Techno-economic and environmental assessment of renewable jet fuel production in integrated Brazilian sugarcane biorefineries
Introduction
Most scientists around the world agree that climate change is real and that anthropogenic greenhouse gases (GHG) emissions are at the root of this issue. According to recent estimates, airline operations were responsible for 2% of such carbon emissions in 2012 [1]. Among actions established by the aviation sector towards lowering the carbon footprint of the sector, three measures initially set for international flights within the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) mechanism stand out: (1) improving fleet fuel efficiency by 1.5% per year until 2020; (2) stabilizing emissions from 2020 onwards through carbon-neutral expansion; and (3) halving carbon emissions in 2050 in comparison to 2005 levels [2]. Since turbines and aircrafts are already highly efficient [3] and 80% of the emissions come from long-haul flights (which cannot be replaced by alternative transport options) [2], the bulk of the transition will come from the adoption of low-carbon jet fuel derived from biomass.
Conventional jet fuels, usually commercialized under A/A-1 (civil) and JP-8 (military) grades, are produced from crude oil, although ASTM International and other standards organizations also specify the synthesis of alternative jet fuels. Four of the five currently approved routes produce alternative jet fuel exclusively composed of paraffinic hydrocarbons (linear, branched, and cyclic), denominated Synthesized Paraffinic Kerosene (SPK). For use in turbines, SPK must be blended with fossil jet fuel in proportions ranging from 10% to 50%, depending on the conversion route used to obtain it [4]. A single pathway for the production of alternative jet fuels comprising both paraffinic and aromatic compounds, denominated Synthesized Paraffinic Kerosene plus Aromatics (SKA), is also permitted by the organization. Although the mixing of SKA with conventional jet fuel up to 50% is mandatory, such routes tend to focus its application at a longer time horizon. Since this type of jet fuel presents a more similar composition to its fossil counterpart, it could theoretically dismiss blend requirements. In short, the five conversion routes approved by ASTM International (as of September 2017) are: Hydroprocessed Esters and Fatty Acids (HEFA-SPK), which processes vegetable oils and animal fats into hydrocarbons; Fischer-Tropsch Synthesis (both FT-SPK and FT-SKA), in which different feedstocks undergo gasification and further catalytic synthesis to a wide range of hydrocarbons; Alcohol to Jet (ATJ-SPK), which converts isobutanol (and, potentially, other alcohols) into hydrocarbons; and Synthesized Isoparaffins (SIP-SPK), which produces jet fuel-like molecules through fermentation of carbohydrates [4]. Feedstocks for alternative jet fuels include either fossil resources, such as coal, natural gas, and shale oil, or biomass, in the form of lignocellulosic material, lipids, alcohols, and simple carbohydrates. For the remainder of this study, only alternative jet fuels obtained from biobased feedstocks are considered, henceforth referred to as renewable jet fuel (RJF).
The employment of RJF in civil aviation appears to be the best short-term solution for the mitigation of aircraft emissions. Use of RJF in commercial flights is already a reality, mostly after 2008 [5], although still on a modest scale. Recent examples include a series of 80 flights by KLM in Embraer E190 aircrafts from Oslo to Amsterdam employing Camelina sativa-based RJF produced by Neste through HEFA processing [6]. Unlike other biofuels, namely biodiesel and bioethanol, worldwide RJF utilization currently lacks incentive mechanisms [7], which are vital for the deployment of industrial units [8].
At present, Brazil is short of a clearly defined national policy to promote the use of RJF, despite recent movements concerning this possibility [9]. Brazil will be obliged to join the CORSIA instrument from 2027 onwards. Within its scope, it is estimated that around 1.5 million tonnes of CO2 emissions will have to be avoided by 2030 to promote carbon-neutral expansion of international flights originating in the country alone. Besides, as a signatory of the Paris Agreement (COP-21), Brazil established an aggressive Nationally Determined Contribution (NDC) towards cutting GHG emissions. In the aviation sector, the carbon-neutral growth of the entire sector in the country starting in 2020 will require aviation to mitigate between 8.3 and 12.4 million tonnes of CO2 emissions in 2030 [10]. Other nations, such as China, have also ratified challenging goals to reduce the carbon intensity of civil aviation up to 65% and peak emissions by 2030 [11]. Besides, the European Union has set shorter-term goals aiming at the displacement of 4% of fossil fuel consumption in 2020 – roughly equivalent to 2 million tonnes of RJF [12].
In order to tackle such ambitious goals, Brazil shows a prolific panorama in terms of renewable energy production and biomass cultivation. One crop is specially cultivated for energy purposes: sugarcane, mostly converted into ethanol, sugar, and electricity. Ethanol distilleries can act as host plants for a series of integrated processes for biobased products, ranging from biodiesel [13] to bio-propylene [14], succinic acid [15], microalgal biomass [16], and advanced biofuels [17], [18], [19], among which RJF production is comprised. Sugarcane mills can supply electricity, process steam, and raw materials to integrated industrial conversion units, thus consisting in a good example of a true biorefinery concept. The main objective of establishing integrated biorefineries is to profit from process integration advantages to leverage one promising, incipient technological route with inputs of materials, energy, and other utilities coming from a consolidated, more robust plant. This is the case when using outputs from a sugarcane mill to supply an RJF production plant so that the latter can achieve better operational stability and economic performance, as well as lower environmental impacts. Although such biorefinery alternatives are not currently common in the country, their potential for RJF production should be evaluated so as to provide accurate and quantitative information to decision-making processes.
