Tata Steel is trialling a novel thermocouple from ABB that generates the energy needed to drive it from the heat in the surrounding process. Combining this energy harvesting technology with wireless communications effectively eliminates the need to run any wires to or from the device.
“It would be a dream come true for an engineer to have a self-powered wireless thermocouple,” says Nikhil Kumar, area electrical engineer for blast furnace No.5 at the Port Talbot steelworks. “You don’t have to run any cable, which saves money on the installation and also eliminates the risk of burning or damaging the cable during operation.”
The ABB device hasn’t missed a single reading in the three months since it was installed, and has not had to resort once to its on-board battery backup, according to Tata Steel.
Forsøget blev indledt for at se, hvordan teknologien ville klare sig i et af de hårdeste driftsmiljøer i industrien. Termoelementet er installeret på en af plantens dampledninger, der arbejder ved 120oC. Høstteknologien kræver en temperaturforskel på kun 30oC mellem processen og dens omgivelser for at kunne styre instrumentets elektronik og sende sine aflæsninger.
Dette står i modsætning til resultaterne fra et andet termoelement, som blev installeret i nærheden for at teste, hvad der sker, når der installeres et energihøstinstrument uden den nødvendige temperaturforskel. Dette andet instrument har måttet stole på dets batteri for hele testens varighed.
Tata Steel has also been trialling wireless adapters fitted to a pair of pressure transmitters. The adapters enable all the instruments to communicate with one another, and with the plant’s control system via a wireless gateway.
"Vi har installeret et maske af instrumenter omkring højovnen for at teste hvordan de klare," siger hr. Kumar. "Netværket har vist sig at være robust, og resultaterne er meget lovende fremad."
He says that the instruments are able to talk to the gateway up to 50m away if there is a clear line of sight. In practice there are numerous walls, pipes and other obstructions around the plant, which brings that distance down.
In fact, the energy-harvesting thermocouple has been operating successfully at a distance of around 20 metres from the gateway. “It hasn’t dropped a reading during the entire trial,” says Mr Kumar.
And even though one of the pressure transmitters is situated inside a pump house that makes it unable to “see” the gateway directly, it has been communicating successfully with the thermocouple, which then passes on the data to the gateway. “It’s quite a clever and robust way of communicating,” says Mr Kumar. “With the instruments communicating with their neighbours as well as the gateway, the mesh can continue to function even if one of them is damaged or unavailable.”
With wiring and installation costs typically accounting for almost 50 percent of the total cost of an industrial instrument, it makes both financial and technological sense to use wireless devices wherever possible.
Energy harvesting provides an ideal alternative to wired or battery-powered devices in processes suited to the use of wireless devices. Energy harvesting takes energy from the environment and converts it into usable electrical energy, which is then used to power the wireless device. As well as thermal energy, energy harvesting technology can also be used to derive power from solar radiation, vibration and kinetic energy from flowing media or moving parts.