Considering the severe fouling of high temperature convection pass in the boilers using high-sodium coals, a novel boiler design with a furnace exit gas temperature (FEGT) below 800 °C was proposed. The design was evaluated in different kinds of boilers with various capacities by examining thermal system arrangement, heat transfer, ignition and combustion, and steel consumption. The results indicate that, more radiation heating surface should be used in the thermal system arrangement of the novel boiler besides the volume-enlarged furnace. A marked decrease in the converted coefficient of radiation heat transfer is found in a volume-enlarged furnace due to the reduction in the average temperature of the flame. Moreover, the volume-enlarged furnace can adversely affect ignition and combustion. The cyclone-fired boiler is considered to be the most appropriate application for the novel design, for its combustion and heat transfer in furnace are carried out in divided chambers. A comparison of steel consumption demonstrates the expense of the novel boiler is approximately increased by 10% relative to the conventional one. In addition, an improved application with flue gas recirculation is described in detail, owing to its advantages of controlling FEGT and maintaining the level of convection heat transfer capability of the boiler.

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