Design Of 300MW S-CO₂ Boiler System And Numerical Simulation Study Of Ash Deposition And Slagging

The supercritical CO₂ cycle power generation technology has remarkable features such as simple system,compact structure and high efficiency.However,since this power generation technology is a brand new technology and there is no commercially operating power plant boiler for reference,there are many difficulties and challenges in the design of supercritical CO₂ boilers.This paper combines the S-CO₂ power cycle with power station boiler combustion technology to design a 300MW S-CO₂ four-angle cut circle coal-fired boiler,and conducts numerical simulation analysis of combustion and slagging in the furnace and ash deposition in the tail flue heat exchanger tube.Firstly,the design of a 300MW supercritical CO₂ Brayton cycle system with secondary reheat and recompression and the determination of key parameters were carried out.Based on the power generation parameters,a vertical tube screen partitioned arrangement was adopted for the furnace chamber and the boiler design was carried out based on the heat transfer method for the partitioned sections of the furnace chamber.The effect of the zonal arrangement of the furnace chamber on the temperature distribution along the air-cooled wall and furnace chamber as well as the pressure drop of the working mass was investigated.The study shows that at a design load,the superheated air-cooled wall is 0.71 of the chamber height,the along-travel flue gas temperature distribution is within a reasonable range,the chamber air-cooled wall temperature has a wide safety margin and the design cost is relatively low;the cycle efficiency of this design unit reaches 51.82%,which is1.79%higher than that of the primary reheat S-CO₂ unit and exceeds that of a conventional water vapour boiler by about The design achieves a cycle efficiency of 51.82%,which is 1.79%higher than that of the primary reheat S-CO₂ unit and approximately 11%higher than that of a conventional water steam boiler.Secondly,based on the above 300MW S-CO₂ coal-fired boiler,the numerical simulation of combustion and slagging in the furnace was carried out to obtain the velocity distribution,temperature distribution and concentration field distribution of each flue gas component in the furnace,and the slagging situation in the furnace was calculated by the slagging model written by Fluent user-defined function.The study shows that the temperature distribution of the flue gas in the furnace is consistent with the design flue gas distribution of the boiler;in addition,the main locations where the pulverised coal particles move with turbulence and collide with the furnace wall are the cold ash hopper,at the furnace outlet and near the burner nozzle;influenced by the flue gas temperature and velocity,the location of slagging in the furnace is mainly concentrated at the inflection point of the cold ash hopper and near the cross-section of the burnout air nozzle in the main combustion zone.Finally,numerical simulations were conducted to study the performance of elliptical tube bundle in ash deposition resistance for the tail flue heat exchanger tube of supercritical CO₂ boiler,and the results showed that:the particle impact rate decreases with the increase of ellipticity of heat exchanger tube,while the particle deposition rate shows a non-linear law,and the deposition rate is the smallest when the ellipticity is 1.5D;the particle impact rate increases with the increase of both flue gas flow rate and particle size,and the deposition rate decreases.The particle impact rate increases with the increase of both flue gas flow rate and particle size,and the deposition rate decreases;with the increase of transverse tube spacing of elliptical tube bundle,the particle impact rate and deposition rate both decrease significantly.In addition,the elliptical heat exchanger bundle has lower particle impact rate and deposition rate compared with the circular heat exchanger bundle.