To maintain control of a gasifier under changing conditions—which allows for optimized performance—knowledge of key system parameters, pressure or temperature for example, must be available. Thermocouples are one of the most common methods of providing near real-time temperature data, but they have limited durability and can fail early in start-up. Replacement requires the gasifier to be shut down. A functioning thermocouple allows for greater control of the gasifier, which increases reliability and performance; a failed thermocouple decreases availability. These factors prompt research and development into extending the life of gasifier thermocouples.
Causes of thermocouple failure include:
- Issues with the placement and installation in the gasifier, slag binding and shear forces, and operational issues like temperature and throughput
- Design and fabrication defects
- Chemical corrosion from slag, vapor, and metallic iron
Several of these problems (e.g. slag) are possibly related to refractory issues.
Thermocouple protection system for gasifiers. (Source)
NETL recommends a thermocouple fabrication procedure to reduce fabrication defects and has developed a filler material to reduce slag penetration. Improvements in well blocks in the refractory material could also better protect the thermocouples. In addition, thermocouples will be tracked in regard to cause and frequency of failure for better understanding. See the NETL presentation, Refractory Materials for Slagging Gasifiers for more information.
More information on NETL-supported R&D in gasifier sensor development is available at the Gasifier Optimization page and in the CCS and Power Systems Crosscutting Research area.