Model nadzoru metrologicznego nad urządzeniami procesowymi do pomiaru THT

The increasing demand for process analyzers used in the supervision of the gaseous fuels odorizing process and the related higher and higher users’ requirements in terms of the quality of the results obtained lead to the growing need to verify the correctness of operation thereof and to confirm the reliability of measurement results. At present, however, there are no appropriate legal regulations concerning the control over this type of apparatus, as well as specifying the uncertainty level that the gas odorant concentration should be determined with. The normative regulations existing in this area are not unequivocal and can be interpreted in different ways, which leads to the situation when process equipment for measuring tetrahydrothiophene (THT) concentration in the gas can often lack proper metrological supervision. It is therefore necessary to properly select and verify appropriate methods to control the correctness of the process equipment indications and their implementation into the periodic check program. An extremely desirable method of supervision is to check or calibrate the analyzers in process conditions, without their dismantling for the time of checking. In turn, this entails the necessity to determine the possibility of conducting periodic metrological supervision over the measurement results correctness of THT process analyzers with the use of reference devices. The article presents a comparison of two methods currently used in metrological supervision of process analyzers for measuring the concentration of THT in the natural gas distribution gird. The results of checks of the proper functioning of these devices obtained by means of comparison with the laboratory test and the on-line comparative measurement method were analyzed. The conducted research verified the main sources of errors that have a significant impact on the correctness of results obtained by means of selected test methods. The results obtained showed the existence of a systematic error for the comparison method with a laboratory test. They also demonstrated the possibility of using the on-line comparative measurement method to carry out periodic calibrations or checks of the correct operation of THT analyzers in process conditions.