Abstract
Cascade cooling systems containing different cooling methods (e.g., air cooling, water cooling, refrigerating) are used to satisfy the cooling process of hot streams with large temperature spans. An effective cooling system can significantly save energy and costs. In a cascade cooling system, the heat load distribution between different cooling methods has great impacts on the capital cost and operation cost of the system, but the relative optimization method is not well established. In this work, a cascade cooling system containing waste heat recovery, air cooling, water cooling, absorption refrigeration, and compression refrigeration is proposed. The objective is to find the optimal heat load distribution between different cooling methods with the minimum total annual cost. Aspen Plus and MATLAB were combined to solve the established mathematical optimization model, and the genetic algorithm (GA) in MATLAB was adopted to solve the model. A case study in a polysilicon enterprise was used to illustrate the feasibility and economy of the cascade cooling system. Compared to the base case, which only includes air cooling, water cooling, and compression refrigeration, the cascade cooling system can reduce the total annual cost by USD 931,025·y−1 and save 7,800,820 kWh of electricity per year. It also can recover 3139 kW of low-grade waste heat, and generate and replace a cooling capacity of 2404 kW.
Highlights
In the process industry, cooling systems are a key element that takes away waste heat or cools down streams to a target temperature
The results showed that the operating temperature of generator, absorber, evaporator and condenser would all affect the coefficient of performance (COP) of the cycle
Selbas et al [22] optimized the subcooled and compression refrigeration cycle through thermo-economy. the results indicated that the superheated vapor compression refrigeration cycle through thermo-economy. the results heat exchangers capital cost of the system increases with the evaporating temperature
Summary
In the process industry, cooling systems are a key element that takes away waste heat or cools down streams to a target temperature. Kilic [13] studied the influence of different operating parameters on system performance, such as an increase of the temperature of the generator and evaporator, decreases in the heat load of absorber and generator, and increases in the COP of the cycle. Thout(i,2), Thout(i,3) and Thout(i,4) are the outlet temperatures of the hot streams of streams the recovery waste heat recoveryair exchanger, air cooler, cooler, and absorption the wasteofheat exchanger, cooler, water cooler, water and absorption refrigeration refrigeration cooler, respectively. They the temperature breakpoints between the cooler, respectively.
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