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Supercritical water can cleanly and efficiently convert coal into hydrogen-rich syngas. The supercritical water coal gasification (SCWG) technology is compared with O2-H2O coal gasification technology from the aspects of cold gas efficiency (CGE) and exergy efficiency (EE). The graphical exergy analyses (EUD methodology) were adopted to the key processes or units in the gasification technologies. The results showed that when the coal-water-slurry concentration (CWSC) is higher, the CGE and EE of the SCWG technology are higher than that of the O2-H2O coal gasification technology. The origins of the exergy destructions in the gasification technologies were analyzed. The heating of water lead to the maximum exergy destructions in the gasification technologies, which account for approximately 40.21% and 53.57% of the total exergy destruction in the gasifier.

A novel power generation system with integrated supercritical water gasification (SCWG) of coal is proposed in this article. The gasification product directly enters the supercritical turbine to generate electricity. After pressure relief, the syngas separated from the unreacted water is transferred to the combined cycle. The influences of coal-water-slurry concentration (CWSC) and the outlet pressure (Ph) of the supercritical turbine on the system performances are studied. The results show that the thermal efficiency increases with increasing CWSC or decreasing Ph. The ultimate thermal efficiency of the system can be obtained when the CWSC is 25 wt% and Ph is 1 bar, which can approach 54.68%. The thermal efficiency of the novel system is higher than that of the power generation system with integrated SCWG of coal and parallel chemical heat recovery.

Supercritical water gasification (SCWG) is a promising technology for clean and efficient coal utilization. The exergy analyses on the processes with integrated SCWG of coal and syngas separation are conducted for clear understanding about the exergy distributions in the processes. The energy level of the heat provided for the gasifier is upgraded to the energy level of the syngas, which is driven by the decrease of energy levels from the coal to the syngas. The minimum temperatures of the heat provided for the gasifier are obtained in different coal-water-slurry concentrations (CWSCs). The total exergy destruction firstly increases, and then decreases with increasing CWSC. The maximum total exergy destruction of the process is obtained when the CWSC is approximately 10%. The exergy efficiency of the process has a converse trend with the total exergy destruction. When the CWSC is in the range of 6% and 20%, the maximum exergy efficiency is 89.18%. The origins for the production of the exergy destruction are also studied.

Supercritical water gasification (SCWG) is a promising clean coal technology. A new power generation system with integrated supercritical water gasification of coal andCO2 capture is proposed in this article. The gasification product consisted of H2, CO, CO2, CH4, and unreacted supercritical water is directly combusted with pure O2to provide heat for other units of the system, and the combustion product is used for power generation in turbines. The combustion product consists only of CO2 and H2O. Thus, the CO2 can be easily captured under atmospheric condition. The thermal efficiency of the system can reach 38.31%, while the CO2 capture rate is 100%. The energy and exergic balances are conducted. The exergy efficiency of the system is 38.56%. The system has advantages over most coal-fired power plants with oxy-combustion or post-combustion technologies and IGCC systems with pre-combustion technologies.

Supercritical water gasification (SCWG) of coal is a promising clean coal technology. Supercritical water can effectively and cleanly convert coal to hydrogen-rich syngas. Three power generation models integrated SCWG of coal are proposed and compared in this article. The gasification products have a large amount of sensible heat. Efficient use of the sensible heat can improve the model performance. Compared to the models with total and without chemical heat recovery, the model with partial chemical heat recovery has the advantages of much less exhausted energy and relative small amount of fuel coal used to heat the water to the supercritical state. The efficiency of the model with partial chemical heat recovery is higher than that of other models, and increases with increasing coal-water slurry concentration (CWSC). The efficiencies of the models with partial chemical heat recovery, without chemical heat recovery, and with total chemical heat recovery are 46.60%, 37.56%, and 42.17% when CWSC is 11.3%, respectively. The thermal efficiency of the PCHR model is higher than most conventional coal-fired power plants and coal-based IGCC projects.

