Energy and exergy utilization, and carbon dioxide emission in vegetable oil production Mustafa Özilgen a , Esra Sorgüven b, * a Department of Food Engineering, Faculty of Engineering, Yeditepe University, 34755 Kayisdagi Istanbul, Turkey b Department of Mechanical Engineering, Faculty of Engineering, Yeditepe University, Atas ¸ ehir 34755, Kayisdagi Istanbul, Turkey article info Article history: Received 26 April 2011 Received in revised form 8 July 2011 Accepted 12 August 2011 Available online 3 September 2011 Keywords: Olive oil Sunflower oil Soybean oil Energy utilization Exergy analysis Carbon dioxide emission abstract Energy and exergy utilization and carbon dioxide emission during production of soybean, sunflower, and olive oils are assessed. In all cases, agriculture is the most energy and exergy intensive process and emits most of the carbon dioxide, and diesel is the dominant energy and exergy source. The cumulative degree of perfection (CDP) for soybean and olive oil is 0.92 and 0.98, respectively, whereas the CDP for the sunflower oil is 2.36. Decreasing diesel consumption with good agricultural practices and substituting with biodiesel from renewable resources would decrease the cumulative exergy consumption, as a result, CDP of olive and soybean oil rises to 1.6 and sunflower oil to 2.9. Major contribution to the carbon dioxide emission is due to the excessive use of fertilizers. The most energy intensive process is olive oil production. However, since the fertilizer consumption here is limited, total carbon dioxide emission is less than those of the other two processes are. On the other hand, excessive fertilizer consumption during the soybean agriculture results in a rather large CO 2 emission. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Globally, 220.9 million ton of soybean oil (56% of production), 9.0 million tons of sunflower oil (7% of production) and 2.9 million tons of olive oil (less than 1% of production) were produced in 2008 [1]. In addition to their role in nutrition, soybean and sunflower oils are raw materials for biodiesel production. Olive oil is a delicassy and health food. Chemical fertilizers, agrochemicals (insecticides, herbicides, and fungicides), irrigation water, diesel and electric power are inputs of the vegetable oil agriculture (Fig. 1). Consumption of chemicals and energy in production leads to pollution. Common steps of vegetable oil production processes include transportation and conveying of the raw material to the factory; cleaning, grinding and pressing; separation, refining, and packaging of the oil; and bottling, boxing, palleting and shrink wrapping of the final product (Fig. 2). The raw material is transported to the factories in trucks, passed over magnets to remove traces of metal and then leaves, stems, and twigs are removed. The seeds or olives are cleaned with water to remove pesticides as well as sand and dirt; ground into a paste, cold-pressed to provide minimal processing and obtain light- flavored oil. The paste is stirred with water for about 30 min, generally by heating; this process allows small oil droplets to join with larger droplets and make separation easier. In traditional processes, oil may be permitted to drip out than separated from water by decantation. In modern facilities, centrifuges are employed to separate liquid from the pomace, and then oil is separated from water by decantation. Separation may include numerous recycling streams to improve the efficiency of the process. Then the oil may be refined, bleached, and deodorized before reaching the consumer. In some practices oil remaining in the pomace is extracted with solvents. Solvent extraction is avoided by many producers since solvents are usually carcinogenic. The left over pomace is generally used as an animal feed, and it is desired to leave some oil in the pomace to maintain acceptable nutritional value [2]. If the vege- table oil is being produced for human consumption, it is refined after heating to 40e85 C and extracting with an alkaline substance such as sodium hydroxide or sodium carbonate to remove color, odor, and bitterness. Vegetable oils are bottled after separating the phases. The Kyoto Protocol was accepted in 1997 and entered into force in 2005; Turkish Parliament approved ratification in 2009. Until July 2010, 191 states have signed or ratified the protocol. Turkey is among the Annex I countries, which agree to reduce their collective greenhouse gas (carbon dioxide, methane, nitrous oxide, sulfur * Corresponding author. Tel.: þ90 216 578 0498; fax: þ90 216 578 0400. E-mail address: [email protected](E. Sorgüven). Contents lists available at SciVerse ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy 0360-5442/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2011.08.020 Energy 36 (2011) 5954e5967
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Energy 36 (2011) 5954e5967
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Energy
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Energy and exergy utilization, and carbon dioxide emission in vegetableoil production
Mustafa Özilgena, Esra Sorgüvenb,*
aDepartment of Food Engineering, Faculty of Engineering, Yeditepe University, 34755 Kayisdagi Istanbul, TurkeybDepartment of Mechanical Engineering, Faculty of Engineering, Yeditepe University, Atasehir 34755, Kayisdagi Istanbul, Turkey
a r t i c l e i n f o
Article history:Received 26 April 2011Received in revised form8 July 2011Accepted 12 August 2011Available online 3 September 2011
0360-5442/$ e see front matter � 2011 Elsevier Ltd.doi:10.1016/j.energy.2011.08.020
a b s t r a c t
Energy and exergy utilization and carbon dioxide emission during production of soybean, sunflower, andolive oils are assessed. In all cases, agriculture is the most energy and exergy intensive process and emitsmost of the carbon dioxide, and diesel is the dominant energy and exergy source. The cumulative degreeof perfection (CDP) for soybean and olive oil is 0.92 and 0.98, respectively, whereas the CDP for thesunflower oil is 2.36. Decreasing diesel consumption with good agricultural practices and substitutingwith biodiesel from renewable resources would decrease the cumulative exergy consumption, as a result,CDP of olive and soybean oil rises to 1.6 and sunflower oil to 2.9.
Major contribution to the carbon dioxide emission is due to the excessive use of fertilizers. The mostenergy intensive process is olive oil production. However, since the fertilizer consumption here is limited,total carbon dioxide emission is less than those of the other two processes are. On the other hand,excessive fertilizer consumption during the soybean agriculture results in a rather large CO2 emission.
� 2011 Elsevier Ltd. All rights reserved.
