Plant Services - August 2008 - (Page 35) HOW TO BALANCE STORAGE AGAINST EXCESS AIR COMPRESSOR CAPACITY ndustrial compressed air users often misinterpret the role the air compressor plays as an energy source in support of manufacturing. Air compressors don’t supply the air directly to the production demands; the connecting pipes serve that purpose. As such, the energy extracted from the system to perform the required tasks actually comes from air already in the pipes. e compressors replenish that air as it’s consumed. is is an important distinction to understand when configuring a compressed air system to perform at optimum efficiency. Every air system reaches a balance between the air the compressors supply to the air distribution system and the air the downstream users withdraw from the distribution system. e energy that compressors input will equal the energy the users consume plus the system’s inherent inefficiencies. Anything left over either goes into or is released from storage. e basic equation representing this fact is: Energy in = energy expended energy stored Also, in a typical plant, production only uses about 50% of the pneumatic output the compressors generate, with the rest lost to inefficiencies, waste and inappropriate uses. Compressed air is often the principal, if not the greatest, production cost component. As such, it offers substantial savings opportunities from reducing consumption and using the air more efficiently (Figure 2). A key factor for realizing the available savings is properly applying storage, which, in this context, refers to the stored energy, as indicated by the pressure contained in the fi xed volume of your air system. Volume alone, however, doesn’t Compressed air is an inefficient energy source. equal storage. ere also must be a change in the pressure within that fi xed volume to produce useable storage. Take, for example, a large receiver installed in the compressor room. If the pressure at the tank inlet is the same as the pressure at the outlet, the useable stored energy contained in the tank is zero. e volume adds to the overall system capacitance, but it can’t be applied to manipulating the energy balance between the system’s supply side and the demand side unless it’s accompanied by a controlled change in pressure. e simplified storage relationship for fi xed volume vessels like air receivers is: 35 Changes occurring to either side of the equation result in the system rebalancing at a new point. Taking proactive, positive measures to manipulate the balance between supply and demand ensures the system always operates at its optimum energy efficiency. Compressed air is an inefficient energy source: Putting between 7 and 8 electrical hp into the compressor motor gives only 1 pneumatic hp of output to the system (Figure 1). A .PLANTSERVICES. http://www.PLANTSERVICES.com
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