Further research on slag-tap boiler can promote the application of fully burning high-alkali coal technology. In this study

a supercritical 350 MW once-through double-U flame slag-tap boiler is taken as the research object and the combustion chamber

slag collection tube bundle and cooling chamber are taken as the calculation units

the thermal calculation is performed from the perspective of heat balance. The flow field

temperature field and component field in the boiler under design condition and at variable loads are studied. The deviations of several flue gas temperature results obtained by thermal calculation and numerical simulation are within 40 K. At the outlet of the combustion chamber

the deviation is only 1.2 K. The temperature deviation of flue gas at the outlet of cooling chamber is 15.6 K. After verification and comparison

it is concluded that the thermal calculation method adopted can be applied to the thermal calculation on double-U flame slag-tap boiler that fully burning high-alkali coal. The flow field is well organized. The recirculation zones formed by swirling flow can increase the movement path of pulverized coal particles in the combustion chamber and promote the burning. When the flue gas flows through the slag collection tube bundle

the temperature greatly reduces. The flow field is also disturbed

which can effectively capture the ash. At variable loads

the velocity field in the boiler decreases proportionally according to the reduction ratio of the amount of coal. However

the size of the recirculation zones is basically unchanged. The temperature level in the boiler reduces

when the amount of coal reduces from 100% to 75%

the flue gas temperature at the outlet of the combustion chamber reduces by about 75 K

and the flue gas temperature at the outlet of the cooling chamber reduces by about 200 K. This study can provide reference for fully burning high-alkali coal in double-U flame slag-tap boiler.