10.1 1.4 0.4 1.884 6.9242 1.0 293 0.1 2.0 2.1 0.6 13.8 14.485 6.9242 1.0 313 4.2 2.0 6.2 29.1 13.8 42.988 1.1372 1.0 293 0.1 2.0 2.1 0.1 2.3 2.489 1.1372 1.0 330 11.6 2.0 13.6 13.2 2.3 15.5

Table 2Thermodynamic and exergetic data of streams for the steam generation process.

Stream _m (kg/s) p (bar) T (K) Quality ePHj (kJ/kg) eCH

j (kJ/kg) eTOTj (kJ/kg) _EPH

j (kW) _ECHj (kW) _ETOT

j (kW)

72 0.0632 1.0 373 0 558.1 2.0 560.1 35.3 0.1 35.473 0.0632 1.0 373 0 44.1 2.0 46.1 2.8 0.1 2.976 0.0203 1.0 373 1 558.1 2.0 560.1 11.3 0.0 11.477 0.0203 1.0 373 0 44.1 2.0 46.1 0.9 0.0 0.978 0.0465 1.0 373 1 558.1 2.0 560.1 26.0 0.1 26.079 0.0465 1.0 373 0 44.1 2.0 46.1 2.0 0.1 2.182 0.0408 1.0 373 1 558.1 2.0 560.1 22.8 0.1 22.883 0.0408 1.0 373 0 44.1 2.0 46.1 1.8 0.1 1.986 1.1168 1.0 373 1 558.1 2.0 560.1 623.3 2.2 625.687 1.1168 1.0 373 0 44.1 2.0 46.1 49.2 2.2 51.590 0.0045 1.0 373 1 558.1 2.0 560.1 2.5 0.0 2.591 0.0045 1.0 373 0 44.1 2.0 46.1 0.2 0.0 0.292 1.1372 1.0 323 0 8.1 2.0 10.1 9.3 2.3 11.5

101 0.3825 1.0 323 0 8.1 2.0 10.1 3.1 0.8 3.9102 0.9096 1.0 373 0 44.1 2.0 46.1 40.1 1.8 41.9103 1.2921 1.0 378 1 582.9 2.0 584.9 753.2 2.6 755.8106 0.3825 1.0 373 0 44.1 2.0 46.1 16.9 0.8 17.6107 0.3825 1.0 303 0 1.5 2.0 3.5 0.6 0.8 1.3


results are presented in descending order of the exergydestruction.

Transesterification reactor is the device with the highest exergydestruction. Here physical exergy is negligible in comparison with

chemical exergy. The high value of the exergy destruction is due tothe chemical reactions, where triolein reacts with methanol pro-ducing biodiesel and glycerine and, concomitantly, the saponifica-tion of FFA with NaOH takes place. Reaction with the highest

Table 3Exergy destruction, exergetic efficiency, and exergy destruction ratios for each main plant component.

_ED (kW) _EF (kW) _EP (kW) e (%) y�D;k (%) yD,k (%)

TRANS-REACTOR 36,112 117,192 81,080 69.19 95.58 33.11STEAM-GEN 1177 1887 710 37.62 3.11 1.08RECTIF 522 574 52.2 9.10 1.38 0.48NEUTR-2 26.6 59.1 32.5 55.01 0.07 0.02HX-1 21.3 32.5 11.2 34.60 0.06 0.02DISTILL-2 9.63 167 157 94.23 0.03 0.01HX-4 7.43 16.3 8.87 54.41 0.02 0.01WASHER 7.15 665 658 98.92 0.02 0.01DISTILL-1 4.10 1523 1519 99.73 0.011 0.004NEUTR-1 1.92 4.44 2.52 56.69 0.005 0.002HX-3 1.38 3.93 2.55 64.84 0.004 0.001HX-2 1.13 2.30 1.17 50.83 0.0030 0.0010CONDENS 0.31 13.41 13.10 97.68 0.0008 0.0003PUMP-3 0.03 0.04 0.01 29.06 0.00008 0.00003Total 37,893 109,185 69,227 63.40


