Research Of Reheater System Thermal Deviation In Ultra-supercritical Tangential Firing Boiler

Tangentially-fired is widely applied to large capacity utility boiler unit in China.Because of its combustion characteristics,it has good combustion coal category adaptability but products severe thermal deviation impacting on boiler thermal efficiency and operating security.In this paper,660 MW ultra-supercritical tangential firing boiler unit was taken as an example and through the furnace combustion numerical simulation,researched the effect of air volume ratio and nozzle swing horizontal deflection angle of over fire air(OFA),under different boiler loads,for thermal deviation of reheater system in horizontal flue and supported corresponding solutions.Based on the simulation results,one improved method of boiler thermodynamic calculation that according to the actual steam flow,namely divided reheater system into two groups along the furnace width,was put forward and the accuracy of this improved method was examined by comparing calculation results to power plant operation datum.And then,applied this method into calculating and analyzing the effect and influence of the structure and arrangement of high temperature reheater to its steam temperature deviation.The research results show that the influence of the air volume ratio of OFA to flue gas temperature deviation of high temperature reheater in horizontal flue larger than its flue gas velocity deviation and flue gas temperature deviation increases with the air volume ratio of OFA.When adjusting and analyzing the air volume ratio of OFA,it is necessary to consider the boiler load,the location of commissioning burners,the boiler combustion efficiency and pollutant discharge amount and others;The influence of nozzle swing horizontal deflection angle of OFA to flue gas velocity deviation of high temperature reheater in horizontal flue larger than its flue gas temperature deviation.When its horizontal deflection angle is negative,it is beneficial to decrease flue gas temperature and velocity deviation of high temperature reheater and strengthen heat transfer capability of heating surface.The improved thermodynamic calculation method can directly reflect the steam temperature deviation in both sides of reheater and support calculation results within the admissible error as steam temperature forecast and the pre-design reference;Through designing asymmetric structure of heating surfaces of high temperature reheater to match its flue gas temperature deviation that can better improve the steam temperature deviation.