1. Introduction
Globally, 220.9 million ton of soybean oil (56% of production),9.0 million tons of sunflower oil (7% of production) and 2.9million tons of olive oil (less than 1% of production) were producedin 2008 [1]. In addition to their role in nutrition, soybean andsunflower oils are raw materials for biodiesel production. Olive oilis a delicassy and health food. Chemical fertilizers, agrochemicals(insecticides, herbicides, and fungicides), irrigation water, dieseland electric power are inputs of the vegetable oil agriculture(Fig. 1). Consumption of chemicals and energy in production leadsto pollution. Common steps of vegetable oil production processesinclude transportation and conveying of the raw material to thefactory; cleaning, grinding and pressing; separation, refining, andpackaging of the oil; and bottling, boxing, palleting and shrinkwrapping of the final product (Fig. 2).
The rawmaterial is transported to the factories in trucks, passedover magnets to remove traces of metal and then leaves, stems, andtwigs are removed. The seeds or olives are cleaned with water toremove pesticides as well as sand and dirt; ground into a paste,cold-pressed to provide minimal processing and obtain light-
x: þ90 216 578 0400.üven).
All rights reserved.
flavored oil. The paste is stirred with water for about 30 min,generally by heating; this process allows small oil droplets to joinwith larger droplets and make separation easier. In traditionalprocesses, oil may be permitted to drip out than separated fromwater by decantation. In modern facilities, centrifuges areemployed to separate liquid from the pomace, and then oil isseparated from water by decantation. Separation may includenumerous recycling streams to improve the efficiency of theprocess. Then the oil may be refined, bleached, and deodorizedbefore reaching the consumer.
In some practices oil remaining in the pomace is extracted withsolvents. Solvent extraction is avoided by many producers sincesolvents are usually carcinogenic. The left over pomace is generallyused as an animal feed, and it is desired to leave some oil in thepomace to maintain acceptable nutritional value [2]. If the vege-table oil is being produced for human consumption, it is refinedafter heating to 40e85 �C and extracting with an alkaline substancesuch as sodium hydroxide or sodium carbonate to remove color,odor, and bitterness. Vegetable oils are bottled after separating thephases.
The Kyoto Protocol was accepted in 1997 and entered into forcein 2005; Turkish Parliament approved ratification in 2009. UntilJuly 2010, 191 states have signed or ratified the protocol. Turkey isamong the Annex I countries, which agree to reduce their collectivegreenhouse gas (carbon dioxide, methane, nitrous oxide, sulfur
b stream availability, kJ/kmolCDP cumulative degree of perfectionCExC cumulative exergy consumption, kJ/kmolh enthalpy, kJ/kmolm mass, kgQ heat, kJs entropy, kJ/(kmol K)T temperature, KW work, kJX exergy, kJm chemical potential, kJ/kmol
Subscripts0 restricted dead statei any speciesin inletk index of heat sourcesout outlet
M. Özilgen, E. Sorgüven / Energy 36 (2011) 5954e5967 5955
hexafluoride) emissions by 5.2% from the 1990 level in the period of2008e2012. In most countries, progress toward clean environmentis achieved only with the support of the public, which comes onlyafter informing the people.
In this study, energy utilization and carbon dioxide emissionduring production of three different vegetable oils are assessed.Although some, not all, of the data are available in the literature forthe inputs employed in the present study, exergy and energyutilization and carbon dioxide emission calculations for sunflower,olive, and soybean oil production covering the entire processesfrom farm to market by considering every step of the processes isnew to the literature. Our results are expected to help to evaluateexergy and energy utilization and CO2 emission associatedwith oneton of product, whichmay be used in the future by the producers tocompare the environmental cost of each product and start actionsfor savings. Environmentally conscious consumers are expected tobenefit from this study when they evaluate the impact of thealternative products on the environment. Exergy analysis may help
Fig. 1. Flow chart of the olive, sunflower and soybeans agriculture. Chemical fertilizers,water for irrigation, chemical pesticides and diesel (including utilization for machinework) are the inputs of the processes.
to identify energetically inefficient steps of processes and point theneed for new technology to improve them.
2. Methodology
First law of thermodynamics phrases conservation of energy;the second law provides insight on irreversibility, quantifies theenergy losses and proposes measures to minimize it. Based on thesecond law, exergy (availability) is defined as the maximum workthat a system can produce, if it is brought to thermal, mechanical,and chemical equilibrium with its surroundings via reversibleprocesses without violating the laws of thermodynamics. Cumu-lative exergy consumption, (CExC), is defined as the sum of exergyof all resources consumed in all the steps of a production process[3]. CExC is a function of the pathway that the process follows, andquantifies the total consumption of exergy, including those of rawmaterials, transportation, work, and heat transfer for production.Since cumulative energy consumption (CEnC) does not consider thenon-energetic raw materials, it cannot provide a measure for theimpact of the process on the environment. CExC of various fuels andindustrial products have been calculated during the last decade[4e8], but CExC calculations are rare in the food industry.
Each unit operation in agriculture and production of oils isanalyzed with the mass, energy and exergy balance equations todetermine the CEnC, CExC, total CO2 emission and the cumulativedegree of perfection (CDP). The governing equations employed hereare:
Mass balance:X
ðmÞin �X
ðmÞout ¼ 0 (1)
Energy balance:X
ðmhÞin�X
ðmhÞout ¼ Q �W (2)
Exergy balance:
XðmbÞin�
XðmbÞout�
Xk
Qk
�1� T0
Tk
��W ¼ Xloss (3)
Where k is the index of heat sources and b is the flow availabilityof a stream (neglecting the kinetic and potential energycontribution):
b ¼ h� T0s�X
xim0i (4)
CDP is the ratio of the chemical exergy of the product to the sumof the exergies of all the raw materials and fuel consumed duringthe production [3]:
CDP value indicates the efficiency of the production technique.An example for this is paper production [3]. The chemical exergy ofpaper is 16.5MJ/kg. Paper can be produced from standing timber byconsuming raw materials with a CExC of 72.0 MJ/kg and fuels witha CExC of 16.1 MJ/kg. Accordingly, CDP is 0.19. If production isperformed in an integrated plant, wherewaste products are used asfuels, CDP rises to 0.28, since CExC of the consumed raw materialsdecrease to 19.0 MJ/kg and CExC of the consumed fuel becomes40.9 MJ/kg. An even better production technique is using wastepaper as raw material, where the CExC of the raw materials is17.0 MJ/kg and CExC of consumed fuel is 5.2 MJ/kg. With thistechnique, CDP rises to 0.74. As this example illustrates, low CDPvalues indicate the need for improved production techniques.
