Radiant section efficiency
Radiant section efficiency
(OP)
Dear all
I have a question regarding pyrolysis furnace efficiencies.
I am calculating the overall thermal efficiency of all furnaces in my plant. But I want to calculate the efficiency of both radiant and convection section.
This is what I am doing:
- Heat input from fuel known
- Heat absorbed in total known
- Stack and bridge wall temperatures known
Since I calculate the fluegas mass flow, cp and the deltaT from bridge wall and stack, by Q=m.cp.DT, I have the convection heat absorbed. By difference from the heat absorbed I should have radiant heat absorbed.
Defining radiant efficiency as QRadiant/Qinput I achieve values of 40-45%, higher than the ones given by Linde of about 35-37%. Can I calculate the convective heat transfer this way?
Thanks
AndreChE
I have a question regarding pyrolysis furnace efficiencies.
I am calculating the overall thermal efficiency of all furnaces in my plant. But I want to calculate the efficiency of both radiant and convection section.
This is what I am doing:
- Heat input from fuel known
- Heat absorbed in total known
- Stack and bridge wall temperatures known
Since I calculate the fluegas mass flow, cp and the deltaT from bridge wall and stack, by Q=m.cp.DT, I have the convection heat absorbed. By difference from the heat absorbed I should have radiant heat absorbed.
Defining radiant efficiency as QRadiant/Qinput I achieve values of 40-45%, higher than the ones given by Linde of about 35-37%. Can I calculate the convective heat transfer this way?
Thanks
AndreChE





RE: Radiant section efficiency
The furnace efficiency will be a function of several variables, including the following:
-furnace gas emmissivity, which is a function of excess air and fuel fired
- furnace adiabatic flame temperature, again a function of excess air and fuel fired and gas recirculation
-fuel heat input divided by (furnace surface area plus furnace exit area), or use the Boltzman number as defined in the Russian Normative Method by Blokh
- wall effectiveness, which is usually a function of wall construction ( membrane waterwall vs loose tubes vs refractory )but is also affected by the slag or ash coating.
- burner patern centerline ( furnace geometry and burner location)
RE: Radiant section efficiency
RE: Radiant section efficiency
Hot diatomic gases O2 and N2 are considered transparent (diathermic) to radiation and they indeed transfer heat by convection in the radiant section .
Robert D. Reed in Furnace Operations, Gulf Publishing Company, shows the radiant capability of CO2 and H2O when burning methane with 25% xs air is just about 30% of the total liberated heat. When the xs air % increases, the capability of radiation drops even more than expected from the cooling effect of higher xs air %.