For the estimation of the potential of adding RJF production to the sugar-energy sector, techno-economic and environmental analyses of technological alternatives must be carried out. The work presented herein was developed by the Brazilian Bioethanol Science and Technology Laboratory (CTBE), in partnership with Embraer S.A. and The Boeing Company, concerning the possibility and feasibility of RJF (within SPK specification limits) production in the Brazilian context from different feedstocks in integrated biorefineries with ethanol distilleries. The Virtual Sugarcane Biorefinery (VSB), an innovative framework developed by CTBE [20], was employed in the sustainability assessment of different biorefinery alternatives. This study considered the establishment of completely self-sufficient biorefineries, i.e. which only take different types of biomass (sugarcane stalks and straw, eucalyptus, and vegetable oils) as main inputs and do not rely on external energy supply (e.g. electricity, natural gas, or other energy sources) for operation. Three production routes were analyzed, following their relevance in a worldwide context and their potential of large-scale deployment in Brazil: HEFA, FT, and ATJ [21]. In the designed scenarios, HEFA routes processed palm, macauba, or soybean oils, while FT conversion was based on gasification of either sugarcane lignocellulosic fractions or eucalyptus, and ATJ converted isobutanol or ethanol into RJF. All work was developed with data from both scientific and open literature, and with CTBE’s know-how on Brazilian sugarcane biorefineries. The annual jet fuel output of each integrated biorefinery scenario is compared to a pre-determined jet fuel substitution target. In this work, RJF production was aimed at 5% of the conventional jet fuel consumption in Brazil in 20141 of 7.5 billion L [22], corresponding to the production of 375 million L of RJF/year.
When assessing techno-economic and environmental impacts of RJF production, authors often consider standalone plants, regardless of the feedstock: lipids (microalgae, Pongamia pinnata, Jatropha curcas, Camelina sativa, Brassica carinata, used cooking oil, and conventional vegetable oils) [23], [24], [25], [26], [27], [28], [29], [30]; lignocellulosic material (LCM), such as poplar and sugarcane bagasse [31], [32], [33], [34]; and alcohols [35]. The potential of RJF production in Brazil has been previously overviewed, also as independent plants [21], [36]. The integration with sugarcane mills itself is an innovative configuration which mitigates risks inherent to RJF technologies. RJF production in integration with sugarcane mills has already been assessed for the ATJ technology in South Africa [35] and for both ATJ and SIP routes in Brazil [37]. Moreover, De Jong et al. [24] confirmed the advantages of integration between RJF production and (unspecified) incubator facilities to the reduction of minimum jet fuel selling price (MJSP) between 4% and 8% in comparison to standalone RJF units. Nonetheless, the scientific literature lacks further efforts in assessing integrated biorefineries for other conversion routes. In this context, this study aims at comparing different strategies for RJF production integrated to sugarcane biorefineries in Brazil. The differentials of this analysis reside mainly in biorefinery simulation using rigorous models for the determination of complete mass and energy balances, as well as in the calculations integrating all steps of the production chain – from the agricultural phase to final fuel use. The biorefineries are ultimately assessed in terms of both economic and environmental performances and the produced RJF is benchmarked against conventional, fossil jet fuel by taking into account both economic and environmental aspects.
Section snippets
Brazilian sugarcane mills
Sugarcane processing in Brazil occurs mainly with three different plant configurations: autonomous ethanol distillery (producing only ethanol from carbohydrates), sugar factory (producing only sugar), and sugar factory with an annexed ethanol distillery (producing both ethanol and sugar). Sugarcane bagasse and, occasionally, sugarcane straw are burned in Cogeneration of Heat and Power (CHP) units for the generation of process steam and electricity to supply the energetic requirements of the
Technical results
Table 4 summarizes the main inputs and outputs of the assessed scenarios. The BASE scenario produces 360 million L of ethanol/year and a considerable amount of surplus electricity to the grid (769 MWh/year). This number is significantly higher than that found in the average Brazilian sugarcane mill, with a non-optimized operation, process inefficiencies, and without straw recovery. In all integrated biorefineries, as detailed in Section 2.3.1, the produced green diesel is used to partially or
Conclusions
The present study assessed the potential of producing RJF in integrated biorefineries with ethanol distilleries in Brazil. The variability of the obtained results shows that the mitigation of GHG emissions in the country is highly dependent on the feedstock, RJF production route, and plant location. FT scenarios had the best economic results: IRR of the integrated biorefineries and MJSP. HEFA biorefineries presented the largest volumes of RJF production due to the processing of vegetable oil
Acknowledgments
The authors would like to thank Embraer S.A. and The Boeing Company for the financial support to the development of this assessment and Marcelo Gonçalves (Embraer) and Onofre Andrade (Boeing) for the assistance in defining scenarios and the enriching discussion of the results.
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