Page 30 - Compression Machinery for Oil and Gas

20 SECTION I Fundamentals of Compression

Corrosive gases (aka “sour” gas) such as sulfur rich or hydrogen sulfide
compounds may be present in some raw production gas streams. This always
requires special treatment and added design and protection to the compressor’s
internal steel and sealing materials to withstand the corrosive gas streams as
much as technically possible. Industry standard treatment systems for corrosive
gases include wetting the gas stream with specialized chemicals (amine or sim-
ilar) in contactor towers then separating the liquid from the gas stream with sep-
arators. Specialized dry chemical absorbents are also commonly used to remove
corrosive gases in lower flow designs.

Driver Type and Fuel Source

There are generally three main types of “prime movers,” which include recip-
rocating engines, gas turbines, and electric motors. Steam turbines are also used
in process applications where steam is generally available for other process rea-
sons. Reciprocating engines are typically used to drive reciprocating compres-
sors and they can often be subdivided into “slow speed” ( 600rpm) and
“medium-to-high speed” (600–1800rpm) classifications. These engines can
have two-stroke or four-stroke cycles and may or may not be turbo-charged.
These “slow speed” engines are often used in an “integral” configuration where
the compressor and engine share a common crankshaft. Separable systems have
physically separate drivers and compressors connected by a gearbox or
coupling.
Gas turbines can be industrial type or aeroderivative type (based on designs
originally intended for aviation applications). Gas turbines operate at much
higher operating speeds and are well suited for operation with centrifugal com-
pressors or where minimizing weight is a priority (such as offshore).
Electric motors can be induction, synchronous, or DC, with induction being
the most common. Electric motor drives pair well with reciprocating compres-
sors based on their similar operating speeds, but electric motors can also be
paired with centrifugal compressors.
One key factor in determining the preferred driver type will be the available
fuel sources. Both gas engines and gas turbines can often run off of fuel gas
pulled from the main process gas. However, electric motors obviously require
an uninterrupted source of electrical power. Other factors such as installation
cost, operating and maintenance costs, efficiency, noise, emissions, reliability,
etc. should also be considered.
See additional discussion on drivers in Chapter 7.

Emissions, Noise, and Safety
Factors relating to emissions, noise, and safety must be considered in any new
compression facility. There are numerous regulatory and permitting require-
ments that must be met in regard to these factors to protect the public health.