Page 272 - Design of Solar Thermal Power Plants

254 4. DESIGN OF THE CONCENTRATION SYSTEM

FIGURE 4.20 Temperature-monitoring picture of receiver at the Dahan power plant [20].

5. In addition to measurement by thermocouple array, the heat-
absorbing surface’s temperature can be measured by noncontact
methods, such as an infrared camera. When an infrared camera is
used, attention must be paid to calibrating it with the receiver in
advance. This is because thermal emittance of a solid surface is
relevant to the thermophysical properties of the surface, and these
properties are relevant to temperature. Normally, thermal emittance
increases along with temperature increases on the surfaces of
objects. Fig. 4.20 shows the temperature-monitoring picture of a
running receiver in the Dahan power plant.
6. If the heat-transfer fluid inside the receiver is cut off due to an event
such as power-off of the entire field, a pump fault, or pipeline
leakage, the heliostat field must be stopped. Such a stoppage
instruction is collected by the flowmeter on the incoming fluid main
pipeline or the tower’s drum level gauge and sent to the solar field
host computer; afterward, the host computer gives instructions to
the heliostat to return to their original positions until the fluid loop
fault is eliminated. To avoid false alarms, two flowmeters should be
placed in series in the main loop, which is better done at the receiver
inlet. Also, the suggested quantity for the drum level gauge is
“two.”
7. For an air receiver, the working status of the heliostat field can be
detected using receiver airflow rate or heat absorber surface
temperature. Due to the high temperature of heat coming from the
air receiver, temperature measurement becomes extremely difficult,
especially in the event of an accident or a failure. It is normally