Heat integration of regenerative Rankine cycle and process surplus heat through graphical targeting and mathematical modeling technique

Heat Integration, an effective energy-saving technology, has been popularized in many fields. In the current paper, Pinch-based Heat Integration technology is applied in the Heat Integration of process surplus heat (PSH) and regenerative Rankine cycle (RRC)-based steam power plant. PSH is recovered by preheating boiler feed water (BFW) to reduce consumption of steam extracted from the turbine. A systematic hybrid methodology of graphical targeting and mathematical modeling is developed. The objective function is minimal fuel consumption of steam power plant, rather than maximal heat recovery. The terminal temperature and heat load of process-heated BFW are two decision variables. The graphical targeting method is proposed to ascertain the bounds and constraints of the two decision variables. A mathematical model incorporating rigorous simulation of turbine is formulated to achieve the optimal Heat Integration scheme. Two case studies, one pertaining to the Heat Integration of RRC and PSH at low temperature and the other involving the Heat Integration of RRC and PSH at medium temperature, are elaborated. The results show that significant fuel savings and cold utility reductions are achieved by using the proposed methodology. Compared with other methods of PSH utilization, the proposed Heat Integration scheme is more feasible and effective.