(615a) Integration of Dcmd Modules in a Cascade for Energy Efficient Desalination/Purification

DCMD presents an opportunity to achieve desalination using low-grade waste heat and highly saline feed waters, where it may be economically competitive with RO, besides providing a very high quality product that could be used for boiler feedwater and without the corrosion problems associated with metal based evaporators. Combined with high packing density polymeric heat exchangers, DCMD may allow large capacity desalination in a very small footprint, which is attractive for urban locations.

The realization of this promise requires integration of the DCMD with heat exchangers in order to re-use the heat input as many times as possible, so that a given amount of waste-heat can produce a maximum amount of water. This paper presents an evaluation of the product recovery and gain-output ratio for different cascades of DCMD modules with heat recovery exchangers and brine heaters and shows which designs will be preferred for maximum energy efficiency and which designs will be preferred for minimum membrane and heat exchanger area.

In addition, cross-flow DCMD modules (Li and Sirkar, 2004) show much promise in reducing temperature polarization, maximizing flux for a given temperature difference between hot and cold streams. Preliminary results will be presented of running an integrated heat recovery system with cross-flow DCMD modules in different configurations. These will help illustrate a heuristic for sizing the stages of cross-flow DCMD modules to maximize energy recovery for a given recovery.