| To evaluate a compressed air system, you must
begin at the end: What are your air requirements at the point of use? Once
you determine exactly what type and how much air you need, you can begin
to factor-in design considerations, costs, and efficiencies. |
| Design Considerations |
| Careful planning of a compressed air system
is essential for smooth operation. System configuration should take into
consideration both your requirements and the physical characteristics of
your installation. |
| Air-cooled vs. Water-cooled. |
| Air-cooled compressors have either integrally-mounted
or separate oil and air coolers. These coolers require adequate ventilation
to perform reliably. For water-cooled compressors, a supply of adequate
pressure and quality water must be available. |
| Single vs. Multiple Units. |
| Air compressors operate most efficiently at
full load. Depending on your usage profile, it may be more costeffective
to purchase multiple compressors to accommodate load variations. |
| Sequencers. |
| Sequencers improve the efficiency and reliability
of multiple compressor systems. With microprocessor controls, they can
stabilize system pressure and even track each unit's service, load, and
maintenance hours. |
| Heat Recovery. |
| Recovering and using the heat generated by
an air compressor conserves energy. Waste heat has many applications including
process use, space heating, and preheating boiler feedwater. |
| Aftercoolers. |
| These heat exchangers cool the compressed
air, thereby condensing much of the moisture for easy removal. This prepares
the air for further treatment. |
| Receiver Tank. |
| If you have widely varying compressed air
loads, you should consider a receiver tank to boost capacity during peak
periods. With a larger receiver tank, you can meet occasional peak demand
with a smaller compressor and avoid high electrical demand charges. |
| Dryers. |
| Removing moisture from compressed air is essential
for virtually all applications. Air quality requirements and ambient conditions
will help determine the type of dryer required. |
| Piping. |
| Pipes must be carefully sized and arranged
to minimize pressure drop and should be sloped to drain towards a drop
leg or moisture trap. |
| Filters, Regulators, & Lubricators. |
| These should be installed at the point-of-use. |
| Condensate Control. |
| Because condensate must be expelled from the
system for reliable operation, drain traps should be included in the system
plan. Additionally, most localities require that any oil be separated from
condensate before the water can be disposed of in the municipal system. |
| Booster Compressors. |
| These compressors will efficiently increase
air pressure from the plant system for equipment or processes that require
up to 500 psig or higher pressure. |
| Air Requirements |
| Air Quality. |
| There are six key levels of compressed air
quality ranging from shop air to breathing air. The quality of air required
will determine which type of filtration and drying system is needed. |
| Air Capacity. |
| Begin with capacity requirements and load
factors for each tool and machine that will use compressed air. These compressed
air requirements are generally available from the equipment manufacturers. |
| Air Pressure. |
| Determine the pressure required at the point
of use. Pneumatic tool manufacturers rate tool capacities at specific pressure
ratings. The minimum required pressure can be determined by the equation: |
| Pr |
= |
Pp + PL where: |
| Pr |
= |
Minimum required pressure, psig. |
| Pp |
= |
Pressure at point of use, psig. |
| PL |
= |
Total pressure loss, psid. |
Total pressure loss includes any losses at the air receiver, dryers, centrifugal
separator, particulate filter, oil removal filter, and oil vapor adsorber,
as well as piping and valves. |
| Once capacity and pressure requirements are
known, the air compressor size and input power requirements can be obtained
from manufacturers. |
| Cost of Compressed Air |
You must go beyond initial cost when evaluating compressed air systems.
During the first year, operating costs for compressed air can be 1 1/2
to 2 times the initial purchase price of the equipment. Efficiency of the
compressor and the overall system efficiency are critical. |
| Electrical Expense. |
| As much as 70% of compressed air cost is electrical. |
| Cooling Cost. |
| If you are considering air-cooled compressors,
factor-in the electricity used to run cooling fan motors. If evaluating
a water-cooled system, consider the quantity and required quality of the
water, as well as treatment, electrical, and disposal costs. |
| Maintenance and Repair Costs. |
| The easier the system is to maintain, the
more you save in the long run. Can the system be maintained and repaired
by your in-house personnel, or does it require out-of-house assistance
for most problems? |
| Leaks and Unnecessary Demand. |
| Any leaks in your system will add to your
operating costs. Unnecessary use of compressed air is wasteful and expensive. |
| Reliability. |
| An unreliable compressed air system can be
disastrous to the bottom line. A lost production day is never made up. |
Six Levels of Compressed Air Quality
|
Application
|
Level
|
Air Treatment Components
|
| Shop Air |
1
|
Filtered Separator |
Sir Tools, Sand Blasting,
Pneumatic Control Systems |
2
|
Refrigerated Compressed
Air Dryer, Particulate Filter |
Instrument Air, Paint
Spraying, Powder
Coating, Packing Machines |
3
|
Refrigerated Compressed
Air Dryer, Oil Removal Filter |
Food Industry, Chemical
and Pharmaceutical Industry
Laboratories |
4
|
Refrigerated Compressed
Air Dryer, Oil Removal Filter,
Oil Vapor Adsorber |
Outdoor Pipelines,
Pneumatic Transport of
Hygroscopic Material,
Breweries, Dairy Industry |
5
|
Particulate Filter,
Oil Removal Filter,
Low Dew Point Desiccant
Dryer, Particulate Filter,
Oil Vapor Adsorber |
| Breathing Air |
6
|
Breathing Air System (continuous or portable) |
|
|
Types of Compressors
/ Selecting an Air Compressor / Maintenance
/ Troubleshooting / Glossary
and Reference Data
|
|
© Copyright
2007 Maintenance Resources, Inc.
|
| Phone: 812.877.7119 -
Fax: 812.877.7116 - E-Mail: info@maintenanceresources.com |
|
Address: 120
South Hunt Street - Terre Haute, IN 47805
|
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