## 2 Simulation Methodology  
The analysis was carried out by simulation using Aspen Plus. Figure 1 depicts the flowsheet of the simulated plant (base scenario), including a pumping section to obtain supercritical pressure, a preheating step to reach the supercritical temperatures, a further preheating to the reaction temperature, the gasification in a tubular reactor, as well as the cooling and depressurization to reduce the temperature and pressure, respectively. Finally, separation processes are required to obtain clean syngas. In this plant, the hot effluent leaving the reactor (hot fluid) feeds a heat exchanger (preheater) to increase the temperature of the feed (cold fluid) after pressurizing from atmospheric to 250 bar. This configuration does not allow the energy self-sufficient process and external supply energy (heater) is required to achieve the inlet temperature to the reactor at the setting values in a range between 450 and 600 \({}^{\circ}\)C (imposed by the ICE and GT used). The specifications of the process units used in the simulation are shown in Table 2.  
In order to study SCWG plants at the industrial level, and based on the current SCWG plants' data reported and exposed in the previous section, this work will consider a model plant with a nominal treatment capacity of 1000 kg/h. Therefore, although the main interest of SCWG is the valorization of organic waste, the focus of this work is to analyze the feasibility of hybridizing an SCWG plant through combined power and heat technologies. In this sense, a well-known compound, such as glycerol, is used as a feedstock since numerous experimental tests have been carried out by different research groups and the published results are widely available in the literature [40; 41; 42]. To calculate the thermodynamic properties of compounds, the equation of state (EOS) used to obtain a better representation of changes in the supercritical region is the predictive Soave-Redlich-Kwong (PSRK) EOS, as reported in the literature [43]. Pump efficiencies are set at 80%. The preheater is designed as a countercurrent heat exchanger, having a minimum temperature difference between the hot and cold streams set in the range from 5 to 25 \({}^{\circ}\)C, depending on each case study's requirements. The gasification reactor is simulated considering chemical equilibrium based on the Gibbs free energy minimization model, with high isolation that guarantees no heat losses. This methodology is widely used as a powerful tool to solve chemical equilibrium when kinetic data are not available or reliable enough [44]. The final \begin{table}
\begin{tabular}{c c c} \hline
**Component Code** & **Equipment** & **Specifications** \\ \hline PUMP & Pump & Discharge pressure: 250 bar \\ PREHEAT & 2 stream countercurrent heat exchanger & Hot stream outlet temperature: \\  & & Minimum temperature approach: 10 \({}^{\circ}\)C \\ HEATER & Heater & Outlet temperature: 450–600 \({}^{\circ}\)C \\  & & Pressure: 250 bar \\  & & Heat Duty: 0 kW \\  & & Pressure: 250 bar \\ COOLER & Cooler & Outlet temperature: 50 \({}^{\circ}\)C \\  & & Pressure: 250 bar \\  & & Outlet pressure: 2 bar \\  & & Temperature: 30 \({}^{\circ}\)C \\ GL-SEP & Gas–liquid separator & Pressure: 2 bar \\ \hline \end{tabular}
\end{table} 
Table 2: Specifications of the process units used in the Aspen Plus simulation. Figure 1: Energy integration with hot effluent from the SCWG reactor (base scenario). Flowsheet of the simulated process in Aspen Plus. separation of the gas mixture is modeled by a flash separator. The pressure losses are low and have not been considered in the simulation. In order to make possible an objective comparison of the results obtained for the proposed case studies, the simulation of the plant configuration corresponding to each case study is carried out considering the common operating parameters shown in Table 3.  
The base scenario is representative of many SCWG plants that take advantage of the hot effluent leaving the reactor to preheat the feed stream.