Gas Processing Fundamentals(1) - "Principles of Gas Processing" #Download no.19

1. OVERVIEW

    The natural gas used in our homes and industries does not come out of the ground ready to be burned for heat and fuel. The gas often contains too many contaminants at the wellhead to meet the quality specifications set by natural gas buyers. In addition, the natural gas stream may contain natural gas liquids (NGLS, or hydrocarbon liquids) that could have increased value when separated from the gas stream. So the gas is put through a series of processes in order to make it usable. Those processes used to remove contaminants and separate. NGL's are referred to as processing.

Symbol	TYPICAL NATURAL GAS  STREAM
Methane       (C1)	For home and industrial use as a fuel ( stove, water heater, etc. )
Ethane          (C2)	Makes glycol, anti-freeze ,plastics, etc.
Propane       (C3)	Used as a commercial fuel .
Isobutane    (C4)	Used in making plastics, and as a gasoline “ Spiker ”
Normal Butane Products. (NC4)	Used as a fuel, also for making plastics and certain rubber products.
Pentane (C5+)	Pentane plus anything “ heavier ” ( or containing more than five carbon atoms ) is basically gasoline.
Symbol	Contaminants
Nitrogen (N2)	Has no BTU value, just takes up space in the gas stream.
Carbon Dioxide (CO2)	Reduces the BTU rating of the gas, and is also corrosive.
Hydrogen Sulfide (H2S)	Is corrosive and toxic.
Water (H2O)	IS corrosive to pipeline, and can lead to the formation of hydrates .

Separation

     Gas processing starts at the wellhead. When gas comes out of the ground, it normally contains liquids such as oil and water. These liquids must be separated from the gas before the producer can sell the gas. This separation is usually accomplished at the wellhead using a device known as a three phase separator.

Three – Phase Vertical Separator

Metering

      The separated gas is then routed through a meter station and sent to a process­ing facility. Metering is a critical function because in order to maximize profits it is important to know how much gas is leaving the well. and how much is arriving at the process­ing facility. A major difference in those amounts could indicate a breakage in the pipeline.

Gas Gathering

       After metering, the gas moves through a pipeline to a processing facility. To process gas efficiently, it is usually piped from many producing locations to a central process­ing facility. This is much more efficient and economical than setting up separate process­ing facilities for each production stream. Bringing various Quantities of gas together at one location for processing is called gas

Gas gathering systems are composed of pipelines and "booster" stations that increase the gas pressure as needed to. move the gas to its destination. These systems can range from one mile to thousands of miles in length.

Processing 

      Once the gas reaches the central processing facility, it is put through several processes to meet sales Quality specifications. These processes can be broken down into two major categories: Removal of contaminants and removal of natural gas liquids (NGLS).