## 1 Introduction
Plant start-up prior to reaching steady-state operation is the step where a peak of energy should be supplied. Thus, energy recovery and heat integration in plants are key concepts that must be considered in the design and configuration steps of these plants. In this way, SKLMF researchers have analyzed different thermodynamic modeling at the simulation level to improve heat integration and power generation [25; 26]. Additionally, to improve the economic feasibility of SCWG technologies, different studies on energy supplies have been reported. One of the most important advances was developed by a team from SKLMF to produce hydrogen from biomass by using SCWG technology promoted by solar energy. First, different systems were constructed and tested at the laboratory scale for proof-of-concept tests, based on concentrated solar energy processes with dish and toroidal surface heliostats [27; 28]. Then, the first SCWG pilot plant based on solar energy was built [29; 30; 31] to analyze the possibilities of its commercialization. The KTH Royal Institute in Stockholm [32; 33] was working at the simulation level on \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Institution (Country)** & **Maximum Treatment** & **Limit of Operating** & **Reference** \\  & **Capacity (kg/h)** & **Conditions** & **1995** \\ \hline Verena. & & & \\ Forschungszentrum Karlsruhe (Germany) & 100.0 kg/h & 700 \({}^{\circ}\)C, 350 bar & [9; 10; 11] \\ Pacific Northwest National Laboratory & 38.0 L/h & 350 \({}^{\circ}\)C, 210 bar & [12] \\ State Key Laboratory of Multiphase Flow & & & \\ in Power Engineering (SKLMF) (China) & 19.2 kg/h & 650 \({}^{\circ}\)C, 300 bar & [13; 14; 15; 16; 17; 18] \\ University of Twente (The Netherlands) & 30.0 kg/h & 650 \({}^{\circ}\)C, 300 bar & [19] \\ Hiroshima University and Chugoku & 41.7 kg/h & 590 \({}^{\circ}\)C, 235 bar & [20; 21] \\ Electric Power (Japan) & & & \\ TU Delft/Gensos (The Netherlands) & 50.0 kg/h & 600 \({}^{\circ}\)C, 240 bar & [22] \\ Paul Scherrer Institute PSI (Switzerland) & 100.0 kg/h & 400 \({}^{\circ}\)C, 300 bar & [23] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: SCWG facilities at pilot and semi-pilot level. integrating the gasification technology (under non-supercritical conditions, to ensure the procurement of high conversion efficiency) with the supercritical water technology (to produce a clean syngas with low content of contaminants, such as tars, sour gas, and alkali compounds, necessary to feed the fuel cell). The product gas is routed to subsequent processes, including SOFC. [PERSON] et al., from Queensland University, carried out a study considering different possibilities of energy integration and process-energy configuration to increase the economic viability of the process. To do that, several alternative technologies, such as solar thermal technology (solar thermal and parabolic trough collector), natural gas combustion, and electrical energy, were analyzed [34]. [PERSON] et al., from the Australian National University, also integrated the concentrated solar thermal technology to drive SCWG plants and its combination with the Fischer-Tropsch process [35; 36]. At the same time, alternative ways were followed to try to move forward in the feasibility of SCWG by integrating it with other technologies, such as supercritical water oxidation (SCWO), hydrothermal liquefaction (HTL), or anaerobic digestion (AD), to improve, especially, the energy term. [PERSON] et al. [37] developed a combined SCWG-SCWO system based on a cool-wall reactor. From the treatment of the sewage sludge, syngas was obtained from SCWG, while SCWO operated with the residual organic liquid to produce a harmless product and release heat. [PERSON] et al. [38] worked on agricultural waste treatment (composed of buffalo sewage and maize silicate) by examining the potential of coupling SCWG and AD in a dual system. A liquid digestate fraction of AD is fed to the SCWG reactor to obtain biogas and value-added products, such as formic acid, xylitol, etc. [PERSON] et al.