TY - JOUR
AU - Trois,, Cristina
AB - Abstract Alternative sources of energy are greatly needed to ensure the availability of fuels in the long run. Microalgae-derived fuels are among the viable options due to their potential to produce sustainable fuels. However, the costs related to the production of microalgal and alternative fuels are still higher compared to conventional fuels. To deal with costs and environmental issues, the blending of microalgal fuels with conventional fuels can be considered as one of the feasible options. Blending has a positive impact on many fuel characteristics including reduction of carbon footprint, costs, freezing point, viscosity, flow, heating and combustion. In this study, jet fuel from Nannochloropsis sp crude bio-oil was blended with Jet A1 in 50/50 volume ratio. The data generated from the 50/50 blend jet fuel were analysed according to the ASTM standards. Samples were tested after 30, 60, 90 and 120 days from the production day. It was reported that majority of parameters including Net heat of combustion, flash point, kinematic viscosity, conductivity and freezing point were compliant with ASTM standards. However, parameters such as density and total acidity were found not complying with ASTM standards. This study can have an implication on carbon footprint reduction because of the blending of fossil-based jet fuel and renewable-based jet fuel known as low carbon footprint fuel. The blending ratio can be beneficial for the green energy world in terms of costs and environmental impacts. 1 INTRODUCTION 1.1 Background The world petroleum resources are being depleted and they might reach a critical point of scarcity in the near future due to the fact that they are non-renewable. This can cause a serious energy crisis with consequences on many economies. These consequences will particularly hit the transportation sector more especially the aviation industry. In today’s highly competitive energy environment, a flexible approach to deal with issues of reliable sources of energy can help in finding alternative and sustainable fuels in order to compete with fossil-based fuels and to slow down their rapid depletion [1–4]. It is an undeniable fact that fossil fuels although they are very reliable in terms of their performance and compliance, they are however not renewable and environmentally friendly. Furthermore, they are characterized by unsteady price fluctuations [5, 6]. Similarly, there is an imperious necessity to identify alternative resources that can be useful for energy production that will benefit the energy sector more particularly the aviation industry [7–9]. Currently, the main challenge remains to develop alternative fuels from natural and renewable resources that can be real competitors as well as reliable and better substitutes for fossil fuels. This situation should be addressed within a reasonable timeframe in order to face an eventual scarcity of petroleum oil. Therefore, two major options can be considered in this regard: Firstly, the production of biofuels that are renewable, sustainable and compliant to standards. They have to be cost-effective, not competing with food, with less water use and low carbon footprint. Secondly, blending of biofuels with fossil fuels can be an option to be considered in a sense that blending will balance and combine the weaknesses and strengths of components involved in blending in order to comply with standards and satisfy the market expectations [10, 11]. Blending fossil fuels and biofuels is one of the options undertaken by fuel producers for costs reduction, environmental compliance including quality assurance and performance related aspects [11–14]. Also, fossil fuel costs are generally lower than the ones for biofuels. Biofuels have the advantage of being environmentally friendly but costly while fossil fuels are affordable but not environmentally friendly [15]. One of the major economic issues for the fuel producer is to use relevant conversion processes which are costs effective to produce high-quality fuel that can satisfy the need of the fuel user or market. Therefore, the final product has to comply with the criteria defined by the standards [16, 17]. In this regard, blending can provide an advantage over other options by generating a jet fuel with low carbon footprint which should also be compliant with standards [18, 19]. However, the costs of the blend will depend on the overall production costs for single fuels involved in the blend and the blending costs. Fuel blending could be one of the options to be considered in the near future as a sustainable possibility for green energy production and carbon footprint reduction [20]. The greatest expectation is such that the blend should be sustainable, compliant and has to be certified