What is the advantage of storing propane and butane as a pressurised/refrigerated liquid?

Question

the fuels are being stored on an LPG fractionation plant...

THANKS :)

my first thought was that it is easier to transport as a liquid and that it may be used as a cooling fluid if refrigerated

Answer 1

One of the advantage is ease of storage because liquids have very high density as compared to gases.

OK, considering LPG consists of 100% propane,10 kg of propane would occupy more than 5 cu m (5000 litres) of volume, propane has mol wt of 44, using PV=nRT

The other advantage I can think of is since it is under pressure, it will not require pump, compressor or blower etc to convey, it is under high pressure it can flow to low pressure with ease.

It is also easy to regulate the pressure.

Answer 2

At normal temperatures and pressures, LPG will evaporate. Because of this, LPG is supplied in pressurised steel bottles. In order to allow for thermal expansion of the contained liquid, these bottles are not filled completely; typically, they are filled to between 80% and 85% of their capacity. The ratio between the volumes of the vaporised gas and the liquefied gas varies depending on composition, pressure and temperature, but is typically around 250:1. The pressure at which LPG becomes liquid, called its vapor pressure, likewise varies depending on composition and temperature; for example, it is approximately 220 kilopascals (2.2 bar) for pure butane at 20 °C (68 °F), and approximately 2.2 megapascals (22 bar) for pure propane at 55 °C (131 °F). LPG is heavier than air, and thus will flow along floors and tend to settle in low spots, such as basements. This can cause ignition or suffocation hazards if not dealt with.

Answer 3

The products coming from the depropanizer or debutanizer are in the liquid form. It is usually cheaper to store them at their vapor pressure in the liquid form rather than to maintain them as a liquid at lower pressure by refrigeration. This of course requires a refrigeration system and the energy to run the system or a compression system similar to an LNG system (see below)

To store them as a vapor just isn't practical because of the huge volume of storage space that would be required.

Only LNG is stored at near atmospheric pressure, then a compression system is required to compress the LNG vapors that boil off of the storage tank so they can be condensed and returned to the tank. This boil off vapor keeps the LNG cold so the majority of the LNG will stay a liquid.

Answer 4

lower pressure in the vessel itself as opposed to storage as a gas and you can fit more cold liquid into a reasonable size container as opposed to a gas (which the only way to increase the mass inside the container is to pressurize it which means a more expensive container)

Answer 5

The liquid is much more dense. You would need vastly larger tanks if you tried to store it as a gas.

Answer 6

You can get more of it in a small container when it is in liquid form.