Energy integration of fired heaters into overall processes

Energy analysis at the conceptual design stage helps in designing an energy efficient process plant. Predictions of performances of different equipments are necessary for optimal utilisation of energy. In this article, simplified model of a fired heater is proposed and an analytical procedure is developed for integration of a fired heater into the overall process. This procedure helps in estimating the minimum fuel required and the minimum air pre-heat temperature for energy efficient integration of a fired heater. It is shown that the minimum fuel requirement, for an integrated process, is independent of the air pre-heat temperature as long as it is more than a minimum. The fired heater efficiency remains same within a minimum and a maximum range of air pre-heat temperature and this property helps to fix the air pre-heat temperature considering emissions from the fired heater. Process heat below the process pinch can be utilised for further reduction in the fuel requirement. In the later case, however, it is demonstrated that there exits a maximum limit up to which process heat below the pinch can be utilised. Energy integration of fired heater also leads to reduction in greenhouse gas emission.