143 Design and Analysis of Energy-Efficient Integrated Crude Palm Oil and Palm Kernel Oil Processes Muhammad Aziz, Takuya ODA, and Takao KASHIWAGI (Received May 28, 2014) This study deals with an innovative design of integrated crude palm oil (CPO) and palm kernel oil processes based on process integration technology. Two types of cogeneration systems were introduced in this integrated process to further improve energy efficiency: a conventional boiler based cogeneration system and an internal combustion engine based cogeneration system. The solid wastes, including empty fruit bunches, fibers and nut shells, are used as fuel for boiler based cogeneration. Moreover, in the internal combustion engine based cogeneration, biogas is produced from the palm oil mill effluent exhausted from the CPO milling process. Energy analysis of the proposed integrated system was performed in terms of energy demand and patterns in both milling processes. The results show clearly the significant energy surplus in both milling processes. Furthermore, the huge potential of CPO and palm kernel oil mills in terms of both oil and energy production has the ability to increase national energy security in Indonesia. Key Words Crude palm oil, Palm kernel oil, Process integration, Energy efficiency, Cogeneration Solutions Research Laboratory, Tokyo Institute of Technology 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan Journal of the Japan Institute of Energy , 94, 143-150（2015） 1. Introduction Indonesia is the largest producer and exporter of palm oil and palm oil products in the world. Production of crude palm oil (CPO) and palm kernel oil (PKO) in Indonesia increased annually by about 10.03 % and 10.07 %, respectively, between 2002 and 2009. This is the result of the large expansion in palm plantations especially in Sumatra and Kalimantan 1) . Furthermore, the total production of CPO and PKO are predicted to reach 31 and 3.65 Tg (3.6 million tons) in 2013/2014, respectively 2) . The palm oil industry has been the biggest source of income in Indonesia for many years. Moreover, CPO and PKO emerged as two of the most important oils in the world and in markets of fats. It is estimated that there are several hundred CPO mills of all sizes in Indonesia. Palm fruit yields CPO and PKO. The demand for CPO and PKO has increased significantly, especially because of the increasing high standard of living following the economic growth in developing countries such as China and India. CPO and PKO have quite different fatty acid compositions. The pulp and kernel consist of about 70 % and 40 % oil, respectively. In total, a fruit bunch usually produces about 20 % CPO and 2 % PKO 3) . CPO has a higher unsaturated acid content than PKO, and contains saturated palmitic acid (42-47 %), oleic acid (37-41 %) and linoleic acid 4) . About 90 % of CPO is used as raw material for food related products, such as margarine and cooking oils, while the remaining 10 % is used as a basic material in soap 5) . Additionally, CPO is becoming an important material for energy production, i.e. biodiesel fuel. Unlike CPO, PKO is rich in lauric acid (44-51 %), which resembles coconut oil 6) . The characteristics of PKO include a high content of saturated acid (lauric and myristic), a low melting point (solid in ambient temperature) and high oxidative stability because of a low level of unsaturation. Hence, there are many uses for PKO including material for hard butter and vegetable fat in ice creams 7) . The milling of both CPO and PKO are considered energy intensive processes because of the huge energy consumption, including heat and electricity. To process 1 t of fresh fruit bunches (FFB) into CPO, the required electricity and steam (including hot water) are 20 kWh and 600 kg 5) 8) 9) , respectively. Additionally, to process 1 t of palm nuts into
Transcript
143
Design and Analysis of Energy-Efficient Integrated Crude Palm Oil and Palm Kernel Oil Processes
Muhammad Aziz, Takuya ODA, and Takao KASHIWAGI
(Received May 28, 2014)
This study deals with an innovative design of integrated crude palm oil (CPO) and palm kernel oil processes based on process integration technology. Two types of cogeneration systems were introduced in this integrated process to further improve energy efficiency: a conventional boiler based cogeneration system and an internal combustion engine based cogeneration system. The solid wastes, including empty fruit bunches, fibers and nut shells, are used as fuel for boiler based cogeneration. Moreover, in the internal combustion engine based cogeneration, biogas is produced from the palm oil mill effluent exhausted from the CPO milling process. Energy analysis of the proposed integrated system was performed in terms of energy demand and patterns in both milling processes. The results show clearly the significant energy surplus in both milling processes. Furthermore, the huge potential of CPO and palm kernel oil mills in terms of both oil and energy production has the ability to increase national energy security in Indonesia.
