• Energy Research

Abstract Solar aided power generation technology has been proved to be one of the most efficient ways to integrate solar energy into a coal-fired power plant. In a typical plant, the solar field size is normally designed with a solar multiple greater than one. Therefore, sometimes collected solar heat becomes surplus when the collected solar heat exceeds the heat demand. Other than being dumped, the surplus solar heat could be either charged into a thermal energy storage system if there is one; or used to preheat (feedwater) continuously. In this paper, the impacts of these two measures (being charged and preheating continuously) on the technical and economic performances of the integrated plant are analyzed in detail by undertaking a desktop case study. The results show that both measures could reduce the surplus solar heat dumped, but the economic performances vary. For the measure of preheating continuously, the maximum solar input is determined by a safety assessment to ensure a stable and safe operation. Surplus heat over this maximum amount has to be dumped. The results also show that for the plant located in Tibet China, both measures could reduce the levelized cost of energy and enhance the effective solar-to-electricity efficiency, compared to dumping case; while continuing preheating measure is superior to being charged technically and economically.

Abstract Increasing energy demands and oil price volatility have made oil shale attracted more and more attention. However, the shale oil recovery requires huge thermal energy and brings serious environmental problems, such as air pollution. In this paper, to reduce fossil fuel consumption, solar energy, a renewable energy, is introduced. The heat demand and the production yield of the shale oil recovery are obtained through the transients models developed in this paper. Then, three possible energy supply options for the shale oil recovery, i.e. natural gas, the solar thermal energy and the combination of these two, are analyzed and optimized in terms of the net present value and the return on investment over lifetime. The results show that for the shale oil recovery, Option 3, solar energy and gas boiler back up, is the optimal one, which has a return on investment value of 3.12 and can generate $ 72.4 M net present value more return than the Option 1, which uses natural gas only in the project lifetime.

Abstract Solar aided (coal-fired) power generation (SAPG) technology has been approved to be an efficient way to use solar energy for power generation. However, most solar-rich areas are often short of cooling water supply, especially in China. The air-cooled condenser could alleviate this issue effectively for power plants in these areas. In this paper, a solar aided power generation with direct air-cool condenser (SAPG + ACC) plant is studied and optimized to maximize its performance. Due to the addition of solar heat in an SAPG plant, the exhaust steam flow rate leaving the turbine changes, especially in power-boost mode, which affects the turbine exit pressure and deviates the condenser from its designed operating condition. To achieve maximum net power output, the correlation among the optimum (turbine) exit pressure (OEP), the solar heat input and the ambient temperature, is obtained in this study. The annual plant's performances with four proposed operating strategies of the air-cooled condenser are compared and analyzed. The results show that for an SAPG + ACC plant, the operating Strategy.3, i.e. operated with the hourly OEP is the optimal one, resulting the plant has annual solar-to-electricity efficiency (SEE) of 17.82% and its levelized cost of electricity (LCOE) is of 0.09 $/kWh.

Abstract Solar Aided Power Generation (SAPG) technology has been proved to be one of the most efficient ways to integrate solar energy into a coal-fired power plant. However, previous studies on SAPG systems have mainly focused on their design and design optimization. There are few studies on their operation. In an SAPG plant, solar heat is used to replace the extracted steam to preheat feedwater. However, the introduction of solar energy inevitably affects the steam flow rate through the boiler, especially when the SAPG plant is in fuel-saving operation mode, thus affecting the boiler's operation. Namely, the steam parameters at the boiler outlets would change with various solar inputs if no control mechanism were applied. A mechanism for adjusting the burners' tilt and attemperation flows in the boiler is therefore proposed in this study, in order to stabilize the temperature of the steam at the outlet of the boiler. To simulate the effectiveness of the mechanism, a transient model of the SAPG plant, including a series of modules for key components in the plant, has been developed in this study. The simulation results in a case study of a 300 MWe SAPG plant, showing the proportion of heat that was absorbed in the boiler was redistributed due to the solar input, without adjusting the burners' tilt and attemperation flows, resulting in temperature drops of superheated/reheated steam when in a fuel-saving mode. However, the simulation in the case study also shows that by swinging the burner tilt angle up to 22.7° and adjusting the attemperation flows in the super-heaters and re-heaters in the boiler, the superheated/reheated steam temperature can be restored from 523 °C and 510 °C respectively back to 543.0 °C, the desired temperature.

Abstract Integrated solar combined-cycle (ISCC) system has better thermal performance than the original gas steam combined-cycle system and a lower initial investment than stand-alone solar thermal plants. However, due to the uncertainty of meteorological conditions, the operation condition of the ISCC system changes continuously. In this study, a dynamic model of the ISCC system is built, and the operation strategies of two ISCC systems with and without the heat storage system are proposed. Accordingly, the dynamic performances of these two ISCC systems on a typical day are compared and analyzed, and the response characteristics of main operation parameters, such as main steam parameters and solar energy power generation, concerning direct normal irradiance (DNI) are obtained. The results show that the stability and security of the ISCC system with a heat storage system are superior to those without the heat storage system during the operation. To verify whether the operation strategy of the ISCC system with heat storage system is universally adaptable under different meteorological conditions, the dynamic performances of the ISCC system are further studied on a good-weather day with a strong DNI and a bad-weather day with weak DNI, respectively.

Abstract To guarantee the space heating in the heating season, conventional combined heat and power (CHP) plants operate in a heat-controlled operation mode, resulting in restricted peak-shaving ability (PSA). To improve the CHP plant’s PSA, a novel solar aided CHP (SA-CHP) system is proposed and simulated in this paper. In the new system, solar heat could be flexibly used to generate power or to supply heat according to the heating and power demands, thereby realizing the heat-power decoupling. A set of models for the SA-CHP system is developed and validated. The PSA, the standard coal consumption (SCC) and the techno-economic performances of a 330 MWe SA-CHP system are comprehensively analyzed in this paper. The results show that the SA-CHP system can significantly improve (up to double) the PSA compared with the CHP plant under the same rated heating power. The feasible operation region area of the SA-CHP system is 74.7% larger than that of the CHP plant. The annual SCC of the SA-CHP system are 17378.23 t less than that of the CHP plant. The net annual revenue of the SA-CHP system is $2.24 M. Besides, techno-economic performances of SA-CHP systems with two different heat storage systems are compared.