When natural gas is produced it comes to the surface through the casing pipe in the well bore through the wellhead as a raw material often containing impurities such as dirt, water and liquid hydrocarbons which must be removed before the gas is sent to a transmission or distribution pipeline. In most cases a lift compressor - a motorized pressurizer - is located on the well pad to move the gas from the wellhead through scrubbers that remove impurities to transmission pipelines that carry the gas to high pressure compressor stations where the gas is then pumped to distribution stations before entering distribution pipelines that carry the refined natural gas to customers that include residential, commercial and industrial consumers of the product.
Scrubbers may be located at a pad site, gathering station (where several wells are tied together before going to a compressor station) or they may be located at a line compressor station. In some cases scrubbers may be located at more than one location depending upon the type of gas (wet versus dry) and atmospheric conditions that may cause condensation that separates water and other liquids from the gas itself. Scrubbers remove dirt and water for disposal, and they remove liquid hydrocarbons such as propane, butane, ethane, etc. for sale to appropriate markets for those byproducts of the production operation.
The pipeline transportation of natural gas requires occasional pressure boosting to keep the gas flowing, and line compressors are usually found at intervals of about 40 to 100 miles, depending upon terrain, inside diameter of transmission pipes, volume of gas being moved in the pipeline and atmospheric conditions. Line compressors are the much larger (and louder) high pressure engines that move large volumes of natural gas over great distances to distribution stations where the gas then enters a network of distribution pipelines for delivery to customers. Without the energy provided by compression it would not be possible to move gas over long distances through pipelines.
When the Dallas Gas Drilling Task Force heard a briefing from Texas Commission on Environmental Quality (TCEQ) on July 26, 2011, the presentation they heard included an averview of TCEQ controls and regulations pertaining to water and air. The TCEQ presentation describes the legal oversight and provides information on allowable quantities of Hazardour Air Pollutants (HAPs) that may legally be emitted into our air with and without a permit. Pictured on page 32 of the above linked document are photos of both unenclosed and enclosed compressor facilities.
Click any photo below for slideshow of compressor station infrastructure
There are three types of line compressor stations differentiated by the type of engine that compresses the gas - Turbine/Centrifugal Compressor, Electric Motor/Centrifugal Compressor and Reciprocating Engine/Reciprocating Compressor. The compressor type selected for any given application depends upon what is required by local ordinances, availability of a nearby electric grid and related considerations that dictate which type is necessary for the location of the compressor station. Obviously, the natural gas industry is going to select compressors based upon lowest cost and what is required by law or ordinance without regard for the amount of air pollution created by the type chosen.
Turbine/Centrifugal Compressors use a natural gas-fired turbine to turn a centrifugal compressor. A very small quantity of natural gas from the pipeline is used to power the turbine, which is a basically a large fan inside a casing.
Electric Motor/Centrifugal Compressors use a high voltage electric motor to drive the compressor and fan. This type of compressor is only practical if located near a source capable of delivering a reliable electric current of sufficient voltage and amperage to sustain operations. Its advantage is that this type of compressor needs no air emission permit since no hydrocarbons are burned as fuel. This type of compressor is commonly required in metropolitan areas where air quality issues are important because of local, state or federal regulations.
Reciprocating Engine/Reciprocating Compressors are large piston engines resemble automobile engines, only many times larger, and are fueled by natural gas from the pipeline. Reciprocating pistons, located in cylinder cases on the side of the unit, compress the natural gas. The compressor pistons and the power pistons are connected to a common crankshaft. The advantage of reciprocating compressors is that the volume of gas pushed through the pipeline can be adjusted incrementally to meet small changes in customer demand.
The possibilities for health, safety or environmental harm resulting from natural gas compressor stations are many and serious. Some of these include explosions and fires, leaks and spills, fugitive emissions of volatile organic compounds (VOCs) and nitrogen oxides (NOx), as well as other potential exposure threats. While all of these types of hazards have been well documented nationwide the most prevalent, by far, is the intentional or accidental release of VOCs and NOx, but all possible threats need to be considered when allowing compressor stations to operate, especially when in close proximity to homes, places of employment or playgrounds, as well as environmentally sensitive locales such as near water resources or agricultural production areas.
