Fired heaters peak temperatures

The first design considerations for the HHV plant began with a system, where a fossil-fired heater replaced the nuclear heat source. However, because of the desired peak temperatures of 850 C (1000 °C for shorter periods) and the design pressure of 50 bar there were feasibility concerns about the lifetime capability of such a fossil-fired heater. Thus a test circuit was chosen comparable to a closed-cycle gas turbine plant as shown in Fig. 5. 

Radiant heat flux is defined as heat intensity on a specific tube surface. Thus, heat flux represents the combustion intensity and is analogous to how hard a fired heater is run. More specifieally, keeping the firing rate within safe limits is equivalent to maintaining the peak heat flux at less than the design limit because high firebox temperatures could cause tubes, tube-sheet support, and refiractory failures. What is the peak flux and why is it so important to keep it within the limit These questions will be answered next. 

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