DEVELOPMENT OF A RECOVERY BOILER LOWER FURNACE HEAT TRANSFER MODEL - PART I: ANALYSIS OF FLOOR TUBE TEMPERATURE EXCURSIONS

摘要

An advanced heat transfer model, using the PHOENICS code as a base, has been developed to simulate heat transfer in the lower furnace of kraft recovery boilers. Simulation results show that the heat transfer regime inside a floor tube can be either forced convection, flow boiling, combined convection/boiling or post-critical heat flux (CHF), depending on the thickness of the frozen smelt on the tube. Under steady-state conditions, high tube temperature excursions may occur only when flow inside the tube is slow and the molten smelt flow is rapid. Under transient conditions where the frozen smelt layer cracks and molten smelt comes into contact with the floor tube, the outer tube surface temperature can increase significantly.