HTF expansion tank 2

[flinana]

I need you advice regarding the use of the expansion tank in a thermosolar power plant.
We are using the expansion tank as a gas eliminator, i.e we recirculate all the HTF through the tank so as to eliminate possible accumulated gases. The thing is that speaking to a colleague from another project he mentioned that using it as we are caused N2 to be absorbed by the system generating therefore more gases.

I have also noticed that it si no better since it cools the oil down since it has to recirculate there and back. W
Shouldnt we use it as an "expansion vessel" as it is supposed to be?

 

[ione]

I think the expansion tank is an indispensable item as it compensates the fluid volume expansion, related to temperature increase, thus preventing pressure increase. Use a closed expansion vessel with a separation membrane to prevent contact between atmosphere and process fluid. Put air/gas venting valves in the highest point of the line (gases will migrate towards this zone).

 

[flinana]

thanks ione, We do have mvalves in all high points, however lots of air bubbles are generated. Pressure is pretty much stable in HTF system.

 

[ione]

Traditional air vent valves are used to eliminate air at the plant filling and start-up phase. Then they should be closed to avoid heating fluid leakages (valves have usually to be rated for temperature up to 200 °C and 10 barg pressure).
To get a deeper action during working phase it could be opportune to fit an automatic deareator in the return line, downstream the heat exchanger, in the lowest point of the circuit.

To give you a more precise idea about what I am referring to, take a glance at the link below.

http://www.caleffi.us/en_US/Technical_brochures/01060/01060.pdf

 

[flinana]

thanks. We reach temperaures up to 400ºC.

 

[ione]

Oh, are you then talking about a concentrating solar plant?

http://www.endress.com/eh/central/i.../$FILE/Concentrating_Solar_Power_Enlarged.pdf

 

[flinana]

Afirmative. 50 MW CSP power plant

 

[ione]

Well, I have to admit CSP is not my field of expertise, so handle with care.
I think expansion vessel and degasser should be two separated units. The aim of a degassing is that of reducing, throughout a thermo-physical process, the amount of dissolved O2 and CO2 in the steam generator feedwater to limits that do not jeopardize the generator’s life. If feedwater is kept in contact with external atmosphere the degassing effect will be partially nullified.

 

[flinana]

We do have a dearator for the steam cycle. However I am talking about the expansion vessel for HTF oil

 

[unclesyd]

We use Therminol HTF in large synthetic fiber plant for process heating. I would check with your supplier of the HTF and get their design guide. I would strongly advise that you get someone with specific expertise with HTF, especially if you are vaporizing it.

We vaporize Therminol and use only the latent heat of The HTF to heat our process. We return condensate to a feed tank system for the vaporizers. We handle non-condensables by using what we call TVA (Therminol Vent Accumulator) on each line and equipment piece hooked to a vacuum system to remove the non-condensables. The system is setup to where any HTF taken off by the TVA is condensed and returned to condensate system. The condensate receivers and feed tanks also have a similar venting system for non-condensables.

http://www.therminol.com/pages/