There are several effluent streams generated at coal fired power plants that require on-site treatment, in particular flue gas desulfurization effluent. One option for treating these effluent streams is called zero liquid discharge (ZLD), which effectively concentrates the dissolved ionic species while separating out water.  In addition to the environmental benefits, some potential economic benefits of full ZLD treatment are the generation of make-up water for use at the power plant and the generation a concentrated salt solution similar in composition to a tradeable commodity called 10-lb brine. However, currently ZLD is an expensive option for treating these effluent streams because of the high energy and capital cost associated with the brine concentration step in the ZLD process. For example, reverse osmosis (RO) membranes can typically concentrate streams to only 90 g/L TDS; and the processes, such as mechanical vapor recompression (MVR), that can concentrate streams to \>260 g/L TDS have low efficiencies (typically \<10%), meaning 10 times the minimum theoretical work to concentrate the effluent stream is needed.

   As such, NETL researchers are focused on demonstrating advanced technologies that can concentrate effluent streams to high TDS while reducing both the energy and capital cost of the brine concentration step by 50%. We will present experimental results and numerical simulations of a novel membrane processes called osmotically assisted reverse osmosis (OARO), which like RO using applied pressures as the driving force, but which can concentrate streams to well above the \~90 g/L TDS limitation of currently-available spiral-wound RO membrane modules. A complete process will have a sufficient number of OARO stages to dilute the sweep solution until it can be desalinated by a final RO stage. This presentation will (1) demonstrate experimentally the feasibility of OARO at the bench scale, (2) validate the membrane transport equations of OARO, (3) present techno-economic analysis results from numerical simulations, and (4) compare both the energy and economic results for the OARO process against commercially-available MVR processes for treating coal power plant effluent streams using ZLD.


Treating Effluent Streams at Coal Power Plants Using Membranes

Division / Sponsors: 
Power Division & Nuclear Engineering Division (NED)

Power Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2020/volume/83747

International Conference on Nuclear Engineering
Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE2020/volume/83761

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