1. Natural Gas Engine Drive Air Compressor Training
Industrial Center, Inc.
Chicago, Illinois
April 9, 1997

2. Air Compressor Basics Presented By:
Allen L. Humphrey Industrial Marketing Manager Ingersoll-Rand Company Portable Compressor Division Air Compressor Group Mocksville, North Carolina

3. Hi !, I’m an expert in Natural Gas !
Isn’t all gas natural!!!
Hi !, I’m an expert in Natural Gas !
Gas utility marketing and sales representatives and the air compressor vendors are now rubbing shoulders in a joint effort to advance natural gas using equipment. They are now getting to know each other.(in the courting stage)
This is an attempt to get the meeting started with a little humor.
Gas Company Guy
Air Compressor Guy

4. I'm in trouble now, another guy full of hot air!!!
I’m an expert in compressed air,! Hot air, cooled, and dried
As they size each other up, they find there is a lot in common, ???
In any event, there is a need for joint co-operation and team selling onnmost NGEDAC jobs.
Air Compressor Guy
Gas Company 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
we have devided up the presentation into these 5 pieces. we’ll need to talk quckly to get everything presented in the allotted time. so let’s get going because compressed air is a very broad topic.

6. Compressed Air Facts
we are going to review some basics to get everyone on the same sheet of paper. this will be quite basic for some of you.

7. 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
The key here is that many organizations never do the work required to understand the real operating cost of their compressed air system, and it’s impact on their overall cost structure..

8. 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 = $
This is self explanatory. These relationships are general but give you an idea of what a 10cfm(3hp) compressor is about.
what it sez is that a 3 hp compressor can cost $1000/yr to operate.
A 100cfm(25hp) unit wld cost $10,000/yr on the same basis.

9. 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.
System leaks and over pressure operation are the largest conributors to wasted energy.
This gives you some idea of the significant cost associated with system leaks.!!

10. Air Basics Three Main Parameters 1. Pressure 2.Capacity 3. Horsepower
The 3 main energy constituents are pressure/capacity and resulting horsepower.

11. 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
System pressure is based on system capacity usage.(CFM)
Added system cfm users will ultimately cause pressure to be reduced.

12. 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
This is much simpler than it looks...
As the system’s air requirements exceed the compressor(s) capacity, air attempts to expand to provide more capacity at lower pressure.
However, it doesn’t catch up and the result is lower pressure.

13. The Cost of Pressure Good Rule of Thumb
Each # (PSI) of system pressure =
0.5% of system horsepower
If you don’t remember anything else, pls remember this.
when you want to estimate savings based on lowering the discharge pressure, this is a good estimating method to use.

14. 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, (Savings)
Excessive pressure is another major cause of high energy, and is an area that most consultants attack, in an attempt to justify their existance.
If this were a 1000Hp unit, the savings would approach $31,168/ year, not a paltry sum of $.

15. 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
This sis basic and good to remember.
Please note the comment about referring capacity back to inlet.

16. 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
It’s important to understand which capacity you are using.
If you are not certain, request clarification from your vendor.
For example, SCFM is used by the chemical; pneumatic and air separtion industries, AND THEY ALL HAVE A DIFFERENT BASIS TO DEFINE SCFM.
i.e. chemical co’s use 14.7/68degF and 32% RH as SCFM basis
Air separation industry uses 14.7/70degF/0% RH.as SCFM basis.
Mosy compressor companies use 14.7/60degF/0%RH as their SCFM std.
The point is that different SCFM standards may differ by 5-10%in capacity.

17. 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
Agin, different vendors assign different test tolerances to their equipment.
Request clarification so you can equate offerings.

18. 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
This summary statement gives a good rule of thumb for the compressed air system operation.

