Reciprocating compressor: high/medium speed vs slow speed

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Page 1: Reciprocating compressor: high/medium speed vs slow speed

© 2012 Valerus. Confidential and proprietary. All rights reserved. © 2012 Valerus. Confidential and proprietary. All rights reserved.

Compression Split – Technical Seminar

September 26, 2013

Tom Birney, Director of Business Development

Page 2: Reciprocating compressor: high/medium speed vs slow speed

© 2012 Valerus. Confidential and proprietary. All rights reserved. © 2012 Valerus. Confidential and proprietary. All rights reserved.

COMPRESSION: COMPARISON OF HIGH / MEDIUM SPEED VS.

SLOW SPEED

Page 3: Reciprocating compressor: high/medium speed vs slow speed

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• Understand how a compressor functions NEWEST PRESENTATION

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• Overview of major components in the system

• Video – Compressor Package in Operation

PREAMBLE – RECIPROCATING COMPRESSOR BASICS

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COMPLETED PACKAGE

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SKID

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COMPRESSOR FRAME

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DRIVER & COUPLING

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COOLER & SHEAVES

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FUEL & UTILITY SYSTEM

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PULSATION BOTTLES

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SCRUBBERS

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PROCESS PIPING

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CONTROL PANEL

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EXHAUST SYSTEM & COOLER PLATFORM

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FINISHED!

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© 2012 Valerus. Confidential and proprietary. All rights reserved.

• Video – Compressor Package in Operation

• Arrow.wmv

PREAMBLE – RECIPROCATING COMPRESSOR BASICS

Page 17: Reciprocating compressor: high/medium speed vs slow speed

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API-11P (ISO-13631) VS API-618

API-11P (ISO-13631): High/Medium Speed Compressors

vs

API-618: Low Speed Compressors

Page 18: Reciprocating compressor: high/medium speed vs slow speed

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API-618 GENERAL OBJECTIVE

1st & 2nd Edition (1964)

• Reciprocating compressors in refinery business

• Drivers

– Integral & separable engines

– Electric motors

– Steam turbines

– Direct acting steam turbines

Current 5th Edition

• Reciprocating compressor in petrochemical, chemical and process gas industry services for handling process air or gas

• Applies to moderate to low speed in ‘critical service’ (Note: ‘critical service’ is not defined.)

• Drivers not covered

– Gas engine

– Steam engines (direct)

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API-618 GENERAL OBJECTIVE

• Design for a minimum 20 year service life

• Three (3) years of uninterrupted service (System design criteria)

• API-618 provides basic

• Compressor design standards

• Application limits

Page 20: Reciprocating compressor: high/medium speed vs slow speed

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HISTORY - API 11P / ISO-13631 VS API 618

• API-618 1st ed. published in 1964. to define standards for

reciprocating compressors for use in refinery service.

• In the early 1970s, packaged separable compressors became

prevalent in oil and gas production and API realized that API-618

was not applicable to this market. Hence, a standard that covers the

complete package was necessary.

Page 21: Reciprocating compressor: high/medium speed vs slow speed

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HISTORY - API 11P / ISO-13631 VS API 618

• API-11P - 1975 specifically covers packaged high-speed

separable reciprocating compressors for oil and gas

production applications.

• The 3rd edition of API-618, paragraph 1.1 was rewritten

to exclude “packaged high-speed separable engine-

driven reciprocating gas compressors.”

• The specification further defined “compressors covered

by this standard are moderate to low speed and in

critical services.” This addressed the growing use of

higher speed separable compressors for non-critical

services in refineries.

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HISTORY - API 11P / ISO-13631 VS API 618

• The 4th edition of API-618, states; “requirements for

packaged high-speed reciprocating compressors for oil

and gas production services are covered in API

Specification 11P.”

• The second edition of API-11P - November 1989

includes the following statement of applicability:

“This standard covers the minimum requirements for a

packager supplied, designed and fabricated, skid-

mounted reciprocating, separable or integral

compressor with lubricated cylinders and its prime

movers used in oil and gas production services…”

Page 23: Reciprocating compressor: high/medium speed vs slow speed

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HISTORY - API 11P / ISO-13631 VS API 618

• 618 Scope specifically states that 618 “does not cover gas engine

drivers”.

• In summary, applying API-618 to a packaged separable compressor

is contrary to the purpose and intent of API standards and could

result in lack of definition for critical requirements.

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DIFFERENCES - API 11P / ISO-13631 VS API 618

• Comments to API-618 5th ed. are available from most

manufacturers of separable compressors.

• Packagers can also provide complete packaging comments to API-

618.

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DIFFERENCES - API 11P / ISO-13631 VS API 618

• In general it should be remembered that API 618 is

written for longer stroke, slower speed units that are

normally block mounted and driven by electric motors.

The logic for some of the requirements does not apply to

packaged shorter stroke compressors driven by either

gas engines or electric motors. It is also important to

note that it may take some time before standards

recognize technological improvements.

Page 26: Reciprocating compressor: high/medium speed vs slow speed

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DIFFERENCES - API 11P / ISO-13631 VS API 618

• Examples:

• paragraph 2.1.1 requires a design suitable for “expected

uninterrupted operation of at least 3 years.”

