You may have seen it in kitchen cookware or old water pipes: hard, mineral-rich water will leave scaly deposits over time. It occurs not only in pipes and cooking utensils at home, but also in pipes and valves that transport oil and natural gas, and pipes that transport cooling water in power plants. It is well known that scale can cause inefficiency, downtime and maintenance problems. In the oil and gas industry, scale sometimes leads to complete closure of operating wells, at least temporarily. Therefore, solving this problem may bring huge rewards. Now, a team of MIT researchers has come up with a potential solution to this huge but little-known problem. They found that a new surface treatment—including nano-texturing of the surface and then applying lubricating fluid—can reduce the rate of scale formation by at least ten times. This week, the results of the research were published in the Journal of Advanced Materials Interface. The paper was written by graduate student Srinivas Subramanyam, postdoctoral fellow Gisele Azimi, and Kripa Varanasi, associate professor of marine utilization in the Department of Mechanical Engineering at MIT. “You can see [scale] almost anywhere,” Varanasi said. In the home, these deposits are mostly an annoyance, but in industry, they can lead to “productivity reduction, and the method of removing [them] may be harmful to the environment”, usually involving the use of harsh chemicals. In power plants and desalination plants, scale can cause significant efficiency losses because it acts as a thermal barrier and affects cooling or condensation in the heat exchanger. The problem arises because water usually contains a lot of dissolved salts and minerals. The ability of water to dissolve these substances depends on solubility, so if the water cools or evaporates, the solution may become oversaturated: it contains more dissolved substances than it can hold, so some substances begin to precipitate out. When the warm and humid air suddenly cools when it encounters a colder surface, it will cause fogging on the cold glass, which is the same principle. In most cases, engineers solve this problem by over-designing the system, Varanasi said: Use a much larger pipe than needed, for example, it is expected that fouling will cause partial blockage, or a larger surface area, in this case Heat exchanger under. Subramanyam points out that this problem is not new: “Ancient cooking utensils have this kind of accumulation,” he said. “We don’t have a good solution yet.” Although it has yet to be proven on an industrial scale, the new method developed by the MIT team may have a significant impact on the speed of scale formation, and in many cases may prevent it completely it. Their method sounds simple: effectively nanotexturing the surface and filling the resulting texture with a lubricant. The texture mainly depends on the size of the bumps and grooves produced; the precise shape does not seem to matter. Therefore, a variety of techniques can be used to create this texture-including applying a textured coating on the surface or chemically etching it in place. The researchers also described a process for selecting a suitable lubricant that not only increases the energy barrier formed by scale, but also spreads to textured solids, making the surface “smooth” and reducing nucleation that can be used for scale formation. Site. Previous attempts to prevent or reduce scale formation usually involve adding a coating (such as Teflon) to the surface to prevent minerals from binding to it. Varanasi explained that the problem with this method is that these coatings wear out, just as the coatings on non-stick frying pans often degrade with use. He said that even if there is a small hole in the coating, it provides a place for scale to start to form. Using the new method, once the nano-texture is formed on the surface, oil or other lubricating fluid is applied to the surface. Varanasi said that tiny nano-scale grooves capture this liquid and hold it firmly in place through capillary action. Unlike solid non-stick coatings, liquid can flow to fill any gaps, spread on the surface texture, and if some is washed away, it can be replenished continuously. “Even if there is mechanical damage, the lubricant can return to that surface,” Subramanyam said. “It can maintain its smoothness for a long time.” Because this lubricating layer is very thin—only a few hundred nanometers thick—it requires only a small amount of lubricant to protect a surface for decades. Varanasi said that a reservoir built in a section of the pipeline can provide lubrication throughout the life of the equipment. In the case of oil pipelines, “lubricant already exists”, the oil captured by the surface texture can protect the surface of the pipeline. Jurgen Rühe, head of the Laboratory of Interface Chemistry and Physics at the University of Freiburg, was not involved in the study, saying that it represents “very important discoveries and important scientific advances.” He called the team’s method of reducing scale formation “new and creative” and said “it may have a potential impact on all areas where water is heated and steam is generated.” The researchers said that after further laboratory testing to determine the best for a particular application After the lubricant and texturing methods, the system can be ready for commercial application in just three years. This work was supported by the MIT Energy Initiative.
Post time: Dec-08-2021