A recent study of the Barnett Shale reported that VOC and NOX emissions from gas production exceeded the emissions from all on-road mobile vehicles in the Dallas-Fort Worth metropolitan region (Armendariz 2009). Natural gas production also emits greenhouse gases including carbon dioxide (CO2) and methane (CH4), which is the primary component of natural gas. The Barnett Shale study estimated that greenhouse gas emissions from gas development were equivalent to the emissions from two 750 megawatt coal power plants. There are several other studies that have investigated both the total emissions (TCEQ 2011; WRAP 2011) and local air quality impacts (TCEQ 2010; PDEP 2010, 2011a, 2011b) of gas production.
The types of VOCs and NOx that are commonly emitted in venting (uncontrolled or controlled releases of gases to prevent blowouts), flaring (the burning of vented gases) or fugitive emissions (uncontrolled and largely unmonitored) include formaldehyde, benzene, toluene, ethylbenzene, xylene, hydrogen disulfide, carbon monoxide(CO), carbon dioxide (CO2), sulfur dioxide (SO2),methane (CH4), and other compounds or elements that are toxic, carcinogenic or neurotoxic, and which are prone to causing major adverse health effects in humans and animals. These are emissions that could be eliminated or greatly curtailed by the implementation and use of vapor recovery systems that would also reduce near-ground level ozone and smog resulting in fewer cases of environmentally-induced cancers, respiratory problems, early childhood mortality, childhood learning defects, male reproductivity problems, mental illness and myriad other adverse health effects that reduce the quality of life and occasional shorten its duration by many years.
Peer-reviewed scientific studies on these emissins and their health effects on humans have been published by numerous sources including The Endocrine Disruption Exchange, which also produced a separate study on Male Reproductive System Problems from exposure to endocrine disruptors. These important studies demonstrate why limiting natural gas exploration and production activities near inhabited areas is essential to good human health.
A recently released peer-reviewed study by the University of Colorado's Colorado School of Public Health entitled Human Health Risk Assessment of Air Emissions from Development of Unconventional Natural Gas Resources reveals the elevated risk levels for certain major health threats for people living within close proximity of natural gas exploration and production sites, and should serve as a warning that natural gas production is not compatible with neighborhoods or other places where people gather for work, recreation or other purposes.
Quoting from a General Monitors white paper on compressor station leak detection, "At a compressor or booster station two main processes typically take place: (1) Gas compression is performed in order to ensure the natural gas flowing through a pipeline remains pressurized and (2) gas chilling/cooling, which reduces the gas temperature. Both processes subject gas compressor equipment to high stresses. Vibration and heat from nearby machinery, for example, can produce cracks on seals and flanges. Hydrogen sulfide, liquids, and undesirable particles in the natural gas stream can corrode pipelines and degrade components. Over time, prolonged exposure to these elements invariably leads to component failure and possibly to leaks of combustible material. Early detection of dangerous compressor gas leaks is critical to help mitigate the risk of fire in volatile locations."
General Monitors concludes, "It is extremely important to take precautions in order to prevent gas compressor explosions and fires. Early gas leak detection is critical in this environment, and General Monitors offers several gas detection technologies that are ideal for use with gas compressors. Ultrasonic, infrared and catalytic bead gas detectors can be used individually or in conjunction with one another to ensure that gas compressors remain safe and explosion-free."
Obviously, the hazards and potential disastrous results are not unknown, which is why companies like General Monitors have developed equipment to determine problems before they become catastrophies.
EXPLOSIONS AND FIRES: Below is a partial listing of recent compressor complex explosions and fires in the United States, some involving injuries or fatalities.
