(Certified Best Practice by BMPCOE)
Polaroid Corporation - Waltham, MA
Approximately five years ago, Polaroid purchased two new air compressors for its production operations at the Integral Coatings Division and integrated the water lines for the aftercoolers on these compressors with the make-up water lines for the high-pressure steam boilers. Typically, industrial-application air compressors are installed with chilled water lines or once-through municipal water lines attached to the aftercoolers. This setup keeps the compressor, oil, and bearings at a safe operating temperature by dissipating the resulting heat that was generated through friction and motor energy in the compressing process. The result creates the situation that one source of energy is consumed to generate another source of energy. For example, if chilled water is used in the aftercoolers, then the discharged water would eventually be returned to the chiller where mechanical and electrical energy would be consumed to re-chill the water and begin the cycle again. For once-through municipal water, the discharged water would be directed to the sanitary sewer (and probably not reused) as the heat from the compressor is removed by the water in the aftercooler.
In Polaroid's situation, the proximity of the air compressors to the high-pressure steam boilers allowed the discharge water to be directed to the boiler as boiler make-up water to generate steam. Typically, boiler make-up water from a municipal source is approximately 50°F to 60°F. However, the boiler must consume more fuel than normal to counter the effects of the cooler water re-entering the system. To solve this problem, Polaroid preheated the make-up water entering the boiler to 95°F by consuming the heat energy dissipated via the air compressors.
Polaroid gained many benefits from its energy conservation technique: destructive heat is removed from the air compressor which allows the compressor to operate efficiently and reliably; additional mechanical and electrical energies are not sacrificed by using a chiller to generate another source of energy; preheated water from the compressor aftercoolers provides an excellent source of make-up water which does not compromise the efficiency of the high-pressure boiler; and expended water is not discharged into the sanitary sewer. Savings for the 750 hp air compressor system is $66,000 per year for preheating the make-up water to the boilers. Eliminating the use of chilled water to cool the compressors resulted in an annual savings of $94,000 in electric energy.