CHEMICAL ENGINEERING TRANSACTIONS VOL. 63, 2018 A publication of The Italian Association of Chemical Engineering Online at www.aidic.it/cet Guest Editors: Jeng Shiun Lim, Wai Shin Ho, Jiří J. Klemeš Copyright © 2018, AIDIC Servizi S.r.l. ISBN 978-88-95608-61-7; ISSN 2283-9216 Potential of Energy Recovery from an Integrated Palm Oil Mill with Biogas Power Plant Boon Siang Tan, Haslenda Hashim*, Zarina Ab Muis, Nor Alafiza Yunus, Wai Shin Ho Process Systems Engineering Centre, Faculty of Chemical and Energy Engineering, Universiti Teknologi Malaysia, UTM Johor Bahru, Johor, 81310, Skudai, Malaysia haslenda@utm.my The Malaysian palm oil industry has made significant contribution to the country’s gross domestic product (GDP) due to the increasing global demand of palm oil over the past decades. However, it is undoubtedly a sector that consumes enormous energy and water. With the uprising concerns of the energy resource shortage and global warming, several green technology policies such as the feed-in-tariff policy have been implemented by government to accelerate the sustainable development of palm oil industry in Malaysia. The establishment of feed-in-tariff has successfully increased the number of palm oil mills that are completed with biogas facilities. Recent studies indicate that there are significant amounts of waste heat released from biogas power plant are utilisable as heat source for palm oil mill processes. As an initiative to develop the research of optimizing the energy efficiency of integrated palm oil mill with the biogas power plant, this study is directed toward the analysis of energy balance and material balance of an integrated palm oil mill with biogas power plant which covered both the palm oil milling process energy demand and the biogas power plant waste heat potential analysis. An integrated palm oil mill with biogas power plant running with 120 t/h fresh fruit bunches input was evaluated. The result indicates that there were a total of 3491.66 kW waste heat which corresponded to 46.82 % of the total biogas engine energy input could be recovered for process heating. By fully utilising the biogas plant waste heat as process heating for palm oil mill processes, it is estimated that up to 9.46 % of the total energy supplied could be saved. 1. Introduction The palm oil industry stays as one of the fast-growing industry as Malaysian palm oil export has shown an uprising trend since 1980s due to the increasing global demands and it is now ranked at second of the largest world crude palm oil (CPO) producers after Indonesia (Chin et al., 2013). However, the palm oil industry has been confronted by several criticisms from the international non-government organisations on the environmental issues particularly the emission of greenhouse gas (CHG) and the excessive amount of palm oil mill effluent (POME) that produced from palm oil milling process (Jamaludin et al., 2016). The biogas generation from POME anaerobic digestion in palm oil mill could be effectively exploited to provide alternative source of energy for the rural electrification (Lee et al., 2017). With the establishment of feed-in tariff (Fit) rates by the government, there are 90 Malaysian mills are completed with biogas facilities which corresponded to 20 % of the nationwide palm oil mills in 2016 (Wan et al., 2016). The biogas from POME is utilised to produce electricity in internal combustion engine with the electrical efficiency from 35 % to 45 % (Loh et al., 2017). Recent studies indicate that more than 55 % of the energy input of the heat engine are converted to thermal energy which commonly released to environment has huge potential to be recovered (Booneimsri et al., 2016). By considering the increasing trend of the palm oil mills that completed with biogas facilities, analysis of material balance and energy balance of the conventional palm oil mill processes including the sterilisation, digestion, sludge separation and fibre-nut-kernel separation alone is not sufficient to provide information of actual heat demands and waste heat potential. A structured material balance and energy balance of an integrated palm oil mill with biogas power plant is presented and discussed