In this post we will be looking at meaning of Natural-Gas Condensate, Types of NGL, Composition and Separating the condensate from the raw natural gas. Do you need to start up Natural Gas business in Nigeria as a foriegner or Nigerian? Contact us for support.
INTRODUCTION
The natural gas condensate is also referred to as simply condensate or gas condensate or sometimes natural gasoline, because it contains hydrocarbons within the gasoline boiling range. There are hundreds of wet gas field worldwide and each has its own unique gas condensate composition. Natural gas condensate is typically composed of hydrocarbons ranging from C4 to C15 in which mainly contain 25-95 % by wt. of C6, C7 and C8 organic compounds.
In natural gas condensate comprises hexane, cyclohexane and benzene as C6 hydrocarbon; heptane and toluene as C7 hydrocarbon whereas octane, ethyl benzene and xylenes consider as C8 hydrocarbon. Natural gas condensate also has minor amount of C5 (5-7% by wt) as pentane and other hydrocarbons up to C15. Beside these gas condensates has trace amount of hydrogen sulfide (H2S), carbon dioxide (CO2), mercaptanes (RSH, R= -CH3, -C2H5) and aromatics.
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What is Natural-Gas Condensate?
Natural-gas condensate, also called natural gas liquids, is a low-density mixture of hydrocarbon liquids that are present as gaseous components in the raw natural gas produced from many natural gas fields. Some gas species within the raw natural gas will condense to a liquid state if the temperature is reduced to below the hydrocarbon dew point temperature at a set pressure.
The natural gas condensate is also called condensate, or gas condensate, or sometimes natural gasoline because it contains hydrocarbons within the gasoline boiling range, and is also referred to by the shortened name condy by many workers on gas installations. Raw natural gas may come from any one of three types of gas wells:
- Crude oil wells: Raw natural gas that comes from crude oil wells is called associated gas. This gas can exist separate from the crude oil in the underground formation, or be dissolved in the crude oil. Condensate produced from oil wells is often referred to as lease condensate.
- Dry gas wells: These wells typically produce only raw natural gas that contains no hydrocarbon liquids. Such gas is called non-associated gas. Condensate from dry gas is extracted at gas processing plants and is often called plant condensate.
- Condensate wells: These wells produce raw natural gas along with natural gas liquid. Such gas is also called associated gas and often referred to as wet gas.
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Types of NGL (Natural-Gas Condensate)
NGLs can be recovered from both natural gas and crude oil. Some NGLs are extracted in the field while most are extracted through processing plants and fractionation
- Natural Gas Condensate
- Crude Condensate
Natural gasoline, or drip gas, is a byproduct of water separation, also called lease condensate. It is called lease condensate because the condensation process occurs in the field vs. a processing plant.
Composition of Natural Gas Condensate
There are many condensate sources, and each has its own unique gas condensate composition. In general, gas condensate has a specific gravity ranging from 0.5 to 0.8, and is composed of hydrocarbons such as propane, butane, pentane, and hexane. Natural gas compounds with more than two carbon atoms exist as liquids at ambient temperatures. Propane, butane, and isobutane are liquid at normal temperatures only under pressure.
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Additionally, condensate may contain:
- Heavier straight-chain alkanes having from 7 to 12 carbon atoms (denoted as C7 to C12)
- Hydrogen sulfide (H2S)
- Thiols traditionally also called mercaptans (denoted as RSH, where R is an organic group such as methyl, ethyl, etc.)
- Carbon dioxide (CO2)
- Cyclohexane and perhaps other naphthenes
- BTX (chemistry) (Aromatics such as benzene, toluene, xylenes, and ethylbenzene).
Separating The Condensate from The Raw Natural Gas
There are hundreds of different equipment configurations to separate natural gas condensate from raw natural gas. The schematic flow diagram to the right depicts just one of the possible configurations. The raw natural gas feedstock from a gas well or a group of wells is cooled to lower the gas temperature to below its hydrocarbon dew point at the feedstock pressure. This condenses a large part of the gas condensate hydrocarbons. The feedstock mixture of gas, liquid condensate and water is then routed to a high-pressure separator vessel where the water and the raw natural gas are separated and removed.
If a pressure boost is required, the raw natural gas from the high-pressure separator is sent to the main gas compressor, which raises the pressure of the gases to whatever pressure is required for the pipeline transportation of the gas to the raw natural gas processing plant. The main gas compressor discharge pressure will depend upon the operating pressure of and the distance to the raw natural gas processing plant and may require a multi-stage compressor. The gas condensate from the high-pressure separator flows through a throttling control valve to a low-pressure separator. The reduction in pressure across the control valve causes the condensate to undergo a partial vaporization referred to as flash vaporization.
The raw natural gas from the low-pressure separator is sent to a “booster” compressor that raises the gas pressure and sends it through a cooler, and then to the main gas compressor. At the raw natural gas processing plant, the gas will be dehydrated and acid gases and other impurities will be removed from the gas.
Then, the ethane (C2), propane (C3), butanes (C4), and pentanes (C5)—plus higher molecular weight hydrocarbons referred to as C5+—will also be removed and recovered as byproducts. The water removed from both the high- and low-pressure separators may need to be processed to remove hydrogen sulfide (H2S) before the water can be disposed of underground or reused in some fashion.