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Natural Gas Engine Drive Air Compressor Training - PowerPoint PPT Presentation

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Natural Gas Engine Drive Air Compressor Training. Industrial Center, Inc. Chicago, Illinois April 9, 1997. Allen L. Humphrey Industrial Marketing Manager Ingersoll-Rand Company Portable Compressor Division Air Compressor Group Mocksville, North Carolina. Air Compressor Basics Presented By:.

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Natural gas engine drive air compressor training l.jpg

Natural Gas Engine DriveAir Compressor Training

Industrial Center, Inc.

Chicago, Illinois

April 9, 1997

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Allen L. HumphreyIndustrial Marketing ManagerIngersoll-Rand CompanyPortable Compressor DivisionAir Compressor GroupMocksville, North Carolina

Air Compressor Basics

Presented By:

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Isn’t all gas natural!!!

Hi !, I’m an expert in Natural Gas !

Gas Company Guy

Air Compressor Guy

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I'm in trouble now, another guy full of hot air!!!

I’m an expert in compressed air,! Hot air, cooled, and dried

Air Compressor Guy

Gas Company Guy

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I. Compressed Air Facts

II. Compressed Air Technologies

III. Regulation & Controls

IV. System Location and Arrangement

V. Compressor System Components - The Basics

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Compressed Air Facts

  • Most facilities consider compressed air a utility on par with electricity, gas, and water

  • However, few operating people know the real operating cost of their compressed air system

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What is cost per CFM ?

A Good Approximation

  • Typical Compressor produces 4 CFM per 1 Hp

  • 1 Hp = 0.746/0.9 = 0.829kW

  • Therefore, 1 CFM = 0.207kW

  • @ 0.06 $/kw-hr, 1 cfm = $0.0124/hr

  • 10 CFM over 8000 hours costs 10 x 8000 x 0.124 = $ 992.00

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Where are NORMAL savings ?

  • Fix System Leaks !!

  • Standard plant air system

    • 8000 hrs per year operation

    • Electrical costs = $ 0.06/kWhr

    • Plant line pressure = 100 PSIG

  • (1) 1/8th inch air leak = 26 CFM

  • 26 x 8000 x $.0124/hr = $ 2,579.00

  • A typical plant can have air leaks = to 20% of total air usage.

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Air Basics

  • Three Main Parameters

    • 1. Pressure

    • 2.Capacity

    • 3. Horsepower

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Pressure(PSI) = Pounds per Square inch

  • Completely dependent on system, controls and safety valves

  • An unregulated compressor will make ever increasing pressure until a failure occurs

  • When plant capacity demand exceeds system capacity(CFM), compressor discharge pressure will drop

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Pressure - Capacity Relationship

P1= Initial pressure V1= Initial capacity

P1 x V1 = P2 x V2

P2= Final pressure V2= Final capacity

If a system needs more capacity(CFM) than available, plant pressure drops in an unsuccessfultrade of pressure for capacity

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The Cost of Pressure

Good Rule of Thumb

Each # (PSI) of system pressure


0.5% of system horsepower

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Pressure Cost Example

  • 100Hp compressor set to discharge at 125 psig to plant system

  • Plant system only requires 110 psig

  • User resets compressor discharge pressure to 110 psig ( a 15 psi reduction)

  • 15 PSI = 7.5 % of Hp = 7.5 Hp

  • 7.5 x .746/.85 = 6.6kW x 8000 hrs x $.06/kWhr = $ 3,168.00 (Savings)

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Capacity(Flow) = CFM(ft3per minute)

  • Basic measure of true compressor output

  • A fixed value in most designs, for a given model

  • Most all capacity measurements are referred back to inlet conditions. Capacity varies only slightly with a change in discharge pressure, for a given model

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Capacity Measurement

  • In the pneumatics industry, ALL capacities are measured referring back to inlet conditions

  • Various formulae are used to define capacity(CFM):

    SCFM; ACFM; ICFM; FAD, etc. Require your vendor to define which and where

  • ASME and CAGI-Pneurop have generally accepted testing standards

  • Capacity tolerances may vary from vendor to vendor. Request definition

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  • Typically, electric motor nameplate HP or NG engine MCHP(Max Continous Hp)

  • The work it takes to compress “X” CFM up to “Y” PSI

  • Driver HP is usually fixed. If either CFM or PSI is increased, the driver may overload, unless regulation, a speed reduction, or a change in either CFM or PSI takes place.

