| The solar aided coal-fired power generation(SAPG)technology has been proven to be an efficient way to use solar thermal energy for large-scale power generation.The solar heat is introduced into a coal-fired units,which can greatly reduce the cost of solar electricity and improve the efficiency,as well as can improve the energy efficiency and reduce the emission of coal-fire units.This paper focusses on the simulation study of the dynamic characteristics of the parabolic trough SAPG plant.The main research contents are summarized as follows:1)Transient simulation modeling of full-condition of the SAPG plantBased on STAR-90,a model-structured modeling method is used to establish a series of transient models of the key component of the SAPG plant,which mainly includes three subsystems such as the solar field,the turbine and the boiler.The sequential module method is utilized to establish the simulation experiment system of the SAPG system according to the flow direction of the working medium,which can be operated with real time or ultra-real time to obtain a transient response which is close to the actual plants.2)Impact research of the introduction of different-scales solar energy on the key parameters of SAPG systemsThrough a desktop transient simulation of a 330 MWe SAPG plant,the key parameters of the SAPG system with different scale solar energy introduction can be obtained,which includes the primary steam flow rate,coal consumption,system output power,primary/reheated steam temperature.The results show that in the fuel-saving operating mode,with the solar input increases,the primary steam flow rate decreases,the coal consumption decreases,and the system output power can be maintained at the rated value.However,the temperature of the primary steam and reheated steam has dropped or even exceeded the requirements of the boiler safe operation specifications.The internal mechanism of this issue is studied in this paper,and on this basis,a developed steam temperature regulation control scheme is proposed,which results in an increased from 27.1 MWth to 99.9 MWth occurs in the solar energy absorption limit of the unit.3)Impact research of the introduction of solar energy on the thermal performance and economic performance of the SAPG systemBased on the research results of the introduction of solar energy on the key parameters of the SAPG system obtained above.The effects of solar energy introduction on the subsystems and the overall performance of the system are studied further.The results show that within the absorption limit,with the increase of solar energy introduction,the thermal cycle efficiency of the SAPG system decreases,the boiler efficiency increases,and the solar thermal power efficiency increases.Compared with the original system,the overall energy efficiency of the SAPG system increases.Correspondingly,when the SAPG is operated in fuel-saving mode and power-boosting mode,respectively,the highest annual solar-to-electricity efficiency can be achieved of 18.5%and 20.2%.and the LCOE can be reduced to 5.1 and 4.6 cents/kWh.Most of China's solar-rich areas are water-scarce areas,so the economic backpressure variation of solar aided air-cooled units is also studied in this paper.Moreover,a full-condition economic backpressure database is obtained.The research results show that compared with other operating schemes such as fixed back pressure and fixed fan power,the thermal performance and economic performance of the SAPG system can be significantly improved.The annual solar-to-electricity efficiency is increased from 8.47%and 15.44%to 17.8%,and the LCOE is reduced from 18.9 and 10.4 cents/kWh to 9.0 cents/kWh.4)Impact research of solar transient characteristics on the safe operation of SAPG systemsThe impacts of solar energy instability and intermittency on the key parameters of SAPG systems under the conditions of solar field starts and clouds cover are studied in this paper.The results show that the fluctuation of primary steam,reheated steam,and steam extraction caused by solar radiation transients is within the acceptable range without heat storage.However,the output power of the SAPG system fluctuates greatly,with a rate of power change can be up to 15.8 MWe/minute,which exceeds the safety allowable range(<3MWe/minute).Based on this,a thermal energy storage is equipped and the effect of a storage on suppressing fluctuations in key parameters of SAPG systems is studied.The results show that the configuration of small-capacity(0.5-hour)storage can effectively reduce the impact of intermittent irradiation on the operation of the SAPG system,maintain the rate of power change of the system within 1 MWe/min.On this basis,the capacity and operation strategy of the thermal storage is further optimized in this paper,which significantly improves the thermal performance and economi(?)performance of the SAPG system,the annual solar-to-electricity efficiency is enhanced from 18.7%to 19.3%,and the LCOE is reduced from 9.3 cents/kWh to 8.8 cents/kWh. |
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