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Sun Mar 2, 2014, 04:05 AM

Advances in Thermal Energy Storage and Boat Propulsion

Advances in Thermal Energy Storage and Boat Propulsion
February 28, 2014

Historical records indicate that the first powered submarines of the late 19th century used steam-thermal energy storage to power a piston engine and drive the propeller. For several decades between the late 19th to mid/late 20th centuries, several short line railways operated shunting locomotives that stored saturated water in high-pressure, insulated tanks. During that period, several efforts aimed at extending the operating range of such locomotives involved using heat-of-fusion thermal energy storage technology, using molten caustic soda that melted at about 320C (600F).

Ongoing developments in the concentrated-solar thermal power industry led to developments in grid-scale thermal energy storage technology that could storage enough heat to generate superheated steam that would drive steam turbines and electrical generators. During the early to mid 20th century, the premium steam powered passenger ships such as the Queen Mary and Queen Elizabeth used steam turbines to generate electric power to drive multiple propellers. Boats and ships that sailed short voyages burned coal and/or wood fuel to raise steam that drove triple-expansion steam piston engines.

The rising price of oil has encouraged various segments of the maritime industry to explore possibilities of using alternative, lower-costing fuel energy for propulsion. One sector uses trains of kites that fly in the powerful trade winds that blow at elevations of between 1,000 and 3,000-feet, to pull maritime craft that sail parallel to the prevailing winds. The higher price of fuel has also sparked renewed interest in steam power and the development of boilers capable of generating steam in excess of 600C (1100F) and steam piston engines that use steam injectors able to deliver steam at over 4,000-psi (275-atmospheres).

The combination of new developments in thermal storage technology for solar-steam power and renewed interest in steam power by the maritime sector has prompted interest in adapting thermal storage technology for short-distance maritime propulsion. Once branch of the solar-thermal power sector uses a mixture of sodium nitrate and potassium nitrate that both occur naturally and melts at some 500C (950F) to store some 80-KJ/Kg (36-BTU/lb) of thermal energy. Ongoing research has identified other materials that can store many times that amount of thermal energy on a per-unit-weight basis.

Heat-of-Fusion Storage:
A mixture of 80% lithium hydroxide and 20% lithium fluoride (by molecular weight) ...


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