  • Horsepower tolerances may vary from vendor to vendor. Request definition

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Air Basics Translations

  • Capacity(CFM) does the work; Pressure effects the rate at which the work is done

  • A trending decrease in plant air pressure typically indicates a requirement for more capacity(CFM), not pressure

  • Increasing or decreasing the existing compressor discharge pressure will normally have negligble effect on the compressor capacity

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Compressor Technology

Air Compressors

Dynamic Displacement

Positive Displacement

Rotary Screw



Single Acting

Double Acting

Oil Free

Oil Flooded

Single Stage

Two Stage

Lower Technology

Higher Technology

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Dynamic Displacement

“Performance Curve”

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Centrifugal Compressors

  • Advantages

    • Only real option over 600+ Hp

    • High air quality- 0 PPM oil carryover

    • Moderate to high efficiency

    • Longer design life than Rotaries

  • Disadvantages

    • Higher initial cost

    • Fluid cooled only

    • Power reduction down to 70% flow

    • Constant speed operation

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Positive Displacement

“Performance Curve”

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Positive Displacement

  • Reciprocating or Rotary Screw Designs

    • Constant cfm; Variable pressure

    • Adaptable to variable speed drive

    • Variable speed and unloading provide close alignment with system demand

  • Oil Flooded Rotary Screws--The design of choice for NGEDAC’s

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Rotary Screw

Oil Flooded- Single Stage

  • Advantages

    • Low 1st cost; Low maintenance $

    • Simple packaged design

    • Adaptable to variable speed drive

  • Disadvantages

    • Somewhat lower efficiency

    • Moderate durability - 10 15 years on average

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Rotary Screw

  • Oil Free

  • Advantages

    • High air quality- 0 PPM oil carryover

    • Moderate efficiency

    • Packaged design

  • Disadvantages

    • Higher initial cost

    • Higher maintenance cost

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Compressor Selection Criteria

  • Evaluated First Cost

  • Efficiency

  • Controls

  • Maintenance

  • Cooling

  • Air Quality

  • Durability

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General Guidelines- First Cost

  • Single-stage rotary screw

    • Typically lowest first cost

    • Greatest market growth, largest population

    • Typically lowest efficiency

  • Possible Alternatives

    • Two-stage rotary screw

    • Oil free rotary screw*

    • Centrifugal*

      *Dependent on air quality requirements

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General Guidelines- Maintenance

  • Capabilities of on site maintenance personnel ? Contract maintenance ?

  • Oil flooded rotaries typically require lowest maintenance

  • “Air-in-the-box” design enables on site overhauls of both compressor system and engine

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General Guidelines- Cooling

  • Fluid-Air cooled - less expensive

  • Most designs have fluid or fluid-air cooled design options available

  • Closed evaporative cooling towers; open towers and external fluid to air coolers are viable cooling options

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Regulation/Controls Applications

  • Average number of compressors = 2.5 per facility

  • Typical system controls: manual/ none

  • Each incremental 1 PSIG of unnecessary pressure cost 0.5% of compressor horsepower

  • Each electric motor driven compressor running unloaded = 35-50% of the full loaded electrical costs

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Regulation Basics

  • Do not run compressors unnecessarily

  • Evaluate current regulation parameters

  • Consider upgrading substandard controls

  • The most efficient operating point is 100% full load.

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Basic Types of Regulation

This information will be covered in detail later in the seminar presentation

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Possible Locations



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  • Advantages

    • Zero floor space

    • Zero heat load

  • Disadvantages

    • Potential weather damage (Freezing, water, etc.)

    • Potential lack of maintenance (Out of sight, out of mind)

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Possible Locations




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Indoors Centralized

  • Advantages

    • Protected from elements

    • Potentially easier access

  • Disadvantages

    • Greatest floor space

    • Potentially long piping runs

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Possible Locations







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Indoors Decentralized

  • Advantages

    • Possible to install closest to large air users

    • Least amount of pressure drop through air lines

  • Disadvantages

    • Highest probability of incorrect regulation

    • Potential to spread noise and heat complaints to broadest number of employees

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Environmental Factors

  • Temperature

  • Ventilation

  • Conditions

    • Atmosphere

    • Personnel

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Temperature - Low

  • Below 350F

    • Possible control freeze problem

    • Possible condensate freeze problem

    • Possible fluid misapplication

  • Recommendations

    • Heaters

    • Heat tracing key elements

    • Relocate

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Temperature - High

  • Above 1000F

    • Possible unit shutdown

    • Increased engine maintenance

    • Possible decreased lubricant life

  • Recommendations

    • Improved ventilation/relocate

    • Higher performance lubricant

    • More suitable equipment design

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  • Insufficient Ventilation

