Operation optimization of existing industrial circulating water system considering variable frequency drive

The traditional circulating cooling water system regulates the flow rate through parallel pumps and valves. Due to fluctuations in operation, there will be lots of energy waste, resulting in inefficient operation of the circulating cooling water system. This research proposed a mixed-integer nonlinear programming (MINLP) method. By installing variable frequency drives (VFDs) on the pumps, changing constant-speed pumps (CSPs) into variable speed pumps (VSPs), we can regulate flow rate with valves and VSPs simultaneously. Optimizing the system using Genetical algorithm (GA) to obtain precise operating parameters, including the configuration of VFDs, the number of CSPs and VSPs and the resistance coefficients of valve in the branch and main pipe. Sensitivity analysis of the model is carried out, and the energy-saving effect of VFD under different temperature differences, pump types and electricity prices, the operating status of the pump and the status of the pipeline are compared. The results indicate that the MINLP genetic algorithm optimization model for industrial circulating water considering variable frequency drive proposed in this paper has a wide range of applicability. It can save an average of 23 % of the total cost under different conditions, and has a promising energy saving effect.