Energy Potential of Coconut and Palm Oil Residues Marianne Salomon * Department of Energy Technology Royal Institute of Technology, Stockholm, Sweden e−mail: [email protected]Miguel Gonzalez Department of Energy Technology Royal Institute of Technology, Stockholm, Sweden e−mail: [email protected]Ernesto Leal Department of Energy Technology Royal Institute of Technology, Stockholm, Sweden e−mail: [email protected]Andrew Martin Department of Energy Technology Royal Institute of Technology, Stockholm, Sweden e−mail: [email protected]Torsten Fransson Department of Energy Technology Royal Institute of Technology, Stockholm, Sweden e−mail: [email protected]ABSTRACT Agricultural residues continue to attract interest for energy recovery purposes as a renewable, CO 2 neutral and increasingly cost competitive alternative to traditional fossil fuels. The possibility of trigeneration in already established industries such as palm oil mills and coconut processing plants is very attractive especially when residues that otherwise represent a disposal problem can be utilized efficiently. The use of agricultural residues in rural areas or in small islands could certainly represent an advantage as the use of expensive fossil fuels adds an additional burden to foster development. Different technological scenarios for the production of electricity, process heat and biodiesel are analyzed using coconut and palm oil residues. Environmental aspects are also included in the analysis. Studies were conducted considering various scenarios to evaluate the feasibility of using these residues for energy purposes. The residues were considered to be combusted directly in steam boilers while steam turbines were used as prime movers to generate electricity. Biodiesel is produced by transesterification of palm oil/coconut oil. The required process heat for palm oil or coconut oil processing as well as the steam required for biodiesel production is supplied by the combustion of the residues. The advantage is that biodiesel is a more flexible and easy-to- distribute fuel that can be used for power generation and/or transportation. The results show * Corresponding author
Transcript
Energy Potential of Coconut and Palm Oil Residues
Marianne Salomon*
Department of Energy Technology Royal Institute of Technology, Stockholm, Sweden
Agricultural residues continue to attract interest for energy recovery purposes as a renewable, CO2 neutral and increasingly cost competitive alternative to traditional fossil fuels. The possibility of trigeneration in already established industries such as palm oil mills and coconut processing plants is very attractive especially when residues that otherwise represent a disposal problem can be utilized efficiently. The use of agricultural residues in rural areas or in small islands could certainly represent an advantage as the use of expensive fossil fuels adds an additional burden to foster development. Different technological scenarios for the production of electricity, process heat and biodiesel are analyzed using coconut and palm oil residues. Environmental aspects are also included in the analysis. Studies were conducted considering various scenarios to evaluate the feasibility of using these residues for energy purposes. The residues were considered to be combusted directly in steam boilers while steam turbines were used as prime movers to generate electricity. Biodiesel is produced by transesterification of palm oil/coconut oil. The required process heat for palm oil or coconut oil processing as well as the steam required for biodiesel production is supplied by the combustion of the residues. The advantage is that biodiesel is a more flexible and easy-to-distribute fuel that can be used for power generation and/or transportation. The results show
that palm oil mills/coconut processing industries can be independent of fossil fuels. Furthermore, they can contribute positively to the energy balance of the communities by helping reduce the dependence on fossil fuels and reducing at the same time greenhouse gas emissions. A tri-generation plant which is flexible enough to allow the prioritization of one of the products based on the residues available and the existing demand will certainly benefit the vegetable oil industry and local communities.
