6.3.2.1 Energy Balance and Fossil-Fuel Savings
The energy efficiencies of the fuels produced via the three farming scenarios: i) base- case rain-fed, ii) base-case irrigated, iii) large scale farming, were quantified using parameters such as NER, NREV and NEV and compared against that of the reference diesel fuel. The results are presented in Table 6.12.
Table 6.12: Energy Balance (Well-to-Wheel System Boundary)
The total energy inputs, expressed as MJ of energy per MJ of fuel consumed in the power plant, for Jatropha biodiesel fuels were at the least 0.42 MJ [base-case rain-fed], but at the most 0.76 MJ [large scale farming], whereas that of the reference diesel fuel was 2.71 MJ. In this work, equal amount of energy density was examined for all fuels by applying a correction factor of 0.962 to the diesel fuel to account for the differences in the energy densities or lower heating value (LHV) of Jatropha biodiesel and the reference diesel fuel. Furthermore, NERs of 2.37, 1.54 and 1.32 were obtained for base-case rain- fed, base-case irrigated and large scale farming respectively. This indicates a positive energy balance for Jatropha fuel in comparison to the fossil source, since the NER was above 1, as opposed to a value below 1 obtained for the reference diesel fuel. These
Table 6.11: Net GHG emission and percentage reduction in GHG Emission as compared with those for the optimized reference diesel fuel system
Impact category Unit Reference Diesel Fuel- Optimised System Jatropha biodiesel Jatropha biodiesel with Irrigation Jatropha biodiesel with Irrigation and Heavy machinery
Climate change kg CO2 eq. per kg fuel 2.18 0.91 1.13 1.68
% -58.07 -48.13 -23.03
Parameters Units Reference
Diesel Fuel Base-case [rain-fed] Base-case [Irrigated] Large Scale Farming
Total Energy Input MJ/MJ 2.71 0.42 0.65 0.76
Energy Density MJ/MJ 1 1 1 1 NER 0.37 2.37 1.54 1.32 NEV MJ -1.71 0.58 0.35 0.24 NREV MJ 0 0.98 0.88 0.88 % Diesel Fuel Replacement % - 58 35 24
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results are similar to Jatropha biodiesel production analysis in [Eshton et al. 2013] because very minimal amount of energy is required for transportation of the biodiesel fuels from oil conversion site to the power plant location. Additionally, the NEV, a parameter indicative of the energy gained or lost, was negative for the reference diesel fuel, but positive for all the Jatropha biodiesel fuels with values of 58%, 35% and 24% for base-case rain-fed, base-case irrigated and large scale farming respectively. The NREV on the other hand was 0.98, 0.88 and 0.88 for base-case rain-fed, base-case irrigated and large scale farming respectively, however, 1 for the reference diesel fuel. This demonstrate the energy gained from the use of fossil fuel. A relatively higher value indicate less amount of fossil energy input is utilised and vice versa. Consequently, this analysis demonstrate how much fossil fuel displacement that could be achieved from the use of these fuels from the three farming scenarios. A fossil fuel displacements of 58% [base-case rain-fed], 36% [base-case irrigated] and 27% large scale farming are achievable with Jatropha biodiesel fuel utilization.
Among the three farming systems, energy consumption increased by 0.23 MJ (base- case irrigated case) and 0.34 MJ (large scale farming scenario). Consequently the net energy ratio reduced to 65% and 56% respectively. Also, the large scale farming system had the least favourable energy balance and Jatropha farming had the largest contribution to energy consumption followed by oil conversion in all the three farming systems and especially for the large scale farming system. Transportation also played significant role in energy consumption in the base-case irrigated case and large scale farming system. The distribution of energy input according to the sub-processes for Jatropha biodiesel production is presented in figure 6.9.
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Figure 6.9: Contributions of energy input from the sub-processes of Jatropha biodiesel fuel used in a 126 MW power plant. Results are presented as MJ of energy input per MJ of Jatropha biodiesel
utilised.
The above unity of the NER, and positive NEV of the biodiesel fuels derived from the three farming systems and used in the power plant indicate that the production and use of Jatropha biodiesel fuel in power generation in Nigeria is achievable and of benefit. That is, the Jatropha biodiesel fuel has higher energy efficiency and favourable to replace or substitute part of the diesel reference fuel system provided the material inputs are kept at their minimum. Furthermore, additional effort to replace the fossil fuel consumption during the production and use of the fuel, especially during transportation would change the energy balance of the system significantly.