exergy destruction is the conversion of J. curcas’ oil. Next devicewith a high exergy destruction value is the steam generator. Here,exergy destruction is due both to chemical biodiesel combustionreaction and to heat transfer in the production of steam fromwater. Following in importance related to exergy destruction it isthe rectification column, where methanol is purified by fractionaldistillation. On devices NEUTR-2 and HX-1, exergy destruction isalso of some importance. On NEUTR-2, the pH value of the streamis decreased in order to separate sodium oleate and sodium chlo-ride. Refrigeration is needed for salt precipitation and three-phaseseparation is also included in the exergy balance of this compo-nent. On HX-1 J. curcas’oil is pre-heated before entering the transe-sterification reactor. In the rest of the devices exergy destruction isnegligible.

Exergy destruction ratio, y�D;k, compares the exergy destructionin the k-th component with the exergy destruction in the overallprocess, ED,tot. As result, this parameter provides an insight intothe exergetic meaning of each of the components of the overallsystem. In this process, 95% of the global exergy destruction takesplace in the transesterification reactor. Steam generator and recti-fication column destroy only 3% and 1.4% of the total exergydestruction respectively. The comparison of the exergy destructionin the kth component with the exergy of the fuel of the overall pro-cess, shows that transesterification reactor destroys 33% of the to-tal fuel exergy, whereas on steam generator only 1% of the totalfuel exergy is destroyed.

Most of the components show an exergetic efficiency higherthan 50%. DISTILL-1, WASHER and CONDENS present an exergeticefficiency higher than 95%. Exergetic efficiency of the transesterifi-cation reactor is 69%. This means that, although in this reactorexergy destruction has a high value, 69% of the fuel exergy is pres-ent on the exergy of the product. The high exergy destruction isdue to the high value of the chemical exergy of the reactants andreaction products. Steam generator presents relatively low exer-getic efficiency: 37.6%. Nevertheless, this is an usual value in thesekind of devices. Exergetic efficiency will increase if irreversibilitieson combustion reaction decrease. Energy of exhaust gas could beused for pre-heating the reactants (air and biodiesel) in order todecrease these irreversibilities. The low exergetic efficiency ofthe rectification column is remarkable: 90% of the fuel exergy ofthe component is destroyed due to the high energy requirementsin the methanol distillation process.

Exergetic efficiency of the overall process is over 63%. Thismeans that the process has a certain potential for improvement.Nevertheless, most of the exergy destruction is unavoidable dueto irreversibilities in process involving chemical reactions. Exergylosses of the overall process are due to exhaust gases and refriger-

ation processes. The total exergy losses amount 2065 kW, that cor-responds to a 2% of the fuel exergy of the total system.

5. Conclusions

Exergy analysis is a useful tool to locate and evaluate the ther-modynamic inefficiencies of the analyzed process. A 95% of theinefficiencies are located in the transesterification reactor.Although in this reactor exergy destruction has a high value, theexergetic efficiency of the component is 69%. This value indicatesthat 69% of the fuel exergy is present on the exergy of the product.The high exergy destruction is due to the high value of the chem-ical exergy of the reactants and reaction products.

In the steam generator 3% of the total exergy destruction takesplace. Exergy destruction is due both to chemical biodiesel com-bustion reaction and to heat transfer in the production of steam.In the rest of the devices exergy destruction is negligible.

Exergetic efficiency of the steam generator amounts 37.6%. Thisvalue could be increased by pre-heating the reactants with theexhaust gases.

Exergetic efficiency of the overall process is over 63%. Chemicalreactions cause most of the irreversibilities of the process. An ad-vanced exergetic analysis will also be conducted to evaluate theavoidable and unavoidable part of the exergy destruction as wellas the mutual influence of the components of the process.

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