by ASTM or any other certification institution. This implies that blended fuel will be subjected to stringent regulations and standards in order for it to be on the market and compete with the existing fuels. Microalgae-based fuels are currently positioning themselves on the market to compete with fossil fuels for power generation and energy production. Many companies such as Algenol, Algae Fuel System, Solazyme, Sapphire Energy, Euglena, Alpha Biotech, AlgaFuel S.A, AlgalOilDiesel, Algae.Tec and many others are successfully involved in the production of algae-based fuels. However, the main challenge for microalgae-based fuels remains the low productivity of lipids and high production costs owing to conversion processes [21]. Consequently, blending microalgae-based fuels with fossil fuels can be undertaken and analysed to find out if it can be an acceptable option despite the existing certification from the standardization institutions. This is more related to the performance of the fuel compared the existing ones. The current study is focusing on compliance from blending algae-based jet fuel and Jet A1. Currently, regarding jet fuel blending options, there is only 50/50 blend that is certified by ASTM [22]. Jet fuels from microalgae have already successfully been tested in both commercial and military aircraft. ASTM has approved the use of biomass-based jet fuel since July 2011 for commercial flights. The ASTM certification is valid only for blending with conventional Jet fuel in a 50/50 volume ratio (B50). The certification is valid for all fuels from biomass which are cleared for take-off. However, the blended jet fuel has not been used consistently by the aviation sector despite the B50 certification. The issue related species oil content, sustainability and production costs for algae-based jet fuel is still a challenge. Certification does not necessarily mean that the blend will be operational with high performance. The blended is expected to have a high level of purity. It should not solidify at lower temperatures and must generate a high amount of energy required for propulsion of the aircraft. The major challenge with algae-based jet fuel is to get species with the ability to generate a high amount of bio-oil with hydrocarbons that are molecularly very identical to petroleum oil. This will allow the production of jet fuel from the same downstream processes used to produce conventional jet fuel. Nannochloropsis sp is one of the types of species with the potential to produce algae Jet fuel because of its composition and the cultivation possibilities in the marine environment. The objective of this study is to prepare and produce a new blend by mixing algae-based Jet fuel with Jet A1 in 50/50 volume ratio. The new Jet fuel blend will be tested according to ASTM standards for aviation fuels to identify parameters which are compliant and non-compliant to ASTM standards chosen as a reference in this study. For parameters which are non- compliant, ways to bring them to comply with ASTM standards will be suggested. However, costs implications or feasibility aspects of the blending, mathematical modelling aspects, are not part of this work. The study will assist in examining the compliance, analysing the behaviour of physico-chemical parameters and the quality of the blend which are probably affected over time. This will assist in considering whether or not blending is a sustainable option for aviation fuels. The contribution will be reflected by the data indicating whether the compliance is possible or not from the 50/50 blended jet fuel. Therefore, blending jet fuels in 50/50 ratio is technically and economically beneficial, it can be used as a sustainable option to reduce dependence on petroleum-derived fuels. Furthermore, the 50/50 blended jet fuel is expected to have a low carbon footprint and low oxygen content including flow properties complying with required standards. 2 CHALLENGES ASSOCIATED WITH JET FUEL BLENDING Blending jet fuels can be much more complicated than a simple mixing of components [23]. The blend is a complex mixture of different carbon chains from C8 to C16 [24–26]. This situation can impact on compliance and overall costs. Jet fuels or any other fuel can be blended using the in-line blending method through a manifold system, batch blending in tanks and onboard blending into marine vessels [23, 27]. Each method has its strengths and weaknesses. In-line blending of jet fuels is achieved by injecting proportional amounts of each component into the mainstream where turbulence promotes thorough homogenization [27, 28]. Mixing depends on the speed of agitation and residence time. In many cases, to achieve the specifications required for compliance, additives are used during and/or after blending