19. II. Compressed Air Technologies

20. Compressor Technology
Air Compressors
Positive Displacement
Dynamic Displacement
Reciprocating
Rotary Screw
Centrifugal
Single Acting
Double Acting
Oil Flooded
Oil Free
Here’s all the choices that exist for compressor designs. Interesting to note I-R mfg all.
I-R produces rotary and centrifugal natural gas engine driven compressors.
Single Stage
Two Stage
Lower Technology
Higher Technology

21. Dynamic Displacement “Performance Curve”
Starting with the most basic differences a dynamic compressor actually has a performance curve i.e. as pressure changes so does flow
Also sensitive to air and water temp as well as altitude
Critical to identify these factors when sizing these units

22. 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
The centrifugal compressors (dynamic) is by it’s design, an oil-free compressor where zero lubricant is injected into the air compressor discharge stream.
I-R has successfullt solved the difficult torsional analysis between a single shafted engine and a 3 or 4 shafted , mutiple stage speed compressor. The result has been excetionally low vibrtions between the engine and compressor, and successful operation.

23. Positive Displacement
“Performance Curve”
By comparison a positive displacement compressor has no true curve and really is not effected by ambient conditons
The slight slope of the curve is really only due to parasitic losses being reduced at lower pressures

24. 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
Positive displacement compressors provide varying capscity(cfm) by varying the driving speed, thus a variable speed driver like a Nat gas engine.
The single stage rotary, because of it’s operating characteristics, is the compressor technology of choice for NGEDAC.

25. Rotary Screw Oil Flooded- Single Stage Advantages Disadvantages
Low 1st cost; Low maintenance $
Simple packaged design
Adaptable to variable speed drive
Disadvantages
Somewhat lower efficiency
Moderate durability years on average

26. Rotary Screw Oil Free Advantages Disadvantages
High air quality- 0 PPM oil carryover
Moderate efficiency
Packaged design
Disadvantages
Higher initial cost
Higher maintenance cost
Limited work has been done to date in the area of NGED oil free positive displacement compressors, due to the high first cost of the oil free compressor elements.

27. Compressor Selection Criteria
Evaluated First Cost
Efficiency
Controls
Maintenance
Cooling
Air Quality
Durability

28. 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

29. 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

30. 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

31. III. Regulation & Controls

32. 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
Most facilities have more than one compressor
Most simply turn all units on first thing in the morning and turn them all off last thing in the evening
Since they may not all be set up complimentary, they are probably running at higher pressures than necessary
Some may not ever load for ? at a time

33. Regulation Basics Do not run compressors unnecessarily
Evaluate current regulation parameters
Consider upgrading substandard controls
The most efficient operating point is 100% full load.
Like the last slide says, the most expensive way to run a compressor is unloaded
Make sure your units are running in concert, not fighting each other
You may need to upgrade your controls to do this, but the cost is very easily justified

34. Basic Types of Regulation
This information will be covered in detail later in the seminar presentation

35. IV. System Location and Arrangement

36. Possible Locations #1
FACILITY
Outdoors is one option...

37. Outdoors Advantages Disadvantages Zero floor space Zero heat load
Potential weather damage (Freezing, water, etc.)
Potential lack of maintenance (Out of sight, out of mind)
It has pro’s and con’s...

38. Possible Locations #1 FACILITY #2
Another common area is inside the building in a corner or against a wall. #2

39. Indoors Centralized Advantages Disadvantages Protected from elements
Potentially easier access
Disadvantages
Greatest floor space
Potentially long piping runs

40. Possible Locations #1 FACILITY #3 #3 #3 #2
And finally, several locations throughout the facility #3 #2

41. 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

42. Environmental Factors
Temperature
Ventilation
Conditions
Atmosphere
Personnel
The next thing to consider is...what are the conditions?

43. Temperature - Low Below 350 F Recommendations
Possible control freeze problem
Possible condensate freeze problem
Possible fluid misapplication
Recommendations
Heaters
Heat tracing key elements
Relocate
Compressors are frequently regulated pneumatically, therefore water in the control lines that freezes will cause problems in the controls
Some standard lubricant’s have a pour point that is close to 35O F - this is would cause obvious problems
Units installed indoors, but with ductwork run outdoors can still see freezing temperatures if the ductwork is left open

44. Temperature - High Above 1000 F Recommendations Possible unit shutdown
Increased engine maintenance
Possible decreased lubricant life
Recommendations
Improved ventilation/relocate
Higher performance lubricant
More suitable equipment design
Many compressors will have insufficient cooling at ambient temperatures above 100O F
This will cause frequent nuisance shutdowns.
in addition, these elevated temperatures will contribute to accelerated wear of parts and lubricants

45. Ventilation Insufficient Ventilation Requirements
Possible unit shutdown
Increased maintenance
Possible decreased lubricant life
Requirements
Air-cooled
Water-cooled
Key component to proper compressor operation
Not uncommon to see machines installed without regard to proper air flow.
The end result is the same as high ambient temperatures.

