High High trip of a natural draft Heater stack temperature 1

[Vivaldi M. Smith]

I am trying to set and configure the High High trip of a natural draft Heater stack temperature. What parameters should I take into account? How Can I set this trip set point.

 

[georgeverghese]

TSHH required to prevent autoignition of uncombusted fuel, in case of accidental loss of burner flame.
Suggest setting the TSHH at some 100degC lower than the autoignition temp of the fuel at this fired heater. Though theoretical auto ignition temp for methane / natural gas is about 550degC, actual experimental values appear to be 800degC at least.

 

[georgeverghese]

Error in previous post: The experimental value of 800-900degC quoted earlier is the surface temp of the ignition source. Perry, in the chapter on process safety/subsection on autoignition, says the ignition surface is at least 200degC hotter than the bulk gas temp due to forced convection gradients at the surface. So the experimental value for autoignition for methane / NG is 900-200 = 700degC. So a suitable safe setting for stack TSHH would be 600degC.

 

[Vivaldi M. Smith]

Thank you very much