to improve specific properties related to flow, heating energy and anti-freezing capacity. Blending jet fuels is very a complex process because the blend is expected to be renewable with low carbon footprint compared to the fossil-based fuel. 3 JET FUEL BLENDING AND ASTM CERTIFICATION Blending can assist in using a reduced amount of fossil fuels. Also, it is environmentally safe to burn blended jet fuel. Generally, blended fuels are commercially viable and environmentally friendly. Predominantly, the blended jet fuel should be sustainable and always complies with standards. Microalgae-derived fuels can be used in a blend to produce high-quality fuels. They have an advantage of generating fuels with a low carbon footprint evaluated at 60% less compared to conventional fuels. Therefore, they are an acceptable option for jet fuel blending. It is compulsory that aviation fuels from any source must be certified before they can be used in any aircraft. They must comply with internationally recognized standards for certification. ASTM certification is the most required. The ASTM approval process is known as a multi-year and multi-million-dollar process [29]. Two different conversion technologies are already certified with ASTM standards for alternative aviation fuels. In 2009, ASTM International approved standards for alternative aviation fuels using the Fisher Tropsch process for the conversion of renewable feedstock sources to Jet fuel [30]. In 2011, the production of jet fuel from hydroprocessed esters and fatty acids (HEFA) was added to the standard under D7566-11. It was recommended that these blended jet fuels can only be used in commercial aviation on a 50/50 blended basis certified under ASTM Standard D1655. Expanding on the approved feedstock list, various biomass resources including algae biomass can be used to produce jet fuel substitutes. Technologies to convert biomass to jet fuel are available but the production capacity is currently small and production costs are not well known, especially for less-developed processes [31]. In this case, blending jet fuels could be an option or an intermediate solution to deal with the issue of production capacity and costs. 4 MATERIAL AND METHODS A sample of Jet A1 was blended with algae-based jet fuel on a 50/50 volume ratio (B50). The algae-based jet fuel was produced in the laboratory after Nannochloropsis sp biomass was cultivated in a photobioreactor, followed by oil extraction, purification, thermal cracking using pyrolysis of crude bio-oil at 350°C and fractionation between 70 and 300°C to get the required fractions for jet fuel [22]. The cultivation was completed in 15 days with high biomass produced on the 10th day. After harvesting the biomass in a centrifuge, oil extraction using a mixture of solvent made with chloroform and methanol on 1/1 volume ratio was completed. The bio-oil combined with solvent was purified by evaporation to remove the solvent and collect the bio-oil. Thermal cracking was undertaken at 300°C in a furnace to break down the carbon chains. It was followed by fractionation from 70 to 300°C to collect fractions needed for jet fuel. Microalgae-based jet fuel was characterized according to ASTM standards and the results are presented in Table 1. The petroleum jet fuel (Jet A1) was supplied by Sapref –Engen in Durban, South Africa. It was a pure product ready for commercial use. Table 1. Algae-based jet fuel: characterization after preparation. Parameter Results ± standard deviation ASTM Limits for conventional Jet fuel Method Density at 15°C [g/l] 0.842 ± 0.015 0.775–0.840 ASTM D7042 Viscosity at −20°C [cSt] 2.4 ± 0.02 8 (maximum) ASTM D445 Flash point [°C] 68 ± 0.5 38 (Minimum) ASTM D93 Water content [%] 0.05 ± 0001 n.d ASTM D6304 Total acidity [mg KOH/g] 0.05 ± 0.001 0.015(Maximum) ASTM D3242 Total contamination[mg/kg] 7.6 ± 0.2 24 (Maximum) IP440/SANS 52 662 Total Sulphur [%] 0.27 ± 0.01 0.3 (Maximum) ASTM D4294 Net heat of combustion [MJ/kg] 44 ± 0.5 42.8 (Minimum) ASTM D4868 Freezing point [°C] −32 ± 0.01 −40°C (Maximum) ASTMD D2386 Conductivity [pS/m] 84 ± 0.5 50–600 ASTM D2624 Parameter Results ± standard deviation ASTM Limits for conventional Jet fuel Method Density at 15°C [g/l] 0.842 ± 0.015 0.775–0.840 ASTM D7042 Viscosity at −20°C [cSt] 2.4 ± 0.02 8 (maximum) ASTM D445 Flash point [°C] 68 ± 0.5 38 (Minimum) ASTM D93 Water content [%] 0.05 ± 0001 n.d ASTM D6304 Total acidity [mg KOH/g] 0.05 ± 0.001 0.015(Maximum) ASTM D3242 Total contamination[mg/kg] 7.6 ± 0.2 24 (Maximum) IP440/SANS 52 662 Total Sulphur [%] 0.27 ± 0.01 0.3 (Maximum) ASTM D4294 Net heat of combustion [MJ/kg] 44 ± 0.5 42.8 (Minimum) ASTM D4868 Freezing point [°C] −32 ± 0.01 −40°C (Maximum) ASTMD D2386 Conductivity [pS/m] 84 ± 0.5 50–600 ASTM D2624 Table 1. Algae-based jet