In order to explore the effects of mixed coal combustion on reducing the carbon content of fly ash in a subcritical 600 MW natural circulation balanced draft boiler

three types of coal with significant differences in characteristics were used

and numerical simulations were combined with experiments to study the mechanism of mixed coal combustion and its relationship with fuel characteristics

burnout rate

and carbon content in fly ash in the stratified combustion process of the balance boiler. Based on the results

a set of coal blending principles are proposed to improve the combustion characteristics of coal powder in power station boilers. Firstly

three extreme operating conditions were set up

and high-quality coal was respectively focused on the upper

middle

and lower layers of the burner for combustion. And then

through computational fluid dynamics(CFD) simulations

it was found that when the coal powder airflow of the balance combustion boiler flowed upward

and the high-quality coal was distributed in the upper layer of the combustion chamber while the poor-quality coal was distributed in the lower layer

the residence time of poor-quality coal in the furnace increased significantly

allowing it to fully combust in the high-temperature area of the upper layer

resulting in a low carbon content in fly ash. Furthermore

based on the analysis of the heat value

volatile matter and ash content of coal powder in different combustion layers under various working conditions

it was found that the difference in heat value and ash content is the main factor influencing combustion characteristics. Based on the actual operating conditions of the coal-fired power plant

a more realistic set of coal blending scenarios was established

and numerical simulations and on-site experiments were conducted

which showed that the overall combustion characteristics of coal powder under each working condition followed the aforementioned rules

and the carbon content in the fly ash reduced compared with the original operating conditions. Finally

the coal blending principles were established

which take into full consideration of the actual operating conditions of the power plant

recommend high-quality coal with low ash content to be used in the upper and middle layers of the combustion chamber while poor-quality coal with high ash content should be used in the middle and lower layers of combustion burner.