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).

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

2:30:00 PM Gas Processing, Petroleum and Gas Processing

Petroleum and Gas Field Processing #Download no.6

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Petroleum and Gas Field Processing #Download no.6

7:12:00 PM Gas Processing, Petroleum and Gas Processing

Acid Gas Removal-Selection Criteria

Natural Gas Processing

One of the most common sources for gas treating is Natural gas , with a huge range in the  ratio of CO2/H2S and with treating by high pressure . If natural gas isn't an application of LNG , it can be treated by  H2S removal if the ratio of CO2 is quite high. If propane  and higher fractions is present, the need of using mixed solvents or physical  is reduced. And vice versa in the case of presence of organic Sulfur 

When natural gas has significant CO2 or H2S ratios:

For large units, it is recommended to use proprietary solvents

For small units,it is recommended to use conventional solvents particularly with modest acid /sour gas levels

Petroleum Refining

The second source is Petroleum refining ,  gas treating source with low CO2 content, in this case the gas may have organic sulfur, COS, organic acids ,cyanides, and ammonia. The acid gas obtained from hydrocracking and hydrotreating basically contains H2S and NH3. The gas H2S specifications and the gas treating pressures have agreat variation for each individual application, and MDEA / DEA / MEA or (formulated amines) are the systematic solvents. The refinery has multiple absorbers, typically, and many regenerators . They are:

*Treating of Fuel gas 

*product/fuel gas of Hydrotreater

*Recycle gas of Hydrotreater

*Hydrocracker product/fuel gas

*Recycle gas Hydrocracker

*LPG liq-liq contactor

*catalyst/Thermal cracker gases

*Services  combined or independent as practical

Treatment of Synthesis Gas 

The treatment of synthesis gas can be distinguishd by high ratio of CO2 and low (or may no) H2S. If there is a limitation of CO2 amount, it is favored to use selective H2S treating by physical solvent, formulated amine, or mixed solvent. If there is no H2S and modest complete CO2 removal is present, it is favored to use physical solvent, hot potassium ,activated MDEA, and mixed amine.

Outline of Data Base

How to select the o process?

Types of gas-treating units are many categories and each of them requires its own simulator, solvents, or technology. However, those projects are required to be studied with several technologies to meet the required specification,

duties, and circulation rate which are truly dependent on the composition of the gas (such as NH3, H2S,and CO2). In addition and to make sure it is economic, the selected optimized process must be evaluated.

The Table below represents the most common processes being used in gas plant industries.

 source: State-of-the-Art In Gas Treating 

for

Mahin Rameshni, P.E.

Chief Process Engineer

Acid Gas Removal-Selection Criteria

9:19:00 PM Gas Processing, Natural Gas Treatment