Both fuel supply and thermal pollution considerations that are becoming progressively more important strongly favor the development of a higher temperature, and more efficient, thermodynamic cycle for electric power plants. About 200,000 hr of operation of boiling potassium systems, including over 15,000 hr of potassium vapor turbine operation under the space power program, suggest that a potassium vapor topping cycle with a turbine inlet temperature of ∼1500 deg F merits consideration. A design study has been carried out to indicate the size, cost, and development problems of the new types of equipment required. The results indicate that a potassium vapor cycle superimposed on a conventional 1050 deg F steam cycle would give an overall thermal efficiency of about 54 percent as compared to only 40 percent from a conventional steam cycle. Thus the proposed system would have a fuel consumption only 75 percent and a heat rejection rate only 50 percent that of a conventional plant. Further, it appears possible that the capital charges for the proposed plant might be lower than those for a conventional plant. A high grade fuel oil or gas will be required, but this is likely to be necessary anyway to meet increasingly stringent limitations on SO2, NOx, and ash emissions.
A conceptual design for one embodiment of a binary vapor cycle coupled to a molten-salt reactor has been prepared to determine whether such a plant is sufficiently attractive to warrant further investigation. Its overall thermal efficiency is estimated to be 54 percent, while its heat rejection to the condensers is about half of that for a modern steam plant. The quantities of material required for the heat exchangers and piping for both a coal-fired supercritical-pressure steam plant and a nuclear-powered potassium vapor and supercritical-steam plant are estimated and compared along with the associated costs. The resulting cost and performance data indicate that the nuclear plant with a potassium-vapor and steam binary cycle may give both lower capital charges and a much higher overall efficiency than a coal-fired super-critical-pressure steam plant.
A new type of steam generator has been devised t o meet the special requirements of high-temperature liquid metal and molten salt reactor systems, The basic design concept i s such that boiling heat transfer i n s t a b i l i t i e s and t h e i r attendant severe thermal stresses a r e avoided even f o r a temperature difference of as much as 1000°F between the feedwater and the high-temperature liquid, thus giving good control characterist i c s even under s t a r t u p conditions. employing a v e r t i c a l reentry tube geometry with the feedwater entering the bottom of the inner small diameter tube (4 / 4 in. diam) through which it flows upward u n t i l evaporated t o dryness. of the small central tube then flows back downward through the a n n u u s between the central tube and the outer tube. t i o n of the heat transferred from the high-temperature liquid t o the superheated steam i n t h e annulus i s i n t u r n transferred t o the water boiling i n the central tube. Design studies indicate that t h i s type of b o i l e r not only avoids thermal s t r e s s and s a l t freezing problems but it a l s o gives a r e l a t i v e l y compact and inexpensive construction. Further, it appears t o make possible a simple plant control system with exceptionally good plant response t o changes i n load demand.
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