Formation of internally circulating flow and control of overall heat-transfer coefficient in a fluidized-bed boiler

Research was conducted on the formation of internally circulating flow in a fluidized-bed boiler and on the control of the overall heat-transfer coefficient. For this purpose, a boiler was designed whose fluidized bed was divided by an inclined partition wall into a main combustion cell and a heat-exchange cell so as to create a revolving flow of the bed material and silica sand in the main combustion cell and a circulating flow between the main combustion and heat-exchange cells. The experiment has demonstrated that circulation of the fluidized medium from the main combustion cell to the heat-exchange cell and recovery, by the immersed heating surface in the heat-exchange cell, of the required amount of heat can only be achieved if the stable bed height of the fluidized medium is above the top of the inclined partition wall and the quantity of the fluidizing air fed from both sides of the main combustion cell exceeds a certain predetermined value. It has also been established that the rate of descent of the fluidized medium in the heat-exchange cell can be effectively controlled by changing the quantity of circulating air fed from underneath the heat-exchange cell. Actual measurements also showed that the overallmore » heat-transfer coefficient changes almost linearly in the heat-exchange cell with changes in the fluidizing air-flow rate within the limits of U/U{sub mf} = 0 to 2. It was thus possible to achieve total control of the load conditions in the internally circulating fluidized-bed boiler. It was possible to achieve total, unlimited control.« less