Experimental study and simulation analysis of heat and deformation in the water walls of an opposed firing boiler under flexible operating conditions

With the extensive use of renewable energy, a large number of existing boilers will work under flexible operating conditions with low and medium loads. To study water walls safety in an opposed firing boiler under flexible load conditions, we conducted experimental research and numerical simulation for three typical flexible conditions. The results showed that compared with the single-side arrangement of burners, the opposing arrangement was beneficial for the uniform distribution of temperature and reduction of the overall thermal stress of water walls (the average stress decreased 17.9% in the opposing arrangement). In addition, a numerical simulation for calculating the distribution of the thermal stress was provided by referring to the cooling water temperature during the experimental process. Finally, an arc-shaped structure was proposed to reduce the stress of the flat plate between arc plates (the average stress reduction rate was from 7.82% to 31.99%) but induce new high stress areas. The modified structure weakened the reduction effect (the maximum thermal stress reduction rate was from 1.00% to 11.46%) but prevented high stress from water walls. The results highlight that the opposing arrangement and the modified arc-shaped structure are effective for reducing the operation risks.