Novel Design of Optimum Heat Exchanger Networks for Textile Dyeing Process to Maximize Wastewater Heat Recovery Efficiency

The current dyeing process uses steam to heat the fresh water used for reactive dyeing. After the dyeing process, the wastewater is forcibly cooled and discharged for biological treatment. A large amount of energy is consumed for heating the fresh water and cooling the wastewater owing to the absence of a heat recovery process. This study suggests a novel design of optimum heat exchanger networks for textile dyeing process to maximize wastewater heat recovery efficiency. First, a process model was developed by integrating a heat exchanger with a heat pump. The model was designed to recover high-temperature and low-temperature wastewater through a heat exchanger and a heat pump, respectively. Second, the heat exchanger network of the developed process model was retrofitted based on pinch analysis to reduce operating costs. From the simulation results, the hot and cold utility consumption of the proposed model was quantitatively analyzed. Finally, a techno- economic analysis (TEA) was conducted to confirm the appropriateness of the proposed process model. The total annualized cost (TAC), based on the equivalent annual cost and the total product cost, was determined for both the current and potential future economies. As a result, the TAC was reduced by 43.2 %, and the economic efficiency of the proposed energy-saving measures demonstrates a payback period (PBP) of up to 0.65 y.