The purpose of a glycol dehydration unit is to remove water from natural gas

Source: wikipedia

Glycol dehydration is a liquid desiccant system for the removal of water from natural gas and natural gas liquids (NGL). It is the most common and economic means of water removal from these streams.^[1] Glycols typically seen in industry include triethylene glycol (TEG), diethylene glycol (DEG), ethylene glycol (MEG), and tetraethylene glycol (TREG). TEG is the most commonly used glycol in industry.^[1]
An example process flow diagram for this system is shown below:

Purpose

The purpose of a glycol dehydration unit is to remove water from natural gas and natural gas liquids. When produced from a reservoir, natural gas usually contains a large amount of water and is typically completely saturated or at the water dew point. This water can cause several problems for downstream processes and equipment. At low temperatures the water can either freeze in piping or, as is more commonly the case, form hydrates with CO₂ and hydrocarbons (mainly methane hydrates). Depending on composition, these hydrates can form at relatively high temperatures plugging equipment and piping.^[1] Glycol dehydration units depress the hydrate formation point of the gas through water removal.


Without dehydration, a free water phase (liquid water) could also drop out of the natural gas as it is either cooled or the pressure is lowered through equipment and piping. This free water phase will contain some portions of acid gas (such as H₂S and CO₂) and can cause corrosion.^[1]


For the above two reasons the Gas Processors Association sets out a pipeline quality specification for gas that the water content should not exceed 7 pounds per million cubic feet . ^[1] Glycol dehydration units must typically meet this specification at a minimum, although further removal may be required if additional hydrate formation temperature depression is required, such as upstream of a cryogenic process or gas plant.

Process description

Lean, water-free glycol (purity >99%) is fed to the top of an absorber (also known as a "glycol contactor") where it is contacted with the wet natural gas stream. The glycol removes water from the natural gas by physical absorption and is carried out the bottom of the column. Upon exiting the absorber the glycol stream is often referred to as "rich glycol". The dry natural gas leaves the top of the absorption column and is fed either to a pipeline system or to a gas plant. Glycol absorbers can be either tray columns or packed columns.

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List of Air Contaminants Produced by Fracking - The Invisible Killers

Source EARTHWORKS

Below you will find a general description of air pollutants associated with oil and gas production. For more detailed information, follow the links provided in each section. To learn about the various sources of these the particular contaminants, visit the Sources of Oil and Gas Air Pollution page.

• Benzene, Toluene, Ethylbenzene and Xylene (BTEX)
• Carbon Monoxide
• Dust
• Hydrogen Sulfide
• Natural Gas
• Nitrogen Oxides
• Ozone
• Particulate Matter
• Sulfur Dioxide
• Volatile Organic Compounds

BTEX compounds. BTEX stands for benzene, toluene, ethylbenzene, and xylene, a group of compounds all that also belong to the broader category of volatile organic compounds, VOCs. Benzene is a known carcinogen, and has also been shown to cause blood disorders and to impact the central nervous system the reproductive system. Toluene may affect the reproductive and central nervous systems. Ethylbenzene and xylene may have respiratory and neurological effects. BTEX compounds can be emitted during various oil and gas operations activities, including flaring, venting, engines, produced water storage tanks, and during the dehydration of natural gas.

Carbon monoxide (CO). Carbon monoxide is emitted during flaring and from the operation of various machinery at oil and gas development sites. It is a colorless, odorless, flammable gas produced by incomplete burning of carbon-based fuels such as oil, natural gas, coal, and even wood. Carbon monoxide is poisonous if inhaled. It inhibits the blood's ability to carry oxygen, and can cause dizziness, unconsciousness, and even death.

Dust. Dust is created whenever there is dirt-moving activity such as construction of well pads, as well as when there is vehicle traffic on unpaved roads. Dust can cause or aggravate nuisances such as hay fever and allergies; stunt the growth of vegetation; and lead to decreased visibility.

Hydrogen sulfide (H2S). Hydrogen sulfide occurs naturally in some oil and gas formations. When oil or gas is extracted from these formations, H2S may be released when gas is vented, when there is incomplete combustion of flared gas, or via fugitive emissions from equipment. Hydrogen sulfide is a toxic gas which has a characteristic rotten egg odor at low concentrations. It is lethal if inhaled at high concentrations.

