Companies that use process cooling water to manufacture their products are increasingly being required to meet restrictions on the type, amount, temperature and composition of their wastewater. One example is in southern California, where water cannot be discharged to the municipal sewer if the water temperature is greater than 105oF (41oC).
This restriction posed a problem for one cosmetics manufacturer in Los Angeles. The company's typical manufacturing operation involved combining ingredients in a 500-gal processing tank equipped with a 60-gal water-heated jacket. The raw materials were heated and mixed at a process temperature of 180oF (82oC) until they were blended into a homogeneous product. The product then was cooled by replacing the heated water in the jacket with circulating tap water.
Dispensing the cooled, mixed product into containers often took between four and six hours, depending on the density of the mixed solution, the temperature of the tap water and the outside ambient temperature. The length of cooling time limited production to one batch per day per process tank. During peak production periods, the company required a second night shift to handle the load.
The cosmetics company needed to devise an efficient method to cool and recirculate its tank jacket water to reduce chilling times and minimize the amount of process water discharged to the sewer.
An Icy SolutionAfter investigating several options, the company chose a closed recirculating thermal storage system. This type of equipment is a departure from the normal concept of a chiller. Instead of the process water recirculating around refrigerant-filled tubes, the water is circulated around a block of ice to achieve the desired heat loss (see figure).
The compact package consists of a 500-gal tank with a 5-hp compressor. The chiller's low-horsepower compressor is adequate because the system is able to store cooling capacity in the “ice bank.” Ice is formed in the reservoir tank on a series of plates designed and spaced to quickly and efficiently freeze a precalculated volume of ice. The ice is formed while the chiller operates during the plant's off hours, which enables the company to take advantage of lower off-peak electrical rates.
Positive ResultsAccording to company managers, the thermal storage equipment paid for itself in the first few months of operation. Although exact figures on the savings generated by the chiller are difficult to obtain, the company has reported the following gains:
- Savings are achieved by taking advantage of lower electrical rates by storing chilling capacity at night.
- Minimal water is being discharged to the sewer. Water formerly lost is now recirculated in a completely closed system.
- Peak periods no longer require additional production personnel and extra night shift batch crews to handle the load.
- Increased equipment efficiency ensures a comfortable excess capacity.
In addition, batches that once took up to six hours to cool now take only one-and-a-half to two hours. Daily bulk production has doubled, and the potential exists to produce up to three batches per day in each processing tank.