As a thermal remediation company, one of our most important factors to keep track of during operation is the subsurface temperature. The subsurface temperature is one of the main parameters used to determine how close to or far from reaching our treatment goals we are. Typical contracts require us to meet certain subsurface temperature requirements before confirmatory soil sampling can begin. This means we need a reliable temperature monitoring system so we can determine when a site has reached its goals.
Thermocouples vs. Fiber Optics
In the past, thermal vendors have been using thermocouples (typically Type T or Type K) to track soil temperatures during operations. The downside of the Type T and Type K sensors, is that they rely on measuring a relatively small thermoelectric voltage generated based on the temperature at the tip of the sensor. Typical issues with this kind of technology are related to electrical interference. Most thermal technologies, whether it is TCH or ERH, use large amounts of electricity to heat the subsurface. The electrical interference from these technologies can cause abnormal and erratic temperature readings. Also, the deeper a site is, and therefore the longer the temperature sensors wires have to be, the less accurate the measurements will be. This interference can throw off the measured temperatures by several degrees, unless properly calibrated and verified.
To combat the electrical interference seen with the typical thermocouple temperature monitoring system, TerraTherm has recently invested in an emerging temperature sensing technology that uses fiber optic cables to record temperature data. This enables us to record more accurate temperature readings of the subsurface without electrical interference. The fiber optic technology is also more accurate than a standard thermocouple, boasting an accuracy of ±0.1°C. The fiber optic sensing cables can also be adapted to capture and record pressure readings, which allow us to keep track of groundwater levels within the treatment zone in real-time. Monitoring groundwater levels in a steam zone is difficult, since most traditional pressure sensors are not rated for boiling temperatures, and since wells cannot be opened up to perform any groundwater measurements during steam projects for health and safety reasons.
Fiber Optics – A More Economic and Sustainable Choice
Another downside of traditional thermocouples is that, although they are cheap, they do not handle chemical/moisture exposure very well and do not usually last through more than one project; therefore new thermocouples must be purchased for each project. With the fiber optic sensor technology, the cables are reinforced with a stainless steel mesh as well as multiple other layers of protection to prevent any wear and tear the cable might be exposed to during normal thermal operations. The cables can then be used at multiple sites, which in the long run can lower the overall cost of the temperature monitoring system and increases the sustainability of the remedy.
Overall, this new fiber optic sensing technology is helping to improve collection of critical temperature data. As fiber optic business continues to grow, the cost of the system will decrease, and the technology will continue to improve, paving its way as the future of subsurface temperature monitoring systems.