Natural Gas. Natural gas is released during venting operations, or when there are leaks in equipment used during oil and gas development. The primary component of natural gas is methane, which is odorless when it comes directly out of the gas well. In addition to methane, natural gas typically contains other hydrocarbons such as ethane, propane, butane, and pentanes. Raw natural gas may also contain hazardous air pollutants such as benzene, toluene, ethylbenzene, xylenes and hexanes, hydrogen sulfide (H2S), and carbon dioxide. Other compounds in natural gas typically include water vapor, helium, and nitrogen. Almost all references to the odor of raw or wellhead natural gas state that it, like methane, is odorless. The Ohio Department of Natural Resources, however, advises landowners that one way to detect an abandoned oil or gas well on their property is if they smell "natural gas" odors coming from their tap water. So, in some cases, there may be a slight hydrocarbon odor associated with venting of natural gas.

Nitrogen Oxides (NOx). NOx are formed during the combustion of fossil fuels, which causes a chemical reaction between nitrogen (which occurs naturally in the atmosphere) and oxygen. During oil and gas production, NOx are formed during flaring operations, and when fuel is burned to provide power to machinery such as compressor engines and other heavy equipment. NOx, in turn, may react with VOCs to form ground-level ozone. Nitrogen dioxide, one of the NOx chemicals, is a criteria pollutant regulated by the EPA, and can be seen, along with other particles in polluted air, as a reddish-brown haze. The health impacts from NOx include respiratory problems, heart conditions, and lung damage,

Ozone. Ozone itself is not released during oil and gas development. But some of the main compounds that combine to form ozone (e.g., volatile organic compounds and nitrogen oxides) are released from oil and gas operations. Ozone, when found at ground-level, is also referred to as "smog," which, when inhaled can cause or aggravate respiratory ailments such as asthma.

Particulate Matter. Particulate matter is composed of small particles that are suspended in the air and settle to the ground slowly. The most common sources of particulate matter from oil and gas operations are dust or soil entering the air during pad construction, traffic on access roads, and diesel exhaust from vehicles and engines used to power machinery at oil and gas facilities. Particulate matter can also be emitted during venting and flaring operations. Depending on the size and chemical composition of the particulate matter, the inhalation of these particles may lead to adverse health effects such as respiratory or breathing ailments, cancer, or premature death. Particulate matter suspended in air may also contribute to decreased visibility (i.e., regional haze).

Sulfur dioxide (SO2). Sulfur dioxide is formed when fossil fuels containing sulfur are burned. Many oil, natural gas, and coal formations contain traces of sulfur. Thus, SO2 may be emitted during flaring of natural gas, or when fossil fuels are burned to provide power to pumpjack or compressor engines or other equipment and vehicles at oil and gas sites. Sour gas processing plants also emit sulfur dioxide. SO2 is regulated by the EPA as a criteria air pollutant, and along with NOx, is a principal contributor to acid rain. Sulfur dioxide reacts with other chemicals to form particulate pollution, which can damage lungs and cause respiratory illness, heart conditions, and premature death.

Volatile organic compounds (VOCs). VOCs are carbon-containing substances that readily evaporate into the air. They can combine with nitrogen oxides to form ground-level ozone, which can cause respiratory ailments such as asthma, and decreased lung function. Examples of VOCs are benzene and toluene.

Hot topic of hydrogen sulfide emissions creates cloud of controversy in gas patch - Can lead to death

Colorado Independent
By David O. Williams | 09.19.11 | 1:49 pm

The hot topic of hydrogen sulfide gas (H2S) emissions associated with natural gas drilling on Colorado’s Western Slope is expected to get a full airing at the monthly meeting of the Colorado Oil and Gas Conservation Commission (COGCC) today and tomorrow in Broomfield.

The presence of H2S in significant quantities in and around Noble Energy wells in the Piceance Basin in 2009 came as a surprise to many gas patch residents and at least one COGCC board member, Richard Alward, who recently told the Glenwood Post Independent, “I have concerns about my own health, and the health of people who live and work in the Piceance.”

A report delivered by the COGCC to Rifle residents earlier this month showed that of Noble’s 353 active wells in the Parachute, Grand Valley and Rulison fields, a total of 312 were found to have some level of H2S gas. Of those, 37 had levels greater than 10 parts per million (PPM), and four had levels greater than 100 PPM. Exposure at higher levels can lead to breathing difficulties and even death.



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We published a similiar report on July 13, 2011 HERE