Storage Tanks and Transfer of Propane (continued)
Once the tank is full, the fill hose ball valve is closed (stopping flow into the tank), the tank bleeder is closed (if used), the pump is shut off, and then the tank valve closed, in that order. Double check that the hose and tank valves are closed. The small unloader valve between the hose ball valve and tank is opened to drain the liquid trapped between the two, so the hose adapter can be safely disconnected from the tank. Failing to bleed the liquid trapped between the tank and ball valve can cause injury as liquid can be vented towards your face when the tank adapter is unscrewed. Remember that liquid propane will freeze skin upon contact, so wear gloves and safety glasses.
Please note: Not anyone and everyone should attempt to fill a cylinder without proper instruction and training. Improper actions could result in serious injury, death, or destruction of property.
Beware that during the filling and disconnect process, propane vapors will be present on the ground around you. Be extra cautious to insure that there are no possible ignition sources nearby or downwind. This is a very real and dangerous fire/explosion hazard. The electrical pump and connections are explosion proof and not considered an ignition source.
Vaporization
With a typical gas appliance, the moment you open the burner valve/knob, pressure drops in the tank and the liquid begins to vaporize. The gas vapor travels through the regulator, line, burner valve, and to the burner orifice. As gas passes through the orifice into the burner venturi, it will pull in (through openings on the burner tube) ambient air that mixes with the gas, creating a combustible mixture. That mixture then travels to the burner where it burns once ignited. The intensity of the flame is controlled by the valve, which increases or decreases the volume of gas, and the quality of the flame is dependent on the air adjustment.
In order for any propane appliance to work, vaporization must occur and the vaporization rate of the supply tank must be ample enough to deliver the required amount of gas. A 20-lb propane tank does not have the vaporization capacity to fuel a residential furnace. The furnace requires much more propane vapor than a single cylinder can deliver, as the liquid in the cylinder can’t vaporize fast enough to satisfy the demand of the load. Ambient temperatures will affect this as well, and the colder the temperature, the lower the vaporization rate.
For example, I adapted a 1-lb Coleman bottle to my portable water heater to save having to carry the larger tank to the hunting cabin. It works great for intermittent use. On a cold day, when we used the water heater continuously for several minutes to fill a large drum, it quit working. One look at the frosted tank and hose told me what I failed to consider. There was insufficient vaporization capacity with the little tank for the atmospheric conditions at the time. Back to the bigger tank we went, and the problem was solved.
The vaporization rate is related to the tank surface area in contact with the liquid, as this is where the heat is required to boil or vaporize. As the tank level decreases, so does the vaporization rate. There are charts available on the web showing the rates based on pounds of liquid and ambient temperature. For instance, 20lbs of propane in a tank at 20?F will supply 51,000 BTUs per hour demand. A double burner Mr. Heater running at maximum will burn 30,000BTUs per hour.
As higher demands require more vapor, the refrigeration effect of vaporization will cool the container to the point that it loses the ability to vaporize. When this happens, pressure will drop and the appliance will fail to operate properly if at all. This could easily happen in temps below freezing, as we are relying on the ambient temperature to boil or vaporize our liquid propane. Higher ambient temps = higher vaporization rates. Remember, LP boils at -44F, so if it’s -45F outside, you could pour liquid propane into a cup and it would sit there and never vaporize.
To compensate for the refrigeration effects of vaporization and increase the vaporization rate, additional heat or more surface area must be introduced to meet the higher demand and offset the refrigeration. This could simply be placing the tank in sunshine, connecting several tanks together with a common manifold, or using a larger tank with more surface area. For greater demands, the gas industry provides various types of liquid propane vaporizers with output ranges from a few gallons per hour to thousands. They are basically heat exchangers that use a secondary heat source to offset the refrigeration of vaporization.
There are several types of vaporizers. The most common for low volumes are the electric, water bath, and direct fired. The electric vaporizer uses electrical heating elements, similar to what is used on a water heater, to heat a water/glycol solution. Inside the glycol tank is a coil of tubing similar to that of a liquor still. Liquid propane enters in one end and vapor exits the other.
Similarly, the water bath does the same thing but on a larger scale. It uses gas from the original supply to operate a burner fired into a tube that heats a water/glycol bath. On the other end of the unit the liquid propane line enters the cabinet to a serpentine heat exchanger, usually constructed with schedule 80 pipe, where it vaporizes. The burner is typically a standing pilot type of enough BTU to maintain the bath temp at 180? under full capacity.
From Natural Gas to Propane Conversion
Now that there is sufficient propane vapor to sustain higher demand, it can be used to supply a number of homes or a small community with gas. So, what if this group of homes were previously using natural gas that was no longer available? There is a solution to that, and it’s possible due to the higher BTU content of propane versus natural gas.
Before answering that, we should know that all gas appliances use certain orifices based on the gas they are intended for. Natural gas orifices are much larger diameter than LP, because you need to burn almost twice the volume of gas to achieve the same BTU’s. Likewise, you only need half the LP gas to match the BTU’s of natural gas; therefore, the orifice size is much smaller for LP appliances. You can convert a natural gas appliance to propane simply by changing the orifices. This is why many gas appliance manufacturers include both orifices.
Let’s go back to the difference in BTU content between the gasses. There is an advantage with LP in that it can be diluted to a lower BTU content to match that of natural gas. This is achieved with a gas-air blender. The blender mixes air with the propane gas to lower the specific gravity to just above that of natural gas or to approximately 1400 BTU/ft3. This mixture will work in natural gas appliances without changing the orifices. If you are on natural gas now, the chances are that you have used blended gas during peak demand in the winter, as this is a common practice.
Blenders are used for municipal distribution systems of large scales. Typically, we, as preppers, wouldn’t need a blender. However, if you are planning to develop your own Bartertown, the technology is out there.
From a retreat perspective where you may have several groups in one place, the demand for gas could be more than what a few grill bottles can provide. In a situation such as this, if the funding is available, one would want to consider installing a fairly large LP tank. I’d say a new or used tank holding 5,000 gallons. It should be installed on concrete piers and a bottle fill station installed. Installing a small standby vaporizer for expanded capacity would satisfy pretty much all your future gas needs.
With an energy system infrastructure in place, you can then look at using LP to operate generators instead of gasoline or diesel. After TEOTWAWKI, consider acquiring an LP delivery truck. It can be used to gather propane from other locations to transport and maintain your retreat LP supply.
Hopefully, what I have written here will give you a basic understanding and some insight regarding propane usage and applications. Find someone in the industry to give you training and hands on experience with the equipment and basic filling functions, and give you ideas on how you can have your own system setup.