INTRODUCTION
Agricultural residues and vegetable oils have attracted more interest in the past years, mainly due to higher oil prices and environmental concerns. They certainly represent an alternative to traditional fuels that sometimes has been overlooked by governments and industries. Although agricultural residues are technically challenging to employ usefully [1], they could certainly contribute to the national/local energy and transportation systems. In some cases, these residues constitute a disposal problem and the most common practice to solve this is to burn the residues in open fires – a practice that is both wasteful and environmentally harmful. On the other hand, vegetable oils are more easily used after they have gone through a transesterification process and converted to biodiesel. Diesel engines can work with a blend of 90% diesel and 10% biodiesel, or B10, without modification [2]. A higher content of biodiesel requires alterations in the engine especially in the case of B100 (100% biodiesel). In spite of the possible environmental benefits of using biodiesel, its production has raised the “fuel or food” debate as the primary purpose of agricultural land is being shifted from food production to energy or transportation purposes. In the cases considered it is not the main issue as there is already an excess in vegetable oil production. Biodiesel can represent a viable alternative to replace diesel, particularly in those countries with excess production of vegetable oils, heavy diesel imports and a weak economy. It will also help dramatically to reduce greenhouse gas emissions and to utilize indigenous resources, particularly, if also any residue associated with the vegetable oil production process is used. In this sense, some of the countries listed by the United Nations as Small Island Developing States, or SIDS, have certain characteristics that could help to foster the use of biofuels as almost all of them are fully dependent on fossil fuel imports for electricity and transportation [3, 4]. These countries have typically a small population, limited resources, are situated in remote areas and largely depend on foreign trade [5]. SIDS also have high costs for infrastructure, transportation, communications and administration, and limited access to freshwater resources [3]. These factors coupled with high energy tariff rates, mainly due to limited options of renewable energy sources and technologies required for harnessing them, are hindering the sustainable development of these states in comparison with other developing countries [5, 4]. For developing countries in general, the interest could be in rural electrification, reduction of fossil fuel imports, environmental concerns and optimization of crop-related industries such as rice, coconut and palm oil industry. For SIDS the interest would rather be focused on the reduction of fossil fuel imports by promoting the utilization of indigenous energy resources. In terms of specific resources, coconut is highly relevant because: i) it is produced in about two thirds of SIDS [5]; ii) usually the production exceeds the internal demand and coconut-based products are commonly exported; iii) biodiesel can be produced from coconut oil; and iv) coconut residues (husk and shell) are presently used only in a limited way for energy
purposes and are presently viewed as a waste stream. Palm oil is also a potential source of diesel replacement mainly because of the high yield per hectare. In average, palm oil mills (POM) produce 316 kg oil per ton of fresh fruit bunch (FFB) and around 450 kg of solid residues per ton of FFB [6, 7]. From these solid residues, fibres and shells that account for 42% of the solid residues can be used directly for energy purposes. These residues are normally burned in steam boilers or in cogeneration plants to supply the POM with the required process heat. The remaining residue, empty fruit bunch (EFB), which accounts for about 60% of the solid residues produced by the mill, is mainly used as fertilizer. However, higher quantities than the ones required for fertilization are produced considering that some estimations propose that up to 60% can be used for energy purposes [1]. Thus, EFB is a disposal problem for POMs and in some cases open incineration is applied as a disposal method. However, significant amount energy is wasted in this way and thus this study aims to evaluate other alternatives to increase the energy efficiency in palm oil mills. It has been reported in previous studies that EFB is a challenging residue in terms of energy conversion due to its high moisture and alkali content [1]. However, there is a possibility of using EFB for electricity generation through gasification [8] and also in modified combustion boilers [1, 9] considering that EFB has similarities in terms of composition to straw [10]. It is required some pre-processing and reduction in the moisture content to the required levels.
OBJECTIVES AND METHODOLOGY
The purpose of this study is to identify the energy potential of coconut and palm oil residues and the feasibility of using them in a combined heat and power plant (CHP) that will also support biodiesel production. The evaluation is focused only in the technical aspects. The economical analysis that is outside the scope of this study but it is suggested as next step in the assessment. In order to perform the technical analysis, case studies using coconut residues among SIDS and palm oil residues in Colombia were analyzed. Each case study was selected based on the primary output preferred: electricity, biodiesel or a balanced combination of both products. The case studies were based on small-scale facilities which can have higher impact on rural development [11] especially in SIDS areas. The various scenarios were analyzed in terms of energy consumption, current production methods and possible fuel consumption. Several alternatives for improving the efficiency of the energy system and for prioritizing the main output were evaluated. The benefits of the improved energy system in terms of reduction in electricity consumption from the grid, reduction of diesel consumption and reduction of CO2 emissions were also considered. The system boundaries were selected accordingly for the CHP plant and the biodiesel plant to be included in the energy system to be analyzed. The coconut and palm oil extraction were not included in the system as it is a separate and already established process and it is beyond the scope of this study. In the case of palm oil only the electricity and heat required for the process was considered.
