(171f) Design of Water Networks Using Rigorous Models

One of the weaknesses in currently methods to solve the water allocation problem (WAP) in process plants is a lack of accurate modeling of water regeneration and water using processes. In general, two kinds of model assumptions are made: regeneration processes have a fixed outlet concentrations (Koppol et al., 2003); and, regeneration processes have a fixed rate of removal (Takama et al, 1980; Guanaratnam, 2005; Karuppiah and Grossmann, 2006; Alva-Argáez, 2007). In reality, outlet concentration and/or rate of removal of regeneration process may vary with inlet concentrations and flowrates for each regeneration process design and also with different flowrates and inlet conditions. Similar assumptions are made in water using processes: fixed loads are used, when these loads are in many cases a function of inlet water conditions and flowrates.

Empirical equations or equations obtained from mathematical models and simulations can be used to better describe regeneration process. We use these equations to determine true outlet concentrations in water using units and to design the regeneration processes together with determining the network structure. Thus, the operating conditions like flowrate and inlet concentrations are taken into account when the design parameters of the regeneration processes are chosen. We propose a mathematical programming framework where the regeneration processes equations are transformed in discrete parameters and binary variables are used to select the optimum design.

Alva-Argaéz, A., Kokossis, A.C., Smith, R. (2007). A conceptual decomposition of MINLP models for the design of water-using systems. Int. J. Environment and Pollution. 29, 177.

Gunaratnam, M.S. (2003). Total water system design. Ph.D. Thesis, University of Manchester Institute of Science and Technology - UK.

Karuppiah, R., Grossmann, I.E. (2006). Global optimization for the synthesis of integrated water systems in chemical processes. Computers and Chemical Engineering, 30, 650-673.

Koppol, A.P.R., Bagajewicz, M.J., Dericks, B.J. and Savelski, M.J. (2003). On zero water discharge solutions in the process industry. Advances in Environmental Research, 8, 151?171.

Takama, N., Kuriyama, T., Shiroko, K., Umeda, T. (1980). Optimal water allocation in a petroleum refinery. Computers & Chemical Engineering, 4, 251?258.