Absorptive Coatings for High Temperature Solar Energy Application

Photo of Jeff Sullivan, Matt Kijowski, Ron Hill (sponsor), Brad Parro Students: Jeff Sullivan, Matt Kijowski, Ron Hill (sponsor), Brad Parro

Sponsor: Chevron

Date: Spring 2011

Requirements:
The four main criteria in order of importance as necessitated by Chevron for each of the coatings are absorptivity, applicability, environmental impact, and cost. Absorptivity is the primary criterion of this project since the higher the absorptivity a coating has, the more effective it will be a converting the sun's energy into useful heat. The coating must also be easy to apply. The receiver is located at the top of the tower, and therefore complicated coating processes would be infeasible without shutting down the entire power plant. Coatings contain many volatile compounds and off-gas under high temperature situations. For this reason, the environmental impact of each coating is also very important. Lastly, cost must be evaluated for each of the coatings. The coatings must withstand a surface temperature of 600°F.

Problem:
Solar power tower receivers, which are used to collect heat and boil high pressure water, receive concentrated solar energy on the order of 700 times insipient solar radiation. The steam that is created is then used to drive a steam turbine power plant. The receiver on a power tower operates under extreme conditions, requiring the use of a special coating on the receiver. The team was tasked with researching, testing, and ranking three to five coatings for solar power tower application. Chevron emphasized the importance of the absorptivity of the coatings in the infrared spectrum.

Solution:
Through research, the team selected four different coatings:
•Krylon 1602 Ultra Flat Black
•Aervoe Zynolyte Hi Temp Paint
•Solec Solkote HI/SORB II
•Lord Aeroglaze Z306
The team determined that the best method of testing the overall absorptivity of each coating was through a heat exchanger experimental setup using a radiant heater. Inlet and outlet temperature measurements were used to determine the temperature difference, which can be used to determine the relative absorptivity of each coating. Evaluation of the four selection criteria indicates that the Solkote HI/SORB II coating performs best. The team recommends Chevron conduct future experimentation at temperatures closer to those experienced in the actual setting.

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