Improving the efficiency of power plants with nanocomposite surface treatments


There is no doubt that the energy industry is moving towards decarbonization and renewable sources. But, despite the $ 2.7 trillion spent on renewables over the past decade, that future is still a long way off.

It all comes down to the economy. It is cheaper to operate an existing fossil fuel power plant than to build new renewable capacity. And although the cost of renewables has fallen dramatically in recent years, much of the developing world does not have access to the resources or expertise to achieve these prices on their own. Even the United States still depends on fossil fuels and waste-to-energy (EfW) plants to provide 60% of its energy as of 2020. Unless there is a drastic change in policy or technology, much of the world will continue to depend on fossil fuels. for at least the next two decades.

Despite the recent shift in focus and investment towards renewables, we cannot ignore fossil fuels. On the contrary, it is perhaps more important than ever for us to seek ways to use fossil fuels in a more sustainable way, because there is considerable room for improvement.

Overall, power generation from fossil fuels operates at around 40% efficiency, which means that most of the potential energy is wasted as heat rather than converted into usable energy. The amount of lost potential and wasted fuel is almost unfathomable. Preventing even a fraction of this energy loss could result in significant savings in terms of expenses and emissions.

Improve energy production with efficient heat transfer

The performance of a power plant can be measured by the amount of energy used by the power plant to generate one kilowatt hour (kWh) of electricity, known as the “heat rate” of the plant. If a factory were able to reduce its heating rate – requiring less energy to create the same amount of electricity – this would correspond to a reduction in both the fuel used and the emissions produced as a by-product. While improvements in heat rate can be achieved by using more energy-dense fuel sources, the greatest improvements come from eliminating sources of inefficient heat transfer throughout the heat cycle. production.

Let’s look at the coal. Although fossil fuels have an average overall efficiency of 40%, steam turbines using coal sources operate at only 34%. More than half of this efficiency loss occurs in the condenser, where efficiency is dictated by how quickly hot saturated steam is converted to liquid water as it transfers heat to a flowing cooler.

Two factors have an impact on this condensation process. The first is how vapor condenses into liquid. As the vapor condenses, it usually forms a thin film of water on the outside of the condenser tubes. And because water is not as conductive as metal, the condensate film ends up acting as an insulating layer between the remaining hot steam and the cold tubes, limiting efficient heat transfer.

Plants can double the efficiency of the condenser by promoting what is called “drip condensation”, where the liquid forms into many small droplets rather than larger layers of film (Figure 1). These droplets tend to roll rapidly over the surface of the condenser tube, increasing the rate of condensation as well as the amount of surface available for heat transfer. Under laboratory conditions, efficient heat transfer can be theoretically improved up to 100 times by preventing the formation of condensate films.

1. Water droplets on an untreated surface (left) and a treated surface (right) demonstrating the difference between film condensation and drip condensation. Courtesy: Oceanit

The second problem affecting the efficiency of the condenser is fouling. Biological organisms and debris particles can build up inside the tubes, creating another layer of insulation that “clogs” the condenser and prevents efficient heat transfer. Fouling alone reduces heat transfer efficiency by up to 10%, increasing fuel consumption by a similar degree.

The costs associated with the fouling of heat exchangers are estimated to be about 0.25% of gross domestic product (GDP) in highly industrialized countries. In addition, these deposits alter the texture of the inner surface of the tubes, disrupting flow and reducing the efficiency of heat transfer. To deal with these issues, many factories frequently clean their condenser tubes, which can require significant downtime and place operational strain on the factory.

Both issues are grip issues. That is, a large part of the loss of efficiency experienced in the condenser is the result of water and particles adhering to the metal tube, creating physical barriers that drastically reduce the transfer of heat between the hot steam on the outside of the tubes and the cold water on the inside. So the solution seems simple: make things harder to stick to the condenser tubes.

Nanocomposite surface treatments Answer the call

Considering the extreme temperatures and the intensity of use, condensers are rather harsh environments. Add to that the rigorous demands of the industry, and it makes sense that despite the obvious room for improvement in efficiency, few ideas were picked up.

Recent advances in coatings and surface treatments, however, offer opportunities to implement drop-in technologies that not only improve efficiency, but can also be applied in situ to aging facilities, allowing for substantial improvements and improvements. immediate efficiency and fuel consumption (Figure 2).

Fig2-HeatX-before-after-coating-condenser-tube plate
2. A heat exchanger before and after the HeatX application. The front image represents approximately six months of use. Since being treated with HeatX, this same exchanger has not needed a full cleaning in over 54 months, bypassing eight intensive cleaning cycles. Courtesy: Oceanit

For example, a team from the Massachusetts Institute of Technology (MIT) recently demonstrated how a thin coating of graphene can be applied to condenser tubes to promote drip condensation with good durability and little impact on water transfer. heat. Tests have shown that this method can improve heat transfer by a factor of four, resulting in an efficiency increase of 2-3% and annual fuel savings of $ 1 million. And while graphene is still quite expensive, the expected price drops over the next few years could make it a viable solution.

Another solution can be found in omniphobic (water and oil repellant) surface treatments such as HeatX, a nanocomposite which imparts extremely low surface energy to the surface to which it is applied. This prevents fouling from adhering and reduces frictional drag on the treated surface without compromising the original heat transfer efficiency of the system. A reduction in fouling also has the added benefit of increasing the time between cleanings.

While these types of surface treatments have been around for some time, previous iterations lacked durability or had to be applied in such a thick layer that they hampered heat transfer. For a surface treatment to be adoptable, it must not only prevent fouling, but also allow efficient heat transfer and require as little rework as possible.

HeatX does this particularly well. In a study of seawater-fed heat exchangers, which are generally very sensitive to biofouling and sand particle erosion, coating less than 2 mils in thickness increased the time between cleanings from six months to over 54 months, which is almost a 10-fold reduction in maintenance costs and a 10-fold reduction in downtime. Upon inspection, the treated surface had no visible biofouling binding and could be cleaned with a simple pressure wash.

With reduced downtime and improved heat transfer, surface treatments like HeatX could improve power plant efficiency by over 3% to 7%. On a test site, this translated into savings of $ 2.125 million per year in reduced fuel costs, resulting in a return on investment (ROI) of almost 600% over a five-year period, with a total recovery period of less than 6 months.

Such efficiency improvements correlate with massive carbon savings. For every 1 GW of capacity, operators can see carbon emission reductions of 300,000 tonnes of CO2 per year. Looking at the big picture, improving condenser function across the United States has the potential to avoid 221.3 million tonnes of CO.2 emissions, equivalent to the sequestration capacity of 129 million acres of forest. If applied globally, 1.26 billion tonnes of CO2 could be avoided from the atmosphere, the same amount of carbon sequestered by 1.5 billion acres of forest each year or 262,000 wind turbines operating each year.

Enabling the fossil fuel industry to move into the renewable energy era

Nanocomposite surface treatments like HeatX offer a tremendous opportunity to redefine the fossil fuel industry as we know it, causing drastic changes within these carbon-intensive processes. As we move towards a greener future, these types of innovations allow change to happen now, minimizing the impact of fossil fuels that we will continue to rely on for years to come.

As more sustainable solutions and policies emerge, alternatives also provide assurance that high standards of performance will be maintained and that the overall economic impact of disruptive changes will remain at a level acceptable to those with the means. livelihoods are at stake. Modern surface treatments can revolutionize all parts and stages of the energy sector, from coal production and refining to ammonia power generation and gas generation. ‘hydrogen.

James Andrews is responsible for marketing with Oceanity, a Mind-to-Market company based in Hawaii.

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