Membrane distillation (MD) is a promising low-cost, green (based on utilization of low-quality heat) alternative to dominant water treatment processes like thermal distillation and reverse osmosis (RO). However, it is still not commercially viable, at least in part due to the low flux per unit energy. By employing the use of electrically conductive spacers, it is possible to provide localized heating near the membrane surface with the use of induction heating and without a compromise in flux compared to that of membrane coating. Compared to conventional external feed heating, the temperature distribution across the feed-membrane interface is much more uniform when heating takes place right there. Hence, maximizing the energy efficiency of the heat input which is the main cost in most thermal distillation processes. This savings becomes especially evident when heat loss across the membrane increases as the process is being scaled up.
The novel use of electrically conductive spacers does not require drastic modifications to current membrane manufacturing processes but instead just replacing the layering of current industrial standard polymeric spacers with electrically conductive ones. Since induction heating uses rapidly changing electromagnetic field from an induction coil and the induction coil can be shaped easily in many ways, the process of integrating induction heating would also be simple and straightforward.
The potential applications include using such improved MD systems for desalination, tertiary wastewater treatment and pervaporation. Reducing the need for external heating and heat loss associated with external heating, along with the improved energy efficiency allows for the miniaturization of membrane distillation systems, allowing for more portable systems to be deployed as standalone water purification or desalination solutions. Furthermore, the smaller footprint could be easily integrated to processes which produce low temperature waste heat, to supplement heat with high energy efficiency to maintain clean water throughput in the fluctuating waste heat output.
The technology developer is seeking for interested parties who are willing to provide monetary support or specific product design know-how to build a marketable prototype for decentralized water treatment utilizing waste heat in area where stable power supply is scarce.
Potentially every membrane distillation system can be fitted with electrically conductive spacers for improved performance. Notably, the membrane distillation market is estimated at $37.5 million market in 2010 and set to grow to US$200 million by 2020. Furthermore, when used in conjunction with localized induction heating, better control of output flux to match the designed clean water production output at a higher efficiency can be achieved when there is lesser available waste heat or solar heat for distillation.
Improved energy efficiency, reduction of size of membrane distillation system, fast startup and shut down (no lag time involved in heating bulk feed externally) and inherently safe heating method.