Pressure Autoclave Vent Gas Flowrate Calculation

[groags]

Hi,
I am trying to determine the expected vent gas flowrates for a Nickel Laterite pressure leaching autoclave. The current pressure control valve is inoperable, as it is too large and vents too much gas when open, making pressure control difficult.

I have determined that N2 is negligible in the headspace of the autoclave and that the vent gas is water vapour and CO2. The expected flowrates of CO2 I can get from knowing the % of C in feed and the autoclave throughput. I have calulated smaller and more accurate CO2 amounts, however determining the amount of H20 is more difficult.

I have calculated the vapour pressure inside the autoclave for different temperatures based on salts in the water and have used this to determine the mol fraction of water in the vent gas at certain autoclave gauge pressures.

This however gives me an extremely large number when converting volume of water to mass of water using the water vapour SG at temperature of 250 degrees C and a gauge pressure of 4100 kPa. I end up with tons per hour when the original valve was sized for kg per hour.

I have tried using PV=nRT with the appropriate numbers but this also gives me a very large number for water vapour. Perhaps I am missing something but does anybody know how to accurately caculate an expected vent gas flowrate in this scenario. I would appreciate the help.

Cheers,
Ronan

 

[cawse001]

Found this post while searching for something else. You may have resolved the issue yourself.

In normal operation you are operating with an overpressure, ie above the saturation pressure for the operating temperature. This prevents the autoclave contents boiling.

Thus, in normal operation the need to vent is driven by the amount of non-condensable gas evolved (CO2 in this case).

The vent composition is then driven by the partial pressures of CO2 and H2O.

Depending on your C content in the ore you will have tonnes per hour, rather than kilograms.

Cheers