Efficient power generation along with thermal treatment of aqueous stream using low grade heat

Highlights: • Process to simultaneously heat treat aqueous streams and produce electricity. • Exergy of hot aqueous streams recovered as electricity with high efficiencies. • Simple process to generate electricity from low-grade or waste heat. • Power generated shown to offset cost of heat treatment of aqueous streams. We report a process that can use a modified turbocharged piston engine to simultaneously heat-treat aqueous streams and produce electricity. The additional electricity generated by this process more than offsets the cost of heat-treating aqueous stream: thus opening up for commercial utilization water treatment approach that was hitherto considered cost prohibitive. The process provides the technological means for remote or off-grid communities to simultaneously treat their aqueous wastes and generate electricity. In this work, we present a detailed technoeconomic evaluation of the process to demonstrate both its technical feasibility and its cost effectiveness. The variation in overall efficiency, specific work, low-grade heat efficiency and treatment cost of the aqueous stream is studied as a function of turbocharger exit pressure, piston engine compression ratio and mass flow ratio of the aqueous stream to air. For an optimized process, the overall efficiency of the system is 50%. The cost of aqueous stream treatment is negative at −0.998 US$ per cubic meter of water treated based on a 15% return on incremental investment.