in this study. DOI: 10.3303/CET1863043 Please cite this article as: Boon Siang Tan, Haslenda Hashim, Zarina Ab Muis, Nor Alafiza Yunus, Wai Shin Ho, 2018, Potential of energy recovery from an integrated palm oil mill with biogas power plant, Chemical Engineering Transactions, 63, 253-258 DOI:10.3303/CET1863043 253 2. Methodology 2.1 Analysis of energy and material balance The integrated material balance of this study was made based on the law of conservation of mass which states that mass can neither be created nor destroyed. The total mass of input (ṁ in) must be equal to the total mass of output (ṁ out). ṁin = ṁout (1) Since the palm oil mill processes are nonreactive and mainly involve the separation process, the energy balance was made based on the equation below (Felder and Rousseau, 2005): Q = ∑ miHi - ∑ miHiinout (2) Qi = miCpi∆T (3) Where the Q̇ represents the enthalpy change of the process, ṁi is the mass flow rate (kg/h) of a species, Hi is the specific enthalpy of the species (kJ/kg), ∆T means the temperature difference (K or °C) whereas Cpi represents the specific heat capacity of the i-species (kJ/kg·K) which tabulated in Table 1. Table 1: Specific heat capacity of the palm oil mill component Species Cpi (kJ/kg·K) Species Cpi (kJ/kg·K) Fresh Fruit Bunch 3.231 (Ab Hadi et al., 2015) Mesocarp Fibre 2.816 (Ab Hadi et al., 2015) Empty Fruit Bunch 1.483 (Nyakuma et al., 2013) Palm Shell 2.083 (Fono-Tamo and Koya, 2013) Nuts 2.291 (Ab Hadi et al., 2015) Palm Kernel 2.567 (Ab Hadi et al., 2015) 2.2 Percentage of energy saving by recovering biogas power plant waste heat % of Energy Saving by Waste Heat Recovery = Total Recoverable Waste Heat from Biogas Power Plant∑ Q (4) 2.3 Case study and data collection The material and energy balance were performed based on the raw data collected from a palm oil mill with capacity of 120 t/h FFB input in Malaysia. The values of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) of the POME were obtained from the laboratory at the palm oil mill whereas the heat engines operating data were collected from the biogas power plant of this case study. 3. Findings 3.1 Palm oil mill material and energy balance Figure 1 shows the process block diagram of integrated palm oil mill with biogas power plant based on 120,000 kg/h FFB input basis. The entire process flow is categorised into 3 main sections namely palm oil mill, POME effluent and biogas power plant. According to Figure 1, stream 1 to stream 49 covered the sterilisation, digestion, oil purification, sludge separation, fibre-nut and shell-kernel separation process whereas stream 20, 50 and 51 were about the POME released from the palm oil mill processes. Table 2, 3, 4, 5 and 6 show the material balance and energy balance for every stream from stream 1 to stream 49 while Table 7 presents the material flow for stream 50 to stream 56. Table 8 shows the biogas heat engine energy balance data that reveals the waste heat potential of the heat engines. Based on the basis of 120 t/h FFB, stream 7 highlighted that there were 80,400 fruitlets which is corresponded to 67 % of the FFB detached in the thresher. Stream 6 indicates that there were 27,720 kg/h of wet EFB (23.1 % to FFB) conveyed for pressing and thus sending back for mulching on oil palm plantation. Apart from EFB and fruitlets, the rest are losses such as the debris of fiber, silts, sands and other solids components. While the detached fruits were sent for digestion and the flesh fruits were then circulated into the pressing machine with hot water to be pressed (Kramanandita et al., 2014). By considering the palm oil flowrates in stream 10 and the flesh fruits flowrates of stream 9, the data shows that flesh fruits produce 33.4 % of palm oil through digestion. This finding is consistent with the values proposed by Subramaniam et al. (2013) in their study. The crude oil produced in pressing station was flowed into continuous clarification tank for separating the sludge from oil by gravity. The moisture of clarified palm oil was removed by vacuum dryer and the end products of the entire oil purification process are the CPO with less than 0.1 % of moisture content and 0.01 % of dust and solid impurities. 