Feedstock production and transportation
Fuel production and distrib u tion
Use of the nished fuel
Energy imputs
Process energy use
Chemical imputs
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Material inputs
AG. Coproducts
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Figure 2 An LCA is used to assess the overall GHG impacts of a fuel, including each stage of its production and use Source: US Environmental Protection Agency (USEPA, 2023 )
that emissions are quantified across the life-cycle of a product, including raw material extraction, production, transportation, use, and disposal using available data and established models. In 2006, the International Organization for Standardization (ISO) published ISO 14040 ( ISO, 2006 ), a framework for developing LCAs to measure a product’s impact and facilitate environmental decision-making, helping to ensure consistency and the ability to compare products and processes. ISO 14040 outlines four key phases to develop an LCA: Goal and scope definition: This phase builds the LCA framework and, among many variables, involves establishing the functional units, objectives, and boundaries for the assessment, defining the purpose of the study and identifying the product system to be assessed. Using the same units for comparing LCAs is crucial. For example, CI measured in kilograms of carbon dioxide equivalent (CO2e) per kg of product (kg CO2e/kg) is different from one measured in kg CO2e/MJ of product (megajoule). The main difference between these two units of measurement is that the former measures the CI based on the mass of the product, while the latter measures it based on the energy content. The system boundaries phase requires the boundaries to be clearly defined (for example, gate-to-gate, gate-to-grave, and overall cradle-
to-gate). As RD and SAF production chains expand, upstream processes like farming practices and fertiliser use might need to be included in the system boundaries, which again will significantly impact the CI score (see Figure 2 ). Inventory analysis: During this phase, data is collected on all relevant inputs (such as raw materials, energy, and water) and outputs (such as emissions, waste, and byproducts) relating to the system boundary established in Phase 1. This inventory forms the foundation for the impact assessment, which will be described in Phase 3. Data comes from sources such as process data, design data, industry data averages, public data, and/or set default values. All data and assumptions need to be referenced, and the collection process and timing of the data must be included. The better the data, the more reliable and accurate the calculations. Depending on the model applied for determining the CI scores of RD and SAF, there are different default values available. This is especially clear when including the feedstock indirect land-use change (iLUC) value. Currently, the iLUC values of the different models available vary widely (see Figure 3 ). Life-cycle impact assessment (LCIA): This phase uses the results of the earlier phases to determine and evaluate the potential environmental impacts associated with the product or system. This is typically defined in the
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