## 7 Economic and Environmental Remarks  
A first approximation of the installation cost of a ORC group can be evaluated as the sum of turbine, pumps, exchangers and fluids costs. The costs of the heat transfer components have been obtained by means of Aspen Tasc(r):  
* Gas/oil heat exchanger 130,000 \(\mathbf{\dot{\epsilon}}\);
* evaporator 190,000 \(\mathbf{\dot{\epsilon}}\);
* regenerator 95,000 \(\mathbf{\dot{\epsilon}}\);
* condenser 100,000 \(\mathbf{\dot{\epsilon}}\).  
For the other components, the following economic estimates have been considered on the basis of information from manufacturers:  
* turbine 150,000 \(\mathbf{\dot{\epsilon}}\);
* electric generator 30,000 \(\mathbf{\dot{\epsilon}}\)
* toluene pump 20,000 \(\mathbf{\dot{\epsilon}}\);
* thermal oil pump 10,000 \(\mathbf{\dot{\epsilon}}\);
* toluene 30,000 \(\mathbf{\dot{\epsilon}}\);
* diathermic oil 15,000 \(\mathbf{\dot{\epsilon}}\);
* balance of the plant (piping, filters, valves, etc.) 115,500 \(\mathbf{\dot{\epsilon}}\).  
The expected total cost for the bottom regenerated cycle could be obtained adding to the sum of all these terms (\(\mathbf{\dot{\epsilon}}\)885,000) a mark-up of 20%, resulting in a total price of 1,062,600 \(\mathbf{\dot{\epsilon}}\).  
Taking into account the estimation of actual fuel saving for the typical operating year, a simple payback period of the investment equal to 4.9 years has been obtained, while considering a discount rate equal to 3% a dynamic payback period of the investment equal to 5.9 years has been obtained.  
The recovery of waste heat downstream of the propulsion engine by means of a bottom ORC has also a good cost/performance ratio, equal to 2214 \(\mathbf{\dot{\epsilon}}\)/kW.  
The adoption of an ORC group as a supplement of the propulsion system, allows saving large amounts of LNG fuel, implying a reduction in atmospheric emissions of pollutant agents, such as carbon dioxide and nitrogen oxides.  
To evaluate the quantity of CO\({}_{2}\) avoided, the specific average amount of CO\({}_{2}\) emitted by the Wartsila 6L50 DF engine, equal to 430 g/kWh, can be considered. By applying this value to the average power produced by the ORC, and on the basis of the hours of use per year of the propulsion system, 1380 ton/year of CO\({}_{2}\) non emitted into the atmosphere can be obtained.  
Not emitted into the atmosphere NOx tons can be derived in the same way. Starting from the engine average emission of 2.5 g/kWh, a total amount equal to 8.4 ton/year of avoided NOx emission has been obtained.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Load**} & \multicolumn{2}{c}{**Engine +**} & \multicolumn{3}{c}{**CONSUMPTIONS**} & \multirow{2}{*}{**Fuel Saved**} & \multirow{2}{*}{**Saving Per Year**} \\  & **ORC Power** & & & & & \\ \hline
**\%** & **kW** & **kJ/kWh** & **Nm3/h** & **Nm3/h** & **Nm3/h** & \(\mathbf{\dot{\epsilon}}\) \\ \hline
100 & 6180 & 7220 & 1143 & 1047 & 96 & 3216 \\
85 & 5325 & 7400 & 996 & 897 & 99 & 186,788 \\
75 & 4755 & 7420 & 881 & 782 & 99 & 11,017 \\
50 & 3190 & 7890 & 625 & 550 & 75 & 11,613 \\
25 & 1575 & 7900 & 313 & 280 & 33 & 1100 \\  & & & & & TOT & 213,733 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Annual savings of the naval ICE with the bottom ORC.