With a slightly different design, using an ammonia heat
pipe instead of a cold water pipe, proposed by Jim Baird and Dominic Michaelis
(British Patent No. GB 2395754), no water from the bottom is released into the
upper strata of the ocean, trapping all the CO2 deep beneath the thermocline.
Little pumping energy is used to circulate the ocean water, simply enough to
pump warm surface water to flow over the evaporator end of the heat pipe. If
the condensing end of the heat pipe is exposed to a thousand feet or more of
near freezing temperatures below the thermocline, no cold water pumping is
required. The parasitic losses are cut in half. The costs for the cold water
pipe are eliminated, along with the cold water return pipe and condenser pumps,
the cleaning system for the condenser, and the overall plant efficiency
approaches 85% of Carnot vs. about 70% with a cold water pipe.
The parasitic losses could be reduced as much as 50% and the complexity, mass (and cost) of the system reduced by at least 30%. The vast reduction in operating costs and environmental impacts would be worth investigation alone.
Also, the use of Solid State Ammonia Synthesis ( SSAS, Holbrook , et.al.) will reduce the energy required to produce ammonia from roughly 12000 to 7000 kWh of electricity per MT of NH3 product. The use of Seawater Reverse Osmosis (SWRO) would be cheaper and more efficient than evaporation for production of drinking and process water. The addition of a fourth energy product, pharmaceutical and/or industrial grade oxygen, may greatly enhance system economics. If pure oxygen is used to burn or oxidize toxic and solid wastes from our cities, the effluent gasses are much easier to clean up and isolate. Further, if the oxygen is used in flash smelting or oxidation of sulfurous compounds, the resulting efficiency for the recovery of copper, platinum series elements, rare earth elements, and radioactive ores can be greatly enhanced. We found this to be the case in copper smelting in the '80's. The notion that OTEC could be used to clean up the waste dumps of the world would attract much more interest from multinational corporations and governments.
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