Propane as an Energy Source- Part 1, by JB


Propane, or liquefied petroleum gas (LPG), is an excellent energy source for several reasons. It stores easily and has a great shelf life. It’s portable and can be adapted for use in internal combustion engines. It can also be used as a refrigerant, and in some situations a viable weapon. Long after the grid goes kaput and gasoline has turned to varnish, propane will still be usable.

Basics of Propane

There are hundreds of thousands, if not millions, of full grill bottles stacked in exchange racks throughout the country. In addition, there’s a multitude of medium and high volume tanks scattered about where one can find propane. Super large tanks are used at industrial sites to supply large volumes of gas for manufacturing. Some municipalities use blended propane-air for large-scale distribution systems, which supply entire cities, and therefore require massive amounts of propane storage. With the right tools and the right knowledge, tapping into these resources in a TEOTWAWKI situation can be very advantageous.

To understand the true benefits of using propane, we must know a few basic fundamentals about it. As with any flammable, explosive gas, it is very dangerous and will kill you if you don’t treat it correctly and safely. It is equally or more dangerous than gasoline, and only those with knowledge and experience should handle any propane equipment.

Propane is an odorless, non-poisonous, asphyxiant gas and can contain some butane, propylene, and other compounds. In order to recognize this dangerous gas, ethyl mercaptan is added, giving it the pungent rotten egg smell. In a gaseous form, it has a specific gravity (density) of 1.52, which makes it heavier than air and creates a hazard. Any leaking or expelled propane gas will sink and accumulate on the ground and in low areas and poses a risk of fire or explosion. For this reason, never store propane indoors or in an enclosed space.

A gallon of liquid propane weighs approximately 4.2 pounds, which makes it lighter than water. Each gallon contains around 91,500 BTUs and will produce 36 cubic feet of gas, with each cubic foot of gas containing 2,516 BTUs. Liquid propane boils at -44 degrees Fahrenheit; therefore, it is classified as highly volatile, and liquid propane against the skin will freeze tissue immediately.

As propane boils into vapor, it will refrigerate as it absorbs latent heat from the container. You can see this effect on a grill bottle where frost or condensation has accumulated below the liquid line during use. This property also makes propane an effective refrigerant.

Propane has a higher BTU content per cubic foot than natural gas at 2516 compared to 1030. What this shows is that propane has twice the energy capacity per cubic foot than natural gas. This is also why there is a difference between natural gas and propane appliances. Neither gas will work with the other without some intervention. We’ll talk more about this later.

Storage Tanks and Transfer of Propane

Typical LP tank pressure can dwell anywhere between 100-200psi, depending on ambient temperature. The colder it gets, the lower the pressure. Straight tank pressure should never be used to operate anything unless you want to die in a huge, deadly fireball while incinerating everything around you. Typical home supply LP tanks use a regulator at the tank to reduce the pressure to 1 psi or lower to the home. Home LP appliances (and most grills) operate with pressures around 10 to 11 inches of water column or (WC). 1”WC= ~.036psi and is achieved by a secondary regulator on the appliance. Grill regulators reduce gas from tank pressure to burner pressure in one step. Very little pressure is needed for normal appliance combustion.

Liquid propane is stored in pressurized tanks, such as the small one-pound Coleman stove bottles*, 20-lb to 100-lb portable bottles, 500 gallon home tanks, or a 60,000 gallon industrial tank. For the most part, the 40- to 100-lb cylinders all use the same type of valve, but newer ones seem to be equipped with the OPD valve. Due to lack of proper training and people overfilling 20-lb grill bottles, a new OPD (overfill protection device) valve was mandated on all grill bottles. It closes the inlet via an internal float when the liquid level reaches its limit. They can be identified by “OPD” stamped into the valve knob. Older tanks will have the old valves with a bleeder port on the side of the valve head and do not have the external acme threads. These valves will not accept the newer grill regulators, as they require the external threads exclusively. All valve types are equipped with the standard left hand internal threads.

Generally home supply tanks range from 250 to 1500 gallons. They don’t have any means to refill portable tanks, and getting any liquid out requires special equipment. As with all LP tanks vapor head space is necessary, so they are only filled to a maximum of 80-85% liquid capacity. Home supply tanks can be either under or above ground.

The larger, industrial-sized tanks are typically used to supply delivery trucks, refill bottles, and/or supply an industrial plant requiring large amounts of fuel for furnaces or refining. They’re typically mounted above ground on concrete piers so that the bottom of the tank can be piped for liquid transfer with a common manifold.

Industrial systems are equipped with a bottle fill/transfer station where forklift or portable bottles can be refilled and this provides a means to fill the larger tanks via rail car or tanker truck. The fill station is similar to what you see near the tank at the local hardware store that refills your grill bottles. The fill station uses an electric pump to pump liquid from the bottom of the supply tank into the bottle. Industrial stations will have another pump to feed tanker liquid into the storage tanks.

I have a quick word on forklift tanks: They are 33-lb tanks specifically designed to supply liquid propane and must be properly mounted on the equipment to operate correctly. They do not have the same fittings seen on portable tanks and are not compatible with any LP home appliance, as they do not supply vapor. In addition, most vehicle applications use liquid propane exclusively.

The standard components of a tank fill station begin with a pump manifold assembly. It is typically connected to a valve on the bottom of the main tank(s) for liquid transfer. The manifold includes a liquid bypass line for when the fill line valve is closed, preventing the pump from dead-heading. Connected to the pump outlet is a wye-strainer then a hose assembly consisting of a ball valve, liquid unloading valve, quick connection adapter for Acme threads (forklift), and a tank fill adapter (fits the LH internal threads on the cylinder valve).

There are generally two methods to filling a non-OPD portable bottle– either by weight or volume. Since a 20-lb tank should only be filled to 85% max, you would stop at 4.2 gallons if metered and 17.8lbs if using a scale. (This weight does not include the tank weight.) A 40-lb cylinder will hold 34lbs of propane or 8.1 gallons and so on. Weight is the better method in that it accounts for any remaining liquid still in the tank once tank weight is taken into account.

If neither a scale or a meter is available, there is another method used to ensure you don’t overfill the tank. The same old way before OPD came along, and to me it’s more reliable than either of the above. On the side of the valve head, there is a small bleeder port requiring a flat head screwdriver or a small crescent wrench. The bleeder port is cracked open just enough to allow gas to vent out during filling. There is a small tube from the port extending down into the tank that ends at the proper liquid level. Liquid will begin to spew from the port once the proper level is reached, indicating the tank is full.

Please note, an overfilled tank is dangerous to use. It will expel liquid instead of gas and cause a fire hazard you want to avoid.

The process for filling a portable bottle begins with connecting the fill hose and adapter to the tank valve. This connection is a left-handed thread. Once secured, the bottle valve is fully opened and then the fill hose ball valve is opened. At this point, you will hear the flow of liquid entering the bottle. The fill station liquid pump is turned on to speed up the process, and the bleeder port is cracked opened if used. Note: The bottle will eventually fill without the assistance of the pump but will take much longer.

If it is an OPD valve tank, the flow into the tank will shut off and you’ll hear the pump strain a little as it starts bypassing. If you are filling a bleeder type valve, liquid will begin to discharge from the bleeder port forming large frosty accumulations. Both of these conditions indicate the tank is full.

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