6.3.2.2 Environmental Life Cycle Impact Assessment
The total emissions generated from the use of Jatropha biodiesel and the reference diesel fuels are expressed as kg emissions per MJ of fuel. The fraction of carbon sequestered during the growth of Jatropha plant and burnt in the engine is approximately 474 kg CO2 per MJ fuel. The CO2 emissions generated from the simulated 126 MW gas turbine power plant on the other hand is 1025.93 kg for Jatropha biodiesel while 1260.37 kg for the reference diesel fuel. Hence, the total emissions from Jatropha biodiesel fuel use could bring about GHG savings of about 19% across the three farming systems. These results are presented in Table 6.13.
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Table 6.13: Net and percentage reductions in total emissions as compared to reference diesel
Using the base-case rain-fed farming system, the Jatropha biodiesel produced as a result have varying effect on the ecology with percentage contributions to total emissions. The percentage contributions to environmental burden from each sub- process in the production and use of Jatropha biodiesel is represented in figure 6.10.
Figure 6.10: Percentage contributions to environmental burden from the sub-processes of Jatropha biodiesel production and use.
Results are presented as MJ of energy consumed per MJ of Jatropha biodiesel used in 126 MW gas turbine at ISO condition. Nearly 100% contributions to climate change is observed to result only from fuel consumption, as well as about 50% and 90%
Impact category Unit Reference Diesel Fuel Base-case [rain-fed] Base-case [Irrigated] Large Scale Farming Climate change kg CO2 eq. per MJ fuel 1260.37 1025.95 1025.96 1025.97 % -18.61 -18.60 -18.60
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contributions to marine and freshwater eutrophication, although in very insignificant quantities. These results are expected because carbon dioxide is one of the emissions classified with greenhouse gases that could bring about increased earth average temperature and is produced mainly as a result of combustion of fuels in engine. Emission to the atmosphere could also result in more eutrophication of fresh and water bodies by enriching its biogenic content. For instant, microscopic floating plants such as algae and water hyacinths consume carbon dioxide to increase bio-matter and uptake other dissolve nutrients such as nitrogen, phosphorus from water while using light as the energy source. This impact water quality, forces increased growth of aquatic plants, decomposition of organic matter in water bodies and depletes dissolved oxygen. Oil conversion contributes to marine ecotoxicity, freshwater ecotoxicity, metal depletion, and fossil depletion significantly by about 70%, 76%, 75% and 50% respectively. Other impacts include terrestrial acidification, photochemical oxidant formation and ionizing radiation.
Oil transportation had the largest impact on terrestrial ecotoxicity with value of about 85% and equally contributed to photochemical oxidant formation, a resulting effect on smug formation. This impact is attributed to the fossil-derived diesel fuel used during transportation of seeds, oil and refined products. The NOx and other volatile organic compounds (VOCs) produced from these diesel engines increases ozone (O3) formation. An excessive formation of this compound at ground level could results in toxicity of plants, animals and even human health. These results indicate the importance of further reducing emissions by replacing fossil-derived fuels with renewable fuels during transportation of materials, products and co-products. Jatropha farming also had effect on several impact categories, however at relatively small quantities asides ozone depletion, in which it had a significant impact. The contributions to ozone depletion could be as a result of agrochemicals such as nitrogen and phosphate fertilizers, pesticides, insecticides or herbicides used during Jatropha farming and production. In summary, the environmental life cycle impact indicate that Jatropha oil use had largest environmental impact, followed by oil conversion, oil extraction, Jatropha farming and oil transportation, in that order but minimal contributions. Furthermore, climate change had the largest share of the impact, followed by marine ecosystem, fossil depletion, and terrestrial acidification. The rest had minimal role in the environmental burden.
However, when the results in Table 6.13 were compared to a reference diesel fuel with an European average, the result showed a negative impact for Jatropha production and
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use across all farming systems (data not shown). This can be accounted to the wide differences in the reference diesel fuel system in Nigeria and that of the European average. The refining and production as described in the European average is highly efficient when compared to Nigerian production and refining process that suffers from poor production capacities, ageing infrastructures, poor maintenance with multiple transportation of materials and products.