Description of case studies To evaluate the feasibility of using coconut/palm oil residues for electricity and heat with the simultaneous production of biodiesel, three case studies were selected for each residue. The residues were analysed in similar conditions to compare their potential. Table 1 shows the characteristics of each residue that was used for the energy analysis described in the next
section. The residues considered differ in composition and heating value, however, some of the technical challenges are similar, namely, high moisture and alkali content.
The assessment of the possibilities for coconut and palm oil residues to provide energy to a process and also support biofuel production were evaluated under different conditions. The analysis was done using Aspen Utilities Planner®. In the palm oil case studies, it was considered that the energy required by the POM and by the biodiesel production process would be provided by residue combustion and by a B100 diesel engine. As it was discussed previously, it is common practice to use the palm oil fibres to supply the process heat required by the POM and in some cases also the electricity requirements. For the coconut case studies, it was considered that the residues covered the energy needs of the biodiesel production process and also that any additional electricity produced will be delivered to the grid. Besides using different residues, the case studies also differ in the context in which they were evaluated. For the three case studies using coconut residues, the requirements and conditions varied depending on particular location. The three SIDS that are considered (Cuba, Samoa and Solomon islands) were selected on the basis of their differences regarding energy needs, biodiesel requirements and available resources. However, these three countries had a common characteristic: their coconut production exceeds their internal consumption leaving open the possibility for exporting the surplus. Relevant data regarding population and energy patterns of these three countries is shown in Table 2. According to Table 2, Cuba is characterised by a high electricity consumption per capita compared to the other two SIDS and thus electricity is a very important product. In contrast, Samoa has the highest diesel consumption per capita mainly used in the transportation sector and thus biodiesel would be a highly valued product. For the palm oil residues, Colombia was considered as a case study in order to show the potential of the palm oil industry to supply their own needs and also contribute with the production of biodiesel for rural electrification and/or transportation. As we can see from Table 2, the electricity consumption per capita in Colombia is less than in the case of Cuba. Particularly, in the case of Colombia, the energy situation is different than for the SIDS as 80% of the electricity is produced in hydropower plants [17]. Regarding diesel, the consumption per capita is less than for the SIDS but a biofuel program has been established to
try to promote the use of biodiesel and ethanol in the country and reduce the consumption of fossil-derived diesel. According to this program, the goal is to have a 5% biodiesel blend commercialized for transportation and power generation in rural areas [18]. In 2007, the government decided that for 2010 diesel mixtures should contain 10% of biodiesel [18]. This means that for 2007, it was required to have an installed biodiesel production capacity of 450,000 tons/y but only 80% of this capacity was available [19, 20].
Table 2. Energy patterns of the case studies [21, 17, 22, 23]
Palm oil case studies A case study of a small-scale palm oil mill in Colombia was selected. The POM is located in the Department of Cesar in Colombia. Palm oil processing requires certain amount of process heat and to provide this, palm oil fibres are normally burned in low efficiency boilers. For the analyzed case, the fibres are burned to generate saturated steam for the process (Fig. 1) and the electricity required for the process is provided by the grid [6]. The shells are sold to a nearby industry as a fuel for their boilers. The remaining residue, EFB, is used mainly as fertilizer or burned in open fires. The different case studies were modelled and analyzed using Aspen Utilities Planner®.
Figure 1. Palm oil mill
Based on this, three options were considered for this palm oil mill (see fig. 2 and fig.4a for a flow chart of different conversion routes). The three options had the same CHP plant configuration but the flows were different. The three case studies are: Case A: Maximum Electricity Production (MEP). This case covers the internal demand
of the palm oil mill and the biodiesel plant requirements and the excess of electricity is exported to the grid.
o Case A1: Sustainable Maximum Electricity Production (SMEP). It has been recommended that up to 30% of the palm oil production is used for biodiesel production as 70% of the palm oil produced in Colombia is for the internal market and the rest is exported [24]. Thus, this case study converts only 30% of the palm oil into biodiesel and uses it for electricity generation purposes.
Case B: Balanced Electricity and Biodiesel Production (BEBP). In this case electricity is produced by the steam cycle to cover the mill needs and the electricity required for the biodiesel production process is provided by a B100 diesel engine.