• A gas engine must be maintained on a monthly basis

and therefore it does not make sense to invest in backup

auxiliary systems such as dual oil filters. Maintenance

on oil filters can be performed concurrently with engine

monthly

Page 27: Reciprocating compressor: high/medium speed vs slow speed

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DIFFERENCES - API 11P / ISO-13631 VS API 618

• Examples:

• Paragraph 2.6.2.3 states that “unless otherwise specified, each cylinder shall have a replaceable, dry-type liner, not contacted by coolant.”

• The main reason for liners on the longer stroke units is to provide an economical means for repair.

On average, for smaller bore cylinders a replacement barrel is less costly than a liner. Additionally, a metal spray processes can be used to rebuild cylinders to original dimensions. Metal spray processes are an even more economical repair technique.

Page 28: Reciprocating compressor: high/medium speed vs slow speed

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DIFFERENCES - API 11P / ISO-13631 VS API 618

• Examples:

• Paragraph 2.6.2.3 continued

• Adding a liner to a 15” stroke adds very little clearance but it is a

significant increase on the shorter stroke separable units.

• This can reduces volumetric efficiency and the flexibility of the

Variable Volume Clearance Pocket.

Additional base Clearance

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DIFFERENCES - API 11P / ISO-13631 VS API 618

• Cylinder Water Jackets:

• Water jackets required to address thermal bore distortion in

long-stroke cylinders

• Originally API-618 asked that water jackets not be included

• Water jackets added in 2nd edition due a unit that ran without gas flow

• Never meant as a method to ‘cool’ gas

• Desire for water jackets ‘institutionalized’ by API-618 requirement for specific approval of ‘air cooled’ cylinders

Page 30: Reciprocating compressor: high/medium speed vs slow speed

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DIFFERENCES - API 11P / ISO-13631 VS API 618

• Examples:

• Paragraph 2.6.3.2 states “air-cooled cylinders shall not be furnished without the expressed written approval of the purchaser.”

• Air-cooled cylinders have been in use for over 30 years with thousands of cylinders in operation and millions of successful running hours. The impact of forced liquid cooling on higher speed units is not nearly as significant as it is on the slower speed units.

Page 31: Reciprocating compressor: high/medium speed vs slow speed

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DIFFERENCES - API 11P / ISO-13631 VS API 618

• Examples:

• Paragraph 2.7.2 requires the purchaser to specify if

valve unloading is required.

• The norm for process machines is to use automatic

valve unloaders for both start up unloading and capacity

control.

• The norm for separable compressors is to unload for

starting with a bypass and to use speed and recycle for

capacity control.

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DIFFERENCES - API 11P / ISO-13631 VS API 618

• Paragraph 2.10.1.1 states “type A distance pieces are

used only for non-flammable or non-hazardous gases.”

• Packaged units are typically designed for ease of

shipment and width is an important design criterion. There

are thousand of units compressing sweet natural gas and

operating safely with API 11P / ISO-13631 type 1 distance

pieces

• With the smaller diameter piston rods used in separable

compressors, shorter rods are preferred to provide proper

stiffness.

Page 33: Reciprocating compressor: high/medium speed vs slow speed

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DISTANCE PIECE

Slinger

High efficiency

oil wiper

Intermediate packing

with optional purge

Pressure packing with

water cooling and purge

Window size allows removal

of complete packing case

Page 34: Reciprocating compressor: high/medium speed vs slow speed

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DIFFERENCES - API 11P / ISO-13631 VS API 618

• Paragraph 2.14.2 table 1

imposes arbitrary

pressure limits for cast

cylinders.

• These limits have not

changed in over 25 years.

Despite QC, finite

element analysis and

manufacturing

improvements.

Ion-Nitrider

Page 35: Reciprocating compressor: high/medium speed vs slow speed

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CYLINDER DESIGN HISTORY

Year 1964 2000

CastingDesign

HistoricalAlgorithms

ComputerModeled

CastingQuality

Good Better

DimensionalStability

MovementCaused Problems

No MovementProblems

Piston RingMaterial

Metallic orHard Non-Metallic

SoftNon-Metallic

HardenedCylinder Bore?

No Yes

Page 36: Reciprocating compressor: high/medium speed vs slow speed

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CYLINDERS

Moderate-Speed Low-Speed

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API 11P / ISO-13631 VS API 618

In conclusion:

Specifying API 618 for high speed packaged compressors can add

considerable cost, for limited benefits and may leave important

packaging issues unspecified. It is better to follow the intent of API and

use API 11P / ISO-13631 . If there are specific issues from API 618

that are important to the purchaser they should be addressed

individually.

Page 38: Reciprocating compressor: high/medium speed vs slow speed

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CAN MODERATE SPEED COMPRESSORS BE APPLIED IN

TRADITIONAL API 618 APPLICATIONS?

