With plastic bottles they create a turbine to generate electricity in rivers and streams

A team of researchers uses recyclable plastic bottles to develop a hydrokinetic turbine, capable of capturing energy on a small scale from the water in rivers and streams. It is an emerging technology for the use of renewable energy at low cost, made with a 3D printer and without environmental impact.

These researchers will apply the 3D printing technique to create the prototype rotor of the aforementioned cross-flow hydrokinetic turbine that will initially generate a power of 40 watts (W). In its manufacture, filaments made from recycled plastic bottles will be used, which will also include biomass materials obtained from bamboo. For this purpose, the bamboo is carbonized at temperatures between 300 and 1100 degrees Celsius and a carbon fiber is achieved that is incorporated into the polymers to reinforce them.

This type of turbine is an emerging technology that allows energy to be obtained continuously (24 hours a day), from water that flows in natural environments. This constancy of supply is not within the reach of solar and often not even wind power.

The progress is the work of specialists from the Institute for Research in Energy Technologies and Advanced Materials of the National University of Río Cuarto in Argentina.

The growing concern about the undesirable environmental and socioeconomic consequences of petrochemical products and limited fossil resources generates great interest in the development of alternative ways of obtaining energy and in the use of biomass, its derivatives and recycled products as sustainable resources for the development of chemicals, polymers and materials.

The team of specialists uses PET (for the acronym in English of polyethylene terephthalate), a compound with which most plastic bottles for food are made. This polymer belongs to the group of synthetic materials called polyesters and is derived from petroleum, of which some 200,000 tons are discarded every year in Argentina alone and only 30% is recycled.

“These turbines make it possible to harness energy from rivers and streams without environmental impact, since they do not require the use of dams. Its manufacture from plastic bottles makes it possible to recycle, reuse and reduce waste, with the consequent contribution to caring for the environment. But this is not a consolidated technology yet, so its implementation is in the middle of research,” mechanical engineer Rodrigo de Prada, who is doing his doctoral thesis on the development of hydrokinetic turbines based on the use of composite materials, told Argentina Investiga. fibers -biomass, carbon- and polymeric matrix of recycled plastics printed in 3D.

In this regard, he pointed out: “In contrast to conventional hydraulic turbines, these work by speed difference. The conventional ones of the large hydroelectric plants work due to the height difference or because they have large flows. In this case, only speed difference is needed, there is no need to have a dam, they can be placed directly in rivers and streams with a stable average speed. All the environmental impact generated by the construction of a dam is avoided, with the infrastructure that it entails and the associated costs”. “This project arises from considering that the rivers of the province of Córdoba have good speeds and that these turbines mean a simple application and do not have a very large environmental impact. They can be placed in different places to collect electrical energy that can be used immediately or stored in battery banks to use it as needed”, commented the researcher. And he highlighted: “These types of turbines are under investigation. The most favorable factor is that the rivers pass energy 24 hours a day, which differentiates this energy from solar and wind, which depend on weather conditions, wind characteristics, the time of year… The kinetic turbine all he needs is for a certain speed to reach him, which in the mountains of Córdoba is easily achievable”.

Rodrigo de Prada works with the filament extruder for 3D printing. (Photo: National University of Río Cuarto / Argentina Investiga)

Sustainable materials in 3D printing

Three-dimensional -3D- printing is one of the most promising and fastest growing manufacturing technologies in recent years. It is possible to manufacture complex structures, in which the size and geometry of the products can be precisely controlled, with the help of computer-aided design. Thus, it achieves an excellent combination between process flexibility and high-performance products. The printers that work using this technology are fed with a filament of thermoplastic material, which is melted by an extrusion nozzle linked to a three-dimensional positioning system.

Rodrigo de Prada will make filaments with polymeric material obtained from the recycling of PET bottles; and then he will 3D print a prototype hydrokinetic turbine rotor using those developed filaments. He will evaluate the mechanical properties of the finished parts and the performance of the prototype rotor.

The work methodology includes cleaning the PET containers with water and detergent and separating the bottom and lid of the container. The center of the bottles is placed in a machine to cut and separate the PET plastic fibers and they are introduced into a hot extruder that allows obtaining the PET filament.

