## 5 Conclusions  
In this study, a process simulation and a cost analysis were carried out for a bio-oil hydrogenation demonstrating plant with an annual throughput of 107 thousand tons of raw bio-oil. The following conclusions were drawn from this study. 1. A process model was developed using Aspen Plus to simulate the bio-oil HDO production process, material and energy balances throughout the plant were carried out, and deactivation of the catalysts due to coking in the mild HDO stage was embedded into the process model using a FORTRAN subroutine. The developed process model was capable of simulating the HDO process with extended ranges of feedstock properties and different reaction kinetics. From the simulation results, the yield of simulated bio-fuel varied between 44.1% and 45% across the selected temperature range of mild HDO reaction (250 \({}^{\circ}\)C-300 \({}^{\circ}\)C), whereas the optimal reaction temperature for the mild hydrogenation stage was found to be 280 \({}^{\circ}\)C, making this trend optimal for industrial design. 2. The simulation results showed that the catalyst deactivation due to coking could decrease the yield of the desired product, and that a larger feedstock flow for maintaining the productivity was required to compensate for the effect of coking deactivation. All these results showed that the catalyst deactivation affected the performance in the practical production process. Thus, the main reason for the catalyst deactivation was the presence of insoluble coke deposits, which affected the hydrogenation reaction in the mild stage, making it one of the decisive factors of the whole process. 3. A cost analysis of the bio-oil HDO production was performed and the minimum required costs were estimated. The total fixed capital cost for the demonstration plant with an annual throughput of 107 thousand tons of raw bio-oil was estimated at $15.2 million. The required variable costs for the unit product in the ideal case was found to be $939.76; where the unit production cost for the practical case, which included the catalyst deactivation, was found to be $1024.27/ton. The additional $76.68/ton came mainly from the expenditures related to the extra catalyst. A sensitivity analysis of the key process variables showed that the bio-fuel yield has the most impact on the unit production cost. Variations of \(\pm\)5% in the bio-fuel yield resulted in production costs rising from 0.92 to 1.2 thousand/ton for the practical scenario. The industrial production of upgraded bio-fuel from the two-stage hydrogenation of bio-oil is economically feasible as the operating costs are $168/ton which is lower than the average gasoline price in 2018. Figure 7: Comparison of simulated production cost and the average cost of Chinese gasoline in 2018 [7; 13]. **Author Contributions:** Conceptualization, Q.X. ; Data curation, X.M. ; Formal analysis, X.M. ; Investigation, X.M. ; Methodology, X.M. ; Software, X.M. and Q.X. ; Supervision, R.Z. ; Validation, Q.X. ; Writing--original draft, X.M. ; Writing--review and editing, S.P. and Q.X. **Funding:** This research was partially funded by National Key Research and Development Program of China, grant number 2017 YFC0212400. **Acknowledgments:** The authors wish to thank the three anonymous reviewers and the editor for their constructive suggestions for improving the manuscript. **Conflicts of Interest:** The authors declare no conflict of interest.