• Energy Research

Heat recovery from a high-temperature wastewater is the major concern in the conventional textile industry. However, limited space in the textile plant is an important constraint for the process enhancement. Therefore, an easily applicable heat recovery system with a small amount of additional equipment to the existing dyeing process is required. To meet the needs from the industry, this study suggests an integrated heat recovery and supply system consisting of single heat exchanger and single storage tank using freshwater as a thermal carrier to utilize the reusable heat in the wastewater. Freshwater is stored in a tank after direct heat exchange with wastewater and is supplied to the next dyeing process. Three different designs of the integrated system were compared based on the lower limit of the wastewater temperature: above 50 °C, 40 °C, and 30 °C for Cases 1, 2, and 3, respectively. The energy and energy flow analyses showed Case 2 to be well balanced between the quality and quantity of the recovered heat, and there was no heat loss via drainage. The heat demand for Case 2 was 795.5 kW, which was the lowest among all cases. Furthermore, an economic analysis showed that the total cost for Case 2 was reduced by 63.2% compared with the base case. Despite the use of an additional heat exchanger and water storage tank, the proposed system was more economical because of the reduced operating costs. Finally, a detailed analysis was conducted by determining the more efficient temperature for heat recovery and supply.

Heat recovery from a high-temperature wastewater is the major concern in the conventional textile industry. However, limited space in the textile plant is an important constraint for the process enhancement. Therefore, an easily applicable heat recovery system with a small amount of additional equipment to the existing dyeing process is required. To meet the needs from the industry, this study suggests an integrated heat recovery and supply system consisting of single heat exchanger and single storage tank using freshwater as a thermal carrier to utilize the reusable heat in the wastewater. Freshwater is stored in a tank after direct heat exchange with wastewater and is supplied to the next dyeing process. Three different designs of the integrated system were compared based on the lower limit of the wastewater temperature: above 50 °C, 40 °C, and 30 °C for Cases 1, 2, and 3, respectively. The energy and energy flow analyses showed Case 2 to be well balanced between the quality and quantity of the recovered heat, and there was no heat loss via drainage. The heat demand for Case 2 was 795.5 kW, which was the lowest among all cases. Furthermore, an economic analysis showed that the total cost for Case 2 was reduced by 63.2% compared with the base case. Despite the use of an additional heat exchanger and water storage tank, the proposed system was more economical because of the reduced operating costs. Finally, a detailed analysis was conducted by determining the more efficient temperature for heat recovery and supply.

Reactive dyeing is primarily used in the textile industry to achieve a high level of productivity for high-quality products. This method requires heating a large amount of freshwater for dyeing and cooling for the biological treatment of discharged wastewater. If the heat of the wastewater discharged from the textile industry is recovered, energy used for heating freshwater and cooling wastewater can be significantly reduced. However, the energy efficiency of this industry remains low, owing to the limited use of waste heat. Hence, this study suggested a cost-optimal heat exchanger network (HEN) in a heat pump-assisted textile industry wastewater heat recovery system with maximizing energy efficiency simultaneously. A novel two-step approach was suggested to develop the optimal HEN in heat pump-assisted textile industry wastewater heat recovery system. In the first step, the system was designed to integrate the heat exchanger and heat pump to recover waste heat effectively. In the second step, the HEN in the newly developed system was retrofitted using super-targeted pinch analysis to minimize cost and maximize energy efficiency simultaneously. As a result, the proposed wastewater heat recovery system reduced the total annualized cost by up to 43.07% as compared to the conventional textile industry lacking a wastewater heat recovery system. These findings may facilitate economic and environmental improvements in the textile industry.

Reactive dyeing is primarily used in the textile industry to achieve a high level of productivity for high-quality products. This method requires heating a large amount of freshwater for dyeing and cooling for the biological treatment of discharged wastewater. If the heat of the wastewater discharged from the textile industry is recovered, energy used for heating freshwater and cooling wastewater can be significantly reduced. However, the energy efficiency of this industry remains low, owing to the limited use of waste heat. Hence, this study suggested a cost-optimal heat exchanger network (HEN) in a heat pump-assisted textile industry wastewater heat recovery system with maximizing energy efficiency simultaneously. A novel two-step approach was suggested to develop the optimal HEN in heat pump-assisted textile industry wastewater heat recovery system. In the first step, the system was designed to integrate the heat exchanger and heat pump to recover waste heat effectively. In the second step, the HEN in the newly developed system was retrofitted using super-targeted pinch analysis to minimize cost and maximize energy efficiency simultaneously. As a result, the proposed wastewater heat recovery system reduced the total annualized cost by up to 43.07% as compared to the conventional textile industry lacking a wastewater heat recovery system. These findings may facilitate economic and environmental improvements in the textile industry.