Gas Compressor

GAS COMPRESSOR NATURAL GAS Compression – NTNU 2010

Compressors used in OIL & GAS Industry - Emphasis on Centrifugal compressor

Mahender Reddy Billam Dresser-Rand AS, Kongsberg.

Gas Compressor 1 – Compressor in Natural gas production & transport 2 – Types and Principles 3 - Centrifugal Compressor Selection process 4 – Compressor Components 5 – Latest developments

What does a Compressor do

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Reduce volume of gas

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Increase pressure of gass

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Control pressure in process

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GAS FROM RESERVIOR TO LAND

TYPICAL OIL PLATFORM

USE IN NATURAL GAS PROCESS 

ON PLATFORM

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- Re-compression – oil production

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- Export compressor (from platform)

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- Gas injection

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Processing plant

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- Export (boosting)

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- Prosessesing (take out water/condensate)

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- cooling circuits

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- Liquification

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Transport - Boosting ( long pipeline )

COMPRESSOR IN OIL & GAS PRODUCTION 

The compressors are responsible for a large part of the power demand in the oil and gas production .

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Example: I year 2007 have installed compressor with power requirmente of over 300000KW.

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Typical recompressor – 2000 kW ( from 500 kW t0 10000 kW)

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Typical export compressor - 25000 kW (often 2 or 3 machines)

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Typical injection compressor - 25000 kW ( ofte 2 machines )

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Typical ”Booster” on land – 25000 to 40000 kW – Many compressors at same station.

DRIVER 

Compressor can drive with both constant speed and variable speed.

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Constant speed give little flexibility, mostly used in prosessindustrien.

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Constant speed electrical motor – typical upto to 5000 kW

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Variable speed electrical motor (ASDS) - typical from 1000 t0 60000 kW

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Gassturbine – variable speed - typical from 1000 to 45000 kW

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Steam turbine - variable speed - typical from 1000 t0 50000 kW

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Traditionally gasturbines are used on platforms because of gas availability and has advantage on weight and dimension compared to electrical motor drivers.

COMPRESSOR ON KOLLSNESS

2 TYPES AND PRINCIPLE

• Compressor Type • Centrifugal - principle

Compressor Types

• Axial - large flow, low pressure • Centrifugal - large to medium flow, high presssure • Helical Screw - low flow, low pressure • Reciprocating - medium to low flow, high pressure

•Offshore North Sea - large flow, high pressure

Axial Compressor

Centrifugal Compressor

Reciprocating Compressor

Helical Screw Compressor

Basic Principles

• Centrifugal Action • A Centrifugal Stage • Energy Conversion

Centrifugal Action

Centrifugal Action

Velocity Relationship

A

Exit Path B

Centrifugal Action Cover

Blades

Disk

High Velocity, Higher Pressure Gas Outlet

Low Velocity, Low Pressure Gas Inlet

Impellers

DIFFUSOR From impellers gas flows in to diffuser

Diffusor

Diffuser converts kinetic energy to pressure energy

How A Centrifugal Works Centrifugal Stage

Return Bend

Return Bend

Diffuser Reduces Velocity Increases Static Pressure

Return Channel

Guide Vanes

Impeller Increases Velocity Increases Static Pressure

ONE COMPRESSOR TRAIN

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IMPELLER

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Transfer energy -pressure og speed

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DIFFUSOR

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Converts kinetic energy to pressure

…

GAS COMPRESSOR 3 – Centrifugal Compressor Selection process

Selection Process 

Inputs required for centrifugal compressor selection 

Typically Know:

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Ts inlet

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Ps inlet

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Pd outlet

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Flow (Q)

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gas composition

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Driver type (Gas Turbine, Steam Turbine, Motor)

Selection Process 

Selection Process 

Aerodynamic Selection and Optimization • Impeller Requirements (including Stress)

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Mechanical Design • Coupling size • Bearing and Seal sizes

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Rotordynamic Design • Could reselect coupling, bearings, seals

Polytropic Work (Head)

