The Effect of Cold Temperatures on Ethanol Gas Tanks

The Effect of Cold Temperatures on Ethanol Gas Tanks

The ethanol in a compressed ethanol gas tank will condense into a liquid state if the tank gets too cold.  The temperature at which this happens depends on the alcohol concentration and the pressure.  In general, temperatures around freezing will cause the ethanol to condense, changing from a gas to a liquid.  As the tank warms up the liquid ethanol will change back to a gas.

However, if the operator were to use the tank before the tank has warmed and the liquid ethanol has changed to gas, the proportion of ethanol and nitrogen will be permanently changed.  The actual ethanol concentration of the tank will no longer match the ethanol concentration stated on the label of the tank. 

1. The initial use of the cold tank will produce lower alcohol concentrations because there will be a higher proportion of nitrogen (nitrogen is the other gas in an ethanol gas tank) and a lower proportion of ethanol.  The condensed ethanol, now in a liquid state, will not be present in the gas that is dispensed.  Nitrogen has a much lower dew point than ethanol, and so will remain in a gaseous state.
2. Once the tank warms and the liquid ethanol returns to gas, the tank will always give a higher alcohol concentration because the proportion of nitrogen to ethanol has changed – there is now less nitrogen and more ethanol than in the original mixture.

The ethanol concentration of a tank that is exposed to very cold temperatures and is allowed to come back to a warmer temperature before being used – before any gas is expelled – will not be changed and the tank can be relied upon to be an accurate calibration standard.