Natural-gas condensate

See also:Natural-gas processing § Contaminants in raw natural gas

Not to be confused with "condensate" in the sense ofliquefied petroleum gas,nor withliquefied natural gas.

Natural-gas condensate,also callednatural gas liquids,is a low-density mixture ofhydrocarbonliquids that are present as gaseous components in the rawnatural gasproduced from many naturalgas fields.Some gas species within the raw natural gas will condense to a liquid state if the temperature is reduced to below thehydrocarbon dew pointtemperature at a set pressure.

The natural gas condensate is also calledcondensate,orgas condensate,or sometimesnatural gasolinebecause it contains hydrocarbons within the gasoline boiling range, and is also referred to by the shortened namecondyby many workers on gas installations. Raw natural gas used to create condensate may come from any type of gas well such as:

• Crudeoil wells:Natural gas that comes from crude oil wells is typically calledassociated gas.This gas could exist as a separate gas cap above the crude oil in the underground reservoir or could be dissolved in the crude oil, ultimately coming out of solution as the pressure is reduced during production. Condensate produced from oil wells is often referred to aslease condensate.
• Dry gas wells: These wells typically produce only raw natural gas that contains no condensate with little to no crude oil and are callednon-associatedgas. Condensate from dry gas is extracted atgas processingplants and is often calledplant condensate.
• Condensate wells: These wells typically produce raw natural gas along withnatural gas liquidwith little to no crude oil and are callednon-associatedgas. Such raw natural gas is often referred to aswet gas.

Composition

There are many condensate sources, and each has its own unique gas condensate composition. In general, gas condensate has aspecific gravityranging from 0.5 to 0.8, and is composed of hydrocarbons such aspropane,butane,pentane,andhexane.Natural gas compounds with more than two carbon atoms exist as liquids at ambient temperatures and pressures.Propane,butane,andisobutaneare liquid at normal temperatures only under pressure. Additionally, condensate may contain:

• Heavierstraight-chain alkaneshaving from 7 to 12carbonatoms (denoted asC
  ₇toC
  ₁₂)
• Hydrogen sulfide(H
  ₂S)
• Thiolstraditionally also called mercaptans (denoted as RSH, where R is an organic group such as methyl, ethyl, etc.)
• Carbon dioxide(CO₂)
• Cyclohexaneand perhaps othernaphthenes
• BTX (chemistry)(Aromaticssuch asbenzene,toluene,xylenes,andethylbenzene)

Separating the condensate from the raw natural gas

Main article:Natural-gas processing

Schematic flow diagram of the separation of condensate from raw natural gas

There are hundreds of different equipment configurations to separate natural gas condensate from raw natural gas. Theschematic flow diagramto 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 itshydrocarbon dew pointat 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 maingas compressor,which raises the pressure of the gases to whatever pressure is required for thepipeline transportationof the gas to the rawnatural gas processingplant. 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 throttlingcontrol valveto a low pressure separator. The reduction in pressure across the control valve causes the condensate to undergo a partial vaporization referred to asflash 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 bedehydratedandacid gasesand other impurities will be removed from the gas. Then, theethane(C
₂),propane(C
₃),butanes(C
₄), andpentanes(C
₅)—plus highermolecular weighthydrocarbons 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 (H
₂S) before the water can be disposed of underground or reused in some fashion.

Some of the raw natural gas may be re-injected into the producing formation to help maintain the reservoir pressure, or for storage pending later installation of a pipeline.

Dangers

Natural gas condensate is generally more flammable and explosive than normal crude oil. Operating in areas where condensate has escaped is dangerous for crew due to the danger of explosions, oxygen displacement and the threat of asphyxiating and anaesthetizing, which can occur within a few human breaths.

Use as a diluent in heavy oil production

Because condensate is typically liquid in ambient conditions and also has very low viscosity, condensate is often used to dilute highly viscousheavier oilsthat cannot otherwise be efficiently transported viapipelines.In particular, condensate is frequently mixed withbitumenfromoil sandsto createdilbit.In 2013, the increased use of condensate as diluent significantly increased its price in certain regions.

