Study On Reducing Operational Cost Of Circulating Cooling Water System

Circulating cooling water systems are absolutely necessary for industry such as chemical industry, power industry, metallurgical industry and refining industry. Consumption of circulating cooling water accounts for 70% in total consumption of water in industry. At the same time, large amounts of electrical energy are consumed during the processes of cooling and transportation. Recently, the study on cooling water system mainly concentrates on aspects of energy-saving, water-saving, development of cooling tower model, and operational optimization of cooling water system.Prices of water and electricity are different in different regions, so the optimal operational conditions of cooling water system in different regions are different. Weather conditions change with different seasons, so the optimal operation parameters of the same cooling water system change with seasons.The optimal model of circulating cooling water system was established in this article, in which the operational cost was as the objective function, and outlet tower temperature of cooling water, dry bulb temperature, related humidity, water price and electricity price were regarded as variables. The optimal system structure and operational parameters were obtained by solving optimization model and then the accuracy of model was validated.Factors which have effect on the system such as outlet tower temperature, dry bulb temperature, related humidity, water price,electricity price, system structure and heat-transfer coefficient were discussed. (1)Circulating water flow rate increases, and operational cost increases and then decreased when the outlet temperature of tower increased, so the optimal outlet tower temperature existed in the system. (2)The operational cost of cooling water system increased with the increase of dry bulb temperature and related humidity.(3)The operational cost of system increased with the increase of electricity price. (4)The circulating water volume and the operational cost reduced with the increase of the heat-transfer coefficient. (5)The operational cost and makeup water volume increased with the increase of water price.The optimization methods of one tower and multi-user system and multi-towers and multi-users system was proposed. For the former, the cooling water volume, air volume and annually operational cost reduced after optimizing operational parameters. For the latter, system structure and operational parameters were simultaneously optimized. According to the different from of water reuse and water supply, the optimization methods could include four cases as follows: Water used in heat exchangers from one tower and return to the same tower. Water used in heat exchangers from multi-tower and return to random but one tower. Water used in heat exchangers from one tower and return to multi- towers. Water used in heat exchangers from multi-towers and return to random multi- towers.Finally, 10,000t/a TDI cooling water system was taken as engineering case, whose structure and operational parameters were optimized. (1)After optimization, cooling water volume was reduced by 50% in summer, 60% in winter. (2)After optimization, air volume was reduced and the operational cost was reduced by about 26% in summer and 50% in winter.