fuel: characterization after preparation. Parameter Results ± standard deviation ASTM Limits for conventional Jet fuel Method Density at 15°C [g/l] 0.842 ± 0.015 0.775–0.840 ASTM D7042 Viscosity at −20°C [cSt] 2.4 ± 0.02 8 (maximum) ASTM D445 Flash point [°C] 68 ± 0.5 38 (Minimum) ASTM D93 Water content [%] 0.05 ± 0001 n.d ASTM D6304 Total acidity [mg KOH/g] 0.05 ± 0.001 0.015(Maximum) ASTM D3242 Total contamination[mg/kg] 7.6 ± 0.2 24 (Maximum) IP440/SANS 52 662 Total Sulphur [%] 0.27 ± 0.01 0.3 (Maximum) ASTM D4294 Net heat of combustion [MJ/kg] 44 ± 0.5 42.8 (Minimum) ASTM D4868 Freezing point [°C] −32 ± 0.01 −40°C (Maximum) ASTMD D2386 Conductivity [pS/m] 84 ± 0.5 50–600 ASTM D2624 Parameter Results ± standard deviation ASTM Limits for conventional Jet fuel Method Density at 15°C [g/l] 0.842 ± 0.015 0.775–0.840 ASTM D7042 Viscosity at −20°C [cSt] 2.4 ± 0.02 8 (maximum) ASTM D445 Flash point [°C] 68 ± 0.5 38 (Minimum) ASTM D93 Water content [%] 0.05 ± 0001 n.d ASTM D6304 Total acidity [mg KOH/g] 0.05 ± 0.001 0.015(Maximum) ASTM D3242 Total contamination[mg/kg] 7.6 ± 0.2 24 (Maximum) IP440/SANS 52 662 Total Sulphur [%] 0.27 ± 0.01 0.3 (Maximum) ASTM D4294 Net heat of combustion [MJ/kg] 44 ± 0.5 42.8 (Minimum) ASTM D4868 Freezing point [°C] −32 ± 0.01 −40°C (Maximum) ASTMD D2386 Conductivity [pS/m] 84 ± 0.5 50–600 ASTM D2624 The characterization of Jet A1 was not disclosed in details by the manufacturer. However, the manufacturing report confirmed the compliance of all parameters according to ASTM standards. The blending procedure used 500 ml of Jet A1 in a beaker and mixed it with 500 ml of microalgae-derived jet fuel. The blending was completed using a magnetic stirrer running at 150 rpm for a period of 2 h at 25°C.The sample was conserved at in a closed glass container. After mixing, the 50/50 blended jet fuel was characterized according to ASTM. Samples were stored and tested for stability using ASTM procedures. 5 RESULTS AND DISCUSSION Samples were kept at a controlled temperature of 25°C in an incubator. The data generated from the characterization of microalgae-derived jet fuel and the blended jet fuel are summarized in Tables 1–3. The results were generated in triplicate and the recorded data in the tables are mean values. Table 2. 50/50 Blended jet fuel (algae-based jet fuel and Jet A1): characterization after blending. Parameter Results ± standard deviation ASTM Limits Method Density at 15°C [g/l] 0.8727 ± 0.02 0.775–0.840 ASTM D7042 Viscosity at −20°C [cSt] 5.3 ± 0.05 8 (maximum) ASTM D445 Flash point [°C] 67 ± 0.5 38 (Minimum) ASTM D93 Water content [%] 0.089 ± 0.05 n.d ASTM D6304 Total acidity [mgKOH/g] 0.03 ± 0.001 0.015 (Maximum) ASTM D3242 Total contamination [mg/kg] 5.64 ± 0.1 24 (Maximum) IP440/SANS 52 662 Total Sulphur [%] 0.0159 ± 0.001 0.3 (Maximum) ASTM D4294 Net heat of combustion [MJ/kg] 43.5 ± 0.5 42.8 (Minimum) ASTM D4868 Freezing point [°C] −40 ± 0.001 −40°C (Maximum) ASTMD D2386 Conductivity [pS/m] 85 ± 0.5 50–600 ASTM D2624 Parameter Results ± standard deviation ASTM Limits Method Density at 15°C [g/l] 0.8727 ± 0.02 0.775–0.840 ASTM D7042 Viscosity at −20°C [cSt] 5.3 ± 0.05 8 (maximum) ASTM D445 Flash point [°C] 67 ± 0.5 38 (Minimum) ASTM D93 Water content [%] 0.089 ± 0.05 n.d ASTM D6304 Total acidity [mgKOH/g] 0.03 ± 0.001 0.015 (Maximum) ASTM D3242 Total contamination [mg/kg] 5.64 ± 0.1 24 (Maximum) IP440/SANS 52 662 Total Sulphur [%] 0.0159 ± 0.001 0.3 (Maximum) ASTM D4294 Net heat of combustion [MJ/kg] 43.5 ± 0.5 42.8 (Minimum) ASTM D4868 Freezing point [°C] −40 ± 0.001 −40°C (Maximum) ASTMD D2386 Conductivity [pS/m] 85 ± 0.5 50–600 ASTM D2624 All characterizations were undertaken by Wearcheck an ISO 9001:2008/ISO 14 001:2004/ISO 17 025:2005 registered company. Tests of the 50/50 blended jet fuel were also completed after 30, 60, 90 and 120 days from the blending day in order to check the stability of various parameters according to ASTM standards. Table 2. 50/50 Blended jet fuel (algae-based jet fuel and Jet A1): characterization after blending. Parameter Results ± standard deviation ASTM Limits Method Density at 15°C [g/l] 0.8727 ± 0.02 0.775–0.840 ASTM D7042 Viscosity at −20°C [cSt] 5.3 ± 0.05 8 (maximum) ASTM D445 Flash point [°C] 67 ± 0.5 38 (Minimum) ASTM D93 Water content [%] 0.089 ± 0.05 n.d ASTM D6304 Total acidity [mgKOH/g] 0.03 ± 0.001 0.015 (Maximum) ASTM D3242 Total contamination [mg/kg] 5.64 ± 0.1 24 (Maximum) IP440/SANS 52 662 Total Sulphur [%] 0.0159 ± 0.001 0.3 (Maximum) ASTM D4294 Net heat of combustion [MJ/kg] 43.5 ± 0.5 42.8 (Minimum) ASTM D4868 Freezing point [°C] −40 ± 0.001 −40°C (Maximum) ASTMD D2386 Conductivity [pS/m] 85 ± 0.5 50–600 ASTM D2624 Parameter Results ± standard deviation ASTM Limits Method Density at 15°C [g/l] 0.8727 ± 0.02 0.775–0.840 ASTM D7042 