254 Stream 26 shows the press cake as by-product generated in the pressing station consisted of 16,818 kg/h wet fiber (with residual oil) and 14,386 kg/h nuts (dry basis) were separated through depericarper, nut cracker, hydro cyclone and clay bath. The separated mesocarp fibers contain about 5 % of residual oil undergo further oil extraction process by using solvent extraction technology and the products are palm fiber oil in red color nature due to the high content of carotene (1,500 – 2,000 ppm). Thus, the de-oiled dry fiber was mixed with shell and sent to boiler station for generating superheated steam at 2.5 MPa which is then used for driving the turbine and then generating electricity for the mill operation. According to the energy data tabulated from stream 1 to stream 49, the total energy consumption of palm oil mill was determined by using Eq(2) and Eq(3) and the result indicates that up to 36,912 kW was needed for running a conventional palm oil milling process. The sterilisation is the major contributor to the total energy consumption due to the tremendous usage of 3 bar saturated steam (S4). The condensate from steriliser (S2), waste water with shells, fiber debris released from hydro cyclone (S35) and the clay bath (S37) were known as Palm Oil Mill Effluent (POME) were then undergo anaerobic digestion to reduce its COD and BOD values (Singh et al., 2010). Table 7 shows the stream summary from S50 to S56. With the ratio of 38.13 m 3 biogas/m3 POME, 1,324 m3 of biogas (1,523 kg/h) was generated and undergo a series of upgrading process to reduce its moisture content and H2S concentration to prevent any possible damages to the biogas heat engine. Based on the case study, there are 3 units of biogas spark-ignition heat engines running at 24 h to generate 2,779.98 kW electrical power where 1,967.54 kW was supplied to the nearby residential areas through national grid while the rest was used on site. However, typical heat engines can only run with maximum efficiency up to 45% while the rest lost in the form of thermal energy to the surrounding. According to Table 8, there were total 2,314.32 kW heat content in engine flue gas at 475 °C which released to the environment without heat recovery. The flue gas waste heat can only be utilised and recoverable from 475 °C to 150 °C to avoid the condensation of sulfuric acid (130°C) which might cause chemical corrosion (Booneimsri et al., 2016). The total jacket water heat loss of 1,908.18 kW is considered as low-grade heat loss as the temperature of hot jacket water is at around 88 °C before entering radiator. By fully utilising the waste heat of biogas power plant, it is expected to save up to 9.46 % of the total energy supplied for palm oil mill processes (Eq(4)). Figure 1: Process block diagram of palm oil mill with biogas power plant 255 Table 2: Energy and material balance summary from Stream 1 to 10 Stream Number Unit 1 2 3 4 5 6 7 8 9 10 Temperature °C 30 110 90 144 100 90 90 144 95 90 FFB kg/h 1.2 x 105 0 0 0 1.1 x 105 0 0 0 0 0 EFB kg/h 0 0 0 0 0 9,367 0 0 0 0 Fruitlets kg/h 0 0 0 0 0 0 8.0 x 104 0 0 0 Flesh Fruits kg/h 0 0 0 0 0 0 0 0 8 x 104 0 Palm Oil kg/h 0 0 120 0 0 624 0 0 0 2.7 x 104 Water, H2O kg/h 0 0 9,360 0 240 1.8 x 10 4 0 0 4,800 2.2 x 104 Steam, H2O kg/h 0 2.04 x 10 4 0 3 x 104 0 0 0 4,800 0 0 Solids kg/h 0 0 1.2 x 104 0 0 0 0 0 0 4,800 Heat Flow kW 3,231 1.52 x 104 1,464 2.3 x 104 9,710 2,234 5,462 3,651 6,295 3,916 Table 3: Energy and material balance summary from Stream 11 to 20 Stream Number Unit 11 12 13 14 15 16 17 18 19 20 Temperature °C 50 80 70 70 90 95 90 90 80 90 FFB kg/h 0 0 0 0 0 0 0 0 0 0 EFB kg/h 0 0 0 0 0 0 0 0 0 0 Fruitlets kg/h 0 0 0 0 0 0 0 0 0 0 Flesh Fruits kg/h 0 0 0 0 0 0 0 0 0 0 Palm Oil kg/h 0 2.7 x 104 50 2.7 x 104 2.7 x 104 940 0 940 940 800 Water, H2O kg/h 2.4 x 10 4 4.6 x 104 50 4.6 x 104 4.6 x 104 4.3 x 104 0 4.3 x 104 4.3 x 104 4.2 x 104 Steam, H2O kg/h 0 0 0 0 0 0 0 0 0 0 Solids kg/h 0 4,800 53 4,747 4,747 5,088 200 4,888 4,888 4,544 Heat Flow kW 1,398 5,717 8 4,995 6,422 4,970 8 4,701 4,179 4,664 Table 4: Energy and material balance summary from Stream 21 to 30 Stream Number Unit 21 22 23 24 25 26 27 28 29 30 Temperature °C 90 95 85 