Natural gas explored from underground often contains solid impurities like sand and rust, as well as water, water vapor, and harmful substances like sulfide and carbon dioxide. Natural gas must be purified before use.
Commonly used physical methods for natural gas purification are:
1. Separation and filtration.
This is major method to remove liquid from solid particles and gases.
2. Condensation separation.
Use low temperature operation to make water and heavy hydrocarbon condensing into liquid, and then separating from the gas.
3. Adsorption method
The phenomenon that a part of the gas or liquid concentrates on the surface of the solid adsorbent is called adsorption. Adsorbent adsorbs only a certain component in a gas mixture so as to separate it from the gas。
4. Absorption method.
Some kind of liquid can selectively absorb a specific component in a gas mixture and separate it from the gas. Such liquid is called absorbent.
According to whether or not there is chemical reaction, there are physical absorption and chemical absorption.
For physical absorption, there are measures to separate absorbed substances and absorbent. This process is called desorption, making absorbent reusable.
5. Direct conversion method.
Use chemical reaction to transform impurities into a harmless compound or a compound that is easily to remove.
6. Synthesis method.
Compound utilization of above methods.
Natural gas dehydration
In the long distance transportation, water in the natural gas must be removed.
Common used dehydration methods are as follows:
- Low temperature dehydration;
- Adsorption method;
- Glycol dehydration.
Desulfurization and decarbonization
Depending on the difference of raw gas, there are largely six methods for desulfurization and decarbonization:
1. Chemical solvent method;
2. Physical solvent method;
3. Direct conversion method;
4. Dry bed method;
5. Membrane separation method;
6. Pressure swing adsorption(PSA) method.
Recovery of liquefied petroleum gas (LPG)
LPG is one of petroleum products. It is acquired from refinery gas or natural gas (including oilfield associated gas) after being pressured, cooled or liquefied. It is a mixture that is mainly composed of three or four carbon atoms hydrocarbons (such as propane, propylene, butane and butene).
At normal temperature and pressure, it is non-toxic, colorless and tasteless gas with merits of high octane value, good anti explosion performance, high calorific value and low storage pressure.
It is a good alternative for vehicle fuel and has following advantages:
1. Cheaper than gasoline;
2. Abundant reserves;
3. Butane and propane can be mixed to form a certain amount of octane, making LPG well in antiknock property.
In the refinery processes, there are distillation gas, thermal cracking gas, catalytic cracking gas, catalytic reforming gas and coking gas. These five kinds of gases contain C1-C5 components. Extracting C3 and C4 components in these gases by separation and absorption devices, liquefied petroleum gas is obtained.
In the process of oil exploitation, oil and oil associated gas spout together. Oil and oil associated gas can be separated by using oil and gas separation device above oil wells. Oil associated gas contains about 5% propane and butane. Using absorption to extract them, high quality LPG of high propane purity and low sulfur content is obtained.
Natural gas is divided into dry gas and wet gas. Methane content in wet gas is below 90%, and alkanes, such as ethane, propane and butane, content is more than 10%. Separating propane and butane from wet gas, LPG is obtained.
In addition, LPG can be obtained from the plant of artificial petroleum production by fuel hydrogenation and semi coking. LPG can also be recovered from synthetic gasoline production factory from water gas.
Quality of LPG depends on is origin and recovery technology. Generally LPG obtained from oilfield associated gas is better than from refinery factory.
UNE owns core technology of natural gas dehydration, desulfurization and deacidification, as well as LPG recovery and system equipment. We can provide clients customized solutions.