Viscosity at −20°C [cSt] 5.3 ± 0.05 8 (maximum) ASTM D445 Flash point [°C] 67 ± 0.5 38 (Minimum) ASTM D93 Water content [%] 0.089 ± 0.05 n.d ASTM D6304 Total acidity [mgKOH/g] 0.03 ± 0.001 0.015 (Maximum) ASTM D3242 Total contamination [mg/kg] 5.64 ± 0.1 24 (Maximum) IP440/SANS 52 662 Total Sulphur [%] 0.0159 ± 0.001 0.3 (Maximum) ASTM D4294 Net heat of combustion [MJ/kg] 43.5 ± 0.5 42.8 (Minimum) ASTM D4868 Freezing point [°C] −40 ± 0.001 −40°C (Maximum) ASTMD D2386 Conductivity [pS/m] 85 ± 0.5 50–600 ASTM D2624 All characterizations were undertaken by Wearcheck an ISO 9001:2008/ISO 14 001:2004/ISO 17 025:2005 registered company. Tests of the 50/50 blended jet fuel were also completed after 30, 60, 90 and 120 days from the blending day in order to check the stability of various parameters according to ASTM standards. Table 3. 50/50 Blended Jet fuel (algae-based jet fuel and Jet A1): storage stability tests. Parameter 30 days 60 days 90 days 120 days ASTM limits Method Density at 15°C [g/l] 0.86 ± 0.01 0.86 ± 0.01 0.862 ± 0.01 0.859 ± 0.01 0.775–0.840 ASTM D7042 Viscosity at −20°C [cSt] 5 ± 0.05 5.1 ± 0.05 5.1 ± 0.05 5 ± 0.05 8 (maximum) ASTM D445 Flash point [°C] 67 ± 0.5 68 ± 0.5 68 ± 0.5 68 ± 0.5 38 (Minimum) ASTM D93 Water content [%] 0.06 ± 0.001 0.06 ± 0.001 0.06 ± 0.001 0.06 ± 0.001 n.d ASTM D6304 Total acidity [mgKOH/g] 0.03 ± 0.001 0.029 ± 0.001 0.030 ± 0.001 0.0289 ± 0.001 0.015 (Maximum) ASTM D3242 Total contamination [mg/kg] 5.6 ± 0.1 5.6 ± 0.1 5.6 ± 0.1 5.6 ± 0.1 24 (Maximum) IP440/SANS 52 662 Total Sulphur [%] 0.0159 ± 0.001 0.0159 ± 0.001 0.158 ± 0.001 0.0157 ± 0.001 0.3 (Maximum) ASTM D4294 Net heat of combustion [MJ/kg] 44 ± 0.5 44 ± 0.5 44 ± 0.5 45.3 ± 0.5 42.8 (Minimum) ASTM D4868 Freezing point [°C] −40 ± 0.001 −40 ± 0.001 −40 ± 0.001 −40 ± 0.001 −40°C (Maximum) ASTMD D2386 Conductivity [pS/m] 92 ± 0.5 125 ± 0.5 130 ± 0.5 128 ± 0.5 50–600 ASTM D2624 Parameter 30 days 60 days 90 days 120 days ASTM limits Method Density at 15°C [g/l] 0.86 ± 0.01 0.86 ± 0.01 0.862 ± 0.01 0.859 ± 0.01 0.775–0.840 ASTM D7042 Viscosity at −20°C [cSt] 5 ± 0.05 5.1 ± 0.05 5.1 ± 0.05 5 ± 0.05 8 (maximum) ASTM D445 Flash point [°C] 67 ± 0.5 68 ± 0.5 68 ± 0.5 68 ± 0.5 38 (Minimum) ASTM D93 Water content [%] 0.06 ± 0.001 0.06 ± 0.001 0.06 ± 0.001 0.06 ± 0.001 n.d ASTM D6304 Total acidity [mgKOH/g] 0.03 ± 0.001 0.029 ± 0.001 0.030 ± 0.001 0.0289 ± 0.001 0.015 (Maximum) ASTM D3242 Total contamination [mg/kg] 5.6 ± 0.1 5.6 ± 0.1 5.6 ± 0.1 5.6 ± 0.1 24 (Maximum) IP440/SANS 52 662 Total Sulphur [%] 0.0159 ± 0.001 0.0159 ± 0.001 0.158 ± 0.001 0.0157 ± 0.001 0.3 (Maximum) ASTM D4294 Net heat of combustion [MJ/kg] 44 ± 0.5 44 ± 0.5 44 ± 0.5 45.3 ± 0.5 42.8 (Minimum) ASTM D4868 Freezing point [°C] −40 ± 0.001 −40 ± 0.001 −40 ± 0.001 −40 ± 0.001 −40°C (Maximum) ASTMD D2386 Conductivity [pS/m] 92 ± 0.5 125 ± 0.5 130 ± 0.5 128 ± 0.5 50–600 ASTM D2624 Table 3. 50/50 Blended Jet fuel (algae-based jet fuel and Jet A1): storage stability tests. Parameter 30 days 60 days 90 days 120 days ASTM limits Method Density at 15°C [g/l] 0.86 ± 0.01 0.86 ± 0.01 0.862 ± 0.01 0.859 ± 0.01 0.775–0.840 ASTM D7042 Viscosity at −20°C [cSt] 5 ± 0.05 5.1 ± 0.05 5.1 ± 0.05 5 ± 0.05 8 (maximum) ASTM D445 Flash point [°C] 67 ± 0.5 68 ± 0.5 68 ± 0.5 68 ± 0.5 38 (Minimum) ASTM D93 Water content [%] 0.06 ± 0.001 0.06 ± 0.001 0.06 ± 0.001 0.06 ± 0.001 n.d ASTM D6304 Total acidity [mgKOH/g] 0.03 ± 0.001 0.029 ± 0.001 0.030 ± 0.001 0.0289 ± 0.001 0.015 (Maximum) ASTM D3242 Total contamination [mg/kg] 5.6 ± 0.1 5.6 ± 0.1 5.6 ± 0.1 5.6 ± 0.1 24 (Maximum) IP440/SANS 52 662 Total Sulphur [%] 0.0159 ± 0.001 0.0159 ± 0.001 0.158 ± 0.001 0.0157 ± 0.001 0.3 (Maximum) ASTM D4294 Net heat of combustion [MJ/kg] 44 ± 0.5 44 ± 0.5 44 ± 0.5 45.3 ± 0.5 42.8 (Minimum) ASTM D4868 Freezing point [°C] −40 ± 0.001 −40 ± 0.001 −40 ± 0.001 −40 ± 0.001 −40°C (Maximum) ASTMD D2386 Conductivity [pS/m] 92 ± 0.5 125 ± 0.5 130 ± 0.5 128 ± 0.5 50–600 ASTM D2624 Parameter 30 days 60 days 90 days 120 days ASTM limits Method Density at 15°C [g/l] 0.86 ± 0.01 0.86 ± 0.01 0.862 ± 0.01 0.859 ± 0.01 0.775–0.840 ASTM D7042 Viscosity at −20°C [cSt] 5 ± 0.05 5.1 ± 0.05 5.1 ± 0.05 5 ± 0.05 8 (maximum) ASTM D445 Flash point [°C] 67 ± 0.5 68 ± 0.5 68 ± 0.5 68 ± 0.5 38 (Minimum) ASTM D93 Water content [%] 0.06 ± 0.001 0.06 ± 0.001 0.06 ± 0.001 0.06 ± 0.001 n.d ASTM D6304 Total acidity [mgKOH/g] 0.03 ± 0.001 0.029 ± 0.001 0.030 ± 0.001 0.0289 ± 0.001 0.015 (Maximum) ASTM D3242 Total contamination [mg/kg] 5.6 ± 0.1 5.6 ± 0.1 5.6 ± 0.1 5.6 ± 0.1 24 (Maximum) IP440/SANS 52 662 Total Sulphur [%] 0.0159 ± 0.001 0.0159 ± 0.001 0.158 ± 0.001 0.0157 ± 0.001 0.3 (Maximum) ASTM D4294 Net heat of combustion [MJ/kg] 44 ± 0.5 44 ± 0.5 44 ± 0.5 45.3 ± 0.5 42.8 (Minimum) ASTM D4868 Freezing point [°C] −40 ± 0.001 −40 ± 0.001 −40 ± 