Targeting for energy integration of multiple fired heaters

Energy integration of a fired heater with the background process helps in targeting fuel requirement and the air preheat temperature prior to its detailed design. Existing integration procedures are applicable only for processes with a single fired heater. However, in certain processes, multiple fired heaters are required to satisfy the total hot utility demand. In this paper, a methodology is proposed to target the minimum number of fired heaters. To synthesize an energy integrated heat recovery network that incorporates a single fired heater, a cold stream should enter the fired heater at the pinch temperature, and the heat capacity of the cold stream should be within a permissible range. For processes with multiple fired heaters, the duties of different fired heaters may be varied to simplify the design of the overall heat exchanger network. Entry conditions for cold process streams to the fired heaters are also established, to satisfy the overall energy target. In certain cases, the fuel requirement and air preheat temperature for every fired heater may have to be re-estimated to set achievable targets.