Corrosion is always a major concern for any chemical processing facility, whether it is the metal alloys that come into direct contact with caustic chemicals or the components that make up the rest of the processing system.
It takes everything to withstand the highly corrosive atmosphere that surrounds the operation of a chemical plant.
A key component of these chemical manufacturing systems are cooling towers used as an efficient way to reduce the heat created during the chemical reaction process.
Process water absorbs heat, such as that from water-jacketed reaction vessels, and transfers it to the cooling tower. The tower is then able to vent the heat to the atmosphere and return the cooled water in an open loop through the process.
However, galvanized metal cooling towers routinely fail the corrosion durability test in chemical plants and are increasingly being replaced by corrosion resistant engineering plastic cooling towers.
For example, a major chemical manufacturer located in North Carolina spent decades replacing its metal towers with the same material without realizing that there was a better alternative.
“We introduced them to engineering plastic towers in 2010 which were installed at their main operating facility in the area,” said Chuck Parnell, sales engineer at Mechanical Equipment Company (MECO). “Before that, they were using metal-clad towers and they were very unhappy with the maintenance and the significant downtime required for these units.”
MECO is an industrial equipment supplier that designs, installs and services mechanical and industrial equipment throughout North and South Carolina. They also design and manufacture process skid systems.
come to a conclusion
Recently, the chemical manufacturer completed construction of a new 20,000 square foot facility for research and development of new products for the petrochemical, industrial, agricultural and domestic markets.
“After more than a decade of using engineering plastic towers, they’re done experimenting,” says Parnell. “We installed the whole mechanical system – pumps, controls, everything – and they only had one request; HDPE cooling towers.
High-density polyethylene (HDPE) cooling towers were introduced by Delta Cooling (www.deltacooling.com) in the 1970s. costly water as well as less downtime for repair or replacement.
Combining durability and cost
Back when the chemical company used metal towers, traces of chemicals from the manufacturing process would mix with the water in the towers, changing the pH and promoting oxidation reactions, similar to what happens with the metal near the oceans.
“If you’re in a coastal region, with salty air, that’s a tough environment for a metal cooling tower,” Parnell added. “Similarly, chemical plants have highly corrosive atmospheres and that has consequences.”
The burden in this case for the North Carolina chemical processor was considerable. Older metal towers usually only lasted a few years before heavy maintenance began.
Then, after about five to eight years, the company was forced to completely replace its entire line of lathes, only to see the cycle repeat itself.
Longevity is perhaps the main feature of HDPE cooling towers. In fact, many of the first towers installed are still in operation today; some up to 40 years later.
Delta backs up this longevity by offering a 20-year warranty on the engineering plastic shell.
Parnell says durability pays off by dramatically reducing total cost of ownership. In fact, he says, the operating costs of an HDPE cooling tower reduce ongoing costs in several ways.
“They require less maintenance, water and electricity, and are priced that actually match most metal-clad options,” Parnell said. “It is obvious.”
Finding a reliable and cost-effective solution is always a priority for anyone investing in a new cooling tower system. The energy savings offered by many HDPE models are also becoming a major selling point.
“As a chemical manufacturer, they focus on instrumentation and control,” Parnell said of his North Carolina client. “They run 24 hours a day, but their cooling needs are dynamic. The ability to tailor the cooling to operate efficiently saves electricity without sacrificing cooling power.
Parnell helped them set up a range of cooling towers that could be optimized for maximum efficiency. First, he selected the Delta Cooling Premier induced draft model for the new facility and split their total cooling capacity (1,050 tons) over three towers: one 250 ton unit and two 400 ton units.
In addition, the cooling towers are equipped with variable frequency fans (VFD). This allows them to vary the fan speed and avoid running them at maximum rpm unless necessary. Matching fan usage to cooling demand brings additional efficiency and savings, but HDPE efficiency goes even further.
“For the same tons of cooling, an HDPE tower can be smaller than a comparable metal tower,” Parnell added. “Delta engineers have come up with a design that minimizes fan power without sacrificing cooling capacity.”
These efficiencies in HDPE cooling tower design have been estimated to reduce energy consumption by up to 40%, which equates to substantial savings for heavy industrial operations.
Additionally, since HDPE cooling towers do not leak or require chemical water treatment, as is often the case with standard metal-clad units, users save on both water consumption and expensive treatment chemicals.
“Based on experience, they determined that high-density polyethylene provided them with a more reliable tower,” Parnell concluded.
In chemical manufacturing, where efficient performance is essential for profitability, HDPE cooling towers are proving to be the formula for success.
Phillip Dryden is a Dallas-based freelance writer with over ten years of experience writing for the mechanical engineering and chemical processing industry.