Using sCO2 as a heat transfer fluid in SAM

Dear Paul,

I sent this question to the contacts email by mistake but now have the right place I think.

In SAM 'HTF type - edit materials properties' I have put in values for supercritical CO2 but the energy output is always negative.

The data file for sCO2 looks quite similar (see attached) to the sam-htf-property-tables file that I found on one of your posts except that sCO2 density is much less than the other HTFs listed.

Do you have any suggestions on what to do?

best regards

John

Dear John,
The default assumptions in SAM's CSP models are for higher-density heat transfer fluids like the oils and molten salt that are available in the default HTF list. If you use a lower-density HTF like super-critical carbon dioxide (sCO2) without changing any other design parameters, the effect will be to increase the flow capacitance. That, in turn, requires a higher mass flow rate to maintain the design temperatures. The higher flow rate is probably resulting in large pressure drops and parasitic pumping loads that might be higher than the system's output and causing the negative output values you observed.
To resolve that issue, you could reduce the total amount of flux on the flow path by reducing the length of the path. For the parabolic trough model, you can do that by reducing the number of collectors per loop.
There are other issues that make modeling a sCO2 HTF in SAM questionable. SAM models pumping parasitic losses assuming that the HTF is an incompressible fluid. Because sCO2 is compressible, the pumping parasitic losses it calculates will be inaccurate.
Because sCO2 requires high pressures (>=80 bar), the receiver tubes, header piping and heat exchangers need to be thicker than for traditional HTF designs. You will need to adjust those design parameters and costs.
Finally, the tower model assumes that the system uses the same HTF in the field and as the storage fluid. If you model a tower system with storage and sCO2 as the HTF, the storage model will be for a high-pressure sCO2 thermal storage system.
Best regards,

Paul.

Dear Paul,

Thanks for your quick reply

John