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SPEED

Low-Speed Moderate-Speed

RPM 200 - 700 700 – 1200

Stroke mm (Inch)

229 – 508 (9 – 20)

76 - 203 (3 – 8)

•Low and Moderate Speed Definitions

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ALLOWABLE SPEEDS

• Piston Speed

• Piston rings

• Wear bands

• Packings

• Rotating Speed

• Valve cyclic (fatigue) life

• Forces and moments

created

Wear is effected by:

Page 41: Reciprocating compressor: high/medium speed vs slow speed

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PISTON SPEED LIMITS

• Current limits for 3 year operation

• Lubricated: 4.3 m/s (850 ft/min )

• Non-lubricated: 3.8 m/s (750 ft/min )

• Acceptable speeds vary with user

• Lower piston speed provide longer operation

• Other factors affect wear part life

– Lubrication

– Surface finish of counter-face

– Pressure loading on wear part

– Non-metallic material selection

– Gas composition and any particulate

– Operating temperature

Page 42: Reciprocating compressor: high/medium speed vs slow speed

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EFFECTS OF OPERATING TEMPERATURE

135° C

(275° F)

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PISTON SPEED VS. DRIVER SPEED

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SPEED COMPARISON

High Speed Moderate Speed Traditional Slow Speed

Drive Speed (RPM)

1000 - 1800 700 - 1200 300 - 700

Piston Speed Lubricated m/s (ft/min)

4.6 – 6.1 (900 – 1200)

2.8 – 4.4 (560 – 870)

2.8 – 4.8 (560 – 910)

Piston Speed Non-Lube

m/s (ft/min) Not Available

2.3 – 3.8 (450 – 750)

2.3 – 3.8 (450 – 750)

Page 45: Reciprocating compressor: high/medium speed vs slow speed

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ROTATING SPEED

• Effects of rotating speed

• Valve cyclic (fatigue) life

• Compressor forces and moments

• Driver RPM capability has increased

• Materials

• Technology

Page 46: Reciprocating compressor: high/medium speed vs slow speed

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ROTATING SPEED

• Valve cyclic (fatigue) life

• Improved technology and materials

• Non-metallic materials

• Prediction and control of impact velocity

• Impact velocity stress rather than bending stress determines life

• Current non-metallic valve experience

• 3 year time between maintenance

• 1200 rpm

• 7 m/s impact velocity

Page 47: Reciprocating compressor: high/medium speed vs slow speed

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EFFECTS OF VALVE LIFT / IMPACT VELOCITY

Page 48: Reciprocating compressor: high/medium speed vs slow speed

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EFFECTS OF VALVE LIFT / IMPACT VELOCITY

VALVE COMPARISON:

Hi Speed Low Speed

Valve Type Non-Metallic Plate, Ring or

Poppet

Non-Metallic Plate, Ring or

Poppet

Valve Lift Mm (Inch)

1.5 – 2.6 (0.06 – 0.1)

1.5 – 2.5 (0.06 – 0.1)

Expected Valve Life

24 Months 36 Months

Page 49: Reciprocating compressor: high/medium speed vs slow speed

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ROTATING SPEED VALVE LIFE

• Other factors effecting valve life

• Valve Type

• Unknown operating points

• Oil sticktion

• Liquids

• Dirt

Page 50: Reciprocating compressor: high/medium speed vs slow speed

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ROTATING SPEED HORIZONTALLY OPPOSED

Inertial forces act in opposite directions

Equal masses result in equal but opposite forces

Page 51: Reciprocating compressor: high/medium speed vs slow speed

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ROTATING SPEED COMPRESSOR BALANCE (1 MW)

• Low-speed horizontally opposed

• 25 to 50 lbs. (11 to 23 kg)

• Moderate-speed horizontally opposed

• 2.5 lbs. (1.15 kg)

• Components weighed and balance components selected during

assembly

Page 52: Reciprocating compressor: high/medium speed vs slow speed

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MODERATE-SPEED COMPRESSOR BALANCE

Page 53: Reciprocating compressor: high/medium speed vs slow speed

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PISTON

Moderate Speed Low Speed

Piston Material Ductile Iron Ductile Iron or Aluminum

Piston Ring and Wear Band

Configuration

Piston Ring + Separate Wear

Band

Piston Ring + Separate Wear Band

Piston Ring and Wear Band

Material

Non-Metallic As Required

Non-Metallic As Required

Wear Band Loading

N/mm2 (psi)

0.035 (5)

0.069 (10) or 0.035 (5)

Page 54: Reciprocating compressor: high/medium speed vs slow speed

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COMPRESSOR COMPARISON

Natural Gas Process

Page 55: Reciprocating compressor: high/medium speed vs slow speed

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CYLINDER

Moderate Speed Slow Speed

Material Ductile Iron

Forged Steel

Ductile Iron Cast Steel

Forged Steel

NACE Option Yes Yes

Water Jacket Not Required As Required or As an Option

Cylinder Liner No As Required or As an Option

Surface Hardness 61 Rc

(Nominal) 25 Rc

Typical

Page 56: Reciprocating compressor: high/medium speed vs slow speed

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CAN MODERATE SPEED COMPRESSORS BE APPLIED IN TRADITIONAL

API 618 APPLICATIONS?

With correct application engineering

YES