Experiments have been conducted with a molten salt loop at Sandia National Laboratories in Albuquerque, NM to resolve issues associated with the operation of the 10MWe Solar Two Central Receiver Power Plant located near Barstow, CA. The salt loop contained two receiver panels, components such as flanges and a check valve, vortex shedding and ultrasonic flow meters, and aq impedance pressure transducer. Tests were conducted on procedures for filling and thawing a panel, and assessing components and instrumentation in a molten salt environment. Four categories of experiments were conducted 1) cold filling procedures, 2) freeze/thaw procedures, 3) component tests, and 4) instrumentation tests. Cold-panel and-piping fill experiments are described, in which the panels and piping were preheated to temperatures below the salt freezing point prior to initiating flow, to determine the feasibility of cold filling the receiver and piping. The transient thermaI response was measured, and heat transfer coefficients and transient stresses were calculated from the data. Analysis is presented which quantifies the thermal stresses in a pipe undergoing thermal shock. In addition, penetration depths were calculated to determine the distances salt could flow in cold pipes prior to freezing shut and validated with panel tests. Freeze/thaw experiments were conducted with the panels, in which the salt was intentionally allowed to freeze in the receiver tubes, then thawed with heliostat beams to assess permanent deformation in the tubes, and to develop procedures to thaw a panel so minimal damage occurs. Slow thermal cycling tests were conducted to measure both how well various designs of flanges (e.g., tapered flanges or clamp type flanges) hold a seal under thermal conditions typical of nightly shut down, and the practicality of using these flanges on high maintenance components. In addition, the flanges were thermally shocked to simulate cold starting the system. Instrumentation such as vortex shedding and ultrasonic flow meters were tested alongside each other, and compared with flow measuremeni from calibration tanks in the flow loop. 4JJ DISTRIBUTION OF THlS DOCUMENT I S UNUh4lTED ACKNOWLEDGMENT We would like to acknowledge the following for their contribution to the molten salt panel and component experiments :

A new hot-salt pump has been developed for moltensalt solar power tower applications that will reduce the capital cost of the plant, eliminate many of the piping, valve and sump problems associated with the handling of molten salt and improve the reliability of a critical part of the operating system of the plant. Previous systems required that the pumps in these plants be housed in shallow sumps that were gravity fed by the storage tanks. This new pump arrangement will eliminate the sumplevel control valves and the potential for overflowing the pump sump vessels. Until now only cantilever pumps were qualified for hot molten-salt service because no suitable bearing materials had been tested. This paper describes the successful qualification of a long-shafted pump with salt-lubricated bearings tested for over 5000 hours with nitrate salt at 565 °C.

A new hot-salt pump has been developed for molten-salt solar power tower applications that will reduce the capital cost of the plant, eliminate many of the piping, valve and sump problems associated with the handling of molten salt and improve the reliability of a critical part of the operating system of the plant. Previous systems required that the pumps in these plants be housed in shallow sumps that were gravity fed by the storage tanks. This new pump arrangement will eliminate the sump-level control valves and the potential for overflowing the pump sump vessels. Until now only cantilever pumps were qualified for hot molten-salt service because no suitable bearing materials had been tested. This paper describes the successful qualification of a long-shafted pump with salt-lubricated bearings tested for over 5000 hours with nitrate salt at 565 °C.

The molten salt pump and valve (P&V) test loops at Sandia National Laboratories (SNL) National Solar Thermal Test Facility (NSTTF) operated between Jan. 1988 and Oct. 1990. The purpose of the P&V test was to demonstrate the performance, reliability, and service life of full-scale hot and cold salt pumps and valves for use in commercial central receiver solar power plants. The P&V test hardware consists of two pumped loops; the “Hot Loop” to simulate the hot (565°C) side of the receiver and the “Cold Loop” to simulate the receiver’s cold (285°C) side. Each loop contains a pump and five valves sized to be representative of a conceptual 60-MWe commercial solar power plant design. The hot loop accumulated over 6700 hours of operation and the cold loop over 2500 hours of operation. This project has demonstrated that standard commercial scale pump and valve designs will work in molten salt. The test also exposed some pitfalls that must be avoided in specifying such equipment. Although certainly not all of the pitfalls were discovered, careful design and specification should result in reliable or at least workable equipment.

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