Aluminum sells today at approximately $1850/ton. The production of aluminum is one of the most energy-intensive processes in the metallurgical industry, and it has recently been proposed that an OTEC plant could be used for the production of aluminum. Metallurgical estimates indicate that approximately 18 kWh of energy is required in the refining process for each kilogram of aluminum produced. Assuming a plant load factor of 85%, calculate the size of an OTEC plant required to produce 250,000 ton/year of aluminum, if there is a temperature gradient similar to that in Problem 11.7. Then calculate the time required to repay an investment cost in the plant and compare your results with the estimate of 3 years obtained in the literature.
Problem 11.7
It has recently been proposed that OTEC could be used to produce ammonia, a chemical currently manufactured from natural gas at a total energy consumption of about 2.5% of the U.S. natural gas consumption. Since the manufacture of ammonia could be accomplished anywhere, the plant could be located in a favorable location, for example, off the coast of Brazil, where the difference in temperature between the upper layer of the ocean and the layer at the 600 m depth is approximately 20 K. Using an OTEC power plant of 500 MWe capacity, estimate the number of tons of ammonia that could be produced per year. For a price of $165/ton of ammonia, estimate the time required to regain the capital investment in the OTEC production plant and compare your estimate with the claim that the capital could be repaid in 2.5 years.