## 3 Results and Discussion
### Case Study A: Hybridization with an ICE (Internal Combustion Engine) Fed with External Fuel
For illustrating purposes, the evolution of the hot and cold fluids in the preheater is presented for a concentration of glycerol of 20 wt.% in the feed stream and a reactor inlet  
Figure 8: Second preheating with ICE exhaust gases. (**a**) Exchanged thermal power and (**b**) required exhaust gas flowrate from ICE versus the reactor inlet temperature in the range from 450 to 530 \({}^{\circ}\)C. Both figures are parametrized as functions of the glycerol mass concentration in the feed stream. temperature of 530 \({}^{\circ}\)C (the other conditions are the same as in Table 3). Figure 9 shows the IQ curves (temperature-thermal power) for the first preheater (fed with cooling water from ICE) and the second preheater (fed with exhaust gases from ICE), respectively. In the first preheater, the minimum pinch point temperature always occurs at the inlet hot stream and outlet cold stream because the available thermal power in the hot stream is much greater than that required in the cold stream. For the second preheater, the minimum pinch point temperature occurs at the inlet hot stream and outlet cold stream (heat exchanger inlet), although not always. In many cases, where thermal power exchange increases, the minimum pinch point temperature can move to the region where the cold fluid changes to a supercritical state (at an intermediate point from the heat exchange inlet) because of the sharp increase in the fluid heat capacity that flattens the slope of the cold fluid heating curve. However, this curve flattening makes possible a better adaptation of the cold stream curve to the hot stream curve, reducing the temperature difference between them and improving the thermal power exchanged and, thus, the energy efficiency through the heat exchanger. In conventional liquid-vapor heat exchangers, the differences between the cold and the hot curves are greater because the phase change occurs at a constant temperature, resulting in a lower thermal power exchange. Along with the thermal power exchanged to heat up the feed stream, ICE also supplies mechanical power to generate mechanical (electrical) energy using a fuel-air equivalence ratio equal to 1 for the combustion of natural gas [55] and an electrical generation yield (\(\eta_{\text{ICE}}\)) of 40% [55]. Figure 10a shows the generation of ICE electricity depending on the reactor inlet temperature demanded in the plant. In addition, the energy available in the hot effluent that leaves the reactor can be transformed into electricity by organic or vapor cycles. Considering a typical cycle yield of 12% [55] for the exchange of thermal power, Figure 10b illustrates the electricity generation under different operating conditions. It can be observed that the electricity generation is greater when the glycerol mass concentration is lower. In Figure 10a, this occurs because the exchanged thermal energy in the preheaters is higher when the glycerol concentrations are lower due to the higher heat capacity of the mixture previously explained. To cover this increase in the demanded energy, the required exhaust gas flowrate increases and, therefore, the external fuel fed to the ICE increases. Consequently, the generated electricity at a low glycerol mass concentration also increases. In Figure 10b, there are two opposite effects that affect the properties of effluent leaving the reactor before reaching the cycle. Taking as an example the case where the reactor inlet temperature is 530 \({}^{\circ}\)C, on the one hand, the effluent temperature is higher when the glycerol concentration increases, so the outlet temperature reactor is 536 \({}^{\circ}\)C at  
Figure 9: **(a)** IQ curve in the first preheater (fed with 10 m\({}^{3}\)/h of cooling water from ICE); **(b)** IQ curve in the second preheater (fed with exhaust gases from ICE). 10 wt.% glycerol, while this temperature increases to 609 \({}^{\circ}\)C at 30 wt.% glycerol.