| The ultra-high parametric steam Rankine cycle is a main technology in the field of power engineering,which is very mature and has little room for efficiency gains.S-CO2 cycle is more efficient in medium to high temperature conditions,and is small,compact and flexible.It has the ability to change loads quickly.facilitating the realization of multiple energy complementary models.This paper focuses on the study of ultra-high-parameter CO2 coal-fired power generation system and conducts innovative research around key scientific issues of coupling mechanism between S-CO2 cycle and boiler and cascade energy utilization,targeting issues of broad optimization of the S-CO2 cycle,large mass flow problems faced when boilers are coupled to cycle and flue gas heat absorption over an entire temperature range.The ultra-high parametric steam Rankine cycle achieves high efficiency mainly through reheating and multi-stages regenerative heating.The current S-CO2 cycle lacks a corresponding broad principle.Based on recompression cycle(RC)the effect of intercooling and reheating arrangement on the cycle is studied in this paper.For the first time,the synergistic principle is introduced to construct a multi-compression S-CO2 cycle and reveals that RC is equivalent to a two-stage compression cycle consisting of two simple Brayton cycles(SC).Under optimal circulation flow ratio conditions,the two SCs work synergistically to build the RC.reducing the heat exhaled to the environment,reducing heat transfer losses and improving cycle efficiency.This finding inspired the construction of multi-compressions cycles,such as RC to further synergize with SC to construct tri-compression cycle(TC).The idea of multi-compressions based on the Synergistics as a general principle of S-CO2 cycle optimization is contrasted with the idea of multi-stages regenerative heating of steam Rankine cycle.which is an important step to improve the theory of S-CO2 cycle optimization.The multi-compressions cycle is suitable for a variety of heat sources,and the combination of reheating and intercooling can effectively improve the cycle efficiency.In order to facilitate the determination of the applicable cycle under different heat source conditions,the regime map of the multi-compressions cycle is proposed based on the main vaper parameters,which lays the foundation for the construction of S-CO2 coal-fired power generation system.In the coupling mechanism of S-CO2 boiler heat source and cycle,it breaks through the limitations of traditional thermodynamic analysis and conduct thermodynamic.hydrodynamic and heat transfer analysis through the internal crossover of engineering thermal physics disciplines.It was found that the S-CO2 cycle flow rate is 6-8 times higher than the steam Rankine cycle under the thermal cycle requirements and faces the large mass flow problem.This problem leads to a large pressure drop in the S-CO2 boiler and an efficiency penalty effect.In order to overcome the penalty effect,partial flow strategy is proposed,a module design of the boiler is formed,the partial flow strategy is revealed to follow the 1/8 reduction principle,and a program for calculating the thermal system of S-CO2 cycle coupled boiler heat load distribution and flow heat transfer characteristics is prepared.Calculations show that the module boiler design based on the 1/8 principle reduces the pressure drop of the S-CO2 boiler to a lower level than the steam boiler,completely solving the problem of large boiler pressure drops.The S-CO2 cycle is compared with the steam Rankine cycle,with a focus on the effect of pressure drop on both cycles.The average heat absorption temperature of the S-CO2 cycle is high,and when combined with coal-fired boilers,the moderate temperature flue gas heat is difficult to absorb.It faces the problem of flue gas heat absorption over an entire temperature range.Therefore,four residual heat absorption methods are investigated based on the cascade energy utilization principle.From the point of view of reducing the total amount of residual heat,a method is proposed to increase the air temperature in the air preheater and increase the turbine inlet pressure.From the perspective of efficient absorption of residual heat,a method for diverting low-temperature CO2 from the cycle side and constructing a combined cycle is proposed.Focusing on the phenomenon of efficiency difference between the top and bottom of the combined cycle.Based on the cascade energy utilization principle,the overlap energy utilization principle is proposed.The core idea is to set a cascade zone in the moderate and high temperature flue gas area,and the flue gas heat is absorbed by the top cycle and the bottom cycle.Four connected-top-bottom cycles are gradually optimized to explore ways to completely solve the problem of residual heat.Since the temperature and pressure parameters of the top and bottom cycles are the same,the overlap energy utilization allows for the sharing of most equipment in both cycles,simplifying the system.Subsequently,the coal-fired power generation system is built near the S-CO2 cycle efficiency limit based on the cascade energy utilization principle and overlap energy utilization principle,with intercooling,reheating and multi-compression as the core,and its efficiency potential is clear.Under the main vaper parameter of 35MPa/630?,the power efficiency reached 50.27%.At the same time,the tri-compression cycle has been improved and the S-CO2 coal-fired power generation sy stem has been proposed,which has advantages in achieving efficient engineering applications.The concept of S-CO2 coal-fired power generation based on a pressurized fluidized bed combustion(PFBC)boiler is proposed to explore the heat source characteristics of S-CO2 boilers.The internal temperature of the PFBC boiler is 850-900?,which is much lower than the temperature in the pulverized coal boiler,which can solve the problem of boiler heating surface over temperature.In addition,the volume of the boiler is reduced after the flue gas is pressurized,which realizes the overall miniaturization of the power generation system.The above characteristics make the concept attractive.This paper constructs two power generation systems with the demarcation of gas turbine inlet flue gas temperature,and analyzes the influence of key parameters such as pressure drop in flue gas side of PFBC boiler and combustion pressure in the furnace on the system performance.At the same time,in order to solve the problem of excessive heat load in furnace,the method of increased excess air coefficient or flue gas recycling to adjust the energy load distribution in PFBC boiler is explored,and the applicable conditions for both are obtained. |
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