Summer time is propane time. From backyard barbecues to recreational vehicles to lakeside cottages, propane tanks are everywhere…and yet, we hardly give this remarkable fuel a thought.
I’m here to change that.
In Canada, about 80 percent of propane is derived through natural gas processing, while the refining of crude oil provides the remaining 20 percent.
Natural gas, as used by consumers, is primarily methane, but the gas that comes out of the ground contains ethane, butane, the pentanes and propane–plus water vapor, hydrogen sulfide, carbon dioxide, helium, nitrogen, and many other compounds.
Gas from oil wells is often dissolved in oil, which must be removed (usually by the simple method of putting the oil in a closed tank and letting gravity do the job). Sometimes this gets rid of the water, too; other times a dehydrating agent is used, typically glycol.
Only then can the natural gas liquids (NGLs), which include propane, be removed. In one method, an “absorbing oil,” which has an affinity for the NGLs, is brought into contact with the natural gas, then extracted and boiled in a still. Since the absorbing oil boils at a lower temperature than any of the NGLs, it boils away and leaves the NGLs behind. In the cryogenic expansion process, the natural gas stream is chilled to around -85 C, at which point methane is still a gas, but the NGLs become liquid.
A similar technique is used to separate the various NGLs. The NGL mixture is heated in stages to the boiling points of the various NGLs. Ethane boils away first, then propane (at -42 C), then butane. Each can be collected as it boils into gas; the final remaining liquid consists only of pentanes.
Pure propane is non-toxic, pretty much odorless (the odor associated with it is added, just like scent is added to natural gas, to make it easier to detect leaks) and, of course, flammable. It’s heavier than air, so if a leak occurs in an enclosed space, the propane will pool at the bottom of the space, forming a highly flammable propane/air mixture. That’s one reason propane should only be burned with plenty of ventilation.
The second is that it requires a large amount of air–at a ratio of 23.5 to 1–to burn propane properly. Propane normally burns very cleanly, producing mainly carbon dioxide and water vapor. But without enough oxygen, it may burn incompletely, producing poisonous carbon monoxide.
Propane is usually distributed to consumers in metal cylinders. When a propane tank is “full,” it’s actually only 80 percent full–that remaining 20 percent is important because, if the temperature rises, the liquid propane will expand, and it needs space to do so. If it doesn’t have enough space, then the relief valve on the tank will open, venting propane vapour, potentially hazardous if the tank is in an enclosed space. (That’s also why propane tanks are usually painted white or silver–those colors reflect heat, keeping the interior cool. Repainting a propane tank a dark color is a bad idea.)
And what can propane be used for? Pretty much everything.
Cars, trucks and tractors–anything with a gasoline engine–can be fairly easily converted to run on propane (although currently only about two percent of the cars in Canada run on propane or liquid petroleum gas) Propane can, of course, be used for cooking. It’s by far the fuel of choice for barbecuing, there are also propane gas ovens and propane-fueled range burners and cook tops. Propane can dry your clothes–and do it better, faster, and for less money than electric models. It can heat your home or cottage–or at least heat the water. It can run a refrigerator (one with no moving parts!). It can even be used to generate electricity.
In fact, it’s possible to create a home or cottage that uses propane for heating, cooking, clothes drying and water heating, and even uses a propane-operated electric generating system to provide any electrical needs. As long as the big underground propane tank is kept supplied, the house doesn’t need anything from any outside network (except the Internet–so far, propane cannot be used to deliver high-speed access).
Haven’t been giving your propane tanks a second thought? Now maybe you will!
But a word of warning: don’t spend too much time in propane contemplation.
Your burgers may burn.
