Fluidized bed reactor, heat removal water pipe and application thereof in acrylonitrile production

A fluidized bed reactor, comprising at least a reaction cooling section and a vertical inner component provided in the reaction cooling section, wherein, when a length of the reaction cooling section in a direction along a central axis of the fluidized bed reactor is designated as L, expressed in a unit of m, and, at a cross section transverse and perpendicular to the central axis of the fluidized bed reactor at an arbitrary position within a region from 45% L above to 38% L below a central point of the reaction cooling section, an area of the cross section of the reaction cooling section is designated as S1, expressed in a unit of m2, and an outer contour circumference of the cross section of the vertical inner component is designated as L1, expressed in a unit of m, and, L1/S1=2.0-4.3 m−1, wherein, when there are a plurality of cross sections, the outer contour circumference of the cross section of the vertical inner component is a sum of the outer contour circumferences of all of the plurality of cross sections.