• Technology

Smart sensors that transform residual heat into electricity

This initiative entails advanced industrial sensor monitoring for prediction of industrial process faults and deviations in the field of energy, through temperature and vibration measurement, without using batteries, and communicating using very wide area wireless networks.

At Sacyr, we are carrying out the “Battery-less Sensor” project, through our Valoriza Medioambiente subsidiary and in collaboration with start-up Alternative Energy Innovations (AEInnova). Its objective is to conduct a feasibility study to determine the suitability of using wireless sensors with wide area communications powered by the residual heat produced by the machines themselves. 

“The project, which has the support of the Catalan Energy Efficiency Cluster, represents an important improvement to our industrial processes. The “Battery-less Sensor” aims to become a benchmark in Industry 4.0, as it presents an alternative to current solutions (wired or battery), minimizing economic costs and eliminating the environmental impact, in line with our commitment to the environment,” explains Marta Calderón, Innovation Projects Manager at Sacyr. 

Sensors have been installed in the granulation line at the Chiloeches (Guadalajara) plant and in the reactors in the CIRTEC plant.



Process improvement in Chiloeches and CIRTEC
Chiloeches is the Valoriza Medioambiente Group plant responsible for management and treatment of end-of-life tires (ELTs), from when they are received at the plant to shipment fully recycled, transformed into various rubber products, reusing 100% of the tire components.

CIRTEC results from a joint venture between Valoriza Medioambiente (50%) and Composan (50%), as an additives plant for asphalt mixtures.

The sensor converts residual heat from the machine and sends data, via a wireless protocol, to a platform that shows the temperature and vibration of that machine in real time. Whatever energy is not used is recovered to keep the sensor working, i.e. it is self-recharging without the need for a battery or wiring.

These data are used for preventive maintenance of the machinery, by means of alerts, to continue production flow in a more stable manner. 

Ramón Mariscal, Production Manager at CIRTEC, explains that there are two temperature sensors and two vibration sensors in two reactors. “In the reactor under heating, we mix rubber with bitumen and other components, so we are very interested in controlling temperature and vibration to favor component mixing. We were interested in controlling the revolutions to see if variations in them help us with preventive maintenance.  The temperature sensor, a PT-100, is connected directly to the communications node or emitter (IoT LoRa), which receives, processes and sends data from the sensor wirelessly, and this, in turn, is connected to the thermoelectric generator, which is what produces the necessary electricity by transforming the residual heat. The LoRa gateway unit, a kind of router, receives the data from the node and sends it to the server via Ethernet,” Mariscal explains.

Temperature control is important to CIRTEC for proper process execution. “The rubber is heated to around 160 degrees centigrade, then we inject the bitumen and allow time for pre-digestion between bitumen and rubber to occur, after that time, we introduce a filler that paralyzes the pre-digestion process and we pass the material to a reactor for cooling. We want to control the temperature appropriate to the process with these sensors, and to inject the bitumen when it has been reached,” Mariscal says.

On the other hand, CIRTEC has fitted another sensor for vibrations. “Bitumen is sticky. When one process follows another, part of the product sticks to the reactor walls and the layer gets thicker and thicker. This increases the friction between the blades that move the material inside the reactor and the reactor walls. The higher the friction, the higher the vibration. Our aim with the vibration sensors is to monitor when there is an increase in vibrations and therefore greater friction, which will tell us that we have to stop and perform a maintenance and cleaning process. We are also studying whether any exaggerated abnormality in vibrations indicates a malfunction in the equipment,” Mariscal stresses.


Sensor benefits

One the advantages of these sensors is that they eliminate energy consumption, as they consume their own energy. “We had no preventive maintenance indicator. We used to use the experience we have accumulated. Our project has only been running for 2 years, and we are still studying all the manufacturing processes.”

The energy it consumes comes from heat, through the temperature difference between the ambient temperature and the surface where we site the generator, on the outer wall of the reactor. This energy is converted into electricity and powers the system, avoiding wiring for both power and data transmission, as the node transmits it wirelessly.  This means sensor operation needs to be assessed both in winter and summer.



Luis Muñoz, Service Manager at Chiloeches, stresses that you can incorporate these sensors into equipment separated from electrical installations. This also promotes occupational safety by preventing accidents in places that are difficult to reach.

“We used standalone equipment that we had to hire every three months with mains electricity. There is a mill installed in Chiloeches where the tires are cut. Before a malfunction occurs, the equipment usually produces abnormal vibration and temperature values, which allow us to get ahead of the fault and to be able to perform preventive rather than corrective maintenance,” says Muñoz.

Now it is important to confirm operation at summer temperatures. The mill reaches a temperature of 60-65 degrees centigrade. The temperature gradient is higher in winter, as there is greater difference with the outside temperature, but in summer, when the gradient is lower, we need to check whether the sensor is working. So we may have more information on the full operation of these sensors, and therefore on project feasibility, after the summer.

In summary, running this project reinforces our commitment to promoting and enhancing collaboration with the innovation community to identify and drive new ideas that contribute to building a better, more sustainable world.

  • Renewable energy

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