Key WordsCrude palm oil, Palm kernel oil, Process integration, Energy efficiency, Cogeneration
Solutions Research Laboratory, Tokyo Institute of Technology2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
Journal of the Japan Institute of Energy, 94, 143-150（2015）
1. IntroductionIndonesia is the largest producer and exporter of
palm oil and palm oil products in the world. Production of crude palm oil (CPO) and palm kernel oil (PKO) in Indonesia increased annually by about 10.03 % and 10.07 %, respectively, between 2002 and 2009. This is the result of the large expansion in palm plantations especially in Sumatra and Kalimantan 1). Furthermore, the total production of CPO and PKO are predicted to reach 31 and 3.65 Tg (3.6 million tons) in 2013/2014, respectively 2). The palm oil industry has been the biggest source of income in Indonesia for many years. Moreover, CPO and PKO emerged as two of the most important oils in the world and in markets of fats. It is estimated that there are several hundred CPO mills of all sizes in Indonesia.
Palm fruit yields CPO and PKO. The demand for CPO and PKO has increased significantly, especially because of the increasing high standard of living following the economic growth in developing countries such as China and India.
CPO and PKO have quite different fatty acid
compositions. The pulp and kernel consist of about 70 % and 40 % oil, respectively. In total, a fruit bunch usually produces about 20 % CPO and 2 % PKO 3). CPO has a higher unsaturated acid content than PKO, and contains saturated palmitic acid (42-47 %), oleic acid (37-41 %) and linoleic acid 4). About 90 % of CPO is used as raw material for food related products, such as margarine and cooking oils, while the remaining 10 % is used as a basic material in soap 5). Additionally, CPO is becoming an important material for energy production, i.e. biodiesel fuel. Unlike CPO, PKO is rich in lauric acid (44-51 %), which resembles coconut oil 6). The characteristics of PKO include a high content of saturated acid (lauric and myristic), a low melting point (solid in ambient temperature) and high oxidative stability because of a low level of unsaturation. Hence, there are many uses for PKO including material for hard butter and vegetable fat in ice creams 7).
The milling of both CPO and PKO are considered energy intensive processes because of the huge energy consumption, including heat and electricity. To process 1 t of fresh fruit bunches (FFB) into CPO, the required electricity and steam (including hot water) are 20 kWh and 600 kg 5) 8) 9), respectively. Additionally, to process 1 t of palm nuts into
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PKO, the required electricity and thermal energy are 17.1 MJ and 156.38 MJ, respectively 10). At present, both electrical and thermal energy for either CPO or PKO mills are generally supplied by stand-alone power and steam generators, which are not well integrated. Fiber and shell are the main fuels used for power and steam generation in a CPO mill. Furthermore, in PKO mills, stand-alone power and steam generators are installed to cover their energy needs; these use diesel oil, biogas from palm oil mill effluent (POME), grid electricity, among other sources. This inefficiency in the energy systems causes a huge amount of energy being consumed, leading to high production costs. To the best of the authors’ knowledge, no study dealing with the integration of PKO and CPO mills has been made, especially in terms of energy analysis.
This study focuses on the idea of integrating both CPO and PKO mills with power and steam generation systems to improve the total energy efficiency, particularly in Indonesia. Two cogeneration systems are adopted to use the waste materials from both mills and convert them to useful energy. The study does not cover the downstream processes of refining for both CPO and PKO.
2. Integrated CPO and PKO ProcessesThe weight of palm nuts separated in a CPO mill
ranges from 11 % to 14 % of the amount of inputted FFB. Therefore, palm kernels from several CPO mills (usually 5 to 10 mills) are collected and processed in one PKO mill, which is usually installed near one of the CPO mills. Fig. 1 shows the main concepts of energy and material circulation in the proposed integrated CPO and PKO processes. Basically, all the materials including solid and liquid wastes
are used in various ways leaving no unused materials. In terms of material and energy use, this material circulation is carbon neutral, leading to the use of no fossil fuel in any of the processes.
