Search

Renewable energy is a key solution in maintaining global warming below 2 °C. However, its intermittency necessitates the need for energy conversion technologies to meet demand when there are insufficient renewable energy resources. This study aims to tackle these challenges by thermo-electrochemical modelling and simulation of a reversible solid oxide fuel cell (RSOFC) and integration with the Haber Bosch process. The novelty of the proposed system is usage of nitrogen-rich fuel electrode exhaust gas for ammonia synthesis during fuel cell mode, which is usually combusted to prevent release of highly flammable hydrogen into the environment. RSOFC round-trip efficiencies of 41–53% have been attained when producing excess ammonia (144 kg NH 3 /hr) for the market and in-house consumption respectively. The designed system has the lowest reported ammonia electricity consumption of 6.4–8.21 kWh/kg NH 3 , power-to-hydrogen, power-to-ammonia, and power-generation efficiencies of 80%, 55–71% and, 64–66%. [Display omitted] • P2A to power system enhances renewable energy usage by solving intermittency issues. • Optimum P2A to power system design and operating parameters determined. • Argon-free nitrogen resulting to non-limiting Haber Bosch recycle-loop fraction. • Novel system has lowest reported ammonia synthesis electricity consumption. • High power-to-ammonia efficiency attained, and excess ammonia available for market. [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]

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]