High Temp Water Heating System (over 500F)

[MechEng Dan]

I am working on a project that will include a high temperature water closed loop to perform heating. The design temperature and pressure is currently established at 2,500 psig / 650 degF. (This high temperature is driven by the process that is being heated.) I have found various resources that discuss up to 440 deg F, but nothing up to the aforementioned pressure/temperature. In particular, the issue is managing the expansion/pressurization of the fluid loop via N2.
If anyone could point to any references or share past project experience, it would be much appreciated.

 

[georgeverghese]

Agreed, does look unusual to go with hot water for say 600degF heating application - typically one would select one of the many hot oils (mineral or synthetic) available to avoid high design pressures. Liquid phase heat transfer coeff is of course better with water, but overall system costs should be lower with a hot oil system with a much lower design pressure.
It may be possible to manage expansion drum blanketing with HP N2 bottles at 3000psig, provided one can size the drum and set the drum levels so that level fluctuations in the drum ( due to thermal expansion of the entire system contents) can be kept lower than the setting of the drum outbreathing PCV.

 

[quark]

I agree with above post. Vapour pressure of Dowtherm G at 650F is about 40psig. The main problem is the specific heat is 3 times lesser and density is 30% more. So, you may need approximately 4 times higher mass flow rates.

 

[moltenmetal]

Using water up at these pressures is dangerous but feasible. Not sure why you're bothering to suppress vaporization by using a nitrogen pad- it doesn't make the system any safer and will actually reduce your ability to transfer heat to/from whatever you're using the hot water for.