The Circulating-water Network Optimization Considering Heat Transfer Enhancement

The industrial water is accounting for 81% of urban domestic water and industrial water and 70% ~ 80% industrial water is circulating cooling water.The continuous flow of the circulating water needs being pushed by pumps.So optimizing the circulating water system can not only reduce the amount of the water,but also save the work of pumps.Thus the optimization can save huge water and energy and bring huge economic benefits for the corporation.This thesis first applies the classic pinch technology and problem table method to determine the minimum flow rate of the circulating cooling water system.Then it expands the neighborhood algorithm which has been used in the hydrogen and water networks to the circulating cooling water network to synthesize the network.The specific steps for the neighborhood algorithm are proposed,and the contribution of the saving amount of circulating cooling water to the saving energy is calculated.Then an example is used to certify the effectiveness of the neighborhood algorithm.In order to determine the cooler levels more efficiently,a three-dimensional diagram plotted by the matlab is used.In the figure,temperature,heat capacity flow rate and heat load are shown in the same figure.The temperature is used as the main parameter and the flow rate as the auxiliary parameter to quickly determine the classification and the matching problem of coolers.For retrofit problems,the second level coolers are checked if they can meet the original cooling requirements.For coolers which cannot meet the requirements,two methods can be considered: heat transfer enhancement and using more fresh water.For this is a retrofit problem,adding twisted tape in the tube side of coolers is a cheaper and easier way to realize compared to other heat transfer enhancement methods.For an industrial case,the circulating cooling water decreases from 267.2 kg.s-1 to 158.5 kg.s – 1,which has fallen to 59.3% of the original amount,thus the pump work is reduced,saving the operation cost of 0.513 million yuan per year.For a complex circulating cooling water system which has many coolers,three-dimensional view method can be combined with the neighborhood algorithm to optimize the circulating cooling water network.A complex case is retrofitted by the combination method,in which the circulating cooling water is decreased to 59.9%,and 0.232 million yuan per year is saved of the operating cost.The effects of the pressure drop on the operating cost are also calculated.Compared to the decreasing of the operating cost caused by the flowrate decreasing,the effects of the pressure drop is lesser.