Browsing by Author "Zhai, Rongrong"

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    Analysis of integration method in multi-heat-source power generation systems based on finite-time thermodynamics
    (Elsevier, 2020-06-12) Liu, Hongtao; Zhai, Rongrong; Patchigolla, Kumar; Turner, Peter J.; Yang, Yongping
    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
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    Annual performance analysis and optimization of a solar tower aided coal-fired power plant
    (Elsevier, 2019-01-10) Li, Chao; Zhai, Rongrong; Yang, Yongping; Patchigolla, Kumar; Oakey, John E.; Turner, Peter J.
    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 MWe 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.
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    Model predictive control of a combined solar tower and parabolic trough aided coal-fired power plant
    (Elsevier, 2021-04-23) Liu, Hongtao; Zhai, Rongrong; Patchigolla, Kumar; Turner, Peter J.; Yang, Yongping
    Investigating the potential to add solar tower and parabolic trough technology to aid coal-fired power generation could be a valuable intermediate step along the route to decarbonisation while making use of an existing assets, that would have a high efficiency and percentage contribution to utilise solar energy to reduce coal consumption. Based on the plant model of a typical 600MW coal-fired plant with the addition of tower and trough solar heat sources developed in Ebsilon Professional platform, the model predictive controller is developed in this study, incorporating the information of predictive weather data and real power load, to minimise accumulative coal consumption in a specific time horizon. Simulations on a typical day and a 10-day consecutive period are performed to observe the benefits and operation processes with a model predictive controller. Compared with a standard controller that doesn’t make use of future solar and load predictions, the typical day simulation shows, that the coal consumption reduction using a predictive control approach is increased by 21.3-tonne (13.6%), and 320.0-tonne (20.3%) in the 10 consecutive day simulation. The absolute difference of reduction tends to be most significant in high radiation conditions (day 2), which gave a 61.7-tonne (34.3%) saving. The improvement appears to be achieved by dispatching the thermal energy storage ability to store more energy and discharging thermal energy optimally. The benefits from this approach is insensitive to forecast error and shows sensitivity to system configurations, which tends to be greater with sufficient solar energy input but inadequate thermal storage capacity. While the general area of solar aided coal-fired plants have been investigated in various configurations by others, this paper is novel in that it examines the benefit of using future weather forecast data within a model predictive controller to significantly improve the potential solar contribution such a plant can use. As such it quantifies the potential improvements such an approach may achieve. In summary, the application in the solar tower and parabolic trough aided coal-fired power generation system improved the understanding of the benefits and the limitations in using the model predictive control in the operation process.
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    Off-design thermodynamic performances of a combined solar tower and parabolic trough aided coal-fired power plant
    (Elsevier, 2020-10-13) Liu, Hongtao; Zhai, Rongrong; Patchigolla, Kumar; Turner, Peter J.; Yang, Yongping
    The solar tower and parabolic trough aided coal-fired power generation has been demonstrated as a promising technology and has potential advantages in utilisation of solar energy in a cost-effective manner. Due to introduction of solar energy, from the solar tower or parabolic troughs, increases to a certain extent, the steam temperature would be difficult to maintain and leads to safety concerns. Therefore, the limitation of integrated solar energy, considering the overlapped influence of different solar energy input, needs to be well identified and managed. This work considered a 600 MWe integrated system as an example. Solar energy from parabolic troughs is used in the preheater while energy from the solar tower is used to reheat steam. The novelty of this study is the interaction of different solar energy input in fossil plants and its benefits is revealed for the first time. The maximum absorbed solar energy, considering the mutual effects of introduced solar energy flows, are explored. Then the system performance under three different loads (100%, 75%, 50%) and hourly operational performance in four typical days are analysed. The paper shows that the feed-water extraction results in the enhancement of maximum solar energy absorbed by reheat steam extraction, is improved by 24.2 MWth (28.5%), 11.5 MWth (20.0%), and 5.6 MWth (14.3%) as feed-water extraction percentages increase at the three load conditions. As a result, the minimum standard coal consumption rates are improved by 13.2 g/kWh (5.2%), 10.7 (4.1%) g/kWh and 9.0 g/kWh (3.1%) respectively. In four typical days, the highest coal consumption reduction is reached in the summer solstice, which is 266.6-tonne, 202.8-tonne and 131.4-tonne under three different loads, while the highest coal consumption is obtained in the winter solstice.
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    Off-design thermodynamic performances of a solar tower aided coal-fired power plant for different solar multiples with thermal energy storage
    (Elsevier, 2018-08-25) Li, Chao; Yang, Zhiping; Zhai, Rongrong; Yang, Yongping; Patchigolla, Kumar; Oakey, John E.
    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 MWe boiler can absorb at 100% load, 75% load and 50% load are 76.4 MWth, 54.2 MWth and 23.0 MWth, 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.
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    Performance analysis of a novel combined solar trough and tower aided coal-fired power generation system
    (Elsevier, 2020-04-15) Liu, Hongtao; Zhai, Rongrong; Patchigolla, Kumar; Turner, Peter J.; Yang, Yongping
    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 660MWe 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 MWth, 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.
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    Thermal performance of different integration schemes for a solar tower aided coal-fired power system
    (Elsevier, 2018-06-23) Li, Chao; Zhai, Rongrong; Yang, Yongping; Patchigolla, Kumar; Oakey, John E.
    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 MWe supercritical coal-fired power system is combined with 53 MWth 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.