After the selective catalytic reduction(SCR)denitration device was installed in an ultra supercritical 1 000 MW unit

the hardened ash accumulated on surface of the air preheater increased significantly.Thus

the harden ash and fly ash collected from the above unit boiler were screened and thermogravimetric analysis was carried out to investigate their characteristics.The results show that

the paralysis weight loss rate of the harden ash is 10.5%

while that of the fly ash is less than 1%.The heating rate has less effect on its weight loss.For the fly ash particles with size less than 125μm

the combustible matters distribute evenly

while for the ones with size larger than 125μm

the fly ash combustion mass fraction increased dramatically.The combustible mass fraction reaches the highest in fly ash particles with size within the range from 50μm to 63μm.