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Web Letter

Several areas of center-city Philadelphia pioneered this over a century ago, with the waste heat from coal-fired electric plants being used to heat hundreds of commercial businesses.

As we improve to more nuclear, the possibilities are fantastic!

John D. Froelich

Upper Darby, PA

Feb 1 2010 - 10:22pm

Web Letter

Nice article, but a bit lacking in a couple of key terms--co-gen and "Binary Cycle."

The Co-gen part is using low-grade heat from steam turbines ("exhaust steam") or industrial heat as a heating source, so that the latent heat of vaporization can be extracted from the steam. This may involve the use of steam compressors to up the pressure of this steam, but more often a customer for this lower temperature steam (150 F [vacuum steam] to ~300 F). A great use is district heating, or heating hydroponic greenhouses that could be used to grow a region's "salad bowl" and flowers, fast-growing fruits, etc., without pesticides in a CO2-enhanced environment, which also creates local jobs and eliminates all the petroleum associated with trucking or flying those items from far away.

The binary cycle involves using either "waste heated air" or "exhaust turbine steam" or simply unwanted low-temperature steam to boil a lower-boiling (at atmospheric pressure reference) fluid, using that to push a turbine, then condensing that fluid using colder air/cold water. Examples include ammonia, trimethylamine, methylamine, ethylamine, HFC-245fa, HFC-236ea, butane, pentane, dimethyl ether and others. You can, by matching the temperature of the heat source and "cold sink" (Lake Erie or Ohio River water, air) extract up to 25 percent more electricity from the same quantity of fuel (coal, natural gas or biomass). Neat eh? These are established ways of operating--a recent entry is the maker of "the Green Machine," which uses HFC-245fa as the working fluid.

Dave Bradley

Buffalo, NY

Jan 31 2010 - 12:39pm

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