COURTESY OF BILL FORSTHOFFER

Basic Thermodynamic Equations

  P m    d  1    Ps   Head     R  Ts  Z avg m      

 (k  1) / k  m 

z = compressibility R = Universal Gas Constant

Redlich Kwong equation used to calculate compressibility(z)

(1545.3/Mw) Mw = Mole Weight k = Isentropic Exponent (Cp/Cv) Cp = Specific Heat at constant pressure Cv = Specific Heat at constant volume

Some Rotor dynamic terminology: Axial vibrations Torsional vibrations

y

z

x

Lateral vibrations

Concepts used in Rotor Dynamics: • Basic principles of vibrations • Knowledge of how a fluid film bearing works • Influence of bearings on the dynamics of the machine • Influence of labyrinth and damper seals on the dynamics of the machine

Some Rotor dynamic terminology: • Rotor: rotating element consisting of shaft, impellers/disks, shrunk-on components like sleeves, balance piston, etc. • Bearings: Journal bearings support the rotor in the lateral direction. (Thrust bearings support the axial load of the rotor while in operation.)

Some Rotor dynamic terminology (Contd.): • Natural frequency: Frequency at which the system vibrates. The frequency of vibration of a system (e.g. rotor-bearing system) with damping is called the damped natural frequency. •Ring of a bell or a tuning fork.

• Critical speed: Is a natural frequency with an ‘active enough’ response that the natural frequency should be designed around. (more on this later)

• Stability: The stability of a system is defined as the “reaction” to any external perturbation. (more on this later)

Compressor Control Recycle Valve

Recycle Increases Suction Flow

Polytropic Pressure Coefficient

Surge!

SURGE LINE

COMPRESSOR DESIGN POINT

105% Speed 100% Speed

90% Speed

Flow

GAS COMPRESSOR 4 – Centrifugal Compressor components

Rotor Assembly Balance Piston Impellers Drive Coupling Mount Shaft Thrust Rotor

Bearing Journals

Impeller Spacers Seal Area

Compressor Internals • Diaphragms • Inlet/Discharge Walls • Interstage Seals

STRAIGHT THROUGH FLOW De-ethaniser-D10R5S

Balance piston Thrust Bearing

bearing

Gas seals

Gas seal

bearing

KOMPRESSOR ACESSORIES - COMPONENTS 

Compressor

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Lube oil system

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Gasseal system – gas or oil

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Gear and Couplings

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Driver - el. motor, gasturbine, steam turbine

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Foundation skid

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Prosess- anti-surge valve, scrubber and cooler

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Instrumentation and control system

REMOVABLE LIFTING LUG

A.V.M (anti vibration mount)

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3 point support BASEPLATE (with central box beam beam))

DRIP PAN CONNECTION

GAS COMPRESSOR 4 – Centrifugal Compressor latest develoments

Latest Developments 

Compact integral Motor driven compressor

Latest Developments 

Compact integral Motor driven compressor - High speed Electrical motors - No gearbox - Magnetic bearings that eliminate need for oil lubrication - Reduced footprint - digital controls instead of analog controls - Emission-free design

Latest Developments Integrated Compression System(ICS)

DATUM I Compressor package

Latest Developments Integrated Compression System(ICS) 

The DATUM I system provides an efficient and compact method of gas-liquid separation that uses centrifugal forces to separate gas, oil and water from the flow. The separation process protects the compression flow-path from potential damage by removing free liquids from the gas stream which can cause subsequent fouling during the compression process.

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DATUM I can be used for upstrem, midstream and downsteam compression. Also for subsea compression.

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By incorporating Dresser-Rand’s proprietary centrifugal separation technology inside the compressor case, the DATUM I system efficiently separates liquid from the gas stream.

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Dresser-Rand’s proprietary centrifugal separation technology; a high-speed, close-coupled, gas-cooled motor; magnetic bearing rotor system; dedicated unit controls; process coolers, valves, instrumentation and interconnecting piping—all packaged in a compact module design.