Crosstex Pipeline, Godley, TX, Nov 18. 2008
Energy Transfer Partners, Madison County, TX, Jan 17, 2013
Copano Energy in Jim Wells County, TX, September 6, 2012
Williams Energy, Lanthrop, PA March 29, 2012
Bill Barrett Corporation, Carbon County, UT, Nov. 22, 2012 - Two injured (severe burns)
Artemas Compressor Station, Mann Township, Bedford County, PA, Houston-based Columbia Gas Transmission, Nov 3, 2011
Pinon Compression Station (BP), Durango, CO June 25, 2012 - 1 killed, 2 injured
Falcon natural gas compressor station, Jonah Field, WY, Dec 7, 2011
FUGITIVE EMISSIONS, VENTING AND FLARING: Whether intentional, automatic (as in safety operations to prevent blowouts and explosions) or accidental, the release into the air of BTEX (benzene, toluene, ethylbenzene and xylene), formaldehyde, hydrogen disulfide, methane, pentane, pentene, butane, propane or other harmful hydrocarbon gases or liquids is a major hazard to human, animal and plant health that must be strictly regulated and controlled. Costs for such regulation and control should be borne by those seeking to profit from the exploration and production of natural gas who typically deny that their operations are the sources for these pollutants even when shown documented proof.
The majority of these pollutants are imvisible to the naked eye, but there is a large volume of infra-red video available that demonstrates release of these pollutants is a constant threat from wellheads, valves, fittings, couplings, pipelines, lift compressors, line compressors, condensate tanks, produced water storage tanks, separators, distillers, dehydrators and just about every other component of the systems necessary to extract, produce, refine and transport natural gas. Some of these videos can be found in the links below:
LEAKS AND SPILLS: Regardless of the precautions taken by the natural gas industry to prevent spills and leaks they still occur on an all-too-frequent basis resulting in environmental pollution and potential health threats to humans, animals and plants. These leaks and spills are a threat to clean air, water and soil, thereby jeopardizing irreplacable resources needed for human survival. While the oil and gas industry is quick to tell you that what they do is safe, and that they have more than 150 years of experience doing it, the fact remains that there are very many documented cases of leaks and spills of hydrocarbons into our atmosphere, as well as of frac chemicals, flowback and produced water and cancer-causing silica sand, all of which are major threats to human health and safety.
As an example of the potential threats caused by leaks of hazardous vapors from drilling sites and compressor stations a news report from the Marcellus Shale of Pennsylvania shows what can happen when fumes ignite.
In addition to links to various accidents resulting in leaks and spills in Cortland County, NY, the links below tell the true story of threats posed to people, animals and our environment by the accidental or intentional leaks and spills on well pad sites, along transmission lines, at compressor and separator (refinery) stations and from trucks transporting chemicals and toxic chemical laced water for deep injection well disposal along streets and highways shared by citizens. These are but a very few of the many violations that have occurred in the Barnett Shale and indicate a pattern of continuing violations of state and federal environmental protection laws that were designed to protect public health and safety. Considering that a single gallon of gasoline can contaminate up to 750,000 gallons of fresh water (according to the World Health Organization), and that most frac chemicals are far more toxic, carcinogenic and/or neurotoxic than gasoline, an understanding of the risks of spills and leaks is imperative, especially for those elected or appointed public officials who make decisions regarding allowing natural gas exploration and production in close proximity to densely-populated urban areas.
What is missing is a TCEQ comprehensive database or listing of violations and penalties accessed. That is primarily due to the fact that TCEQ is not an objective environmental agency that seeks to protect public health and safety. It is staffed by oil and gas industry people and its top tier managers are appointed by the governor with a mandate to promote economic growth even if it means allowing destruction of our environment in the process. Information on toxic leaks and spills has to be gleened from individual media reports or the works of citizens who report what they find without the scientific basis to present a credible case against the polluters. But, if one looks closely enough and reads enough of the "anecdotal" evidence available, then it is easy to see that the depth of the problem is real and profound.
Compressor stations and complexes are but one part of the problem, but because of their size, scope and function they are a very important part of the problem, and are probably the largest single contributor of HAPs in the state of Texas. The current Luna South Gas Processing Facility proposed by Trinity East Energy for construction just 600 feet from a brand new soccer complex will, according to Trinity East representatives' own numbers, be the tenth largest stationary source of air pollution in the entire City of Dallas. That compressor complex would present a more direct threat of fire and explosion, fugitive emmissions, or leaks and spills of any other natural gas operation planned or being considered in Dallas.
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