Drip gas and uses

Drip gas,so named because it can be drawn off the bottom of small chambers (calleddrips) sometimes installed in pipelines from gas wells, is another name for natural-gas condensate, a naturally occurring form ofgasolineobtained as a byproduct of natural gas extraction. It is also known as "condensate", "natural gasoline", "casing head gas", "raw gas", "white gas" and "liquid gold".Drip gas is defined in the United StatesCode of Federal Regulationsas consisting ofbutane,pentane,andhexanehydrocarbons.Within set ranges ofdistillation,drip gas may be extracted and used todenaturefuel alcohol.Drip gas is also used as a cleaner andsolventas well as a lantern and stove fuel.

Historical use in vehicles

Some earlyinternal combustion engines—such as the first types made byKarl Benz,and earlyWright brothersaircraft engines—usednatural gasoline,which could be either drip gas or a similar range of hydrocarbons distilled from crude oil. Natural gasoline has anoctane ratingof about 30 to 50, sufficient for the low-compression engines of the early 20th century. By 1930, improved engines and higher compression ratios required higher-octane, refined gasolines to produce power withoutknockingor detonation.

Beginning in theGreat Depression,drip gas was used as a replacement for commercial gasoline by people in oil-producing areas. "In the days of simple engines in automobiles and farm tractors it was not uncommon for anyone having access to a condensate well to fill his tank with 'drip,'" according to the Oklahoma Historical Society. Sometimes it worked fine. "At other times it might cause thundering backfires and clouds of foul-smelling smoke."

Certain manufacturers such as John Deere made farm tractors specifically designed to run on heavy, low-octane fuels which were commonly called "distillate"or" tractor fuel ".Other names weretractor vaporising oil(United Kingdom) and "power kerosene" (Australia). Often the tractors were referred to as "all-fuel".The most important factor in burning heavy fuels in a spark-ignition engine is proper fuel vaporization. Tractors designed to run on those fuels usually used a "hot" intake air manifold that allowed exhaust heat to warm the manifold and carburetor to aid vaporization. Given the poor vaporization at low temperatures, all-fuel tractors were started on gasoline, then switched to the heavy fuel. They were equipped with a small gasoline tank and a large fuel tank, both of which fed into a common valve supplying the fuel to the carburetor.

The engine would be started on gasoline and the tractor would then be worked until the engine was sufficiently warm to change over. At that point, the fuel valve would be turned to switch the fuel supply from the gasoline tank to the fuel tank and the heavy fuel would flow to the carburetor. Shutters or curtains were typically used to restrict airflow to the radiator, keeping the engine sufficiently hot for efficient operation. Coolant temperatures in the 200 degree F range were normal.John Deeretwo-cylinder all-fuel tractors worked well on heavy fuel, as their long piston strokes, slow engine speeds and low compression ratios allowed for effective use of the fuel. Most were also equipped withthermosiphoncooling systems that used no water pumps. Natural convection allowed the water to flow up and out of the engine block and into the top of the radiator, where it cooled and dropped and fell to continue the cycle.

Woody Guthrie's autobiographical novelSeeds of Manbegins with Woody and his uncle Jeff tapping a natural gas pipeline for drip gas. The gas also has a mention in Terrence Malick's movieBadlands.

Drip gas was sold commercially at gas stations and hardware stores in North America until the early 1950s. Thewhite gassold today is a similar product but is produced at refineries with thecarcinogenbenzeneremoved.

In 1975, the New Mexico State Police's drip gas detail – three men in pickup trucks – began patrolling oil and gas fields, catching thieves and recovering barrels of stolen gas. The detail stopped its work in 1987.

The use of drip gas in cars and trucks is now illegal in many states. It is also harmful to modern engines due to its low octane rating, much higher combustion temperature than that of gasoline, and lack of additives. It has a distinctive smell when used as a fuel, which allowed police to sometimes catch people using drip gas illegally.

See also

• Energy portal

External links

• Processing raw natural gas
• Preparing raw natural gas for sales
• Natural Gas Processing(part of theUS EPA's AP-42 publicationand includes a schematic diagram)