Fig. 2 shows a schematic of the material and energy flows of the proposed integrated CPO and PKO processes. The integrated processes mainly consist of the CPO mill process, PKO mill process and power and steam processes. The power and steam processes are composed of boiler based cogeneration and internal combustion engine (ICE) based cogeneration, producing both electricity and steam. Boiler based cogeneration uses solid wastes as fuel. It basically consists of combustor, steam boiler, turbine, generator and back-pressure receiver. Furthermore, the generated steam is in a high pressure condition (about 1.7- 2.0 MPa), which is used to rotate the steam turbine generating the electricity. The steam exhausted from the turbine, with a pressure of 0.3 MPa, then flows to a back-pressure receiver before it is used in the CPO and PKO mills. Conversely, ICE based cogeneration uses biogas from a biogas plant to achieve mechanical energy, which is further used to rotate the generator to generate electricity. As the flue gas exhausted from the ICE engine has quite high temperatures (about 300-600 °C), this heat is recuperated to generate hot water, which is used for both the CPO and PKO mills, together with the steam produced in the boiler based cogeneration system.
Starting from the palm plantation, raw FFB is harvested and brought to the CPO mill for CPO clarification. In this stage, palm kernels, which will go to PKO mill, are also separated. As subsidiary products, solid and liquid wastes are also exhausted from the CPO mill
Fig. 1 Basic energy and material circulation in the proposed integrated CPO and PKO processes
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and are used as fuel for the cogeneration system. The solid wastes from the CPO mill include EFB and palm pressed fiber (PPF). EFB is used as fuel for the cogeneration system or as mulch, which is returned to the palm plantation. PPF is used as fuel in the boiler based cogeneration.
CPO mills also produce a large amount of liquid residual waste, which is usually called as POME. POME is usually hot (70-90 °C) when discharged and becomes the most problematic waste in a CPO mill in terms of environmental issues. POME is acidic - with pH ranges from 4 to 5 - and has a high biological oxygen demand (BOD) and chemical oxygen demand (COD) and if discharged without effective treatment, will result in high pollution of the land and waterways with a significant negative impact on aquatic life downstream 11) 12). It is a brown colloidal suspension containing about 95% water and 0.6-0.7 % oil and grease. As an extraction residue, it is rich in organic matter including proteins, carbohydrates and lipids along with nitrogenous materials 13) 14). POME is nontoxic waste because there is no chemical addition in any of the extraction processes.
In this study, POME is further treated through an anaerobic process, which degrades it mainly into methane, carbon dioxide and water in the biogas plant. The sequences of reactions in an anaerobic process include hydrolysis, acidogenesis and methanogenesis and are explained in detail by Ahmad et al. 15). As the major pollutant in POME, lipids are degraded to glycerol, which is further degraded and converted to methane 16) ～18). To activate this anaerobic
reaction, several groups of microorganisms are required to maintain the process operation. The biogas produced is used as fuel for ICE cogeneration.
In the PKO mill, palm nuts are processed starting with nut drying. The cracking process in PKO milling produces a solid waste of palm nut shells. Generally, palm nuts are about 60 % shell and 40 % kernel. The separated palm nut shells are used as fuel for boiler based cogeneration together with the EFB and PPF from CPO mills. The PKO mill also produces the additional solid waste of palm kernel cake (PKC). Basically, the amount of PKO produced from the kernels is about 47-50 % of the weight 19) 20). The extraction process for PKO can be performed through mechanical extraction, solvent extraction or a combination of the two. In this study, mechanical extraction was selected because its energy consumption is lower than solvent extraction 19). Additionally, PKC can be used as material for animal feed such as for ruminants, poultry, rabbits and fish.
