What Is Gas Liquids Extraction, and What Are Gas Liquids Used for?
Processing natural gas separates all the various hydrocarbons and liquids from it to produce pipeline-quality dry natural gas. On the other hand, natural gas liquids are used in various industries for producing fuel and even plastics.
What Are Natural Gas Liquids?
Natural gas liquids are natural gas components separated from the gaseous state in liquid form. They're hydrocarbons, meaning molecules composed of carbon and hydrogen. They also belong to the same family as natural gas and crude oil.
There are many uses for NGL's spanning nearly every sector of the economy:
Petrochemical plants use them as inputs to produce materials such as plastics;
They're burned for space heat or cooking;
They are blended into vehicle fuels.
Why Are Natural Gas Liquids Important?
Higher prices on crude oil have led to increased demand for these products, making drilling in liquid-rich resources more profitable than it once was due to their high content rate of natural gas liquids (NGL). Natural gas liquids have high value as separate products and have many different applications.
Depending on their vapour pressure, natural gas liquids are categorized into three main types:
Low vapour pressure NGL (condensate);
Intermediate vapour pressure NGL (natural gasoline);
High vapour pressure NGL (liquefied petroleum gas).
Based on their applications, there are many different types of natural gas liquids:
Ethane (C2H6) - Applications for ethane include plastics production and petrochemical feedstock- as raw materials fed into an industrial process to produce a new product. Some of the end products of these processes are plastics, detergents, and antifreeze.
Butanes (C4H10) - Butane can be blended with other fuels, such as gasoline and propane. Such a blend produces synthetic rubber for tires and lighter fuel. Pure butane is also used in refrigeration in its liquid form. When combined with propane, butane becomes liquified petroleum gas (LPG).
Isobutane (C4H10) - Isobutane is used in various industrial applications, including as a refinery feedstock and petrochemical feedstock. Some well-known end-use products include aerosols and refrigerants.
Propane (C3H8) - Propane has a number of applications and uses. Residential and commercial heating is just one example. Propane is also used as cooking fuel. Some vehicle owners also use propane as fuel for their cars.
Pentanes (C5H12) - Pentanes are mainly used in natural gasoline and as a blowing agent for polystyrene foam. There is also a special category, called Pentane Plus (also known as natural gasoline), which is blended with vehicle fuel and exported for bitumen production.
Industries Using Natural Gas Liquids
Each type of natural gas liquid has its own primary sector of use. As their applications vary, the primary sectors for NGLs can also be different:
Ethane is primarily used in the industrial sector.
Propane is used in the industrial, residential and commercial sectors.
Butane is mainly used for transportation and in the industrial sector.
The application of the isobutanes is mostly in the industrial sector.
Pentane and Pentane Plus are used for transportation.
How Are Natural Gas Liquids Extracted?
There are two methods for removing NGLs from the natural gas stream: absorption and cryogenic expansion.
The Absorption Method
The absorption method for NGL extraction is very similar to how dehydration works. The primary difference lies in the usage of absorbing the oil in NGL absorption instead of glycol in the process of dehydration.
The absorption method is used when it is necessary to pick up heavier natural gas liquids like butane and pentane because the absorbing oil has an affinity with them. The absorption process occurs in an "absorption tower" where the gas comes into contact with absorbing oil which soaks up most of the natural gas liquids. Then the mixture of absorption oil and NGLs is heated to a temperature higher than the boiling point for the NGLs, but below the boiling point of the oil.
This process yields a recovery of 75% butanes and 85-90% natural gasoline from the natural gas feedstock.
The Cryogenic Expansion Process
The lighter hydrocarbons, unlike the heavier NGLs, are harder to recover from the natural gas feedstocks. This is where the cryogenic expansion process comes into place. In this process, the temperature of natural gas is lowered to -120 degrees Fahrenheit by using external cooling agents. One of the most common and at the same time effective methods of cooling natural gas is the turbo expander process.
This process uses an expansion turbine to quickly drop the temperature of the gas, causing the natural gas liquids to start condensing. Apart from being efficient, this method can also save some serious energy costs by converting a portion of the released energy.
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What Is NGL Fractionation?
The fractionation process is used in natural gas processing plants to separate the natural gas liquids into individual products. Fractionation works based on the different boiling points of the different hydrocarbons in the stream. This process consists of a series of steps, starting from the lighter NGLs being taken out from the natural gas stream.
The fractionation is the second step in the process of natural gas treatment. The first step includes the extraction of the liquids from the natural gas. And the second is the separation of these liquids into their base components, such as ethane, propane, butane, and methane.
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