Natural Gas Engine Drive Air Compressor Training

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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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Isnt all gas natural!!!
Hi !, Im an expert in Natural Gas !
Gas Company Guy
Air Compressor Guy
4
I'm in trouble now, another guy full of hot air!!!
Im an expert in compressed air,! Hot air,
cooled, and dried
Gas Company Guy
Air Compressor Guy
5
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
• _at_ 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 x V1 P2 x V2

• P1 Initial pressure V1 Initial capacity

P2 Final pressure V2 Final capacity
If a system needs more capacity(CFM) than
available, plant pressure drops in an
unsuccessful trade 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
Oil Free
Single Acting
Double Acting
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 NGEDACs

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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 350 F
• 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 1000 F
• 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
WetReceiver
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Dryers - Moisture Content
Rule of Thumb
Aftercooler
60ºF
80ºF
100ºF
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 10-200 F below the lowest
  temperature the compressed airlines will see

Rule of thumb
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Real World Systems
WARNING

• 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 600 F
• sensitivity to lubricant
• fairly steady plant demand

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Real World System
WetReceiver
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 _at_ 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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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
WARNING

• 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