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to remove 18- to 24-million Btu of heat from the molten billet logs each hour,” Seever said. “For that reason we have typically worn out all of our previous cooling towers, the traditional metal-clad type, in five years or less. Aſter that, we were faced with either repairing or replacing them.”


Going in a New Direction For most applications, either alternative—repairing or


replacing cooling towers—is a costly situation. Either way, production is interrupted, and the out-of-pocket cost can be surprisingly exorbitant. “We were frankly tired of that replacement cycle,” Seever


said. “So, we looked for an alternative to the metal-clad cooling tower. Stainless steel models were available, but at a prohibitive cost. Ten we considered another technology that featured a high-density polyethylene [HDPE] plastic fill, manufactured by Delta Cooling Towers [Roxbury Township, NJ]. We liked that approach particularly because the fill had the capability to withstand high temperatures. It is rated to 160°F [71°C], which gives us a nice safety margin.” Seever said that most of cooling towers Sierra has owned


or looked at had fill temperature ratings of about 120–140°F (50–60°C). Because his company’s molding process sometimes heated coolant water to more than 140° the fill in those towers would melt. “As soon as you melt the cooling tower fill, you lose cooling


efficiency, and you have to replace the fill or the entire tower,” said Seever. “Otherwise, you really start to generate a lot of steam and cause other problems inside the tower itself.” Seever added that another advantage of the HDPE tower


is that it is impervious to corrosion. If the tower is galvanized metal, it doesn’t seem to matter what type of corrosion inhibi- tor you put on it; eventually the corrosion will break through it and start eating the steel. Te Delta model that Sierra purchased was a 738-ton TM


Model. TM Series induced-draſt, counter-flow models are available in single unit capacities from 250 to 2000 cooling tons, and may be clustered to provide much greater capacities.


Beyond Cooling Capacity Other major benefits that attract many industrial, commer-


cial and institutional users to the advanced, engineered HDPE cooling tower design include significantly reduced mainte- nance and energy costs. HDPE is not only impervious to corrosive water-treatment


chemicals, but also to corrosive elements that are oſten present in the air, whether harsh chemical vapors emitted from nearby industrial plants or natural corrosives such as salt air. Seever said he visited another company, a paper-processing


mill that had an exceptionally corrosive environment. “Because of the paper processing, they get fugitive particles in their cooling system water, and those particles provide all


Sierra Aluminum had worn out all of its previous cooling towers, which were traditional metal- clad units. Each one lasted five years or less.


kinds of nutrients that promote the growth of bacteria,” he explained. “Tey were slugging their cooling tower with full- strength sodium hypochlorite [chlorine], but that treatment was not damaging their Delta tower. So, from that perspective, we figured that the steam and the heat that we generate—com- pared to the strong bleach that they were using—meant that we won’t have anything to worry about in terms of the service life of our new tower. I asked the plant manager, ‘Would you buy the same tower again?’ He said, ‘Definitely.’ Tat’s all I needed to hear.” Te Delta towers are available with direct-drive fans, which


can greatly reduce maintenance and electricity costs. With direct-drive motors, there are no belts or gear reduc-


ers, internal gearbox or bearings to take care of, and it is unnecessary to “tune up” the balance of the fans, as is oſten required with shaſt- or belt-driven motors. Normal mainte- nance includes lubricating the motor bearings once a year as part of normal preventive maintenance (PM) program. Direct-drive motors can be PMed while they are running, so there is negligible maintenance downtime. Te efficiency of direct-drive fan motors coupled with


variable-speed drives can also reduce energy costs consider- ably. Te tower Sierra purchased includes a direct-drive motor plus a frequency drive that the company installed so that a thermostat can be used to maintain a consistent water temper- ature in the process. Tis results in large reductions in kilowatt usage since the full motor horsepower is rarely needed. “My anticipation is that with this drive configuration we


will save tens of thousands of dollars each year on energy costs, compared with what we were spending with our previ- ous tower,” Seever said.


Edited by Yearbook Editor James D. Sawyer from material supplied by Delta Cooling Towers.


Energy Manufacturing 2014 75


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