Conceptual issues regarding the effective area of air distribution plates

The effective area of the air distribution plate refers to the cross-sectional area of the entire plate

This post was last edited by zgj2405 on 2009-11-21 at 19:19. Whether the structure and dimensions of the air distribution device are appropriate directly determine the quality of fluidization of the material in the fluidized bed, which in turn affects the boiler’s ignition and operation, its combustion and load characteristics, as well as its safety and economic efficiency. The air distribution device of a fluidized bed boiler mainly consists of an air distribution plate (including a support plate and air nozzles), an air chamber, and a slag discharge pipe. The main functions of the air distribution device are: (1) supporting the stationary bed material layer ； (2) Ensure uniform distribution of air across the entire cross-section of the furnace, and provide sufficient dynamic pressure head to enable uniform fluidization of the bed material and feedstock, thereby preventing adverse phenomena such as channeling, surging, excessive bubble sizes, and fluidization dead zones ； (3) Those large particles that have been almost completely burned, exhibit poor fluidization properties, and tend to accumulate on the air distribution plate should be removed promptly to prevent fluidization stratification, ensure that the normal fluidization state is not disrupted, and maintain safe production ； (4) During fluidization, the bed material does not flow back in the direction of the air chamber (slag leakage). The air distribution plate consists of a support plate and an air cap. The function of the support plate is to bear the weight of the wind cap and the material being circulated, as well as to initially distribute the airflow. To facilitate fixing and support, the actual manufacturing dimensions of the ceiling slab should be larger, with an additional 50–100 mm added to each side. Considering the expansion of the ceiling slab, its dimensions can also be set to match those of the outer wall of the furnace. The determination of the effective area of the support plate plays an important role in the design of fluidized bed boilers. The size of the effective area of the support plate is directly related to the load characteristics of the boiler. In design, the operating wind speed is determined first, and then the effective area Ad of the ceiling grid is calculated based on that value. In equation (6-1), Ad represents the effective area of the support plate, in m2 ； Q1 —— Primary air volume through the air distribution plate, Nm3/s ； T——bed temperature,℃ ； P — Pressure on the air distribution plate, Pa ； Wm——Fluidization velocity at the air distribution plate. After the cross-sectional area of the air distribution plate is determined, its width and depth dimensions also need to be fixed. The width is usually taken as the width of the furnace chamber, and the depth can be determined by dividing Ad by this width.

3# zgj2405: You still haven’t clearly explained the concept of the effective area of the air distribution plate. This description is cited in many books; I’ve found a description that helps to clarify it a bit: “The effective area of the air distribution plate equals the cross-sectional size of the vertical section of the fluidized bed.” Refer to “Fluidized Bed Combustion Technology” published by Water & Hydropower Press. In the case of cylindrical furnaces, there is usually a certain taper below the material layer, that is, a frustum shape. Based on this understanding, the actual effective area of the air distribution plate is smaller than the cross-sectional size of the vertical section of the fluidized bed (with the proportion determined by the degree of taper)