For the manufacture of the hydrokinetic turbine rotor, de Prada relies on the experience of its work group in the development of a prototype of the turbine rotor made from ABS plastic –acrylonitrile butadiene styrene–. He will define the rotor to be developed for the turbine prototype and will elaborate it on a 3D printer, using printing parameters that allow obtaining the best balance between mechanical properties, ease and quality of printing, as well as adhesion characteristics.

The mechanical properties of the filament fibers and formed pieces will be evaluated through mechanical tests of traction, compression, bending and sorption –physical and chemical process by which one substance adheres to another–. Then, the prototype rotor will be integrated into the turbine and generator. And the performance of the set will be evaluated in a test bench, a framework in which parameters such as power coefficients, torque, turbine revolutions per minute will be recorded; speed and flow of water.

–Have you already proven that biomass resources can be applied as reinforcement in composite materials?

-It is being tested. Biomass resources are being obtained from different sides. I get them from bamboo cane. After carbonizing these resources, we were able to obtain a kind of carbon fibers, which we have been trying to incorporate into the polymers in order to achieve reinforcement. It is a subject that we have been studying a lot; It is a matter of percentages, that is, the amounts of biomass resources that are needed with respect to the polymeric part, to see how much it helps to increase or decrease the mechanical properties that the composite material will have.

–What is a turbine rotor?

–The rotor is the part of the turbine that rotates; It takes advantage of the hydraulic energy of water to convert it into electrical energy. The water hits the rotor and makes it spin. From the rotation that occurs, an electromagnetic field is generated and in the stator, which is a fixed part of the turbine, is where that energy is captured and translated into electric current.

–How can turbines be made from plastic bottles?

–The manufacture of hydraulic turbines with plastic is something that we have been investigating. I had been working with ABS plastic. PETs are one of the easiest to recycle. The lid and bottom of the bottle are cut, and work is done with the central tube. We have to design and manufacture a machine to place that plastic and cut it into fibers, which is put into an extruder, where it goes through a hot nozzle that ends up generating a filament, which is what is then introduced into the printer. 3D to make the designs. It’s pretty easy to go from the fiber of the plastic from that bottle tube to filament. The hot nozzle shapes it into a filament. On the other hand, it is planned to grind the part corresponding to the lid and the bottom of the bottle. This grinding is placed in a plastic extruder and filament is also manufactured. They are different methods to take advantage of the entire bottle.

–Do you need a plastic bottle grinder?

– Within the group we do not have the machine to obtain PET fibers or the plastic grinder. We are looking for financing to build them, which we estimate could be for the second half of the year. Now we acquire the fibers.

–Have you made turbines from the plastic of recycled bottles?

-Not yet. I have been making turbines with recycled ABS.

– What is the objective of the work?

–My doctoral scholarship project focuses on achieving the hydrokinetic turbine, manufacturing it with 3D printing, using recycled plastic and reinforcing it with fibers of biomass material. The first is the design of the turbines with conventional materials and with recycled plastic. Now we are in the manufacture of the filament, which is fundamental, because the terminations that the 3D printer will give when manufacturing the turbine depend on the mechanical properties of the filament. Once the filament has the appropriate mechanical properties, the different turbine designs will be printed to see which one fits best. We are building a test bench for this type of turbine. We will be designing and modifying different parameters in each of the turbines that we are going to print, adjusting until we get the best performance. In this first instance, we seek to achieve a small prototype, above all, because we cannot test something larger on the test bench. We are working on a prototype of 40 several, which is interesting, because the kinetic energy is generated continuously 24 hours a day.

Will it be a transferable device?

Yes, we believe that this is going to be transferable. It is an alternative electric power generation. Manufacturing by 3D printer is low cost. Incorporating recyclable plastics, with the addition of reinforcements from biomass materials, makes it even more economical. It is something that is going to be able to be used, that is going to be easy to manufacture.

(Source: Deolinda Abate Daga / National University of Río Cuarto / Argentina Investiga)