D2.2 - High Temperature Sensors for In-Situ Process-Monitoring in Harsh Environments

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
D2 - High Temperature Sensors II
F. Hammer, U. Kunstfeld, E. Messerschmid - Universität Stuttgart (Germany)
543 - 548


Continuously increasing emission requirements and cost pressure inevitably lead to the optimization of combustion processes. Therefore, the exhaust gas losses have to be minimized by reducing the excess air to the so called emission rim. This is a point near stoichiometry where products of incomplete combustion (e.g. CO, H2) suddenly increase due to the lack of oxygen. Hence, a combustible gas sensing technology should be applied directly inside the exhaust pipe for realtime measurement. Harsh environmental conditions lead to the use of a robust mixed potential solid electrolyte gas sensor. High sensitivity with high time resolution, thermal, mechanical and chemical robustness enabless highly dynamic in-situ control of the combustion process by positioning the high temperature sensor directly inside the flue tube. Initially developed for space application, the miniaturized high temperature sensor can ideally be used in both industrial and domestic applications through additional advantages such as low power consumption and low cost at high quantity.
The paper reports the working principle, design, production of the sensor and integration into a new high temperature and corrosion resistant housing and the temperature control strategy evolved in order to compensate the influence of the high measurement gas temperatures of more than 450°C. Both results from the laboratory tests with synthetic gas and the field tests will be shown.
Exemplarily, the results of a newly developed in-situ wall monitoring system for coal-fired power plants will be presented. The increasing risk of creating reducing and corrosive atmosphere at the water cooled boiler walls arise with the reduction of excess air to increase efficiency and lower costs. CO levels of more than 0,5 Vol.% together with O2 levels of less than 1 Vol.% will lead to CO-corrosion that causes unpredictible failures resulting power plant shutdown and stillstand in combination with high costs for corrective maintenance and repair. In order to predict or prevent these failures a direct measurement of the wall atmosphere next to the combustion chamber is necessary and possible when using the presented high temperature sensor system. Over a period of 5 years the field tests have been done on a 450 MW coal fired power plant and demonstrated its function and reliability. It could have been shown, that CO as sole indicator for corrosive wall conditions is sufficient. Lifetime of the monitoring system turned out to be more than 2 years. Lifteime tests are still ongoing.