Case C: Maximum Biodiesel Production (MBP). For this case all available palm oil produced by the mill is converted to biodiesel and sold as transportation fuel. The requirement of process heat and electricity are covered by the steam cycle.
o Case C1: Sustainable Maximum Biodiesel Production (SMBP). In this case only 30% of the palm oil production is converted to biodiesel and sold as fuel.
Figure 2. Palm Oil mill mass balance
Coconut case studies Three case studies among the selected SIDS with an excess in coconut production and thus able to export coconut oil were analyzed. These cases were also selected based on the specific needs for each country. Case A: Maximum Electricity Production (MEP) – Cuba. This case study is
characterized by a high electrical capacity installed per capita (99% of Cuban power plants use fossil fuels) and low specific diesel consumption per capita.
Case B: Balanced Electricity and Biodiesel Production (BEBP) - Solomon Islands. This is a case where both electricity and biodiesel are equally valued considering that the island has low installed electricity capacity per capita and moderate diesel consumption.
Palm oil solid residues (1 ton/h)
Palm oil (1.0 ton/h)
Electricity
Process heat
Biodiesel (0.9 ton/h)
Emissions
Glycerine (0.1 ton/h)
Methanol (0.15 ton/h)
Case C: Maximum Biodiesel Production (MBP) - Samoa. This case study assumes the biggest biodiesel production because of the highest specific diesel consumption per capita mainly used in the transportation sector.
The general description based on the mass flows through the analyzed systems is shown in fig. 3. All the mass flow values are based on 1 ton/h of copra (dry meat of the coconut) and residues.
Figure 3. Coconut mill mass balance
Energy and environmental analysis The cogeneration alternative considered for both residues (coconut and palm oil residues) was the steam cycle as it is a well established technology and can generate the electricity and process heat required for the industrial processes and for the biodiesel plant. For the proposed case studies, it was assumed that:
• A steam cycle with a condensing turbine will be used as it is a well-known and well-established technology
• The steam boiler efficiency is 80% and the turbine efficiency is 85%. • The steam boiler pressure is 40 bar and the turbine condensation pressure is 0.1 bar • The CO2 emissions from diesel combustion are 0.109 kg/MJ [25]. • The indirect CO2 emissions from methanol production from fossil fuel sources are
0.095 kg/MJ [25]. However, the aim is to replace this fossil fuel-derived methanol with one coming from biomass residues.
• The methanol consumption is 0.202 kg/kg biodiesel [26]. • The heating value of biodiesel is 37.5 MJ/kg [27]. • The CO2 reduction credits for displacement of grid power is 0.17 kg CO2/MJel based
on an average value between the one reported by Tan et al.[26] and the Colombian Energy Ministry [28].
• The electricity produced is replacing electricity based on fossil diesel. • The net heating value of the coconut residues (a mixture between coconut shells and
husks) is 18 MJ/kg [26].
Copra + residues (1 ton/h)
Electricity
Biodiesel (0.29 ton/h)
Emissions
Glycerine (0.04 ton/h) Methanol
(0.06 ton/h)
Copra cake (0.18 ton/h)
• Thermal efficiency of utilization of the two fuels in vehicles are assumed to be equivalent [29, 30]. In this way, the two fuels can be compared directly based on the heating value.
• Biodiesel production is achieved by using transesterification of vegetable oils. Transesterification is widely used to reduce vegetable oil viscosity [31] and it is being widely implemented specially in palm oil producing countries. In this process, vegetable oil and methanol react in the presence of a catalyst (e.g. Na K) and produce biodiesel and glycerine. The heat and electricity required for this process is supplied by the residues.
The case studies differ in some aspects and thus the energy analysis for each one will be described separately.
Palm oil case studies In the proposed polygeneration system from palm oil residues:
• Electricity is supplied to the palm oil extraction process and biodiesel production plant and the excess is sold to the grid.
• Process heat is supplied to the palm oil extraction process (saturated steam at 5 bar) and to the biodiesel production plant.
• The methanol required for the production of biodiesel is made available to the mills from external sources. It is assumed that the methanol required is coming from fossil fuel sources.
• Biodiesel is produced from palm oil. • Glycerine is a by-product of the biodiesel production process.