Solar hybrid coal-fired power plant can use solar heat with temperature lower than 300 °C to generate power efficiently by replacing the bled-off steam from a steam turbine to heat the feed water. In this paper, a model of the solar field and power block has been developed to investigate the thermodynamic and economic performances of a solar hybrid coal-fired power plant under a variety of operating conditions and structure layouts. The effects of the key operating parameters on the performances of the solar hybrid coal-fired power plant are numerically investigated. A technical and economical optimization of the solar multiple has been presented. Furthermore, the annual solar-to-electric efficiency, annual solar power output and levelized cost of electricity of the solar hybrid coal-fired power plant are also analyzed. It is found that the efficiencies in the region of 13–20% can be achieved, and this for levelized cost of electricity in the region of 0.7–1.1 ¥ /kW h e , depending on the solar multiple and substituting method.

The methods of utilizing coal for power generation include direct combustion in air integrated with a steam cycle and gasification with O2/air integrated with a combined cycle. Special equipment is needed for the removal of NOx, SOx, CO2, and PM2.5, and the cost is high. The technology needed to perform supercritical water gasification (SCWG) can efficiently convert coal to a clean gaseous product. A novel model integrating SCWG with power cycles and heat recovery for power generation is proposed. The gasification product has a large amount of sensible and latent heat. The heat in the high temperature range is used to produce high-temperature and -pressure steam for power generation, whereas the heat in the low temperature range is recovered to preheat water before being heated to the supercritical state. The temperature that separates the high temperature range and low temperature range is the characteristic parameter T. The influences of T, which represents the extent of heat recovery, and the coal–water slurry concentration (CWSC) on the model performance are studied. The efficiency curves have a maximum value when T equals approximately 250 °C in all CWSCs. The model efficiency increases with increasing CWSC at a certain T. The model efficiency can reach 42.18% when CWSC = 11.3% and T = 250 °C.

S–CO2 (Supercritical-CO2) coal-fired power plant is a promising technology for efficient and clean utilization of coal for power generation. The conversion and transfer of the energy and exergy in the power plants with double-reheat and single-reheat processes are studied. With the main gas parameters of 32 MPa/893.15 K, the power generation efficiencies of the S–CO2 coal-fired power plant with double-reheat and single-reheat processes are 49.06% and 48.72%, respectively. The corresponding exergy efficiencies are 48.02% and 47.69%, respectively. The origins of exergy destructions in different units are studied using the Energy Utilization Diagram (EUD) method. The exergy distributions of the power plants are presented. For the power plant with double-reheat process, the work output, the exergy exhaust into the atmosphere, the exergy destruction in combustion process, the exergy destruction in heat transfer processes, the exergy destruction caused by pressure loss, and the exergy destructions in turbo systems account for 48.02%, 9.66%, 20.45%, 17.56%, 1.08%, and 3.23% of the total exergy input of the power plant, respectively.

S–CO2 (Supercritical-CO2) coal-fired power plant is a promising technology for efficient and clean utilization of coal for power generation. The comparative study between the S–CO2 coal-fired power plant and the power plant with steam Rankine cycle from aspects of energy and exergy balances is conducted. The conversion and transfer of the energy and exergy in the power plants are revealed. With the main gas parameters of 32MPa/620 °C and double-reheat process, the power generation efficiencies of the S–CO2 coal-fired power plant and the power plant with steam Rankine cycle are 49.06% and 48.12%, respectively. The corresponding exergy efficiencies are 48.02% and 47.10%, respectively. The energy-saving mechanism of the S–CO2 coal-fired power plant is revealed: the smaller boiler efficiency and larger exergy efficiency of the boiler system in the S–CO2 coal-fired power plant make the energy level of the energy being transferred to the S–CO2 cycle is higher than that of the energy being transported to the Rankine cycle. The CO2 absorbs the high-level energy and produces more mechanical power through the S–CO2 cycle to obtain higher power efficiency.