85 85 50 50 70 60 60 Palm Oil kg/h 140 2.6 2.6 x 10 4 0 2.6 x 104 750 0 0 0 0 Water, H2O kg/h 152 3,897 3,897 3,871 26 7,218 1,814 1,814 0 0 Steam, H2O kg/h 0 0 0 0 0 0 0 0 0 0 Solids kg/h 344 3 3 0 3 0 0 0 0 0 Fibre kg/h 0 0 0 0 0 8,850 0 0 0 0 Nuts kg/h 0 0 0 0 0 1.4 x 10 4 1.4 x 104 0 1.4 x 104 1.4 x 104 Shell kg/h 0 0 0 0 0 0 0 0 0 0 Kernel kg/h 0 0 0 0 0 0 0 0 0 0 Heat Flow kW 37 1,847 1,653 382 1,270 1,245 563 148 549 549 256 Table 5: Energy and material balance summary from Stream 31 to 40 Stream Number Unit 31 32 33 34 35 36 37 38 39 40 Temperature °C 45 30 45 30 30 30 30 30 70 70 Palm Oil kg/h 0 0 0 0 0 0 0 0 0 0 Water, H2O kg/h 0 0 0 6,500 5,000 1,500 400 1,100 1,088 12 Steam, H2O kg/h 0 0 0 0 0 0 0 0 0 0 Solids kg/h 0 0 0 0 0 0 0 0 0 0 Fibre kg/h 0 0 0 0 0 0 0 0 0 0 Nuts kg/h 0 0 0 0 0 0 0 0 0 0 Shell kg/h 7,242 7,242 958 0 670 287 287 0 0 0 Kernel kg/h 0 0 6186 0 155 6,031 0 6,031 0 6,031 Heat Flow kW 189 126 223 227 189 186 19 167 89 302 Table 6: Energy and material balance summary from Stream 41 to 49 Stream Number Unit 41 42 43 44 45 46 47 48 49 Temperature °C 50 45 120 66 250 250 250 150 30 Palm Oil kg/h 750 0 632 118 0 0 0 0 0 Water, H2O kg/h 5,404 5,404 0 0 0 0 0 0 5,400 Steam, H2O kg/h 0 0 0 0 54,000 7,000 47,000 47,000 0 Solids kg/h 0 0 0 0 0 0 0 0 0 Fibre kg/h 8,850 0 0 8,850 0 0 0 0 0 Nuts kg/h 0 0 0 0 0 0 0 0 0 Shell kg/h 0 0 0 0 0 0 0 0 958 Kernel kg/h 0 0 0 0 0 0 0 0 155 Heat Flow kW 681 283 43 461 43,212 5,602 37,610 35,938 208 Table 7: Energy and material balance summary from Stream 50 to 56 Stream Number Unit 50 51 52 53 54 55 56 Temperature °C 60 46 30 28 28 37 36 Pressure kPa 101 101 8 4 4 101 101 Palm Oil Mill Effluent (POME) kg/h 75,792 30,424 0 0 0 0 0 Treated POME kg/h 0 0 0 0 0 30,424 87,874 Biogas kg/h 0 0 1,523 0 0 0 0 Upgraded Biogas kg/h 0 0 0 1,523 1,523 0 0 Table 8: Biogas heat engine energy balance data Unit Engine 1 (BG1) Engine 2 (BG2) Engine 3 (BG3) Average Fuel Flow Rate Nm3/h 444.41 403.42 356.05 Energy Input (Qin) kW 2,752.87 2,498.95 2,205.56 Electrical Output kW 986.47 981.07 812.44 Engine Radiation Loss kW 43.75 41.41 43.06 Generator Radiation Loss kW 28.13 26.62 27.68 Jacket Water Heat Loss kW 651.08 616.27 640.83 Lower Temperature Circuit Heat Loss kW 83.34 78.88 82.03 Total Exhaust Gas Loss at 475 °C kW 960.12 754.69 599.51 Total Exhaust Gas Loss from 475 °C to 150 °C kW 656.92 516.37 410.19 257 4. Conclusions An integrated material and energy balance of palm oil mills with biogas power plant was computed based on the data collected from a palm oil mill with the capacity of 120 t/h fresh fruit bunches. All the mass flow rates of streams were calculated based on the law of conservation of mass while the energy content of each stream was calculated based on the component specific heat capacity that were retrieved from literature reviews. The total heat flow of each stream was calculated from the summation of component energy flow, and it served as an important information in determining the actual energy requirement of each palm oil mill process. The energy data revealed that total energy amount of 36.912 kW was needed for running the palm oil mill processes including the process of sterilisation, digestion and other process heating usage. The energy balance of biogas heat engine shows that there were total 1,583.48 kW of heat engines flue gas waste heat were recoverable while the total jacket water heat loss of 1,908.18 kW has great potential to be recovered for lower temperature process heating. By fully utilising the biogas power plant waste heat, it is expected to save up to 9.46 % of the total energy required by the palm oil mill processes. Acknowledgments The authors would like to thank for the myriad support of mill senior managers and mill engineers who provided the advices and constructive comment throughout the data collection process. This study was supported by the Faculty of Chemical and Energy Engineering, Universiti Teknologi Malaysia. Reference Ab Hadi A., Mohammad A.W., Takfriff M.S., 2015, Spreadsheet Modelling for Temperature Profile Inside Palm Oil Fresh Fruit Bunch, Journal of Industrial Engineering Research, 1(6), 25-32. 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