Fig. 2. Common steps of vegetable oil production processes.
M. Özilgen, E. Sorgüven / Energy 36 (2011) 5954e59675956
The system boundaries involve the agricultural production, oilproduction, waste management, packaging, and distribution.Hydrosphere, lithosphere, and atmosphere act as water and carbonreservoirs, and are included within the system boundaries (Fig. 3).Nutrient rich water consumed during production and processwater is fully recycled. Fertilizers, pesticides, and micronutrientsconsumed during the agriculture are non-renewable chemicals,and the environmental cost for these raw materials is accountedfor. Electricity used in all processes is generated from fossil fuels.The energy or exergy consumed due to human labor is not
accounted for, since it was practically impossible to collect repre-sentative data.
Data about agriculture of olives [9], sunflower [10] andsoybeans [11] are obtained from the literature to study energyand exergy utilization and carbon dioxide emission. Informationregarding energy utilization and processing rates of the equip-ment are obtained from the manufacturer web sites. All thecalculations are done considering agriculture and processingof one metric ton (1000 kg) of olives, sunflower seeds, orsoybeans.
Fig. 3. System boundaries of vegetable oil production process.
M. Özilgen, E. Sorgüven / Energy 36 (2011) 5954e5967 5957
Coastal regions with temperate climate are the major olive andsunflower growing areas in Turkey. Big cities Istanbul, Ankara, andIzmir are the major consuming areas. There are numerous vege-table oil producing factories between the fields and the consumingcities. The average distance between the fields and the factories isabout 50 km, and the distance between factories and the consumerit is about 550 km. These numbers are determined by consideringthe population of the cities. The distance between the fields and thefactory is multiplied by two to determine the actual distancetraveled, 100 km, since the trucks usually go the fields empty andcome back to the factory loaded with olives or sunflower seeds. Theproduct delivery trucks are considered to be making one-way triponly, since in practice they usually carry other products on the wayback. The same distances were considered in all the calculations toend up with comparable results.
3. Results and discussion
3.1. Energy and exergy consumption and carbon dioxide emissionsduring agriculture and transportation of the plant material
3.1.1. Chemical fertilizers and manureEstimates of energy and exergy utilization and carbon dioxide
emission during agriculture and transportation of olives, sunflowerseeds and soybeans to the factory are given in Table 1. Total energyassociated with production (including packaging, transportation,and application) is 78.2 MJ/kg for nitrogenous, 17.5 MJ/kg forphosphorus and 13.8 MJ/kg for potassium fertilizers [12]. The CExCvalues of nitrogenous, phosphorus and potassium fertilizers are32.7 MJ/kg [3], 7.52 MJ/kg [13] and 4.56 MJ/kg [14], respectively.When the crop yield is 0.5 tons of olives/ha, 1.42 kg/ha of
Table 1Energy and exergy utilization and carbon dioxide emission during olive, sunflower and soybean agriculture.
Input Energy utilization/ton of olives (MJ/ton) CExC/ton of olives (MJ/ton) CO2 emission/ton of olives (kg/ton)
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nitrogenous, 0.41 kg/ha of phosphorus, 0.38 kg/ha of potassiumchemical fertilizers are used [9]. This data leads to calculation ofenergy utilization associated with production of one ton of olives tobe 222.1 MJ with nitrogenous,14.4 MJ with phosphorus and 10.5 MJwith potassium fertilizers. The total energy utilization associatedwith the chemical fertilizers is 247.0 MJ/ton of olives. Similarly,exergy consumed for cultivation of one ton of olives is 92.9 MJ fornitrogenous, 6.2 MJ for phosphorus and 3.5 MJ for potassiumfertilizer production, implying that the total exergy consumed inassociation with fertilizer use is 102.5 MJ/ton of olives. When wecombine the data provided by Kongshaug [15] and Helsel [12] wecalculate that CO2 emission associated with chemical fertilizerproduction to be 0.09 kg CO2/MJ with nitrogeneous, 0.15 kg CO2/MJwith phosphorus and 0.51 kg CO2/MJ with potassium fertilizerproduction; which leads to the calculation of the total emission tobe 27.5 kg CO2/ton of olives.
When the crop yield is 1.8 tons of sunflowers/ha, 60 kg/ha ofnitrogenous and 30 kg/ha of phosphorus fertilizer are used insunflower cultivation [10], leading to calculation that energy utiliza-tion associated with nitrogenous and phosphorus fertilizers as2606.7 MJ/ton of sunflowers and 291.7 MJ/ton of sunflowers, respec-tively. Exergy consumption associated with the nitrogenous andphosphorus fertilizers are 1090.0 MJ/ton and 125.3 MJ/ton, respec-tively. The total energy and exergy utilization associated with the useof chemical fertilizerswas 2898.4MJ/tonof sunflowers and1215.3MJ/ton of sunflowers, respectively (Table 1). When we apply the sameprocedure as that of the olives, we calculate the emission associatedwith chemical fertilizers as 282.2 kg CO2/ton of sunflower seeds.
When 1977 kg/ha of soybeans are produced, energy equivalentof the chemical fertilizers is 3514 MJ/ha [11]; implying that thespecific energy utilization is 1777.4 MJ/ton of soybeans. As alreadydiscussed in the case of agriculture of olives, the minimum emis-sion is associated with nitrogenous fertilizer to be 0.09 kg CO2/MJ,and the maximum emission is associated with production ofpotassium fertilizer to be 0.51 kg CO2/MJ, therefore, we may expectto have 160.0e906.5 kg CO2/ton of soybeans of emission, with theaverage being 533.2 kg CO2/ton of soybeans (Table 1). When sameamounts of nitrogenous and potassium fertilizers are used toproduce one ton of soybeans, CExC allocation is calculated to be371.6 MJ for nitrogenous, 293.7 MJ for potassium, and 665.3 MJ forthe total of both fertilizers.
