Origin
LPG is a practical and multifunctional source of energy, during the use of which there is no pollution of the environment ascertained. However, it also has some potentially dangerous properties. Therefore, it is necessary to put special care and apply specific design, exploitation rules and maintenance at all stages of its production, storage, transportation and end use. The properties of LPG should be very well known in order to maintain high safety levels during exploitation.Physical and Chemical Properties
The physical and chemical properties of the liquefied petroleum gases are described according Bulgarian State Standard 5670-83 "Hydrocarbon Liquefied Gases".
Name | Propane | Butane |
|---|---|---|
| Chemical formula | С3Н8 | С4Н10 |
| Density of the liquefied gas, kg/cubic meter | 520 | 580 |
| Density of the vapours, kg/cubic meter | 1,97 | 2,6 |
| Density of the vapours in relation to air | 1,56 | 2,06 |
| Limits of combustion | ||
| Lower, % | 2,1 | 1,9 |
| Upper, % | 9,5 | 9,1 |
| Temperature of self-combustion, °С | 466 | 405 |
| Pressure of vapours at t 50 °С, MPa | 1,6 | 0,43 |
Dependent on their purpose, liquefied petroleum gases are produced in three different brands - A, B, and C. There are also two types of mixtures produced - winter mixture (60% propane and 40% butane) and summer mixture (40% propane and 60% butane). They have the property to stay in gas phase in conditions of regular temperature and atmospheric pressure but liquefy immediately after being put even under comparatively weak pressure.
Physical properties | Characteristics |
|---|---|
| Colour | As a gas - invisible, transparent, in liquid state; When LPG in liquid state leaks, a white mist is formed; frost or ice appears around the place of the leak. |
| Smell | Odorless in pure state; an odorizing agent is added in order to provide discovering of leaks in an organoleptic way before reaching of the lower limit of combustion; the place of the leak is searched for using soap solution, and never flame. |
| Taste | Tasteless |
Properties | Significance |
| Combustion | Forms combustible mixtures with air at concentration of LPG from 2 to 10%. |
| Pressure of the gas phase | Grows in a direct ratio to the growing of the surrounding temperature. |
| Density (liquid phase) | Half of the water weight (1 liter = 0,54 kg approximately). |
| Density (gas phase) | Twice heavier than air weight (in cases of leaks, LPG spreads close over the ground and could penetrate in draining holes, sewers, etc. |
| Growing factor of the liquid phase | With increasing of temperature, the volume of the liquid phase grows - 12 times as much as those of water (free, unused capacity of the reservoir during storage is needed). |
| Point of boiling | Very low, it evaporates quickly and passes into gas phase. This is related to absorption of heat, leading to cold burns, freezing of equipment and so on). |
| Point of ignition | Very low (ignites under - 70°С) |
| Temperature of combustion | Over 140°С |
| Relation of volumes of liquid to gas phase during evaporation | 1:270 - the gas cloud is formed very quickly. |
Expansion of the liquid phase
Butane and propane are in liquid phase in the lower part of the container and in gas phase in the upper part. In liquid phase, LPG is expanding under the impact of temperature rises. For example, with rising of the temperature from -10°C to + 10°C the volume of the liquefied gas grows with about 6% (at steady weight levels).
It is always necessary to leave unused capacity (in gas phase) in a given container in order to execute the expanding in the liquid phase without permitting the risk of increasing the working pressure of the cylinders , bulk tanks or automobile cisterns. For the bulk tanks of the automobile gas equipment, this maximum filling capacity is 80% of their water capacity, as the unused space is left for the expansion in the liquid phase, and, respectively, for the increased pressure phase due to temperature rises in the gas phase.
Boiling temperature
In conditions of normal atmospheric pressure, butane boils at -2°С, and propane - at -42°С. The comparatively low boiling temperature of propane provides its effective use even in the coldest winter days.
Pressure
The pressure rises with the rising of the temperature
The pressure in the gas phase of butane at temperature of 15°С is about 1,7 bar or 0,17 MPa, and at 50°С is about 4,7 bar or 0,47 MPa.
The pressure in the gas phase of propane at temperature of 15 °С is about 7,5 bar or 0,75 MPa, and at 50°С - about 16 bar or 1,6 MPa.
In liquid phase, they are lighter than water and not soluble in it.
Butane and propane are twice more viscose than air or nature gas.
LPG does not exercise corrosive action on metals.
LPG dissolves specific substances - fat, varnish, oils, and provokes intensive expansion of the natural rubber.
