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• Integration of four novel sCO 2 cycles with coal-fired power plant. • Efficiency of sCO 2 cycle is higher than steam Rankine cycle by 3–4%pts. • sCO 2 cycles can reduce the cost of electricity by 6–8% than steam Rankine cycle. • Increasing turbine inlet temperature by 140 °C increases efficiency by 3–4%pts. • Increasing turbine inlet temperature doesn't show reduction in cost of electricity. Supercritical carbon dioxide (sCO 2) cycles can achieve higher efficiencies than an equivalent steam Rankine cycle at higher turbine inlet temperatures (>550 °C) with a compact footprint (tenfold). sCO 2 cycles are low-pressure ratio cycles (~4–7), therefore recuperation is necessary, which reduces the heat-addition temperature range. Integration of sCO 2 cycles with the boiler requires careful management of low-temperature heat to achieve higher plant efficiency. This study analyses four novel sCO 2 cycle configurations which capture the low-temperature heat in an efficient way and the performance is benchmarked against the state-of-the-art steam Rankine cycle. The process parameters (13–16 variables) of all the cycle configurations are optimised using a genetic algorithm for two different turbine inlet temperatures (620 °C and 760 °C) and their techno-economic performance are compared against the advanced ultra-supercritical steam Rankine cycle. A sCO 2 power cycle can achieve a higher efficiency than a steam Rankine cycle by about 3–4% points, which is correspond to a plant level efficiency of 2–3% points, leading to cost of electricity (COE) reduction. Although the cycle efficiency has increased when increasing turbine inlet temperature from 620 °C to 760 °C, the COE does not notably reduce owing to the increased capital cost. A detailed sensitivity study is performed for variations in compressor and turbine isentropic efficiency, pressure drop, recuperator approach temperature and capacity factor. The Monte-Carlo analysis shows that the COE can be reduced up to 6–8% compared to steam Rankine cycle, however, the uncertainty of the sCO 2 cycle cost functions can diminish this to 0–3% at 95% percentile cumulative probability. [ABSTRACT FROM AUTHOR]

• A general integration method of multi-heat-source systems is proposed. • The external and internal irreversibility due to finite-time was considered. • The distribution diagram of the optimum thermodynamic structure was drawn. • Four coupled systems were applied to determine the optimum integration position. Multi-heat-source power generation system is a promising technology to reduce fossil fuel consumption and save investment costs by integrating several heat sources and sharing power equipment components. Researchers have conducted many case studies based on specific power plants to find the preferred integration scheme. However, there is still no unified theory to guide the integration of different energy sources. To explore a common method to integrate various energy sources, this work developed a general multi-heat-source integrated system model based on finite-time thermodynamics, considering the external and internal irreversibility due to the constraint of finite-time and finite-size. The generalised expressions for optimum integration method are explored and expressed in dimensionless parameters. This study indicated the system with two heat-sources performs differently in four regions due to the variation of endothermic temperatures. The characteristics of energy flow and irreversibility reveal that by adding a second heat-source, the first heat-source energy can be substantially reduced at the cost of system efficiency slightly decreasing. Then four application cases for solar-aided coal-fired power plants are conducted to check its feasibility and potential to provide the performance bound of integrating multi-heat-sources. [ABSTRACT FROM AUTHOR]

Solar-aided coal-fired power generation systems have been extensively studied and exhibit several advantages in the utilisation of solar energy. The issue with the solar augmentation of coal-fired plants is the limitation of the potential solar contribution that is practical to achieve when considering boiler safety issues. This study proposes the combination of parabolic troughs and solar towers to collect solar energy, that is then introduced into the preheaters and boilers of coal-fired power plants. Under the same investment conditions, this combination of solar technologies can provide more solar exergy and reduce the practical constraints on the solar contribution. The paper shows that the potential for a 660MW e power plant, integrated with a combined solar field allows the highest solar exergy share of 8.51% to be reached. This enables an increased fuel saving of at least 1.58 and 4.24 g/kWh compared to other systems, that gives a minimum coal consumption of 253.17 and 255.83 g/kWh, respectively. The combined solar field provides a maximum available solar exergy of 69.43 MW th , which is 7.83%–11.88% higher than the alternative compared systems. The enhanced solar exergy contribution and cost-effectiveness can be observed in this novel system under different solar loads and cost conditions. • Original combined solar trough and tower aided coal-fired power is proposed. • Solar exergy share increased by 0.57–1.65% under the same investment condition. • In proposed system, minimum 1.58–4.24 g/kWh coal fuel can be further saved. • Optimum configuration of solar field for better cost-effectiveness is explored. [ABSTRACT FROM AUTHOR]

