Conventional water system optimization often only considered flowrate of fresh water

but ignored flowrates of desalted water

deaerated water

all-level steam and condensate water. The relationship among those types of water is lack of analysis. The minimum freshwater flowrate for the whole water system cannot be determined in one step via the conventional water system optimization model. In order to overcome such a limitation

this paper proposed a general model of water-using process including multiple water types

and presented a general superstructure of industrial water network optimization and a related mathematical model. The material balance equations that relate all types of water are integrated in the model. The commercial software

GAMS

was used for modeling and solving a water system for a certain refinery plant. The results of the case study indicate that the flowrate of desalted water is declined and flowrate of reuse water is increased. Thus the total flowrate of fresh water of overall water system is decreased from 489.44 t·h-1 to 283.94 t·h-1 with rain water flowrate keeping unchanged as 469.36 t·h-1 and the water conservation ratio reaches 21.4% on the basis of the summation flowrate of freshwater and rain water. The quantity of water intake per ton crude oil is reduced from 0.649 t to 0.510 t

which approaches the advanced level in China. Case study shows that the freshwater flowrate for the whole refinery water system can be calculated effectively via the proposed optimization model and it demonstrates the applicability of the model.