3. System Calculations and AnalysisThe calculations for the proposed integrated CPO
and PKO mills were performed based on Fig. 2. Table 1 shows the composition of the FFB, which enters the mill for CPO clarification. The flow rate of FFBs entering the CPO mill is fixed at 1 t h－1. The ambient temperature and atmospheric pressure are assumed to be 25 °C and 101.33 kPa, respectively. Furthermore, the PKO mill in this study processes the palm nuts collected from 5 CPO mills including the integrated CPO mill. Hence, the total
Fig. 2 Schematic material and energy flows of the proposed integrated CPO and PKO processes
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weight of palm nuts entering the PKO mill is 600 kg h－1, including 480 kg from the other 4 CPO mills. Fig. 3 shows the mass balance of the proposed integrated CPO and PKO mills. This mass balance is established based on the literature 1) 3) 7) 8) 21) ～ 23) and direct observation of some mills in Sumatra, Indonesia, including PTPN IV, PTPN V and some private milling companies.
The FFB enters the sterilization process, which
consumes the largest volumes of steam in all the milling processes. The objectives of sterilization include preventing the formation of emulsions during CPO clarification, deactivating the fruit enzyme to stop the build-up of free fatty acid, softening the mesocarp and conditioning the nut to minimize kernel breakage. The cooking pressure and temperature in sterilization are set to 300 kPa and 140 °C, respectively. The cooked FFB enters the stripping process, which is a rotating drum stripper to detach the fruit from the EFB. The fruit flow to the digester where they are treated mechanically and converted into a homogeneous oily mash. Hot water is added to facilitate this homogenization. Subsequently, the fruit is fed into a screw press where the press cake is separated from the mixture of oil, water, debris, and any other material, which is discharged as dirty crude oil. The hot water is added to reduce the viscosity of the discharged crude oil. The solid press cake including PPF and palm nuts is separated and fed to the depericarper.
Table 1 Basic composition of FFB
MaterialWeight percentage
(wt.%)Heat capacity(kJ kg-1 K-1)
Water 15 4.18Nut shell 6.8 1.88Kernel 5.2 1.59Palm oil 23.5 1.46Fiber 14.0 1.80EFB 22.0 1.67Mud, etc. 12 2.22
Fig. 3 Mass balance of the proposed integrated CPO and PKO processes
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The crude oil is further clarified through solid screening (mechanical vibration) and oil sifting based on the density differences in the clarification tank. Oil from the top is then skimmed off and flows to the next process, vacuum drying. The final CPO is then cooled and stored. The lower layer of sludge is moved to the desander for removing solid waste such as sand and mud. Subsequently, the remaining oil in the sludge is separated using a centrifugal separator. Finally, the liquid waste (POME) flows to the cooling pond of the biogas plant for biogas production.
In contrast, the press cake from the pressing process is moved to a vertical column of the depericarper to separate the fiber (PPF) from the palm nuts using blown air. The palm nuts descend and are collected and sent to the PKO mill. The collected palm nuts from several CPO mills are fed to a drying silo for conditioning and drying. Generally, a drying silo uses hot air as the drying medium, hence, the heat source can be extracted from sources such as the generated steam and flue gas exhausted from cogeneration systems. Subsequently the palm nuts are cracked mechanically resulting in a mixture of nut shells and kernels. Nut shells are separated from the kernels through winnowing and a hydrocyclone. The hydrocyclone uses water and centrifugal forces for separation. The
floating kernels in the hydrocyclone are then collected and enter into an air drying process until a moisture content of about 7 wt.% on wet basis is reached. The dried kernels are moved to a screw press for oil extraction. Before screw pressing, pretreatment of the kernels is usually performed including size reduction and flaking. The extracted oil then goes to the separation process for PKO clarification.
Both solid and liquid wastes flow to the cogeneration systems for power and steam generation. Fig. 4 shows the schematic diagram of biogas plant and cogeneration systems. Table 2 shows the specifications of the cogeneration systems
ICE based cogenerationElectricity generation efficiency (%) 30Total efficiency (%) 80Exhausted gas temperature (°C) 450Min. temp. approach in HX (°C) 30Hot water outlet temperature 90
Fig. 4 Schematic diagram of biogas plant and cogeneration systems
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used in this study. For assistance in system design and energy calculation, a steady-state process simulator ProII (Invensys Corp.) was used, particularly for calculations on boiler based cogeneration. The solid wastes, including EFB, PPF and nut shells, are fed to the boiler in the cogeneration system for combustion. The calorific values of EFB, PPF and shells are assumed to be 18.80, 19.05 and 18.88 MJ kg－1, respectively 24). Additionally, dried EFB needs to be shredded before being fed into the boiler. The generated steam flows and expands in the steam turbine, causing the rotational energy to spin the generator, which generates the electricity. The exhausted steam from the turbine passes to the back-pressure receiver before it is distributed to processes that require steam. Because the volume of steam generated in the boiler is larger than that required for milling processes, the remaining steam is cooled down in the condenser and recycled back to the boiler.
