Tomasz Zyska*, Waldemar Wójcik*, Baglan Imanbek**, Oxana Zhirnova**
*Lublin University of Technology; **Kazakh National Research Technical University after K.I. Satpayev
One of the methods of obtaining energy from renewable sources is the biomass gasification. For economic reasons, and taking into account the security aspects, it is important to ensure that the process is optimal. The gasification process can be optimized regarding the product energy, especially concentration of hydrocarbons and their derivatives or tar substrates, such optimization requires precise knowledge of temperatures in the gasification reactor. The temperatures inside the reactor determine the speed and quality of gasification process and are one of the most important parameters for control and monitoring systems of gasifier operation. Thermocouples are most widely used for temperature monitoring. That is the reason why it is important to acquire precise temperature readout regardless of aging processes. The significance of accurate temperature determining has been demonstrated with the use of a simplified mathematical model of a reactor assuming ideal reagents mixing. The presented mass and energy balance equations have led to determine the temperature changes during the analyzed process. The final equation is a base for the optimization of the gasification process and contains quantity of measured temperature. The main problem is the accuracy of temperature measurement. The authors have developed the in-situ method of diagnostics of thermocouples, that allows determination of the relative deviation of the sensor thermoelectric force during its operation. Besides characteristic parameters such as material properties the model includes the internal heat transfer, as well. The presented diagnostic method consists in determining the electromotive force of a newly installed sensor, and then determination of characteristic parameters using two selected values of testing current. During operation of the monitored sensor, periodic determination of the relative deviation of the Seebeck coefficient is required. This relative deviation should be compared to its permissible level, that is specified for the process being monitored. The proposed method belongs to the class of comparative ones, where the comparison is related to the indications of the same sensor (the new one and in-service). Experimental verification of the presented method was carried out using gasifier with nominal thermal load of 50kW, fed with wood pellets. The temperature of synthesis gas was measured by the two sensors, the reference sensor and the second one, that was driven by pulses of a testing current. For both current directions the thermoelectric force has been determined. The difference of the obtained electromotive forces is diagnostic information, that is needed to calculate the relative change of the Seebeck coefficient. The proposed solution allows diagnosing thermocouples located in confined areas. Moreover, additional benefit is the possibility of sensors diagnosis without stopping the process being monitored. It is important for both economic and technological reasons.
zgazowarka, pomiar temperatury, diagnostyka
gasifier, temperature measurement, diagnostics
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