Temperature measurement in extreme industrial environments poses many challenges, especially in incinerators, waste incinerators, and biomass furnaces. Severe operating conditions, including high temperatures above 1200 °C, temperature fluctuations, corrosive substances, and mechanical wear and tear, significantly impact the lifetime and accuracy of temperature sensors. This article will explore the problems faced by industries operating in such environments. Accordingly, we highlight a heavy-duty temperature sensor solution with an extended service life.
High temperatures over 1200 °C are often exceeded due to the introduction of new combustion substances, which are regularly added to the incineration process. There are frequent overruns and exceedances of maximum operating temperatures in industrial furnaces. This leads to the destruction of the thermocouples and their protective tubes. Incineration, e. g. of waste, also releases harmful substances such as acids and chlorine, which further cause ulcers on the thermocouples, most often at the installation sites. Mechanical abrasion, due to the high airflow, further damages the protective tubes. The installed pipes are also exposed to lining build-up and lumps falling into the furnace, causing even more damage.
For decades, we have been searching for the most durable, robust, and high-temperature-resistant tube for thermocouples. We tested different options but often encountered problems that limited the duration of continuous measurements to at least one year. In addition, we faced problems that were not accepted by users, such as high costs, the need for preheating, or breakage. High temperatures require the use of platinum thermocouples, which can be expensive if they need to be replaced frequently.
We have come to the conclusion that effective mechanical protection is the key to achieving a longer lifetime of thermocouples. This is what led us to the development of a notably thick metal protective tube, which wears down more slowly, is more resistant to falling objects, and tolerates high temperatures well. Despite the fact that temperatures above 1200 °C still affect its durability, the thickness of the pipe helps to control this phenomenon. Our goal was to achieve a lifetime of thermocouples with protective tubes that last from one overhaul to the next, i.e. at least one year. Experience shows that thermocouples with thicker metal tubes last a year in these demanding conditions.
After achieving the required durability, we focused on the accuracy of the measurements. We knew that users needed to replace K-type (Ni-CrNi) thermocouples with S-type (Pt10RhPt) platinum thermocouples, as only the latter ensures accurate measurements at temperatures above 1000 °C and has an immensely positive effect on energy efficiency. Special attention is paid to the installation of the platinum thermocouple in the housing. This way the user gets the best possible results, at least as long as they don’t interfere with the element and compromise the protection that platinum needs.
Until now, users have widely used K-type thermocouples, as only these, according to standardized specifications, result in a working range of up to 1200 °C and provide a thermal voltage of up to 1270 °C. However, their actual operating temperature is limited to 1000 °C, and that is only with thicker thermocouple wire diameters. Faulty procurement leads to a short life of such designs of temperature sensors, where mechanical damage was often the main cause of failure (damage to the protective tube occurred before the failure of the element).
When we achieved a longer service life for the temperature sensors, we switched to the mandatory platinum thermocouples, which tolerate high temperatures much better, even up to 1700 °C. If intact, they are accurate and have manageable creep. When the creep increases and the accuracy deteriorates, it is time to replace the platinum thermocouples.
When an element is replaced in an overhaul, we buy the old platinum and return it for processing. The user always receives a new item, and it is more cost-effective to buy back the old platinum.
To find out how you can save money by using platinum thermocouples, see Collecting and reusing platinum after recycling.
In addition, the transducers (4-20 mA signal) were deliberately placed outside the thermocouple housing, as the connection points of the temperature sensors are exposed to high temperatures, which reduces the lifetime of the transducers. The new installation site has extended the lifetime of the temperature sensors and transducers. If the user wants to see the measuring point on the display, a local display can be installed: the On-site display – loop-powered display.
If the user needs intermediate checks of the accuracy of the temperature sensor, the sensor can be made ON SITE and calibrated reference measuring equipment can be supplied. For more information see HIGH TEMP temperature sensors for high temperatures.
We found that the extended lifetime of the temperature sensor in incinerators depends on the extended lifetime of the temperature sensor protection tube, as changing sensors at high temperatures is extremely difficult and dangerous. Replacing a built-in element from a furnace where the temperature is constantly above 1250 °C is a difficult and very dangerous task. That’s why our aim is to incorporate elements that:
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They are always available for opinions and explanations:
expert in temperature measurements: Aleksandra Lepenik
measurement expert: Zoran Lepenik
Related articles:
Collecting and reusing platinum after recycling.
Mojca Kugler and Aleksandra Lepenik, July 2023
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