Water scarcity in the United States and worldwide makes reliability in wastewater treatment plants all the more urgent.

Cold weather poses serious challenges to treatment plants. In particular, freezing temperatures can jeopardize the piping infrastructures that enable plants to produce clean water. Piping systems are like a plant’s circulatory system.

Damage to one pipe can lead to a cascading effect on the entire infrastructure. Given the complexity of treatment systems, the isolation and repair or replacement of a single damaged pipe can require an expensive, time-consuming shutdown of machinery.

Today, thanks to modern-day freeze protection technologies, such as heat trace cables, treatment plants have ways to safeguard mission-critical pipelines and other components against severe cold-weather events.

WINTER CHALLENGES

As challenging as the variables of wastewater treatment can be, winter weather makes operations even more demanding for plant supervisors and technicians. Snow, ice and freezing rain can create obstacles that keep a plant from running at peak performance.

Cold temperatures slow down the activity of microorganisms that do the work of breaking down contaminants. It also can lead to frozen and cracked pipes, hoses, valves, pumps and process components as well as ice formation on outside tanks and reservoirs.

If left unprotected, almost any plant machine or component can freeze. Once that happens, the plant may need to be partially or completely shut down for repairs. Then wastewater must be stored until the facility restarts, or released partly or fully untreated, leading to environmental contamination, fines for permit violations and bad publicity.

A major cause of extended downtime is waiting for vital replacement parts. Besides cracks and flooding, limited freezing of water or vapors in pipes can lead to changes in system conditions that render treatment less effective and less efficient.

THE NEED FOR PROTECTION

As much as two-thirds of capital expenditures for wastewater treatment plants can go toward pipelines and pumping stations.¹ Given this investment, extra measures are required to keep processes performing optimally during cold weather.

When pipelines freeze, the consequences are severe. Leaks and bursts pose a danger to staff safety, the environment, and the plant’s financial status and reputation. A recent example is the historic 2021 winter storm in Texas. The brutal cold engulfed vast swaths of the Southwest, shuttering water treatment facilities and hindering repairs.

Damages at Texas plants included broken pipes, valves and basins, and impacts to chemical feed systems. This led to service disruptions for water systems in more than 140 counties, affecting some 14.9 million people at the storm’s peak.

A PROVEN SOLUTION

To ensure continuous treatment during the winter, freeze protection is essential. Electric heat trace cables can play a major role, offering reliable, safe and energy-efficient performance.

Heat tracing cables prevent pipes from freezing by use of a resistive element that heats up when electricity passes through. This keeps the pipe and liquid inside at a constant temperature. Self-regulating cables automatically adjust the heat output in response to temperature changes, increasing the heat output as pipe cools and decreasing output where the temperature is rising.

Treatment plant areas that benefit from heat tracing include the headworks, supply pump stations, influent lift stations, filtration systems and outdoor chemical feed systems. Other areas that should be considered include stairs and walkways, loading docks, and platforms to ensure team members’ safety. Faucets and washdown equipment exposed to cold may also need protection. Generally, reactors and digesters have enough mass to prevent freezing.

 HOW THEY WORK

Self-regulating heat trace cables have been proven for more than 30 years in the hydrocarbon and chemical industries. They provide a conductive ground path when installed on nonconductive surfaces, such as plastic or painted pipe.

The heater cable derives its self-regulating characteristic from the inherent properties of the conductive core material. As the core material temperature increases, the number of conductive paths in the core material decreases, automatically decreasing the heat output.

As the temperature decreases, the number of conductive paths increases, causing the heat output to increase. This occurs at every point along the length of the cable, adjusting the power output to the varying conditions along the pipe. Because the cable is self-regulating, it can be overlapped where the installation requires, without creating hot spots or burn out.

DESIGNING THE SOLUTION

When specifying heat trace cable, it is important to establish parameters, which are determined by pipe sizes and lengths, material, number of attached valves and pumps, and the type of pipe supports. Other factors are the supply voltage, weather data for the area, and the minimum startup temperature.

Some treatment processes can release flammable gases and vapors, such as from oils, solvents or gasoline from accidental spills, and biogas from anaerobic digestion. In confined spaces, high concentration of gases can build up, creating the risk of explosion triggered by an electrical arc.

The NFPA 820, Standard for Fire Protection in Wastewater Treatment and Collection Facilities 2020 edition specifies that most pumping stations, spaces and buildings that make up a wastewater treatment plant must be considered hazardous locations.

Therefore, in North America, heat trace cable should be rated for hazardous locations as defined in Article 500 of the National Electrical Code. Heat tracing cable solutions for wastewater applications in Europe should be certified to ATEX, IECEx, CENELEC, EU or other regional hazardous location standards for metal and nonmetal pipes, tanks and vessels.

INSTALLING CABLES

Before installing heat trace cable, users should consult the manufacturer’s specific instructions. Failure to do so will likely void warranties and agency approvals. The integrity of the system depends on how accurately the heat trace cable is installed. Improperly installed systems have resulted in system failures and physical injuries.

In general, heat trace cables can be installed in straight runs (found to be the more standard protocol) or spiraled around the pipe. Spiraling is used when a limited number of cable types are available; the practice has become less common in recent years. In straight tracing, the cable is installed on the lower quadrant of the pipe to prevent damage from falling objects or from being walked on. In either approach, the cable should be applied flat to the pipe.

The cable can be attached using fiberglass tape. The cable should fit snugly against the pipe and should be secured every 12 inches. Metal straps, wire, vinyl electrical tape and duct tape should not be used for attachment.

If the cable must be cut, that should be done after it is attached to the pipe, and after confirming allowances for terminations, connections and heat sinks. Cable should be looped around valves, hangers and other small in-line devices so that they can be accessed or removed without cutting the cable.

Moisture penetration of the heat trace system is the single largest source of problems. Particular care must be given to the proper sealing of all electrical connections and splices. Cable sealing kits provide a proper seal for the cable itself. Other electrical connections, including heater to power wiring, thermostat connections, and panel and breaker connections, should be sealed or moisture-proofed in an approved fashion.

After installation, it is important to periodically inspect the cable and system components for damage, ensuring that the cables are free of nicks, tears or gouges. The inspection also should verify that additional cable has been installed at each valve, flange, pipe support and other devices to allow easy access. Connections, splices and end-seals must meet code requirements. 

THERMOSTATS AND CONTROLLERS

Heat tracing requires temperature control. When selecting the proper thermostat or controller, it is necessary to consider the devices’ voltage and amperage ratings, as well as the suitability of their housings for the environment, specifically ensuring that the enclosures are explosion-proof, watertight and corrosion-resistant.

Heat tracing cable can have benefits beyond freeze protection. Many chemicals used in wastewater treatment, such as ferric chloride, sulfates and polymers, are aggressive and require process temperature maintenance, a task for which heating trace cable is well suited.

Wastewater treatment is one of the most important environmental processes. During colder months, heat trace cables help maintain efficient system performance and counter seasonal upsets by keeping water and chemicals flowing. This helps prevent facility flooding, the expense of replacement parts and repairs, environmental damage and plant downtime.

References:

^[1] Reducing the Costs of Water and Wastewater Treatment Pipelines, April 2, 2021, Fluence

ABOUT THE AUTHOR

Kevin Green (kevin.green@emerson.com) is national sales manager for Nelson Heat Trace, Emerson.