By Diane M. Calabrese / Published July 2023
Heat exchangers nudge organization from a disorganized form of energy, one that can still do work if given a little direction. Of course, heat exchangers, like everything else in the world, get dirty.
Debris on exchanger tubes impedes heat flow from warmer to cooler. To allow heat to accomplish as much as possible before it becomes useless, devices that depend on heat transfer by conduction must be kept clean.
In some settings, though, the environment poses extra challenges to maintaining clean devices and ensuring the conservation they enhance. Consider a power plant.
Where there is coal, there is ash. But even if a power plant skips the coal and chooses nuclear or hydropower to generate electricity, dirt still accumulates.
Components of power plants that become covered with dusty ash or scale or any combination may also become a fire risk. Short of that risk, the components such as tubes in heat exchangers will not be operating at peak efficiency.
There’s cleaning that must be done to keep power plants at optimal performance. Waterjets often are deployed in the effort.
At the WJTA Conference and Expo in 2009, T. Shawver from NLB Corporation in Wixom, MI, presented a paper about the utility of cleaning heat transfer tubes with automated waterjets. Sufficient horsepower from pumps and automated deployment of jets was already simplifying the removal of ash and scale from transfer tubes.
Even in 2009, the use of high-pressure waterjets to clean plants was not new. Shawver described the process as one that had been going on for 30 years.
Manual and automated methods of waterjet cleaning both take place in power plants today. Automation boosts speed, and speed is second only to safety in cleaning components of a power plant. A plant must be shut down for cleaning to take place. The slower the process, the longer the plant is offline.
In addition to minimizing time re-quired for cleaning, good results with waterjet cleaning keep plants running at peak efficiency. Deposits on condenser tubes interfere with heat transfer. Not only does the interference lower efficiency, but it also adds to stress on the equipment, which reduces longevity.
An alternative to waterjetting is abrasive blasting, but the latter adds to cleanup requirements unless dry ice pellets are used as the abrasive. Because waterjetting uses the minimum amount of water to achieve usable force, the collection of wastewater is not an arduous task.
The exterior of heat exchanger tubes must be kept clean. So, too, must the interior of tubes. An operator with a lance could clean the inside of each tube separately, but semi-automated systems make it possible to tackle the tubes in groups, or arrays, with jets mounted on a frame working simultaneously in different tubes. The jets work at about 40,000 psi. They often have side jets on the rotating head on the lance.
Use of water inside power plants is the norm. The electric power producing sector uses more water each day than any other industry. Research into ways to reduce water use for cooling is getting a lot of attention. In any case, the amount of water used for cleaning via waterjetting inside power plants counts as insignificant.
Heat exchangers make the most of the transfer of heat from a higher-temperature to a lower-temperature body. Wrap hands around a pot of steeping tea on a cold winter day, and the heat from the pot will warm hands thanks to conduction.
Conduction—one form of heat transfer (convection and radiation are the other forms)—is exploited inside power plants to make the most of heat. By running a coolant (e.g., water) in one direction through a heat exchanger, and a hot gas (e.g., steam) through a coiled tube within the exchanger in the other direction, heat is conducted to the water, warming it as the steam cools.
The why of heat exchangers is conservation. They are used at junctures where there is the opportunity to accomplish two tasks that must be done—cooling one substance and heating another—by capturing heat before it dissipates in an unusable form.
Thermal power plants get a lot of attention because they cannot transform all heat into electricity. True, no transformation of energy is 100 percent efficient as we know from the second law of thermodynamics.
But the amount of heat that becomes unusable (entropic) concerns engineers (who seek maximum efficiency) and everyone who does not want to waste natural resources. The fuel in a thermal plant may be coal or natural gas (fossil fuels), nuclear, or solar.
Yes, solar. Burning of fossil fuels or splitting of uranium nuclei can yield the thermal energy to heat a reservoir of water and produce steam and ultimately turn turbine blades. Solar thermal plants create steam from tapping heat from the sun and using it to heat water.
Thermal power plants do not begin generating electricity until a turbine begins to spin, which through spinning turns wire coils in a generator. The whirling wires and magnet in the generator start the flow of electrons: electricity.
Hydroelectric dams, wind turbines, and solar panels (made of photovoltaic cells) get the flow of electrons (electricity made) started more immediately. Solar panels provide the most direct paths, given the photovoltaic cells that make them up are semiconductors (and when bombarded by photons from the sun’s rays release electrons).
Because heat exchangers in power plants may be just a big elongated tube or cylindrical tank through which the many tubes course, they are quite amenable to cleaning with waterjets. In other words, they are not a maze of interconnecting tubes and parts—no bends—not that bends preclude the method.
According to the U.S. Energy Information Administration, as of November 8, 2022, there were 11,925 utility-scale electric power plants in the United States. EIA defines utility-scale as a generating capacity of one megawatt (MW). Each plant in the total may have more than one generator and use more than one type of fuel.
The utility-sale electric power plants as defined by EIA are only part of the total number of generators. In the tally cited above, EIA puts the total number of electric generators (including utility-scale) at 24,645.
Given the number of plants, there is abundant opportunity for waterjetting contractors with the ability to clean inside power plants. Working inside power generating facilities, however, may require meeting security criteria as well as being able to demonstrate meeting all mandated safety training.
CISA and OSHA
The Cybersecurity and Infrastructure Security Agency (CISA) has responsibility for ensuring that other federal agencies monitor risks and develop plans to mitigate risk at facilities that they regulate. Thus, CISA looks over the shoulder of the Department of Energy (DOE), which is responsible for ensuring safe operation within the energy sector.
CISA concerns itself with identifying vulnerabilities that could be exploited by terrorists. Because the energy infrastructure involves so many players—80 percent is owned by those in the private sector and serves everyone in the nation—its complexity opens it to intruders. (For example, the installation of ground-level transformers at EV charging stations could be considered another opening to those who would do harm.)
Depending on the power plant where a contractor wins an assignment, CISA, DOE, and the Department of Transportation (DOT) may have criteria in place that must be met by those working on site. DOT (under PHMSA, Pipeline and Hazardous Materials Safety Administration) has responsibility for the pipelines serving the energy sector.
There are three million miles of main pipeline serving the energy sector and as many as twice that many miles with branches. (Pipelines, too, require cleaning—those inside power-generating facilities as well as those supplying them.)
Removing scaling, biofilm, and oil coatings from pipelines is another task for which waterjetting tools may be deployed. Approaches are developed around the type of line, the construction material(s) in the line, diameter of the line, and so on.
Working inside a power-generating plant is no different from working inside most industrial facilities. A contractor will only get in the door after winning the bid by responding to a request for proposals (RFP). To qualify to bid, a contractor will have to demonstrate necessary certifications.
Power plant owners are responsible for training their own employees and documentation of training of anyone working on site as a contractor. OSHA standard 1910.269 (Electric power generation, transmission and distribution) applies. It runs to 46 pages.
If a plant were going to use a contractor to clean heat exchangers, for example, it would be the responsibility of the “host employer’s installation” to provide the contractor with “information about design and operation” (1910.269(a)(3)(i)(C)). Expect plant owners to produce exacting RFPs that specify how they want work done as well as design specifications.
We know the keen interest the EPA takes in emissions from power plants. The EPA also scrutinizes water use and has compiled many studies to determine whether it’s better to recirculate water for cooling or not. Power plants go both ways, but efficiency—aided by clean components—is the goal of all.