DYNAMIC STABILITY OF THE S-CO2 ENERGY CONVERSION CYCLE AS AFFECTED BY SENSOR RESPONSE TIME

摘要

The effect of sensor response time on the regulation of important process variables in the split-flow recompression supercritical carbon-dioxide Brayton power cycle was investigated through dynamic simulations. The temperature at the outlet of the hot-side of the precooler is a measured input to a controller that acts to maintain a setpoint temperature at this location during operational transients. The hypothesis was that a measurement lag in the response of this sensor to a change in the underlying process variable could induce an oscillatory behavior in the controller. The cycle response was investigated for change in electric load under conditions that might be expected of an electric grid demand request for a base-load commercial nuclear plant and for an envisioned heat-following solar-energy conversion plant. An assumed measurement response time of eight seconds that reflects operating experience in commercial pressurized water reactors for a degraded thermowell mounted resistance temperature detector resulted in temperature oscillations across the cycle. The largest oscillations occurred at the inlet to the high-temperature recuperator with a peak-to-peak amplitude of ten degrees Celsius and a period of ten seconds. The significance of temperature oscillations induced by sensor response time needs to be evaluated in light of plant duty-cycle transients and the effect of temperature cycling on the structural integrity of components. It is noted that a manufacturer of printed circuit heat exchangers suggests that controller-induced oscillations be avoided to prevent material fatigue due to thermal cycling.