ABSTRACT

This study presents the results of a numerical investigation of water circulation in an in-service boiler at full and part loads. Two different computational models were developed. The first model simulates the combustion process while the second model simulates water circulation inside the boiler tubes. The results include the heat flux distribution along the different furnace walls (boiler tubes), the flow field, and the temperature distribution inside the furnace of the boiler at full and part loads. The circulation ratio and the other flow properties (velocity, steam quality, rate of steam generation, void fraction, and surface temperature) in some of the water circulation loops are also calculated. The results indicate that high-velocity values appear in the regions in the vicinity of the flames and low-velocity values are shown in the regions of entrained air outside the flame regions. The temperature contours along the vertical plane of the two middle burners indicate a temperature variation from 2300 K at the flame boundaries to 1200 K close to the walls. The rear wall exhibits the most serious heat flux values where large areas are subjected to heat flux close to the maximum. The side walls exhibit high values of heat flux in the middle region of the wall on the right side of the burner and close to the bottom at the opposite wall. The heat flux distribution along the top wall indicates relatively low values of the heat flux rates. The results indicate a clear reduction in heat flux values at part loads. The maximum value is reduced from 610 kW/m² at full load to 540 kW/m² at 75% load and to 430 kW/m² at 60% load. A code that allows the user to display key results and generate a graphical picture of the variation of heat flux, fluid velocity, steam quality, void fraction, and tube surface temperature was also developed.