# PTG-HEFA Hybrid Refinery as Example of a SynBioPTx Concept--Results of a Feasibility Analysis
## 4 Conclusions  
Against the background of a growing aviation sector and the urgent demand on very large amounts of sustainable aviation fuels (SAF), an approach combining existing HEFA technology together with alternative hydrogen supply for processing realized via renewable PTG has been analysed in a comprehensive feasibility study. Ten different scenarios with regard to electricity supply for the PTG part, the hydrogen supply via electrolysis or steam reforming, different feedstocks for the HEFA part, as well as different product mixes were investigated from technical, economic, and environmental points of view. The technical assessment shows the specific mass and energy balances for the scenario-specific designs of such PTG-HEFA hybrid refineries. They differ, for instance, with regard to hydrogen demand, process energy and related product streams. The least hydrogen is required when processing palm oil to HEFA-SPK (scenario 8) and from a technical point of view it is favorable to generate hydrogen by steam-reforming, as the electrolysis causes the predominant part of the electricity demand of the plant and, in the dynamic and stand-alone scenario (2 and 3), creates technical challenges for storing the hydrogen that can be avoided with constant hydrogen production. The environmental assessment results allow one to conclude that for all scenarios at least 50% GHG mitigation can be achieved; but following the EU RED with 60% for new plants, just five of 10 concepts achieve that requirement. The use of as much renewable electricity as possible for the PTG part, integrated or other biogenic process energy, and the choice of feedstocks are the most relevant options for high GHG mitigation potentials. Accordingly, all stand-alone scenarios, steam reforming with naphtha from the HEFA plant, or steam reforming with biomethane and the usage of UCO as feedstock are environmentally more favorable. The economic assessment reveals that the specific fuel production costs highly depend on feedstocks and PTG-related costs. Total production costs are several times higher compared to the current market price of jet fuel. Disregarding scenario 10 where diesel is the main product, the lowest  
Figure 5: Comparison of production costs and GHG emissions for different scenarios and exemplary favorable regions. HEFA-SPK production costs are offered, in order, by the scenarios where palm oil is used as feedstock or hydrogen is produced by steam reforming of internal naphtha or natural gas. Furthermore, the analysis done regarding favorable regions for the PTG part does not show significant benefits of one scenario over the others, as all have very low GHG emissions but are in the upper range of the price spectrum of all examined scenarios. Although producing slightly higher GHG emissions than the stand-alone options, placing the reference scenario in Sweden would result in the most favorable option as the production costs are the lowest when considering different regions. Taking all investigated scenarios and assessments into account, the lowest GHG mitigation costs arise when internally produced naphtha is used for the hydrogen production by steam reforming (scenario 6). Focussing on diesel as the main product (10) causes just slightly higher GHG mitigation costs but does not offer the required GHG mitigation potential of 60% or more. The next best option in terms of mitigation costs, placing the reference scenario in Sweden, has, compared with the previous two options, the highest GHG mitigation potential at 73%. The limited HEFA capacities can cover only a small part of the energy demand of the world aviation sector, and all scenarios show higher costs than current kerosene supply does. Although other technologies for renewable sustainable aviation fuels are under R&D&D and new aviation technologies might become relevant in the long-term, the same applies to aviation and all other transport sectors as well: total energy demand needs to be drastically reduced and SAF have to be applied in parallel.