Highlights • Solar aided coal-fired power system is simulated for typical meteorological year. • Annual efficiency and levelized cost of electricity are characterized. • Annual coal consumption reduced over 14,000 tons for a 600 MW e power system. • Thermal storage capacity is optimized to achieve lowest cost of electricity. Abstract The integration of solar energy into coal-fired power plants has been proven as a potential approach in the utilization of solar energy to reduce coal consumption. Moreover, solar augmentation offers low cost and low risk alternatives to stand-alone solar thermal power plants. In this study, the annual performance of a solar tower aided coal-fired power (STACP) system is investigated, and the influence of thermal storage system capacity on the annual solar generating power and annual solar-to-electricity efficiency is explored. The thermal storage system capacity is optimized to obtain the lowest levelized cost of electricity (LCOE). At the same time, the influence and sensitivity of several important economic factors are explored and assessed. Results demonstrate that compared to a coal-fired power system, the reduction in the annual average coal consumption rate of the STACP system with high direct normal irradiance (DNI), medium DNI, and low DNI are 5.79, 4.52, and 3.22 g/kWh, respectively. At a minimum, the annual coal consumption can be reduced by 14,000 t in a 600 MW e power generation unit. Because the same solar field is considered under different DNI conditions, the LCOE in the high DNI, medium DNI, and low DNI scenarios are all fairly similar (6.37, 6.40, and 6.41 ¢/kWh, respectively). When the solar multiple is 3.0, the optimal thermal storage capacity of the STACP system, with high, medium, and low DNIs are 6.73, 4.42, and 2.21 h, respectively. The sensitivity analysis shows that the change in economic parameters exerts more influence on the STACP system with the high DNI compared with the other two scenarios. [ABSTRACT FROM AUTHOR]

Abstract Solar aided coal-fired power system has been proven to be a promising way to utilise solar energy in large scale. In this paper, the performances of the solar tower aided coal-fired power (STACP) system at 100% load, 75% load, and 50% load for different days are investigated and the maximum solar power that the boiler can absorb under different plant loads are explored. Then, the effects of solar multiple (SM) and the thermal energy storage (TES) hour on the daily performance of STACP system are investigated. Results show that the maximum solar power that a 600 MW e boiler can absorb at 100% load, 75% load and 50% load are 76.4 MW th , 54.2 MW th and 23.0 MW th , respectively. Due to the augmented energy from the solar field, the maximum standard coal consumption rate is reduced by 13.53 g/kWh, 12.81 g/kWh and 8.22 g/kWh at 100% load, 75% load and 50% load, respectively. With an increase of solar power input, the boiler efficiency, overall system efficiency and solar thermal-to-electricity efficiency show a downward trend. In addition, the daily coal consumption of summer solstice is the lowest while the winter solstice is the highest for a particular SM and TES hour. Highlights • Performances of STACP system are investigated at different loads with different solar shares. • The maximum solar energy that the boiler can absorb is determined. • Performances of STACP system are investigated at different weather conditions. • Daily performance of STACP system are explored with different SM and TES hours. [ABSTRACT FROM AUTHOR]

A Solar Tower Aided Coal-fired Power (STACP) system utilizes a solar tower coupled to a conventional coal-fired power system to reduce pollutants, greenhouse gas emissions and the investment of solar energy facilities. This paper examines three different schemes for integrating solar energy into a conventional boiler. For each scheme, an energy and exergy analysis of a 600 MW e supercritical coal-fired power system is combined with 53 MW th of solar energy in both a fuel saving mode and a power boosting mode. The results show that, for all these integration schemes, the boiler’s efficiency and system’s efficiency are reduced. However, the standard coal consumption rate is lower in comparison to conventional power plants and the standard coal consumption rate in the fuel saving mode is lower than that in the power boosting mode for all three schemes. Comprehensively considering both the standard coal consumption rate and efficiency, the scheme that uses solar energy to heat superheat steam and subcooled feed-water is the best integration option. Compared with a coal-fired only system, the saved standard coal consumption rate of the above mentioned scheme in fuel saving mode and power boosting mode can reach up to 11.15 g/kWh and 11.11 g/kWh, respectively. Exergy analysis shows, for STACP system, exergy losses of boiler and solar field contribute over 88% of whole system’s exergy loss. [ABSTRACT FROM AUTHOR]

Pollutant emissions from coal-fired power system have been receiving increasing attention over the past few years. Integration of solar thermal energy can greatly reduce pollutant emissions from these power stations. The performances of coal-fired power system (S1), solar aided coal-fired power system with thermal storage (S2), and solar aided coal-fired power system without thermal storage (S3) with three capacities of each kind of system (i.e., nine subsystems) were analyzed over the entire life span. The pollutant emissions and primary energy consumptions (PECs) of S1, S2, and S3 were estimated using life cycle assessment (LCA). The evaluation value of global warming potential (GWP), acidification potential (AP), respiratory effects potential (REP) and PEC were obtained based on the LCA results. Furthermore, the system investments were estimated, and grey relation theory was used to evaluate the performance of the three types of systems comprehensively. Finally, in order to find the effect of some main factors on the solar aided coal-fired power system (SACFPS), uncertainty analysis has been carried out. The LCA results show that the pollutant emissions and PEC mainly take place in the fuel processing and operation stages for all three system types, and S2 performs the best among the three systems based on the grey relation analysis results. And the uncertainty analysis shows that with longer life span, the power system have better performance; with higher coal price, the power system will have worse performance; with lower solar collector field cost, the solar aided coal-fired power system will be more profitable than the base-case coal-fired power system. [ABSTRACT FROM AUTHOR]