Research On High Temperature Corrosion Of Water-cooled Wall Of 660MW Supercritical Down-fired Boiler

So far,supercritical down-fired boilers are only in the domestic commercial operation,and is less than 10 years.There is little research on the high-temperature corrosion of supercritical down-fired boilers.This paper provides some reference for the transformation of high-temperature corrosion and related design of supercritical down-fired boilers.In this paper,a 660 MW supercritical down-fired boiler using high sulfur coal and low NOx emission graded combustion technology is researched.The boiler was found of serious high-temperature corrosion in the side water wall after two years' operation later.As the corrosion is in excess of the electricity construction requirements on water wall,hundreds of water wall tubes were replaced.According to the calculated corrosion rate which has been 0.93mm/a,a large replacement of water wall tubes will have to happen again in running less than two years.The high-temperature corrosion in the supercritical down-fired boiler was analyzed concretely.The result of electron microscopy analysis of the corrosion products showed that the corrosion was mainly caused by high-temperature reductive sulfur.By research on furnace reductive atmosphere,water wall temperature,sulfur content of furnace coal,and etc.which are the influence factors of high-temperature reductive sulfur corrosion,the prevention and control measures of high-temperature corrosion were put forward,including to improve the reductive atmosphere on the lateral water wall by adding wall air,to optimize the water wall temperature,to control of the sulfur content of furnace coal,to spray anti high-temperature corrosion materials.In order to verify the effect of the adherent wind on improving the reductive atmosphere on the lateral water wall,FLUENT software was used to simulate the furnace temperature,O2,CO near the lateral water wall.The numerical simulate results showed that adding sidewall wind could reduce the furnace wall temperature of the corrosion zone in the water wall,improve the oxidative atmosphere and reduce content of CO near the lateral water wall,thus slowing down the occurrence of high-temperature corrosion.Based on the results of numerical simulation,a method of improving the reductive atmosphere near the corrosion zone in the water wall by adding three layers of adhered wind in the wing wall elevation of 19.4m,22.1m,21.0m,25.7m and 29.5m is proposed.At the same time,optimizing water wall temperature,arc spraying on high-temperature corrosion areas,and other preventive measures were raised.Finally,since the above B class maintenance during 2014 overhaul,the boiler has been running continuously for nearly three years.In 2016 overhaul,an inspection on high-temperature corrosion in the water wall was also carried out,and no any water wall thickness reduction and corrosion productions on the water wall surface were found.The high-temperature corrosion in the water wall of the supercritical down-fired boiler is well controlled.