In the proposed system, electricity and process heat are produced from fibres and EFB. Shells were not considered as a possible fuel in the CHP plant as they are a separate source of income for the POM (the POM sells this residue to a nearby cement industry). In the cases considered electricity production is highly dependant on the POM’s heat demand. The heat demand varies through the year (POM’s operate the whole year around) as there are periods where the production is slightly reduced due to the availability of FFB. Fig. 4 shows a schematic of the CHP plant that was modelled using Aspen Utilities Planner®. The CHP plant supplies the electricity and process heat required by the POM. In addition to this, the CHP plant also provides part of the steam required by the biodiesel plant. The CHP plant configuration does not vary in the three cases. The parameters that vary are the steam extracted for the biodiesel plant. The diesel engine provides the electricity required by the biodiesel plant and part of the heat except in Case C and C1. In those two cases, all the energy requirements are supplied by the CHP plant as it will be explained later. Case A: Maximum Electricity Production (MEP). The aim of this case is to have
electricity as the system’s primary output. For that reason, the possibility of selling the produced biodiesel as transportation fuel was not considered. In this case, the power output from the steam cycle is maximized and the maximum biodiesel production (100% of the palm oil produced in the mill) is used in a modified B100 diesel engine for power generation. The exhaust of the diesel engine is used as heat input for the biodiesel plant together with additional process heat from the steam cycle. The electricity required by the biodiesel plant is supplied by the diesel engine (fig 4b). The required process heat and electricity for the POM is provided by the steam cycle (fig 4).
o Case A1: Sustainable Maximum Electricity Production (SMEP) is the same as case A with the difference that only 30% of the palm oil produced in the mill is converted to biodiesel and used in a modified B100 diesel engine.
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(b)
Figure 4. a) CHP system for the 3 palm oil case studies b) Case A and Case A1 (MEP), palm oil
residues
Case B: Balanced Electricity and Biodiesel Production (BEBP). In this case electricity/heat production from the CHP plant using palm oil residues is used for covering the mill’s needs and the excess of electricity is exported to the grid (see fig. 5). The biodiesel engine is used to cover the heat demand of the biodiesel plant together with the steam cycle. The electricity required by the biodiesel plant is provided by the B100 diesel engine. The excess of electricity produced by the CHP plant and diesel engine is exported to the grid. This system is characterized for a higher flexibility during operation which is suitable for part load and peak load operation. Some biodiesel is sold as transportation fuel.
Figure 5. Case B (BEBP), palm oil residues
Case C: Maximum Biodiesel Production (MBP). For this case all the palm oil produced by the mill is converted to biodiesel. All biodiesel is sold out and none of it is
(a)
Boiler Biodiesel Plant heat
Feedwater pump Makeup water
Condenser
G
Fibers
Boiler EFB
Mixer
Mixer POM process heat
used for electricity generation purposes. The steam cycle (CHP plant) the residues to supply the heat required by the POM and also for the biodiesel plant. The electricity required for the POM and the biodiesel plant is also supplied by the CHP plant.
o Case C1: Sustainable Maximum Biodiesel Production (SMBP). In this case only 30% of the palm oil is converted to biodiesel which is sold directly to the market. For this case, the steam cycle covers the energy needs of the POM and also of the biodiesel plant.
Figure 6. Case C (MBP), palm oil residues
Coconut case studies
Case A: Maximum Electricity Production (MEP) – Cuba. The main objective of this case study is to replace as much fossil fuel as possible in the power generation sector. In this case study, both a steam cycle and a biodiesel engine working with B100 are used for power production. This implies that all biodiesel produced in the plant is actually used in an engine for electricity generation (see fig. 7a). Figures 7a and 7b show the energy and mass flows in the system. As electricity is the primary output of the system, the exhaust from the diesel engine is used for feedwater preheating in the steam cycle and also providing the steam required for the biodiesel plant.
(a)
(b)
Figure 7. Case A (MEP), coconut residues
Boiler Extraction
Feedwater pump Makeup water
G Coconut residues
FW preheat
From the diesel engine
(a)
(b)
Figure 8. Case B (BEB), coconut residues
Case B: Balanced Electricity and Biodiesel Production (BEBP) - Solomon Islands. This is a case where both electricity and biodiesel are produced equally. In order to achieve this, a steam cycle and a modified B100 biodiesel engine are used (see fig. 8). The steam cycle produces only electricity for export to the grid, while the biodiesel engine produces a small amount of electricity but also delivers the heat required by the biodiesel plant. This system is characterized by a higher flexibility compared with the other 2 cases (MEP or MBP), which enables a better optimized operation during part load and peak load periods.