0.001 −40 ± 0.001 −40°C (Maximum) ASTMD D2386 Conductivity [pS/m] 92 ± 0.5 125 ± 0.5 130 ± 0.5 128 ± 0.5 50–600 ASTM D2624 5.1 Storage stability test Generally, medium-term storage stability tests of at least 1000 h (~30 days) [32, 33] are required to confirm if some parameters which are time-dependent do not critically affect the physico-chemical properties of the 50/50 blended jet fuel. In this study, the storage stability test for the 50/50 blended jet fuel was undertaken after 30, 60, 90 and 120 days from the day of preparation/production. In general, the analysis of data recorded in Tables 1–3 shows that the majority of parameters are within or slightly beyond the limits described by ASTM. Particularly, it is observed in Table 3 that the variation of measurements for some few parameters recorded after 30, 60, 90 and 120 days were not very significant and they remained within the limits required for ASTM compliance. It can be inferred that the 50/50 blending of jet fuels is a suitable option and can be undertaken at a larger scale. This is supported by the fact that no significant fluctuations in data were recorded for most parameters for a period of up to 120 days from the production. However, some parameters such as density and total acidity should be improved according to ASTM standards. 5.2 Density Density at 15°C is beyond ASTM limits as indicated in Tables 2 and 3 dealing with data for the 50/50 blended jet fuel. However, the difference between the ASTM maximum limit and the recorded data in this study for this parameter is not significant. The density of jet fuel is very important and must be within the limits prescribed by the standards or the aircraft weight loading calculations since jet fuel is customarily metered by volume. Also, it relates to specific energy and volatility of jet fuel. To improve the density of the jet fuel, fuel filtration through a membrane system can assist in removing some particulate matter probably from the algae-based jet fuel that might have caused the increase of density. Undesirable substances will be retained by the filter media and a cleaner blended jet fuel with density within ASTM limits can be collected. 5.3 Kinematic viscosity Kinematic viscosity is directly linked to fuel fluidity or fuel pumpability over the operating temperature range and relates to droplet size in sprays produced by burner nozzles. The ASTM maximum limit for viscosity at −20°C is 8 cSt. In this study, the recorded data for viscosity at −20°C presented in Tables 1–3 have ranged from 2 to 5.3 cSt and it is compliant with the standards. The lowest value is recorded in Table 1 regarding algae-based jet fuel. However, it has increased in the 50/50 blended jet fuel as indicated in Table 3 for different measurements. 5.4 Flash point Flash point is one of the parameters that relate to jet fuel volatility, it can, therefore, have an impact on combustibility. It is a leading factor in determining fire safety regarding fuel handling. In the present study, the flash point remains almost stable. It has slightly fluctuated between 67 and 68°C as indicated in Tables 1–3. These values are compliant with ASTM standards requiring a minimum of 38°C. The analysis of the recorded data on flash point for the 50/50 blended jet fuel shows the 50/50 blended jet fuel has lower flammability and it has less hazardous behaviour because of the higher flash point. This is a strong point regarding the 50/50 blended jet fuel produced in this study which shows its potential for safety and hazard related issues. In this regard, the blend can be used in a hot environment where safety issues for fuels are not easy to be handled. 5.5 Water content Water content has to be at the very lowest concentration in jet fuel. So far there are no exact limits defined by ASTM standards regarding this parameter in jet fuel. Determining the level of water content in jet fuel will assist in minimizing the water reaction controlled by the presence of materials that react with water and affect the stability of the jet fuel–water interface. It is very important that jet fuel be free from water contamination. During the flight, the temperature of jet fuel in the tanks decreases due to the low temperatures in the upper atmosphere. This causes precipitation of the dissolved water from the jet fuel. Therefore, the separated water drops to the bottom of the tank, because it is denser than the jet fuel. Since water is no longer in solution, it can form droplets that can supercool to below 0°C. Analysing this parameter, water separation index can be also measured to determine the ability of the jet fuel to release entrained or emulsified water when passed through a fibreglass filter coalescer. The data in Tables 1 and 2 show lower values of water in the algae-based jet fuel compared to the 50/50 blended jet fuel. During storage the quantity of water has decreased in the 50/50 blended jet fuel from 0.089 to 0.06% and this quantity has remained constant up 120 days for the 50/50 blended jet fuel as indicated in Table 3. 