Objectives
General Purpose
The general goal of COCO is to avoid or mitigate high temperature corrosion of candidate low cost material systems for new generation Brayton cycle CSPs.
COCO’s hypotheses are based on developing stable, lower cost and less corrosive molten salt mixtures and using coatings on mechanically stable stainless steels to replace Ni base materials.
Salts
Possible uses of new developments of the different mixtures with molten salt for solar thermal plants (CSP).
Molten salt
The use of a mixture of molten salt based on ternary and quaternary carbonate and/or chloride will potentially allow temperatures above 700°C, which would significantly increase the Rankine cycle efficiency currently implemented in CSP plants and would also meet some of the requirements for a new generation of turbines based on the Brayton cycle.
Coatings
Coatings based on the application of slurry paints are currently developed for s-CO2 and molten salt corrosion protection. This coating process is appropriate for solar plant components including tanks and the inner surfaces of tubes and pipes, being one of the lowest costs known coating process as it does not require sophisticated and expensive equipment.
Fe and Ni aluminide phases developed on austenitic steels are very resistant to molten carbonates and also to CO2 oxidation and carburization. Extensive testing is however needed at 700°C and under both the newly optimized salt mixtures and s-CO2.
Corrosive Reduction
The use of coatings has proven in several industrial sectors to be an excellent option for prevent/reduce corrosive processes at high temperatures for many years.
Lower Cost
The use of coatings on lower cost materials, not only reduces capital expenditure (CAPEX) but also O&M costs (OPEX), as the coated elements usually exhibit longer lives..
Design
The coatings can be designed and adapted to the specific corrosive behavior of salts newly developed without having to redesign the alloys and without affecting their mechanical properties.