**4. Results and Discussion**

Tables 9–12 detail the economic assumptions used to build the pre-feasibility model of the proposed biorefinery concept. The assessment is based on the discounted cash flow from which the actual feasibility of the project can be inferred through the calculation of the net present value (NPV) of the project, as well as the internal rate of return (IRR) and the payback period (PP). These three economic parameters are common indicators in investment decisions. In particular, the NPV yields the current value of the investment project, as well as its profitability, by updating the entire cash flow of an investment to its present value using a proper discount rate based on macroeconomic conditions. For the NPV, it is stated that an investment should be accepted if the NPV >0 and rejected if the NPV <0. IRR is obtained by calculating the discount rate that produces an NPV equal to zero, whereas the payback is defined as the minimum period (in years) needed to recover the initial capital investments made, i.e., the year in which the cumulative cash flows become positive.

**Table 9.** Initial investment for the proposed multi-product biorefinery.





**Table 11.** Costs associated with maintenance, operation, and feedstock.

**Table 12.** Revenues associated with the proposed biorefinery concept.


The first steps in the analysis comprised the estimation of benefits and costs for each process stage to determine overall cash inflows and outflows. The cash flows considered were the initial investment, operation, and maintenance costs and revenues from sales of electric energy (considering self-consumption), thermal energy, biomethane for mobility, and EOs. All cash flows, except for the initial investment that occurs only in the startup phase of the project, extend over the 10 years of the project's life, with all costs and revenues updated for the corresponding year. The total annual cash flow is the sum of all costs and revenues for each year. The annual revenue is given by multiplying the annual electricity production by the electricity price and the corresponding savings in the purchase of electricity due to self-consumption, sales of thermal energy, sales of vehicular biomethane, and sales of EOs. Lastly, the cumulative NPV is determined to give the present value of negative and positive investment cash flows. All analyses were performed at current prices, revenues, and value-added tax rates. The inflation rates implemented for 2021 and 2022 are based on Bank of Portugal forecasts and did not consider the current inflation rate due to adverse economic conditions arising from the war in Ukraine and post-COVID constraints.

Figure 2 presents the cumulative cash flows associated with the project in current prices. The calculation of economic parameters was carried out using the discounted cash inflows and outflows estimated in the figure, comparing economic costs and benefits over the project lifetime using a discount rate of 5.75%.

**Figure 2.** Cumulative cash flows for the multi-product biorefinery concept in current prices. **Figure 2.** Cumulative cash flows for the multi-product biorefinery concept in current prices.

The proposed multi-product biorefinery presents an NPV of EUR 4342.6, an IRR of 18.1%, and a PB of 6 years. These results show that the project has a good chance of delivering positive economic benefits in the conditions studied. However, the analysis should go beyond the specific numbers, and the economic attractiveness of the project should be assessed using similar projects as baseline scenarios. In this case, direct comparison with other literature studies on EO extraction is difficult due to the novelty of the multi-product biorefinery presented here. The proposed multi-product biorefinery presents an NPV of EUR 4342.6, an IRR of 18.1%, and a PB of 6 years. These results show that the project has a good chance of delivering positive economic benefits in the conditions studied. However, the analysis should go beyond the specific numbers, and the economic attractiveness of the project should be assessed using similar projects as baseline scenarios. In this case, direct comparison with other literature studies on EO extraction is difficult due to the novelty of the multi-product biorefinery presented here.

From an investor's point of view, a more general financial benchmark for biomass projects can be used for comparison: projects with NPVs higher than zero, IRRs greater than 10%, and PBs less than 10 years should advance from the pre-feasibility stage and assessment towards an investment decision should continue. Given these premises, it can be concluded that the pre-feasibility study of the biorefinery concept proposed in this work is promising in terms of its economic viability. Future studies may consider performing a comprehensive cost and benefit analysis and an overall assessment of the strategic, economic, and financial cases for the multi-product biorefinery concept studied. This analysis may include detailed market research and technical analysis, sustainability assessment, and investment appraisal regarding the implementation of this and other innovative concepts to enhance the value of endogenous resources. From an investor's point of view, a more general financial benchmark for biomass projects can be used for comparison: projects with NPVs higher than zero, IRRs greater than 10%, and PBs less than 10 years should advance from the pre-feasibility stage and assessment towards an investment decision should continue. Given these premises, it can be concluded that the pre-feasibility study of the biorefinery concept proposed in this work is promising in terms of its economic viability. Future studies may consider performing a comprehensive cost and benefit analysis and an overall assessment of the strategic, economic, and financial cases for the multi-product biorefinery concept studied. This analysis may include detailed market research and technical analysis, sustainability assessment, and investment appraisal regarding the implementation of this and other innovative concepts to enhance the value of endogenous resources.
