Abstract
The temperature distribution on the backside of the water-wall tubes in the first 600 MW CFB boiler operating at 60%, 80% and 100% of the boiler Maximum Continuous Rating (MCR) loads was experimentally determined and the thermal-hydrodynamic performance of water-wall system based on the mass and energy equations using the measured temperature was calculated. The results showed that the temperature of the water-wall tubes increased as the furnace height increased, showing a positive response characteristic in the water-wall system. However, the temperature of the water-wall tubes in the upper furnace was obviously declined at the places where the superheaters and cyclone separator inlet-channels were arranged. This suggests that the arrangement of the heat-transfer surfaces in the upper furnace was significantly influenced the temperature distribution of the water-wall tubes. Meanwhile, the calculated total pressure-drop and mass flux in the water-wall system increased as the boiler’s load raised, showing an energy-efficiency for the vertical once-through boiler. In addition, the metal temperature was calculated to check the working condition of the water-wall tubes and the results showed the highest metal temperature of 426.3 °C of the water-wall tubes was found at the tip of the fin at 100% MCR. This temperature was far below the permissible temperature of the metal, implying that a safe working condition of the metal at three loads was guaranteed. Nonetheless, analysis into the heat-transfer characteristics of the water in the water-wall reflects that the water temperature in the water-wall at 80% MCR load was adjacent to the boundary of the large specific-heat region, implying that heat-transfer deterioration was more likely to occur at such condition. Therefore, the metal temperature of the water-wall tubes operating at 80% MCR load requires the most concern and monitor to avoid overheating of the water-wall tubes.
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