5.6 Total acidity Generally, total acidy is a parameter that indicates the corrosive potential of fuel to metals. Trace organic acids can affect water separation properties. In this study total acidity has been found higher than the limit required by ASTM which is equal to 0.015 mg KOH/g. Table 1 has recorded a total acidity of 0.05 mg KOH/g while in the 50/50 blended jet fuel obtained after production for which the data is presented in Table 2 the total acidity is 0.03 mg KOH/g. This is still beyond the maximum limit of 0.015 mg KOH/g required by ASTM standards. Table 3 shows that the total acidity is still higher and beyond the ASTM limit. It is between 0.0289 to 0.03 mg KOH/g during the storage stability test period. Therefore, because of the higher total acidity found in the algae-based jet fuel as well as the 50/50 blended jet fuel and knowing that the acidity does not have a significant impact on the fuel performance but can mainly cause corrosion, it will be indispensable to use corrosion inhibitor to reduce the potential corrosivity of the jet fuel. The corrosion inhibitor is known as a lubricity improver, consequently, inhibiting corrosion will also improve the lubricity of the jet fuel because many aircraft fuel system components, especially pumps, rely on the fuel to lubricate moving parts. 5.7 Total contamination Contaminants in jet fuel are made of existent gum such as non-volatile residue left on jet fuel evaporation, dissolved and undissolved particulate matters which are undesirable including dirt and rust. The analysis of data recorded in Tables 1–3 shows that the level of contaminants has remained below the maximum of 24 mg/kg required by SANS. It is imperative to have very pure jet fuel after preparation, therefore, reducing the level of contaminants after obtaining the final product is more than a necessity. In this regard, a membrane filtration as mentioned earlier can be an option not only to improve density but mostly to get pure blended jet fuel. 5.8 Total sulphur Sulphur must be controlled because sulphur oxides formed during combustion can cause corrosion of turbine metal parts. Generally, the origin of sulphur in the conventional jet fuel may come from crude petroleum oil. In the case of the 50/50 blended jet fuel produced during the course of this study, there is a possibility that a fraction of sulphur originates also from the microalgae strain. Marine algae strains may contain sulphur that is found between layers of sedimentary rocks formed by the layering of seabed deposits and free organic material settling. In this study, sulphur has been found lower than the limit prescribed by ASTM standards. The recorded data for algae-based jet fuel in Table 1 as well as the one for the 50/50 blended jet fuel in Tables 2 and 3 are showing that the levels of total sulphur are below the maximum of 0.3% required by ASTM standards in terms of compliance. However, even if the total sulphur is below the value recommended for compliance, it is imperative to consider desulfurization in order to minimize the effects of sulphur in jet fuel and in the environment. Sulphur causes the formation of secondary particulate matter in jet fuel and the emission of sulphur oxide can because of major health issues. 5.9 Net heat of combustion This parameter is directly linked to the amount of energy generated by jet fuel and its performance. It is one of the key parameters that are highly needed for most fuels in general and jet fuel in particular. It is a calculated value denoting the amount of heat energy obtainable from fuel to provide the power needed to run an aircraft from take-off to landing. The ASTM required a minimum value for aviation fuels is 42.8 MJ/kg. In this study algae-based, jet fuel recorded a Net heat of combustion of 44 MJ/kg as indicated in Table 1. The 50/50 blended jet fuel presented in Table 2 has recorded a Net Heat of Combustion equivalent to 43.5 MJ/kg while the stored 50/50 blended jet fuel presented in Table 3 has kept its Net Heat of Combustion at 44MJ/kg during the storage test period. A slight increase of the Net Heat of Combustion of up to 45.3 MJ/kg was recorded on the 120 the day of the storage test period. Overall, the Net Heat of Combustion has remained compliant with the ASTM limit of 42.8 MJ/kg. This is an indication that the 50/50 blended jet fuel has the potential to produce enough energy needed for the aircraft thrust. 