[Translate to Chinese:] Pumping Glycol
[Translate to Chinese:]
Glycol is a thin, clear, colourless and odour-free liquid. Two common types are Ethylene Glycol and Propylene Glycol.
When mixed with water, the solution has excellent properties for heat/cooling as the freezing point lowers and the boiling point rises. The S.G. and viscosity remains low, the fluid is not corrosive or flammable however Ethylene Glycol is toxic when inhaled and/or swallowed.
Glycol oxidizes on contact with air, forming compounds and acids. These reactions are accelerated at higher temperature applications, though stabilizers can be added to the solution.
Glycol mixtures are available in different dilutions under different brand names from established chemical manufacturers. They are commonly sold in plastic drums/containers and can be stored easily at room temperature.
It is recommended they be kept air-tight and added to a system. The Glycol will take on moisture easily so storing in a dry, ambient, preferably dark room (if the container is clear) is recommended.
Glycol fluid has excellent heat retention and maintains a flowable viscosity without forming crystals at low temperatures where water would freeze, it is typically used for maintaining the working temperature of a system where external conditions may differ.
Examples of this may be as an ingredient in anti-freeze chemicals to maintain the workings of an engine or mechanical system in cold temperatures or cooling a room or system.
Where food, cosmetic or pharmaceutical preparations are being processed, it is crucial to use Propylene Glycol as this has a very low toxicity.
Propylene Glycol can be used in products in food ingredients, pharmaceuticals and cosmetics for its stabilizer properties and as a solvent. More recently it is contained within the liquid added to e-cigarettes.
Another major application for Glycol is as an ingredient in the production of plastics such as polyurethane and polyethylene terephthalate.
Glycol is also used as an ingredient in varnish and polishes, paints and inks, cleaning products and adhesives.
Thanks to its capacity to absorb moisture easily it is injected at high pressure during the processing of natural gas to remove water vapour.
The main consideration for the pumping of Glycol is the temperature, flow rate and pressure.
The fluid is not corrosive so almost all materials are chemically compatible; it is temperature that is the limiting factor in selection.
Where the temperature is not dangerous and the pressure is low, a mechanical shaft seal centrifugal pump is most common. Due to the nature of a mechanically sealed pump, leaks are a risk.
Where pressures and temperatures are higher it strongly recommended that a mag drive pump is used.
As the temperature is raised the viscosity of the Glycol mix becomes lower and the fluid becomes more ‘searching’, leaving mechanical seals more vulnerable.
A mag drive centrifugal pump uses an o-ring sealing system to contain the fluid so there is no abrasive degradation from moving parts.
Viton, PTFE and Buna-N are typically ok for high temperatures as is a cast iron or stainless steel construction.
Where the S.G. or is higher the impeller may need trimming to accommodate.
Glycol mixtures eventually degrade with impurities, particularly at higher temperatures so to prevent corrosion and other reactions it is recommended for circulation applications to inspect the internals of the pump for any signs of corrosion from new compounds.