Log In Sign Up

Search for any green Service

Find green products from around the world in one place

Window cleaning

Singapore Safety Glass

Tag: electrostatic repulsion

Table Salt in Plastic Recycling

Posted on by dishanth
Table Salt in Plastic Recycling

As far back as 6050 BC, salt has been used for various purposes, including religious offerings and valuable trades. The word “salary” was derived from the word salt because it was highly valued, and production was legally restricted in ancient times, so it was historically used as a method of trade and currency.

Table salt is an important and inexpensive kitchen staple today and is used for various uses, including seasoning, food preservation, food texture, cleaning,  and boiling water. We even use salt in healthcare (such as for cleaning wounds) and for deicing roads and sidewalks. But now table salt is entering a new domain: plastic recycling.

Researchers from Michigan State University are proving that salt in plastic recycling has the properties to outperform much more expensive materials that are being explored to help recycle plastics. The MSU team uses pyrolysis to break down the plastics into a mixture of simpler carbon-based compounds, including gas, liquid oil, and solid wax. Pyrolysis is the process of heating an organic material in the absence of oxygen.

One of the challenges of plastic recycling has always been an undesirable wax byproduct, which accounts for over half of the pyrolysis output. The wax obtained from the pyrolysis of waste plastic is generally regarded as a low-value product that requires further treatment in a refinery for it to be considered valuable as chemicals, diesel, petroleum, and gasoline.

Salt in plastic recycling is used as a catalyst to pyrolyze polyolefins (the family of thermoplastics that include polyethylene and polypropylene); the MSU team produced mostly liquid oil that contains hydrocarbon molecules similar to what is found in diesel fuel, which is not suitable for producing new polymers. There was no undesirable wax; over 50% is generally seen when platinum on carbon or aluminum is used as a catalyst. In this experiment, the result was 86% liquid form and 14% gas.

Using salt in plastic recycling as a catalyst also means the salt can be reused simply by washing the liquid oil with water. The team also found that table salt helped in the pyrolisis of metalized plastic films commonly used in food packaging, such as potato chip bags, which currently aren’t being recycled.

Because table salt is relatively inexpensive, using salt in plastic recycling could drastically reduce the costs associated with these processes. The researchers found that table salt can offer a transformative approach toward an inexpensive (4 cents per kg) and efficient pyrolysis methodology for converting mixed plastics waste to useful hydrocarbon products.

The use of table salt in plastic recycling is a relatively new phenomenon. Traditionally, salt has not been used directly in plastic recycling processes. It has been used indirectly in cleaning and preparing plastic items. It can be used as an abrasive agent to help scrub any residues. It is also used to scrub off adhesive labels from plastic containers.

In recycling facilities, electrostatic separation processes are used to separate different types of plastic based on their electrostatic charges. Salt can affect the conductivity of plastics and help in the separation. Furthermore, the traditional recycling process typically involves mechanical methods such as shredding, melting, and extruding rather than chemical reactions that involve salt. This study can drastically change the way plastic is recycled.

The salt in plastic recycling study from Michigan State University is still in its initial phases. Still, if it catches on, it could be an important movement towards how we recycle plastics and can result in more plastic being recycled and repurposed. It’s fascinating that something so simple and abundant, like table salt, can be used to help tackle one of the world’s most pressing issues.

 

 

 

 

Source   Happy Eco News

This is how solar panels can be kept clean – without using water

Posted on by dishanth
This is how solar panels can be kept clean – without using water
  • Solar power is expected to reach 10% of global power generation by 2030.
  • But the accumulation of dust on the solar panels can reduce output by 30%, while cleaning them uses about 10 billion gallons of water a year.
  • MIT engineers have developed a waterless cleaning method to remove dust on solar installations in water-limited regions.
  • The new system uses electrostatic repulsion to cause dust particles to detach and virtually leap off the panel’s surface.

Solar power is expected to reach 10 percent of global power generation by the year 2030, and much of that is likely to be located in desert areas, where sunlight is abundant. But the accumulation of dust on solar panels or mirrors is already a significant issue — it can reduce the output of photovoltaic panels by as much as 30 percent in just one month — so regular cleaning is essential for such installations.

But cleaning solar panels currently is estimated to use about 10 billion gallons of water per year — enough to supply drinking water for up to 2 million people. Attempts at waterless cleaning are labor intensive and tend to cause irreversible scratching of the surfaces, which also reduces efficiency. Now, a team of researchers at MIT has devised a way of automatically cleaning solar panels, or the mirrors of solar thermal plants, in a waterless, no-contact system that could significantly reduce the dust problem, they say.

