Analysis And Design Of Water Networks With Multiple Contaminants

Water crisis has severely constrained the sustainable development of world economy and society,and even begun to affect the survival of mankind.Water system integration has become one of the research hotspots in water conservation science and technology due to its remarkable water-saving effect.Most water systems in process industry contain multiple contaminants.Mathematical programming method is currently the main tool for the synthesis of water systems with multiple contaminants.However,this kind of method still has certain limitations when applying to complex water systems.This dissertation studies the synthesis of multi-contaminant water systems based on the engineering insight of the processes.The main contents are as follows:1.The influences of the regenerated concentrations of contaminants on regenerated stream consumption are analyzed for water-using networks with multiple contaminants,and the key contaminant which has the most influence on regenerated stream consumption is identified.The multi-contaminant water networks with regeneration unit are classified into simple ones and complex ones according to the characteristics of the networks.For simple networks,the regenerated stream consumption can be predicted easily when the regenerated concentration of the key contaminant changes,and the maximum allowable concentrations of non-key contaminant is deduced.For complex networks,the increasing rate of the regenerated stream consumption caused by the regenerated concentrations of contaminants is calculated and the contaminant corresponding to the biggest increasing rate is identified as the key contaminant.The method proposed is important to the evaluation of appropriate regenerated concentrations for the design or retrofit of the water networks with multiple contaminants.2.A new approach is developed for the design of batch multi-contaminant water-using networks with regeneration unit.For the water network integration of multipurpose batch plants in a single campaign,the time indice is introduced and taken as the primary criteria,together with concentration potential concepts and the feature of regeneration reuse network,to determine the precedence order of the water-using processes and estimate the concentrations of the regenerated stream.For the water network integration of multiproduct batch plants operated in cyclic mode,the final results can be obtained by adjusting the process sequence slightly based on the design method for the continuous processes.In addition,the specific type of regeneration unit,i.e.,sequencing batch reactor(SBR),is selected.The incorporation of SBR with water-using processes is discussed as well.The approach proposed can be applied to the water networks with regeneration unit of fixed regenerated concentration model and that of fixed removal ratio model.3.A numerical-indicator-based method is presented for the design of distributed wastewater treatment systems with multiple contaminants.In designing a distributed treatment system,it is unnecessary stream mixing caused by performing a process that increases the treatment flow rates of the downstream processes,and thus increases the total treatment flow rate of the system.Based on this insight,a new numerical indicator,Total Mixing Influence Potential(TMIP),is introduced to determine the process sequence.In the design procedure,the TMIP value is calculated based on pinch principle.The results of a few literature examples show that designs with very low(even minimum)total treatment flow rates can be obtained with the method proposed.In addition,the calculation effort does not increase significantly when the number of streams,contaminants and/or treatment units increases.4.A heuristic rule-based method is presented for the design of the distributed wastewater treatment networks with maximum inlet concentration constraints,based on the insight that one of the important essences of distributed wastewater system integration is to reduce the total treatment flow rate by minimizing unnecessary mixing amount of streams.To meet maximum inlet concentration constraints or environmental regulations,some treatment process(es)might take recycling structure.The initial network structure(s)is first developed according to the heuristic rule proposed.Then,the final design is obtained by adjusting the initial network(s)based on contaminant mass load balances,identification of the pinch point and maximum inlet concentration constraints simultaneously.It is shown that the designs obtained with the proposed method are comparable to those obtained with mathematical programming approach.In addition,the method proposed is simple and of clear engineering insight.