Energy Harvesting Widens Wireless' Appeal

Developments in energy harvesting promise to banish battery issues.

By Seán Ottewell, Editor at Large

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In terms of the second goal, Emerson ran the devices at different speeds working off a backup battery or the harvester. "Part of our learning here was that having backup power in the IPM was important because the motors are duty cycled in normal operation. It was a big lesson in reliability: the device(s) had to keep on running," notes Milavickas.

The prototypes at Firestone will get replaced with final versions when these are released to the market in the next few weeks, following completion of hazardous area approvals.

Meanwhile, the trial at OXEA is progressing in a similar fashion, with new lessons learned and new rules of thumb emerging all the time. "For example, we now know that a half-hp motor may be too small. Typically we look for multi-hp size motors as targets. Also we find that continuously operating assets are best," says Milavickas.

Emerson currently is evaluating other types of energy harvesting technologies, too, but these are at the very early field trial stages.

For its part, Perpetuum already has exhibited energy harvesters connected to Honeywell and Yokogawa wireless transmitters using the IPM. A gas plant in Wales currently is trialing an upgraded vibration monitoring device; new product announcements of various sorts likely will appear over the next few months.

In March, Micropelt, Freiburg, Germany, a company that specializes in thin-film-technology-based thermogenerators that turn waste heat into electric power, published its final report on field trials carried out at two Dutch chemical companies in 2012.

The trials ran from March to November at Huntsman Holland, Botlek Rotterdam, and Dishman, Veenendaal, and involved a Micropelt thermogenerator coupled with a prototype intelligent battery-pack module and a wirelessHART temperature transmitter, both from Emerson (Figure 2).

At Huntsman, the system was used to monitor temperature at a specific location of an outside tank. The temperature transmitter was powered by the module, which switched between a primary battery cell and the buffered energy created by the thermogenerator. The thermogenerator was clamped to a nearby steam pipe — a gross temperature gradient of 12°C between the hot surface and ambient air (which was simple to attain given the natural convection in the outside location) allowed the harvester to maintain its stated 8.5-V output.

At Dishman, the field test took place in a small (less than 20 m2) non-ventilated room from which steam is distributed to various plant locations via three non-insulated pipes. The measured temperature on the hot side of the thermogenerator chip varied between 80°C and 90°C.

[Related: Wireless: Handhelds Hold Sway]

Among the report's key conclusions are: at both field tests, the average gross power output of the thermogenerator was 10 mW (battery-equivalent to 58 Ah/7.2 V per year); the dynamic temperature profiles at the chemical sites provided a viable energy harvesting power source for wireless instruments when coupled with the intelligent battery-pack module; the module supplied power from the thermogenerator 99% of the time; the primary battery cell of the module must cover brown-out and maintenance periods; and the thermogenerator could power the WirelessHART instrument, which had a scan rate of 8 seconds, as long as the pipe temperature was 50°C or more.

The trials also showed that the module's switching between the thermogenerator and the primary battery doesn't cause any operational consequences for the instrument. In addition, they confirmed that installation of the thermogenerator is relatively simple — using a special adapter, it could be fit to pipe and flanges in a matter of minutes.

"Energy harvesting as an energy source is not new. It's the deployment that is new. For example, we worked with ABB on a prototype WirelessHART device in 2010. We are not talking a revolution here, more of an evolution," notes Wladimir Punt, Micropelt's vice president, sales and marketing.

In 2010, the company carried out a successful proof-of-concept project at a Shell plant in The Netherlands. The trial used a prototype device and lasted several weeks. "The two 2012 trials built on this work and it was very important for us to get much closer to an end product as a result of them," notes Punt.

As a result of the trial, Huntsman Holland now will consider wireless instruments for all future projects, he says. "Whether a fully autonomous instrument will be used has to be decided on a case-by-case basis," Punt adds.

More broadly, the trials point up that using a thermogenerator instead of a battery is a good solution, both outside and inside, he stresses. "Especially for difficult-to-reach measuring spots in the plant, it is attractive to install a thermogenerator instead of a battery for the wireless instrument. In existing plants, this is interesting because additional measuring devices can be installed without additional cabling, offering an opportunity to have a better understanding and control of the process."

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