Optimization Design Of Circulating Cooling Water System

The circulating cooling water system was a familiar utility system, it was common for circulating cooling water systems in industries such as chemical, electricity, oil refining, but its energy consumption was very high. The water consumption for circulating cooling water system was85%-92%of its for whole factory, and power consumption for circulating cooling water system was20%-30%of its for whole factor. The study on cooling water system mainly concentrated on aspects of cooling tower model, energy-saving or water-saving, operational optimization of cooling water system.The cooling tower played a very important role in the circulating cooling water system, so it was necessary to study the characteristics of the cooling tower. In this paper, rigorous mathematical model of cooling tower was built and it was solved by using Runge kutta method programmed with C language. By using the model to simulating the cooling tower, the variations including the change of air dry bulb temperature, air humidity, water temperature and heat-exchanging driving force along the tower were received in different air conditions, various values of water to air mass ratio and different inlet water temperature. It was the foundation for the entire system optimization.The total cost of circulating cooling water system included operating cost and equipment cost. In this paper, the cost model of circulating cooling water system was established. The heat exchanger cost that was expressed with heat transfer area was introduced as a part of the equipment cost. A simple circulating cooling water system with a sole tower and a sole user was as an example, the influence of heat transfer area, circulating water flow, outlet water temperature and water to air mass flow rate on cost was discussed. It found that there were many factors which affected the total cost of circulating cooling water system and it had complex correspond relations between the various factors.The lowest total cost of circulating cooling water system was treated as the objective function to optimize the whole system configuration by using GA. The water flow, air flow and the heat exchanger area were selected as optimization variable and rigorous mathematical model of cooling tower was combined to calculate the outlet water temperature and the outlet air humidity. For the first time, the influence of the size of the heat exchange on the whole system was investigated. Real examples of circulating cooling water system were optimized and determined the better system operating parameters and device configuration by using above optimization algorithm; it included the total amount of water flow, air flow, the optimum inlet and outlet water temperature of heat exchanger, water flow, the optimum heat exchange area and so on.By comparing the optimal values with the actual value, the total cost of the circulating cooling water system in production process of MDI was reduced about42%,33%and31%respectively at three different environmental conditions; the total cost in production process of TDI reduced about32.1%.Be compared with the optimal values in literature, the total cost increased about11.5%because of considering inlet water temperature limit for combining with the actual production. The results provided reliable theoretical basics for saving energy and reducing consumption in the circulating cooling water system of the actual industrial.