In 1998, 1.2% of the world’s energy demand and approximately1.2% of the total greenhouse gas emissions was associated with
fertilizer production; fortunately, energy consumption for chemicalfertilizer production is decreasing over the years and approachingto the theoretical minimum in modern factories, e.g. 40 MJ/kg ofnitrogenous fertilizer [15,16]. Providing the chemical fertilizersfrom energy efficient chemical plants may help to reduce energyutilization. Chemical fertilizer use in agriculture is generally notbased on soil analysis, and is much more than the actual need [17].Introducing some microorganisms to the soil may stimulatenitrogen fixation, solubilize the insoluble minerals, and reduce theneed to produce and transport large amounts of chemical fertilizers[18]. Fertilizer management practices may reduce energy utiliza-tion up to 72%; consequently, herbicide utilization and pollutionalso decrease [19e22].
Manure is a major input in soybean agriculture in India [11](Table 1). In Nigeria 0.35 MJ/kg energy consumed to producepelletized manure and about 94% of the consumed energy isprovided by electric power utilization (emission factor ¼ 0.14 kgCO2/MJ) and the rest by man power [23]. If we should use the sameratio, we will calculate carbon dioxide emission associated withmanure production as 100.8 kg CO2/ton of soybeans (Table 1). Inorder to calculate the CExC of manure, the chemical exergy of theraw materials and the CExC of the fuel consumed during theproduction are added. 4221 kg cow dung and 12663 kg marketrefuse are consumed to produce 9000 kg of organic manure [23].The chemical exergy of animal waste is 8.4 MJ/kg [24], and the CExCto generate 1 MJ of electricity from fossil fuel is 4.17 MJ/MJ [3].Correspondingly, the CExC of the organic manure is calculated to be5.3 MJ/kg. The total exergy consumption related to organic manureuse in soybean production is 511.0 MJ/ton.
3.1.2. AgrochemicalsWhen average yield is 0.5 tons of olives/ha, 24 kg/ha of herbicide
(energy equivalent ¼ 418.2 MJ/kg) and 1.8 kg/ha of insecticide(energy equivalent ¼ 363.8 MJ/kg) are used [9], the total energyutilization for agrochemicals in agriculture of olives is 3317.0 MJ/ton of olives (Table 1). Emission factors are 6.3 � 2.7 kg CO2/kg ofherbicides and 5.1 � 3.0 kg CO2/kg of insecticides [25]. Then wecalculate emission associatedwith total of herbicide and insecticideuse to be 48.6 kg CO2/ton of olives (Table 1). During production of1.8 ton of sunflower seeds/ha, 2.5 kg/ha of herbicides (energyequivalent 171.4 MJ/kg of active ingredient) are used [10], implyingthat energy utilization associated with herbicides is 238.1 MJ/ton ofsunflower seeds (Table 1). Lal [25] reported that the emission is
M. Özilgen, E. Sorgüven / Energy 36 (2011) 5954e5967 5959
5.1 � 3.0 kg CO2/kg of insecticides and 3.9 � 2.2 kg CO2/kg offungicides. When we use the data provided by Kallivroussis et al.[10] with the mean values reported by Lal [25], we may estimate5.6 kg CO2 emission/ton of sunflower seeds, associated with the useof chemicals (Table 1). When 1977 kg/ha of soybean is produced,energy utilization for agrochemicals is 297 MJ/ha [11], implyingthat the specific energy utilization for agrochemicals is 150.2 MJ/ton of soybeans (Table 1). Since mostly herbicides are used insoybean agriculture [26] carbon dioxide emission is estimated as2.3 kg CO2/ton soybeans (Table 1). Kaltsas et al. [27] reported use ofinsect traps instead of pesticides during cultivation of organicolives. Improving the efficiency of these traps and extending theiruse to the other crops may reduce the environmental impact andenergy cost of the agrochemicals.
There is a large range of CExC values for agrochemicals in theliterature. Earlier works reported rather low CExC values. Forexample CExC for herbicides is given as 32.7 MJ/kg [3], for insecti-cides as 7.5 [13] and for fungicides as 4.6 [14]. Brehmer [28]analyzed a wide range of agrochemicals and concluded that thereis a noticeable variation based on the active ingredients. His resultsshow that the CExC values vary between 172 and 564 MJ/kg forherbicides, between 21 and 667MJ/kg for insecticides and between38 and 474 MJ/kg for fungicides. Here the average values of theranges determined by Brehmer [28] are used for the calculations.Correspondingly, a total CExC of 3004.8 MJ, 318.8 MJ and 132.2 MJ isused for the agrochemicals to produce one ton of olives, sunflowerseeds, and soybeans, respectively.
3.1.3. Diesel utilizationDuring cultivation of 0.5 ton of olives/ha, energy equivalent of
machine work plus additional diesel utilization is 2454.4 MJ/ha [9],implying that the specific diesel energy utilization is 4908.8 MJ/tonof olives. Since emission factor ¼ 0.94 kg CO2/kg of diesel [25],density ¼ 0.832 kg diesel/L, energy equivalent ¼ 57.5 MJ/kg ofdiesel [29] and CExC ¼ 53.2 MJ/kg [3] carbon dioxide emissionassociated with diesel utilization is calculated to be 80.3 kg CO2/tonof olives and exergy consumption to be 4545.5 MJ/ton of olives(Table 1). During cultivation of 1.8 ton/ha of sunflower seeds64.0 kg/ha of fuel is used, implying that energy and exergy utili-zation are 2042.7 MJ/ton and 1891.6 MJ/ton of sunflower seeds,respectively [10]. When emission factor and density of the fuel arethe same as those of diesel, we can calculate the carbon dioxide
Table 2a. Energy and exergy consumption and CO2 emission associated with production of olassociated with primary and secondary packaging of olive oil.
Packaging material Energy utilization for packagingoil from one ton of olives (MJ/ton)
Polylactic acid for making bottles 371.3Paper labels for bottles 49.9Cardboard for bottles 8.6Stretch film for secondary packaging 11.9Total 441.7
Processing step and equipment details Capacity (tonof olives/h)
emission associated with fuel utilization to be 33.4 kg CO2/ton ofsunflower seeds (Table 1).
