| Energy is an essential material basis for human survival and development.Recently, fossil fuels such as oil, natural gas and coal are ued as basic resources.As the fossil energy is dying up day by day and the outstanding of the problems related to environmental pollution and ecological damage. Countries in the world are paying more attention to the development and utilization of renewable energy such as solar energy, biomass energy and wind energy.Solar thermal power generation technology is a mean of large-scale development and utilization of solar energy, and has a broad application prospect. The solar parabolic trough power plant has been spreaded and applicated as the only commercial solar thermal power generation technology nowadays. However,due to the intermittent and instability of solar energy, the spread and application of parabolic trough solar power generating technology is severely fettered. Solar-fossil fuel hybrid power system is an effective method to overcome the problem that intermittent and instability of soalr energy. Based on the principle of"matching of temperatures for cascade utilizing the energy"and research of solar supported coal-fired electric generation system both at home and abroad, combined the feature of parabolic trough collector and coal-fired electric generation system, solar supported coal-fired electric generation system was proposed when the optimum temperature of parabolic trough collector is reached. The integrated mode of solar supported coal-fired electric generation system was constructed, and the performance of thermal and thermo-economic was analyzed.The main research topics and results are as follows:1. Based on the optimum temperature of parabolic trough collector, the high-efficient integrated mode was proposed and applied in a conventional 300MW coal-fired unit. In the integrated mode, the thermal efficiency increase first and then decrease with the increasing of working temperature of collector, however, the efficiency of thermal power cycle is quite the opposite. Hence, there must be the optimum working temperature of parabolic trough collector. The high-efficient integrated mode for a conventional 300MW coal-fired unit was proposed and thermodynamic model was constructed in this paper. The results show that, when solar irradiation is 600W/m2, the optimum temperature of collectors is 306.55℃.The thermal performance of integrated mode is best when the heated surface of boiler replaced by the heat enrgy collected by trough collectors, that solar-to-electricity conversion efficiency is 44.7% and coal-saving consumption is 17.49 g/ kWh . At the same outlet temperature of collectors, the thermal performance of water extracted from the feed water pump is better than that integrated mode whose water extracted from condensate pump for direct solar generation system. Whether direct or indirect heat exchanger type solar collector, when solar heat is used to replace the parameters extraction of high endothermic to heat hot water, its thermoeconomics is superior to that replace the endothermic of the low-parameter extraction.2. Based on the stuctural theory of thermoeconomics and the second law of thermodynamics, the thermoeconomic model of 300MW solar supported coal-fired electric generation system was constructed. Two integrated modes were taken as example to analyze thermoeconomics performance. The results show that, when the temperature of the working fluid heated by collector is enhanced, exergy efficiency have improving tendency gradually and the thermoeconomics performance is better, not different of the tendency that the thermal efficiency of concentrator increase first and then decrease. However, the unit non-energy cost and unit exergy economic cost become higher. Compared to coal-fired units, the unit exergy economic cost of solar field is higher and the unit thermaleconomic cost of integrated mode is higher than coal-fired only system. It shows that reducing the thermaleconomic cost of solar field is very significant for improving the economical performance of solar supported coal-fired electricity generation system.3. Accroding to two classical 200MW and 600MW coal-fired units, the thermal performance of solar supported coal-fired electricity generation system is analyzed and calculated. The unit cost of generate electricity was introduced to analyze and assess the tech-economical performance of integrated mode. The results show that, in the same solar radiation intensity, and integrated with large-capacity coal-fired unit level, the solar-thermal conversion efficiency is higher. The solar-to-electricity conversion efficiency is 38.4% when the integrated mode for a conventional 600MW coal-fired unit. When integrated with coal-fired units of the same capacity, with the conditions seted in this paper, the thermal power efficiency of reducing 1# bled steam is slightly higher than the integrated model. However, the unit generate electricity cost of reducing 1# bled steam is lower than that of reducing all the high pressure bled steams, whose economical performance is better. The unit generate electricity cost of reducing 1# bled steam is 0.58 yuan/kWh and is slightly higher than coal-fired only system whose unit generate electricity cost is 0.58 yuan/ kWh . The innovation of this paper can be listed as follows:1. The high-efficient integrated mode of parabolic trough collectors and coal-fired power generation was proposed based on the optimum temperature of parabolic trough collector.2. The high-efficient integration modes for 200MW,300MW and 300MW conventional coal-fired units were revealed.The high-efficient integrated mode of parabolic trough collectors and coal-fired power generation overcomes effectively the fetter of spread and application of parabolic trough solar power generating system due to intermittent and instability of solar energy. The high-efficient integrated mode of parabolic trough collectors and coal-fired power generation based on the optimum temperature of parabolic trough collector is academically valuable in the field of solar-fossil fuel hybrid power system and has an important reference value for the integrated mode of parabolic trough collectors and coal-fired power generation. It is very significant for large-scale development and utilization of solar and promoting sustainable development of energy, enviroment and social humanity. |
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