Direct fired heaters are typically employed for hydrocarbon reforming, pyrolysis type of processes. High process temperatures are achieved by direct transfer of heat from the products of combustion of fuels. Heat is released by the process of combustion which is transferred to fluids inside tubes which are arranged along the walls and roof of the combustion chamber.
Tubes containing the process fluid are subject to combustion process gases and high temperatures.
Control of pollutants such as NOX is another aspect that is important for proper functioning of these heaters. The combustion process and heat transfer within such are heater are very complex. Simple methods are inadequate to analyze and predict performance. Experimental measurements are difficult and even impossible. The example above shows a combustion process and heat transfer in a direct fired reactor modeled using computational fluid dynamics.