Study On The Optimization Of Water-using Network In Completely Batch Processes With Multiple Contaminants

Water has been being strategic resource in the21st century with the economic booming and the rapid increase of population. Water-using network synthesis (WNS), aiming to reduce freshwater use and waste discharge, plays a more and more important role in the development of industrial processes. The batch operation mode has been applied widely in the field of medicine, fine chemical engineering, food and so on. Compared to the continous process, the constraints of operation time and concentration of contaminants should be met at the same time in the batch processes. The studies on optimization of batch water-using network in literatures mainly focus on single contaminant system, while the multiple contaminants system has occupied much more proportion in industrial processes. Thus, the study on the batch water-using network with multiple contaminants system has the vital significance. Base on the literatures of batch water-using network synthesis and the methods of handling multiple contaminants in continuous processes, the study on the water-using network in batch processes with multiple contaminants has been conducted in this paper as follows:(1) The time intervals have been divided according to the operation time in batch mode, and a water sources-storage tanks-water sinks superstructer and the non-linear programming model have been constructed, aiming to minimize the usage of freshwater. The constraints of all contaminants in the warer-using processes are considered, including the constraints of inlet and outlet concentration and the mass load. The number of storage tanks is taken as a variable and the mathematical model is solved by GAMS to obtain the freshwater usage and flow and concentration in each time interval in a sinle period and multiple periods as well as the steady water-using network. Two cases have been calculated to illustrate the feasibility of the approach proposed here.(2) The key contaminat has been identified and the water source with maximum outlet concentration of the key contaminat is discharged directly to the wastewater tank, in order to simplify the water-using network superstructure. Then, the maximum and minimum of flow of each wate-using unit is added to accelerate the convergence. Firstly, the remaining water sources in the previous period and the water remaining in tanks are all considered as water sources in next period. Secondly, only the water remaining in tanks are reused in next period. Lastly, the model of considering flow change is built instead of the dilute solution hypothesis. Cases are solved to improve the effective of the technique, which can get the steady water-using network in less operating periods than the literature.(3) The approach of study on the synchronizing parallel water utilization in batch processes has been proposed in this paper. The water sources in the same batch or in the different batches are allowed to mix together to provide recycle water for the water sinks. The water-using network superstructure is simplified by comparing the concentration of the key contaminant and then the model is solved by GAMS in a single period and multiple periods. A case is solved to illustrate that the minimum freshwater usage and the optimized water-using network are attained in the meanwhile.