Case C: Maximum Biodiesel Production (MBP) - Samoa. This case study has as main
objective to maximize biodiesel production. For that purpose, the steam cycle (a CHP plant) uses all residues to produce the heat required for the biodiesel plant and the required electricity for the complete system. A surplus of electricity is produced by the CHP plant and only a minor quantity of biodiesel is used internally for transportation.
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(b)
Figure 9. Case C (MBP), coconut residues
Boiler
Extraction
Feedwater pump Makeup water
G
Boiler
Condensing
Extraction
Feedwater pump
Mixer Makeup water
Condenser
G
Coconut residues
RESULTS AND DISCUSSION The results from the analysis prove that both coconut and palm oil residues can contribute significantly in the production of electricity, biodiesel and process heat. Also, it is clearly shown that the proposed schemes can make the oil mill completely self-sufficient in terms of energy sources. The detailed results of each case study are shown below for both residues.
Palm oil case studies The system analysed for the palm oil case studies also included the supply of electricity and process heat to the palm oil production process. The analysis was done for a standard palm oil mill processing plant where electricity is supplied by the grid. The production of electricity and biodiesel for the three main case studies is shown in fig. 10a. The maximum biodiesel production is around 60 000 ton/y which represent 13% of the biodiesel requirement in Colombia in 2007. This case has the highest potential in terms of emission reductions where about 234 500 tons of CO2 per year can be avoided by replacing 53 400 ton/y of diesel (see fig. 10c). Although the economical analysis was not included in the scope of this study it is important to mention that in 2008, the average price of CO2 emissions in Europe was 20 €/ton [32].
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Figure 10: Palm oil case studies a) Biodiesel and electricity production; b) Net energy output and net emissions reduction
ratios; c) Potential for replacing fossil diesel and CO2 emission reduction
The maximum amount of electricity that can be produced under the conditions considered in the analysis is 222 GWh/y. This is approximately 2% of the installed capacity in Colombia in 2006. The potential of emission reduction is lower that in the MBP case. Figure 10c shows that about 55 000 tons per year of diesel can be replaced for power generation purposes in the MEP case and thus 159 300 ton/y CO2 emissions can be avoided. The BEBP case has also an important impact in terms of emissions savings as shown in fig. 10. It can contribute with 117 GWh/y of electricity and 30 000 tons of biodiesel per year which is translated into 179 000 ton of saved CO2 per year and 51 300 tons/y of replaced fossil diesel. However, as it was mentioned previously, it is considered that the conversion of crude palm oil to biodiesel could be sustainable only if a maximum of 30% of palm oil is used. In those lines, a further analysis of the 2 extreme cases (maximum biodiesel production - MBP, and maximum electricity production - MEP) using 30% of the total palm oil production was done. The results of the SMBP and SMEP analyses are shown in fig. 11.
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Figure 11: Sustainable palm oil case studies
a) Biodiesel and electricity production; b) Net energy output and net emissions reduction; c) Diesel replaced.
For the SMBP and SMEP cases, the magnitude in terms of emission reductions is not as big as for the cases shown in fig. 10. Nonetheless, their contribution is still relevant considering
that several mills could divert 30% of their production to the biodiesel plant to either supply electricity to nearby areas and/or own consumption or to sell the biodiesel to the local market for transportation or rural electrification purposes. The SMEP and the SMBP cases can contribute with 65 GWh/y of electricity and 15 000 tons of biodiesel per year, respectively (see fig. 11a).
The same trend shown in figure 10 is also visible in the SMBP and SMEP cases, with the highest potential for emission reduction in the SMBP case with 57 400 ton/y (see fig. 11). The SMEP can contribute with a reduction of 35 000 ton CO2/y as shown in fig. 11b. Both cases can replace around 13 500 ton/y of diesel according to fig. 11c.
Coconut case studies For coconut residues, similar to the case of palm oil residues, there is enough energy available from the residues to cover both the mill’s and the biodiesel plant’s energy needs and export electricity to the grid. The size of the plants and main product is determined according to the local needs in each considered SIDS.
