Fluids & Treatment -Glycols and Alcohols

 

The solutions of alcohols in water - methanol and ethanol waters - have both good and bad properties for circulating fluid use. Methanol water has a low frictional pressure drop and a relatively high heat transfer coefficient. However, it is highly volatile, highly flammable, and highly toxic.

Ethanol waters are less toxic and less flammable than methanol waters, but are still highly flammable. They also are more viscous, and have a larger pressure drop and lower heat transfer. Corrosion inhibitors can be added to make them non-corrosive. Ethanol is more expensive than methanol but less expensive than the ethylene glycol solutions.

Ethylene glycol in water is a common and often favorable alternative. It offers low corrosivity, volatility and flammability. Properly prepared and inhibited, it is relatively non-corrosive. It is the most common antifreeze for automotive use.

The main disadvantages of ethylene glycol are:

  1. They are somewhat toxic and must be stored and handled with care.
  2. The viscosity becomes high at low temperatures.
  3. They have a definite life and the pH should be checked yearly; and spent solution replaced.

Propylene glycol solution is an alternative with the only true advantage of being less toxic than ethylene glycol. Below about a 20°F freezing point, the viscosity gets excessively high, resulting in high pumping costs.


Glycols and alcohols are available as concentrated liquids, salts as granular or powdered solids, and potassium acetate as a 50 percent solution. The brine is mixed, on- or off-site, with water prior to being charged into the piping system.

The quality of the water used with the glycols is important. It must be "soft" and have a low concentration of chloride and sulfate ions. Factory inhibited ethylene and propylene glycol solutions are sold by manufacturers.