Research On Deep Peak Shaving System Establishment Of Coal-Fired Power Unit Integrated With Thermal Energy Storage And Its Application Mode For Large-Scale Wind Power Consumption

The target of 3060 dual carbons is China’s energy strategy for a long time in the future,and the development of renewable energy is an effective means to achieve this target.When a high proportion of renewable energy power generation is connected to the power grid,the coal-fired power unit needs to make deep flexible operation to adapt to the load change of renewable energy power generation.However,due to the influence of the minimum stable combustion load of the boiler and denigration operation parameters,the unit load of the coal-fired power unit cannot be further reduced,resulting in the increase of abandoning large-scale wind and solar energy power.The thermal energy storage technology can achieve the deep peak shaving of coal-fired power unit to meet the needs of large-scale renewable energy access to the power grid.So the relevant researches have very important theoretical significance and practical engineering value for realizing the dual carbon target.In this thesis,based on the full investigation of the literature,the method of deep peak shaving of coal-fired power unit based on thermal energy storage is proposed.On the basis of ensuring the lowest stable combustion load of the boiler,the power output of coal-fired power unit is further reduced by using thermal energy storage technology,so as to improve the flexible operation of deep peak shaving of coal-fired power unit.According to the thermal characteristics of coal-fired power unit,three schemes of deep peak shaving are proposed,namely,electric heating thermal energy storage,main steam extraction thermal energy storage and reheat steam extraction thermal energy storage for deep peak shaving.The optimal deep peak shaving scheme is established through thermodynamic analysis and applied to consume large-scale wind power.The research results are as follows.The thermal system model of 600 MW subcritical coal-fired power unit was established,and the accuracy of the thermal model was verified by comparing the designed value and operation value of the original unit with simulation value.Based on the comprehensive consideration of the minimum stable combustion load of boiler and the minimum steam mass flow rate of low-pressure turbine,it is proposed to take 50%THA as the reference load for deep peak shaving and 15% THA as the target of deep peak shaving capacity.The deep peak shaving system integrated with electric heating thermal energy storage(DPSE),deep peak shaving system integrated with main steam extraction and thermal energy storage(DPSM)and deep peak shaving system integrated with reheat steam extraction and thermal energy storage(DPSR)are established for different heat storage sources.DPSE uses electric to heat molten salt to store heat for deep peak shaving,and then the stored heat enters the thermal system of coal-fired power unit to increase the unit load.DPSM utilizes the thermal energy storage of extracted main steam to heat molten salt and phase change material for deep peak shaving.The sensible heat of molten salt and latent heat of phase change material enter the thermal system of coal-fired power unit to increase unit load in heat discharging process.DPSR uses the sensible heat of extracted reheat steam to heat molten salt,and the latent heat of extracted reheat steam to heat pressure water to store thermal energy for deep peak shaving,and the stored heat is released into the thermal system to increase the power output of coal-fired power unit.Considering the energy coupling relationship between heat charging and discharging modes and thermal system of coal-fired power unit,the influence law of heat charging and discharging modes on the performance of deep peak shaving of coalfired power unit is analyzed.Taking coal consumption of comprehensive power generation as the system performance evaluation index,DPSE has a large energy loss and poor comprehensive performance due to the thermoelectric conversion efficiency of less than 45%.The DPSM and DPSR have relatively higher comprehensive performance due to the reduction of thermoelectric conversion and direct stored thermal energy storage of extracted steam,but DPSM has greater energy loss due to the main steam throttling and depressurization,so DPSR has better comprehensive performance.The reheat steam of DPSR has higher sensible heat and lower saturation pressure,so molten salt is used to store sensible heat of steam,and pressure water is used to store latent heat of steam.The heat stored in molten salt is used to heat bypassed feed water to reduce extracted steam from high/intermediate pressure turbine,the heat stored in pressure water is used to replace condensate water to reduce extracted steam from low pressure turbine.Such a heat charging/discharging scheme can broaden up and down operation range of the unit under peak shaving period.In order to more comprehensively analyze the thermodynamic perfection of the three deep peak shaving schemes and the irreversible loss of the system during operation.Exergy analysis method was adopted to explore the changes of exergy efficiency and exergy loss rate of each device in the system.The feasibility of DPSR was analyzed and judged.The results showed that the irreversible conversion of electric converted into thermal energy in heat charging process of DPSE is the highest with the exergy efficiency as the evaluation index,and its exergy income efficiency is the lowest.DPSM and DPSR can reduce exergy loss caused by electric converting into thermal energy by extracting steam,but the exergy loss is larger when the extracted steam of DPSM is throttled and depressurized,and the exergy income efficiency is lower.DPSR has the advantage of lower reheat steam pressure and small entropy increase during throttling and depressurization,and its exergy income efficiency is the highest.Therefore,from the perspective of energy quality,DPSR scheme is the best choice.For the power grid dispatching,from the perspective of large-scale wind power consumption,the wind power plant and DPSR are integrated,and the large-scale wind power consumption system of coal-fired power unit integrated with wind turbine and thermal energy storage is established.Two operation modes of wind power consumption are proposed.The mode of direct consuming unstable wind power converts the unstable wind power into thermal energy,which is used as the heat source for heating the bypassed feed water and enters the thermal system of coal-fired power unit.The mode of consuming surplus wind power by thermal energy storage will use wind power to heat the molten salt and store heat mixed with the molten salt heated by reheat steam.The stored heat is released to the original unit to increase power output in discharging process.The operation income model of the large-scale wind power consumption system of coal-fired power unit integrated with wind turbine and thermal energy storage is established.From the view of income,such as the income of power generation,coal consumption and carbon trading,the operation income is comprehensive analyzed.The relationship between the operating income and wind power consumption is obtained.This can provide a reference basis for the investment and income calculation of establishing a high proportion of renewable energy consumption system in the future.