Compressed air often is used for a number of applications that easily could be served by a low-pressure (less than 15 psig) electric-blower system. For example, a facility has six extrusion lines that consume large volumes of compressed air for flock and coolant blow-off operations. Installation of centrifugal blowers to serve the same function eliminates the compressed-air consumption for this application and allows facility staff to shut off a 300-hp compressor.
Look for these common inappropriate uses of compressed air and consider the suggested alternatives:
Open Blowing: Compressed air is applied with an open, unregulated tube, hose or pipe. Typical applications for open blow-off are part and debris clearing, machine tool cooling, drying and cleanup. Alternative: Replace with blower systems or flow distributing devices, such as nozzles, air amplifiers or air knives.
Sparging/Agitation: The process of aerating, agitating, oxygenating or percolating a liquid with compressed air. Alternative: High-volume, low-pressure blower systems driven with electric motors can be used for many sparging or agitating applications.
Aspirating: Compressed air is used to induce the flow of another gas. Alternative: As with sparging above, blowers can be used to induce the flow of another gas.
Personnel Cooling: Operators use compressed air to cool themselves. Alternative: Space and occupant cooling should be adequately supplied by HVAC systems.
Air-Powered Diaphragm Pumps: Air-powered pumps are a convenient way to transfer chemicals or treated water since their plastic components are corrosion resistant. Alternative: Specially designed electrically driven pumps with plastic bodies are available for pumping chemicals and treated water.
Induced Vacuum Systems: Compressed air often is used to create a vacuum for process systems. Alternative: Independent vacuum systems should be used, such as electric vacuum-pumping systems, which are far more efficient.
Cabinet Cooling/Pressurization: Compressed air commonly is used to provide cooling or positive pressurization of electronic cabinets located in warm or dirty environments. Cooling typically is provided by air-powered vortex tubes that provide a cold air stream output from a compressed air input. Alternative: Cabinet cooling should be provided by blower or heat-pipe systems, depending on the environment. For dirty environments, install heat-pipe units that maintain the internal cabinet temperatures without interchange of external air.
Distribution system inefficiencies
Oftentimes the most substantial inefficiencies lie in the distribution system. These include the most common offender, air leaks, as well as excessive pressure settings, high pressure drop filters and poor piping design.
Lose the leaks
Air leaks are an inevitable part of any compressed air system and can account for 10% to 30% of a facility's compressed-air demand. Leak-abatement programs are highly effective in minimizing air loss in a system and should be included as part of a regular preventive maintenance program that ideally is performed quarterly.
Leaks usually range from less than 1 cfm to greater than 60 cfm. For example, a 1/8-in. round orifice (nozzle, hole, leak, etc.) discharges about 26 scfm of compressed air at 100 psig. Many leaks occur at threaded connections and are the result of decayed or absent pipe thread sealant at fitting junctions. Other typical leaks are found in rubber hoses, filter/lubricator/regulator gaskets or drains, cracked filter bowls and at quick-couplers. In a shampoo-production facility, 133 compressed-air leaks were found and tagged. The total leak load of these 133 leaks was estimated to be 337 scfm.
Reduce supply pressure
It is prudent to operate compressed-air systems at the lowest pressure that meets production requirements. It is common, however, to observe air supply pressures in excess of 100 psig at an industrial facility. In certain cases, this pressure setting is warranted. But in most cases it is due to the absence of or improper adjustment of a regulator since most industrial operations require 85 psig or less.
When the supply pressure is greater than required, larger volumes of air are expelled for any given end-use, including leaks, which equates to wasted energy. For example, reducing the compressor pressure settings by 2 psig typically will reduce energy consumption by 1% .
Each use should be regulated separately and be supplied with compressed-air pressures specifically set to meet the needs of that process. Select regulators that have low pressure drop, minimize pressure swings and provide consistent supply pressure. If only one application in the plant requires a significantly higher pressure, it likely is more efficient and cost-effective to use a booster or a separate compressor dedicated to that application.
The bottom line
As energy costs escalate, it increasingly is important to improve efficiency of demand-side uses of compressed-air systems. Controlling the volume of flow and supplying flow only when needed can all reduce consumption while still meeting production requirements. This can be done by using efficient nozzles and simple solenoids or mechanical valves. Also, numerous inappropriate compressed-air uses can be eliminated by adopting alternatives such as high-volume blowers, vacuum systems and electric-motor-driven systems.
Compressed-air systems widely are used in the industrial sector and act as a primary energy source for innumerable industrial applications. Paying careful attention to the demand side of the system can reveal significant opportunities for reducing compressed-air use and increasing energy savings.
Christopher Schmidt is project engineer for Energy & Resource Solutions, Haverhill, Mass. E-mail him at CSchmidt@ers-inc.com. Mark D'Antonio is vice president of engineering operations for ERS. E-mail him at MDantonio@ers-inc.com. Alan MacDougall is energy analyst for ERS. E-mail him at firstname.lastname@example.org.