Solar Tower molten salt

Dear all

after simulating with SAM a couple of CSP power plants using an Air Cooled Condenser we have a question: Following the advices of the NREL SAM technical manual (June 2011) the ITD- Initial Temperature Difference- in combination with the ambient temperature at design is defining the back pressure of the steam turbine at design conditions. The decrease of ITD for a given ambient temperature lowers the back pressure of the steam turbine at the design point. The air mass flow and hence the auxiliary consumption is higher for lower ITDs.

For our design case: Ambient temperature- 32°C- and the ITD at 16 °C SAM is calculating a gross electric output of approx. 1,090,500 MWh/a. Changing the ITD to 27 °C results in a gross electric output of approx. 1,111,000 MWh/a.
We expected a different behavior of the ACC for an increased ITD and the results did even more surprise us when we looked at the time series: For the case of the increased ITD the gross electric output was always above the design case with the lower ITD.
The condensate pressure was nearly always higher in case of the higher ITD (which matched our expectations) then for the lower ITD (down to the lowest allowed condensate pressure).

We would appreciate it if anybody could give us a good explanation and perhaps help us regarding the correct design of the ACC with SAM.

Thank you very much in advance.

Best regards.

Hello Philipp,

I'm not sure if this answers your question, but if you try to evaluate the influence of ACC size on annual performance you need to adjust the cycle efficiency as well. If you chose a higher ITD (and thus a higher design backpressure of the turbine) your cycle efficiency will decrease. Only changing ITD does not cover the whole effect of ACC size. If you include the lower cycle efficiency in SAM you may get the expected lower annual output as a result.
Does this help?

Regards
Timo

Philipp,

Timo is right. When you adjust the ITD, you are telling the model the conditions under which the system will achieve the thermal efficiency that you've specified. If you increase the ITD, you should also modify the thermal efficiency (and/or the design ambient temperature) to accurately describe the design-point behavior of the system. The off-design penalty in the modified system will follow once the parameters are corrected.

Best,
Mike

 
In a solar power tower plant. How can I know the pressure and temperature coming out of the low pressure turbine (inlet to the condenser) ?

Hi Alasadi,

SAM's Molten Salt Power Tower model reports the "PC condenser water outlet temperature" and "PC condensing pressure". It does not report metrics for the condenser inlet.

Best regards,
Paul.

Hi Paul.
Thanks for the quick response.
Is there another way to know the pressure and temperature entering the condenser in the SAM ?

Best regards,
Alasadi