The liquid waste (POME) from both the CPO and PKO mills are collected and exhausted to the cooling pond. Table 3 shows the specifications for the POME used in this study. Basically the biogas plants consist of treatment ponds including cooling, anaerobic, aerobic and maturation ponds. The fresh, hot POME is cooled to a temperature of approximately 35 °C and its pH is adjusted in the cooling and acidification ponds. The retention time in these ponds is 1-2 days.
Subsequently, the POME enters the anaerobic pond, which is covered with a flexible membrane and biogas is produced. The retention time in the anaerobic pond is the longest, about 60 days. The amount of biogas fed to the gas engine is set at 80 % of the rated biogas production capacity. A flaring system is installed to burn the rest of the unused biogas. Before entering the gas engine, biogas is treated for H2S scrubbing and moisture removal. Biogas mainly consists of methane and carbon dioxide. The gas engine rotates the generator to produce electricity. Furthermore, the heat of the flue gas from the engine is recovered to produce hot water using a heat exchanger.
The rest of the liquid waste goes to the aerobic and maturation ponds, including the facultative pond, for
aeration, with a retention time of about 14 days. The ponds are necessary to further reduce the organic content in the wastewater before it is discharged. The final discharged liquid waste is expected to have a BOD of less than 100 ppm, making it permissible for use as liquid fertilizer for the plantation or to be discarded into the river. The treated liquid waste can be dispersed through a trench that is distributed throughout the plantation area or it is separated as a sludge and liquid waste. The sludge is then transported to the plantation as a fertilizer, while the liquid waste enters the aerobic and maturation ponds before it is discarded into the river.
4. Results and DiscussionAn analysis of the energy consumption and its
patterns for the integrated CPO and PKO processes was performed. Initially, an energy analysis of the boiler based cogeneration was conducted. Table 4 shows the calculated results for boiler based cogeneration. In this study, it is assumed that all solid wastes are burnt completely inside the combustor. Based on the calculations, the required steam flow rate was 2.65 t h－1 and the generated electricity from boiler based cogeneration was about 235 kW. The steam exhausted from the turbine enters the back-pressure receiver. As the total steam required for both milling processes was 395 kg h－1, about 2.2 t h－1 of steam could be recycled back to the boiler after being cooled down in the condenser.
Table 5 shows the calculation results of the ICE based cogeneration system. From a total milling of 1 t-FFB h－1 and 600 kg-nut shells h－1, the generated electricity that
Table 3 POME treatment and biogas specifications
Specifications ValuePOME density (×103 kg m-3) 0.98Produced biogas per 1 t-POME (m3 t-1) 23POME temperature (°C) 80Methane percentage (vol.%) 55Methane net calorific value (MJ m-3) 50Methane density (kg m-3) 0.66Ratio of biogas used as fuel to total rated capacity (%) 80
Table 4 Calculation results of boiler based cogeneration
Table 5 Calculation results of gas engine based cogeneration
Specifications ValueProduced biogas (m3 h-1) 24.9Total calorific value (MJ h-1) 684.4Generated electricity (kW) 57.0Recovered heat amount (MJ h-1) 342.2Hot water temperature (°C) 90Hot water amount flow rate (kg h-1) 1253.4
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could be produced from biogas was about 57 kW. Moreover, the total hot water generated was about 1.2 t h－1.