 

The new system uses electrostatic repulsion to cause dust particles to detach and virtually leap off the panel’s surface Image: MIT News Office/ David L. Chandler

 

The new system uses electrostatic repulsion to cause dust particles to detach and virtually leap off the panel’s surface, without the need for water or brushes. To activate the system, a simple electrode passes just above the solar panel’s surface, imparting an electrical charge to the dust particles, which are then repelled by a charge applied to the panel itself. The system can be operated automatically using a simple electric motor and guide rails along the side of the panel. The research is described in the journal Science Advances, in a paper by MIT graduate student Sreedath Panat and professor of mechanical engineering Kripa Varanasi.

 

 

Despite concerted efforts worldwide to develop ever more efficient solar panels, Varanasi says, “a mundane problem like dust can actually put a serious dent in the whole thing.” Lab tests conducted by Panat and Varanasi showed that the dropoff of energy output from the panels happens steeply at the very beginning of the process of dust accumulation and can easily reach 30 percent reduction after just one month without cleaning. Even a 1 percent reduction in power, for a 150-megawatt solar installation, they calculated, could result in a $200,000 loss in annual revenue. The researchers say that globally, a 3 to 4 percent reduction in power output from solar plants would amount to a loss of between $3.3 billion and $5.5 billion.

“There is so much work going on in solar materials,” Varanasi says. “They’re pushing the boundaries, trying to gain a few percent here and there in improving the efficiency, and here you have something that can obliterate all of that right away.”

 

Many of the largest solar power installations in the world, including ones in China, India, the U.A.E., and the U.S., are located in desert regions. The water used for cleaning these solar panels using pressurized water jets has to be trucked in from a distance, and it has to be very pure to avoid leaving behind deposits on the surfaces. Dry scrubbing is sometimes used but is less effective at cleaning the surfaces and can cause permanent scratching that also reduces light transmission.

Water cleaning makes up about 10 percent of the operating costs of solar installations. The new system could potentially reduce these costs while improving the overall power output by allowing for more frequent automated cleanings, the researchers say.

“The water footprint of the solar industry is mind boggling,” Varanasi says, and it will be increasing as these installations continue to expand worldwide. “So, the industry has to be very careful and thoughtful about how to make this a sustainable solution.”

Other groups have tried to develop electrostatic based solutions, but these have relied on a layer called an electrodynamic screen, using interdigitated electrodes. These screens can have defects that allow moisture in and cause them to fail, Varanasi says. While they might be useful on a place like Mars, he says, where moisture is not an issue, even in desert environments on Earth this can be a serious problem.

The new system they developed only requires an electrode, which can be a simple metal bar, to pass over the panel, producing an electric field that imparts a charge to the dust particles as it goes. An opposite charge applied to a transparent conductive layer just a few nanometers thick deposited on the glass covering of the the solar panel then repels the particles, and by calculating the right voltage to apply, the researchers were able to find a voltage range sufficient to overcome the pull of gravity and adhesion forces, and cause the dust to lift away.

Using specially prepared laboratory samples of dust with a range of particle sizes, experiments proved that the process works effectively on a laboratory-scale test installation, Panat says. The tests showed that humidity in the air provided a thin coating of water on the particles, which turned out to be crucial to making the effect work. “We performed experiments at varying humidities from 5 percent to 95 percent,” Panat says. “As long as the ambient humidity is greater than 30 percent, you can remove almost all of the particles from the surface, but as humidity decreases, it becomes harder.”

Varanasi says that “the good news is that when you get to 30 percent humidity, most deserts actually fall in this regime.” And even those that are typically drier than that tend to have higher humidity in the early morning hours, leading to dew formation, so the cleaning could be timed accordingly.

“Moreover, unlike some of the prior work on electrodynamic screens, which actually do not work at high or even moderate humidity, our system can work at humidity even as high as 95 percent, indefinitely,” Panat says.

 

In practice, at scale, each solar panel could be fitted with railings on each side, with an electrode spanning across the panel. A small electric motor, perhaps using a tiny portion of the output from the panel itself, would drive a belt system to move the electrode from one end of the panel to the other, causing all the dust to fall away. The whole process could be automated or controlled remotely. Alternatively, thin strips of conductive transparent material could be permanently arranged above the panel, eliminating the need for moving parts.

By eliminating the dependency on trucked-in water, by eliminating the buildup of dust that can contain corrosive compounds, and by lowering the overall operational costs, such systems have the potential to significantly improve the overall efficiency and reliability of solar installations, Varanasi says.

The research was supported by Italian energy firm Eni. S.p.A. through the MIT Energy Initiative.

 

 

Source World Economic Forum