Performance Characteristics Of Fluidized Bed Heat Exchanger And Particle Transportation For High-temperature Solar Receiver And Thermal Energy Storage

Concentrating solar power?CSP?technology can provide grid-friendly electricity combined with large-scale thermal storage.Supercritical carbon dioxide?s CO₂?Brayton cycle has a high thermal efficiency and a small equipment size,which is regarded as a representative next-generation concentrating solar power technology.The turbine inlet temperature of s CO₂ Brayton cycle exceeds 700?,which requires a heat exchanger to work at high temperature condition stably.The shallow multistage fluidized-bed heat exchanger is featured with a high heat transfer coefficient and a wide operating temperature range,which is a potential option to serve as a main heater in Supercritical CO₂ Brayton cycle of CSP.A lab-scale 30k W particle heat exchanger of fluidized bed was designed to investigate the characteristics of particles and the heat transfer characteristics between particles and tubes.Numerical simulation was built based on Euler-Euler Two Fluid Model.The influence degree of particle size,particle thermal conductivity and fluidized gas velocity on the heat transfer coefficient between particles and buried pipes was investigated combined with the factorial design and the multiple linear regression model.The research content is summarized as follows:A lab-scale 30k W shallow multistage fluidized heat exchanger was designed and tested.The critical fluidization velocity is about 0.12m/s.The flow characteristics were analyzed and the particle residence time distribution was obtained.The experimental results show that the particles have good flow and transport characteristics in shallow multi-stage fluidized bed heat exchanger,while the axial flow of particles is mainly thrust flow.As the fluidization speed increases,the average residence time decreases,then the flow of particles changes to full mixed flow.The experiments have been carried out with the particle flow rate in a range of 5-30g/s and the fluidization speed of 1-2 times of the critical value.The influence of bed temperature,fluidization speed and particle mass flux on the heat transfer coefficient is obtained.The results show that the heat transfer coefficient increases with the increase of bed temperature and particle mass flux while the fluidization speed has little effect on the particle heat transfer coefficient.There are differences in the heat transfer coefficients between buried tubes and particles.The heat transfer coefficient is greater for particles and buried tubes which are closer to the bottom.The heat transfer coefficient of particle side reached 590-860 W/?m²·K?at a fluidization speed of 1.5times of the critical value.As to a 100MW supercritical CO₂ Brayton system of CSP,the temperature range of heat exchanger was 650-900?,the thermal efficiency was about 98.7%,the exergy efficiency was about 80.6%,the effectiveness was about 61.9%.Numerical simulation was carried out based on Euler-Euler Two Fluid Model to calculate the heat transfer coefficient between particles and buried tubes.The instantaneous gas-solid flow characteristics and the heat transfer between particles and buried tubes were analyzed.The deviation was within 10%between simulation and experiment results.The factorial design and the linear regression model were used to study the effects of particle size,particle thermal conductivity and fluidizing gas velocity on heat transfer.It was found that the particle size was a main factor while the fluidization speed was a minor factor.