Why Natural Gas?
Learn About Natural Gas
The process of extracting natural gas from the rocks buried beneath the earth’s surface. The wells in the gas field produce by allowing pressured gas in the rock formations to flow or be lifted to the surface in a controlled manner.
– Wellhead – is a series of valves, flanges, gauges and vertical piping that delivers fluids/gas from the well to the surface of the earth.
– Gathering Lines – deliver gas from wells and transport it to the processing plant or directly to the transmission system.
Processing is the process of removing impurities and by products such as water, carbon dioxide, sulfur, helium and heavy hydrocarbons from the natural gas that is processed.
Transmission is the process of moving gas from producing regions or storage fields to major consuming areas.
– Compression – is the process of increasing the pressure of the gas moving through a pipeline, so that more gas can be moved a further distance. Large pipelines may operate in the range of 3,000 psi and be up to 60″ in diameter.
– Compressor – is the device used to add pressure to the gas moving through the pipeline. Compressors are typically powered by natural gas engines and are rated in hundreds or thousands of horsepower per compressor.
Natural gas can be stored in underground storage fields. Storage fields are typically old gas fields that have been depleted of natural gas, salt-domes that have been hollowed out by solution mining, or other porous rock that is surrounded by impermeable rock.
– Injection – is the process of pumping natural gas into storage fields, using during off-peak summer months
– Withdrawal – is the process of pumping natural gas out of storage fields, usually during periods of winter peak demand
CITY GATE STATIONS
City Gate Stations mark the point where natural gas leaves the transmission system and enters the DISTRIBUTION System. City Gate Stations have equipment that reduces the pressure of the gas, meter/measure it, add odorant and may include heaters to heat the gas if the pressure drop is large enough to cause it to drop below 32F.
The Distribution System moves the natural gas from City Gate Stations to the users. Distribution Systems typically operate in the 2 – 60 psi range for residential areas, often higher in industrial areas. The operating pressure depends on how old the system is, what it is made of (ie: cast iron, steel, plastic), what load it needs to serve and how far it is from the City Gate Station.
Natural Gas – A fossil fuel composed mostly of methane (CH4). It is found in underground reservoirs. Natural gas is colorless, odorless and lighter than air. Odorant is added to natural gas to give it a smell that can be detected in case of leaks.
City Gate Station – A facility at which pressures are lowered, odorant is added and gas is transferred from a transmission line to a distribution system for a defined service area.
Distribution Line – System of low-pressure pipes used to move gas to customers within a service area.
Compressed Natural Gas – Natural gas that is compressed for storage in portable tanks. CNG is primarily used as a transportation fuel for cars, trucks and buses.
Gathering System – Pipelines, compressors and additional equipment used to move gas from from the wellhead to a processing facility.
Local Distribution Company – A company that delivers natural gas to end users in a geographic area.
Main – Gas pipe generally laid along street right-of-ways from which extends smaller lateral service lines to individual customer gas meters.
Mercaptan – A distinctive odorant added to natural gas. The rotten-egg smell ensures that gas escaping into the atmosphere will be detected.
Processing Natural Gas – The extraction of impurities such as water vapor, H2S (hydrogen sulfide) and CO2 from newly produced gas or gas in storage.
Odorant – Any material added to natural gas to impart a distinctive odor to aid in leak detection, commonly Mercaptan.
Service Line – The pipe the carries the gas from the distribution mains in the street, across private property to the customer’s meter.
Storage – Underground – The use of subsurface porous rock formations for storing gas. Depleted natural gas production fields are often used for storage. Typically, natural gas is pumped into a field during the summer when demand and commodity prices usually are lower and pumped out of storage during winter when demand is high.
Transmission Lines – A gas pipeline that transports large quantities of highly pressurized natural gas over long distances.
Transportation – The movement by a pipeline operator of natural gas owned by another party, typically a distribution company or end-user. Transportation Service is a type of tariff many gas companies offer to large users who desire to purchase their gas from someone other than the Local Distribution Company (LDC).
BCF – Billion Cubic Feet of natural gas
BTU – British Thermal Unit, a unit of measure for heat energy. The quantity of heat necessary to raise the temperature of one pound of water one degree Fahrenheit under a stated pressure.
CCF – One Hundred Cubic Feet; residential billing units are common in CCF. One cubic foot of natural gas contains about 1,000 BTUs; 1 – CCF contains about 100,000 BTUs. CCF is a volumetric measurement. Because the exact composition of the natural gas can be different, so can the BTUs it contains. One THERM is EXACTLY 100,000 BTUs of any fuel. Some gas companies therefore use the Therm as their unit of sale. Often the Therm and CCF are used interchangeably, but technically, they are not exactly the same thing unless the natural gas is pure methane.
CNG- Compressed Natural Gas. Natural gas that is compressed into storage cylinders for use in transportation fuel in buses, trucks, cars and forklifts. CNG is NOT the same as liquid propane gas that is typically contained in cylinders.
GCR – Gas Cost Recovery factor – Most gas utility companies bill their customers based on the actual cost of gas as a separate charge from the Distribution Charge and other charges on the bill. The GCR factor is the cost for the gas itself, before delivery and other charges are added on.
LDC – Local Distribution Company – a company that delivers natural gas in a defined geographic area.
MCF – One Thousand Cubic Feet – a common volumetric unit of measurement for natural gas. 1 – MCF has about 1 million BTUs in it, when natural gas has about 1,000 BTUs per cubic foot.
MMCF – One Million Cubic Feet – a volumetric unit of measurement for natural gas.
NGV – Natural Gas Vehicle – a vehicle designed or converted to run on compressed natural gas (CNG)
Psi – Pounds per square inch – the common method of measuring natural gas pressure. One psi is equal to 28″ of water column. A common delivery pressure for residential applications is 1/4 psi or 7″ water column. A common delivery pressure for industrial customers may be 10 psi. Power plants may get gas pressure delivered in several hundred psi or have a compressor on-site to boost the pressure to run combustion turbines.
To learn about the basics of natural gas gathering and delivery, visit the Interstate Natural Gas Association of America’s web site atwww.ingaa.org.
See also the Natural Gas Supply Association web site at www.naturalgas.org
Source: DTE Energy/MichCon Communications Department, edited by Bob Fegan 1-2008