Controlling Exothermic Processes
Plastic cooling towers help ensure that reactions between harsh chemicals are kept under control and that processes are not interrupted.
Like other chemical manufacturers, the staff at Kuehne Chemical Co. Inc. knows that you have to control the chemical reactions involved in making products, particularly products that involve the reaction between harsh chemicals. One of the prime enemies of controlling a chemical reaction is the excessive heat generated by the reaction itself, which can make a process unstable and corrupt the outcome. This can causes product quality problems and introduce elevated hazardous conditions.
Based in South Kearny, N.J., Kuehne Co. is a privately held chemical manufacturer with a core competency of manufacturing concentrated solutions of bleach (sodium hypochlorite). The bleach is shipped to customers who dilute it for use in applications such as water and wastewater treatment, paper processing, and cleaning and disinfection products. Kuehne also repackages and distributes semi-bulk chlorine, caustic soda and caustic potash - chemicals that are used in the bleach production process.
The manufacturing of bleach - Kuehne Co.’s primary product - involves the production of a concentrated ultra pure brine solution, explains Richard Wilkes, director of corporate engineering. Through electrolysis, a chlorine molecule is split away from the brine. The resulting gaseous chlorine is quickly reacted with sodium hydroxide, and the resulting “fused” product is bleach.
“It appears to be a fairly simple process, but we have to control the heat of reaction in the bleach-making process,” says Wilkes.
Heat exchangers that utilize cooling water as the exchange medium cool the process some but not all of the way to the appropriate temperature range, Wilkes says. The water then circulates through a cooling tower, where the heat of the chemical reaction is dissipated into the atmosphere. Once cooled, the water recirculates via pipelines from the tower back to the heat exchangers. The continuous loop process is used to continuously draw heat from the combined chemical reactions, Wilkes explains.
Until recently, one of the most vulnerable components of Kuehne Co.’s heat reaction control process was the cooling towers, which required frequent maintenance, including cleaning and adjustments to the fan drive system. The most expensive part of the maintenance, however, was that it required cooling tower downtime. The forced downtime also required that the bleach process be shut down for extended hours.
|Keuhne controls the heat of reaction in the bleach-making process using cooling water circulated through heat exchangers and engineered plastic cooling towers|
“The cooling towers are a cost-effective alternative to keeping the heat of reactions down,” Wilkes explains. “However, we can’t operate the process without the cooling tower system being online. So, cooling tower uptime is definitely a key piece to processing our bleach products.”
To ensure maximum uptime of operations and the reliable shipment of products to customers, the team at Kuehne decided to explore alternatives that would reduce downtime. The company’s aging metal-clad cooling tower was reaching the end of its service life, so the company decided to replace that unit and increase the plant’s cooling capacity. Rather than use metal-clad cooling towers to cool the process, Kuehne selected engineered plastic cooling towers with integrated direct-drive fan motors.
“The bleach manufacturing process is a tough environment. Chlorine-based products tend to heavily corrode metals,” Wilkes says. “We began trying to find some alternative materials to the galvanized steel type of tower shell.”
Using engineered plastic to construct a cooling tower has a sound foundation: most modern cooling tower fills - the packing material underneath the shell - are constructed of honeycombed thermoplastic. Given that, “a plastic shell also appeared to be a good solution,” Wilkes says. “In our research of newer designs, we found Delta Cooling Towers, which makes a seamless, high-density molded polyethylene shell. Because it is corrosionproof, we felt that this type of unit would be great for our application.”
After reviewing various models offered by the Rockaway, N.J.-based cooling tower manufacturer, Kuehne selected a TM Series two-cell model, a modular design that is available with one to six cells and can provide 250 to 2,000 cooling tons.
Purchasing with an eye toward long-term performance and expansion, Kuehne designed a maintenance-free platform large enough for the two-cell model but with the modular expansion capacity to upgrade to even a six-cell model later, if needed, Wilkes says.
|Kuehne installed a two-cell engineered plastic cooling tower with a direct-drive fan system. The company planned for future expansion by building a platform that allows the cooling tower to be upgraded to a six-cell unit if needed.|
Once installed, the engineered plastic cooling towers met the firm’s cooling expectations, Wilkes says. The engineered plastic material provides comparatively maintenance-free operation.
“One of the things that we’ve found is that the surface tension for particles in the plastic cooling tower basin is much less than that of steel basins,” Wilkes says. “Even after more than two years since the startup, there has been no wind-blown particulate buildup and no mud whatsoever in the tower basin. We do scheduled blowdowns on the tower, but, unlike the metal-clad basins, the blowdowns of the plastic towers are completely washing any foreign materials right down the waste pipe. That means no cleaning of the tower basin.”
One of Wilkes’ favorite features of the new cooling tower is the direct-drive fan system. “Instead of having a large shaft-driven or belt-driven fan drive, [we] liked the direct-drive unit with the new Delta system. As a result, Kuehne was able to realize a reduction in total horsepower requirements as well as maintenance,” says Wilkes. “Our old cooling tower had a 75-hp shaft-drive motor system. The new modular setup has four independent 10-hp direct drive motors. So, that’s a reduction of 35 hp, which saves on energy costs for the same cooling tonnage.”
Wilkes adds that with a direct-drive motor, there are virtually no maintenance costs because there are no belts or gear reducers, internal gearbox or bearings to take care of. It is not necessary to tune up the balance of the fans as with shaft- or belt-driven motors.
“Basically, we’re just lubricating the motor bearings once a year as part of our PM [preventive maintenance] program,” he says. “And you can PM the direct-drive motors while they are running. So, there is negligible maintenance downtime for the tower, and that’s the big payoff.” PC
To learn more about cooling Towers from Delta Cooling Towers Inc., Rockaway, N.J., call (800) 289-3358 or visit www.deltacooling.com.