Boiler flue design for coal-fired power plant

[Ranma05]

I am trying to incorporate Roark's plate theory into the design of a large flue (x-sectional area = 648 sq ft). Basically, I am using it to tell me how far apart I can place stiffeners based on a plate thickness of 0.25 in.

The proposed construction of the flue is from plates of 36 X 10 feet for the bottom and top, and 18 x 10 feet for the sides. The steady state pressure is 1 in of water, with a fly ash loading of 30 psi.

So far, I have assumed that since the stiffeners are to be welded to the plates, and the vertical plates welded to the horizontals, this signifies fixed boundary conditions on all edges.

However, when I run numbers through the calculator at efunda (assuming small deflections), the only spacing that doesn't violate the small deflection constrait is ridiculously small (stiffeners every square foot). I have seen that other flues have stiffeners every 4 feet.

I think that I may be wrong in assuming small deflections (< half the thickness of the plate).

Randy

 

[davefitz]

the design flue pressure is based on the transietn pressure folloiwng an MFT or failure fo the ID fan dampers. NFPA requires a +/-35 in wc minimum desing pressure, which is a bit larger than 1 in wc

 

[davefitz]

Also, the assumption of small deflections ( scaling "small" to the plate thickess) does not seem appropriate. I think the requred design critieria would be 95% yield in the structural members ( during MFT event) or deflections that reduce the net cross sectional area for flow for the fluegas or ash by 5%