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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 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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Outline:

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


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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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Horsepower

  • 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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II. Compressed Air Technologies


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Compressor Technology

Air Compressors

Dynamic Displacement

Positive Displacement

Rotary Screw

Centrifugal

Reciprocating

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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III. Regulation & Controls


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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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IV. System Location and Arrangement


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Possible Locations

#1

FACILITY


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Outdoors

  • 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

#1

FACILITY

#2


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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

#1

FACILITY

#3

#3

#3

#2


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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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Ventilation

  • 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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V. Compressor System Components-The Basics


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Basic Selection Criteria


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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

Pre-filter

After-Cooler

Dryer

Compressor

After-filter

“Wet”Receiver


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Dryers - Moisture Content

“Rule of Thumb”

Aftercooler

100ºF

80ºF

60ºF

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)

Purpose

  • Reduce oil carryover

    Benefit

  • Improved air quality

  • Improved product quality

    • Instrument air applications

    • Painting


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Dry Receiver (Recommended)

Purpose

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

    Benefit

  • 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.)

WARNING:

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

“Wet”Receiver

After-Cooler

Dryer

After-filter

Compressor

Air Cooled

oil coalescing

filter

1000 CFM

Compressor

Refrigerated airdryer with a 400 F dewpoint

1000 gallon

receiver


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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

Lubricated

50-100 PPM

Lubricated

50-100 PPM

Non - Lubricated

0 PPM

Non - Lubricated

0 PPM

Rotary Compressors

Rotary Compressors

Oil Flooded

3-10 PPM

3-10 PPM

Oil Free

0 PPM

Oil Free

0 PPM

Centrifugal Compressors

0 PPM

Centrifugal Compressors

0 PPM

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

WARNING:

Again overall system requirements should dictate system design


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Air Compressor Basics

Thank you for your kind attention


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