Heavy-duty trucks (capacity ¼ 10 tons, velocity ¼ 90 km/h)utilize 0.287 L/km of fuel [30]. When the plant material is trans-ported to 50 km away from the factory, energy and exergyconsumptions and carbon dioxide emission for transportation ofthe plant material are calculated to be 80.9 MJ/ton, 75.2 MJ/ton and0.2 kg CO2/ton (Tables 4 and 5).
3.1.4. IrrigationDuring agriculture of olives (yield ¼ 0.5 ton olives/ha) 30.2 MJ/
ha of energy is utilized for irrigation [9].When the irrigation systemis run with electricity (emission factor ¼ 0.14 kg CO2/MJ), energyand exergy utilization and emission associated with irrigationduring production of one ton of oils are calculated to be 60.4 MJ,251.9 MJ and 8.5 kg, respectively (Table 1). No irrigation isemployed in the fields where Kallivroussis et al. [10] and De et al.[11] obtained their data.
3.1.5. SeedsDe et al.’s [11] data implies that 972.6 MJ energy is utilized to
produce seeds for cultivation of one ton of soybeans. Whenpercentage of diesel (85.5%, emission factor ¼ 0.02 kg CO2/MJ) andelectric power (14.5%, emission factor ¼ 0.14 kg CO2/MJ) are thesame as those of soybean agriculture, emission and CExC associatedwith seeds production is calculated to be 36.4 kg CO2/ton soybeansand 1358.1 MJ/ton of soybeans, respectively (Table 1). Energyutilization for seeds production is negligibly small in olive orsunflower cultivation due to extremely small seed to product ratio.
3.1.6. Agriculture in generalTable 1 indicates that the highest energy and exergy utilization
is associated with agriculture of olives and the highest emission isassociated with agriculture of soybeans. Olives are generally culti-vated in the fields, where the land cannot be used for economicallymore favorable products [27]. Eide [31], while studying the influ-ence of the size of the dairies on the carbon dioxide emissionreported that energy efficiency increases with the capacity. Highamounts of diesel utilization in agriculture of olives may actuallypoint the problem associated with the small size of the orchards.Diesel consumption data as reported by Polychchronaki et al. [9]includes energy utilization for transportation of the olives to the
ive oil packaging materials. b. Energy and exergy consumption and CO2 emission
CExC for packaging oil fromone ton of olives (MJ/ton)
CO2 emission during packaging oilfrom one ton of olives (kg/ton)
538.1 12.455.7 5.074.3 1.117.2 0.4
685.3 18.9
Energy utilizationfor processingone ton of olives (MJ/ton)
CExC for processing oneton of olives (MJ/ton)
CO2 emission duringprocessing one tonof olives (kg/ton)
441.7 685.3 18.927.0 112.6 3.6
33.4 139.3 4.7
33.4 139.3 4.7
535.5 1076.5 31.9
Table 3Energy and exergy consumption and CO2 emission associated with olive oil production process.
Processing step and equipmentdetails
Capacity (ton ofolives/h)
Energyconsumption(MJ/h)
Energy utilization forprocessing one tonof olives (MJ/ton)
CExC for processingone ton of olives(MJ/ton)
CO2 emission duringprocessing one tonof olives (kg/ton)
Labeller (Shanghai Peiyu Machinery, Ltd,China; Model SPC-SORL-TL)
5000 to 30 000 bottles/h 24 0.1 0.4 0.0
Packaging 535.5 1076.5 31.9Transportation of olive oil to 550 kms 222.1 206.6 3.0Waste management Batch process �1.4 �5.8 57.3
Continuous process �2.8 �11.7 114.4Total 10028.6 10762.6 323.1
M. Özilgen, E. Sorgüven / Energy 36 (2011) 5954e59675960
market; therefore, diesel consumption does not appear as a sepa-rate entry in Table 3.
In order to demonstrate how different agricultural techniqueschange the results, CEnC, CExC and CO2 emission for soybeanproduction is calculated based on four different data [11,14,26,32].
Table 4Energy and exergy consumption and CO2 emission associated with the sunflower oil pro
Labeller (Shanghai Peiyu Machinery,Ltd, China; Model SPC-SORL-TL)
5000 to 30 000 bottles/h 24
Packaging 10Transportation of sunflower oil
to 550 km4
Total 77
Energy and exergy consumption and carbon dioxide emittedassociated with seeds is omitted in this comparison. Results aresummarized in Figs. 4e6 and Table 7. The total amount of fertilizersconsumed is reported as 17.4 kg/ton by Fore et al. [26], 43.4 kg/tonby Sheehan et al. [32] and 75.8 kg/ton of soybean by De et al. [11].
duction process.
ergy utilization for processinge ton of sunflower seedsJ/ton)
CExC for processing oneton of sunflower seeds(MJ/ton)
CO2 emission duringprocessing one ton ofsunflower seeds(kg/ton)
79.2 3425.7 317.480.9 75.2 0.2
3.7 15.4 0.5
1.8 7.5 0.211.1 46.3 1.6
32 550.4 18.5
43.6 181.8 6.1
42 1426.1 47.9
13.5 56.3 1.9
70 458.2 28.2
2.4 10.0 0.0
71 2152.9 63.844.2 413.1 6
95.4 8819.1 492.3
Table 5Energy and exergy consumption and CO2 emission associated with the soybean oil production process.
Processing step andequipment details
Capacity (ton of soybean/h) Energyconsumption(MJ/h)
Energy utilization for processingone ton of soybean (MJ/ton)
CExC for processing oneton of soybean (MJ/ton)
CO2 emission during processingone ton of soybean (kg/ton)
Labeling 5000 to 30 000 bottles/h 24 1.0 4.2 0.0Packaging 482.4 861.2 25.5Transportation to
550 km177.7 165.3 2.4
Total 7619.1 9051.4 860.0
M. Özilgen, E. Sorgüven / Energy 36 (2011) 5954e5967 5961
Pimental and Patzek [33] reported that 4800 kg/ha of lime is usedin addition to the nitrogeneous, phosphorus and potassium fertil-izer utilization, which are 3.7 kg/ha, 37.8 kg/ha and 14.8 kg/ha,respectively. According to their data nearly half of the totalconsumed energy (3746 Mcal/ha) comes from lime (1349 Mcal/ha).Inspite of this rather large consumption of fertilizers, total energyconsumption is comparable to other data sets, since diesel andelectricity consumption are comparatively less than the rest of thepublished data sets. However, exergy consumption and carbondioxide emission values are effected dramatically. Lime productionis an energy intensive process, where 10 MJ of exergy is consumedand 0.79 kg of CO2 is emitted per kg of lime [33]. The CExC value iscalculated based on Pimental and Patzek [33] to be 19427 MJ/ton ofsoybean, where 93.5% of the total exergy consumption is due tofertilizers. The CO2 emission per ton of soybeans calculated basedon Pimental and Patzek [33] is 1534 kg, where 98.3% of this is due tofertilizer consumption. This result draws attention to the pointabout excessive fertilizer utilization as criticized by Esengun et al.[17] (Figs. 4e6).