    • Possible unit shutdown

    • Increased maintenance

    • Possible decreased lubricant life

  • Requirements

    • Air-cooled

    • Water-cooled

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Ventilation - The High Air Temperature (HAT) Vicious Cycle

CompressorGenerates Heat

Insufficient Ventilation Causes Heat To Remain Around Unit

Unit TemperatureSpirals Upward

This Heat is Ingested By Engine-Compressor Increasing Operating Temperatures Of Unit

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Miscellaneous Conditions

  • Atmosphere

  • Personnel

    These important subjects will be covered later in the Seminar

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Real World Systems

Design Criteria

  • Air Quality required by User

    • Moisture content ?

    • Oil carryover ?

    • Contaminants

  • Pressure Drop

  • Demand Characteristics

  • Energy profile

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Ideal Components For a Compressed Air System

  • Compressor

  • Aftercooler

  • Wet Receiver

  • Pre-Filter

  • Dryer

  • After Filter

  • Dry Receiver

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Ideal Components Layout

“Dry” Receiver







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Dryers - Moisture Content

“Rule of Thumb”





Air Compressor

100% RH

100% RH

100% RH

Effect of Compressed Air Temperature on sizing of drying equipment.

A 20º F reduction in temperature condenses 50% of the water vapor in saturated air.(Collect it; trap it; dispose of it)

A 20º F. rise in temperature doubles (200%) the moisture holding capacity of the air.

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After Filter (Recommended)


  • Reduce oil carryover


  • Improved air quality

  • Improved product quality

    • Instrument air applications

    • Painting

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Dry Receiver (Recommended)


  • Provide a reservoir of clean dry air to meet fluctuating system demands


  • When sized and installed correctly can minimize airline pressure fluctuations

  • Prevents short term capacity requirements from overloading cleanup equipment

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Real World Systems

Moisture Content

  • Pressure Dewpoint - Temperature at which water vapor condenses into liquid in a compressed airline

    Select a dewpoint 10-200F below the lowest temperature the compressed airlines will see

Rule of thumb:

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Real World Systems

This applies only to general industrial application. Specific applications have specific dewpoint requirements (i.e., paint booths, instruments, etc.)


Contact equipment OEMs

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Real World Systems

“Typical” Real World System

  • A 1000 CFM system with

    • lowest plant ambient temperature of 600F

    • sensitivity to lubricant

    • fairly steady plant demand

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Real World System






Air Cooled

oil coalescing


1000 CFM


Refrigerated airdryer with a 400 F dewpoint

1000 gallon


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Real World Systems

Pressure Drop

  • Pressure Drop is the cost of air quality

    • Every air clean up device will utilize 2-10 PSI to perform its function

      • Air dryers typically 3-5 PSI

      • Air filters typically 2-10 PSI (dependent on how long the element has been in place)

        Remember @ 1/2% energy for each PSI, additional filters may become needlessly expensive

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Real World Systems

Demand Characteristics

  • Receiver size and placement varies depending on plant demand cycle and receiver size

  • Possible to supply a new intermittent large air user with a properly sized and installed receiver tank

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Reciprocating Compressors

Reciprocating Compressors


50-100 PPM


50-100 PPM

Non - Lubricated


Non - Lubricated


Rotary Compressors

Rotary Compressors

Oil Flooded

3-10 PPM

3-10 PPM

Oil Free


Oil Free


Centrifugal Compressors


Centrifugal Compressors


Real World Systems

Typical Compressor Carryover Values:

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Real World Systems

Oil Content Requirements

  • Whether the oil is removed at the compressor, or at the point of use, should be determined by overall plant requirements

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Real World Systems

Although some equipment may benefit from (or even require) lubricant in compressed air, many other applications (paint booths, instrumentation) cannot tolerate it


Again overall system requirements should dictate system design

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Air Compressor Basics

Thank you for your kind attention