scope:

Introduction

Guideline VDI 2459 deals with measuring concentrations of carbon monoxide emissions. Part 6 [1] describes the principles of determining carbon monoxide (CO) by non-dispersive infrared spectroscopy (NDIR); Part 7 describes the iodine pentoxide method [2]. This wet-chemical method could in principle also be used as a reference measurement method for comparison measurements in accordance with the German Technical Instructions on Air Quality Control (TA Luft) [3], the German Ordinance on Large Firing Installations (13. BImSchV) [4] and the Ordinance on Incinerators for Waste and Similar Combustible Materials (17. BImSchV) [5] or for comparison measurements in accordance with the Guidelines on Suitability Testing, Installation, Calibration and Maintenance of Continuous Emission Monitoring Instruments [6], which are made specific and presented uniformly in guideline VDI 3950 Part 1 [7]. However, the use of the iodine pentoxide method in practice has shown that it is primarily suitable for laboratory work on checking calibration gases and less so for field measurements, since it requires high expenditure and extreme care which can only be met with limitations in the case of stack gas measurements.

It has therefore become customary practice to use the NDIR method for individual measurements as well and to calibrate continuous CO measuring instruments via comparison measurements using a second NDIR analyser which has been calibrated using calibration gases. A calibration of this type has the fundamental disadvantage that systematic errors due to cross-sensitivities, for example nitrous oxide (N2O), cannot be reliably excluded.

Alternatively, the method described in this guideline can be used, which is based on gas-chromatographic separation and catalytic reduction of the CO to methane (CH4). Since no other practicable reference methods which are independent of calibration gases are currently available, this measurement method can be used as a convention method [7], and by tracing it back to national reference standards, it can also be used as a reference method.

If the measurement method is to be performed using another detector (for example atomic emission detector (AED)) in order to determine CO directly, the user is responsible for verifying the comparability of the results with the method described in this guideline.