3.2. Energy and exergy consumption and carbon dioxide emissionfor packaging
From one ton of olives 250 kg oil is produced, therefore 125bottles (bottle volume ¼ 2 L, bottle weight 50 g, cap weight ¼ 5 g)are needed. While producing one kg of polylactic acid (PLA) 1.6 kgof fossil fuel with 54 MJ of energy is utilized and 1.8 kgCO2 is emitted [34,35]. When energy is provided from naturalgas (CExC ¼ 48.7 MJ/kg [3]), the CExC of PLA is calculated to be78 MJ/kg, implying that for 125 bottles (one ton of olives) 6.9 kg,
Table 6Energy and exergy utilization and carbon dioxide emission associated withproduction of the olive, sunflower, and soybean oils.
371.3 MJ of energy and 538.1 MJ of exergy will be utilized and12.4 kg of CO2 will be emitted (Table 2). For a typical 2 L bottle(side surface area 942.48 cm2) 7.98 g of paper label is needed [36],for 125 bottles 997.5 g of label is used. When 35% of the labels areproduced with recycled paper, energy utilization for producing648.4 g of labels needed for olive oil produced from one ton ofolives is calculated to be 49.9 MJ. When half of this energy issupplied by natural gas and the other half is supplied by electricpower CO2 emission for label making is calculated to be 5 MJ/tonolives (Table 2). The CExC for paper produced from standingtimber is 88.1 MJ/kg. This value reduces to 59.9 MJ/kg if the plantis integrated and the wastes are used as fuel [3]. Here, the averageof these two values is used as the CExC for paper. The CExC valuesfor the paper produced from waste paper are 22.2 MJ/kg [3].When 35% of the labels are produced from recycled paper, thetotal CExC for labels is calculated to be 55.7 MJ/ton of olives. Thelabeling machine (Shanghai Peiyu Machinery Manufacturing Co.,Ltd, China, Model: SPC-SORL-TL) had a capacity of labeling 5000to 30000 bottles/h and utilizing 24 MJ/h. The required energy forlabeling 125 bottles is calculated to be 0.1 MJ/ton of olives and theassociated CExC and CO2 emission are 0.417 MJ/ton and 0.014 kgCO2/ton of olives, respectively.
When 9 bottles are placed in a 320 mm*320 mm*324 mmcardboard box and 24 cartons are placed on a pallet, for secondarypackaging of 125 olive oil bottles 13.9 corrugated cartons and 0.58pallets are needed. Amount of cardboard needed to make onecarton is about 6195.2 cm2. Chow et al. [37] reported that0.75e1.25 MJ/m2 energy is utilized for cardboard making. Whenthe average CEnC, 1.00 MJ/m2, is used, 8.62 MJ of energy con-sumption is estimated to produce cardboard per one ton of olives.When 90% of the energy is supplied from electricity (emissioncoefficient ¼ 0.14 kg of CO2/MJ [38]) and the rest from natural gas(emission coefficient¼ 0.06 kg of CO2/MJ [38], CExC of natural gas is48.7MJ/kg [3]), CO2 emission associatedwith cardboard productionis 1.14 kg CO2/ton olives and CExC is 74.3 MJ/ton of olives. New hightechnology plastic pallets are 100% recyclable and can make about250 trips, therefore energy consumption and CO2 emission asso-ciatedwith pallet making is not considered here [39]. For secondarypackaging of one pallet 10 m (375 g) of stretch film is needed,implying that for one ton of oil 0.58 pallets, i.e. 0.22 kg stretch filmis used. Thus, 11.9 MJ of energy and 17.2 MJ of exergy are utilized,and 0.4 kg of CO2 will be emitted while producing material for
Fig. 4. Comparison of cumulative energy consumptions in soybean production.
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secondary packaging of the oil produced from one ton of olives. It isshown in Table 2 that the total energy and exergy utilization andemission associated with the material used for primary andsecondary packaging of olive oils are 441.7 MJ/ton, 685.3 MJ/ton ofolives and 18.9 kg/ton of olives, respectively. Oil content of thesunflower seeds is reported to be 50% [40]; therefore, 500 kg oil(250 bottles) is required for one ton of sunflower seeds; implyingthat energy and exergy utilization and carbon dioxide emissionassociated with packaging of sunflower oil is twice as much asthose of olive oil (Table 4). Whenwe consider that the oil content ofthe soybeans are 80% of that of olives, energy and exergy utilizationand emission associated with packaging of soybean oil is calculatedas 482.4 MJ/ton, 861.2 MJ/ton of soybeans and 25.5 kg CO2/ton ofsoybeans, respectively (Table 5).
Fig. 5. Comparison of cumulative exergy c
3.3. Energy and exergy consumption and carbon dioxide emissionduring olive oil and sunflower oil production
Common steps of oil production, including conveying, cleaning,grinding, pressing, separation and storage is described in Fig. 2.When the crops reach to the factory they are transported to thewashers with conveyors. Energy consumption data by each piece ofequipment employed in the oil plants are obtained from the websites of the equipment manufacturers, then energy consumptionfor processing one ton of olives, sunflower seeds and soybeans iscomputed as depicted in Tables 3,4 and 5, respectively.
Olive carrying conveyor (Polat Machinery; Turkey,capacity¼ 6 ton olives/h, motor power for carrying olives ¼ 4.0 MJ/h, aspirator power for removing leaves and grass¼ 10.9 MJ/h); olive
onsumptions in soybean production.
