Compressed Air Contamination in Commercial Printing
Compressed air contamination is a major issue in almost all printing environments. Compressed air frequently comes directly in to contact with the paper where water and oil will destroy the final product. Open blowing of compressed air is used to separate sheets, control the flow of sheets, transfer between presses, sheet insertions and sometimes equipment cooling (hot bearings for example). Water and oil on the printed sheet creates a loss of products that has no recovery value and must be disposed of in an environmentally safe fashion.
Most equipment printing press manufacturers expect to install their equipment in a system with at least some contamination. This will force them to install point of use clean up and control equipment (filters, regulators and lubricators) which increases capital costs. Additionally the different pressure of these components increases the operating cost in the form of higher supply pressure to overcome the pressure drop of these point of use components. Since the printing press manufacturer is not responsible for the operating costs there is seldom any engineering for the point of use components. Capital cost is the primary consideration when selecting this equipment. The least expensive components will more than likely have significantly greater differentials. Some applications such as air bearings can not tolerate any contaminations. This will result in extra filtration and drying equipment at the point of use.
Most supply systems will have (at least limited) clean up equipment consisting of a refrigerated dryer and filtration. A few will use more the more expensive desiccant dryer technology. The “system” for printing applications needs to be free of all liquids absolute for all operating conditions, which can be accomplished by refrigerated and desiccant technologies. Compressed air supply from the compressor room that is clean and dry will not require POU dryers and filtration. This reduces capital costs, filter maintenance costs and pressure drop.
Compressed Air Basics
The Department of Energy (DOE) has determined that air compressors are one of the largest users of electricity in industry. Although at one time the DOE considered electric motors as the largest user of electricity, savings through improved electric motor efficiency are dwarfed by those available through improving the compressed air system design and operation.
Energy savings through improved design and operation of the air system can range from 20-50%. Most facilities consider compressed air a utility on par with electricity, gas, and water. Unlike other utilities, few people know their cost per CFM.
Here is a good way to find out
- Assumptions
- Motor Service Factor = 110%
- Power Factor = 0.9
- A typical compressor produces 4 CFM per 1 HP
- 1 HP = 110% x 0.746 KW/0.9= 0.912 KW
- Therefore,1 CFM = 0.228 kW
- At 0.06 $/kW/hr : 1 CFM = $0.0137/hr
- Therefore, 10 CFM over 8000 hr will cost: 10 x 8000 x .0137 = $1096.
Where are your savings?
In a typical plant, air leaks account for 20% of the total air usage!
Standard plant system using Basic Air System Drawing 8000 hr per year operation
- Electrical costs = 0.06 $/kwhr
- Line pressure = 100 PSIG
- Plant Demand (CFM) ; 400CFM
- Air leaks (CFM) ; 20% ; 80CFM
- Total Compressor Demand ; 480CFM
Electrical Cost for Compressed Air
| 400 CFM x 8000 hrs X .0137/hr = |
$43,840 |
| 80 CFM x 8000 hrs X .0137/hr = |
$ 8,768 |
| TOTAL = |
$52,608 |
Leaks are also creating enough additional load to mandate operation of both compressors.
- No Standby Unit
- No preventative maintenance can be performed on either compressor
The number of leaks required to create 80 CFM at 100 PSIG:
- Three, 1/8" air leaks ; 78 CFM or
- One, 1/4" air leak ; 100 CFM
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