From all the cogeneration systems, the total generated electricity was about 292 kW. According to the literature 5) 8) ～ 10), the electricity consumed in each of the CPO and PKO mills for a feed amount of 1 t h－1
of raw materials (each FFB and palm nut) was 20 and 11 kW, respectively. Considering the electricity required for the utilities (compressor, pump, shredder, etc.) in the cogeneration systems is about 20 % of the generated power, there is still a surplus electricity capacity of about 200 kW. Hence, compared with the existing conventional CPO and PKO mills, this integration has clear advantages leading to highly energy-efficient milling.
In Indonesia, according to the Minister of Energy and Mineral Resources Regulation No. 04/2012, the basic feed in tariff (FIT) for electricity generated from biomass and biogas was 975 Indonesian Rupiah (IDR) (1 USD = approx. 11,800 IDR on 16 June 2014) if connected to the medium voltage grid. Hence, the additional revenue that could be earned was about 195,000 IDR for the production in each mill of 1 t-FFB and 600 kg-palm nuts. Considering the average production of CPO mills in Indonesia is about 45 t-FFB h－1, the total revenue from electricity sales to the grid reaches about 8 million IDR h－1.
It is clear that the existence of CPO and PKO mills can be justified because of their potential for producing both oils and energy. Energy production, especially electricity generation, from palm oil mills is considered to be carbon neutral because of its biomass use. According to the data from Statistics Indonesia, the total production of CPO oil in Indonesia in 2012 was about 15 Tg 25). Assuming that 1) the ratio of produced CPO to FFB is one to five, 2) the average
CPO mill capacity is 45 t-FFB h－1, 3) the daily operating time is 20 h, and 4) the palm nuts from five different CPO mills are collected and processed in one of the PKO mills, then the total surplus electricity from the CPO and PKO mills is about 1.5 GW. This capacity will increase following the increase in oil production from palm oil. Hence, the effective use of energy in CPO and PKO mills is very important for supporting national energy security.
Furthermore, as CPO and PKO mills are generally located near plantations that are located in remote areas, electricity generation in CPO and PKO mills is expected to improve the national electrification rate, which will ultimately raise the national standard of living.
From this study, it was also observed that the energy use in current CPO and PKO mills is still inefficient. Therefore, improvements in energy use must be pursued, especially when related to minimizing energy loss throughout the processes. Table 6 summarizes some examples of improvements that could be made for further efficient energy use. The points mainly concern effective energy recovery through circulation and cascaded use in each milling process and cogeneration systems.
5. ConclusionsThe proposed process integration of CPO and
PKO mills and cogeneration systems can improve the energy efficiency in the mills, improving their economic performance. The total generated power and heat are significantly more than required by both mills, and hence could be sold to a power utility as additional income via FIT program. Use of waste material is environmentally friendly and could simplify waste management. Additionally, if the mills are located in remote areas where connection to a grid
Table 6 Improvements that could be made for further efficient energy use
No Improvement points Description1 Steam recovery in sterilization The conventional autoclave that is used in sterilization causes a huge steam
loss when it is opened. Use of a suction blower before opening the autoclave can recover the steam. Furthermore, continuous sterilization is preferable because of the possibility for continuous steam recovery.
2 Heat recovery of POME Fresh POME has quite a high temperature, hence, its heat can be used for preheating of solids (EFB, palm nuts) or water before the boiler and heat exchanger (ICE cogeneration).
3 Heat use of hot water and steam for drying As the volumes of steam and hot water are a surplus in the whole process, and their heat can be used to preheat the air, which is used as a drying medium such as in silo drying and kernel drying.
4 Heat recovery of recycled water before a condenser The volume of exhaust steam from a turbine is significantly larger than that required in milling processes. This rest of the steam can be used for biogas drying, water pre-heating, etc.
5 Power generator with higher energy efficiency Application of a power generation system with higher efficiency such as gasification, fuel cell technology, etc. for both solid wastes and biogas
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is not available, the surplus electricity could be supplied to the surrounding staff quarters and residential area, creating an independent micro grid. As a result, the economic activities around the mills could be improved leading to a higher standard of living.
AcknowledgmentsThe authors express their sincere appreciation to
BPPT (Indonesia Agency for Assessment and Application Technology) for all their collaboration and advice. The authors also gratefully acknowledge Yanmar Co. Ltd., Japan, for financial assistance in this research.
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