Fig. 6. Comparison of carbon dioxide emission in soybean production.
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washing unit (Polat Machinery; Turkey, capacity ¼ 6 ton olives/h,power ¼ 3.6 MJ/h); crushing machine (Polat Machinery, Turkey;Model PMS 370, capacity ¼ 3000 kg olives/h, powerutilization¼ 69.3 MJ/h); modular mixing machine (Siemens, ModelQ4 100L 4A, capacity ¼ 300 kg of olives/h, powerutilization ¼ 23.76 MJ/h); pressing machine (Anyang GEMCOEnergy Machinery, China, Model D-1688, capacity ¼ 0.3 tons/h,energy utilization ¼ 39.6 MJ/h); centrifuge (Polat Machinery,Turkey; Model PX 40, capacity ¼ 5000 kg olives/h, powerutilization ¼ 69.91 MJ/h); and phase separating machine (PolatMachinery, Turkey; Model PMS 405 capacity ¼ 2000 kg of olives/h,power utilization¼ 19.8 MJ/h) are employed in the design (Table 3).In filling process 11.2 MJ of electricity is consumed for filling 1000bottles/h of olive oil. Carton printing and box making machine (Fullservo carton making machine, Shanghai Liu Xiang General Equip-ment Co., Ltd, China) is capable of producing 250 cartons/min andhas a power of 486 MJ (including dryer); therefore, energy requiredfor printing and producing 13.9 cartons is calculated to be 27.0 MJ/ton of olives. The associated CExC and CO2 emission for one ton ofolives are 112.6 MJ and 3.56 kg CO2, respectively (Table 2). For thecarton fillingmachine (Shanghai Peifeng Electronics Co., Ltd., China,capacity ¼ 15 box/min, power ¼ 36 MJ), energy and exergy
Table 7Raw materials and fuels consumed to produce 1 ton of soybean.
utilization and CO2 emission for processing one ton of olives arecalculated to be 33.4 MJ, 139.3 MJ and 4.7 kg, respectively (Table 2).
Energy and exergy utilization and carbon dioxide emission dataof the equipment which may be employed in the sunflower oil aredepicted in Table 4. Cleaning machine, (TQLZ63 � 100) witha capacity of 5000 kg sunflower seeds/h and a power utilization of0.5 MJ/h, grinding machine (Jiadi Machinery, China, Model TMJ-4)with a capacity of 6000 kg sunflowers/h and a power utilizationof 66.6 MJ/h; oil pressing machine (Anyang GEMCO EnergyMachinery, China; Model YZS-120) with a capacity of 300 kgsunflower/h and a power utilization of 39.6 MJ/h, extractor (JiadiMachinery, China; Model D-1688) with a capacity of 260 kgsunflower seeds/h and a power utilization of 11.3 MJ/h and refiningequipment (Jiadi Machinery, China; Model 10T) with a capacity of400 kg sunflower seeds/h and a power utilization of 136.8 MJ/h.
Energy and exergy utilization for primary and secondary pack-aging of sunflower and soybean oils are calculated by following thesame procedure as that of the olive oil. Oils were assumed to betransported to an average distance of 550 km; by following thesame procedure as the transportation of sunflower seeds orsoybeans, energy utilization and carbon dioxide emission associ-ated with transportation are calculated and depicted in Tables 3e5.
3.4. Energy and exergy consumption and carbon dioxide emissionsduring waste management
After the extraction of the olive oil, 0.5e1.1 kg of wastewater/kgof olives is produced [41]. A typical wastewater may consist of80e83% water, 15e18% organic compounds, and 2% potassium andphosphate salts, etc [25]. Some of these substances are toxic andnot biodegradable; therefore, the waste cannot be used as fertilizer,or irrigation water [42]. One of the best options for management ofthe olive oil wastewater would be combustion of the waste afterconcentration by evaporation [25]. When the wastewater is fed tothe evaporator at a rate of 0.85 kg/s, 1620 J/s of energy is utilized toachieve evaporation, 1450 J/s of energy is gained upon condensa-tion, and 2650 MJ/s of more energy is obtained after combustion,
Fig. 7. Comparison of the cumulative energy and exergy consumptions to produce oil from one ton of olives, soybeans and sunflower seeds.
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with a net energy gain of 2480 J/s [25]. Implying that in a batchprocess, which produces 0.50 ton of waste water/ton of olives, thenet energy gain may be 1.4 MJ/ton of olives. This corresponds to anexergy gain of 5.8 MJ/ton of olives, since less electricity will beconsumed. Suspended solids contents of the wastewater from bothbatch and continuous separation processes are identical [41];therefore, we may estimate that the net energy and exergy gain as2.8 MJ/ton of olives and 11.7 MJ/ton of oils, respectively. Whenevaporation is achieved by consumingmainly natural gas (emission
Fig. 8. Comparison of the carbon dioxide emissions to produce
factor¼ 0.06 kg CO2/MJ [38]), 57.3 kg CO2/ton of olives is emitted ina batch extraction process or 114.4 kg CO2/ton of olives is emitted ina continuous extraction process (Table 3).
Waste vegetable oils may be converted into biofuel, or used asan alternative to diesel in heating oil burners. Energy consumptionin the production of biodiesel is 3.7 MJ/kg. Since most of the bio-diesel, production process is run with electricity and 0.14 kg of CO2is emitted/MJ of electricity used, we may calculate the emissionassociated with waste management as 0.5 kg CO2/kg of fresh oil
oil from one ton of olives, soybeans and sunflower seeds.
Table 8Chemical exergy estimation for olive, sunflower, and soybean oil.
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[26,43]. Since more energy and exergy (67 MJ/kg) will be obtainedafter burning the biodiesel, energy and exergy utilization in asso-ciation with biodiesel production for waste management will notappear in Tables 3e5.
