Liquid nitrogen can provide a fast, environmentally friendly way to clean tubular heat exchangers.

Anyone in the industrial refrigeration industry likely is familiar with the cooling capabilities of liquid nitrogen (LN2). A cryogenic fluid with a boiling point of -320.4°F (-195.8°C), LN2 commonly is used in the food industry to “flash” freeze meat, fruits and vegetables, and dairy and bakery products. Liquid nitrogen also is used to cool materials that are heat-sensitive or soft - for example, plastics, certain metals and pharmaceuticals - to allow machining or fracturing.

Of late, another application for LN2 has begun to take root. Harnessed in a portable device that delivers LN2 at ultra-high pressures, the substance can be used to provide an effective way to clean tubular heat exchangers.

Because the cleaning achieved with the LN2 technology is more thorough than many mechanical methods, it might allow some plants to extend the amount of time between cleanings.

Tubular heat exchangers are built to transfer heat efficiently from one substance to another. However, over time, material builds up in the tubes, reducing the effectiveness of the system. Most tubular heat exchangers are cleaned by sandblasting, high-pressure water jet blasting, bullet cleaning or drill rods. These mechanical cleaning methods are effective in many applications, but they do have drawbacks. Cleaning the long, narrow tubes in a heat exchanger can be an arduous and hazardous process that demands equipment downtime. Mechanical methods can increase wastewater disposal costs due to hazardous waste discharge, and their force and abrasiveness can damage the heat exchanger tubes and other sensitive components if the cleaning is not handled properly. In industries such as chemical and pharmaceutical manufacturing, such processes can introduce the risk of cross-contamination.

Liquid nitrogen jet cleaning avoids these problems. When used at extreme temperatures of up to -260°F (-162°C) and extreme pressures, LN2 quickly converts to a gas. In the conversion, the gas expands nearly 700 times, providing an aggressive yet safe cleaning environment. Because nitrogen dissipates back into the atmosphere, all secondary waste streams are eliminated. All that remains for disposal is the material that was removed.

Harnessed in a portable device that delivers LN2 at ultra-high pressures, this versatile substance can be used to provide a fast, effective, environmentally friendly way to clean tubular heat exchangers.

Fast, Effective Cleaning

One company that is exploiting LN2 for its cleaning capabilities is Nitrocision, Idaho Falls, Idaho. The company’s proprietary technology was developed at the Idaho National Engineering and Environmental Laboratory and has been used by NASA to clean shuttle boosters, among other applications. According to company president Ron Warnecke, the biggest benefits gained by using the technology for heat exchanger tube cleaning are speed and effectiveness.

“In one recent test, a company with 20'-long tubes was spending 8 minutes per tube cleaning their heat exchangers using mechanical drilling with water cooling,” said Warnecke. “With the liquid nitrogen technology, the cleaning time was reduced to just 35 seconds per tube, and the cleaning was more thorough. The company reported a substantial increase in the performance of the heat exchanger after the liquid nitrogen cleaning compared to mechanical drilling.”

Warnecke notes that the upfront cost for the technology is higher than most mechanical cleaning methods. For facilities that opt to contract out their cleaning services, the expense primarily depends on the cost of the liquid nitrogen as negotiated with the supplier, as well as on the tube length, diameter and number of tubes that need to be cleaned. Typically 2.5 to 3 gal of LN2 per minute are needed to clean each tube, and cleaning takes about 30 sec per tube. However, the savings that can be achieved through the reduced cleaning time, as well as the elimination of wastewater problems, usually makes the technology less expensive overall.

“At one plant, a cleaning process that used to take three to four weeks with mechanical drilling now takes just four days. Since each day of downtime costs $450,000 in lost revenue, the liquid nitrogen cleaning process has saved the operation a substantial amount of money,” said Warnecke.

Additionally, because the thorough cleaning achieved with the LN2 technology, it might allow some plants to extend the amount of time between cleanings, which would provide additional savings in labor and downtime.

Typically 2.5 to 3 gal of LN2 per minute are needed to clean each tube, and cleaning takes about 30 sec per tube.

Expanded Applications

Until now, the LN2 high-pressure jet technology primarily has been used for cleaning, coating removal and cutting processes in high-tech aerospace applications. Recently, however, the technology has begun capturing the interest of an increasing number of companies looking for new ways to clean heat exchanger tubes in industrial applications, particularly in sensitive fields.

In January 2008, Conco Systems’ Industrial Services Division, a tube-cleaning service based in Houston, Texas, was granted an exclusive license to use Nitrocision’s LN2 jet technology.

“The real benefit to this technology, other than its speed, is that it doesn’t produce any secondary waste streams, unlike systems that use water. The technology could be a first choice application for any process where water interaction should be avoided,” said Eric Fayard, marketing manager for Conco Systems Inc.

In addition to its large power generation customer base, Conco anticipates that its LN2 tube-cleaning service will expand into industries it does not currently serve, including chemical manufacturing, refining, pharmaceutical manufacturing, catalyst loading and nuclear reactor cleaning.

Warnecke admits that the technology is not a fit for every application. Plants with heat exchangers that can be cleaned sufficiently using mechanical methods, or where the resulting waste stream is not hazardous, likely would not be able to justify switching to the LN2 technology. However, for plants with such concerns, the technology might provide an solution to the challenges of mechanical tube cleaning.

For more information, contact Nitrocision at (208) 552-2354 or visit Contact Conco Systems Inc. at (800) 569-5523 or (412) 828-1166, or