5.10 Freezing point This parameter is one of the most important regarding jet fuel performance, it limits higher molecular weight hydrocarbons that crystallize at low temperatures; it, therefore, influences low-temperature pumpability during the flight. At higher altitudes where temperatures are very lower, the jet fuel will have a tendency of solidifying. Therefore, the lowest freezing point is the most needed. The analysis of Table 1 shows that algae-based jet fuel has a high freezing point which does not comply with ASTM standards while during the experiment algal crude bio-oil was exposed to the lowest temperature of −80°C without solidifying. However, the 50/50 blended jet fuel indicates a freezing point that complies with ASTM standards. For the 50/50 blended jet fuel, the freezing point has remained constant and it complies with ASTM standards as indicated in Tables 2 and 3. This complying value of the freezing point may be due to the presence and the action of the anti-freezing or ice inhibitor additive present in the Jet A1 which forms part of the blend. Therefore, blending conventional jet fuel and algae-based jet fuel can assist in improving the freezing point of the blend in case one of the components from the blend has a higher freezing point not complying with ASTM standards. 5.11 Conductivity This parameter represents the concentration of dissolved substances in the jet fuel. It has to be sufficiently high in order to dissipate any electrostatic charges generated during fuel handling operations, so as to prevent fire or explosion hazards. Analysing Table 1 and comparing the data in Tables 2 and 3 it is indicated that the conductivity is within the range required by ASTM standards in all cases. Comparing the conductivities of the 50/50 blended jet fuel after preparation and the ones during the storage test period there is an overall increase of conductivity values. This can be due to the increase of the concentration of dissolved substances caused by the decrease in water content during storage test period as mentioned earlier. 6 CONCLUSIONS This study has attempted to establish the possibility of using a blended jet fuel made of algae-based- jet fuel with Jet A1 in 50/50 volume ratio. The algae-based jet fuel was obtained from Nannochloropsis sp. The main aim of the study was to verify the extent to which compliance to ASTM standards and performance of aviation fuels was going to be met when blending a biomass-based Jet fuel and a petroleum jet fuel. Therefore, ASTM standards for aviation fuels D1655 were chosen to characterize the 50/50 blended jet fuel. Conversely, it was not also possible to undertake a complete characterization because of limited resources and time frame allocated to this study. Nevertheless, it was found that most of the selected parameters were complying with ASTM standards for the 50/50 blended jet fuel. However, parameters such as density at 15°C and total acidity were found non-compliant to ASTM standards. The cause of non-compliant could be due to the fact that the algae-based Jet fuel was not at the same level of cleanness compared to Jet A1 used in the 50/50 blend. It needs more refining processes such as reforming and upgrading to reach the same level of purity as it is for Jet A1. However, there is another way to get highly pure algae-derived Jet fuel by using separation processes such as membrane filtration or rectification in order to improve parameters such as density, total acidity and reduce sensibly the contamination level. However, there will be a need for more studies involving costs modelling and innovative technology to improve all parameters required for the 50/50 blended jet fuel. A storage stability tests undertaken on 30, 60,90 and 120th day after the 50/50 blended jet fuel preparation indicated that most of the parameters have remained stable and compliant to ASTM standards. The 50/50 blended jet fuel can be produced at large scales and commercialized due to the fact that most of the properties comply with ASTM standards. Furthermore, the presence of algae-based jet fuel into Jet A1 has the potential to make the 50/50 blended jet fuel environmentally friendly but still not economically competitive because the production of algae-based jet fuel is still expensive. Overall the 50/50 blending for jet fuel using algae-based jet fuel and Jet A1 is a sustainable option for jet fuel. It reduces carbon footprint and it is an economically viable compared to algae-based jet fuel. 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TI - Jet fuel blend from Algal Jet Fuel and Jet A1 in 50/50 volume ratio
JF - International Journal of Low-Carbon Technologies
DO - 10.1093/ijlct/ctz014
DA - 2019-06-01
UR - https://www.deepdyve.com/lp/oxford-university-press/jet-fuel-blend-from-algal-jet-fuel-and-jet-a1-in-50-50-volume-ratio-vozrkCQdot
SP - 234
VL - 14
IS - 2
DP - DeepDyve
ER -