| Due to the potential of continuous and stable power generation,solar thermal power generation is considered to be an important direction for large-scale utilization of renewable energy.However,the low annual power generation efficiency and high power generation cost are still the barriers of the development of solar thermal power generation.Integrating the solar energy and the fossil energy together,which improve the efficiency of solar power generation by fossil energy,is consider as an practical and effective of solar energy development.In addition,the process of solar concentrating and collecting is a key process for both the hybridization of solar and fossil energy and the solar thermal power generation.The high energy loss and low conversion efficiency of this process is the main problem of solar thermal energy utilization.Based on the National Natural Science Foundation of China(973 proj ect)and the important scientific and technological projects of the Chinese Academy of Sciences,this academic dissertation analyzed the evaluation method of multi-energy power generation system and the reduction of energy loss in the process of solar concentrating and conversion.Most studies of solar-aided coal-fired power generation system are focused on specific cases or unit.It should be pointed out that although operational characteristics have been acquired in various case studies,a unified theoretical guidance for design and evaluation between different schemes is yet hardly achievable,which is universally crucial for regulators,investors and designers because a reasonable and unified evaluation criterion is the basis for regulation establishment,investment appraisal and scheme design.In this paper,various specific integration schemes for SCPGS are reasonably classified and unified by theoretical modelling.The fundamental mechanisms of how the integration schemes affect the performance of SCPGS has been thoroughly revealed by discovering the "superposition effect" nd the "promotion effect".The comprehensive evaluation factor is proposed concerning both the coal-savability and efficiency-promotability of SCPGS.In addition,examples of application are given as the demonstration for the merits of comparisons between diverse SCPGSs under a common framework.Due to the fixed orientation,the energy loss of widely used single-axis tracking method of solar parabolic trough concentrator(PTC)is large and the efficiency is low.The double-axis sun-tracking,which could track the azimuth of the sun completely,is had to be applied due to the problems such as an excessively complicated mechanical structure.To solving this,a rotatable axis tracking method is proposed.The method can reduce the energy loss of the solar concentrating heat collecting process and improve the concentrating heat collecting efficiency.In addition,compared with the double-axis tracking,the proposed method has the potential for large-scale application due to less mechanical complexity.In this study,the physical model of the PTC with rotatable axis tracking is established.Based on the physical model,the operation regulation method of the PTC with rotatable axis tracking in the range of full latitude is obtained based on the theoretical solar irradiation conditions.In addition,under the actual irradiation conditions,the obtained trough solar operation regulation method was verified to prove its practical applicability.Based on the method of rotatable axis tracking of PTC and practical conditions,a 300 kWth parabolic trough collector experimental bench were designed and established.Based on the experimental bench,an experimental study was carried out on the energy loss reduction and the verification of rotatable axis tracking.The experimental results show that the rotatable axis tracking of PTC can improve the solar-thermal efficiency of the PTC by 10 percent points in winter,and annual efficiency by 5 percent points.An irreversible loss experimental study on the energy conversion of the PTC found that the concentrated exergy loss accounts for 70%of the total loss in winter,which is the main irreversible loss of PTC.And the rotatable axis tracking achieves efficiency improvement by reducing the loss of the concentrating process.At present,the optical performance of the PTC is difficult to directly measure in the field.In this study,a on-site test method for the optical performance of PTC is proposed.The method was applied to the 300 kWth parabolic trough collector experimental bench to verify the method and the optical efficiency of the bench was test as 70.77%.It shows that the optical performance of the parabolic trough collector experimental bench is good.The widely used north-south solar-tracking and the proposed rotatable-axis tracking methods are all tracking the sun completely.However,due to the intrinsically transient characteristics of solar radiation and the passively accompanying operation of traditional completely sun-tracking strategy,the occasion of excessive integrated solar thermal energy may lower the global performance or even shut the whole system due to safety.This phenomenon should be pay attention,especially for the solar-aided coal-fired power generation system,where is no thermal energy storage to serve as a thermal buffer.In this study,the active off-focus sun-tracking strategy is proposed to adjust the heat gain of PTC.Furthermore,by combining the rotatable axis sun tracking and the active off-focus sun-tracking strategy together,the active composite sun-tracking strategy is proposed.In this way,the heat gain of solar field is boosted and controllable at the same time.Based on the 300 kWth PTC experimental bench,the active composite sun-tracking strategy is experimentally verified by stabilizing the heat gain(relative deviation<2%)under DNI fluctuation(relative variation = 35%).After that,the verified active composite sun-tracking strategy is applied to the case of the solar-aided coal-fired power generation system.The comparison results shows that the solar-aided coal-fired power generation system with active composite sun-tracking strategy comprehensively stands out of all the reference systems.It is proved that the proposed active composite sun-tracking strategy could improves the system performance comprehensively. |
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