Natural Gas Pipelines Process

Introduction

Currently, over 95 percent of natural gas used in the United States moves from well to market entirely via pipeline.

Natural gas pipeline networks are generally broken into three distinct systems:

Gathering systems carry natural gas from individual wells for bulk processing at a treatment facility,

Transmission systems carry the processed natural gas, often over long distances, from the producing region to local distribution systems around the country.

Local distribution systems deliver natural gas into our homes, businesses and power plants.

Natural gas pipelines are generally smaller in diameter than petroleum pipelines. Pipelines in the gathering and distribution systems range from 6" to 16" in diameter, with certain segments as narrow as 1/2". The pipes making up the interstate transmission system range in diameter from 16" to 48".

Compressors

Natural gas can travel through literally thousands of miles of pipeline in the journey from the well to your home. Compressors placed at key intervals - usually every 40 to 100 miles along the pipeline network - keep the natural gas moving evenly and reliably.

A so-called "reciprocating" compressor uses a piston to reduce the volume of its compression chamber, increasing the pressure of the gas inside. When the outlet valve opens, the pressurized gas rushes out into the next section of the pipeline. Most reciprocating compressors are powered by natural gas drawn directly from the line.

Natural gas pipelines also employ turbine compressors, which are similar in design to the jet engines found on commercial aircraft. And in a few limited circumstances, where strict air emission rules require, pipelines also use compressors powered by electric motors.

“City Gates”

A distribution system, such as a local utility, connects to the interstate pipeline at a "city gate." This facility reduces the pressure of the natural gas from its transmission rate (from 200 to 1,500 pounds per square inch) down to a rate more appropriate to consumer usage (as low as 3 psi). The city gate also adds sour-smelling Mercaptan to the naturally odorless gas to make it easier to quickly sniff out a natural gas leak.

Storage

Production rates and pipeline throughput are relatively fixed, but demand for natural gas - a popular home-heating fuel - is significantly higher during the winter months. This makes delivery-side storage capacity essential to assuring a steady, reliable supply of natural gas when you need it most.

Natural gas is most often stored in depleted (empty) natural gas or oil fields. These underground formations have already proven they can securely trap and contain natural gas, so they make useful reservoirs for natural gas delivered through the interstate pipeline. Natural gas may also be stored in underground salt caverns -- geologic formations whose walls are impermeable to natural gas.

Also there are over 100 natural gas utilities that liquefy natural gas for aboveground storage. This is not an unusual practice and it offers another safe, proven natural gas storage alternative for the future.Liquefied natural gas is also proving to be an important new option for transporting natural gas from regions not served logistically or economically serviceable by pipelines.

Liquefied Natural Gas (LNG)

Some natural gas sources are too difficult or too expensive to reach via pipeline. Converting natural gas to liquid form - which occurs at approximately -260F - decreases its volume by more than 600 times and allows other transportation options, such as specially outfitted tanker ships and trucks, to be used. Once the liquefied natural gas reaches its destination, it is revaporized and transported through existing pipelines.

The insulated tanks that store LNG use "autorefrigeration" to keep their contents cold. First, the natural gas is chilled to -260F° -- the temperature at which it condenses from gas to liquid. At that point, any heat gained from the atmosphere outside the tank is offset by the cooling effect of the resulting LNG evaporation within the tank. (Just wet your hand and let it air dry; you’ll feel evaporation’s cooling effect for yourself.) Any re-vaporized natural gas can be vented and recovered for use.

source :http://www.adventuresinenergy.org