Complementary Uses for Waste Heat and Cryogenic Storage
The scheme pictured above is from the University of Leeds Engineering. The process involves using low cost off-peak power to cool air to liquid cryogen. During peak load hours, the cryogen is combined with waste industrial heat to generate peak load power in a turbine.
The above schema comes from Oregon State University Engineering, depicting a process for turning waste heat into mechanical power for cooling. Heat-to-cooling efficiencies of up to 80% are claimed. The OSU process combines micro-channel heat exchange with an organic rankine cycle turbine to drive the refrigerant compressor. If used to generate electric power from waste heat, efficiencies of only 15% to 20% are claimed.
The schema above is from the University of Leeds Engineering. It depicts a combined use of waste heat from power production for either cooling -- using absorption refrigeration -- or for assisting in the generation of electric power using cryogenic storage.
It is easy to see how the OSU micro-channel / organic rankine cycle process might be used in such a trigeneration scheme, substituting for the absorption cooling in the scheme above.
The purpose of combining different processes together -- as in either CHP or IGCC etc -- is to achieve higher efficiencies and more economical production.
While the above waste heat retrieval processes are more efficient than thermoelectric conversion, they are less suited for mobile uses due to their greater complexity. But for use on industrial and utility scales, such processes are likely to prove as useful for integration into total power schemes as the emerging flow cell batteries.
An advantage of the cryogenic storage approach is that whenever a relative excess of electricity persists over an extended time, the cryogen can be separated into liquid N2 and liquid O2 and sold for a profit.