Browsing by Author "Liu, Hongtao"

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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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    Dynamic evolution of humic acids during anaerobic digestion: exploring an effective auxiliary agent for heavy metal remediation
    (Elsevier, 2020-10-28) Wang, Xiqing; Lyu, Tao; Dong, Renjie; Liu, Hongtao; Wu, Shubiao
    Information on the dynamic evolution of humic acid (HA) from anaerobic digestate and the potential of HA serving as an effective agent for remedying heavy metals is rather scarce. This study monitored the evolution of the structure and functional groups and metal-binding abilities of HA during chicken manure and corn stover anaerobic digestion (AD) processes. Higher increases in aromatic (41-66%) and oxygen-containing functional groups (37-45%) were observed in HA from the AD of corn stover, resulting in higher metal-binding abilities for Cu(II), Co(II), and Ni(II) than those of chicken manure AD. Moreover, HA extracted from fast (before day 12 for chicken manure and day 16 for corn stover), and slow (day 40) methane production stages performed different complexation capacities for the heavy metals. These results reveal the mechanisms of HA and heavy metal interactions, and confirm the potential of HA extracted from AD process for the remediation of heavy metals.
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    Mechanisms of genuine humic acid evolution and its dynamic interaction with methane production in anaerobic digestion processes
    (Elsevier, 2020-10-14) Wang, Xiqing; Muhmood, Atif; Lyu, Tao; Dong, Renjie; Liu, Hongtao; Wu, Shubiao
    Humic acid (HA), a byproduct formed during the biological conversion of organic matter into biogas in the anaerobic digestion (AD) process, contains complex structures and redox functions. However, the evolution mechanism of HA and its interaction with CH4 production during the AD process have not been fully explored, particularly with respect to various substrates and temperature conditions. In this study, we investigated the evolutionary dynamics of the structure and function of genuine HA that naturally formed in the AD processes of chicken manure and corn stover under mesophilic (37 °C) and thermophilic (55 °C) conditions. The results demonstrated that the HA evolution mechanisms in AD of chicken manure and corn stover have different pathways. The AD of core stover showed higher degree of aromaticity (41.2–66.7% and 45.3–68.4% for mesophilic and thermophilic respectively) and humification index (1.5–4.2 and 2.8–4.5 for mesophilic and thermophilic respectively) than those (28.3–45.3% and 30.2–54.5% of aromaticity and 0.6–1.2 and 1.3–3.7 of humification index) in AD of chicken manure. The results from HSQC NMR spectroscopy and 2D-COS-FTIR spectroscopy demonstrated an accelerating effect of the higher temperature on the evolution of HA through humification. Moreover, the concurrent decomposition and re-polymerization of HA during both AD processes, resulting in positive and negative effects on CH4 production in the fast and slow CH4 production stages, respectively. The dynamic interaction was due to variations in the electron transferring ability and structure of the formed HA. The results could not only advance our understanding of the mechanisms of HA evolution and its interaction with the performance of AD process, but also support further research toward improving AD performance by regulating HA formation and transformation.
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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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    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.