Most of the energy utilized in the oil production is in the form ofelectric power (Tables 2e5). Electric power may also be producedfrom wind, hydroelectric or nuclear power, etc. Electric power,which is obtained from all of these resources, is combined innational or international networks. The relation between theamounts of carbon dioxide emitted and electric power consumeddepends on the contribution of each resource into overall electricpower generation. One MJ of electric power utilization causes0.14 kg of CO2 emission [30]. In countries where electricity isproduced by burning fossil fuels only, amount of CO2 emittedshould be higher in comparison with the countries where majorityof electric power is obtained from hydroelectric power plants.Consumers usually do not have information about electricity usedfor the product they purchased and its environmental impacts[41,44]. Results from a survey indicated that 79% of households and81% of small and medium sized enterprisers are aware of the factthat the use of fossil fuels contributes to climate change, but they donot necessarily relate this to carbon dioxide emissions [45].Providing information to the consumers about the energy cost andCO2 emission associated with each product may also convince theproducers to use cleaner energy sources.
Here the oil production process is modeled as a generic plant, inorder to achieve comparable results for the three different oilsinvestigated. Comparison of the numerical results obtained fromour calculations with published data on olive oil, soybean oil andsunflower oil production processes show a good agreement. In thisstudy, the total energy consumption during olive oil production iscalculated to be 1070.8MJ/ton of olive oil. Avraamides [46] reportedtotal energy consumption of 962.8 MJ/ton of olive oil. Our estima-tion for the total energy consumption during sunflower oilproduction is 1068 MJ, whereas Nilsson [47] reported an energyconsumption of 1181.5 MJ/ton of sunflower oil. For soybean oilproduction our estimation is 1645 MJ/ton of soybean oil; Sheehanet al. [32] reported a consumption of 1481 MJ of electricity toproduce one ton of soybean oil. The differences between our esti-mations and the reported data are about 10%.
3.5. Cumulative degree of perfection
Calculation of chemical the exergy of oils are based on theircomposition as described by Sorguven and Özilgen [4] (Table 8).Chemical exergy of the olive oil is the highest, due its high oleic acidcontent. The CDP is calculated as the ratio of the chemical exergy ofthe main product to the total exergy consumption, including rawmaterials and fuels (Table 6). Exergy input from the renewableinputs, including solar energy, are not taken into account. CDP ofolive oil, soybean oil, and sunflower oil is 97.6%, 92.1% and 236.5%,respectively. Although the CExC to produce oil from 1 ton of crop is
comparable for all three oils, since the oil content of sunflower seedis twice as much as olive as and 2.5 times larger than soybean(Table 6), CDP of sunflower oil is much larger.
Energy intensity has been decreasing and approaching to thetheoretical minimum in most subsectors over the years [45]. If theenergy utilization trends reported by Nuibe [44] continue over thenext five years, at least 5% more decline can be expected in all theprocesses employed in this study. About 15% deviation may beexpected between the equipment produced by different manufac-turers; deviation in different agricultural practices may be larger.Energy consumption and CO2 emission estimates are subject tochangewith the scenario. Energy consumptionmay increase, as theequipment gets older. Therefore, about �20% error may be expec-ted in the values we report. The results of this study are based onthe assumption that olives and sunflower seeds and soybeanscontain 25%, 50% and 20% oil, respectively. Oil yield of sunflowersvary substantially [40]. If the calculations should be based on thevarieties with less oil content, the results may change accordingly.
During the recent years, excellent studies are done to compareeither the efficiency or point out the inefficiency of the existingplants and practices [31,48e52]. Exergy efficiency of vegetable oilproduction process may be improved by benefiting from thenovelty reported in these studies, such as using waste heat fromheat pump elsewhere in the plant [53]. Combined contribution ofthese and similar studies are expected to cause substantial increasein energy efficiency and reduce carbon dioxide emission in the oilproducing plants in the near future. In the present study, we havetried to be as realistic as possible. In Turkey, the producers arehighly keen to reduce exergy and energy cost of their processes.Carbon dioxide emission to the atmosphere is planned to be taxedsoon. We have tried to choose as environment friendly inputs andprocesses as possible. We believe that the manufacturers willconsider them for their production as studies like this one drawtheir attention to those points.
In the present study energy and exergy utilization and carbondioxide emission during edible vegetable oil production have beenconsidered. Vegetable oils are also raw material for biodieselproduction. Interested readers are referred to the excellent studiesin the literature discussing the issue within that context [54,55].
4. Conclusions
During the agriculture, least amount of exergy is consumed toproduce sunflower; i.e. 3425.7 MJ/ton of sunflower. Soybean agri-culture required an exergy consumption of 6092.9 MJ/ton and oliveagriculture required 7904.7 MJ/ton. The CExC values of oil producedfrom the same amount of crop are comparable; i.e. 10762.6 MJ/tonof olive, 8819.1 MJ/ton of sunflower and 9051.4 MJ/ton of soybean(Fig. 7). However, the large difference between the oil content ofthese crops differentiates the CExC of the produced oil; i.e.17638.2 MJ/ton of sunflower oil, 43050.3 MJ/ton of olive oil and45256.8 MJ/ton of soybean oil (Table 6).
M. Özilgen, E. Sorgüven / Energy 36 (2011) 5954e59675966
The CDP of soybean and olive oil is 0.92 and 0.98, respectively,whereas the CDP of the sunflower oil is 2.36. Since the oil content ofthe sunflower seed is much larger than olive and soybean (i.e. 50%),its CDP is much larger.
Agriculture is the most energy and exergy intensive process andemits most of the carbon dioxide for each of the investigated cases(Fig. 8). Here diesel consumption is the dominant source of energyand exergy consumption. Decreasing the diesel consumption withgood agricultural practices and employing biodiesel may improvethe situation. If we substitute diesel (CExC ¼ 53.2 MJ/kg) withbiodiesel obtained from renewable resources (CExC ¼ 8.8 MJ/kg) asdescribed by Sorguven and Özilgen [4], the CExC values woulddecrease to 3859.6 MJ/ton of olives, 1847.1 MJ/ton of sunflowerseeds and 2347.1 MJ/ton of soybeans. As a result, CDP of olive andsoybean oil rises to 1.6 and sunflower oil to 2.9.
The malpractice of excessive fertilizers and agrochemicals usemakes themajor contribution to carbon dioxide emission. Themostenergy intensive process is olive oil production. However, since thefertilizer consumption here is limited, total carbon dioxide emis-sion is less than those of the other two processes are. On the otherhand, excessive fertilizer consumption during the soybean agri-culture results in a rather large CO2 emission.
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