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Figure 12: Coconut case studies a) Biodiesel and electricity production; b) Net energy output and net emissions reduction;
c) Potential for replacement of fossil diesel.
Figure 12 shows the main results for the 3 coconut models analysed. Although the size of the coconut system is smaller compared to the palm oil cases, it is important to highlight the contribution of such systems in the reduction of greenhouse gas emissions. As shown in Fig. 12a and 12c, significant amounts of fossil diesel can be saved by using coconut oil for electricity and coconut residues for biodiesel production. These savings come from the direct replacement of diesel in the power generation and transportation sectors. For the MBP case, 11% of the total amount of diesel fuel used on the island of Samoa can be replaced with biodiesel, and for the BEBP case this could reach 6% for the Solomon Islands. However, the impact in the MEP case for Cuba is not so dramatic with a diesel replacement of less than 1%. This is mainly due to the higher total diesel consumption in Cuba compared to the other 2 cases, as the country has a much higher population and a more intensive economy, and lower yield of coconut fruits per hectare.
CONCLUSIONS
It has been shown that palm oil mills with biodiesel production and coconut-oil-based biodiesel plants can cover their own energy needs and also contribute positively by producing electricity and biodiesel locally. The systems proposed are more efficient than the current solutions and methods used in the considered SIDS and in Colombia, where energy recovery of agricultural residues is not implemented nowadays. Furthermore, the different scenarios considered show the inherent flexibility of the systems thus allowing the possibility to prioritize one of the main products, electricity or biodiesel. The plants can also be scaled according to the requirements and residues available. Furthermore, the products can be prioritized based on the needs of the industry and the market development. For the coconut residue study cases, the degree of development of the local industries plays a crucial role in the possible implementation of the suggested systems. For the case of Samoa and Solomon Islands where there is a good yield of coconut per hectare, the implementation of a plant for biodiesel and electricity production is very attractive due to the availability of coconut oil and coconut residues. In the case of Cuba this should be considered carefully as the benefits are not so remarkable due to the poor yield of coconut per hectare which reduces the efficiency and adversely affects the economical feasibility of the plant. In the case of palm oil residues, the palm fruits production technology has been optimized allowing a high yield per hectare. A plant like the one considered in the case studies could almost cover the gap in the internal demand of biodiesel to fulfil the B10 directive of the Colombian government. In addition to this, the plant can cover its own energy needs (no longer dependant on the national grid to operate) and at the same time export electricity to the national grid and biodiesel for rural electrification or transportation purposes. The net benefit of plants like this, in terms of CO2 emissions, will come from the production of biodiesel or if the electricity required by the POM and exported to the grid is replacing electricity produced from diesel considering that hydropower contributes to 80% of the electricity production in Colombia (in the interconnected areas). As it has been shown in the results of the analysis, the possible greenhouse gases emission savings and benefits associated with energy recovery from coconut/palm oil residues are very clear. From the results obtained the most relevant contributions of coconut and palm oil residues to the energy system in the scenarios considered are: reduction of greenhouse gas emissions,
replacement of non-renewable energy sources and reduction in the dependence on external energy imports,
contribution to the security of energy supply, reduction of the economical burden associated with fuel imports.
These could be important arguments when trying to implement the mechanisms foreseen in the Kyoto protocol. These aspects can be considered when evaluating the feasibility of using agricultural residues for energy purposes, particularly when linked to follow-on economic analyses which will be the next step in this study. After 2012, the feasibility of projects associated with energy recovery from agricultural residues will depend, among other factors, on the replacement measures associated with a post-Kyoto agreement and on the development of the global market for fossil fuels and vegetable oils.
NOMENCLATURE
B10 Diesel mixture with a 10% biodiesel content B100 Diesel containing 100% biodiesel BEBP Balanced Electricity and Biodiesel Production CHP Combined Heat and Power Plant EFB Empty fruit bunch FFB Fresh Fruit Bunch MBP Maximum Biodiesel Production MEP Maximum Electricity Production POM Palm oil mill SIDS Small Island Developing States SMBP Sustainable Maximum Biodiesel Production SMEP Sustainable Maximum Electricity Production
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