## 4 Economic Evaluations
### Operating Costs  
The operating costs mainly consist of costs for materials and energy consumption, whereas the taxes are not included in this study. The total annual operating time is assumed to be 8000 h. Operating costs include the costs for bio-oil, hydrogen, and catalyst (the average cost of catalyst for the deep and mild stages). The cost of bio-oil is assumed to be the production cost of the pyrolysis process of biomass under ideal conditions [13]. The purchase price of hydrogen considered here is $1.50/gallon of gasoline equivalent (GGE) or nearly $1.50/kg [13]. Prices for the external steam supply to heat the HDO reactors and for cooling water are based on the Chinese industrial standard. The labor costs are estimated as 120 employees in total with an annual salary of $9000. The other costs include the general overheads and the plant maintenance which account for up to 2% of the fixed capital cost. The overall unit production costs of two scenarios are shown in Table 5[7; 9], which include the practical unit production and the ideal unit production costs. The ideal production assumes that the catalyst activity is not affected by catalyst coking, whereas the practical production takes in account the coking deactivation of the catalyst. By comparing the two cases, one can see that the costs for bio-oil, hydrogen, cooling water, and steam supply are virtually unchanged, because the increases in feed rates for those material and energy streams to maintain the same yield of desired product are not significant. However, the unit cost of the product increases by approximately 10%, because a higher feeding rate of fresh catalyst is required to balance the effect of catalyst coking deactivation. A sensitivity analysis of the influences on the production costs was performed for both the practical and ideal scenarios, and the resulting minimum and maximum production costs [13; 20] that reflect the impact of common variations of the key input parameters from the base case are shown in Figures 5 and 6 The costs of materials and utilities as well as the yield of final products are included. Bio-fuel yield has the strongest positive influence on the production cost; this implies that slight improvements in the overall performance of bio-oil upgrading process could reduce the cost of fuel significantly. In addition, the production costs are sensitive to the purchase price of raw bio-oil, as the cost for acquiring feedstock can vary widely between locations and throughout the year. Moreover, the influence of the catalyst is significant in the practical scenario but is negligible in the ideal case, which is due to the fact that the feeding rate of fresh catalyst in the latter is negligible in comparison with the former because no coking deactivation of the catalyst occurs. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Unit Costs (\$/t)** & **Practical Production Costs** & **Ideal Production Costs** \\  & & **(\$/t)** & **(\$/t)** \\ \hline Bio-oil & 188.55 [13] & 419.75 & 415.05 \\ Catalyst (Ni-based) & 34,444 [7] & 76.68 & 0.0032 \\ Hydrogen & 1500 [13] & 115.21 & 113.7 \\ Steam & 28.88 & 346.21 & 344.58 \\ Cooling water & 0.46 & 0.063 & 0.062 \\ Labor costs & & 28.88 & 28.88 \\ Fixed costs & & 21.13 & 21.13 \\ Other costs & & 16.36 & 16.36 \\ Total & & 1024.27 & 939.76 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Estimation of raw material costs for the two cases [7; 9]. The comparison of production costs estimated in this study with different research studies [7; 13] and of average gasoline prices throughout 2018 is shown in Figure 7. Both practical and ideal (where no catalyst coking occurs) production costs estimated in this study are higher than the results from other research studies. The reason for this is that only the hydrogenation process of bio-oil has been considered in this study, whereas both processes of pyrolysis and hydrogenation were included in [PERSON] et al. [13] and [PERSON] et al. [7].