46. Ventilation - The High Air Temperature (HAT) Vicious Cycle
Compressor Generates Heat
Insufficient Ventilation Causes Heat To Remain Around Unit
Unit Temperature Spirals Upward
Most common cause of compressor shutdown is HAT - High Air Temperature
The end result is that the compressor shuts down. The worst case scenario is that the compressor continues to run until it completely fails.
Insufficient ventilation also causes engine problems if intake air becomes excessive.
This Heat is Ingested By Engine-Compressor Increasing Operating Temperatures Of Unit

47. Miscellaneous Conditions
Atmosphere
Personnel
These important subjects will be covered later in the Seminar
Every manufacturer knows their equipment's requirements. This is stated in terms of both flow and acceptable back pressure.
What about ductwork? It’s a great source of cooler air with added benefits. It is critical to ensure that if added pressure losses are incurred that booster fans are utilized.
Engines are rated based on ambient temperatures; altitiude; and coolant temperature going to the turbo aftercooler(when supplied). Thus site conditions are an important ingredient in sizing and operation.

48. V. Compressor System Components-The Basics

49. Basic Selection Criteria

50. Real World Systems Design Criteria Air Quality required by User
Moisture content ?
Oil carryover ?
Contaminants
Pressure Drop
Demand Characteristics
Energy profile

51. Ideal Components For a Compressed Air System
Compressor
Aftercooler
Wet Receiver
Pre-Filter
Dryer
After Filter
Dry Receiver
A classic ideal system contains all of the following components

52. Ideal Components Layout
“Dry” Receiver
After-Cooler
Pre-filter
Dryer
Compressor
not all systems have all these components.
this arrangement provides good quality dry air at the exit.
It also includes components that can provide excessive drop when their elements become saturated, prior to changeout.
After-filter
“Wet”Receiver

53. 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.

54. After Filter (Recommended)
Purpose
Reduce oil carryover
Benefit
Improved air quality
Improved product quality
Instrument air applications
Painting
Typically, the coalescing filter, a.k.a.. oil removal filter, is equally as cost effective as a dryer.

55. 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
It is rare to see both a wet and dry receiver in a compressed air system
In reality, the costs involved in installing two receivers are quickly recovered with energy and quality savings.

56. Real World Systems Moisture Content
Pressure Dewpoint - Temperature at which water vapor condenses into liquid in a compressed airline
Select a dewpoint F below the lowest temperature the compressed airlines will see
Rule of thumb:

57. 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

58. 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
As an example...let’s look at a “typical” application

59. Real World System “Wet” Receiver After- Cooler After-filter Compressor
Dryer
After-filter
Compressor
Air cooled compressor with aftercooler
Simple 1000 gallon receiver to meet compressor needs
400 F dewpoint dryer 200 F below 600 F plant min. temp
Centralized oil removal filter
Air Cooled
oil coalescing
filter
1000 CFM
Compressor
Refrigerated air dryer with a 400 F dewpoint
1000 gallon
receiver

60. 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)
1/2% energy for each PSI, additional filters may become needlessly expensive
If very few components require lubricated air, most cost effective solution would be to utilize centralized oil removal filter and add lubricators at point of use.

61. 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
this is an area that is typically ignored in system design.
many problems in existing systems can be resolved by simply improving air storage to meet system demand

62. Real World Systems Typical Compressor Carryover Values:
Reciprocating Compressors
Lubricated
PPM
Non - Lubricated
0 PPM
Rotary Compressors
Oil Flooded
3-10 PPM
Oil Free
Centrifugal Compressors

63. 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
In other words some systems may require oil downstream.
most locations and only require removal at the paintbooth, etc.

64. 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

65. Thank you for your kind attention
Air Compressor Basics
Thank you for your kind attention