Satisfactory methods to predict radiant heat transmission in enclosures containing a radiating gas at uniform temperature are available. These methods have been traditionally used in solutions of kinetic models.
Kinetic models are strongly temperature dependent with a difference of 10°K able to double the reaction rate. In the present investigation, calculation techniques which make allowance for the non-uniformity of gas temperatures in an enclosure are applied to the kinetic models. The furnace problem considers only the radiation section with the assumption that detailed knowledge of combustion and fluid flow pattern within the enclosure is available.
If the gas space in the enclosure and the bounding walls are divided into zones, a zone being taken small enough so that it may be considered isothermal, then for steady-state operation one can write an energy balance on each zone. For any specific problem, every term in these equations with the exception of the net wall fluxes may be written as a function of unknown temperatures only; furthermore the number of equations is exactly equal to the number of unknown temperatures and wall fluxes so that a solution is possible, though exceedingly difficult due to the existing non-linearities.
The net wall fluxes are calculated by the kinetic model, the flux at any point being a function of the overall heat transfer coefficient, the extent of reaction, and the temperature of the reacting gases, each of which in turn is a complex function of reaction gas composition and velocity.
The chief problem of this investigation was one of evaluating the emission from both a gas zone and a surface zone and the radiant interchange between all zones, making due allowance for absorption along every path from one zone to another.
The primary result of this dissertation has been the application of radiant dominant heat transmissions in enclosures (which make allowances for temperature non-uniformity in gas mass) to a pyrolysis reactor. The result of this reactor-furnace hybrid model is the ability to determine optimum tube placement, furnace size, and fuel consumption, while accounting for the effect of carbon deposition in the reactor.
The methods developed in this dissertation were instrumented on an IBM 370-15 computer. This machine made it possible to make parametoric studies which predict the effect of changing furnace and reactor variables.
The high severity steam cracking furnace results in the greatest production per pound of fuel consumed. A yield of 73% represents maximum fuel economy. However, the associated problems of coke formation and high tube metal temperature must first be overcome Wore these yields can be realized.
Robertson, Richard W. J., "Effect of gas temperature gradients and radiant heat transmission on kinetic model behavior" (1974). Dissertations. 1298.