5.2　Flue Gas Ducts

5.2.1　Flue gas ducts shall be arranged to avoid any pocket，dead zone and section with the lower flow velocity.

5.2.2　Where the outlet flue gas ducts of several induced draught fans are routed to the flue gas header，an isolation damper should be installed at the outlet of each induced draught fan.Additionally，the flow velocity at each cross section of the flue gas ducts should not vary significantly，and flue gas impingement shall be avoided.

5.2.3　Manholes shall be provided at the following locations，and should be arranged at the lower position on sidewall of the flue gas ducts for easy access：

a）In the outlet flue gas ducts of the air preheater（manhole in the inlet flue gas ducts of the air preheater shall be determined on specific cases）；

b）In the inlet windbox or the inlet flue gas ducts of the induced draught fan；

c）In the flue gas header to the stack or at the bottom of the stack.

5.2.4　Ash handling holes shall be provided at the locations where ash is prone to accumulate，and shall be located at the bottom of flue gas ducts.

5.2.5　Breeching shall have a minimum clear distance beyond the last（present or future）convection row of 0.8 m for access and flue-gas distribution.At least one take-off shall be provided every 12 m of convection-section tube length.

5.2.6　If the flue gas ducts is connected to the stackat two sides，a vertical partition wall with an inclined angle of 45° from the centerline of the flue gas ducts should be constructed inside thestack，and a slope should be constructed at the lower position of the partition wall at each side（as illustrated in Figure 2）.And if the flue gas ducts is connected to the stack at one side，a baseplate that is inclined upwards along gas flow should be installed（as illustrated in Figure 3 and Figure 4）.

Figure 2　Flue gas ducts connected to stackat two sides（ζ=0.62）

Figure 3　Flue gas ducts connected to stack at one side（ζ=0.70）

Figure 4　Flue gas ducts connected to stack with segmented plate at one side（ζ=0.46）

Note：ζ shown in Figures 2-4 refers to a local resistance coefficient used for calculating the local resistance at the location where the flue gas ducts is connected to the stack.

5.2.7　Openings cut into the stack shall be limited in size to a clear width no greater than two-thirds of the stack diameter.For two openings opposite each other，each chord shall not exceed the stack radius.Openings shall be reinforced to fully restore the required structural capacity of the uncut section.